JPH0288701A - Method for reproducing injection molding raw material for powder metallurgy - Google Patents

Abstract

PURPOSE:To remove the binder and to recover powder of metal and/or ceramic from scrap at high yield by treating the scrap, which is produced at the time of injection-molding to the desired shape after kneading the metal powder and/or ceramic powder with the specific organic polymeric binder, with a specific organic solvent. CONSTITUTION:The organic binder of polyethylene, various kinds of polyolefins, various kinds of acrylic series polymer, polystyrene and their copolymer or various kinds of wax, etc., are added to various kinds of the metal and/or ceramic powders in 10-20wt.%, and after sufficiently kneading, is injection- molded to the desired shape and after removing the binder, is sintered to manufacture the sintered product. By treating the scrap produced at the time of injection-molding with the organic solvent of aromatic compound of benzene, xylene, etc., alcohol, ether, etc., to remove the binder, the metal and/or ceramic powders are recovered at high yield and reused as the raw material for injection-molding product.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for regenerating raw materials for injection molding of ceramics or metals for powder metallurgy.

[Prior Art] Generally, in the process of manufacturing sintered products of ceramics or metals, a compact before sintering is obtained as a green compact by compression molding raw material powder. Since this method usually uses punches to apply pressure from above and below, the shape of the molded product obtained is limited to relatively simple shapes such as cylinders and cylinders, and it is difficult to obtain products with more complex shapes. It is necessary to pressurize the sintered product after cutting, grinding, etc.

In order to improve these problems, various so-called near-net shape technologies have been studied to bring the shape of the molded object closer to the product, but injection molding is the most suitable for molding complex shapes. Some of them are being adopted industrially. In this injection molding method, a mixture of ceramic or metal powder mixed and kneaded with 10 to 20% by weight of a binder mainly composed of an organic polymer is fed into an injection molding machine as pellets of an appropriate shape. A so-called green molded body having the shape of Thereafter, the green molded body is dehindered, ie, degreased, by an appropriate method to obtain a so-called brown body, which is then sintered to form a product.

[Problems to be solved by the invention] Among these processes, degreasing can be performed by dissolving and extracting the binder using an appropriate organic solvent, or by dissolving and extracting the binder using a fluid in a supercritical state, which has been attracting attention in recent years. However, the former has the problem that when the binder is dissolved, the solvent migrates to the organic polymer side and swells, damaging the shape of the molded product, while the latter is soluble in fluids in a supercritical state and is used as a binder. The problem is that a practical prescription has not been established because the possible substances are limited.

Therefore, the current industrial degreasing method is to heat the molded product at a temperature increase rate that does not cause deformation, and to volatilize and remove the binder as a low molecular weight gas through thermal decomposition. Therefore, in addition to moldability, the properties required for the binder used in this method are:
It is very important to have the properties of being easy to thermally decompose and difficult to carbonize.

On the other hand, the injection molding method inevitably generates scrap such as sprue runners, and especially when raw materials are expensive, it is essential to reuse this scrap to reduce the manufacturing cost of the product. . However, as mentioned above, the binder used in this method must have good thermal decomposition properties in consideration of the degreasing process, so it tends to deteriorate each time it is subjected to thermal history during molding, and the molding conditions This causes instability and, in turn, increases variation in the quality of green molded products.

That is, in this manufacturing process, contradictory properties are required of the binder from the two viewpoints of the degreasing process and the reuse of the raw material mixture. If the material is repeatedly reused, it becomes impossible to obtain a green molded product with the quality required for subsequent processes, and in most cases, the raw material must be discarded.

In view of the above-mentioned drawbacks, the technical problem of the present invention is to enable the reuse of raw materials without impairing the quality of green molded products, and is a method for improving the yield of injection molding raw materials for powder metallurgy. Our goal is to provide the following.

[Means for Solving the Problems] A thermoplastic organic polymer can be used as the main component in the binder of the raw material mixture in the step of obtaining a green molded body by injection molding.

Thermoplastic polymers, with the exception of highly heat-resistant polytetrafluoroethylene, require solvents to dissolve them, and if a binder with an appropriate composition is used, the properties of ceramic or metal powders will be impaired. It can be removed by dissolution without any problem.

From this point of view, the present inventors investigated a binder formulation that is soluble in organic solvents and has excellent moldability and degreasing properties.
This is what led to the present invention.

That is, according to the present invention, when manufacturing a ceramic or metal product by powder metallurgy, a mixture of ceramic or metal powder and a binder whose main component is an organic polymer is mixed, mixed, and pulverized, and the mixture is injected into a desired shape. An injection molding raw material for powder metallurgy, characterized in that the scrub generated during the injection molding process is subjected to extraction treatment with a solvent to remove the binder and recover ceramic or metal powder contained in the scrap. A reproduction method is obtained.

In the present invention, scrap generated during the injection molding process refers to sprue runners, etc. Sprue refers to the supply hole or mixture solidified in the conduit that is injected into the injection mold, and the runner refers to the injection molding process. This is the solidified mixture that forms in the groove that connects the sprue of the machine and the gate of the mold cavity.

In the present invention, the binder deteriorates due to thermal history during the molding process, and the mixture becomes usable. By dissolving and extracting the mixture, the ceramic or metal powder is recovered and reused as a raw material for injection molding for powder metallurgy. This provides a method to do so. Therefore, according to the present invention, it is possible to achieve a powder yield of substantially 100%, which is especially effective when the raw material powder is expensive. Naturally, the extracted binder must be discarded, but as mentioned above, the amount of binder added is as small as 10 to 20% by weight, so this will not be a problem unless a particularly expensive one is used.

As the binder used in the present invention, anything can be used as long as it is soluble in a general organic solvent at a temperature of up to about 150°C. Examples include polyethylene, various polyolefins, various acrylic polymers, polystyrene, and Examples include copolymers thereof and various waxes. The reason why the extraction temperature was set at around 150°C is because there is a concern that excessively high temperature conditions may affect the powder. Any solvent may be used as long as it does not affect the powder; examples include aromatic compounds such as benzene and xylene, esters such as ethyl acetate, aliphatic compounds such as hexane, alcohol, and ether. Can be mentioned.

Various types of extraction equipment can be used; for example, if a Soxhlet extractor is used,
Not only is the extraction efficiency high, but the solvent can be reused, which is advantageous.

Examples will be described below, but it goes without saying that the present invention is not limited thereto.

[Example] An alloy of 5US304 was made into powder with an average particle size of about 11 μm by a water atomization method. This powder and number average molecule ft:
60,000 polybutyl methacrylate (PBMA)
, an ethylene-vinyl acetate copolymer with a vinyl acetate content of 25 mole% and a number average molecular weight of 110,000 (
EVA), polyethylene wax (PEWAX) with a number average published value of 2.000 and dioctyl phthalate (DOP)
Weigh it to the weight percentage shown in Table 1, mix it up, crush it,
A mixture for injection molding was obtained. This mixture was injection molded at a temperature of 160°C, and the resulting sprue runners were heated in xylene at 100°C for 5 hours using a Soxhlet extractor.
, the extraction was performed. When the carbon of the 5US304 powder taken out from the extractor was analyzed, it was 87p, p, m,
Almost 100% of the binder was removed, and the powder could be reused as a raw material powder.

[Effects of the Invention] As described above, according to the present invention, it is possible to make the raw material yield of ceramics or metal powder, which is an injection molding raw material for powder metallurgy, substantially 100%. It greatly contributes to reducing the cost of manufacturing products, and is extremely useful industrially.

Claims (1)

[Claims] 1. When manufacturing ceramic or metal products by powder metallurgy, injection molding is performed by mixing, kneading, and pulverizing a mixture of ceramic or metal powder and a binder whose main component is an organic polymer into the desired shape. A method for recycling injection molding raw materials for powder metallurgy, characterized in that scraps generated in a molding process are subjected to extraction treatment to remove the binder and recover ceramic or metal powder from the scraps.