Method of producing mechanical parts by mold casting

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a mold casting process and a mold casting apparatus used for carrying out the process, as well as a method for producing mechanical parts by application of the mold casting process.
2Description of the Prior Art
There is conventionally known a mold casting process wherein a temperature gradient is applied to a mold to provide a directional solidification, but timing for releasing a casting from the mold is not considered in any way (see Japanese Utility Model Application Laid-open No. 82746/86).
When a cast product is obtained by a casting process using a mold in order to improve the productivity thereof, the following problems are encountered: Due to a high heat transfer coefficient of the mold and the form of the product, the solidification and shrinkage of the cast product is partially greatly accelerated, so that a portion of the product is restrained by the mold, resulting in thermal cracking of the product and damage such as deformation and wearing of the mold.
To provide a product free from casting defects such as cavities, it is necessary to take corresponding measures, but no special measures have been taken in the prior art.
In achieving a product including a first formed portion of a harder structure and a second formed portion of a softer structure in a casting process using a mold, a procedure used in the prior art is to rapidly cool a first formed portion shaping region of the mold with cooling water and to prevent rapid cooling of a second formed portion shaping region of the mold by a block formed of a material such as a shell sand.
The prior art process is accompanied by the following problem: Thermal insulation between the first and second formed portions is not taken into account positively and for this reason, a heat transfer takes place therebetween, and the manner of such heat transfer is not even. Thus, the structures of the both formed portions are widely different from the intended structure.
With a cast product having a thinner portion and a thicker portion integral with the thinner portion, there is a problem that the cooling rates for both portions are different from each other and hence, releasing a resulting product from a mold at a timing suitable for the thinner portion results in that the thicker portion cannot have a sufficient shape retainability at the time of release, whereas releasing the resulting product at a timing suitable for the thicker portion leads to the possibility of producing thermal cracking in the thinner portion.
Further, in producing a mechanical part blank in a casting process using a mold, it is necessary to correct its shape when a deformation, a bend or the like are produced in the resulting mechanical part blank released from the mold. However, the mechanical part blank after being cooled has a small ductility and hence, a large-sized shape correcting or setting device having a higher pressing force must be provided, resulting in an increase in cost of equipment and in addition, a cracking or the like may be produced, resulting in a defective product.
Yet further, in efficiently producing a high strength cast product having a fine structure through a rapid solidification of a molten metal utilizing a high heat transfer coefficient of a mold, it is required to increase the pouring rate in order to prevent a failure of running of the molten metal. However, increasing the pouring rate only produces casting defects such as cavities and pin holes in the resulting product, because the molten metal is liable to include slag and gas thereinto. In addition, even if a slag removing portion is provided in a molten metal passage communicating with a cavity, a slag removing effect is less achieved, because the molten metal within the slag removing portion may be rapidly solidified to form a solidified layer.
There is also known a mold comprising a convex shaping portion to form a recess in a resulting product, and in such conventional known mold, its body and convex shaping portion are integrally formed of the same material (see Japanese Patent Application Laid-open No. 8382/80).
The aforesaid convex shaping portion may be worn by the flow of molten metal or damaged due to an adhesion force of the cast product attendant upon the solidification and shrinkage thereof. For this reason, if the mold body and the convex shaping portion are integrally formed as described above, a repairing operation on a large scale must be carried out for providing a padding by welding, a machine working or the like to the mold body. Such repairing operation is very troublesome and brings about a reduction in production efficiency.
Moreover, to prevent the trapping of gas into a molten metal, it is a conventional practice to provide a vent hole opened into a cavity in a mold, or to provide a gas venting slit in a split face of a mold.
However, with the above mold, even though gas in the cavity can be forced out and removed by the molten metal before pouring, a gas venting effect is poor after pouring because the molten metal enters and is solidified in the vent hole or slit. This results in that gas produced in the cavity from the molten metal after pouring cannot be sufficiently removed.
SUMMARY OF THE INVENTION
It is a first object of the present invention to provide a mold casting process as described above and a mold casting apparatus of the type described above for use in carrying out this process, wherein a cast product is released from the mold before thermal cracking of the product occurs, thereby giving an acceptable cast product, while avoiding damage to of a mold due to the solidification and shrinkage the cast product.
To accomplish the above object, according to the present invention there is provided a mold casting process comprising the steps of rapidly cooling a surface layer of a casting material which is in contact with a mold and releasing a resulting product from the mold when the surface layer has been converted into a shell-like solidified layer.
With the above mold casting process, since the resulting product is released from the mold when its surface layer has been converted into the shell-like solidified layer, a shape retainability of the surface layer can be assured to give an acceptable product, while preventing the mold from being damaged to provide an extended service life thereof.
Additionally, it is possible to improve the production efficiency, because releasing of the product is conducted in a higher temperature region.
In addition, according to the present invention, there is provided a mold casting apparatus comprising a cooling circuit and a heating circuit provided in a mold for producing a cast product by casting, and a cooling-temperature controller and a heating-temperature controller connected to the cooling circuit and the heating circuit, respectively, the heating-temperature controller having a function for activating the heating circuit to heat the mold prior to pouring of a molten metal and for deactivating the heating circuit or reducing the output from the heating circuit after starting of pouring, and the cooling-temperature controller having a function for activating the cooling circuit after pouring to cool the mold, thereby rapidly cooling a surface layer of the cast product to convert it into a shell-like solidified layer.
With the above mold casting apparatus, it is possible to easily and reliably carry out the above-descrived casting process. Particularly, since the apparatus is constructed so that the mold may be heated prior to pouring, it is possible to improve the running of the molten metal and to avoid cracking or the like of the product due to rapid cooling of the molten metal.
It is a second object of the present invention to provide a mold casting process of a high productivity in which a product is released from a mold before it thermally cracks, thereby. Producing a defect-free cast product, while avoiding damage of the mold due to the solidification and shrinkage of a cast product.
To accomplish the above object, according to the present invention, there is provided a mold casting process comprising the steps of pouring a molten metal under a condition where a cavity defining portion of a mold which defines a cavity and a portion defining a molten metal passage such as a gate and a runner have been heated; starting cooling of the cavity defining portion at pouring, thereby converting a surface layer of a cast product being shaped in the cavity into a shell-like solidified layer, and starting cooling of the molten metal passage defining portion after completion of pouring, thereby bringing unrequired portions shaped by the molten metal passage into the solidified state to release the unrequired portions from the mold; and then stopping cooling of the cavity defining portion and the molten metal defining portion when their temperatures have dropped a value near a preheated temperature and thereafter recovering the temperatures of the cavity defining portion and the molten metal defining portion to the preheated temperature.
With the above mold casting process, the surface layer of the cast product is converted into the shell-like solidified layer by providing such a cooling as described above, and the unrequired portions shaped by the molten metal passage are rapidly cooled and are released from the mold in this state. Therefore, the releasing operation can be reliably conducted, and a shape retainability of the solidified layer can be assured to give a cast product free from defects, while preventing damage to the mold to ensure a prolonged service life thereof.
In addition, the mold releasing and recovering to the preheated temperature as described above make it possible to substantially reduce the operating time for one run of casting as compared with the prior art mold casting process awaiting a perfect solidification of a cast product, and this leads to an improvement in productivity.
It is a third object of the present invention to provide a mold casting process and a mold casting apparatus for use in carrying out the process, in which a cast product is released from a mold before it thermally cracks, thereby producing a defect-free and high quality cast product, while avoiding damages of the mold due to the solidification and shrinkage of the product.
To attain the above object, according to the present invention, there is provided a mold casting process for casting a product by using a mold having a casting cavity and a molten metal passage communicating with the cavity, comprising the steps of pouring a molten metal into the cavity through the molten metal passage, rapidly cooling and solidifying the molten metal within the molten metal passage to close the molten metal passage, and then rapidly cooling a surface layer of a product which is in an unsolidified state within the cavity while applying a pressing force thereto, and releasing a resulting product from the mold when the surface layer of the product has been converted into a shell-like solidified layer.
With the above mold casting process, the surface layer of the cast product is rapidly cooled through application of a pressing force, and releasing of the resulting product is conducted when the surface layer of the casting material has been converted into the shell-like solidified layer, as described above. Therefore, in releasing the resulting product, a shape retainability of the solidified layer can be assured to produce a defect-free and high quality cast product, while preventing damage of the mold to provide an extended service life thereof. In addition, since releasing of the resulting product is conducted in a higher temperature region thereof, the productivity can be improved.
In addition, according to the present invention, there is provided a mold casting apparatus comprising a mold having a casting cavity and a molten metal passage communicating with the cavity, pressing means provided on the mold for pressing a molten metal within the cavity, a first cooling circuit mounted in a molten metal passage defining portion of the mold, a heating circuit and a second cooling circuit mounted in a cavity defining portion, a heating-temperature controller connected to the heating circuit, and first and second cooling-temperature controllers connected to the first and second cooling circuits, respectively, the heating-temperature controller having a function for activating the heating circuit to heat the cavity defining portion prior to pouring of the molten metal and for deactivating the heating circuit or reducing an output from the heating circuit after starting of pouring, the first cooling-temperature controller having a function for activating the first cooling controller to rapidly cool the molten metal within the molten metal passage after pouring into the cavity is finished, thereby closing the molten metal passage, the second cooling-temperature controller having a function for activating the second cooling circuit after starting of pouring to cool the cavity defining portion, thereby rapidly cooling a surface layer of a cast product to convert it into a shell-like solidified layer, and the pressing means being adapted to apply a pressing force to the cast product which is in an unsolidifiled state within the cavity after the molten metal passage has been closed.
With the above mold casting apparatus, it is possible to easily and reliably carry out the above-described process. Particularly, because the apparatus is constructed so that the mold is heated prior to pouring of the molten metal, it is possible to improve the running of the molten metal and also to avoid cracking of the product which may otherwise occur from rapid cooling of the molten metal.
It is a fourth object of the present invention to provide a mold casting process and a mold casting apparatus for use in carrying out the process, wherein such a product can be achieved as having a first formed portion of a harder structure and a second formed portion of a softer structure.
To attain the above object, according to the present invention, there is provided a mold casting process for casting a product having a first formed portion of a harder structure and a second formed portion of a softer structure by using a mold, comprising the steps of heating the mold under a condition where a heat transfer is suppressed between a first formed portion shaping region and a second formed portion shaping region of the mold and a temperature of the first formed portion shaping region is lower than that of the second formed portion shaping region of the mold, and rapidly cooling the first formed portion shaping region and slowly cooling the second formed portion shaping region accompanying starting of the pouring under a condition where heating of the mold is stopped or an amount of heat applied to the mold is reduced.
With the above mold casting process, a distinct difference in temperature can be generated between the first and second formed portion shaping regions of the mold to reliably obtain a product having a first formed portion of a harder structure and a second formed portion of a softer structure.
In addition, according to the present invention, there is provided a mold casting apparatus for casting a product having a first formed portion of a harder structure and a second formed portion of a softer structure, comprising a first formed portion shaping region, a second formed portion shaping region and a heat insulating material interposed between the two regions, the mold being provided with a heating circuit for heating the two regions prior to pouring of a molten metal in a manner that the first formed portion shaping region stays at a lower temperature than that of the second formed portion shaping region, and for stopping the heating or reducing an amount of heat applied to the two regions at the start of pouring, and a cooling circuit being provided for rapidly cooling the first formed portion shaping region and slowly cooling the second formed portion shaping region at the start of pouring.
With the above mold casting apparatus, since the heat insulating material is interposed between the first and second formed portion shaping regions, it is possible to achieve an accurate and rapid controlling in temperature of both the regions before and after pouring, and to present a distinct difference in temperature between both the regions, thereby ensuring that there is achieved a product having a first formed portion of a harder structure and a second formed portion of a softer structure.
It is a fifth object of the present invention to provide a mold casting process which enables production of a defect-free article having a thinner wall portion and a thicker wall portion integral with the thinner wall portion.
To accomplish the above object, according to the present invention, there is provided a mold casting process for casting a product having a thinner wall portion and a thicker wall portion integral with the thinner wall portion in a mold casting manner, wherein a mold is used including a mold body and a movalbe core slidably mounted in the mold body for shaping the thinner wall portion in cooperation with the mold body, and wherein the movable core is removed from the thinner wall portion after pouring when a surface layer of the thinner wall portion has become a solidified layer, and a resulting product is removed from the mold when a surface layer of the thicker wall portion has become a solidified layer.
With the above mold casting process, the state of contact of the mold with the thinner wall portion is released early and hence, the thinner wall portion cannot thermally crack. The contact of the mold with the thicker wall portion is then released, i.e., a resulting product is released from the mold when the surface thereof has become a solidified layer. Therefore, a defect-free cast product can be obtained with a good efficiency, and the mold cannot be damaged, leading to a substantially prolonged service life of the mold.
It is a sixth object of the present invention to provide a method for producing a mechanical part, in which a resulting mechanical part blank is released from a mold before it thermally cracks, while avoiding damage of the mold due to the solidification and shrinkage of the mechanical part blank, and the shape of the mechanical part blank can be reliably corrected into a proper one by using a small-sized shape correcting or setting device.
To accomplish the above object, according to the present invention there is provided a method for producing a mechanical part, comprising a mold casting step wherein a mechanical part blank resulting from pouring of a molten metal into and casting thereof in a mold is rapidly cooled its surface layer in contact with the mold and is then released from the mold when the surface layer thereof has become a solidified layer, and a shape correcting step of subjecting the mechanical part blank, which is at a higher temperature immediately after released from the mold, to a pressing treatment.
With the above method, since a resulting mechanical part blank is released from the mold in the mold casting step when the surface layer thereof has become the solidified layer, the mechanical part blank product can be retained in shape by the solidified layer and free from thermal cracks, and also damages of the mold are avoided to provide an extended service life thereof. In addition, since releasing is conducted when the mechanical part blank is in a higher temperature region, the casting efficiency can be improved.
Since the mechanical part blank is at a high temperature in the shape correcting step, a small-sized setting device is sufficient to carry out a reliable shape correction, leading to a reduction in cost of equipment.
In this way, the above producing method makes it possible to provide a defect-free mechanical part with a lower cost.
It is a seventh object of the present invention to provide a mold casting apparatus which enables efficient production of cast products of a high quality.
To attain the above object, according to the present invention there is provided a mold casting apparatus including a filter which is incorporated in a molten metal passage communicating with a casting cavity and which provides a controlled run of the molten metal.
With the above mold casting apparatus, the molten metal can be solidified rapidly utilizing a high heat conductivity of the mold to provide a high strength product having a fine structure.
In addition, since the speed of cooling the molten metal by the mold is high, it is necessary to increase the pouring speed and due to this, the run of the moten metal may be disordered in the molten metal passage to include slag, gas and the like thereinto. However, the slag and the like are removed by the filter, and the molten metal once disordered is controlled in flow by the filter and then introduced into the cavity. Therefore, the inclusion of gas is suppressed to the utmost, and this makes it possible to eliminate the adverse influence due to the increase in pouring rate and to efficiently produce a good quality product.
It is an eighth object of the present invention to provide a mold casting apparatus wherein a mold including a convex shaping portion can be easily repaired.
To attain the above object, according to the present invention there is provided a mold casting apparatus including a convex shaping portion provided on a heat resistant member detachably mounted in a mold body.
With the above mold casting apparatus, when the convex shaping portion is worn or damaged, the mold can be restored to the original state by merely replacing the worn or damaged convex shaping portion with a new one. Therefore, a large-scaled repairing of the mold is unnecessary, and the efficiency of production of cast articles can be improved.
It is a ninth object of the present invention to provide a mold casting apparatus having a good gas venting property.
To attain the above object, according to the present invention there is provided a mold casting apparatus comprising a mold including an air flow channel extending along a back side of a casting cavity, the cavity and the air flow channel communicating with each other through a slit adapted to permit flowing of air thereinto but inhibit flowing of a molten metal thereinto.
With the above mold casting apparatus, venting of a gas within the cavity can be effected with a good efficiency, whereby the charging efficiency of a molten metal can be improved to provide a high quality product free from casting defects such as pin holes, cavities and the like.
In addition, even though the molten metal may enter the slit and may be solidified therein, the solidified material can be easily removed by blowing compressed air into the air flow channel.

The above and other objects, features and advantages of the invention will become apparent from reading of the following description of the preferred embodiments, taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1 to 3 illustrate a first mold casting apparatus for casting a cam shaft blank of a cast iron, wherein
FIG. 1 is a perspective view of the whole apparatus;
FIG. 2 is a view taken in a direction indicated by an arrow 2--2 in FIG. 1;
FIG. 3 is a sectional view taken along a line 3--3 in FIG. 2;
FIG. 4 is a front view of a cam shaft blank;
FIG. 5 is an equilibrium state diagram of an Fe-C system;
FIG. 6 is a graph illustrating a relationship between the temperature of a surface layer of a cast iron cam shaft blank material and the time elapsed after pouring of a molten metal;
FIG. 7 is a sectional view of a setting device;
FIG. 8 is a sectional view taken along a line 8--8 in FIG. 7;
FIG. 9 is a graph illustrating a relationship between the temperature of the cam shaft blank material and the tensile strength thereof;
FIGS. 10 to 12 illustrate a second mold casting apparatus for casting a cast steel cam shaft blank, wherein
FIG. 10 is a perspective view of the whole apparatus;
FIG. 11 is a view taken in a direction indicated by an arrow 11--11 in FIG. 10;
FIG. 12 is a sectional view taken along a line 12--12 in FIG. 11;
FIG. 13 is a front view of a cam shaft blank;
FIG. 14 is a graph illustrating a relationship between the temperature of a surface layer of a cast steel cam shaft blank material and the time elapsed after pouring of a molten metal;
FIG. 15 is an equilibrium state diagram of an Al-Si system;
FIG. 16 is a graph illustrating a relationship between the temperature of a surface layer of a cam shaft blank material of an aluminum alloy casting and the time elapsed after pouring of a molten metal;
FIGS. 17 to 19 illustrate a third mold casting apparatus for casting a cast iron cam shaft blank, wherein
FIG. 17 is a view of the whole apparatus;
FIG. 18 is a view taken in a direction indicated by an arrow 18--18 in FIG. 17;
FIG. 19 is a sectional view taken along a line 19--19 in FIG. 18;
FIG. 20 is a graph illustrating a relationship between the temperature of a mold and the time elapsed from the start of pouring of a molten metal for a cast iron cam shaft blank;
FIGS. 21A and 21B are microphotographes each showing a metallographical structure of a cast iron cam shaft blank;
FIGS. 22 to 24 illustrate a fourth mold casting apparatus for casting a cam shaft blank of a steel casting, wherein
FIG. 22 is a view of the whole apparatus;
FIG. 23 is a view taken in a direction indicated by an arrow 23--23 in FIG. 22;
FIG. 24 is a sectional view taken along a line 24--24 in FIG. 23;
FIG. 25 is a graph illustrating a relationship between the temperature of a mold and the time elapsed from the start of pouring of a molten metal for a cast steel cam shaft blank;
FIG. 26 is a graph illustrating a relationship between the temperature of a mold and the time elapsed from the start of pouring of a molten metal for a cam shaft blank of an aluminum alloy;
FIGS. 27 to 29 illustrate a fifth mold casting apparatus for casting a cast iron cam shaft blank, wherein
FIG. 27 is a front view in longitudinal section of the apparatus;
FIG. 28 is an enlarged sectional view of a mold;
FIG. 29 is a view taken in a direction of an arrow 29 in FIG. 28;
FIGS. 30 to 32 illustrate a sixth mold casting apparatus for casting a cast steel cam shaft blank, wherein
FIG. 30 is a front view in longitudinal section of the apparatus;
FIG. 31 is an enlarged sectional view of a mold;
FIG. 32 is a view taken in a direction of an arrow 32 in FIG. 31;
FIGS. 33 to 38 illustrate a seventh mold casting apparatus for casting a cast iron cam shaft blank, wherein
FIG. 33 is a perspective view of details of the apparatus;
FIG. 34 is a view taken in a direction of an arrow 34--34 in FIG. 33;
FIG. 35 is a sectional view taken along a line 35--35 in FIG. 34;
FIG. 36 is a sectional view taken along a line 36--36 in FIG. 34;
FIG. 37 is a sectional view taken along a line 37--37 in FIG. 34;
FIG. 38 is a sectional view taken along a line 38--38 in FIG. 37;
FIGS. 39A and 39B are microphotographs each showing a metallographical structure of a cast iron cam shaft blank;
FIGS. 40 to 42 illustrate a eighth mold casting apparatus for casting a cast iron nuckle arm blank, wherein
FIG. 40 is a broken sectional front view of details when a mold is open;
FIG. 41 is a broken sectional front view of the details during casting;
FIG. 42 is an enlarged view of the details shown in FIG. 41;
FIG. 43 is a graph illustrating a relationship between the time elapsed after pouring of a molten metal and the amount of mold thermally expanded and the amount of nuckle arm blank material shrunk under a condition where a movable core is not cooled;
FIG. 44 is a graph similar to FIG. 43 under a condition where the movable core is cooled;
FIG. 45 is a graph illustrating a relationship between the time elapsed after pouring of a molten metal and the temperatures of a mold and a nuckle arm blank material;
FIG. 46 is a front view of a mold, similar to FIG. 2;
FIG. 47 is a sectional view taken along a line 47--47 in FIG. 46;
FIGS. 48A and 48B are views each showing each of two types of heat resistant members;
FIG. 49 is a sectional view of details of another mold;
FIG. 50 is a sectional view taken along a line 50--50 in FIG. 49;
FIG. 51 is a front view of a mold, similar to FIG. 2;
FIG. 52 is a sectional view taken along a line 52--52 in FIG. 51;
FIG. 53 is an enlarged sectional view taken along a line 53--53 in FIG. 51;
FIG. 54 is an enlarged sectional view taken along a line 54--54 in FIG. 53;
FIGS. 55A and 55B are perspective views each showing each of two types of heat resistant members;
FIG. 56 is a front view of a mold, similar to FIG. 2; and
FIG. 57 is an enlarged view of details of the mold shown in FIG. 56.

DESCRIPTION OF THE PREFERRED EMBODIMENTS
[I] Production of Cast Iron Cam Shaft
(i) Casting of Cam Shaft Blank
FIGS. 1 to 3 shows a mold casting apparatus M1 including a mold 1. The apparatus M1 is used to cast a cam shaft blank for an internal combustion engine (mechanical part blank) 2.sub.1 shown in FIG. 4.
Referring to FIG. 4, the cam shaft blank 2.sub.1 is conventionally well-known and includes a plurality of sets of cam portions 2a adjacent ones of which are one set, journal portions 2b respectively located between the adjacent cam portions 2a and at opposite ends of the cam shaft blank 2.sub.1, neck portions 2c each located between the adjacent cam portions 2a and journal portions 2b, and smaller diameter portions 2d respectively located outside the cam portions 2a at the opposite ends and between the adjacent sets of the cam portions 2a.
The mold 1 is formed of a Cu-Cr alloy containing 0.8 to 4% by weight of Cr and has a thermal conductivity of 0.4 to 0.8 cal/cm/sec./.degree.C.
The mold 1 is constructed of a first die 1.sub.1 and a second die 1.sub.2 of a split type and is opened and closed by an operating device which is not shown. Mold faces of the first and second dies 1.sub.1 and 1.sub.2 define a sprue 3, a runner, a gate 5, a cam shaft blank-molding cavity 6, and a vent hole 7.
Each of the first and second dies 1.sub.1 and 1.sub.2 is provided with a heating circuit 8, a cooling circuit 9 and knock-out means 10. Because these portions are substantially the same for the both dies 1.sub.1 and 1.sub.2, the description thereof will be made for the first die 1.sub.1.
The heating circuit 8 comprises a plurality of insertion holes 11 perforated in the first die 1.sub.1, and bar-like heaters 12 each inserted into and held in each of the insertion holes 11. Each of the insertion holes 11 is disposed so that a portion thereof may be in proximity to a section in the first die 11 for shaping each of the smaller diameter portions 2d of the cam shaft blank 2.sub.1.
The cooling circuit 9 comprises an inlet passage 14 horizontally made in an upper portion of the first die 1.sub.1, an outlet passage 15 horizontally made in an intermediate portion of the first die, and a plurality of communication passages 16.sub.1 and 16.sub.2 made in the first die 1.sub.1 to extend horizontally and vertically in an intersecting relation to each other to connect the inlet passage 14 and the outlet passage 15, so that cooling water introduced into the inlet passage 14 may be passed through the individual communication passages 16.sub.1 and 16.sub.2 and discharged from the outlet passage 15. The inlet passage 14, the discharge passage 15 and the individual horizontal communication passage 16.sub.1 are disposed so that a portion of each of them may be in proximity to a region of the first die 1.sub.1 for shaping a nose 2e which is a chilled portion of the resulting cam portion 2a.
Each of the heaters 12 in the heating circuit 8 is connected to a heating-temperature controller 17 having a function for activating the heating circuit 8 prior to pouring of a molten metal, i.e., energizing each heater 12 to heat the first die 1.sub.1, and deactivating the heating circuit 8 after starting of pouring, i.e., deenergizing each heater 12.
Because the individual heater 12 is spaced from the nose 2e shaping region of the first die 1.sub.1, the temperature of that region is lower than that of other regions during heating. Of course, each of the heaters 12 in the second die 1.sub.2 is also connected to the heating-temperature controller 17.
The inlet passage 14 and the outlet passage 15 of the cooling circuit 9 are connected to a cooling-temperature controller 18 having a function for activating the cooling circuit 9 after starting of pouring, i.e., permitting the cooling water to flow through the cooling circuit 9 to cool the first die 1.sub.1, rapidly cooling that surface layer of the resulting cam shaft blank 2.sub.1 which is in contact with the first die 1.sub.1, thereby converting it into a shell-like solidified layer.
During cooling, it is possible to rapidly cool the nose 2e to reliably achieve chilling thereof, because the inlet passage 14, the outlet passage 15 and the individual horizontal communication passages 16.sub.1 are in proximity to the nose 2e shaping region of the first die 1.sub.1 and also because that region is at a temperature lower than that of the other regions at the heating stage. Of course, the cooling circuit 9 of the second die 1.sub.2 is also connected to the cooling-temperature controller 18.
The knock-out means 10 comprises a plurality of pins 19, a support plate 20 for supporting one ends of the pins 19, and an operating member 21 connected to the support plate 20. Each of the pins 19 is slidably received in each of insertion holes 22 which are provided in the first die 1.sub.1 and opened into the sprue 3, the runner 4 and the cavity 6. In the cavity 6, an opening of each insertion hole 22 is disposed in a region for shaping each journal portion 2b of the resulting cam shaft blank 2.sub.1.
Description will now be made of an operation for casting a cam shaft blank 2.sub.1 in the above-described mold casting apparatus M1.
First, a molten metal of an alloy chilled cast iron containing constituents given in Table 1 is prepared.
TABLE 1______________________________________Chemical constituents (% by weight)C Si Mn Ni Cr Mo______________________________________3.5 1.8 0.6 0.4 0.5 0.5______________________________________
The alloy chilled cast iron has a composition as indicated by a line A1 in an equilibrium phase diagram shown in FIG. 5, with an eutectic crystal line Le1 intersecting the line A1 at approximately 1150.degree. C.
The mold 1 is heated by the heating circuit 8 prior to pouring of the molten metal, wherein a region for shaping the smaller diameter portion 2d is maintained at approximately 450.degree. C., and the region for shaping the nose 2e is at 150.degree. C. The aforesaid molten metal is poured at a temperature in a range of 1380.degree. to 1420.degree. C. into the mold 1 to cast a cam shaft blank 2.sub.1. The amount of molten metal poured at this time is 5 kg.
If the mold 1 has been previously heated as described above, the run of the molten metal is improved during pouring, and it is possible to avoid cracking of the resulting cam shaft blank and so on due to the rapid cooling of the molten metal.
After pouring is started, heating of the mold 1 by the heating circuit 8 is stopped and at the same time, the mold 1 is started to be cooled by the cooling circuit 9.
FIG. 6 illustrates a temperature drop for the surface layer of the cam shaft blank material 2.sub.1 in contact with the mold 1 in a relationship with the time elapsed after pouring.
The surface layer of the cam shaft blank material 2.sub.1 is rapidly cooled under a cooling effect of the mold, and when the temperature of the surface layer is dropped down to about 1150.degree. C. (eutectic crystal line Le1) indicated by a point a.sub.1, the cam shaft blank 2.sub.1 becomes solidified with the surface layer thereof converted into a shell-like solidified layer.
In this case, if the temperature of the surface layer is lower than 700.degree. C. indicated by a point a.sub.5, it is feared that thermal cracking may be produced in the resulting cam shaft blank 2.sub.1. In addition, if the temperature of the surface layer is lower than 800.degree. C. indicated by a point a.sub.4, it is also feared that adhesion of the resulting cam shaft blank 2.sub.1 to the mold 1 and so on may be produced due to the solidificational shrinkage of the cam shaft blank material 2.sub.1 to cause damages such as deformation and wearing of the mold 1.
Thereupon, when the temperature of the surface layer of the cam shaft blank material 2.sub.1 has reached a temperature of 950.degree. C. indicated by a point a.sub.2 to 850.degree. C. indicated by a point a.sub.3 in about 3 to about 8 seconds after pouring, the mold is opened, and the knock-out pin means 10 is operated to release the resulting cam shaft blank 2.sub.1 from the mold.
The cam shaft blank 2.sub.1 provided by the above procedure has no thermal cracks produced therein, and the mold 1 is not damaged in any way. Moreover, the cam shaft blank 2.sub.1 is covered with the shell-like solidified layer and hence, deformation in releasing the blank is suppressed to the utmost.
Further, the nose 2e of each cam portion 2a is positively chilled, because the region of the mold 1 for shaping the nose 2e has been heated to a relative low temperature and rapidly cooled at the cooling stage.
The optimal timing for releasing the cam shaft blank 2.sub.1 of the aforesaid alloy chilled cast iron is when the temperature of the surface layer thereof is in a range of about 1150.degree. to 800.degree. C. and thus between the eutectic crystal line and 350.degree. C. therebelow, and experiments have made clear that the same is true even when other cast irons such as a spherical graphite cast iron are employed.
(ii) Setting of Shape of Cam Shaft Blank
FIGS. 7 and 8 shows a shape correcting of setting apparatus 25 which comprises an upper pressing member 25.sub.1 and a lower pressing member 25.sub.2. Each of the pressing members 25.sub.1 and 25.sub.2 includes, at its longitudinally central portion and opposite ends, pressing portions 27.sub.1, 27.sub.2 each having a V-groove 26.sub.1, 26.sub.2 adapted to engage each of outer peripheral surfaces of the smaller dismeter portion 2d at the central portion of the cam shaft blank 2.sub.1 and of the opposite end journal portions 2b at the opposite ends of the cam shaft blank 2.sub.1.
The cam shaft blank 2.sub.1 which is at a high temperature immediately after release from the mold is clamped between both the pressing members 25.sub.1 and 25.sub.2 and pressed by application of a pressing force thereto through the upper pressing member 25.sub.1. This pressing treatment is conducted one or more times through rotation of the cam shaft blank 2.sub.1, thereby providing a cam shaft (mechanical part).
FIG. 9 illustrates a relationship between the temperature and the tensile strength of the cam shaft blank 2.sub.1. When the temperature of the cam shaft blank 2.sub.1 is in a range of 750.degree. to 1,000.degree. C., the cam shaft blank 2.sub.1 is easy to deform, so that the setting in shape thereof can be reliably carried out with a relatively small pressing force.
In this embodiment, the aforesaid setting step is conducted under conditions of a pressing force of 150 to 450 kg and a pressing time of 5 to 15 sec., whereby if the cam shaft blank 2.sub.1 released from the mold is bent, then the bending can be corrected. For example, with a cam shaft blank 2.sub.1 having an overall length of 450 mm, if the center of the central smaller diameter portion (a diameter of 30 mm) deviates by 0.8 mm or more with respect to a line connecting the centers of the journal portions (a diameter of 40 mm) at the opposite ends, then such deviation can be corrected within 0.3 mm.
[II] Production of Cast steel Cam Shaft
(i) Casting of Cam Shaft Balnk
FIGS. 10 to 12 show a mold casting apparatus M2 including a mold 28. The apparatus M2 is used to cast a cam shaft blank 2.sub.2 shown in FIG. 13.
The mold 28 is formed of a Cu-Cr alloy in the same manner as described above. The mold 28 is constructed of a first die 28.sub.1 and a second die 28.sub.2 into a split type, and opened and closed by an operating device which is not shown. The mold surfaces of the first and second dies 28.sub.1 and 28.sub.2 define a sprue 29, a runner 30, a gate 31, a cam shaft blank-molding cavity 32 and a vent hole 33.
Each of the first and second dies 28.sub.1 and 28.sub.2 is provided with a heating circuit 34, a cooling circuit 35 and knock-out means 36. These portions are the same for both the dies 28.sub.1 and 28.sub.2 and hence, only those for the first dies 28.sub.1 will be described below.
The heating circuit 34 is comprised of a plurality of insertion holes 37 perforated in the first die 28.sub.1 and bar-like heaters 38 inserted into and held in the corresponding insertion holes 37.
Each of the heaters 38 is connected to a heating-temperature controller 39 having a function for activating the heating circuit 34 prior to pouring of a molten metal, i.e., energizing each heater 38 to heat the first die 28.sub.1, and deactivating the heating circuit 34 after starting of pouring, i.e., deenergizing each heater 38. Of course, each of the heaters 38 in the second die 28.sub.2 is also connected to the heating-temperature controller 39.
The cooling circuit 35 is comprised of a horizontal inlet passage 40 made in an upper portion of the first die 28.sub.1, a horizontal outlet passage 40 made in a lower portion of the first die, and a plurality of vertical communication passages 42 made in the first die 28.sub.1 to connect the inlet and outlet passages 40 and 41, so that cooling water introduced into the inlet passage 14 may be passed through the individual communication passages 42 and discharged from the outlet passage 41.
The inlet passage 40 and the outlet passage 41 are connected to a cooling-temperature controller 43 which has a function for activating the cooling circuit 35 after starting of pouring, i.e., permitting the cooling water to flow through the cooling circuit 35 to cool the first die 28.sub.1, rapidly cooling that surface layer of the cam shaft blank material 2.sub.2 which is in contact with the first die 28.sub.1, thereby converting it into a shell-like solidified layer. Of course, the cooling circuit 35 of the second die 28.sub.2 is also connected to the cooling-temperature controller 43.
The knock-out means 36 comprises a plurality of pins 44, a support plate 45 for supporting one ends of the pins 44, and an operating member 46 connected to the support plate 45. Each of the pins 44 is slidably received in each of insertion holes 47 which are provided in the first die 28.sub.1 and opened into the sprue 29, the runner 30 and the cavity 32.
Description will now be made of an operation for casting a cam shaft blank 22 in the above-described mold casting apparatus M2.
Fifty to seventy % by weight of a scrap material (steel) and 50 to 60% by weight of a return material as main feeds are charged into a high frequency furnace and dissolved therein, and sub-feeds such as C, Fe-Cr, Fe-Mo, Fe-V, etc., are added thereto to prepare a molten metal of an alloy cast steel composition corresponding to an alloy tool steel (JIS SKD-11) given in Table II.
TABLE II______________________________________Chemical constituents (% by weight)C Si Mn P S Cr Mo V______________________________________1.40- .ltoreq.0.4 .ltoreq.0.6 .ltoreq.0.030 .ltoreq.0.030 11.0- 0.8- 0.20-1.60 13.0 1.2 0.50______________________________________
The above alloy cast steel is in a composition range A2 indicated by an obliquely-lined region in a Fe-C equilibrium phase diagram shwon in FIG. 5, wherein a solid phase line Ls intersects the composition range A2 at approximately 1,250.degree. C.
The molten metal is increased in temperature in an atmosphere of an inert gas such as argon gas and subjected to a primary deacidification wherein 0.2% by weight of Ca-Si is added at a temperature of 1,500.degree. to 1,530.degree. C. and a secondary deacidification wherein 0.1% by weight is added at a temperature of 1,650.degree. to 1,670.degree. C.
The mold 28 is previously heated to a temperature of 150.degree. to 450.degree. C. by the heating circuit 34 prior to pouring. The molten metal deacidified is poured into the mold 28 at a temperature of 1,630.degree. to 1,670.degree. C. to cast a cam shaft blank 2.sub.2. The amount of molten metal poured at this time is 5.0 kg.
If the mold 28 has been previously heated as described above, the flow of the molten metal is improved during pouring, and it is possible to avoid cracking of the resulting cam shaft blank and so on due to the rapid cooling of the molten metal.
After pouring is started, heating of the mold 28 by the heating circuit 34 is stopped and at the same time, the mold 28 is started to be cooled by the cooling circuit 35.
FIG. 14 illustrates a temperature drop for the surface layer of the cam shaft blank material 2.sub.2 in contact with the mold 28 in a relationship with the time elapsed after pouring.
The surface layer of the cam shaft blank material 2.sub.2 is rapidly cooled under a cooling effect of the mold 28, and when the temperature of the surface layer is dropped down to about 1,250.degree. C. (eutectic crystal line Le1) indicated by a point b.sub.1, the cam shaft blank material 2.sub.2 becomes solidified with the surface layer thereof converted into a shell-like solidified layer.
In this case, if the temperature of the surface layer is lower than 950.degree. C. indicated by a point b.sub.5, it is feared that thermal cracking may be produced in the resulting cam shaft blank 2.sub.2. In addition, if the temperature of the surface layer is lower than 1,000.degree. C. indicated by a point b.sub.4, it is also feared that adhesion of the resulting cam shaft blank 2.sub.2 to the mold 28 and so on may be produced due to the rapid and large solidificational shrinkage of the cam shaft blank material 2.sub.2 to cause damage such as deformation and wearing of the mold 28.
Thereupon, when the temperature of the surface layer of the cam shaft blank material 2.sub.2 has reached a temperature of 1,200.degree. C. indicated by a point b.sub.2 to 1,100.degree. C. indicated by a point b.sub.3 in about 4 to about 5 seconds after pouring, the mold is opened, and the knock-out pin means 36 is operated to release the resulting cam shaft blank 2.sub.2 from the mold.
The cam shaft blank 2.sub.2 provided by the above procedure has no thermal cracks produced therein, and the mold 28 is also not damaged in any way. Moreover, the cam shaft blank 2.sub.2 is covered with the shell-like solidified layer and hence, deformation in releasing the blank is suppressed to the utmost.
The optimal timing for releasing the cam shaft blank 2.sub.2 of the aforesaid alloy cast steel is when the temperature of the surface layer thereof is in a range of about 1,250.degree. to 1,000.degree. C. and thus between the solid phase line Ls and 250.degree. C. therebelow, and experiments have made clear that the same is true even when carbon cast steels are employed.
The feed materials which may be charged is not limited to those corresponding to the above-described alloy tool steel, and include those prepared from a main feedstock consisting of a scrap material and a return material, and sub-feed(s) selected alone or in a combination from alloy elements such as C, Ni, Cr, Mo, V, Co, Ti, Si, Al, etc., added thereto in a manner to contain 0.14 to 1.8% by weight of C.
(ii) Setting of Shape of Cam Shaft Blank
This setting step is effected using a setting apparatus similar to that described above, but the conditions therefor are of a temperature of 950.degree. to 1,200.degree. C., a pressing force of 150 to 450 kg and a pressing time of 5 to 15 sec. for the cam shaft blank 2.sub.2.
[III] Production of Cam Shaft of Aluminum Alloy Casting
The mold casting apparatus M2 for the above-described cast steel cam shaft is used for casting a cam shaft blank 2.sub.2. In a casting operation, a molten metal of an aluminum alloy composition corresponding to JIS ADC 12 given in Table III is first prepared.
TABLE III______________________________________Chemical constituents (% by weight)C Si Mg Zn Fe Mn Ni Sn______________________________________1.5- 9.6- .ltoreq.0.3 .ltoreq.1.0 .ltoreq.1.3 .ltoreq.0.5 .ltoreq.0.5 .ltoreq.0.33.5 12.0______________________________________
The aluminum alloy is in a composition range A3 indicated by an obliquely-lined region in an Al-Si equilibrium phase diagram shown in FIG. 15, wherein an eutectic line Le2 intersects the above composition range A3 at approximately 580.degree. C.
The mold 28 is previously heated to a temperature of 100.degree. to 300.degree. C. by the heating circuit 34 prior to pouring. The molten aluminum alloy is poured into the mold 28 at a temperature of 700.degree. to 740.degree. C. to cast a cam shaft blank 2.sub.2. The amount of molten metal poured is 2.0 kg.
If the mold 28 has been previously heated as described above, the run of the molten metal is improved during pouring, and it is possible to avoid cracking of the resulting cam shaft blank 2.sub.2 and so on due to the rapid cooling of the molten metal.
After pouring is started, heating of the mold 28 by the heating circuit 34 is stopped and at the same time, the mold 28 is started to be cooled by the cooling circuit 35.
FIG. 16 illustrates a temperature drop for the surface layer of the cam shaft blank material 2.sub.2 in contact with the mold 28 in a relationship with the time elapsed after pouring.
The surface layer of the cam shaft blank material 2.sub.2 is rapidly cooled under a cooling effect of the mold 28, and when the temperature of the surface layer is dropped down to about 1,250.degree. C. (eutectic crystal line Le2) indicated by a point c.sub.1, the cam shaft blank material 2.sub.2 becomes solidified with the surface layer thereof converted into a shell-like solidified layer.
In this case, if the temperature of the surface layer is lower than 280.degree. C. indicated by a point c.sub.4, it is feared that thermal cracking may be produced in the resulting cam shaft blank 2.sub.2. In addition, if the temperature of the surface layer is lower than 350.degree. C. indicated by a point c.sub.3, it is also feared that adhesion of the resulting cam shaft blank 2.sub.2 to the mold 28 and so on may be produced due to the rapid and large solidificational shrinkage of the cam shaft blank material 2.sub.2 to cause damages such as deformation and wearing of the mold 28.
Thereupon, when the temperature of the surface layer of the cam shaft blank material 2.sub.2 has reached a temperature of 500.degree. C. indicated by a point c.sub.2 in about 4.5 seconds after pouring, the mold is opened, and the knock-out pin means 36 is operated to release the resulting cam shaft blank 2.sub.2 from the mold.
The cam shaft blank 2.sub.2 provided by the above procedure has no thermal crack produced therein, and the mold 28 is also not damaged in any way. Moreover, the cam shaft blank 2.sub.2 is covered with the shell-like solidified layer and hence, deformation in releasing thereof is suppressed to the utmost.
The optimal timing for releasing the casting of the aforesaid alloy is when the temperature of the surface layer thereof is in a range of about 580.degree. to 350.degree. C. and thus between the eutectic crystal line Le2 and 230.degree. C. just therebelow, and experiments have made clear that the same is true even in the case of aluminum alloys such as Al-Cu, Al-Zn and the like.
(ii) Setting of Shape of Cam Shaft Blank
This setting step is effected using a setting apparatus similar to that described above, but the conditions therefor are of a temperature of 300.degree. to 500.degree. C., a pressing force of 130 to 300 kg and a pressing time of 5 to 15 sec. for the cam shaft blank 2.sub.2.
It should be noted that the heating-temperature controller 17, 39 may be designed to have a function of reducing output from the heating circuit 8, 34 and thus decreasing an energizing current for each heater 12, 38 after starting of pouring in each of the above-described casting steps [I] to [III].
[IV] Casting of Cam Shaft Blank of Cast Iron
FIGS. 17 to 19 shows a mold casting apparatus M3 including a mold 48. The apparatus M3 is used to cast a cam shaft blank 2.sub.1 as a cast iron casting, as shown in FIG. 4.
The mold 48 is of the same material as described in the above item [I].
The mold 48 is constructed of a first die 48.sub.1 and a second die 48.sub.2 into a split type, and opened and closed by an operating device which is not shown. The mold surfaces of the first and second dies 48.sub.1 and 48.sub.2 define a sprue 49, a runner 50, a gate 51, a cam shaft blank-molding cavity 52 and a vent hole 53.
Each of the first and second dies 48.sub.1 and 48.sub.2 is provided with first to third preheating mechanisms 54.sub.1 to 54.sub.3, first to third cooling mechanisms 55.sub.1 to 55.sub.3 and knock-out means 56. These portions are the same for both the dies 48.sub.1 and 48.sub.2 and hence, only those for the first die 48.sub.1 will be described below.
The first preheating mechanism 54.sub.1 comprises heaters 58.sub.1 each disposed in each of first sections 57.sub.1 each defining a cam portion shaping region 52a in a cavity defining portion 57 of the first die 48.sub.1, and a first preheating-temperature controller 59.sub.1 connected to the individual heaters 58.sub.1.
The second preheating mechanism 54.sub.2 comprises heaters 58.sub.2 each disposed in each of second sections 57.sub.2 each defined a shank portion shaping region 52b for molding each journal portion 2b and smaller diameter portion 2d in the cavity defining portion 57, and a second preheating-temperature controller 59.sub.2 connected to the individual heaters 58.sub.2.
The third preheating mechanism 54.sub.3 comprises a plurality of heaters 58.sub.3 disposed in a molten metal passage defining portion 61 of the first die 48.sub.1 for defining a molten metal passage consisting of the sprue 49, the runner 50 and the gate 51, and a third preheating-temperature controller 59.sub.3 connected to the individual heaters 58.sub.3.
The first cooling mechanism 55.sub.1 comprises cooling water passages 62.sub.1 each mounted to extend through each of first sections 57.sub.1 in the cavity defining portion 57 of the first die 48.sub.1, and a first cooling-temperature controller 63.sub.1 connected to the individual cooling water passages 62.sub.1.
The second cooling mechanism 55.sub.2 comprises cooling water passages 62.sub.2 each mounted to extend through each of second sections 57.sub.2 in the cavity defining portion 57, and a second cooling-temperature controller 63.sub.2 connected to the individual cooling water passages 62.sub.2.
The third cooling mechanism 55.sub.3 comprises a plurality of cooling water passages 62.sub.3 mounted to extend through the molten metal passage defining portion 61 of the first die 48.sub.1, and a third cooling-temperature controller 63.sub.3 connected to the individual cooling water passages 62.sub.3.
The knock-out means 56 comprises a plurality of pins 64, a support plate 65 for supporting one ends of the knock-out pins 64, and an operating member 66 connected to the support plate 65. Each of the pins 64 is slidably received in each of insertion holes 67 provided in the first die 48.sub.1 and opened into the sprue 49, the runner 50 and the cavity 52. In the cavity 52, an opening of each insertion hole 67 is disposed in the shunk portion shaping region 52b.
Description will be made of an operation for casting the cam shaft blank 2.sub.1 in the above-described mold casting apparatus M3.
First, there is prepared a molten metal of a cast iron composition corresponding to JIS FC20 to FC30 lgiven in Table IV.
TABLE IV______________________________________Chemical constituents (% by weight)C Si Mn P S______________________________________3.2-3.6 1.7-1.8 0.5-0.7 .ltoreq.0.1 <0.1______________________________________
In a Fe-C epuilibrium phase diaggram shown in FIG. 5, the eutectic crystal line LE1 intersects a composition region of the above cast iron at approximately 1,150.degree. C.
Into the molten metal, there is added 0.15% by weight of Fe-Si, so that the resulting cam shaft blank 2.sub.1 has a composition given in Table V.
TABLE V______________________________________Chemical constituents (% by weight)C Si Mn P S______________________________________3.2-3.6 1.9-2.1 0.5-0.7 .ltoreq.0.1 .ltoreq.0.1______________________________________
The mold 48 is preheated by the individual preheating mechanisms 54.sub.1 to 54.sub.3 prior to pouring, as shown in FIG. 20, so that the individual sections 57.sub.1 defining the corresponding cam portion shaping regions 52a are maintained at approximately 70.degree. C. as indicated by a point e.sub.1 of a line D1; the individual second sections 57.sub.2 defining the corresponding shunk portion shaping regions 52b are at approximately 120.degree. C. as indicated by a point f.sub.1 of a line D2, and the molten metal passage defining portion 61 is at approximately 110.degree. C. as indicated by a point g1 of a line D3. The molten metal after inoculation is poured into the mold 48 at a temperature of 1,380.degree. to 1,420.degree. C. to cast a cam shaft blank 2.sub.1. The amount of molten metal poured is 5 kg.
If the mold 48 has been previously preheated as described above, the run of the molten metal during pouring is improved, and it is possible to avoid cracking and the like of the cam shaft blank 2.sub.1 due to the rapid cooling of the molten metal.
As indicated by the point e.sub.1 of the line D1 in FIG. 20, the first cooling mechanism 55.sub.1 is operated at the same time as the starting of pouring, thereby starting the cooling of the individual first sections 57.sub.1 to most rapidly cool the molten metal present in the individual cam portion shaping regions 52a for achivement of chilling of each of the resulting cam portions 2a.
In addition, as indicated by a point g.sub.2 of the line D3 in FIG. 20, the third cooling mechanism 55.sub.3 is operated just at the end of pouring, thereby starting the cooling of the molten metal passage defining portion 61 to start the rapid solidification of the molten metal located in the molten metal passage 60 into a early solidified state.
Further, when the temperature of the individual second section 57.sub.2 has reached 145.degree. to 180.degree. C., e.g., 150.degree. C. as indicated by a point f.sub.2 of the line D2 in FIG. 20, the second cooling mechanism 55.sub.2 is operated to start the cooling of the individual second sections 57.sub.2 to rapidly cool the molten metal located in the individual shunk portion shaping regions 52b.
As seen in FIG. 6, if the surface layer of the cam shaft blank material 2.sub.1 is rapidly cooled under the above-decribed cooling effect until the temperature thereof drops to about 1,150.degree. C. (eutectic crystal line Le1) indicated by the point a.sub.1, the cam shaft blank material 2.sub.1 becomes solidified with its surface layer converted to a shell-like solidified layer.
In this case, if the temperature of the surface layer is lower than 700.degree. C. indicated by the point a.sub.5, it is feared that thermal cracking may be produced in the resulting cam shaft blank 2.sub.1. In addition, if the temperature of the surface layer is lower than 800.degree. C. indicated by the point a.sub.4, it is also feared that adhesion of the resulting cam shaft blank 2.sub.1 to the mold 48 and so on may be produced due to the solidificational shrinkage of the cam shaft blank material 2.sub.2 to cause damage such as deformation and wearing of the mold 48.
Thereupon, when the temperature of the surface layer of the cam shaft blank material 2.sub.2 has reached 850.degree. C. indicated by the point a.sub.3 from 950.degree. C. indicated by the point a.sub.2 in about 3 to about 8 seconds after pouring, and when the temperatures of the individual portions 57.sub.1, 57.sub.2 and 61 of the mold 48 have reached ranges of points e.sub.2 to e.sub.3, points f.sub.3 to f.sub.4 and points g.sub.3 to g.sub.4 in FIG. 20, the mold is opened, and the knock-out pin means 56 is operated to release the resulting cam shaft blank 2.sub.1 and unnecessary portions shaped by the molten metal passage 60 from the mold.
Then, when the temperature of the first section 57.sub.1 is dropped down to approximately 75.degree. C. as indicated by the points e4 of the line D1; the temperature of the second section 57.sub.2 is down to approximately 125.degree. C. as indicated by a point f.sub.5 of the line D2 and further, the temperature of the molten metal passage defining portion 61 is down to approximately 115.degree. C. as indicated by a point g.sub.5 of the line D3 in FIG. 20, the operations of the individual cooling mechanisms 55.sub.1 to 55.sub.3 are stopped to stop the cooling of the first and second sections 57.sub.1 and 57.sub.2 and the molten metal passage defining portion 61.
The first to third preheating mechanisms 54.sub.1 to 54.sub.3 are operative even after the start of pouring to control the temperatures of the first and second sections 57.sub.1 and 57.sub.2 and the molten metal passage defining portion 61 as indicated by the lines D.sub.1 to D.sub.3, so that the temperatures of the first and second sections 57.sub.1 and 57.sub.2 and the molten metal passage defining portion 61 can be immediately restored to the preheated temperatures. This enables starting of the subsequent casting operation.
The cam shaft blank 2.sub.1 produced by the above procedure has no thermal cracking produced therein, and the mold 48 is also not damaged in any way. Moreover, the cam shaft blank 2.sub.2 is covered with the shell-like solidified layer and hence, cannot be deformed during release thereof. Even if it were deformed, the amount deformed is very slight.
Further, each first section 57.sub.1 is cooled just at the start of pouring and hence, the molten metal located in each cam portion shaping region 52a is rapidly cooled, thereby ensuring that each cam portion 2a can be reliably chilled.
FIG. 21A illustrates a microphotograph (100 times) showing a metallographic structure of the cam portion 2a, and FIG. 21B illustrates a microphotograph (100 times) showing metallographic structures of the journal portion 2b and the smaller diameter portion 2d. It is apparent from FIG. 21A that a white elongated cementite crystal is observed in the structure of the cam portion 2a and this demonstrates that the cam portion 2a is chilled.
When the cavity defining portion 57 and the molten metal passage defining portion 61 have been cooled until the surface layer of the cam shaft blank material 2.sub.1 has became a solidified layer, as described above, the resulting cam shaft blank is released from the mold. In addition, after releasing, a preheated-temperature restoring operation conducted for both the defining portions 57 and 61 by the above-described procedure makes it possible to achieve one run of the casting operation in an extremely short time of about 28 seconds as apparent from FIG. 20, leading to an improvement in productivity.
The optimal timing for releasing the cast iron castings of the cast irons corresponding to the above-described JIS FC20 to FC30 is when the temperature of the surface layer thereof is in a range of about 1,150.degree. to 800.degree. C. and thus between the eutectic crystal line Le1 and 350.degree. C. therebelow, and experiments have made clear that the same is true even in the case of cast iron castings employing other cast irons such as a spheroidal graphite cast iron.
It is noted that the above-described cooling operation is conducted according to the lines D2 and D3 for a casting having no chilled portion.
[V] Casting of Cam Shaft Blank of Cast Steel
FIGS. 22 to 24 show a mold casting apparatus M4 including a mold 68. The apparatus M4 is used to cast a cam shaft blank 2.sub.2 as shown in FIG. 13 as a steel casting.
The mold 68 is formed of a Cu-Cr alloy in the same manner as described above. The mold 68 is constructed of a first die 68.sub.1 and a second die 68.sub.2 into a split type, and opened and closed by an operating device which is not shown. The mold surfaces of the first and second dies 68.sub.1 and 68.sub.2 define a sprue 69, a runner 70, a gate 71, a cam shaft blank-molding cavity 72 and a vent hole 73.
Each of the first and second dies 68.sub.1 and 68.sub.2 is provided with first and second preheating mechanisms 74.sub.1 and 74.sub.2, first and second cooling mechanisms 75.sub.1 and 75.sub.3, and knock-out means 76. These portions are the same for both the dies 68.sub.1 and 68.sub.2 and hence, only those for the first dies 68.sub.1 will be described below.
The first preheating mechanism 74.sub.1 comprises a plurality of heaters 78.sub.1 disposed in a cavity defining portion 77 of the first die 68.sub.1, and a first preheating-temperature controller 79.sub.1 connected to the individual heaters 78.sub.1.
The second preheating mechanism 74.sub.3 comprises a plurality of heaters 78.sub.2 disposed in a molten metal passage defining portion 81 of the first die 68.sub.1 for defining a molten metal passage consisting of the sprue 69, the runner 70 and the gate 71, and a second preheating-temperature controller 79.sub.3 connected to the individual heaters 78.sub.3.
The first cooling mechanism 75.sub.1 comprises a plurality of cooling water passages 82.sub.1 mounted to extend through the cavity defining portion 77 of the first die 68.sub.1, and a first cooling-temperature controller 83.sub.1 connected to the individual cooling water passages 82.sub.1.
The second cooling mechanism 75.sub.3 comprises a plurality of cooling water passages 82.sub.2 mounted to extend through the molten metal passage defining portion 81 of the first die 68.sub.1, and a second cooling-temperature controller 63.sub.3 connected to the individual cooling water lines 82.sub.2.
The knock-out means 76 comprises a plurality of pins 84, a support plate 85 for supporting one ends of the knock-out pins 84, and an operating member 86 connected to the support plate 85. Each of the pins 84 is slidably received in each of insertion holes 87 provided in the first die 68.sub.1 and opened into the sprue 69, the runner 70 and the cavity 72.
Description will be made of an operation for casting the cam shaft blank 2.sub.2 in the above-described mold casting apparatus M4.
A molten metal of the same alloy cast steel composition as that described in the item [II] is prepared and subjected to similar primary and secondary deacidifying treatments.
The mold 68 is preheated by both preheating mechanisms 74.sub.1 to 74.sub.2 prior to pouring, as shown in FIG. 25, so that the cavity defining portion 77 is maintained at approximately 120.degree. C. as indicated by a point k.sub.1 of a line H1, and the molten metal passage defining portion 81 is also at approximately 110.degree. C. as indicated by a point m.sub.1 of a line H.sub.2. The molten metal deacidified is poured into the mold 68 at a temperature of 1,630.degree. to 1,670.degree. C. to cast a cam shaft blank 2.sub.2. The amount of molten metal poured at this time is 5.0 kg.
If the mold 68 has been previously preheated as described above, the run of the molten metal during pouring is improved, and it is possible to avoid cracking and the like of the resulting cam shaft blank 2.sub.2 due to the rapid cooling of the molten metal.
As indicated by a point m.sub.2 of the line H1 in FIG. 25, the second cooling mechanism 75.sub.2 is operated at the same time as the start of pouring, thereby starting the cooling of the molten metal passage defining portion 81 to start the rapid solidification of the molten metal located in the molten metal passage 80 into an early solidified state.
In addition, when the temperature of the cavity defining portion 77 has reached 280.degree. to 330.degree. C., e.g., 290.degree. C. as indicated by a point k.sub.2 of the line H1 in FIG. 25, the first cooling mechanism 75.sub.1 is operated to start cooling of the cavity defining portion 77 to rapidly cool the molten metal located in the cavity 72.
As seen in FIG. 6, if the surface layer of the cam shaft blank material 2.sub.2 is rapidly cooled under the above-described cooling effect so that the temperature thereof drops to about 1,250.degree. C. (solid phase line Ls) indicated by the point b.sub.1, the cam shaft blank 2.sub.2 assumes a solidified state with its surface layer converted to a shell-like solidified layer.
In this case, if the temperature of the surface layer is lower than 950.degree. C. indicated by the point b.sub.5, it is feared that thermal cracking may be produced in the resulting cam shaft blank 2.sub.2. In addition, if the temperature of the surface layer is lower than 1,000.degree. C. indicated by the point b.sub.4, it is also feared that adhesion of the resulting cam shaft blank 2.sub.2 to the mold 68 and so on may be produced due to the rapid and large solidification shrinkage of the cam shaft blank material 2.sub.2 to cause damage such as deformation and wearing of the mold 68.
Thereupon, when the temperature of the surface layer of the cam shaft blank material 2.sub.2 has reached 1,100.degree. C. indicated by the point b.sub.2 from 1,200.degree. C. indicated by the point a.sub.3 in about 3.5 to about 6.5 seconds after pouring, and also when the temperatures of both portions 77 and 81 of the mold 68 are in range of points k.sub.3 to k.sub.4 and points m.sub.3 to m.sub.4 in FIG. 25, the mold is opened, and the knock-out pin means 76 is operated to release the cam shaft blank 2.sub.2 and unnecessary portions shaped by the molten metal passage 80 from the mold.
Then, when the temperature of the cavity defining portion 77 is down to approximately 150.degree. C. as indicated by a point k.sub.5 of the line H2 and the temperature of the molten metal passage defining portion 81 is down to approximately 140.degree. C. as indicated by a point m.sub.5 of the line H3 in FIG. 25, the operations of the individual cooling mechanisms 75.sub.1 and 75.sub.2 are stopped to stop the cooling of the cavity defining portion 77 and the molten metal passage defining portion 81.
The first and second preheating mechanisms 74.sub.1 to 74.sub.2 are operative even after the start of pouring to control the temperatures of both defining portions 77 and 81 as indicated by the lines H.sub.1 and H.sub.2, so that the temperatures of both defining portions 77 and 81 can be immediately restored to the preheated temperatures after the cooling has been stopped. This enables starting of the subsequent casting operation.
The cam shaft blank 2.sub.2 produced by the above procedure has no thermal cracking produced therein, and the mold 48 is also not damaged in any way. Moreover, the cam shaft blank 2.sub.2 is covered with the shell-like solidified layer and hence, cannot be deformed during release thereof. Even if it were deformed, the amount deformed is very slight.
[VI] Casting of Cam Shaft Blank of Aluminum Alloy Casting
The mold casting apparatus M4 for the steel casting described in the above item [V] is used for casting a cam shaft blank 2.sub.2 as an aluminum alloy casting.
In a casting operation, a molten metal of the same aluminum alloy composition as that described in the item [III] is prepared.
The mold 68 is preheated by both preheating mechanisms 74.sub.1 to 74.sub.2 prior to pouring, as shown in FIG. 26, so that the cavity defining portion 77 is maintained at approximately 120.degree. C. as indicated by a point p.sub.1 of a line N.sub.1, and the molten metal passage defining portion 81 is also at approximately 110.degree. C. as indicated by a point q.sub.1 of a line N.sub.2. The molten metal of the aluminum alloy is poured into the mold 68 at a temperature of 700.degree. to 740.degree. C. to cast a cam shaft blank 2.sub.2. The amount of molten metal poured at this time is 2.0 kg.
If the mold 68 has been previously preheated as described above, the run of the molten metal during pouring is improved, and it is possible to avoid cracking and the like of the resulting cam shaft blank 2.sub.2 due to the rapid cooling of the molten metal.
As indicated by a point q.sub.2 of the line N.sub.1 in FIG. 26, the second cooling mechanism 75.sub.2 is operated at the same time as the start of pouring, thereby starting the cooling of the molten metal passage defining portion 81 to start the rapid solidification of the molten metal located in the molten metal passage 80, bringing it early into a solidified state.
In addition, when the temperature of the cavity defining portion 77 has reached 140.degree. to 170.degree. C., e.g., 150.degree. C. as indicated by a point p.sub.2 of the line N.sub.1 in FIG. 26, the first cooling mechanism 75.sub.1 is operated to start the cooling of the cavity defining portion 77 to rapidly cool the molten metal located in the cavity 72.
As seen in FIG. 16, if the surface layer of the cam shaft blank material 2.sub.2 is rapidly cooled under the above-described cooling effect so that the temperature thereof drops to about 580.degree. C. (eutectic crystal line Le2) indicated by the point c.sub.1, the cam shaft blank 2.sub.2 assumes a solidified state with its surface layer converted to a shell-like solidified layer.
In this case, if the temperature of the surface layer is lower than 280.degree. C. indicated by the point c.sub.4, it is feared that thermal cracking may be produced in the resulting cam shaft blank 2.sub.2. In addition, if the temperature of the surface layer is lower than 350.degree. C. indicated by the point c.sub.3, it is also feared that adhesion of the resulting cam shaft blank 2.sub.2 to the mold 68 and so on may be produced due to the rapid and large solidificational shrinkage of the cam shaft blank material 2.sub.2 to cause damage such as deformation and wearing of the mold 68.
Thereupon, when the temperature of the surface layer of the cam shaft blank 2.sub.2 has reached 500.degree. C. indicated by the point c.sub.2 in about 3.0 to about 10.8 seconds after pouring, and also when the temperatures of both portions 77 and 81 of the mold 68 are in the range of points p.sub.3 to p.sub.4 and points q.sub.3 to q.sub.4 in FIG. 26, the mold is opened, and the knock-out pin means 76 is operated to release the resulting cam shaft blank 2.sub.2 and unnecessary portions shaped by the molten metal passage 80 from the mold.
Then, when the temperature of the cavity defining portion 77 is down to approximately 125.degree. C. as indicated by a point p.sub.5 of the line N.sub.2 and the temperature of the molten metal passage defining portion 81 is down to approximately 115.degree. C. as indicated by a point q.sub.5 of the line N.sub.3 in FIG. 26, the operations of the individual cooling mechanisms 75.sub.1 and 75.sub.2 are stopped to stop the cooling of the cavity defining portion 77 and the molten metal passage defining portion 81.
The first and second preheating mechanisms 74.sub.1 to 74.sub.2 are operative even after start of pouring to control the temperatures of both defining portions 77 and 81 as indicated by the lines N.sub.1 and N.sub.2, so that the temperatures of both defining portoins 77 and 81 can be immediately restored to the preheated temperatures after the cooling has been stopped. This enables starting of the subsequent casting operation.
The cam shaft blank 2.sub.2 produced by the above procedure has no thermal cracking produced therein, and the mold 48 is also not damaged in any way. Moreover, the cam shaft blank 2.sub.2 is covered with the shell-like solidified layer and hence, cannot be deformed during release thereof. Even if it were deformed, the amount deformed is very slight.
In some cases, cooling of the cavity defining portion 57, 77 in each of the casting operations in the items [IV] to [VI] may be started before completion of pouring, and cooling of the molten metal defining portion 61, 81 may be started immediately after completion of pouring.
[VII] Casting of Cam Shaft Blank of Cast Iron
FIGS. 27 to 29 shows a mold casting apparatus M5 which is used to cast a cam shaft blank 2.sub.1 as shown in FIG. 4 as a cast iron casting.
The mold casting apparatus M5 is constructed in the following manner.
Crucible 89 opened at its upper surface is contained within a heater 88 likewise opened at its upper surface, with upward openings of the heater 88 and the crucible 89 being closed by a lid 90. A mold 91 is disposed on the lid 90, and pressing means for pressing a molten metal present in a cavity of the mold 91, e.g., a pressing cylinder 93 in the illustrated embodiment is disposed, with its piston rod 94 directed upwardly, on a support frame 92 on the lid 90. The piston rod 94 has, at its lower end, a larger diameter portion 95 of a copper alloy, which is of a water-cooled construction, but instead thereof, a lower end portion of the larger diameter portion 95 may be formed of a ceramic material.
The mold 91 comprises a cavity defining portion 97 including a cavity 96 for casting a cam shaft blank, and a molten metal passage defining portion 99 having a frustoconical molten metal passage 98 in communication with a lower end of the cavity 96. In the illustrated embodiment, the cavity 96 and the molten metal passage 98 communicate with each other through the cavity defining portion 97. The molten metal passage 98 communicates at its lower end with the crucible 89 through a molten metal supply pipe 101 suspended on the lid 99.
The cavity defining portion 97 is constructed of first and second components 97.sub.1 and 97.sub.2 into a split type, and mold surfaces of the two components 97.sub.1 and 97.sub.2 define a through hole 100, the cavity 96, and a pressing hole 102 communicating with the cavity 96 and adapted to slidably receive the larger diameter portion 95 of the piston rod 94. The two components 97.sub.1 and 97.sub.2 are opened and closed by an operating device which is not shown.
The molten metal defining portion 99 is also constructed of first and second blocks 99.sub.1 and 99.sub.2 into a split type in association with the cavity defining portion 97, and mold surfaces of the both blocks 99.sub.1 and 99.sub.2 define the molten metal passage 98. The reference numeral 103 designates an operating cylinder for opening and closing the two blocks 99.sub.1 and 99.sub.2.
The cavity defining portion 97 and an inner portion 99a of the molten metal passage defining portion 99 are formed of a highly heat conductive material, e.g., a Cu-Cr alloy containing 0.8 to 4% by weight of Cr, with a heat conductivity thereof being of 0.4 to 0.8 cal/cm/sec./.degree. C. An outer portion 99b of the molten metal passage defining portion 99 are formed of a steel.
In the molten metal passage defining portion 99, a first cooling circuit 104.sub.1 is mounted in each of the both inner portions 99a. The first cooling circuit 104.sub.1 includes a water passage 105a located around the molten metal passage 98, and a water passage 105b communicating with the water passage 105a and distributed throughout the inner portion 99a, with a supply port and a discharge port (both not shown) being provided in the water passage 105b.
The both first cooling circuits 104.sub.1 are connected to a first cooling-temperature controller 106.sub.1 which has a function for operating each of the first cooling circuit 104.sub.1 to rapidly cool and solidify the molten metal within the molten metal passage 98 after charging of the molten metal into the cavity 96, thereby closing the molten metal passage 98.
In the cavity defining portion 97, each of the first and second components 97.sub.1 and 97.sub.2 is provided with a heating circuit 107, a second cooling circuit 104.sub.2 and knock-out means 108. These portions are the same for the both components 97.sub.1 and 97.sub.2 and hence, only those for the first component 97.sub.1 will be described.
The heating circuit 107 is constituted of a plurality of insertion holes 109 perforated in the first component 97.sub.1, and bar-like heaters 110 inserted into and held in the corresponding insertion holes 109, respectively. Each of the insertion holes 109 is disposed with a portion thereof being in proximity to a region for shaping each smaller diameter portion 2d of the cam shaft blank 2.sub.1 in the first component 97.sub.1.
The second cooling circuit 104.sub.2 comprises an upper inlet passage 111 horizontally made in the first component 97.sub.1, a lower outlet passage 112 likewise made in the first component 97.sub.1, and a plurality of communication passages 113.sub.1 and 113.sub.2 made in the first component 97.sub.1 to extend horizontally and vertically in an intersecting relation to each other to connect the inlet and outlet passages 111 and 112, so that water introduced into the inlet passage 111 is passed via the individual communication passages 113.sub.1 and 113.sub.2 and discharged through the outlet passage 112. The inlet passage 111, the outlet passage 115 and the individual horizontal communication passages 113.sub.1 are disposed so that a portion of each of them may be in proximity to a region in the first component 97.sub.1 for shaping the nose 2e which is a chilled portion of the cam portion 2a.
The individual heaters 110 of the heating circuit 107 are connected to a heating-temperature controller 114 which has a function for activating the heating circuit 107 and thus energizing the individual heaters 110 to heat the first component 97.sub.1 prior to pouring of a molten metal into the cavity 96, and deactivating the heating circuit 107 and thus deenergizing the individual heaters 110 after starting of pouring.
During heating, each heater 110 is spaced apart from the nose 2e shaping region of the first component 97.sub.1 and hence, the temperature of that region is lower than other regions. Of course, the individual heaters 110 of the second component 97.sub.2 are also connected to the heating-temperature controller 114.
The inlet passage 111 and the outlet passage 112 of the second cooling circuit 104.sub.2 are connected to a second cooling-temperature controller 106.sub.2 which includes a function for activating the second cooling circuit 104.sub.2 and thus permitting a coolin water to flow through the second cooling circuit 104.sub.2 to cool the first component 97.sub.1 after starting of pouring, thereby rapidly cooling a surface layer of the cam shaft blank material 2.sub.1 in contact with the first component 97.sub.1 to convert the surface layer into a shell-like solidified layer.
During cooling, the noses 2e can be rapidly cooled to ensure that they are reliably chilled, because the inlet passage 111, the outlet passage 112 and the individual horizontal communication passages 113.sub.1 are in proximity to the noses 2e shaping regions of the first component 97.sub.1 and also because those regions are at a lower temperature than that of other regions at the heating stage. Of course, the second cooling circuit 104.sub.2 of the second component 97.sub.2 is also connected to the second cooling-temperature controller 106.sub.2.
The knock-out means 108 comprises a plurality of pins 115, a support plate 116 for supporting one ends of the pins 115, and an operating member 117 connected to the support plate 116. Each of the pins 115 is slidably received in each of insertion holes 118 opened into the cavity 96.
The pressing cylinder 93 has a function for applying a pressing force to an unsolidified cam shaft blank material 2.sub.1 present in the cavity 96 to maintain it up to a releasing point, after the molten metal psaage 98 has been closed.
The following is the description of an operation for casting a cam shaft blank 2.sub.1 in the above-described mold casting apparatus M5.
There is prepared a molten metal of the same cast iron composition as that described in the item [IV], and the molten metal is subjected to a similar inoculation, followed by placement into the crucible 89 for heating.
The cavity defining portion 97 is heated prior to pouring of the molten metal, so that a region for shaping each smaller diameter portion 2d is maintained at a temperature of 100.degree. to 150.degree. C., and the region for shaping the nose 2e is at a temperature of 50.degree. to 100.degree. C.
A gas pressure is applied to the surface of the molten metal in the crucible 89 at a molten metal temperature of 1380.degree. to 1420.degree. C. to pour the molten metal into the cavity 96 through the molten metal supply pipe 101, the molten metal passage 98 and the through hole 100, thereby casting a cam shaft blank 2.sub.1. The amount of molten metal poured at this time is 5 kg.
If the cavity defining portion 97 has been previously heated as described above, the running of the molten metal during pouring is improved, and it is possible to avoid cracking and the like of the cam shaft blank 2.sub.1 due to rapid cooling of the molten metal.
The pouring rate is controlled at a constant level in a range of 0.6 to 1.5 kg/sec., and this makes it possible to prevent the production of casting defects such as cavities and the like due to inclusion of gases, oxides and the like.
After starting of pouring, heating of the cavity defining portion 97 by the heating circuit 107 is stopped and at the same time, the cavity defining portion 97 is started to be cooled by the second cooling circuit 104.sub.2.
Then, after the molten metal has been charged into the cavity 96, the molten metal passage defining portion 99 is cooled by the first cooling circuit 104.sub.1, rapidly cooling and solidifying the molten metal in the molten metal passage 98 to close the latter. The operation of the first cooling circuit 104.sub.1 is continued immediately before releasing of the resulting cam shaft blank. The molten metal in the molten metal supply pipe 101 is passed back into the crucible 89 after solidification of the molten metal in the molten metal passage 98.
Then, the pressing cylinder 93 is operated to press the molten metal in the cavity 96, i.e., the unsolidified cam shaft blank material 2.sub.1 with a pressure of 0.8 to 1.2 kg/cm.sup.2 by the larger diameter portion 95. This operation of the pressing cylinder 93 is continued immediately before releasing of the resulting cam shaft blank.
Thereafter, the resulting cam shaft blank 2.sub.1 is released from the mold, and the timing therefor is as described in the item [I] with reference to FIG. 6.
According to the above procedure, an effect similar to that in the item [I] can be provided and particularly, in this case, it is possible to provide a good quality cam shaft blank 2.sub.1 free from interal defects, because rapid cooling of the cam shaft blank material 2.sub.1 is conducted while applying a pressure.
[VIII] Casting of Cam Shaft Blank of Cast Steel
FIGS. 30 to 32 show a mold casting apparatus M6 which is used to cast a cam shaft blank 2.sub.2 as a steel casting as shown in FIG. 13. The apparatus M6 has the same arrangements as those described in the item [VII] except for a mold 119. Therefore, in the Figures, the like reference characters are used to designate like parts; and the description thereof is omitted and primarily, the mold 119 will be described below.
The mold 119 comprises a cavity defining portion 121 including a cavity 120 for a cam shaft blank, and a molten metal passage defining portion 123 having a frustoconical molten metal passage 122 communicating with a lower end of the cavity 120, and is formed of, for example, the same material as that described in the item [VII]. In the illustrated embodiment, the cavity 120 and the molten metal passage 122 communicate with each other via a through hole 124 in the cavity defining portion 121. The molten metal passage 122 communicates at its lower end with the crucible 89 through the molten metal supply pipe 101 suspended on the lid 90.
The cavity defining portion 121 is constructed of first and second components 121.sub.1 and 121.sub.2 into a split type, and mold surfaces of the two components 121.sub.1 and 121.sub.2 define a through hole 124, the cavity 120, and a pressing hole 125 adapted to slidably receive the larger diameter portion 95 of the piston rod 94. The two components 121.sub.1 and 121.sub.2 are opened and closed by an operating device which is not shown.
The molten metal defining portion 123 is also constructed of first and second blocks 123.sub.1 and 123.sub.2 into a split type in association with the cavity defining portion 121, and mold surfaces of the both blocks 123.sub.1 and 123.sub.2 define the molten metal passage 122.
In the molten metal passage defining portion 123, a first cooling circuit 126.sub.1 is mounted in each of the both inner portions 123a. The first cooling circuit 126.sub.1 includes a water passage 127a located around the molten metal passage 122, and a water passage 127b communicating with the water passage 127a and distributed throughout the inner portion 123a, with a supply port and a discharge port (not shown) being provided in the water passage 127b.
Both the first cooling circuits 126.sub.1 are connected to a first cooling-temperature controller 128.sub.1 which has a function for operating each of the first cooling circuit 126.sub.1 to rapidly cool and solidify the molten metal within the molten metal passage 122 after charging of the molten metal into the cavity 120, thereby closing the molten metal passage 122.
In the cavity defining portion 121, each of the first and second components 121.sub.1 and 121.sub.2 is provided with a heating circuit 129, a second cooling circuit 126.sub.2 and knock-out means 130. These portions are the same for both components 121.sub.1 and 121.sub.2 and hence, only those for the first component 121.sub.1 will be described.
The heating circuit 129 is constituted of a plurality of insertion holes 131 perforated in the first component 121.sub.1, and bar-like heaters 132 inserted into and held in the corresponding insertion holes 131, respectively.
The individual heaters 132 are connected to a heating-temperature controller 114 which includes a function for activating the heating circuit 129 and thus energizing the individual heaters 132 to heat the first component 121.sub.1 prior to pouring of a molten metal, and deactivating the heating circuit 129 and thus deenergizing the individual heaters 132 after starting of pouring. Of course, the individual heaters 129 of the second component 121.sub.2 are also connected to the heating-temperature controller 133.
The second cooling circuit 126.sub.2 comprises a horizontal inlet passage 134 made in an upper portion of the first component 121.sub.1, a horizontal outlet passage 135 made in a lower portion of the first component, and a plurality of vertical communication passages 136 made in the first component 121.sub.1 to connect the inlet and outlet passages 134 and 135, so that a cooling water introduced into the inlet passage 134 is permitted to flow through the individual communication passage 136 and discharged through the outlet passage 135.
The inlet passage 134 and the outlet passage 135 are connected to a second cooling-temperature controller 128.sub.2 which includes a function for activating the second cooling circuit 126.sub.2 and thus permitting cooling water to flow through the second cooling circuit 126.sub.2 to cool the first component 121.sub.1 after the starting of pouring, thereby rapidly cooling a surface layer of the cam shaft blank material 2.sub.1 in contact with the first component 121.sub.1 to convert the surface layer into a shell-like solidified layer.
The knock-out means 130 comprises a plurality of pins 137, a support plate 138 for supporting one ends of the pins 137, and an operating member 139 connected to the support plate 138. Each of the pins 137 is slidably received in each of insertion holes 118 provided in the first component 121.sub.1 and opened into the cavity 120 and through hole 124.
The following is the description of an operation for casting a cam shaft blank 2.sub.2 in the above-described mold casting apparatus M5.
There is prepared a molten metal of the same cast iron composition as that described in the item [II], and the molten metal is subjected to similar primary and secondary deacidifying treatments, followed by placement into the crucible 89 for heating.
The cavity defining portion 121 has been heated to a temperature of 50.degree. to 180.degree. C. by the heating circuit 129 prior to pouring of the molten metal. A gas pressure is applied to the surface of the molten metal in the crucible 89 at a molten metal temperature of 1630.degree. to 1670.degree. C. to pour the molten metal into the cavity 120 through the molten metal supply pipe 101, the molten metal passage 122 and the through hole 124, thereby casting a cam shaft blank 2.sub.2. The pouring rate and the amount of molten metal poured are the same as those in the item [VII].
After starting of pouring, heating of the cavity defining portion 121 by the heating circuit 129 is stopped and at the same time, the cavity defining portion 121 begins to be cooled by the second cooling circuit 126.sub.2.
Then, after the molten metal has been charged into the cavity 120, the molten metal passage defining portion 123 is cooled by the first cooling circuit 126.sub.1, rapidly cooling and solidifying the molten metal in the molten metal passage 122 to close the latter. The operation of the first cooling circuit 126.sub.1 is continued immediately before releasing of the resulting cam shaft blank.
Then, the pressing cylinder 93 is operated to press the molten metal in the cavity 120, i.e., the unsolidified cam shaft blank material 2.sub.2 with a pressure of 0.8 to 1.2 kg/cm.sup.2 by the larger diameter portion 95. This operation of the pressing cylinder 93 is continued immediately before releasing of the resulting cam shaft blank.
Thereafter, the resulting cam shaft blank 2.sub.2 is released from the mold, and the timing therefor is as described in the item [II] with reference to FIG. 14.
According to the above procedure, an effect similar to that in the item [II] can be provided and particularly, in this case, it is possible to provide a good quality cam shaft blank 2.sub.2 free from interal defects, because rapid cooling of the cam shaft blank material 2.sub.2 is conducted while applying a pressure.
[VIII] Casting of Cam Shaft Blank of Aluminum Alloy Casting
The mold casting apparatus M6 for a steel casting described in the item [VIII] is used in casting a cam shaft blank as an aluminum alloy casting.
In casting, there is prepared a molten metal of the same aluminum alloy composition as that described in the item [III], and the molten metal is placed into the crucible 89 and heated therein.
The cavity defining portion 121 has been heated to a temperature of 100.degree. to 140.degree. C. by the heating circuit 129 prior to pouring of the molten metal. A gas pressure is applied to the surface of the molten metal in the crucible 89 to pour the molten metal into the cavity 120 through the molten metal supply pipe 101, the molten metal passage 122 and the through hole 124 at a temperature of 700.degree. to 749.degree. C. and a pouring rate of 0.3 to 0.8 kg/sec., thereby casting a cam shaft blank 2.sub.2. The amount of molten metal poured at this time is 2.0 kg.
If the cavity defining portion 121 has been previously heated as described above, the running of the molten metal during pouring is improved, and it is possible to avoid cracking and the like of the resulting cam shaft blank 2.sub.2 due to rapid cooling of the molten metal.
After starting of pouring, heating of the cavity defining portion 121 by the heating circuit 129 is stopped and at the same time, the cavity defining portion 121 is started to be cooled by the second cooling circuit 126.sub.2.
Then, after the molten metal has been charged into the cavity 120, the molten metal passage defining portion 123 is cooled by the first cooling circuit 126.sub.1, rapidly cooling and solidifying the molten metal in the molten metal passage 122 to close the latter. The operation of the first cooling circuit 126.sub.1 is continued immediately before releasing of the resulting cam shaft blank.
Then, the pressing cylinder 93 is operated to press the molten metal in the cavity 120, i.e., the unsolidified cam shaft blank material 2.sub.2 with a pressure of 0.2 to 0.5 kg/cm.sup.2 by the larger diameter portion 95. This operation of the pressing cylinder 93 is continued immediately before releasing of the resulting cam shaft blank.
Thereafter, the resulting cam shaft blank 2.sub.2 is released from the mold, and the timing therefor is as described in the item [III] with reference to FIG. 16.
According to the above procedure, an effect similar to that in the item [III] can be provided and particularly, in this case, it is possible to provide a good quality cam shaft blank 2.sub.2 free from interal defects, because rapid cooling of the cam shaft blank material 2.sub.2 is conducted while applying a pressure.
The pressing pressure has been applied to the molten metal within the cavity 96, 120 by the pressing cylinder 93 in the items [VII] to [IX], but it should be understood that a pressing pressure may be applied to the molten metal within the cavity 96, 120 by a riser. In addition, the heating-temperature controller 114, 133 may have a function for reducing an output from the heating circuit 107, 129 and thus decreasing an energizing current for the individual heater 110, 132. Further, any manner may be used to pour the molten metal into the cavity 96, 120, and for example, the molten metal may be poured horizontally or from above. Yet further, the cavity defining portion 97, 121 may be integral with the molten metal passage defining portion 99, 123.
[X] Casting of Cam Shaft Blank of Cast Iron
There is prepared a cam shaft blank 2.sub.1 as a cast iron casting as shown in FIG. 4. In the cam shaft blank 2.sub.1, a nose 2e of each cam portion 2a as a first component is of a hard structure and in this embodiment, of a chilled structure, and other portions, i.e., a base circular portion 2f of each cam portion 2a, each journal portion 2b, each neck portion 2c and each smaller diameter portion 2d are of soft structures and in this embodiment, of eutectic graphite or graphite flake structures.
FIGS. 33 to 38 show a mold casting apparatus M7 including a mold 141 for casting a cam shaft blank 2.sub.1. The mold 141 is constructed of a first die 141.sub.1 and a second die 141.sub.2 into a split type, and is opened and closed by an operating device which is not shown. Mold surfaces 141a of the first and second dies 141.sub.1 and 141.sub.2 define a sprue 142, a runner 143, a gate 144, a cam shaft blank molding cavity 145 and a riser gate 146.
The first and second dies 141.sub.1 and 141.sub.2 are of substantially the same construction and hence, only the first die 141.sub.1 will be described. The first die 141.sub.1 comprises a body 147 including the sprue 142, the runner 143 and the gate 144, and a molding block 150 having the cavity 145 and the riser gate 146 and fitted in a recess 148 in the body 147 with a heat insulating material 149.sub.1 interposed therebetween.
The molding block 150 comprises a slowly-cooled portion 151 including a base circular portion shaping zone r.sub.1, r.sub.2 (FIGS. 35, 36) for shaping the whole or one half of the base circular portion 2f of the cam portion 2a, a journal portion shaping zone r.sub.3 for shaping the journal portion 2b, a neck portion shaping zone r.sub.4 for shaping the neck portion 2c and a smaller diameter portion shaping zone r.sub.5 for shaping the smaller diameter portion 2d to serve as a second component shaping region, and a plurality of plate-like rapidly-cooled portions 154.sub.1 and 154.sub.2 mounted in through holes 152 and 153 in the body 147 and the slowly-cooled portion 151 of the first die 141.sub.1 to serve as a first component shaping region and including a nose shaping zone r.sub.6, r.sub.7 (FIGS. 36, 37) for shaping the whole or one half of the nose 2e of the cam portion 2a.
A heat insulating material 149.sub.2 similar to that described above is interposed between the slowly cooling member 151 and each of the rapidly-cooled portions 154.sub.1 and 154.sub.2, but in the vicinity of the mold surfaces 141a, the slowly-cooled portion 151 is in direct contact with the rapidly-cooled portions 154.sub.1 and 154.sub.2. This permits a heat transfer between the slowly-cooled portion 151 and the rapidly-cooled portions 154.sub.1 and 154.sub.2, but such heat transfer is substantially suppressed.
The body 147 and the rapidly-cooled portions 154.sub.1 and 154.sub.2 are formed of a Cu-Cr alloy containing 0.8 to 4% by weight of Cr and has a heat conductivity of 0.4 to 0.8 cals/cm/sec./.degree.C.
The slowly-cooled portion 151 is formed of graphite and has a heat conductivity of 0.005 to 0.4 cals/cm/sec./.degree.C. In addition to graphite, other materials for forming the slowly-cooled portion 151 can be employed such as ceramics, copper alloys, steels, etc., and in any case, materials having a heat conductivity lower than that of the rapidly-cooled portions 154.sub.1 and 154.sub.2 are preferred.
Each of the heat insulating materials 149.sub.1 and 149.sub.2 used are of a ceramic sheet made of an inorganic fiber such as alumina and silica fibers.
A cooling circuit 155.sub.1 is provided in the body 147 and comprised of a vertical cooling-water inlet passage 156 made in the body 147 along the sprue 142, a vertical cooling-water outlet passage 157 made in the body 147 along the molding block 150 at the opposite side from the sprue 142, and a horizontal communication passage 158 made in the body 147 to connect to both passages 156 and 157 at their lower portions.
The slowly-cooled portion 151 is also provided with a heating circuit 159 and a cooling circuit 155.sub.2. The heating circuit 159 comprises a pair of vertical insertion holes 160 perforated in the slowly-cooled portion 151 in a manner to sandwich the individual rapidly-cooled portions 154.sub.1 and 154.sub.2 and in close proximity to the mold surfaces 141a, and bar-like heaters 161 mounted in the corresponding insertion holes 160. The cooling circuit 155.sub.2 comprises vertical cooling-water inlet and outlet passages 162 and 163 made in the slowly-cooled portion 151 to sandwich the individual rapidly-cooled portions 154.sub.1 and 154.sub.2 and to extend away from the mold surfaces 141a, and a horizontal communication passage 164 made in the slowly-cooled portion 151 to connect both passages 162 and 163 at their lower portions. In this case, the volume of the slowly-cooled portion 151 occupied by the cooling circuit 155.sub.2 is smaller.
Further, a cooling circuit 155.sub.3 is provided in each of the rapidly-cooled portions 154.sub.1 and 154.sub.2 and comprises horizontal cooling-water inlet and outlet passages 165 and 166 made in the rapidly-cooled portion 154.sub.1 and 154.sub.2, and a horizontal communication passage 167 connecting the passages 165 and 166 in the vicinity of the nose shaping zone r.sub.6, r.sub.7. In this case, the volume of the rapidly-cooled portion 154.sub.1, 154.sub.2 occupied by the cooling circuit 155.sub.3 is larger.
The individual heater 161 of the heating circuit 159 in each of the first and second dies 141.sub.1 and 141.sub.2 are connected to a heating-temperature controller 168 which includes a function for energizing each heater 161 to heat the slowly-cooled portion 151 prior to pouring of a molten metal, and deenergizing each heater 161 as pouring is started.
During heating, transferring of heat from the slowly-cooled portion 151 causes the rapidly-cooled portions 154.sub.1 and 154.sub.2 to be also heated, but such transferring of heat is substantially suppressed, because the heat insulating material 149.sub.2 is interposed between the both members 151 and 154.sub.1, 154.sub.2 and also because the members 151 and 154.sub.1, 154.sub.2 are in direct contact with each other at their reduced portions. Thus, the temperature of the rapidly-cooled portions 154.sub.1 and 154.sub.2 become lower than that of the slowly-cooled portion 151, resulting in a distinct difference in temperature therebetween.
The inlet passages 156, 162 and 165 and the outlet passages 157, 163 and 166 of the cooling circuits 155.sub.1 to 155.sub.3 in the first and second dies 141.sub.1 and 141.sub.2 are connected to a cooling-temperature controller 169 which includes a function for permitting a cooling water to flow through the individual cooling circuits 155.sub.1 to 155.sub.3 to cool the body 147, the slowly-cooled portion 151 and the rapidly-cooled portions 154.sub.1 and 154.sub.2, as pouring of a molten metal is started.
During cooling, the slowly-cooled portion 151 is slowly cooled due to its lower heat conductivity and the smaller volume occupied by the cooling circuit 155.sub.2. On the other hand, the rapidly-cooled portions 154.sub.1 and 154.sub.2 are rapidly cooled due to its higher heat conductivity and the larger volume occupied by the cooling circuit 155.sub.3. In this case, a distinct difference in temperature is produced between the slowly-cooled portion 151 and the rapidly-cooled portion 154.sub.1, 154.sub.2, because of the heat insulating material 149.sub.2 interposed between the both portions 151 and 154.sub.1, 154.sub.2 and also because of the difference in temperature before pouring.
This enables the nose 2e in each cam portion 2a of the resulting cam shaft blank 2.sub.1 to be formed of a chilled structure and also enables other portions of the resulting cam shaft blank 2.sub.1 to be formed in an eutectic graphite or graphite flake structure.
Description will be made of an operation for casting a cam shaft blank 2.sub.1 in the above-described mold casting apparatus M7.
There is prepared a molten metal of the same cast iron composition as that described in the item [IV], and the molten metal is subjected to a similar inoculation.
The mold 141 is heated by the heating circuit 159 prior to pouring of the molten metal, so that the slowly-cooled portion 151 is maintained at a temperature of 150.degree. to 450.degree. C., and the individual rapidly-cooled portions 154.sub.1 and 154.sub.2 are maintained at a temperature 120.degree. C. The molten metal after inoculation is poured into the mold 141 at a temperature 1380.degree. to 1420.degree. C. to cast a cam shaft blank 2.sub.1. The amount of molten metal poured at this time is of 5 kg.
If the mold 141 has been previously heated as described above, the running of the molten metal during pouring is improved, and it is possible to avoid cracking and the like of the resulting cam shaft blank 2.sub.1 due to rapid cooling of the molten metal.
After starting of pouring, heating of the mold 141 by the heating circuit 159 is stopped, and at the same time, the mold 141 is started to be cooled by the cooling circuits 155.sub.1 to 155.sub.3, so that the slowly-cooled portion 151 is slowly cooled and the individual rapidly-cooled portions 154.sub.1 and 154.sub.2 are rapidly cooled.
This cooling operation is continued until the solidification of the cam shaft blank material 2.sub.1 has been completed with the entire outer periphery thereof converted into a shell-like solidified layer. Thereafter, the mold is opened, and the resulting cam shaft blank 2.sub.1 is released from the mold.
The temperature of the solidified layer at this releasing is preferred to be in a range of from the eutectic crystal line to 350.degree. C. therebelow. This makes it possible to avoid thermal cracking of the resulting cam shaft blank 2.sub.1 and also avoid damage of the mold 141 due to the solidificational shrinkage of the cam shaft blank material 2.sub.1.
In the cam shaft blank 2.sub.1, each nose 2e is of a chilled structure having fine Fe.sub.3 C particles (white portion), as apparent from a microphotograph (100 times) shown in FIG. 39A for illustrating a metallographical structure, and other portions, for example, a journal portion 4 is of a structure having graphite flake particles (blank portion), as apparent from a microphotograph shown in FIG. 39B for illustrating a metallograpgical structure.
Each nose 2e of the aforesaid chilled structure is excellent in wear resistance, and the journal portion 2b or the like of the aforesaid graphite flake structure has a toughness and a good workability.
In this embodiment, the casting material is not limited to the cast iron, and a carbon cast steel and an alloy cast steel can be used. Further, the heating-temperature controller 168 may be designed so that an energizing current to the individual heaters 161 is reduced as pouring is started, thereby decreasing the amount of heat for heating the mold 141.
The mold casting processes described in the items [I] to [X] are not limited to the production of the cam shaft blank, and are also applicable to the casting production of various mechanical parts such as crank shaft, brake caliper and nuckle arm blanks.
[XI] Casting of Nuckle Arm Blank of Cast Iron
As shown in FIGS. 40 to 42, a nuckle arm blank 170 as a cast iron casting includes a blank body 170a as a thicker portion and a cylindrical portion 170b integral with the body 170a as a thiner portion.
A mold casting apparatus M8 for casting the nuckle arm blank 170 comprises a pair of left and right or first and second stationary base plates 171.sub.1 and 171.sub.2 between which a plurality of guide posts 171 are suspended. A movable frame 173 is slidably supported on the guide posts 172, and a piston rod 175 of a operating cylinder 174 is attached to the first stationary base plate 171.sub.1 and connected to the movable frame 173.
The mold 176 for a nuckle arm blank comprises a mold body 177 and a movable core 178 mounted in the mold body 177 for shaping the cylindrical portion 170b in cooperation therewith. The mold body 177 is comprised of a movable die 177.sub.1 attached to a die base 179 of the movable frame 173, and a stationary die 177.sub.2 attached to a die base 180 of the second stationary base plate 171.sub.2. The movable core 178 is slidably received into an insertion hole 181 provided in the stationary die 177.sub.2, and a piston rod 183 of an operating cylinder 182 is attached to the second stationary base plate 171.sub.2 and connected to the movable core 178. The reference numeral 184 designates a knock-out means in the movable die 177.sub.1 and the stationary die 177.sub.2. Each knock-out means 184 comprises a plurality of pins 186 slidably received in insertion holes in each of the movable die 177.sub.1 and the stationary die 177.sub.2, and an operating cylinder 189 attached to the movable frame 173 and having a piston rod 188 connected to a support plate 187.
Each of the movable die 177.sub.1 and the stationary die 177.sub.2 is provided with a cooling circuit 191 including a cooling-water channel distributed over the entire region of each of the dies 177.sub.1 and 177.sub.2, and a heating circuit 194 including bar-like heaters 193 inserted into and held in a plurality of insertion holes, respectively. A cooling circuit 196 including a cooling-water channel 195 (FIG. 42) is also provided in the movable core 178.
Description will now be made of an operation for casting a knuckle arm blank 170 in the above-described mold casting apparatus M8.
As shown in FIG. 41, the movable die 177.sub.1 is moved and mated to the stationary die 177.sub.2, with the movable core 178 placed in a space between both the dies 171.sub.1 and 171.sub.2, and the mold is clamped, thereby defining a cavity 197 for knuckle arm blank 170. The heating circuit 194 is operated to heat the movable die 177.sub.1 and the stationary die 177.sub.2.
There is prepared a molten metal of the same cast iron composition as that described in the item [IV)], and the molten metal is subjected to a similar inoculation, followed by pouring into the cavity 197 for casting of the knuckle arm blank 170.
After starting of pouring of the molten metal, heating of the movable die 177.sub.1 and the stationary die 177.sub.2 by the heating circuit 194 is stopped and at the same time, the cooling circuits 191 in both dies 177.sub.1 and 177.sub.2 are operated to start cooling thereof. During this casting operation, the cooling circuit 196 in the movable circuit 178 is kept inoperative.
Surface layers of the blank body 170a and the cylindrical portion 170b are rapidly cooled under a rapidly-cooled effect of the movable die 177.sub.1, the stationary die 177.sub.2 and the movable core 178. When the temperature of the surface layers is down to about 1150.degree. C. (eutectic crystal line Le1) as described above, the blank body 170a and the cylindrical portion 170b becomes solidified with their surface layers each converted into a shell-like solidified layer.
The appearance of the solidified layer is earlier on the cylindrical portion 170b because of its thinner wall, as compared with that on the thicker blank body 170a.
Thus, when the surface layer of the cylindrical portion 178 has been converted into the solidified layer, the movable core 178 is retracted from the cylindrical portion 170b, as shown by a chain line in FIG. 42.
Thereafter, when the surface layer of the blank body 170a has been converted into the solidified layer, the movable die 177.sub.1 is moved to provide the mold opening, and the resulting nuckle arm 170 is released from the mold by the knock-out means 184.
FIG. 43 illustrates a relationship of the amount of mold 176 thermally expanded and the shrinkage of knuckle arm blank 170 with respect to elapsed time after pouring of the molten metal, wherein a line S1 corresponds to that of the cylindrical portion shaping region of the mold 176; a line T1 corresponds to that of the blank body shaping region of the mold 176; a line S2 corresponds to that of the cylindrical portion 170 of the knuckle arm blank 170; and a line T2 corresponds to the blank body 170a of the knuckle arm blank 170.
It can be seen from FIG. 43 that removal of the movable core 178 should be conducted after a lapse of about 4 to 6 seconds from the pouring, and releasing of the knuckle arm blank 170 from the mold should be conducted after a lapse of about 12 to about 16 seconds. If such removal and releasing are conducted earlier, the cylindrical portion 170b and the blank body 170a have no shape retention because of their unsolidified states. On the other hand, if removal and releasing are conducted later thermal cracking of the resulting knuckle arm blank 170 and damage of the mold 176, particularly the movable die 177.sub.1 and the stationary die 177 are produced.
FIG. 44 illustrates a relationship similar to that in FIG. 43, except that the cooling circuit 196 in the movable core 178 is operated after the starting of pouring in the above-described casting operation, so that cooling of the movable core 178 is also used.
FIG. 45 illustrates a relationship between the temperatures of the mold 176 and the knuckle arm blank 170 and the time elapsed after pouring of the molten metal. A line U1 corresponds to that of the blank body shaping region of the mold 176; a line V1 corresponds to that of the cylindrical portion 170b when the movable core 178 has not been cooled; a line V2 corresponds to that of the movable core 178 which is not cooled; a line W1 corresponds to that of the cylindrical portion 170b when the movable core 178 has been cooled; and a line W2 corresponds to that of the movable core 178 cooled.
As illustrated in FIG. 45, to prevent thermal cracking of the cylindrical portion 170b, a consideration is the difference between the amount shrinkage of of cylindrical portion 170b and the amount thermal expansion of of movable core 178 and thus a difference in temperature between the cylindrical portion 170b and the movable core 178 with respect to the lapse of time after pouring of the molten metal. However, if the movable core 178 is cooled, a difference in temperature at the limit time point for removal of the movable core 178 indicated by lines W1 and W2 can be maintained for a period of time longer than those indicated by lines V1 and V2 when the movable core 178 is not cooled. This makes it possible to moderate the severity of removal of the movable core 178, while widening a range of time points at which the movable core 178 is to be removed.
In the above embodiment, it is possible to carry out a directional solidification of a molten metal with a temperature gradient provided for the mold 176 by controlling the heating circuit 194 and the cooling circuits 191 and 196.
[XII] Mold for Casting Cam Shaft Blank
FIGS. 46 and 47 illustrate a first die similar to the first die 1.sub.1 of the split type mold 1, except that the heating circuit 8, the cooling circuit 9 and the like are omitted.
The first die 1.sub.1 is comprised of a mold body 200 forming a main portion, and a plurality of plate-like heat resistant members 201.sub.1 and 201.sub.2 attachable to and detachable from the mold body 200.
In the cam shaft blank 2.sub.1 illustrated in FIG. 4, that portion 2g of each smaller diameter portion 2d which is connected with the cam portion 2a and each neck portion 2c are annular recesses. Thereupon, convex portions for shaping them are provided in the heat resistant members 201.sub.1 and 201.sub.2.
The heat resistant members 201.sub.1 and 201.sub.2 are of two types, one of which includes a semi-annular convex portion 202 for shaping one half of the connection 2g, as shown in FIG. 48, and the other includes a semi-annular convex portion 203 for shaping one half of the neck portion 2c, and a semi-annular concave portion 204 adjacent to the convex shaping portion 203 for shaping a part of the journal portion 2b, as shown in FIG. 48B.
Each of the heat resistant members 201.sub.1 and 201.sub.2 is formed of a shell sand and fitted in a recess 205.sub.1, 205.sub.2 of the first die 1.sub.1 ; and forms a pair with each of the heat resistant members 201.sub.1 and 201.sub.2 also likewise fitted in the second die (not shown) during closing of the mold, thereby shaping each connection portion 2g and each neck portion 2c.
If constructed in the above manner, when wearing due to running of the molten metal or a damage due to adhesion attendant upon the solidificational shrinkage of the cam shaft blank material 2.sub.1 or the like are produced in each heat resistant member 201.sub.1, 201.sub.2, it is possible to reconstruct the mold 1 only by replacement of such heat resistant member 201.sub.1, 201.sub.2 by a new one. With each of the heat resistant members 201.sub.1 201.sub.2 formed of a shell sand as described above, it is preferred to replace them by new ones for each casting operation from the viewpoint of their heat resistance.
FIGS. 49 and 50 illustrate a mold including a heat resistant member 201.sub.2 which is formed of a material such as a metal, a ceramic, carbon, etc., and which is attached to the mold body 200 by a bolt 206. Although not shown in the Figures, the other resistant member 201.sub.1 is similarly formed. In this case, the heat resistance of the heat resistant members 201.sub.1 and 201.sub.2 can be improved and hence, is capable of resisting many runs of casting operations, leading to a decrease in the number of replacing operations.
The technological thought of the use of the above-described heat resistant members is not limited to the casting production of the cam shaft blanks and is also applicable to the casting production of various castings having recesses.
[XIII] Mold for Casting Cam Shaft Blank
FIG. 51 illustrates a first die similar to the first die 1.sub.1 described in the item [XII].
As shown in FIG. 51 to 54, the first die 1.sub.1 comprises a mold body 207 forming a primary portion, plate-like heat resistant members 208.sub.1 and 208.sub.2 added to the mold body 207 for shaping a plurality of neck portions and a connection portion.
The mold body 207 includes a pair of air flow channels 209 made along a back side of a cavity 6, and holes 210.sub.1 and 210.sub.2 opened to the cavity 6 in neck portion-shaping and connection portion-shaping regions of the cavity 6, so that the heat resistant members 208.sub.1 and 208.sub.2 are mounted into the corresponding holes 210.sub.1 and 210.sub.2, respectively. A bottom of each of the holes 210.sub.1 and 210.sub.2 communicates with the two air flow channels 209.
As shown in FIGS. 55A and 55B, one 208.sub.1 of the heat resistant members 208.sub.1 and 208.sub.2 serves to shape a neck portion 2c, and the other 208.sub.2 serves to shape a connection 2g. These members are substantially of the same construction and hence, description will be made of the neck portion shaping heat-resistant member 208.sub.1 and the description of the other 208.sub.2 is omitted, except that the same characters are applied to the same portions.
The heat resistant member 208.sub.1 is formed of a material such as a metal, a ceramic, etc., and includes a semi-annular cut recess 211 at a portion close to the cavity 6 and corresponding to the neck portion 2c, and a semi-annular cut recess 212 communicating with the both air flow channels 209. Further, the heat resistant member 208.sub.1 is provided on its one side face with three projections 213 abutting against an inner surface of the hole 210.sub.1 in the mold body 207. Two of the three projections 213 are disposed at places to sandwich an opening of the cut recess 211, and the remaining one is disposed on a bottom surface of the cut recess 211.
The height of each of the projections 213 is of 0.1 to 0.2 mm, and two slits 215 are defined between the adjacent projections 213 and between the both recesses 214 and the inner surface of the hole 210.sub.1. The slits permit the communication between the cavity 6 and both air flow channels 209.
The width of the slit 215 corresponds to the height of the projection 213. If the slit 215 has such a very small width, it has a function for permitting flow of air thereinto but inhibiting flow of a molten metal thereinto.
The air flow channels 209 are connected to a vacuum pump 217 and a compressor 218 through a switch valve 216.
With the above construction, in casting, both air flow channels 209 are connected to the vacuum pump 217 through the switch pump 216. During pouring of a molten metal, a gas within the cavity 6 is discharged through a vent 7 and the individual slits 215, and a gas produced after pouring is efficiently discharged through the individual slits 215.
After the resulting cam shaft blank 2.sub.1 has been released from the mold, the both air flow channels 209 are connected to the compressor 218 through the switch valve 216, so that compressed air is supplied to both air flow channels 209. Thus, even if the solidified material which might be produced due to entering into the individual slits 215 is present in the latter, the compressed air causes such solidified material to be discharged.
[XIV] Mold for Casting Cam Shaft Blank
FIGS. 56 and 57 illustrate a first die similar to the first die 1.sub.1 of the split type mold 1 described in the item [I] and shown in FIG. 2, but a pair of cavities 6 are provided, and the heating circuit 8 and the cooling circuit 9 or the like are omitted. A mold 1 is formed of a Cu-Cr alloy containing 0.75 to 1% by weight of Cr and has a heat conductivity of 0.2 to 0.9 cal/cm/sec./.degree. C.
A filter 220 made of a SiC porous material having an average pore diameter of about 1-5 mm is placed in each of a molten metal passage, i.e., a sprue 3, communicating with the cavities 6, a runner 4 communicating with one of the cavities 6 and a gate 5 communicating with the other cavity 6.
In addition to SiC, a ceramic material selected from the group consisting of Al.sub.2 O.sub.3, SiO.sub.2, Si.sub.3 N.sub.4 and the like may be used.
In each filter-placed portion 221, first and second frustoconical recesses 222.sub.1 and 222.sub.2 having larger diameter end faces opposed to each other are defined on molten metal entry and exit sides of the filter 220 in a state that the first die 1.sub.1 and a second die (not shown) has been mated to each other. For example, as shown in FIG. 57, the diameters d1 and d2 of a smaller diameter end face and the larger diameter end face of the first recess 222.sub.1 are of 20 and 30 mm, respectively, while the diameters d3 and d4 of a smaller diameter end face and the larger diameter end face of the second recess 222.sub.2 are of 25 and 15 mm, respectively. Accordingly, for sectional areas of the individual end faces, there is established a relationship of the larger diameter end face of the first recess 222.sub.1 > the larger diameter end face of the second recess 222.sub.2 > the smaller diameter end face of the first recess 222.sub.1 > the smaller diameter end face of the second recess 222.sub.2.
Setting of the sectional areas of the individual end faces in such a relationship enables an efficient filteration of a molten metal and also enables a throttling effect to be provided to increase the pouring rate.
After preparation of a molten metal of the same cast iron composition as that described in the item [IV], the molten metal was subjected to a similar inoculation and then to a casting process using the mold 1 under the following conditions.
The conditions were such that a preheating temperature of the nose shaping region of the mold 1 was of about 70.degree.-150.degree. C.; preheating temperatures of other regions were of about 120.degree.-450.degree. C.; a pouring temperature was of 1380.degree. to 1420.degree. C.; a pouring time was of 4-15 seconds; and the amount poured was of 9 kg. After a lapse of about 3 to 8 seconds from the pouring, the temperature of the surface layer of the cam shaft blank material was at a temperature of 950.degree. to 850.degree. C., and when that surface layer was converted into a solidified layer, the resulting cam shaft blank was released from the mold.
The above procedure makes it possible to reduce the time required from the start of pouring to the releasing of the resulting cam shaft blank and to efficiently produce a high quality cam shaft blank 21. This is attributable to the removal of slag by each of the filters 220 and the control of running of the molten metal to suppress the inclusion of gas to the utmost. In addition, because the pouring rate is increased, it is possible to prevent a failure of running of the molten metal.
Table VI shows % incidence of casting defects when the filter 220 was used and not used. It is apparent from Table VI that the use of the filter 220 enables the % incidence of casting defects to be suppressed substantially.
TABLE VI______________________________________ FilterCasting defect when not used When used______________________________________Pin hole 50 to 60% 2 to 3%Inclusion of slag 10 to 20% 1 to 2%______________________________________
It should be noted that the filter 220 may be placed in the sprue 3, the runner 4 or the gate 5.
The above-described slit 215, the heat resistant members 201.sub.1, 201.sub.2, 208.sub.1 and 208.sub.2 and the filter 220 may be provided in the above-described several mold casting apparatus, as required.

Number	Date	Country
62-4629	Jan 1987	JPX
62-4630	Jan 1987	JPX
62-19077	Feb 1987	JPX
62-183151	Jul 1987	JPX
62-120636	Aug 1987	JPX
62-207944	Aug 1987	JPX
62-234640	Sep 1987	JPX
62-234641	Sep 1987	JPX
62-236598	Sep 1987	JPX

Number	Name	Date
3123877	Silvester	Mar 1964
4380261	Suzuki et al.	Apr 1983
4934442	Fatamura et al.	Jun 1990

Number	Date	Country
66059	Mar 1989	JPX
2212425	Jul 1989	GBX

Method of producing mechanical parts by mold casting

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