JP4880491B2 - Granulated powder for mold forming, method for producing the same, and method for producing sintered parts using the granulated powder - Google Patents

Description

  The present invention relates to a method for producing a sintered part by a mold method, and in particular, a granulated powder suitable for producing a sintered part having a small product shape and unevenness, a method for producing the same, and the granulated powder. The present invention relates to a method for manufacturing a sintered part by a mold forming method using a ceramic.

  Using a molding apparatus having a mold having a mold hole and a pair of upper and lower punches slidably fitted in the mold hole, a raw material is formed in a cavity formed by the mold hole and the lower punch of the mold The sintered metal parts manufacturing method by the so-called die method, which sinters the molded body obtained by compressing and molding the raw material powder with the upper and lower punches by filling the powder, can be shaped into a near net shape, the material cost and processing cost Has the advantage that it can be reduced, or that the production method is easy and suitable for mass production, and has been widely used.

In such a mold forming method, a product having a complicated shape having irregularities on the upper and lower surfaces can be formed by dividing the upper and lower punches into multiple stages. However, when the product shape is reduced, the width of the punch for forming the unevenness has to be reduced, and the punch is likely to buckle or break. On the other hand, if the shape of the upper and lower punches is not multi-staged, and the end surface of the upper and lower punches is shaped as a rugged shape that becomes the female shape of the product, the bulk of the raw material powder when filling the cavity is different, When the thickness of each part is different, the molding density is different in each part of the product.
That is, the thin portion of the molded body has a high density, and the thick portion of the molded body is not sufficiently compressed and has a low density. For example, in the case of a product in which a convex part is formed on the product and the convex part slides with another member, it is necessary to form the convex part sliding with the other member at a high density. As described above, since the convex portions have a low density, a desired product cannot be formed.

In the injection molding method, a product-shaped female mold was formed in the same manner as in plastic injection molding, using a raw material obtained by adding 40-60% by volume of a plastic binder such as a thermoplastic resin or wax to metal powder. A product having a complicated shape can be obtained by injection molding into a mold and shaping, and then removing the binder from the resulting molded body and then sintering. According to such an injection molding method, since the pressure acts evenly in a mold having a complicated shape due to the liquid pressure of the plasticized binder, a molded body having a relatively uniform density is obtained even in a complicated shape. be able to.
However, since the molded body contains about 40 to 60% by volume of the binder, it takes time to remove the binder, and there is a problem that the amount of shrinkage is large. In addition, in the injection molding method, the powder is filled by pressurizing with hydraulic pressure, so that it is difficult to fill the gap in the small mold smaller than the size of the injection port (gate), and the plasticized binder is filled exclusively. Therefore, depending on the shape of the product, there is a problem that it is difficult to obtain a product with a uniform density.

  Under such circumstances, a method has been proposed in which a raw material powder is mixed with 10 to 45% by volume of a plastic binder and molded by molding (Patent Documents 1 and 2, etc.). In this method, a predetermined amount of raw material powder to which a larger amount of a plastic binder is added than in the case of a normal mold forming method is put into a mold of a mold and pressed by an upper and lower punch, and while flowing the raw material powder, Filling the concave part of the mold (convex part of the molded body), the fluidity of the raw material powder is enhanced by a large amount of the plastic binder, and the large amount of the plastic binder uniformly transmits the pressing force of the punch, This is a method of uniform density. According to this method, a molded body having a complicated shape can be molded with a relatively uniform molding density by the hydraulic pressure of the plastic binder without using a mold or an injection device dedicated to the injection molding method, and injection molding. In this case, the amount of the binder can be reduced and the removal time of the binder can be shortened.

Japanese Patent Laid-Open No. 02-141502 Japanese Patent Laid-Open No. 08-027501

  However, in the method of adding a large amount of a plastic binder such as the above-mentioned Patent Documents 1 and 2 to the raw material powder and molding it by the mold molding method, theoretically, since the pressure is applied by the upper and lower punches, It should be easy to fill the powder, but in reality, a product with a uniform density cannot be obtained and has not yet been put to practical use.

  Therefore, the present invention is capable of concretely realizing a method of adding a large amount of a plastic binder to a raw material powder and molding it by a mold molding method, and causes a product having irregularities to cause buckling or breakage of a punch. It aims at providing the manufacturing method which can be manufactured with a uniform density. In this case, another object of the present invention is to make it possible to use the existing mold forming equipment as it is without any special modification.

In order to achieve the above object, the present inventors have conducted extensive research, and as a result, it has been found that the above production method can be specifically realized by adjusting the properties of the granulated powder that binds the metal powder with a plastic binder. did.
The present invention is based on this finding, and the granulated powder for molding the mold of the present invention is a metal powder or a metal powder and a graphite powder of 1.4% by mass or less based on the metal powder is bound with a binder. Granulated powder for molding, wherein the metal powder is sized to pass through a sieve having a particle size of 250 mesh (61 μm), and the tap density is 3.7 Mg. / M ³ or more iron-based alloy powder, and the binder is composed of cellulose and at least one of higher fatty acids, derivatives thereof and wax, and the proportion of the binder in the granulated powder is 5 to 30 volumes. The granulated powder has a particle size passing through a mesh of 35 mesh (447 μm), and the apparent density of the granulated powder is 2.0 Mg / m ³ or more.

Moreover, the manufacturing method of the granulated powder for metal mold | die shaping | molding of this invention is a magnitude | size which passes a sieving of a 300 mesh (46 micrometers) particle diameter preferably, and a tap density is 3.7 Mg / m < ³ >. A raw material powder comprising the above iron-base alloy powder or a raw material powder comprising the iron-base alloy powder and a graphite powder of 1.4% by mass or less based on the iron-base alloy powder is prepared. Cellulose and higher fatty acid , A derivative component and at least one of waxes, and a binder component in a ratio of 5 to 30% by volume with respect to the raw material powder is prepared. In the dispersion medium in which cellulose is soluble, the raw material powder and the above A kneading step in which a binder component is added and kneaded, a granulation step in which the kneaded product is extruded and then rolled to spheroidize, and a drying step in which the dispersion medium in which cellulose is dispersed from the granulated product is volatilized and removed. To be And butterflies.

  By using the granulated powder for molding of the mold of the present invention, it becomes possible to specifically realize a method of molding by a mold molding method by adding a large amount of a plastic binder to the raw material powder. In other words, using a mold forming method, a single-stage punch can be used to prevent the buckling and breakage of the punch, and even with a small gap between the molds, it is possible to form a compact with a uniform density and a complex shape. It has a special effect of becoming. Further, since the amount of the binder added is smaller than that in the case of the injection molding method, the binder removal time can be shortened. With these effects, the range of application of the product by the mold forming method can be expanded.

  Below, the granulated powder for the metal mold | die shaping | molding of this invention, the manufacturing method of granulated powder, and the manufacturing method of the sintered component using this granulated powder are demonstrated.

[Granulated powder]
In order to introduce the metal powder into the minute recesses of the mold, the metal powder needs to be fine and spherical. That is, it is possible to uniformly fill minute concave portions of the mold by being fine, and dense filling can be achieved by being spherical.

  From the viewpoint of the fine metal powder, the metal powder to be used needs to have a size that allows the particle size to pass through a 250 mesh screen. The powder that passes through the mesh having a particle size of 250 mesh is a powder having a maximum particle size of 61 μm. When a large metal powder exceeding this size is mixed, the concave portion of the mold is very small. Therefore, it becomes difficult to obtain a molded body having a uniform density. It is preferable that the particle size of the metal powder is a powder that passes through a 300-mesh sieve (powder having a maximum particle size of 46 μm) because it is easy to fill the concave portion of a smaller mold. On the other hand, since an excessively fine powder increases the cost, the average particle size of the metal powder is preferably about 10 to 30 μm.

From the viewpoint of the above spherical metal powder, when the metal powder to be used is an iron-based alloy powder, a tap density of 3.7 Mg / m ³ or more is suitable. That is, since the powder close to a sphere tends to be densely packed, the tap density is improved. A powder having a tap density of less than 3.7 Mg / m ³ is unsuitable because the powder has poor roundness and is difficult to be densely packed.

In addition, in order to make the fluidity uniform in each part of the raw material powder and make the flow of the metal powder into the recess of the mold uniform, the metal powder should be a single alloy powder rather than a mixture of various metals. preferable. In addition, when a single alloy powder is used, an effect is obtained in which each part of the sintered metal part to be obtained has a uniform composition, and each part has a product having uniform characteristics. Furthermore, if the hardness of the metal powder is low, the metal powder itself is likely to be plastically deformed when pressed by a punch, and if the metal powder is plastically deformed, the flow of the metal powder to the gap portion of the mold is impaired and uniform. The present inventors have found that it is difficult to achieve a high density.
From these points, in the present invention, it is an essential requirement to use an iron-based alloy powder as the metal powder. That is, the iron-base alloy powder has Fe as a main component and other elements are solid-dissolved in the Fe matrix, so that the hardness (base hardness) of the powder is high and plastic deformation is difficult. However, if the C content is all dissolved in the iron-based alloy powder, the powder becomes too hard, and no plastic deformation occurs between the metal powders during molding, and no entanglement between the metal powders occurs. The shape is maintained only by the binder action of the molding lubricant, and the strength of the molded body is significantly reduced. Further, when the molding lubricant is removed from such a molded body, it becomes difficult to retain the shape of the molded body, and the mold tends to lose its shape. For this reason, about C content, if it is 1.4 mass% or less in the form of graphite powder, it may be added to the granulated powder.

  The hardness of the iron-based alloy powder is preferably an alloy powder having a Vickers hardness of 150 Hv or more and more preferably in the range of 200 to 800 Hv as a guide. When the powder has a Vickers hardness of less than 150 Hv, plastic deformation is likely to occur, and the density of the molded body tends to be uneven. On the other hand, when the Vickers hardness of the iron-based alloy powder exceeds 800 Hv, the powder becomes too hard and the above-described problems become remarkable.

  The binder is composed of cellulose and a molding lubricant component composed of at least one of higher fatty acids, derivatives thereof or waxes. Moreover, a binder needs to be 5-30 volume% as a ratio to granulated powder.

  Cellulose plays the role of a dispersing agent that uniformly disperses metal powder or metal powder and graphite powder in a solution in which the binder component is dissolved in the granulated powder manufacturing process described later, and increases the strength of the kneaded product. Also, in the process of extrusion molding, cutting, rolling, etc. of the kneaded product, it also plays the role of shape retention of the granulated powder.

Higher fatty acids, their derivatives or waxes are bound to metal powders or between metal powders and graphite powders in granulated powders, and they are transferred from a powder container (hopper) used during normal mold molding to a feeder (powder box). The role of giving the granulated powder an appropriate strength to the extent that it can be easily crushed by the applied pressure during compression molding, when the powder is supplied or when the die cavity is filled with a feeder (powder box). Take on. Also, at the time of compression molding, the role of reducing the friction between the metal powder and between the metal powder and the mold wall surface and causing the fine metal powder to flow into the fine concave portions (convex portions of the molded body) of the mold. Bear.
Higher fatty acids, their derivatives or waxes that play such a role can be used as molding lubricants in the mold molding method. As the higher fatty acids, stearic acid, its derivatives such as erucic acid amide, and other stearic acids. Zinc, lithium stearate or the like is used. As the wax, ethylene bisstearamide or ethylene bisstearamide added with an aliphatic carboxylic acid monoamide such as lauric acid amide or stearic acid amide can be used. These may be used singly or in combination.

  If the binder composed of the cellulose and the molding lubricant component is less than 5% by volume in the granulated powder, the fluidity of the raw material powder becomes poor, and the metal powder flows sufficiently in the recesses of the mold. The density cannot be reduced. On the other hand, if the proportion of the binder in the granulated powder exceeds 30% by volume, the amount of the binder becomes excessive, it takes a long time to remove the binder, and the proportion of the metal powder in the compact becomes small and shrinks. As the amount increases, the dimensional accuracy decreases significantly.

  Regarding the ratio of cellulose to the molding lubricant component in the binder, if the cellulose ratio is too low, the effect of the cellulose becomes poor, and if the ratio of cellulose is excessive, the action of the molding lubricant component becomes poor. For this reason, it is preferable that the ratio of the cellulose in a binder shall be 5-15 mass%.

  The granulated powder preferably has high fluidity and high apparent density. That is, when the fluidity of the granulated powder is high, the flow of the raw material powder from the hopper (powder container) to the feeder (powder box) and the filling of the raw material powder from the feeder (powder box) to the die cavity become good. Further, when the apparent density is high, the amount of the raw material powder filled in the die cavity does not vary and the molded body weight is stabilized stably. For this reason, the granulated powder is preferably spherical.

From this viewpoint, it is necessary that the granulated powder having the above composition has an apparent density of 2.0 Mg / m ³ or more. When the apparent density is smaller than 2.0 Mg / m ³ , the degree of sphericalness is reduced and the fluidity is deteriorated, and the filling amount into the die cavity varies, and the weight of the molded body varies.

  The size of the granulated powder is a powder that has passed through a 35 mesh screen (particle size of 447 μm or less), preferably 40 mesh screen, from the viewpoint of fluidity and filling into the die cavity. Use powder that passed through a sieve (particle size of 381 μm or less). Coarse granulated powder that does not pass through a 35 mesh screen deteriorates fluidity and varies the filling amount into the die cavity. On the other hand, when the iron-based alloy powder generated by crushing the granulated powder and the minute granulated powder are mixed, the fluidity and the filling property are lowered, so that the powder passed through a 200 mesh sieve ( It is preferable to use after removing the powder (particle size of 74 μm or less), preferably the powder passed through a 100 mesh sieve (particle size of 140 μm or less).

[Production method of granulated powder]
As granulation methods, there are various types of granulation methods. From basic features, rolling granulation method, fluidized bed granulation method, extrusion granulation method, compression granulation method, crushing type It is roughly divided into granulation method and injection type granulation method.
The rolling type granulation method is a method in which a material is used for rolling operation by a rotating drum, a rotating pan, etc., and granulated by agglomeration or coating. The fluidized bed granulation method is a method in which a liquid binder is sprinkled in a dry fluidized bed (spouted bed) to perform agglomeration granulation, or a solute in the sprinkling is coated and granulated on fluidized particles. The extrusion granulation method is a method in which a plastic material is extruded from a die by a screw, piston or roll type extruder to form a cylindrical granulated product. The compression granulation method is a method in which a dry powder or a low-humidity powder is compression-molded using a punch, a mold or the like. The pulverization type granulation method is a method in which a powder aggregate (molded product) is cut with a rotating blade to form a fine aggregated granulated product. The injection-type granulation method is a method in which a molten substance is dispersed in air, oil, or water, and is granulated by cooling and solidifying.
In addition, mixing, kneading, dissolution, melting, etc. are adjusted as pretreatment for basic operations of granulation, and operations such as classification, drying, baking, crushing, etc. are performed as post-treatments. There are a number of types that have both. The present invention has been made as a result of the inventors' diligent research and finding the optimum combination in order to obtain a granulated powder having the above characteristics in these various granulation methods. A method for producing the granulated powder of the present invention suitable for the mold forming method will be described.

The manufacturing process of granulated powder is shown in FIG. Hereinafter, each step will be described with reference to FIG. The raw material powder is as described above, and an iron-base alloy powder having a particle size passing through a mesh having a mesh size of 250 mesh (61 μm) and a tap density of 3.7 Mg / m ³ or more can be used. Moreover, you may add 1.4 mass% or less graphite powder with respect to this iron-based metal powder. Two types of binder components, cellulose and a molding lubricant component, are used.

  As shown in the kneading step of FIG. 1, the prepared raw material powder 1 and the molded lubricant component 2 are put into a kneading device (kneader) 4 together with a dispersion medium 3 for dispersing cellulose, and the raw material powder is uniformly dispersed in the liquid. The kneaded product is prepared by stirring, mixing, and kneading. FIG. 1 shows an example of a kneading device 4 in which a raw material powder is uniformly kneaded in a liquid by giving a disturbing flow motion to the liquid and the raw material powder by rotating a shaft 6 having blade portions 5. Some have a plurality of blade portions 5 on the shaft 6. In addition, it is preferable to add a surfactant to the dispersion medium at the time of kneading because an effect of dispersing the raw material powder more uniformly during the dispersion or an effect of uniformly dispersing in a shorter time can be obtained. In addition, since it takes time for cellulose to absorb water and swell and disperse uniformly in the dispersion medium, it is preferable to disperse cellulose in the dispersion medium in advance prior to introduction into the kneading apparatus. As a dispersion medium for cellulose, water, ethanol, polyoxyethylene, polyoxypropylene, alkyl ether, and a mixture thereof can be used. Examples of surfactants are nonionic or amphoteric products such as trade names: Emulgen, Amphital, etc. An activator is used.

  As shown in the extrusion process of FIG. 1, the obtained kneaded product 7 is extrusion-molded using an extrusion apparatus 8, and the kneaded product is made into pellets (columnar kneaded product) 9 of an appropriate size. The extrusion device 8 shown in FIG. 1 is a pre-extrusion type screw granulator, which pressurizes and compresses the kneaded material by the thrust of the screw, and extrudes the kneaded material with a die 10 attached to the tip. Yes, with the most standard mechanism. When the kneaded material is extruded into a string shape for a long time, it may be cut into an appropriate length. In this case, for example, a rotating cutter or the like is provided on the front surface of the die 10 in FIG. 1, and the cutter can be cut to an appropriate length by rotating the cutter at an appropriate rotational speed. The obtained extruded kneaded product has a substantially cylindrical pellet shape. In addition to the above-mentioned pre-extrusion type screw granulator, various types such as horizontal extrusion type screw granulator, roll type extrusion granulator, basket type granulator, gear type extrusion granulator, cylinder type extrusion granulator, etc. An extrusion granulator can be used.

  The substantially cylindrical kneaded material 9 obtained is rolled by using a rolling device 11 as shown in the rolling step of FIG. FIG. 1 shows an example of a rolling device known as a spherical sizing machine. The substantially columnar kneaded material 9 that has been put in is composed of a centrifugal force of a plate 13 that rotates horizontally, and an uneven frictional force provided on the plate. Therefore, the kneaded material is rotated in a rolling motion while twisting on the inner wall surface of the casing. As the spheroidizing rolling process, the spheroidizing may be performed by rolling between upper and lower plates which are adjusted to an appropriate gap and rotate in opposite directions.

  By passing through the extrusion process, the cutting process, and the rolling process of such a kneaded product, the kneaded product can be made into a substantially spherical and uniform diameter. In this production method, in order to obtain a granulated powder having a desired diameter, the diameter of the extrusion hole 10a of the extrusion device 8 may be set to an appropriate one, and an extremely spherical and uniform granulated powder can be obtained very easily. Can be manufactured. That is, the diameter of the substantially spherical kneaded material hardly changes even after the drying step described later, and the size of the substantially spherical kneaded material obtained through the rolling step from the extrusion step becomes the size of the granulated powder. Accordingly, in order to obtain a granulated powder that passes through a 35 mesh sieve (particle size of 447 μm or less), the diameter of the extrusion hole of the extrusion device is set to 450 μm in consideration of volume reduction due to removal of the dispersion medium. In order to make the granulated powder into a powder that passes through a 40 mesh sieve (particle size of 381 μm or less), the diameter of the extrusion hole may be about 400 μm.

  The granulated powder 16 is obtained through a drying process in which the dispersion medium is volatilized and removed from the substantially spherical kneaded product obtained as described above. As a method for removing the dispersion medium, the dispersion medium may be simply heated to vaporize and evaporate, or may be exposed to a vacuum environment and vacuum dried. FIG. 1 shows an example of a drying device 14, which is known as a band dryer. While conveying a substantially spherical kneaded material 12 on a belt 15 with holes, it is heated by applying warm air from the bottom of the belt. The dispersion medium in the kneaded product is removed by volatilization. The kneaded material may be heated from above and / or from the side by passing the belt through a heating furnace. That is, any apparatus can be used as long as the dispersion medium can be volatilized and removed from the kneaded product.

  However, at the drying temperature at which the dispersion medium is volatilized and removed, part of the molded lubricant component needs to be in a molten state among the binder components. That is, at the time of the solution in which the binder component is dissolved in the dispersion medium, the solution is in a gel state and binds the raw material powder, but when these binder components are not melted at the time when the dispersion medium volatilizes, the raw material The binding of the powder is impaired, and there is a possibility that the granulated powder formed into a substantially spherical shape collapses. Therefore, it is necessary to select a combination of the dispersion medium and the molded lubricant component in which the melting point of the molded lubricant component exists below the vaporization temperature of the dispersion medium.

By the way, water is particularly recommended as a dispersion medium because it is very easily available and does not cause any adverse effects on the human body or the environment even if it volatilizes. In using such water as a dispersion medium, it is preferable to use stearic acid (melting point: 60 ° C.) or erucic acid amide (melting point: 80 ° C.) having a melting point below the vaporization temperature of water. In particular, stearic acid is distributed in a large amount as a molding lubricant for powder metallurgy and is available at low cost, so that it is preferable to use this.
Thus, when water is used as the dispersion medium and cellulose is used as the binder component and at least one of stearic acid and erucic acid amide is used, the substantially spherical kneaded product obtained as described above is used. If heated to a temperature range of 80 to 120 ° C., even if the water volatilizes, a part of the binder component (at least one of stearic acid and erucic acid amide) melts and binds the raw material powder, The granulated powder can be dried without causing the granulated powder to collapse. In addition, when using water as a dispersion medium, since there exists a possibility that rust may generate | occur | produce on the surface of the iron-base alloy powder which is a raw material powder, you may add an appropriate amount of a rust preventive agent in a dispersion medium.

  In order to make the granulated powder obtained by the above steps into a target particle size, a powder that passes through a 35 mesh (447 μm) sieve, preferably a 40 mesh (381 μm) sieve, is used. However, since it also contains a fine iron-based alloy powder derived from the granulated powder crushed in the granulation step, it is further sieved with a mesh of 200 mesh (74 μm), preferably 100 mesh (140 μm), Use the granulated powder remaining on the sieve mesh. The granulated powder thus classified has a lower limit of 74 μm, preferably 140 μm, and an upper limit of 447 μm, preferably 381 μm.

[Method of manufacturing sintered parts]
The above-mentioned granulated powder of the present invention is substantially spherical and has a uniform size, and is more fluid than the raw material powder used in the general mold molding method, and is performed by a general mold molding method. It is possible to easily supply the powder from the powder container (hopper) to the feeder (powder box) and to fill the die cavity with the feeder (powder box).
Further, compression molding of the filled granulated powder is performed by a general mold forming method, and includes a mold having a mold hole, and a pair of upper punch and lower punch that are slidably fitted in the mold hole. This is performed by using a molding apparatus provided, filling the cavity formed by the mold hole of the mold and the lower punch with the raw material powder, and compression molding the upper punch and the lower punch. At this time, the granulated powder was crushed, and the iron-based alloy powder was (1) difficult to plastically deform, (2) a fine particle size, and (3) a rounded particle shape close to a spherical shape. Thus, the friction of the forming lubricant component between the iron-base alloy powders having the characteristics (1) to (3) and between the iron-base alloy powder and the mold wall surface is reduced. Since it is made to flow and fill in a concave part (convex part of a molded object), the molded object of a uniform molding density is obtained in each part.

  Further, since the granulated powder is excellent in fluidity and filling property as described above, it is a product having a concave portion and / or a convex portion with a small width and a concave portion and / or a convex portion having different heights in each part of the product. However, a sufficiently uniform molding density can be obtained by using a pair of one-stage punches as the upper and lower punches. For this reason, it is possible to simplify the mold mechanism while omitting the use of a multi-stage punch that uses a punch having a small width that easily causes breakage or buckling. Even when multi-stage punches are used, the flowability and filling properties of the granulated powder make it possible to efficiently flow the iron-based alloy powder inside the mold cavity, which is lower than before. Since compression molding can be performed with pressure, the possibility of breakage or buckling can be greatly reduced even when a punch having a small width is used.

The above molding can be performed at room temperature (cold) as in the case of a normal powder metallurgy method. In this case, the metal powder flows and fills in the fine mold gap while sliding between the metal powder and between the mold inner wall and the metal powder by the molding lubricant. Alternatively, the mold may be warmly molded by heating it above the softening point temperature of the molding lubricant. In this case, the softened molding lubricant is easy to flow during pressurization, improving the fluidity of the raw material powder, and the pressure during pressurization propagates uniformly in each part due to the softened molding lubricant. Easy to obtain density. However, if the molding lubricant is softened at the time of extraction after molding, the molded product will be easily deformed at the time of extraction, and the molding lubricant will adhere to the inner wall of the mold, so the extraction will be below the softening point of the molding lubricant. Need to be done after cooling.
In order to perform such molding, the mold may be provided with heating means and cooling means, and heating and cooling may be performed alternately. However, the softening point temperature of the molding lubricant due to heat generation on the mold surface during continuous molding. After molding is completed, molding is performed by selecting a molding lubricant that lowers the temperature of the mold wall surface due to the heat conduction of the mold and is equal to or lower than the softening point temperature of the molding lubricant. Alternatively, by performing molding by heating the mold to a temperature that can be molded in the above-described state, it is possible to perform molding that combines the advantages of cold molding and warm molding without providing a separate cooling means. Can do.

The molded body obtained as described above contains a large amount of a binder component (in the case of the present application, a molding lubricant) in the same manner as in the injection molding method, and, as in the case of the injection molding method, exceeds the volatilization temperature of the binder component. The binder component is volatilized and removed by heating. If the rate of temperature increase near the thermal decomposition temperature of the binder component used at this time is high, the binder component rapidly gasifies and expands, causing the mold to lose its shape. Need to be done gradually.
However, since the granulated powder of the present invention has a smaller amount of the binder component compared to the injection molding method, the binder removal step can be completed in a shorter time than in the injection molding method.

In the molded body after removing the molding lubricant described above, the metal powders are not yet diffused, are not metallicly bonded, and are extremely brittle. Therefore, sintering is performed in order to diffusely bond metal powders in a metallic manner.
The sintering temperature varies depending on the composition of the metal powder, but about 1000 to 1300 ° C is appropriate. In the sintering process, the metal powder that is fine and nearly spherical as described above is used, so the contact area of the metal powder is large, so that densification by sintering is likely to proceed, and the density ratio is 80% or more at the above temperature. A dense sintered body is obtained. In addition, it is known that the dimensional change during sintering is affected by the density of the compact, but since the above compact has a uniform density in each part, the dimensional change in each part during sintering is uniform. Thus, the obtained sintered metal part is excellent in dimensional accuracy.

[Example 1]
As the iron-based alloy powder, an iron-based alloy powder equivalent to JIS 440C of JIS standard having a particle size and tap density shown in Table 1 was prepared. In addition, graphite powder (manufactured by Asbury Co., Ltd., trade name SW1651), cellulose (manufactured by Nippon Soda Co., Ltd., trade name HPC-M), and stearic acid (manufactured by Dainichi Chemical Co., Ltd., trade name) as a molding lubricant. W-02) was prepared.
Using water as a dispersion medium, these iron-based alloy powder, graphite powder, cellulose, and molding lubricant were mixed with water in the proportions shown in Table 1 in a kneading apparatus (Fuji Powder Co., Ltd., trade name kneader) and kneaded. . Water was added at a rate of 600 g per 10 kg of the raw material powder.
The obtained kneaded product was put into an extrusion apparatus (trade name Dome Gran manufactured by Fuji Paudal Co., Ltd.) and extruded into a pellet shape of φ0.3 mm. Next, the pelletized kneaded product was put into a spherical granulator (trade name Malmerizer, manufactured by Fuji Powder Co., Ltd.) and rolled to obtain a substantially spherical kneaded product having a diameter of 0.35 mm. The obtained substantially spherical kneaded product was heated to 100 ° C. with a dryer to remove moisture and produce a granulated powder.
The obtained granulated powder is sieved with a mesh of 35 mesh (447 μm), and the powder that has passed through the mesh is further sieved with a mesh of 100 mesh (140 μm), and the powder remains on the mesh, That is, a granulated powder having a particle size of 140 to 447 μm was prepared as an experimental granulated powder. The apparent density of the granulated powder was 2.3 Mg / m ³ .

The obtained granulated powder was used to evaluate the formability in mold molding. The evaluation of the formability was performed by the following method. That is, as shown in FIG. 2, a single-stage punch having three vertical grooves 22 each having a square of 50 mm × 50 mm, a width of the lower end surface of the punch surface of 5 mm, a recess depth of 20 mm, and a recess bottom width of 5 mm is formed. A flat single-stage punch of 50 mm × 50 mm was used as the lower punch 23 as the upper punch 21. Further, as shown in FIG. 3 (a), the granulated powder 16 is filled into the cavity 25 of the mold 24, and then the upper punch 21 is lowered to compress the granulated powder as shown in FIG. 3 (b). .
At this time, the inflow of the granulated powder 16 into the concave portion of the vertical groove 22 of the upper punch 21 was evaluated by measuring the raised height of the convex portion of the molded body after molding. That is, in the case of a granulated powder having good fluidity and filling property of the granulated powder, as shown in FIG. 4 (a), the convex part height is formed to 20 mm. However, in the case of a granulated powder having a poor quality, the height of the convex portion is insufficient as shown in FIG. Table 2 also shows the results of measuring the raised height of the convex portions of the molded body after molding.

  The filling of the granulated powder into the die cavity formed by the mold hole of the mold shown in FIG. 3 (a) and the lower punch is a general feeder (powder box) used in a normal mold forming method. ). That is, the feeder on the bottomless box is connected to a driving device such as a hydraulic cylinder by a flexible hose from the elevated hopper that stores the raw material powder, and is advanced on the upper surface of the mold, and the raw material powder is dropped into the die cavity. This is a method of performing one filling cycle by retreating the upper surface of the raw material powder filled and deposited in the inside to the standby position while rubbing flatly at the lower edge of the feeder.

In Table 1, the numbers described in the sieve column of the particle diameter of the iron-based alloy powder are mesh numbers of the meshes, and the negative values described in the column are the powders that passed through the mesh numbers. It shows that there was. The particle size (μm) in the right adjacent column indicates the maximum particle size of the iron-based alloy powder in that case.
Sample No. 20 in Tables 1 and 2 is an example of a commonly used mold forming method, that is, a conventional example. Pure iron powder having a normal particle diameter is added with 2% by mass of electrolytic copper powder and 1.0%. It is an example in the case of using a mixed powder in which a mass% graphite powder is blended and a stearic acid powder is blended and mixed as a molding lubricant.

By comparing the samples of sample numbers 01 to 07 in Table 1 and Table 2, the influence of the particle size of the iron-based alloy powder can be examined.
From these, when the particle size of the iron-based alloy powder is a size that passes through a 250-mesh sieve (sample numbers 01 to 04), the raised height of the convex portion of the compact is good, but the iron-based alloy powder is When coarse powder that does not pass through a 250 mesh screen (Sample Nos. 05 to 07) is used, the raised height of the convex portion of the molded body is lowered, and the fluidity and filling properties of the raw material powder may be impaired. Recognize.

By comparing the samples Nos. 03 and 08 to 10 in Table 1 and Table 2, the influence of the tap density of the iron-based alloy powder can be examined.
From these, in the samples (sample numbers 03, 09, 10) in which the tap density of the iron-based alloy powder is 3.7 Mg / m ³ or more, the raised height of the convex portion of the compact is good, but the tap density of the iron-based alloy powder is Is 3.7 Mg / m ³ or less (Sample No. 08), it is found that the raised height of the convex portion of the molded body is low, and the fluidity and filling property of the raw material powder are low.

By comparing the samples Nos. 03 and 11 to 15 in Tables 1 and 2, the influence of the added amount of the binder component can be examined.
From these, in the sample (Sample No. 11) in which the added amount of the binder component is less than 5% by volume, the fluidity and filling property of the raw material powder are insufficient, and the raised height of the convex portion of the molded body is low. . On the other hand, in samples (sample numbers 03, 12 to 15) in which the amount of the binder component added exceeds 5% by volume, the flowability and filling properties of the raw material powder are sufficient, and the raised height of the convex portion of the molded body is high. However, in the sample (sample number 15) in which the amount of the binder component added exceeds 30% by volume, the binder component is excessive and the molding can be performed satisfactorily, but the binder component protrudes from the gap between the mold and the upper and lower punches. As a result, it was necessary to clean the mold hole and the upper and lower punches before the next molding. From this, it was confirmed that the sample (sample number 15) in which the added amount of the binder component exceeds 30% by volume has an excessive binder component and is not suitable for continuous molding.

By comparing the samples Nos. 03 and 16 to 19 in Table 1 and Table 2, the influence of the ratio of cellulose to the molding lubricant component in the binder component can be examined.
From these, the sample (sample number 16) in which the content ratio of cellulose in the binder component is less than 5% by mass could not be extruded even when mixed, and the extrusion could not be performed. In addition, a sample having a cellulose content of more than 15% by mass (sample No. 19) was obtained as a good kneaded product, and a spherical kneaded product could be produced through the subsequent extrusion process and rolling process. The granulated powder obtained after drying due to insufficient molding lubricant component to bind the iron-based alloy powder was crushed and only fine powder was obtained, and the experimental granulated powder was not obtained by the classification process .
On the other hand, in the samples having a cellulose content of 5 to 15% by mass (sample numbers 03, 17, and 18), a good kneaded product is obtained, and the subsequent extrusion process, rolling process, drying process, and classification process are performed. As a result, a good granulated powder was obtained, and a good raised height of the convex part of the molded product was obtained in the molding test.

  Note that the sample No. 20 in Table 1 and Table 2 is an example of a general mold forming method that has been used conventionally, and the raised height of the convex portion of the molded body is extremely low, and the fluidity and fillability are low. It is scarce and it turns out that there is a problem in formability. On the other hand, it can be seen that all the samples within the scope of the present invention have a high raised height of the convex portion of the molded body and are excellent in fluidity and filling properties.

[Example 2]
Sample powder No. 03 of Example 1 using an iron-based alloy powder (maximum particle size: 46 μm, tap density: 4.0 Mg / m ³ ) as a raw material powder, and 1.0% by mass of graphite powder added thereto As a binder, the proportion of cellulose in the binder is 10% by mass, the remainder is 20% by volume of the binder of stearic acid with respect to the raw material powder, and the rolling step is omitted in the method of Example 1. A granulated powder was prepared (Table 3, Sample No. 21). In addition, granulation was performed by a granulation method different from the fluidized bed granulation method (same as sample number 22) and the heated granulation method (same as sample number 23) to produce granulated powder.

In the fluidized bed granulation method, as shown in FIG. 5, the fluidized gas 27 is introduced into the fluidized bed dryer 26 from below to force the powder to circulate and flow the binder 28 into the powder 28. By spraying droplets 29 and bringing the sprayed droplets of the binder into contact with the fluidized powder, the formation of liquid bridges between the particles by the action of the solid-liquid interfacial energy causes agglomeration. It is a method of drying while.
In this example, the same raw material powder and binder as sample No. 03 of Example 1 were used as powder, and the raw material powder was forcibly circulated and fluidized using a fluidized bed granulator (manufactured by POWREC Co., Ltd.). Then, a solution obtained by dissolving the binder component in water was sprayed to perform granulation and drying.

The heating granulation method is a kind of agitation granulation method, which does not use a binder solution and is powdery at room temperature and does not have a binding force, but melts into a liquid at a certain temperature and exhibits a binding force as a binder. In this method, a powder to be a binder is added in advance to a powder, heated and granulated while being completely dispersed by a mixer, and cooled at an appropriate particle size to obtain a granulated powder.
In this example, the same raw material powder as sample No. 03 of Example 1 was used as the raw material powder, only stearic acid was used as the binder, and these were used with a Henschel type mixer (Fukae Pautech Co., Ltd.) The jacket was heated to heat and granulate the raw material powder.

The obtained granulated powder was classified in the same manner as in Example 1, and then molded by the same method as in Example 1 to produce 50 compacts for each condition. About this molded object, the raised height of the molded object convex part was measured like Example 1. FIG. The obtained molded body was heated to 700 ° C. to remove the binder, and then heated to 1250 ° C. in a vacuum atmosphere with a vacuum degree of 10 torr for sintering.
About the obtained sintered compact, the weight was measured and the width of the weight dispersion | variation in each condition was evaluated using 6 (sigma). Further, the obtained sintered body was cut and the metal structure of the cross section was observed. These evaluation results are shown in Table 3.

From Table 3, the granulated powder that has both the requirements for the iron-base alloy powder and the requirements for the binder component has the same raised height of the protrusions of the molded body by any method, and the flowability and filling properties of the raw material powder. It can be seen that a granulated powder having no problem can be obtained. However, in the sample (sample number 21) in which the rolling step is omitted from the method for producing the granulated powder of the present invention, the weight variation of the sintered body is large.
This is considered to be due to the fact that the apparent density of the granulated powder is reduced by omitting the rolling step, and therefore the filling amount of the granulated powder into the mold cavity varies.

In addition, in the case of the fluidized bed granulation method (sample number 22) and the heat granulation method (sample number 23) different from the present invention, since the spherical granulated powder is obtained, the filling amount into the cavity of the mold However, although the variation in weight was small, rough atmospheric pores were confirmed in the metal structure of the sintered body.
This is because, in these granulation methods, graphite powder having a specific gravity different from that of the iron-based alloy powder was not uniformly granulated, and a portion where the graphite powder segregated occurred, so that the graphite was present in the base of the iron-based alloy during sintering. It is thought that pores (so-called Kirkendall void) remained after diffusing and disappearing. Therefore, it is considered that the granulated powder obtained by the fluidized bed granulation method (sample number 22) or the heat granulation method (sample number 23) is likely to cause aggregation of a light powder having a low specific gravity.

  On the other hand, in the sample (Sample No. 03) that has undergone the kneading step, the extrusion step, the rolling step, the drying step, and the classification step, the presence of coarse air holes is not confirmed, and the granulated powder of the present invention is a powder having a different specific gravity. Even in such a case, it was confirmed that a granulated powder having a uniform component composition can be formed without causing aggregation and segregation, and that no coarse pores are generated after sintering.

[Example 3]
As a metal powder, pure iron powder (Table 4, sample number 24) having a size that passes through a 300 mesh (46 μm) sieve mesh and a tap density greater than 3.7 Mg / m ³ , Fe-6.5Co -1.5Mo-1.5Ni-0.5Mn alloy powder (sample number 25), ferritic stainless steel (SUS316 equivalent steel) powder (sample number 26), Fe-3Si alloy powder (sample number 27), Fe-6 .5Si alloy powder (Sample No. 28) was prepared. These metal powders were blended with other components in the same manner as in Sample No. 03 of Example 1 to obtain granulated powders in the same manner, and the moldability in mold molding was similarly evaluated. The results are shown in Table 4. The Vickers hardness of each metal powder is also shown in Table 4. In Table 4, as an example using martensitic stainless steel (SUS440C equivalent steel) powder, the value of the sample of sample number 03 of Example 1 is shown again.

  From Table 4, the sample using pure iron powder as the raw metal powder (sample number 24) is molded in comparison with the sample using iron-based alloy powder as the raw metal powder (sample numbers 03, 25 to 28). The raised height of the body convex portion is a low value. On the other hand, the samples using the iron-based alloy powder (sample numbers 03, 25 to 28) all show a sufficient height of the protrusions of the molded body, and it can be seen that the formability is high. This is thought to be because pure iron powder has low powder hardness, and plastic deformation occurred during compaction molding, resulting in decreased fluidity and filling properties of the metal powder. Moreover, in the present Example, it was confirmed that the iron-base alloy powder having a powder hardness of 150 Hv or more has high formability.

  From the above, the granulated powder of the present invention has extremely excellent fluidity and filling properties, and has a uniform component composition without segregation even when it contains component powders having different specific gravity such as graphite powder. Therefore, when applied to the mold forming method, it has been proved to exhibit high formability. Moreover, since the molded object obtained by the granulated powder of this invention has few binder amounts compared with the molded object in the case of an injection molding method, it also has the effect that the time of binder removal can be shortened.

  If the granulated powder for molding of the present invention is used, a method of molding by a mold molding method by adding a large amount of a plastic binder to the raw material powder can be realized. In other words, by using a mold forming method, a single-stage punch can be used to prevent punch buckling and breakage, and even if the gap between the molds is very small, it is possible to form a compact body with a uniform density. It has a special effect of becoming. Further, since the amount of the binder added is smaller than that in the case of the injection molding method, the binder removal time can be shortened. Due to these effects, it is possible to expand the application range of the product by the mold forming method suitable for the sintered part having a small product shape and unevenness.

It is the schematic explaining the granulation process of this invention. It is a perspective view of the upper punch used in the Example. It is the schematic explaining the shaping | molding state of an Example. (A) shows the state which filled the granulated powder in the cavity. (B) shows a state in which the powder is compressed by the upper punch. (A) is a perspective view of a molded article having a sufficient height of a convex portion obtained by an example. (B) is a perspective view of a molded article obtained by a comparative example and having an insufficient convex part height. It is the schematic of the fluidized-bed granulator used for the granulation process of the comparative example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Raw material powder 2 Molding lubricant 3 Dispersion medium 4 Kneading apparatus 5 Blade | wing part 6 Shaft 7 Kneaded material 8 Extruding device 9 Cylindrical kneaded material 10 Die 10a Extrusion hole 11 Rolling device 12 Spherical kneaded material 13 Plate 14 Drying device 15 Belt 16 Spherical granulated powder 21 Upper punch 22 Vertical groove 23 Lower punch 24 Mold 25 Cavity 26 Fluidized bed dryer 27 Fluidized gas 28 Powder 29 Binder droplet

Claims (10)

A granulated powder for molding a metal powder, or a metal powder, and a graphite powder of 1.4% by mass or less based on the metal powder and granulated by binding with a binder,
The metal powder is an iron-based alloy powder having a particle size of 250 mesh (61 μm) passing through a sieve mesh and a tap density of 3.7 Mg / m ³ or more,
The binder is composed of cellulose and at least one of higher fatty acids, derivatives thereof and waxes, and the proportion of the binder in the granulated powder is 5 to 30% by volume,
For mold forming, wherein the granulated powder has a particle size passing through a mesh of 35 mesh (447 μm) and the apparent density of the granulated powder is 2.0 Mg / m ³ or more Granulated powder.   The granulated powder for molding a metal mold according to claim 1, wherein the metal powder is an iron-base alloy powder having a Vickers hardness of 150 Hv or more.   The granulated powder for molding according to claim 1 or 2, wherein a ratio of cellulose in the binder is 5 to 15% by mass. A raw material powder comprising an iron-base alloy powder having a particle size of 250 mesh (61 μm) and having a tap density of 3.7 Mg / m ³ or more, or the iron-base alloy powder and the iron Prepare raw material powder consisting of 1.4 mass% or less graphite powder with respect to the base alloy powder,
It comprises cellulose and at least one of higher fatty acids, derivatives thereof and waxes, and prepares a binder component in a proportion of 5 to 30% by volume with respect to the raw material powder,
A kneading step of charging and kneading at least one of the raw material powder and the higher fatty acid, a derivative thereof and a wax in a dispersion medium in which the cellulose is dispersed;
A granulation step in which the kneaded product is extruded and then rolled to spheroidize, and a drying step in which the dispersion medium is volatilized and removed from the granulated product,
The manufacturing method of the granulated powder for metal mold | die shaping | molding characterized by comprising.   The method for producing a granulated powder for mold forming according to claim 4, wherein the metal powder is an iron-base alloy powder having a Vickers hardness of 150 Hv or more.   The method for producing a granulated powder for molding a mold according to claim 4 or 5, wherein a ratio of cellulose in the binder is 5 to 15% by mass.   Water is used as a dispersion medium, cellulose and at least one of stearic acid and erucic acid amide are used as the binder component, and the drying step is performed by heating to a temperature range of 70 to 120 ° C. The manufacturing method of the granulated powder for metal mold | die shaping | molding in any one of Claim 4 to 6.   The method for producing a granulated powder for molding a mold according to any one of claims 4 to 7, wherein a surfactant is added to the dispersion medium.   The obtained granulated powder is classified with a mesh of 35 mesh (447 μm), and includes a classification step for obtaining a powder that has passed through the mesh. A method for producing granulated powder for mold forming. In the method for producing a sintered metal part, using a granulated powder obtained by granulating a metal powder with a binder, compression molding by a mold molding method, removing the binder by heating the obtained molded body, and then sintering.
While using the granulated powder according to any one of claims 1 to 3 as the granulated powder,
A method for producing a sintered part, comprising using a pair of one-stage punches comprising an upper punch and a lower punch.

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