JPS5853704B2 - Method of manufacturing sintered mechanical parts - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION As a technique of conventional powder metallurgy, silicon, molybdenum, or iron compounds or oxides thereof are often added to sintered metal.

This is done for various purposes depending on the application, such as increasing the magnetic properties of magnetic members, and strengthening the friction characteristics or wear resistance of sliding members. It is common to use a method of mixing powder and additive particles.

By the way, a drawback of this mixing method is the problem of mold wear during compression molding of the mixed powder.

That is, all of the additive particles mentioned above have very high hardness, such as the Vickers hardness of ferrosilicon powder of 1000 to 1300, and therefore the wear of the molding die is much more significant than in normal cases.

In order to solve this problem, the applicant previously proposed coating the hard particles with the same type of metal as the sintering base material, but the present invention improves this method into a simpler and more economical method. It is characterized in that a part of the powdered lubricant such as zinc stearate that is blended into the raw material powder is used to coat the hard particles.

The present invention will be explained below with reference to Examples.

Example 1 An example in which the hard particles are ferrosilicon A sintered alloy with Fe=2.5% Si is selected and produced by a method of mixing ferrosilicon powder with a silicon content of 42% and iron powder.

Note that the amount of powdered lubricant blended into the raw material powder is usually about 1%, so this was also used here.

Therefore, the mixing ratio of the raw material powders is 94 parts of iron powder, 6 parts of the above ferrosilicon powder, and 1 part of zinc stearate as a lubricant.

(All are based on weight.) First, as a comparative sample using the conventional method, iron powder, ferrosilicon powder, and zinc stearate powder were weighed in the above proportions, and these were
-mixer for 30 minutes.

Now, the raw material powder for samples according to the present invention is prepared by the procedure described below.

First, 1 part of zinc stearate is divided into two parts, and one part is mixed with 94 parts of iron powder.

The remaining one is dissolved in carbon tetrachloride, 6 parts of ferrosilicon powder is immersed therein, and after thorough stirring, the carbon tetrachloride as a solvent is volatilized.

In this way, ferrosilicon powder whose periphery is coated with a lubricant is obtained.

This was combined with the above-mentioned iron powder and mixed outside for 30 minutes using a V-mixer as in the conventional method.

In this way, instead of consuming the entire amount of powder lubricant to coat the hard particles, mixing two parts with the iron powder reduces the friction between the iron powder, which makes up the majority of the raw material powder, and at the same time reduces the friction between the powder lubricants and the powder lubricant. This is to achieve the purpose of lubrication without increasing the total amount of agent.

The test piece was a hollow cylinder with an inner diameter of 20mm, an outer diameter of 301L, 1111mm, and a length of 20 threads.The mold for molding this was made of alloy tool steel 5KDI for the die and core rod, and the upper punch and lower punch were made of 5KD1■. .

Using this mold, the above two types of raw material powders are mixed at 4 to 61 cm/c.
Compression molding was performed at a pressure of rA, and the density of each side of the resulting molded product and the force required to extrude the molded product from the mold were measured and compared.

First, regarding the compact density, as shown in the graph of FIG. 2, there is almost no difference between the conventional method and the method of the present invention.

This is rather a natural result since the total amount of lubricant contained in each raw material powder is the same, and it means that there is no need to adjust the molding conditions or press/mold when converting from the conventional method to the method of the present invention. It is a convenient thing to do.

However, in terms of frictional resistance and wear, there is a significant difference between the conventional method and the method of the present invention.

The degree of extrusion of the compact depends on the frictional resistance between the compact and the mold wall, and the difference between the two methods shown in Figure 1 is that the direct contact between the hard particles and the mold is This proves the effectiveness of the present invention through prevention.

Next, regarding mold wear, the number of moldings is 2 in the conventional method.
000, the diameter of the core rod was worn down by 50μ, whereas in the method of the present invention, the wear was only 20% of the diameter, 010μ.

Example 2 Example in which the hard particles are metal silicon In this example, the 6 parts of ferro silicon powder in the previous example was changed to 2.5 parts of metal silicon powder, and therefore the iron powder was changed from 94 parts to 97.5 parts. It was done in exactly the same way.

The results are the same as in the previous example, as shown in Figures 3 and 4, and the wear of the mold is 13μ in the case of the method of the present invention, compared to 60μ in the conventional method.
It was μ.

From the above description, the advantages and disadvantages of the present invention can be summarized as follows.

■ When blending a powder lubricant, a step of coating the hard particles with a portion of the powder lubricant is required, which slightly increases labor and cost.

However, (1) Since the extrusion force of the molded product is reduced, the occurrence of latent crank and other negative effects on the molded product are prevented.

Furthermore, ■ workability is improved because the life of the mold is extended, and together with the reduction in mold costs, manufacturing costs are reduced.

That is, although the present invention has the disadvantage of (1), the advantages of (2) and (2) are far greater.

[Brief explanation of drawings]

Figures 1 and 2 are graphs showing the relationship between test piece molding pressure, compaction extrusion force, and compaction density in Example 1, and Figures 3 and 4 are graphs to the same effect in Example 2'. .

Claims (1)

[Claims] 1. When manufacturing sintered machine parts by adding and mixing a predetermined amount of powder lubricant to a mixed powder of metal powder and hard particles, and molding and sintering this using a normal method of powder metallurgy, the predetermined amount of A method for forming a green compact characterized by dividing a powder lubricant into two parts, coating hard particles with one half, and adding the other half to a mixed powder of metal powder and hard particles coated with a lubricant. .