Method and device for feeder head-poor or feeder head-free casting of hypoeutectic cast iron alloys

Abstract

A method and device for feeder head head-poor or feeder head-free casting of a component by means of a hypoeutectic cast iron melted mass includes providing a mold with a sprue, at least one gating and an overflow having a thermal module. The thermal module of the gating and overflow is below that of a region of the component having the largest thermal module. The gating and overflow are solidified before the region of the component having the largest thermal module. The mold is formed, such that it exerts pressure on the cast iron melted mass after solidifying of the gating and the overflow by means of a volume change in the direction of the enclosed cast iron melted mass, in such a way that reduction of the volume of the cast iron melted mass is compensated during solidifying.

Description

BACKGROUND OF THE INVENTION

The subject matter of the invention is a method and device for feeder head-poor or feeder head-free casting of hypoeutectic cast iron alloys.

In many areas of technology, weight reduction represents an important basic requirement of components to be used that are made of cast iron alloys; at the same time, the requirements for strength of such components increases enormously. Thus, for example with motors of commercial vehicles, the stated goal is the least possible power-to-weight ratio with a simultaneous lengthening of the service life and the most cost-effective manufacture as possible in a high production run. This can only be achieved, especially for such components which contribute a high proportion of weight to the end product, by pursuing possibilities for weight reduction with a simultaneous increase in strength and cost efficiency in the manufacture.

Components to which the above noted requirements are related in a large degree, for example, are the crankcases of internal combustion engines of commercial vehicles. Such crankcases typically are made from GJL, that is, a cast iron with scaled graphite; however, also cast iron with nodular graphite (GJS) or with vermicular graphite (GJV) with their better strength characteristics can be used, which increase the manufacturing expenses, however.

Of course, the invention is not limited to the manufacture of crankcases; it can be used additionally with all components made from cast iron with graphite portions.

For all cast iron with graphite portions, a reduction of the carbon indeed increases the strength, on the one hand, but on the other hand by shifting into the hypoeutectic area, the tendency for shrinkage holes increases greatly. In order to counteract this, typically a costly gating and feeder head technology is used in order to sealingly feed the castings in the solidification phase. This method, however, is expensive since a number of circuit materials for the feeder head and gating are required; the circuit material can easily make up a quarter or more of the weight of a casting. The post-machining expense likewise is very high for the removal and recycling of the circuit material.

Based on this state of the art, the object of the present invention is to provide a method and device which allows the carbon content with GJL, GJS, and GJV to be reduced substantially in order to achieve a high strength of the component to be cast and simultaneously to reduce the circuit material to a minimum without the formation of shrinkage holes.

SUMMARY OF THE INVENTION

The solution of the present invention is based on the consideration that the volume change of the cast iron melted mass is not equalized as it has been up to now by means of the “replenished” liquid material from the feeder head, but the mold itself changes its volume and in a manner that the volume change of the mold takes place in the direction of the solidified cast iron melted mass. In order to achieve an equalization of the contraction or shrinkage of the cast iron melted mass with this process, it is necessary to form the necessary gating and overflow/ventilation such that they are already solidified when the cast iron melted mass in the cast component is still fluid or at least is still fluid in the parts at risk for shrinkage holes. If a volume change of the mold takes place in the direction of the cast iron melted mass under these conditions, each volume change of the melted mass is equalized by means of a mold change. It is obvious that these mold changes are to be taken into consideration upon design of the mold.

In order to effect the volume change of the mold, it was discovered that this can be achieved advantageously when the mold itself contains an inner mold, which increases its volume under the effect of heat of the cast iron melted mass filled in it and the inner mold that increases its volume, also under the effect of heat of the cast iron melted mass, can be compressed substantially smaller than it expands under this effect of heat. In order to enable the volume increase of the inner mold to act against the enclosed cast iron melted mass, it is therefore necessary to enclose the inner mold undergoing the volume change in an outer mold, which permits an outward expansion of the inner mold only up to the point that the volume increases of the inner mold are compensated via the equalizing of the contraction of the cast iron melted mass.

It is particularly advantageous if the inner mold is embodied as a sand mold, whereby the mold material of the sand mold contains components affecting the volume increase and with the effect of heat from the cast iron melted mass, increases the volume of the mold material on all sides. It is important, therefore, that the volume increase must be greater than the compressibility of the mold material under the effect of the cast iron melted mass. A compressibility of the mold material is provided under certain conditions when a frame or carrier that softens or burns under the effect of heat in the mold material creates intermediate spaces between grains of sand that are then no longer closely adjacent one another.

The inner core contained in the inner mold also can comprise other, non-expandable or easily compressible mold material if an expandable mold material negatively affects the total system.

A further advantageous method for effecting the volume change contemplates that in the solidification phase, via a stable outer mold, a pressure is exerted on the inner mold, such that the volume enclosed by the outer mold is compressed by the forces acting externally on the outer mold. The inner mold for the casting is formed, such that it applies the exerted force on the cast iron melted mass without expanding or contracting or being compressed itself by the effect of heat to a great degree. The force applied on the outer form, therefore, can be static or also dynamically increased and is applied until the cast iron melted mass is solidified.

In order to enable a well-timed solidification of the gating and overflow/ventilation, it was discovered that the thermal module of each gating or each overflow (each vent) advantageously is selected in a region, which lies at least 30% under the largest thermal module in the component.

Under the general conditions provided by the method of the present invention, a saturation level of the hypoeutectic cast iron melted mass used that is less than or equal to 0.95 is particularly advantageous.

The method of the present invention can be used for GJL- as well as for GJS- and GJV-cast iron qualities. The latter two qualities are particularly advantageous because of their high feed requirements under normal conditions.

In addition, the object can be solved advantageously by a device of the present invention. The device originates from a sand mold, whereby the sand mold has a thermal module for the gating and overflow/ventilation, which is substantially smaller than the largest thermal module in the component to be cast. The mold material used for the sand mold is selected such that it expands much more under the effect of heat of the cast iron melted mass than it is compressed under this effect of heat. The sand mold is enclosed in a solid outer mold, which releases free spaces for the at least one sprue and the at least one overflow and which is resilient against the pressure built up by the expansion of the mold material only up to the point that it compensates expansions of the mold material, which are not absorbed by the contraction of the cooled melted mass.

The mold material is a material mixture, which contains at least one component whose volume increases under the effect of heat. In an advantageous manner, this is the component with the greater volume share, because with small expansions, a substantial volume increase can be achieved.

With bonded sand molds, quartz sand can be used as the component which increases its volume under the effect of heat of the cast iron melted mass. Quartz sand not only provides the desired expansion properties, but is simultaneously the primary component of the mold material with a very high volume share and is therefore particularly suitable.

Steel is used as the material for the outer mold, because steel, on the one hand, has the desired rigidity and on the other hand, permits a known amount of elastic deformation, in order to compensate an eventually occurring excessive expansion of the mold material. In practice, a material thickness of 12 mm with castings of crankcases has shown that the thickness to be selected depends naturally on the size and geometry of the casting, however.

In order to permit a problem-free reuse of the outer mold, it is necessary to embody this as at least a two-piece part, whereby both mold parts are connected releasably with one another in an advantageous manner.

BRIEF DESCRIPTION OF THE DRAWINGS

Examples of the invention and further advantageous embodiments will be described in greater detail with reference to the accompanying drawings, in which:

FIG. 1 is a schematic representation of a casting mold for casting a sample according to a first variation of the method;

FIG. 2 is a schematic representation of a casting mold for casting a sample according to a second variation of the method; and

FIG. 3 is a schematic representation of a casting mold for casting a crankcase.

DETAILED DESCRIPTION OF THE SPECIFIC EMBODIMENTS

As previously discussed, the method originates from a casting mold which changes its volume and indeed in a manner that the volume change of the mold takes place in the direction of the solidified cast iron melted mass. In order to achieve an equalization of the contraction of the cast iron melted mass with this process, the gating and overflow/ventilation are formed such that these regions are already solidified when the cast iron melted mass in the cast component are still fluid or at least are still fluid in the parts that are in danger of forming shrinkage holes. If a volume change of the mold takes places under these conditions in the direction of the cast iron melted mass, each volume change of the melted mass is equalized by a mold change.

An assembly in principle representation, which is suited for performing the method of the present invention, is shown in FIG. 1. For purposes of simplification, a spherical sample is shown as the component to be cast.

The sample is cast with the aid of an inner mold 2, which is embodied as a sand mold. The inner mold 2 is surrounded and contained by an outer mold 3, in addition to a mold hollow chamber 1 for the sample, a sprue 4 arranged on the upper side 6 of the inner mold 2 with a pouring downgate connected thereto, which leads from the upper side 6 into the lower region of the mold, where the pouring downgate 5 changes over into a horizontal area. From the horizontal area of the pouring downgate 5, a gating 7 leading upward from this is provided, which connects the mold hollow chamber 1 with the pouring downgate 5. For ventilation of the mold hollow chamber 1, an overflow channel 8 is provided which leads upward from the vertex of the hollow chamber 1, extends through the inner mold 2, and connects the mold hollow chamber 1 with the surrounding atmosphere.

The solid outer mold 3 comprises two mold halves, like the inner form 2, a lower mold half 9 and an upper mold half 10. Both mold halves 9, 10 of the outer mold 3 are formed to be trough-like, surrounded on their open sides by a peripheral flange 11, and with their open sides facing one another, enclosing both mold halves of the inner mold 2. The connection of the two mold halves 9, 10 of the outer mold 3 takes place by means of screws 12. The upper mold half 10 has free spaces in the area of the sprue 4 and in the area at which the overflow channel 8 opens outward through the inner mold.

The inner mold is embodied such that the gating 7 leading to the mold hollow chamber 1 and the overflow channel 8 leading from the mold hollow chamber 1, respectively, have a thermal module which is substantially smaller than the largest thermal module of the sample to be cast. As already stated, the inner mold 2 is a sand mold, which comprises a mold material that expands under the effect of heat of the cast iron melted mass. As a mold material, a material mixture made from base material and a binding agent can be used, whereby the base material and binding agent, in turn, can be a material mixture. For example, the base material can be quartz sand and the bonding of the quartz sand takes place by means of an organic bonding agent (for example in cold-box or in hot-box methods) or by means of an inorganic binding agent (for example salt kernels). With the selection of the components for the sand mold, it is to be noted that the sand mold can be compressed substantially less under the effects of heat of the cast iron melted mass than it expands under this effect of heat.

For casting of a sample, a hypoeutectic cast iron melted mass solidified to cast iron with scaled graphite is filled into the sprue 4 and distributed over the pouring gate 5 and gating 7 into the mold hollow chamber 1. When this is filled, the melted mass rises into the overflow channel 8, which simultaneously is the ventilation channel, until the mold surface is reached. After complete filling of the hollow chambers of the mold, the introduction of the melted mass is interrupted and the casting is cooled by the migration of the heat into the surrounding sand mold. Because of the dimensioning of the gating and overflow, a relatively fast solidification of the melted mass takes place in these regions, so that the remaining, still fluid cast iron melted mass is enclosed in the mold hollow chamber 1. By the migration of the heat from the cast iron melted mass into the regions of the inner mold 2 surrounded by the mold hollow chamber 1, the component contained in mold material of the inner mold 2 which reacts to the heat effect with expansion (for example quartz sand) expands, so that in these regions, a volume increase of the inner mold 2 takes place. By means of the heating of the mold material, a melting or burning of the binding agent used for bonding the sand mold can occur, which does not lead however to an appreciable compressibility of the affected mold regions when the binding agent or the method used for bonding is selected, such that the sand grains lie directly on one another, that is, are adhered to one anther without appreciable intermediate layers of binding agent on the joints. These types of methods for bonding sand molds are known and do not require further explanation.

By means of the expansion of the mold material heated via the cast iron melted mass, a volume expansion of the inner mold 2 takes place as previously discussed. However, a barrier is formed in view of an outward expansion, that is, from the mold hollow chamber 1 by means of the outer mold 3, so that pressure forms that is directed from all sides uniformly onto the cast iron melted mass. If the cast iron melted mass contracts under these conditions in the solidification process, this pressure serves for a volume equalization, such that the contraction of the cast iron melted mass, and therewith the inner mold, is compensated by the volume increase of the mold material.

With the embodiment of the outer mold 3, it can be ensured that volume changes of the inner mold 2, which are not absorbed by shrinkage of the cast iron melted mass, are accommodated by the outer mold 3 in such that the latter is elastically deformable to the degree necessary.

So that the previously described volume changes of the inner mold are uniformly distributed over the entire casting, for example over the entire sample, no uncontrollable mass changes on the casting occur; consideration of the minimally occurring mass change is possible if necessary.

A further variation of the method of the present invention is shown in FIG. 2. Also here a principle representation is shown and for purposes of simplification, a spherical sample to be cast is shown.

As with the variation according to FIG. 1, also with the example in FIG. 2, the reduction of the volume of the cast iron melted mass provided upon cooling of a hypoeutectic cast iron melted mass is to be equalized by a mold change.

Also in the example of FIG. 2, an inner mold 20 having two mold halves is used; the inner mold 20 is surrounded by an outer mold 21 and contains additionally a mold hollow chamber 22 for the sample, a sprue 24 arranged on the upper side 23 of the inner mold 20, with a pouring gate 25 connected thereto, which leads from the upper side 23 into the lower region of the mold, where it changes over into a horizontal region. From the horizontal region of the pouring gate 25, a gating 26 leading upward from this is provided, which connects the mold hollow chamber 22 with the pouring gate 25. For ventilation of the hollow chamber 22, a ventilation channel 27 leading from the vertex of the hollow chamber upward is provided, which extends through the inner mold 20 and connects the mold hollow chamber 22 with the surrounding atmosphere. The inner mold 20 is embodied, such that the channel 25 leading to the mold hollow chamber 22 and the ventilation channel 27 leading from the mold hollow chamber 22, respectively, have a thermal module which is substantially smaller than the largest thermal module of the sample to be cast.

The solid outer mold comprises a shell 28 enclosing the vertical outer wall of the inner mold 20, a moveable floor 29 arranged within the shell 28, and a moveable cover 30 likewise arranged within the shell 28, whereby the shell 28, floor 29, and cover 30 enclose the inner mold 20. The cover 30 has free spaces in the area of the sprue 24 and in the area at which the ventilation channel 27 opens outward through the inner mold 20.

For the inner mold 20, mold materials can be used with this variation of the method, which react in a volume-neutral manner to the effect of heat of the cast iron melted mass or expand or contract only minimally or are compressed only minimally. The useable selection of the possible mold material, therefore, increases substantially. The binding agent of the inner mold 20 is selected such it bears up against the forces on filling the cast iron melted mass; however, a pressure force applied externally over the outer form 21 is applied substantially uniformly in all directions, so that contraction of the cast iron melted mass enclosed in the mold hollow chamber 22 is equalized uniformly over the entire inner mold.

The casting process itself runs such that the cast iron melted mass is provided via the sprue 24 into the mold, where it moves over the pouring gate 25 and gating 26 into the mold hollow chamber 22. In the mold hollow chamber 22, the melted mass rises and the air located therein is released via the overflow channel 27. Finally, the melted mass rises also in the overflow channel 27 and supplying of the cast iron melted mass via the sprue 24 is terminated. By means of the selection of the thermal module of the gating 26 and overflow channel 27, these areas solidify first and the melted mass in the mold hollow chamber is still fluid at this time point. As soon as the gating 26 and overflow channel 27 are solidified, a force on the outer mold, designated in FIG. 2 with arrows, is applied over the moveable floor 29 and the movable cover 30, which acts on the cast iron melted mass enclosed in the mold hollow chamber 22 via the inner mold 22 enclosed in this and upon volume change of the cast iron melted mass, leads to an adaptation of the inner mold 20 distributed over the entire volume of the inner mold 20. The actual changes of the inner mold 20 occurring by the shrinkage of the cast iron melted mass are very minimal and can be determined via trials, so that, if necessary, compensation by means of the design of the inner mold 20 is possible.

The inner cores are designed with use of this method such that they do not change their volume or shape from either the effect of heat of the cast iron melted mass or from the pressure applied by the outer mold 21.

Although in the examples of FIGS. 1 and 2, the method of the present invention is illustrated in connection with the casting of spherical samples, it is to be understood that limitations as to the shape of a casting exist only with regard to permitting that the gating, the overflow and ventilation channels, respectively, have a thermal module which is much smaller than the largest thermal module in the component to be cast.

Cast components, for whose manufacture the method of the present invention can be used with particular advantage, are crankcases of internal combustion engines. FIG. 3 shows in schematic representation an assembly for casting a crankcase. In this example, the method variation is used which was described previously in connection with FIG. 1, so that a further illustration of the principle factors with regard to the assembly and method is not necessary. The embodiment of FIG. 3, therefore, is limited to a representation of the arrangement of the crankcase in the mold.

In a two-part outer mold 31, a two-part inner mold 32 is arranged, in whose lower mold half, a mold hollow chamber 33 is formed as a negative shape of the crankcase. The cylinder bores lie below in the mold hollow chamber 33, the cores for the cylinder bores are arranged in the mold hollow chamber 33; a cylinder bore core 34 can be seen in the broken-out area shown. Further inner cores can be provided of course, but are eliminated in the figure for purposes of better illustration. As with the other embodiments, also here a sprue 35 is formed on the upper side of the mold, which opens into a pouring gate 36 leading downward into the inner mold. The pouring gate 36 changes over in a lower region of the lower mold half of the inner mold 32 into a horizontal part, from which an upward gating 37 leads to the mold hollow chamber 33. Ventilation channels 38 and overflow channels 39 lead from the mold hollow chamber 33 through the upper mold half to the surrounding atmosphere.

The solid outer mold 31 comprises, like the inner mold 32, two mold halves, a lower mold half 40 and an upper mold half 41. Both mold halves 40, 41 of the outer mold are formed to be trough-like, surrounded on their open sides by a peripheral flange and surrounding with their open sides facing one another, both mold halves of the inner mold 32. The connection of the two mold halves 40, 41 of the outer mold 31 takes place by means of screws. The upper mold half 41 has free spaces in the area of the sprue 35 and in the regions at which the ventilation channel 38 and the overflow channel 39 open outwardly through the inner mold 32.

In an alternative embodiment, as shown on the left of FIG. 3, it also can be provided that the upper mold half is embodied in two parts, such that it is subdivided into a circumferential shell 42 and a cover 43. Such an embodiment is advantageous, in that the cover 43 can be placed on after filling of the melted mass and need not have any free spaces for sprue, overflow or ventilation channels. The cover 43 is secured then via a corresponding further screw connection 44.

As already stated with regard to the remaining example, the gatings 37, overflow channels 39, and ventilation channels 38 are embodied such that their respective thermal module is smaller than the largest thermal module of the component. In the example of FIG. 3, the region with the largest thermal module is shown in the broken-out region, designated with reference numeral 45.

The material of the inner mold 32 and the outer mold 31 in the example of FIG. 3 is identical with that of FIG. 1. This also relates to the casting operation itself, so that it is not necessary to describe this again. Reference is made to corresponding portions of the description of FIG. 1.

Should the shrinkage of the cooled melted mass not be completely compensated with the method of the present invention with specialized shapes of the component to be cast in particularly defined areas of the component, the possibility exists of using a closed feeder head in combination with the method of the present invention. This permits the sealed feeding also of such critical areas and causes little expense because of its minimal dimensions with regard to the circuit material.

The previously described embodiments of the method as well as the device can be developed of course by the knowledge of the practitioner in numerous ways, without departing from the basic concept of the present invention. These embodiments therefore represent only examples.

The specification incorporates by reference the disclosure of German priority document 10 2004 027 592 filed Jun. 5, 2004.

The present invention is, of course, in no way restricted to the specific disclosure of the specification and drawings, but also encompasses any modifications within the scope of the appended claims.

Claims

1. A method for feeder head-poor or feeder head-free casting of a component by means of a hypoeutectic cast iron melted mass, comprising the following steps: providing a mold with at least one sprue, at least one gating and at least one overflow having a thermal module; providing the thermal module of the gating and the overflow to be below that of a region of the component having the largest thermal module; solidifying the gating and overflow before the region of the component having the largest thermal module; and exerting a pressure on the cast iron melted mass with the mold after solidifying of the gating and the overflow by means of a volume change in the direction of the enclosed cast iron melted mass, in such a way that reduction of the volume of the cast iron melted mass is equalized during solidifying.

2. The method of claim 1, wherein the volume change is effected, such that the mold has an inner mold, which expands under the heat effect of the enclosed cast iron melted mass, such that the volume of the inner mold increases on all sides, the inner mold can be compressed substantially less than it can expand under the heat effect, wherein the inner mold is surrounded by an outer mold, which allows an outward expansion of the inner mold only as far as necessary for compensation of a volume increase of the inner mold via the contraction of the cast iron melted mass.

3. The method of claim 2, wherein the inner mold comprises a mold material containing at least one element that expands under the effect of heat.

4. The method of claim 3, wherein the at least one element is the element with the largest volume share of the mold material.

5. The method of claim 2, wherein the inner mold is a bonded sand mold.

6. The method of claim 1, wherein the mold comprises an inner mold which reacts to the heating action from the cast iron melted mass in a volume neutral manner or with a minimal expansion or with a minimal contraction, wherein the inner mold is surrounded by a solid outer mold, wherein from the time point of the solidifying of the gating and overflow, a force is applied externally on the outer mold, wherein said force effects the volume change of the mold and compresses the entire contents of the outer mold; and wherein the force is applied until solidifying of the component.

7. The method of claim 6, wherein the force applied on the outer mold is a static or dynamically increasing force.

8. The method of claim 1, wherein the thermal module of the gating and the overflow is at least 30% below the largest thermal module of the component.

9. The method of claim 1, wherein a cast iron melted mass is used, which solidifies hypoeutectically to cast iron with scaled graphite.

10. The method of claim 1, wherein a cast iron melted mass is used, which solidifies hypoeutectically to cast iron with nodular graphite.

11. The method of claim 1, wherein a cast iron melted mass is used, which solidifies hypoeutectically to cast iron with vermicular graphite.

12. A device for feeding-poor or feeder headless casting of hypoeutectic cast iron melted mass, comprising: a bonded sand mold having a gating and overflow, wherein the gating and overflow have a thermal module that is so far below the largest thermal module of the component that the gating and overflow solidify first, wherein the sand mold comprises a mold material that expands under a heat effect of the cast iron melted mass, and wherein the mold material itself is slightly less compressible under the heat effect of the cast iron melted mass than it is expanded under the heat effect; an outer mold surrounding the sand mold, wherein the outer mold encompasses the sand mold on all sides and has free spaces for a sprue and overflow, wherein the outer mold is formed, such that it allows an outward expansion of the inner mold only as far as necessary for compensation of a volume increase of the inner mold via the contraction of the cast iron melted mass.

13. The device of claim 12, wherein the mold material is a material mixture, wherein at least one of the materials contained in the mixture increases its volume under an effect of heat of the cast iron melted mass.

14. The device of claim 13, wherein the at least one material that increases its volume comprises the largest portion of the mold material.

15. The device of claim 14, wherein the at least one material that increases its volume is quartz sand.

16. The device of claim 12, wherein the outer mold is a steel mold.

17. The device of claim 16, wherein the wall thickness of the outer mold is at least 8 mm.

18. The device of claim 18, wherein the outer mold comprises at least two mold parts, wherein the mold parts are connected releasably to one another.