Patent Application
20080038142
Suitable embodiments of the present invention will now be explained with reference to attached drawings. Further, it should be understood that the embodiments explained below are not limited to the scope of the present invention described in claims. And, it should be understood that the total constitution described below is not essential requirement for the present invention.
Example 1 of the present invention will now be explained with reference to
In the first process, due to the heat of the heater 7 being pre-controlled by the temperature control system 9, the temperature of the periphery of the through-hole 1 is kept higher than the evaporating temperature of the aqueous solution L, and lower than the melting temperature of the lubricant. Then, the automatically openable and closable valve is opened to apply the aqueous solution L in which water soluble lubricant having at least 3 g of solubility for 100 g of water at 20° C. is dissolved in water by spraying from the spray member 6 to the molding portion 1A of the die 2 heated by the heater 7, with the lower punch 3 being fitted into the through-hole 1 to define the molding portion 1A. As a result, the solution L is evaporated and dried out, and thus crystals are allowed to grow on the peripheral surface of the through-hole 1, so that a crystallized layer B of the lubricant is uniformly formed. Using a water soluble lubricant having at least 3 g of solubility for 100 g of water at 20° C. can be produced precipitate in an aqueous solution around the room temperature. Therefore, trouble such as the clogging of the spray member 6 is occurred when applying by spray member 6. Meanwhile, for example, if an aqueous solution does not keep a higher temperature, conventional higher fatty acidic soaps comprising sodium stearate, sodium palmitate, sodium myristate, sodium laurate cannot be obtained at least 3 g of solubility for 100 g of water.
Next, as illustrated in a second process shown in
The powder molding product A thus press-molded becomes ejectable when the die 2 is moved further downwardly until the upper surface of the die 2 becomes essentially as high as the lower surface of the lower punch 3, as illustrated in a fourth process shown in
Next, as to a good water solubility, it will be explained the point that the solubility is at least 3 g of solubility for 100 g of water at 20° C. As can be seen from the solubility for various fatty acid soaps illustrated in
Preferred examples and comparative examples will now be explained with reference to Tables 1 to 3. In each of the preferred examples and comparative examples shown in Tables 1 to 3, iron powders (average particle diameter: 90 μm) were used as the raw powder, to which was added 0.2% by weight of Lithium stearate (average particle diameter: 5 82 m) serving as the lubricant, which were then mixed for 30 minutes using a rotary mixer, so that 7 g of the resultant mixture of the raw powder was filled into a mold forming a cylindrical column having a 1 cm2 pressurization area, and then 100 powder molding products were successively formed at a molding pressure of 8 t/cm2. And in the examples, after the aqueous solution of the water-soluble lubricant dissolved in water was applied to the molding portion heated at 150° C. in the mold, it was evaporated and dried to form the crystallized layer, and then the raw powders were filled into this molding portion. In the comparative example 1, after the solution of lithium stearate (average particle diameter: 5 μm) dispersed in acetone was applied to the molding portion of the mold heated at 150° C., it was dried to form the film, and then the raw powders were filled into this molding portion. The comparative example 2 is a case in which the lubricant was not applied to the mold. Density R in each Table shows difference between maximum and minimum values in the density of 100 molding bodies continuously molded.
Comparison result from Tables 1 to 3 indicates that the pressure required for ejecting a compact from a die in the examples were less than or equal to that of the comparative example 1. Besides, the densities were improved in the examples as compared to the comparative example 1. Moreover, the densities R in the examples noticeably became smaller than that of the comparative example 1. Therefore, it is apparent from the result that the molding can be stably carried out according to the examples, even though it is carried out successively.
As is clearly indicated in Tables 1 to 3, the aforesaid lubricant may suitably be a water soluble phosphate based metal salt, and the one having a phosphate group in its structure, such as dipotassium hydrogen phosphate, disodium hydrogen phosphate, tripotassium phosphate, trisodium phosphate, potassium polyphosphate, sodium polyphosphate, riboflavin potassium phosphate, riboflavin sodium phosphate or the like.
As is also seen from Tables 1 to 3, it is suitable that, as a water soluble sulfate-based metal salt, the lubricant may include a sulfate-based group in its structure, such as potassium sulfate, sodium sulfate, potassium sulfite, sodium sulfite, potassium thiosulfate, sodium thiosulfate, potassium dodecyl sulfate, sodium dodecyl sulfate, potassium dodecylbenzensulfate, sodium dodecylbenzenesulfate, Food Blue No. 1. (C37H34N2Na2O9S3), Food Yellow No. 5. (C16 H10 N2 Na2O7S2), potassium ascorbyl sulfate, sodium ascorbyl sulfate.
As is also seen from Tables 1 to 3, it is suitable that, as a water soluble borate based metal salt, the lubricant may include a borate-based group in its structure, such as potassium tetraborate, sodium tetraborate.
Tables 1 to 3 also show that as a water soluble silicate based metal salt, the lubricant may suitably include a silicate-based group in its structure, such as potassium silicate, sodium silicate.
Still also, Tables 1 to 3 show that as a water soluble tungstate based metal salt, the lubricant may suitably include a tungstate-based group in its structure, such as potassium tungstate or sodium tungstate.
Table 1 to 3 show that as a water soluble organic acid based metal salt, the lubricant may suitably include an organic acid based group in its structure, such as potassium acetate, sodium acetate, potassium benzoate, sodium benzoate, dipotassium terephthalate, disodium terephthalate, potassium ascorbate, or sodium ascorbate.
It is also seen from Tables 1 to 3, that as a water soluble nitrate based metal salt, the lubricant may suitably include a nitrate-based group in its structure such as potassium nitrate, sodium nitrate.
It is still also seen from Tables 1 to 3 that as a water soluble carbonate-based metal salt, the lubricant may suitably include a carbonate based group in its structure, such as potassium carbonate, sodium carbonate, potassium hydrogen carbonate or sodium hydrogen carbonate.
Alternatively, one or more of the foregoing lubricants may be used as the lubricant.
And the water soluble lubricant should have a concentration greater than or equal to 0.01% by weight but less than a concentration of a saturation. This is because the concentration of less than 0.01% by weight makes it difficult to obtain a stably forming with constant temperature and speed since water content to apply and evaporate on the mold for forming is too large quantities and thus the mold temperature is lower, while at the saturated concentration or above it does not allow the lubricant to be completely dissolved so that it is precipitated as a solid, thus casing troubles such as the clogging of the spray member 6 when applying lubricant by a spray member 6.
For dissolvent water, water from which metal and halogen elements are removed is preferable, such as distilled water or ion exchange water. This is because some lubricants, though it depends on a kind thereof, are precipitated due to the readiness to substitute metal components in water, thus casing troubles, while water containing a large amount of halogen components is likely to cause a bond to a compact or to produce a harmful substance such as dioxin or the like during a sintering process.
Further, some lubricants, though also depending on a kind thereof, facilitate the growing of microorganisms and thus the solution is easily decayed, thereby causing a change in components, emitting bad smell. However, adding an antiseptic agent can prevent the growing of microorganisms. For the antiseptic agent, it is preferable to use one which does not impair lubrication property, produces low harmful effects to a human body, and includes no halogen components, such as sodium benzoate or the like.
Furthermore, some lubricants have a problem that foaming easily occurs, and thus when the aqueous solution (L) is applied to the molding portion (1A), such molding is likely to occur foaming so that a raw powder is caked. However, by adding a water-soluble solvent such as alcohol or ketone, or a defoaming agent, such foaming can be prevented. For alcohol or ketone, it is preferable to use one which does not impair the lubricating action, causes less damages to a human body, and does not include halogen components, such as ethanol, acetone or the like.
In some cases, using a water soluble solvent such as alcohol and ketone with a lower boiling point or a lower latent heat of evaporation than water can reduce hours for evaporation or dry, eliminating the need for keeping the mold body 2 at high temperature.
In a case where these lubricants, additives or dissolvent water include halogen elements, a substance that is highly toxic even in minute amounts such as dioxin is likely to be created under such a condition that sintering is performed with carbon components being coexistent, as is often used in powder metallurgy of iron. Therefore it is preferable to include no halogen elements therein.
As for the temperature of the mold body 2 and the mixed raw powder M, keeping them at high temperature is desirable because it contributes to reduction of hours for drying, accompanied by effects of warm molding and the like. If there is caused no particular trouble, however, it can be kept at ordinary temperature. On the other hand, when setting them at high temperature, it is preferable to choose such a lubricant that is not melt down at a preset temperature, since the melt lubricant makes it difficult to stably perform warm molding due to the melt lubricant caking a raw powder, flowing down to the bottom of the mold (the molding portion 1A). If there is caused no particular trouble, however, it may be in a semi-molten state, in a highly viscous state, or otherwise, at least one lubricant of the mixed two ore more lubricants may be in a molten state. Since zinc stearate and lithium stearate that have been conventionally used have melting temperatures of about 120° C. and about 220° C., respectively, it has heretofore been difficult to stably perform warm molding at a temperature higher than these temperatures. Among the lubricants proposed in the present invention, however, there are a number of lubricants that have a higher melting point than 220° C., and some of them have a higher melting point than 1000° C. Therefore it is possible to easily and stably perform warm molding by raising the temperature almost to an oxidization temperature of the raw powder or heat resistance of mold (molding portion A). In that case, however, there occur problems such as fluidity of the raw powder, and thus it is preferable to use the lubricant that does not melt even under high temperature, as the one to be added into the mixed raw powder M. For example, the powdery lubricants of the present invention or solid lubricants such as graphite or molybdenum disulfide which can be used a high temperature of at least 200° C. are preferable. Alternatively, it is also preferable to mold only by lubrication of the mold itself without using the lubricant into raw powder.
According to the description of the foregoing embodiment, there is provided a method for forming a powder molding product, comprising a filling the molding portion 1A in the mold body 2 with the raw powder M, and then inserting upper and lower punches 3, 4 into the molding portion 1A to thereby form the powder molding product, wherein prior to filling the molding portion 1A with the raw powder M, the aqueous solution L in which lubricant is dissolved in a solvent is applied to the molding portion 1A to a uniform phase, and then the aqueous solution L is evaporated to thereby form a crystallized layer B on the molding portion 1A. Thus, the fine and uniform layer B for lubrication is formed on the peripheral surface of the molding portion 1A, thereby enabling the reducing of a pressure required for ejecting the powder molding product A from the molding portion 1A as well as the improving of the density of the powder molding product A.
Also, there is provided a mold apparatus for powder molding, comprising the mold body 2 with the through-hole 1 for molding a side of the powder molding product A, the lower punch 3 to be fitted into the through-hole 1 from beneath, the upper punch 4 to be fitted into the through-hole 1 from above, the spray member 6 from which the lubricant aqueous solution L is faced into the through-hole 1, the heater 7 provided around the molding portion 1A of the powder molding product A, the molding portion 1A being defined by the through-hole 1 and lower punch 3 which is fitted into the through-hole 1, and the temperature control system 9 keeping a temperature of the heater 7 higher than an evaporating temperature of the aqueous solution L, if required but lower than a melting temperature of said lubricant. And prior to filling the molding portion 1A with the raw powder M, the lubricant aqueous solution L is applied to the molding portion 1A which is heated, and then the aqueous solution L is evaporated to thereby form the fine and uniform crystallized layer B on the peripheral surface of the molding portion 1A. Thus, the fine and uniform crystallized layer B for lubrication is formed on the peripheral surface of the molding portion 1A, thereby enabling the reducing of a pressure required for ejecting the powder molding product A from the molding portion 1A as well as the improving of the density of the powder molding product A, and realizing the stable and successive molding.
And in the first process, due to the heat of the heater 7 being pre-controlled by the temperature control system 9, the temperature of the surface 10 of the through-hole 1 is kept higher than the evaporating temperature of the aqueous solution L, and lower than the melting temperature of the lubricant beforehand. Then, the automatically openable and closable valve is opened to apply the aqueous solution L of the lubricant by spraying from the spray member 6 to the molding portion 1A of the die 2 heated by the heater 7, with the lower punch 3 being fitted into the through-hole 1 to define the molding portion 1A. At this moment, the angle X of contact of the aqueous solution L, which would be the angle Y of contact without the surface treatment layer 11, is allowed to be the smaller angle X of contact owing to the surface treatment layer 11, thus allowing the aqueous solution L to be prevented from being repelled, to thereby the aqueous solution L is applied to the entire surface of the though-hole 1 and wet the same. As a result, the aqueous solution L is evaporated and dried out, and thus crystals are allowed to grow entirely on the surface treatment layer 11 of the through-hole 1, so that a crystallized layer B serving as a lubricating layer of the lubricant is uniformly formed.
Next, as illustrated in a second process shown in
The powder molding product A thus press-molded becomes ejectable when the die 2 is moved further downwardly until the upper surface of the die 2 becomes essentially as high as the upper surface of the lower punch 3, as illustrated in a fourth process shown in
As is apparent from the foregoing, the surface 10 of the through-hole 1 is formed with the surface treatment layer 11 so as to have the smaller angle X of contact with the aqueous solution L than the angle Y of contact of the die 2 with the aqueous solution L, in accordance with the foregoing experiment. Thus, when the aqueous solution L is applied, the wetting action of the aqueous solution L relative to the surface 10 is improved so that the aqueous solution L can be extended over the surface treatment layer 11, eventually over the entire surface of the through-hole. Consequently, the entire surface of through-hole 1 can be formed with the crystallized layer B by performing water evaporation. As a result, high-density powder molding product A can be stably obtained.
According to Example 3, therefore, the automatic open able and closable valve is opened so that the aqueous solution L of the lubricant is sprayed from the spray member 6 and applied to the molding portion 1A of the die 2 that is heated by the heater 7. At this moment, part of the aqueous solution L is likely to be attached to the upper surface 2A of the die 2. Nevertheless, the aforementioned angle Y′ of contact of the aqueous solution L with the upper surface 2A on which the surface treatment layer 21 is provided, becomes larger than the angle X′ of direct contact thereof with the die 2, whereby the aqueous solution L is allowed to be repelled, thus preventing the aqueous solution L to collect on the surface 2A.
As is apparent from the foregoing, since the upper surface 2A is formed with the surface treatment layer 21 so as to have the larger angle Y′ of contact with the aqueous solution L than the angle X′ of contact of the die 2 itself with the aqueous solution L, whereby the water repellent property on the upper surface 2A can be improved, making the aqueous solution L less likely to pile up or collect on the upper surface 2A (the surface treatment layer 21), thus preventing the aqueous solution L from collecting on the upper surface 2A (surface treatment layer 21), which in turn makes the raw powder M housed in the feeder 5 less likely to be contacted by the aqueous solution L, thereby enabling the raw powder M to be prevented from caking.
According to example 4, above the through-hole 1 is provided the spray member 6 serving as applying means for spraying the aqueous solution L so as to attach the aqueous solution L to the molding portion 1A. The spray member 6 is arranged so as to face the through-hole 1. The aqueous solution L contains components which improve the wetting action relative to the surface 10 of the through-hole 1. The wetting action improving components are ones that can make the angle X″ of contact of the aqueous solution L with the surface 10 smaller, for example, surfactant is used.
Thus, the automatically open able and closable valve is opened to apply the aqueous solution L of the lubricant by spraying from the spray member 6 to the molding portion 1A of the die 2 heated by the heater 7, with the lower punch 3 being fitted into the through-hole 1 to define the molding portion 1A. At this moment, the angle X″ of contact of the aqueous solution L, which would become large without the wetting action improving components, is allowed to be small enough owing to the components, thus allowing the aqueous solution L to be prevented from being repelled, to thereby be applied to the entire surface 10 of the though-hole 1 and wet the same. As a result, the aqueous solution L is evaporated and dried out, and thus crystals are allowed to grow entirely around the surface of the through-hole 1, so that a crystallized layer B of the lubricant is uniformly formed.
As is apparent from the foregoing, since the aqueous solution L contains components which improve the wetting action in order to decrease the angle X″ of contact with the surface 10, the wetting action of the aqueous solution L in the through-hole 1 is improved when the aqueous solution L is applied, thus allowing the aqueous solution L to be extended over the entire surface of the though-hole 1, so that the aqueous solution L is evaporated to thereby allow the crystallized layer B to grow entirely, thus enabling the high-density powder molding product to be stably obtained.
Further, hereinafter examples and comparative examples will now be explained with reference to Table 6. In each of the examples and comparative examples shown in Table 6, iron powders (average particle diameter: 90 μm) were used as the raw powder, and 7 g of the mixture of the raw powder was filled into a mold forming a cylindrical column having a 1 cm2 pressurization area, and then powder molding products were formed at a molding pressure of 8 t/cm2. And in the preferred examples, 1% solution of dipotassium hydrogen phosphate as water-soluble lubricant was applied to the molding portion of the die coated with hydrophilic material and heated to 250° C., and then it was evaporated and dried out to form the crystallized layer, and then the raw powders were filled into this molding portion. In the comparative example 1, after the lubricant was applied to the molding portion of an ordinary die heated to 250° C., it was dried and then the raw powder was filled into this molding portion. In the comparative example 2, after the lubricant was applied to the molding portion of an ordinary die heated to 150° C., it was dried and then the raw powder was filled into the molding portion. The comparative example 3 is a case in which an ordinary die was heated to 150° C., and then the raw powder was filled into the molding portion without the application of lubricant. In either example, SKH-51 as typically employed for tool steel was used for the molding portion of such ordinary die.
Comparison result from Table 6 indicates that molding was found impossible if it was performed at 250° C. using dies without the hydrophilic coating, due to the lubricant being nut fully attached to the molding portion. According to the Examples 1-6 where molding was performed, using dies with the hydrophilic coating, molding was found possible at temperature higher than 150° C., and it was found that high-density molding product denser than those formed at 150° C. can be obtained.
Further, the present invention is not limited to the forgoing embodiment but may be variously modified within the scope of the invention. In the foregoing embodiment, said aqueous solution is applied to the molding portion and then evaporated the aqueous solution to form the crystallized layer on the molding portion prior to filling the raw powder, and then the punches fitted into the molding portion to thereby forming the powder molding product, however, it is not always necessary to form the crystallized layer on the molding portion by applying the solution thereto and then evaporating the same, prior to filling the raw powder. For example, after forming a first powder molding product, a second powder molding product may be formed by filling a second raw powder, utilizing the crystallized layer formed when the first powder molding product is formed, without applying the aqueous solution to the molding portion, and then the aqueous solution may be applied to the molding portion prior to filling a third raw powder, and then the aqueous solution is evaporated, to thereby form a second crystallized layer on the molding portion. The aqueous solution may be applied to the molding portion in such an intermittent continuance.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004-055363 | Feb 2004 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP05/02994 | 2/24/2005 | WO | 00 | 6/12/2007 |
