JPS5812321B2 - Method for manufacturing sintered bodies of gray cast iron powder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention involves mixing carbon powder with cast iron powder, particularly gray cast iron powder obtained by pulverizing chips from cutting or grinding a cast product in a factory (generally called milling powder), and compression molding the mixed powder. By sintering the resulting material, it is possible to obtain a sintered compact in which a very large amount of free graphite exists as a whole, and the compact is particularly useful as a high-grade sliding member.

Examples embodying the present invention will be described below.

■ Among the raw material powders, the gray cast iron powder is made by pulverizing the chips (hereinafter referred to as "dry powder") obtained by cutting or grinding the cast product in a factory using a pulverizer.

Dalai powder can be obtained at an extremely low cost, and since it is a brittle material, it is easy to crush.

The gray cast iron powder used in the experiment was FC1 with the following composition.
It is made by pulverizing the powder of the cast product No. 5, and its particle size distribution is as shown in the table below. It is desirable that the powder with a particle size of 40 mesh or less has a coefficient of 90 or more, and the powder with a particle size of 40 mesh or more is 10%. If the above amount is mixed, both moldability and sinterability will deteriorate.

(1) Composition: Carbon 3.55%, Silicon 2.69%
%, manganese 0.46%, phosphorus 0.13%, sulfur 0.05%, balance iron (2) Particle size distribution Next, carbon powder, which is another material powder, can be commercially available and has a particle size of 200%. It is preferable that it be smaller than mesh.

2 Compression Forming The above-mentioned gray cast iron powder and carbon powder are mixed and placed in a mold for compression molding.

Although it is slightly more formable than gray cast iron powder alone,
It was confirmed that when the molding pressure was 8000 Kp/cr, the moldability was fair and the molded product could be handled safely.

3 Sintering The molded body as shown in Fig. 1, molded at a molding pressure of 800 QKp/cI as described above, was sintered in an ammonia decomposition gas atmosphere at a sintering temperature of 1100°C and 1150°C for 30 minutes. This is shown in FIGS. 2 to 3.

FIG. 2 shows the relationship between the mixing ratio of gray cast iron powder and carbon powder and the tensile strength of the sintered compact. As the mixing ratio of carbon powder to gray cast iron powder increases, the tensile strength decreases.

The tensile strength of the base material, that is, the cast product of FC15, is approximately 17 Kp/
mm2, so when the sintering temperature is 1150°C and the mixing ratio of carbon powder to gray cast iron powder is up to 5% by weight, it is possible to obtain a sintered compact whose tensile strength is even higher than that of the base material. Even when the sintering temperature is 1100° C., if the mixing ratio of carbon powder to gray cast iron powder is about 1% by weight, a sintered compact having a tensile strength greater than the tensile strength of the base material can be obtained.

It has been confirmed that this sintered compact has an extremely large amount of free graphite in the cast iron structure as a whole, and that decarburization during sintering is extremely small. It is assumed that this depends on the nature of

Normally, in the case of carburizing, the amount of carbon to be carburized is about 0.5 cm at most, and is limited to the area near the surface of the compact, but according to the present invention, the amount of carbon carburized is incomparably more than that of the conventional method. It is possible to obtain a sintered compact in which carbon is impregnated, and it is unique in that free graphite exists not only near the surface of the compact but throughout the compact, making it extremely useful as a high-grade sliding member.

Next, Figure 3 shows the relationship between the mixing ratio of gray cast iron powder and carbon powder and the dimensional change before and after sintering. In the case of 1, almost no dimensional change is observed regardless of the sintering temperature, and when the mixing ratio is 5% by weight or more, the dimensions of the compact are larger after sintering than before sintering, and If the mixing ratio is less than 5% by weight, the dimensions of the compact will be smaller after sintering than before sintering.

Also, as is clear from Fig. 3, when the sintering temperature is 1150°C, the dimensional change is larger when the mixing ratio is 5% by weight or less, compared to when the sintering temperature is 1100°C; When it exceeds the weight factor, the dimensional change is small.

From the above results, when the mixing ratio of carbon powder to gray cast iron powder is 5% by weight and the sintering temperature is 1150°C, there is almost no dimensional change as described above, and the tensile strength is approximately the same as that of the base material. , are the most suitable conditions for producing this type of sintered compact.

If the proportion of carbon powder mixed into the gray cast iron powder exceeds 10 weight factors, the tensile strength becomes even smaller, the dimensional change becomes even larger, and no improvement is seen in the properties of the compact.

Therefore, when considering the price of carbon powder, etc., it is presumed that there is almost no merit in producing a molded body with the above-mentioned mixing ratio exceeding 10 inches.

As detailed above, the present invention compresses and molds a mixed powder of gray cast iron powder and carbon powder, and sinters it.
Due to the nature of these powders, it is possible to obtain a sintered compact with a metal structure containing an extremely large amount of free graphite, making it extremely useful as a high-grade sliding member.

Furthermore, by selecting the mixing ratio of carbon powder and the sintering temperature, it is possible to obtain a sintered compact with almost no dimensional change between before and after sintering, and which has a higher tensile strength than the base material.

[Brief explanation of drawings]

Figure 1 is a perspective view showing the molded body used in the experiment, Figure 2 is a diagram showing the relationship between the mixing ratio of gray cast iron powder and carbon powder and the tensile strength of the sintered body, and Figure 3 is the gray cast iron powder. It is a figure which shows the relationship between the mixing ratio of carbon powder and carbon powder, and the dimensional change before and after sintering.

Claims (1)

[Claims] 1 A mixed powder obtained by mixing 90 to 99.5 weight parts of gray cast iron powder obtained by cutting or grinding chips obtained by cutting or grinding a cast product with 0.5 weight parts to 10 weight parts of carbon powder was compression molded. A method for producing a sintered body of gray cast iron powder, characterized by performing post-sintering.