JPH0211642B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention is a molding agent or lubricant necessary when press-molding powder by a powder metallurgy method,
Raw material powder for powder metallurgy suitable for press-molding a mixed powder of nonmetallic powder such as carbide, nitride, oxide, boride, sulfide, and silicide with metal powder or mixed powder with metal powder. Regarding molding aids. In general, manufacturing processes in powder metallurgy can be roughly divided into a powder mixing and pulverizing process, a granulation process, a drying and sieving process, a press molding process, a preliminary sintering process, and a sintering process. Among these processes, in the granulation process, it is necessary to make the powder easy to handle, and it is necessary to adjust the shape, size, and hardness of the granulated powder based on the fluidity and filling properties of the powder in the subsequent press forming process. Therefore, it is necessary to mix a molding agent or a lubricant in the granulated powder. In the press forming process, in order to reduce friction between the powder poured into the mold, friction between the powder poured into the mold and the mold wall, and friction at the contact area between the pin of the mold and the die. A molding agent or lubricant is required to keep the shape of the pressed powder compact. Conventionally used molding agents or molding agents such as lubricants include paraffin, camphor,
Examples include stearic acid and zinc stearate. Among these conventional molding aids, there is no suitable solvent for paraffin due to various problems such as safety and health, work, cost, and solubility.Generally, acetone is used as a solvent, but due to its low solubility, paraffin is heated slightly. The method used is to mix it with powder by making it liquid with paraffin. As a result, the distribution of paraffin in the powder becomes uneven, causing problems such as clogging of the mesh during the drying and sieving process, and a portion of the powder containing a large amount of paraffin not passing through the mesh. In addition, forming aids are unnecessary and harmful in the sintering process, so they are removed in the preliminary sintering process, but paraffin decomposes in the preliminary sintering process, becomes carbon, and adheres to the surface of the compact. Due to these problems, the preliminary sintering method and conditions are very difficult. In particular, when preliminary sintering is performed in a vacuum, decomposed paraffin adheres to the inside of the furnace, reducing the degree of vacuum. Furthermore, when a sintered body is obtained from a mixed powder using paraffin as a forming aid, cavities appear, which are thought to be caused by the non-uniform distribution of paraffin, and this poses the important problem of reducing the strength of the sintered body. . Camphor, which is used as a molding aid, is easily soluble in ether, but poses problems in terms of operational safety and health.Although it is soluble to some extent in ethanol, it poses problems in the granulation process due to the evaporation rate of ethanol. In addition, compared to paraffin, camphor has a lower viscosity, so the strength of the compact is lower, and if the strength of the compact is low, cracks are likely to occur in the compact after preliminary sintering, and it is difficult to make a sintered compact. There is a problem that sometimes nests are more likely to occur. Stearic acid and zinc stearate do not have a suitable solvent, so methanol or ethanol is used as a solvent, but like camphor, there are problems in the granulation process.
Furthermore, due to its low solubility, it is difficult to distribute it uniformly in the powder during the granulation process, which causes the problem that cracks and cavities are likely to occur when it is made into a sintered body. The present invention is a forming aid for raw material powder suitable for powder metallurgy, which was completed as a result of repeated research aimed at solving the various problems mentioned above. The molding aid for raw material powder of the present invention is a compound obtained by reacting a glycerin condensate with an olefin oxide and/or a fatty acid. The molding aid for raw material powder of the present invention is easily soluble in organic solvents, particularly methanol, ethanol, acetone, etc., poses no problems in terms of handling, safety and hygiene, and is a compound made by reacting olefin oxide and/or fatty acid. These solubility, adhesion, and stickiness act to uniformly distribute the forming aid in the powder during the granulation process, and the granulated powder has adhesion and stickiness. It helps to reduce variations in shape, size, and hardness and makes stable granulated powder. In addition, in the press molding process, the forming aid for raw material powder of the present invention is used in the granulation process to reduce variations in the shape, size, and hardness of the granulated powder, and to maintain appropriate hardness and viscosity. When press-molding powder, the forming aid is uniformly distributed in the granulated powder.The granulated powder has excellent fluidity and filling properties, making it easier to press the green compact uniformly. In addition, since the strength of the green compact is increased and the green compact has appropriate mold releasability, a compact that is less prone to press cracks and chipping can be obtained. In the preliminary sintering process, the forming aid for raw powder of the present invention evaporates at a low temperature and the evaporation rate is also appropriate, so that gas does not enter the green compact even during the gas decomposition of the forming aid. There is no adverse effect, and therefore cracks are less likely to occur in the green compact after preliminary sintering. When a green compact from which the forming aid of the present invention has been removed through preliminary sintering is sintered, cracks and pores in the sintered compact caused by the direct and indirect effects of the forming aid are generally removed. An excellent sintered body can be obtained. A glycerin condensate is a substance formed by a condensation reaction of glycerin [CH ₂ OH-CHOH-CH ₂ OH], that is, a structure in which multiple glycerin molecules are bonded together, and specifically, the molecular weight is The molecular weight is tens of thousands, and those having a molecular weight of 30,000 to 40,000 are particularly preferred. Olefin oxides include propylene oxide, 1-butene oxide, isobutylene oxide, 1-pentene oxide, 2-pentene oxide, isoamylene oxide, etc., but in particular, the molding aid for the raw material powder of the present invention obtained by addition reaction with ethylene oxide. Judging from the characteristics of granulation, press moldability, etc., these agents are suitable. Fatty acids include animal and vegetable oil fatty acids, hydrogenated animal and vegetable oil fatty acids, and petroleum acids, among which higher fatty acids having 8 or more carbon atoms are suitable, such as caprylic acid, capric acid, myristic acid, palmitic acid, stearic acid, arachidic acid, Examples include behenic acid, cerotic acid, melisic acid, suberic acid, azelaic acid, sebacic acid, brassylic acid, elaidic acid, oleic acid, erucic acid, pelargonic acid, and margaric acid. The molding aid for raw material powder of the present invention has high solubility in organic solvents, and has lubricity, stickiness, and mold releasability, so it exhibits extremely excellent effects in the granulation process and press molding process. Furthermore, when the forming aid becomes unnecessary and is removed in the preliminary sintering process, the forming aid for the raw material powder of the present invention evaporates at a low temperature, does not have a rapid evaporation rate, and evaporates easily in the vacuum furnace. However, it is an excellent molding aid with almost no residue. Powder metallurgy includes porous parts, sintered steel, iron and
Copper alloys/nonferrous alloys, high melting point alloys, heat-resistant and corrosion-resistant alloys,
There are electrical contact materials, nuclear materials, solid lubricating materials, and friction materials, and the forming aid for raw material powder of the present invention is effective for these powder metallurgy materials, especially in the preliminary sintering process of cemented carbide, cermet, etc. It exhibits remarkable effects on powder metallurgy-related materials that are susceptible to damage.
In addition, powders such as carbides, nitrides, borides, silicides, and sulfides of group 4a, 5a, and 6a metals, powders containing metal powders or metal oxides, and molding aids for metal powders include the raw materials of the present invention. Powder forming aids are effective. Next, the forming aid for raw material powder for powder metallurgy of the present invention will be explained in detail according to Examples. Example 1 Weight composition: 40%TiC-15%WC-15%TiN-20
% _Mo2C -10%Ni mixed and pulverized powder is mixed with a forming aid and granulated into -40 to +100 mesh after sieving.
Compression molding into a cylinder of 10 x 10 φ mm at a pressure of 1.0 ton/cm ² , pre-sintering in vacuum at 400℃ to remove the molding aid, and sintering in vacuum at 1400℃ for 1 hour. A comparison was made using the following as an auxiliary agent. a Add 3% by weight of the molding aid of the present invention, which is a glycerin condensate reacted with ethylene oxide and oleic acid. b The molding aid of the present invention made by reacting a glycerin condensate with ethylene oxide and stearic acid.
wt% addition. c The molding aid of the present invention made by reacting a glycerin condensate with propylene oxide and oleic acid.
wt% addition. d 3% by weight of paraffin as a comparative molding aid
Addition. e 3% by weight of polyethylene glycol was added as a comparative molding aid. f 2% by weight of rosin was added as a comparative molding aid. The conditions of the compacts obtained from the mixed powders to which the forming aids a, b, c, d, e, and f have been added and the conditions of the nests and pores of each sintered compact obtained by sintering the compacts are as follows. Table 1
It was shown to. Incidentally, the degree of condensation of the glycerin condensate used for the molding aids a, b, and c of the present invention is about 360 to 400. However, the degree of condensation is determined as the number of monomers constituting the glycerin condensate. From the results in Table 1, the powder compacts using the molding aids a, b, and c of the present invention for raw powder are in extremely good condition compared to those using the comparative molding aids d, e, and f. In addition, it was confirmed that there were fewer cavities and pores in the sintered body.

[Table] Example 2 A mixed and pulverized powder with a weight composition of 95% WC and 5% Co was mixed with 3% by weight of a forming aid and granulated by a spray drying method.
Powder compacts were produced at pressures of 0.7 and 0.9 ton/cm ² and sintered in the same manner as in Example 1. The molding aids used here were molding aids a, b, and c for raw material powders of the present invention shown below, and paraffin d was added as a comparative molding aid. a The molding aid of the present invention made by reacting a glycerin condensate with ethylene oxide and caprylic acid. b The molding aid of the present invention, which is made by reacting a glycerin condensate with propylene oxide and palmitic acid. c The molding aid of the present invention made by reacting a glycerin condensate with ethylene oxide and margaric acid. Table 2 shows the state of the cavities and pores in each sintered compact obtained by sintering green compacts using the forming aids a, b, c, and d at different pressing pressures. The glycerin condensate used here is the same as that used in Example 1.

[Table] From the results in Table 2, the press pressure was
It was confirmed that a sufficiently dense sintered body was obtained even at a low value of 0.5 ton/cm ² and was superior to the comparative paraffin d. Moreover, the green compacts using the molding aids a, b, and c of the present invention had glossy surfaces and high precision without cracks. Example 3 A molding aid for raw material powder of the present invention prepared by reacting the glycerin condensate used in Example 1 with ethylene oxide and oleic acid was added to each sample having the component composition shown in Table 3, a, b, c, d, e and those with paraffin added as a comparative molding aid f, g,
Each of h, i, and j is press-formed into a cylinder shape of 10×10φmm at 1 t/cm ² . Each of these samples was placed in hydrogen, nitrogen,
After preliminary sintering at 400℃ for 1 hour in a hydrogen-nitrogen mixed gas and in vacuum, the total carbon content of each sample was analyzed, and the increase in the total carbon content of the mixed pulverized powder before addition of the forming aid was calculated. The obtained results are shown in Table 4.

【table】

[Table] As a result of Table 4, the carbon content of the molding aid for raw material powder of the present invention increased by 0.02 to 0.05% by weight, whereas the carbon content of the comparative molding aid using paraffin increased by 0.15 to 0.05% by weight. The amount is as high as 0.25% by weight, and the variation tends to be large. From this, it was confirmed that the molding aid for raw material powder of the present invention has little residual carbon and is stable in terms of quality control. Example 4 _60wt % _Al2O3-40wt % _ZrO2 (contains _3mol % _Y2O3 )
The molding aids a, b, and c of the present invention are prepared by reacting the glycerin condensate used in Example 1 with olefin oxide or fatty acid in the mixed powder of
were added in the same manner as in Example 1, and the mixed powders containing the forming aid of the present invention were sintered at 1550°C for 2 hours while oxygen gas was flowing in. A green compact and a sintered body were obtained in the same manner as in Example 1. a Compound obtained by reacting a glycerin condensate with ethylene oxide, b Compound obtained by reacting a glycerin condensate with propylene oxide, c Compound obtained by reacting a glycerin condensate with oleic acid, thus obtained. The compacted powder and sintered compacts were examined in the same manner as in Example 1, and both compacted compacts were found to be in extremely good condition, and the sintered compacts were dense with almost no coexisting pores. It was hot.

Claims (1)

[Scope of Claims] 1. A forming aid for raw material powder for powder metallurgy, characterized by comprising a compound obtained by reacting a glycerin condensate with olefin oxide and/or fatty acid. 2. A forming aid for powder metallurgy raw material powder according to claim 1, wherein the olefin oxide comprises ethylene oxide and/or propylene oxide. 3. Claim 1, wherein the fatty acid is a higher fatty acid having 8 or more carbon atoms.
A forming aid for raw material powder for powder metallurgy according to item 1 or 2.