JPH0413804A - Manufacture of green compact having hollow part - Google Patents

Abstract

PURPOSE:To prevent deformation of a green compact by adding the specific cross linking assist agent to binder and heating on the way of compacting at the time of manufacturing the green compact having hollow part by kneading metal or ceramic powder with the binder and extruding from nozzle part having a center core. CONSTITUTION:At the time of sintering after forming the green compact having hollow part by compacting the metal or ceramic powder, to the metal or ceramic powder of raw material, the binder of polyethylene, etc., and organoperoxide series cross linking assist agent of dicumyl peroxide, etc., are added and kneaded to make raw material for green compact. This is extruded from an extruding head 3 providing the center core 4 and the extruded green compact 5 is heated with an induction heating coil 6 arranged at extending part of the center core 4 and strength in the green compact 5 is increased by cross linking reaction with the cross linking assist agent in the binder. After conveying it with a belt 7 as the green compact without any deformation, the sintering is applied, and the sintered product using the metal or the ceramic as raw material and having the hollow part and excellent dimensional accuracy, can be manufactured with high yield.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for producing a green molded body to be subjected to a sintering process in the process of producing powder metallurgy products.

[Prior Art] Generally, in the process of manufacturing sintered products of metals and ceramics, the green compact, which is used for sintering, is
It is obtained by compression molding raw material powder.

However, since this method involves filling a mold with raw material powder and applying pressure from above and below, the shape of the green compact obtained is limited to a relatively simple shape. Especially with thin-walled hollow shapes.

Not enough pressure is applied to the powder inside the mold,
Due to problems such as large frictional resistance during extraction, the shape constraints become even more significant.

On the other hand, in recent years, 10 to 20 wt. The process of manufacturing products by degreasing and sintering green molded bodies obtained by this method is beginning to be adopted industrially.

Although this manufacturing method is effective in increasing the complexity of the molded object shape, in the case of the hollow thin-walled shape described above, the raw material mixture contains metal or ceramic powder at a high filling rate, so the density is high. However, when extruded in a horizontal direction, there is a problem in that the molded product is easily deformed by its own weight.

To prevent this, it is possible to make the extruder vertical or to use a crosshead so that the extrusion direction is vertical.

However, in such a method, processing after extrusion must be performed between the goo and the floor surface, which limits the production speed and causes equipment problems. In addition, when extrusion-molding hollow-shaped ordinary plastics, sizing is carried out industrially using various methods, but the green molded bodies are fragile because the raw material mixture contains a large amount of powder. However, it is difficult to apply these sizing techniques as they are.

Therefore, the technical problem of the present invention is to solve the above drawbacks.

This was developed as a result of studying how to prevent deformation when extruding hollow shapes using a mixture of metal or ceramic powder and a binder.

It is an object of the present invention to provide a method for improving the manufacturing yield of the hollow extrusion molded body.

[Means for Solving the Problems] According to the present invention, a mixture production step of mixing and kneading a metal or ceramic raw material powder and a binder containing an organic polymer as a main component to produce a mixture; and an extrusion molding step of producing a green molded body having a hollow part by extrusion molding from a mouthpiece provided with a core, in which the mixture producing step is performed in advance by It has a crosslinking aid addition step in which a crosslinking aid, typically an organic peracid, is added to the binder.

The core has an extension part extending from the mouth part in the extrusion direction, and the extrusion molding process is performed by using a predetermined heating means.
A method for producing a green molded body having a hollow portion, comprising a crosslinking step of increasing the temperature of the extension part to decompose the crosslinking aid contained in the green molded body and crosslinking the binder. is obtained.

That is, 1 the present invention involves degreasing and sintering a green molded body obtained by extruding a mixture of metal or ceramic raw material powder mixed and kneaded with a binder mainly composed of an organic polymer into a hollow shape. A method for manufacturing a sintered body having a hollow part.

1. Adding a crosslinking aid, typically an organic peracid, to the binder.

2. Providing an extension from the mouthpiece of the molding machine to the core for forming the hollow part of the molded product in the extrusion molding process.

3. Raise the temperature of the extension part by high-frequency induction heating.

A step of crosslinking the binder by decomposing the crosslinking aid contained in the binder while the molded body is in contact with the core extension during extrusion molding.

Configure it to give.

The molded body is reinforced by the crosslinking reaction of the binder.

It is characterized by being able to prevent deformation of the molded body.

Another major feature of the present invention is that the green molded product obtained by such a method has extremely little deformation even during the degreasing process because the binder has changed from thermoplastic to thermosetting.

Therefore, in order to maximize the features of the present invention, selection of the binder and crosslinking aid is important. Regarding the binder, polyethylene is a typical material that easily undergoes a crosslinking reaction due to the action of radicals and is suitable for the purpose of the present invention in terms of ease of handling and cost. Further, any crosslinking aid may be used as long as it gives radicals by thermal decomposition, but it is necessary to use it properly depending on the molding temperature of the binder, and in the case of polyethylene, dicumyl peroxide is suitable. Other typical examples include penzoyl peroxide and butyl peroxide, but it is needless to say that they are not limited to these.

[Example code] Next, embodiments of the present invention will be described with reference to the drawings.

Low-density polyethylene: 3 parts by weight of M n -Z n-based ferrite calcined powder with an average particle size of 1.0 μl: 100 parts by weight
Parts by weight, 23 parts by weight of ethylene-vinyl acetate copolymer, and 3 parts by weight of paraffin wax were weighed and kneaded in a pressure kneader at 130°C for 40 minutes. Thereafter, 0.5 parts by weight of dicumyl peroxide was added and the mixture was left for another 10 minutes, then discharged from the kneader and allowed to cool. This mixture was pulverized until it passed through a φ5 mm screen to obtain a raw material mixture for molding.

This raw material mixture was extruded from an extrusion molding apparatus shown in FIG. 1 through a die having a cross-sectional shape as shown in FIG. The center core 4 has a work coil 6 provided at a position surrounding the center core.
The extension is heated by.

The temperature is maintained at 160°C. The extruded body 5 is thereby kept in shape and given strength by the crosslinking reaction of the binder, so that it does not undergo deformation until it reaches the position of the take-off belt 7.

Table 1 shows the cross-sectional dimensions of the molded body thus obtained.

The measurement site for one dimension is shown in FIG.

This molded body was cut into lengths of 40 mm, and
Degreasing was performed under the conditions of heating to 500° C. with C/Hr, and then sintering at 1,200° C. for 3 hours. As a result, a sintered body without any deformation was obtained.

Comparative Example A raw material mixture prepared in the same manner as in the example except that dicumyl peroxide was not added was extrusion molded in the same manner as in the example except that the core extension was not heated. The cross-sectional shape of this molded body is shown in Table 1 as in the Examples.

As a result, when the molded products were degreased under the same conditions as in the example, bulging deformation was observed on the surface of 14 out of 20 products.

Margin below Table 1 FIG. 2 shows the shape of the mouthpiece of the extrusion head.

FIG. 3 shows the dimensional measurement sites of the cross section of the extruded product.

1... Extrusion screw, 2... Cylinder, 3...
・Extrusion head, 4... Core, 5... Molded object, 6...
- Work coil for induction heating, 7... take-up belt.

Unit: mm [Effects of the Invention] As explained above, according to the present invention, thin metal or ceramic sintered bodies having hollow parts that cannot be obtained by conventional pressing methods can be manufactured with high dimensional accuracy. It is very large and extremely useful industrially.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an outline of an extrusion molding apparatus. Procedural amendment (voluntary) Specification July 29, 1991 Wataru Fukasawa, Commissioner of the Patent Office 1゜ 2゜ 3゜ 4゜ Display of incidents 1990 Patent Application No. 115860 name of invention A person who corrects the manufacturing method of a green molded body having a hollow part Relationship to the case Patent applicant Name To-Kin Co., Ltd.

Claims (1)

[Scope of Claims] 1) A mixture production step of producing a mixture by mixing and kneading raw material powder of metal or ceramics and a binder whose main component is an organic polymer; and an extrusion molding step of producing a green molded body having a hollow part by extrusion molding from a part of the green molded body. The extrusion molding step includes a crosslinking aid addition step of adding a typical crosslinking aid; the core has an extension extending from the mouthpiece in the extrusion direction; A method for producing a green molded body having a hollow portion, comprising a crosslinking step of increasing the temperature of the extension part to decompose the crosslinking aid contained in the green molded body and crosslinking the binder.