JPH04124203A - Binder for powder metallurgy and method for degreasing green compact - Google Patents

Abstract

PURPOSE:To facilitate degrease of a powder green compact and to easily manufacture a powder metallurgical product of complicate shape by using the specific organic macromolecular binder at the time of manufacturing the sintered product by the powder metallurgical method by using a metal or a ceramic powder as the raw material. CONSTITUTION:The binder is composed of a first organic macromolecule of at least one kind of polyethylene and ethylene-vinyl acetate copolymer so as to contain >=20wt.% of the green compact of binder and further, a second organic macromolecule except the first organic macromolecule is contained in the above binder and is the macro molecule of <=250 deg.C ceiling temp. The binder is mingled and kneaded with the metal or ceramic powder and the mingled material obtd. is formed to the green compact by injection compacting or extruding compacting, etc. After that, the compact is heated at <=280 deg.C heating temp. and the binder is thermal-decomposed and evaporated to manufacture the degreased body with the binder remained in the green compact. After that, this degreased body is sintered to make the sintered product.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention produces powder by degreasing and sintering an injection molded or extrusion molded product consisting of metal or ceramic powder and a binder whose main component is an organic polymer. The present invention relates to a manufacturing method for obtaining a metallurgical compact, and particularly to a method for manufacturing a powder metallurgical compact by thermally decomposing and volatilizing components contained in a binder in a degreasing process by heating.

[Prior Art] In the process of obtaining a sintered product using metal or ceramic powder as a raw material, the conventional general method is to manufacture a molded body to be subjected to sintering by compression molding the raw material powder. The shape of the molded product obtained by this method is limited to a relatively simple shape such as two cylinders because the raw material powder filled in the mold is pressurized from above and below with a punch.
To obtain products with more complex shapes, it is necessary to grind and polish the sintered products. This has been one of the factors that has hindered the cost reduction and expansion of applications for sintered products.

As a solution to this problem, we added a binder mainly composed of organic polymers to the raw material powder to give it thermoplasticity and fluidity, and then injection molded it.

A method of obtaining a product by forming a desired shape by extrusion molding, followed by defoaming and sintering is becoming practical.

This method has the advantage of being able to produce molded bodies of complex shapes in large quantities with high dimensional accuracy. On the other hand.

In this method, sufficient fluidity is imparted to the raw material powder.
Since it is necessary to add a large amount of binder (more than 40% by volume), degreasing is often performed before sintering, and this degreasing process not only increases costs but also involves various technical problems. ing.

That is, one of the technical problems is that the molded product after defoaming, that is, the degreased product, is fragile and has poor handling properties. This brittleness of the degreased body is thought to be due to the fact that in the above-mentioned molding method, the pressure applied to the raw material powder is much lower than in the conventional compression molding method, so the bonding strength between the powder particles is reduced.

[Problem to be solved by the invention] However, for example, the conventional technique 1 mentioned above.

In the former case, it was difficult to obtain a molded body with a complicated shape because the raw material powder filled in the mold was pressurized from above and below with a punch. In the latter case, the volume ratio of the binder is 40% because it is necessary to impart sufficient fluidity to the raw material powder.
% or more, it is necessary to perform a degreasing process as a pre-process of the sintering process, which not only causes high costs.

This degreasing step may cause the molded product to become brittle, resulting in problems in handling the molded product and resulting in a deterioration in yield.

Accordingly, a first technical object of the present invention is to provide a binder for powder metallurgy that allows the production of sintered bodies of complex shapes at low cost and easily.

A second technical problem of the present invention is to heat a molded article produced by injection molding, extrusion molding, etc. using the composition at a heating temperature of 280 degrees C or less to thermally decompose and volatilize the binder, and It is an object of the present invention to provide a method for degreasing a molded body, which ensures one strength by leaving a part of the binder in the molded body, and produces a degreased body that is easy to handle.

[Means for Solving the Problems] According to the present invention, the first organic polymer comprises a first organic polymer and a second organic polymer different from the first organic polymer, and the first organic polymer comprises:
Consists of at least one of polyethylene and ethylene-vinyl acetate copolymer.

A binder for powder metallurgy is obtained, which is characterized in that the binder contains 20% or more of the total weight of the binder.

According to the present invention, there is obtained a binder for powder metallurgy, wherein in the binder, the second organic polymer is made of a polymer compound having a ceiling temperature of 250 degrees or less.

According to the present invention, metal or ceramic powder and any of the binders described above are mixed and kneaded, molded by injection molding, extrusion molding, etc., and the molded product obtained is heated at a temperature of 280° C. or lower to form a molded product. A method for degreasing a molded body is obtained, which is characterized by thermally decomposing and volatilizing the binder inside.

[Function] In the present invention, the first organic polymer consisting of at least one of polyethylene and ethylene-vinyl acetate copolymer is contained as a binder in a weight ratio of 205 or more in the binder molded body. Further, a binder in which a second organic polymer other than the first organic polymer contained in the binder is made of a polymer compound having a ceiling temperature of 250 degrees or less is mixed with metal or ceramic powder.

The mixture obtained by kneading was produced into a molded body by a method such as injection molding or extrusion molding, and then heated at a heating temperature of 280°C or less to thermally decompose and volatilize the binder, leaving the binder in the molded body. A degreased body is produced. This degreased body is then sintered to produce a sintered product.

[Example code] An embodiment of the present invention will be described below with reference to the accompanying drawings.

Generally, the thermal decomposition characteristics of organic polymer compounds differ depending on their chemical structure, and the rate of one decomposition reaction varies even at the same temperature.

FIG. 1 is a diagram showing an example of thermal decomposition characteristics of a polymer compound. This figure shows polybutyl methacrylate and ethylene.
The results of thermogravimetric analysis of vinyl acetate copolymers are shown; 1 shows the so-called TG left curve of polybutyl methacrylate and 2 shows the ethylene-vinyl acetate copolymer.

The measurement conditions were atmospheric, and the temperature increase rate was 50"C/H.
It is r. As is clear from the figure, there is a considerable difference between the two, and a mixture of these polymers in an appropriate ratio is used as a binder.

It has been found that the amount of binder remaining in the degreased body can be controlled by appropriately setting the degreasing conditions.

By the way, there is a difference in the shape of the curves between 1 and 2 in Figure 1, but when looking at polymer compounds from the perspective of thermal decomposition characteristics,
It can be roughly classified into depolymerization type and random decomposition type, and polybutyl methacrylate falls into the former category.

Ethylene-vinyl acetate copolymer belongs to the latter category. That is, whereas the former produces monomer quantitatively,
The latter is thought to be due to various reactions occurring depending on the temperature, such as random scission of the main chain and detachment of other side chains.

In general, one of the important factors when considering the thermal properties of organic polymers is the ceiling temperature. This is because when a polymer compound undergoes radical cleavage, a reaction occurs in parallel in which the generated radicals recombine, but at temperatures above a certain window, the reaction rate of radical cleavage becomes greater than the reaction rate of recombination.

This is the temperature at which the decomposition reaction takes priority as a whole.

For the example shown in FIG. 1, the temperature is about 200 DEG C. for polybutyl methacrylate and about 350 DEG C. for ethylene-vinyl acetate copolymer.

Therefore, based on this point of view, the binder component used for metal or ceramic molding is selected.

Also, let's talk about the degreasing temperature for heating the binder from the molded body to thermally decompose and volatilize it.

For the above-mentioned reasons, it is necessary to set the temperature appropriately depending on the components contained in the binder, but it is preferable to carry out the process at as low a temperature as possible, or to precisely control the remaining amount of the binder.

On the other hand, focusing on binder components, ethylene-vinyl acetate copolymer is often used as a so-called hot melt adhesive, and its low melt viscosity makes it extremely useful for injection molding and extrusion molding of raw material powders for metals and ceramics. It is a high molecular compound. Looking at the thermal decomposition properties, this polymer has a relatively high thermal decomposition temperature.

Similarly, polyethylene has similar properties. In addition, it is desirable for polymer components other than these two to decompose and volatilize once at the temperature at which the two components remain, so it is necessary to have a ceiling temperature below 1, but if it is too low, it will cause crosstalk and decompose during the molding process. Because of this, the ceiling temperature is 250℃.
It is desirable to keep it below ℃. Specifically, acrylic polymers such as polystyrene have similar properties suitable for the purpose of the present invention.

From the above explanation, the binder component of the metal or ceramic sintered body should contain one or both of polyethylene and ethylene-vinyl acetate copolymer, and at the same time contain a material with a ceiling temperature of 250°C or less. desirable. Further, the combined content of one or both of polyethylene and ethylene-vinyl acetate copolymer must be at least 20% by weight, and the degreasing temperature must be at least 280°C.

The reason for this will be specifically explained below in Examples.

High-density polyethylene with an average molecular weight of about 210,000,
Ethylene-vinyl acetate copolymer with vinyl acetate content of 14% and average molecular weight: approximately 120,000, average molecular weight: approximately 14
10,000 polybutyl methacrylate, average molecular weight: about 140,000 polystyrene.

Dibutyl phthalate was weighed according to the ratios shown in Table 1, and kneaded in a pressure kneader at 150°C for 30 minutes. This mixed material is processed by an extrusion molding machine equipped with a rotating blade, with a diameter of approximately 4 mm.
It was made into a pellet with a length of about 5 mm. This pellet was injected into 6C1+mX30 am X 5 by an injection machine.
A molded body having a shape of mm was placed in a heating degreasing furnace having an internal volume of approximately 200 g, and degreased.

The atmosphere is atmospheric flow, and the flow rate is 5. Q/Win.

The temperature increase pattern at this time is shown in FIG. This is done by raising the temperature from room temperature to the degreasing temperature at a rate of 40°C/Hr.

Degreasing temperature is 240℃, 260℃, 280℃.

It shows that the temperature was 300°C and 320°C.

The relationship between the degreasing rate and time when degreasing under these degreasing conditions is shown in Figures 3 to 7 for molded bodies of raw materials of composition 1.2.3. 1 composition 3 is expressed as.

Incidentally, the degreasing rate was determined from the change in weight of the molded article.

As is clear from these figures, when the holding time exceeds 10 hours, the remaining amount of binder approaches a constant value, and this value becomes smaller as the holding temperature becomes higher. Table 1 shows the composition ratios of molded bodies combining other binder compositions, and Table 2 shows the amount of binder remaining when molded bodies with these composition ratios were heated and held for 12 hours.

Then, the bending strength of these degreased molded products was measured, and 10 pieces each were tested at 1° and 200°C for 2
The number of defects such as cracks and blisters that occurred after firing for several hours was investigated. The results are also shown in Table 2. Figures 8 and 9 show the bending strength in Table 2.

The number of defective sintered bodies is plotted with respect to the amount of binder remaining. According to this, the bending strength is J17 with binder remaining.
It decreases rapidly below ~8wt%. Separate research has shown that when the bending strength is less than 10 kg/c, the degreased molded product is extremely brittle and often breaks during transportation, posing problems in handling. Therefore, the amount of binder remaining in the molded body is at least about 5
vt% is necessary.

Regarding the number of defects occurring during the firing process, the maximum amount of binder remaining without causing total heat defects is about 8%.

From these results, the content of ethylene or ethylene-vinyl acetate copolymer in the binder suitable for the purpose of the present invention is 20w.
t% or more, and the degreasing temperature is 280°C or less.

[Effects of the Invention] As described above, according to the present invention, it is possible to provide a binder for powder metallurgy that can produce sintered products with complex shapes by injection molding and extrusion molding.

Further, according to the present invention, it is possible to provide a method for degreasing a molded body, which produces a degreased body having excellent handleability and sinterability by molding using the thermoplastic mixture.

Furthermore, according to the present invention, by sintering the degreased body, a sintered product having a complicated shape can be efficiently produced.

A sintered body that can be manufactured at low cost can be provided.

These properties are very useful industrially.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the thermal decomposition characteristics of organic polymer compounds (polybutyl methacrylate and ethylene-vinyl acetate copolymer), and Figure 2 is a diagram showing the rise pattern to the degreasing temperature in the degreasing process. 1. Figures 3 to 7 are diagrams showing the relationship between the degreasing rate and time for compositions 1.2.3 of the molded bodies shown in Table 1. ) Figure 4 shows the case where the degreasing temperature (holding temperature) is 260 degrees, and Figure 5 shows the case where the degreasing temperature (holding temperature) is 280 degrees. Figure 6 shows the case where the degreasing temperature (holding temperature) is 300 degrees, Figure 7 shows the case where the degreasing temperature (holding temperature) is 320 degrees,
Figure 8 is a diagram showing the relationship between the bending strength and the remaining amount of binder in Table 2, and Figure 9 is a diagram showing the relationship between the number of good sintered bodies and the remaining amount of binder in Table 2. be. @ between (?1) Figure 3 Figure 4 Figure 5 Figure 6 Time (1-1r,) Figure 7 Time (Hr,) Figure 9 Binder remaining j (WtZ) Procedural amendment (voluntary) 1991 February 3rd

Claims (3)

[Claims] 1. The first organic polymer is made of at least one of polyethylene and ethylene-vinyl acetate copolymer, and the first organic polymer is made of at least one of polyethylene and ethylene-vinyl acetate copolymer. A binder for powder metallurgy characterized by containing 20% or more by weight of a binder. 2. The binder for powder metallurgy according to claim 1, wherein the second organic polymer is made of a polymer compound having a ceiling temperature of 250 degrees or less. 3. The metal or ceramic powder and the binder according to the first or second claim are mixed and kneaded, molded by injection molding, extrusion molding, etc., and the resulting molded body is heated at a temperature of 280°C or less to remove the particles in the molded body. A method for degreasing a molded body, characterized by thermally decomposing and volatilizing the binder.