JPS592732B2 - Sintered alloy friction material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a friction material made of a sintered alloy, and in particular provides a sintered friction material that contributes to miniaturization of brake devices.

In recent years, there has been a trend toward miniaturization of various types of brake devices, and in particular, with the spread of minicycle bicycle brakes, there is an urgent need to miniaturize band brakes and caliber brakes used for rear wheels.

Conventional materials include (1) woven, rubber molded or resin molded friction materials, (2) well-known copper-based or iron-based sintered friction materials, and (3) heat-treated steel materials such as S.
CM-21 steel (JIS standard) is used.

However, each of these friction materials has drawbacks when used under severe conditions by reducing the braking area of the brake for the purpose of downsizing the brake.

For example, the friction material (1) is inexpensive and has a relatively high coefficient of friction, but it has poor heat resistance and cannot be used when a large amount of absorbed energy per unit braking area is required.

The friction material (2) has excellent heat resistance and wear resistance, and also has a large absorption energy per unit braking area, but has a friction coefficient of about 0.15 to 0.40, and has a Because there is a limit to reducing the braking area, and because sintered friction materials are generally manufactured using a pressure sintering method, they are very expensive compared to other friction materials, making them difficult to use as friction materials for bicycles. Hardly used.

Steel materials subjected to heat treatment (3), such as SCM-21 steel (JIS standard), have heat resistance, are relatively inexpensive, and are currently in practical use as friction materials for bicycle brakes aimed at downsizing.

However, it has the disadvantage of poor wear resistance and greater wear on the mating material than other friction materials.

Furthermore, there are problems such as the fact that the braking force is not constant due to the unstable coefficient of friction, and that seizure is likely to occur under usage conditions where the absorbed energy per unit braking area is large, and there is a limit to miniaturization.

The present invention aims to provide a sintered friction material that satisfies the above objects and has high frictional resistance and excellent wear resistance, and is also economical.

This invention material is manufactured as follows.

Weight section S i 3N4, + 8-25 section, P; 0.
It is made by blending the respective powders so that 3 to 1.5%, C; 0.2 to 1.5%, and the balance is iron, and press-molding and sintering them.

(The following sums indicate weight ratios) This material has excellent frictional properties as is, but it is also possible to add lead, indium, which has lubricity to the matrix strength,
A total amount of 1 to 6% of low melting point metals such as bismuth, tin, or CaF2, or BaF2. LiF type 1 or 2
By containing 3 to 8% of seeds in total and imparting lubricity, the coefficient of friction is stabilized and the amount of wear on the mating material is reduced.

The reasons for selecting the composition range etc. will be described below.

Well-known sintered alloy friction materials include base metals, usually steel and copper alloys or iron and iron alloys, lubricating substances such as IJ lux lead and graphite to provide smooth operating characteristics, and alumina and silica. It is composed of hard particles and a friction-increasing substance to improve retention of frictional resistance and wear resistance.

Nitrogen and silicon are hard particles that have high hardness like oxides such as alumina and silica, and are added to improve the coefficient of friction and wear resistance, and the appropriate amount is 8 to 25 parts. It is.

If the amount added is less than 8 parts, the effect will not be fully exhibited, and the effect of improving the friction coefficient and wear resistance will be small.

If the amount added is 25 parts or more, the strength of the sintered material itself is weakened, the wear resistance is even lowered, and the wear on the mating friction surface is increased.

Hard particles of oxides such as alumina and silica, or nitrides such as silicon nitride, which are friction-enhancing substances, have a large effect on the friction coefficient and wear resistance, but in order to exert their effect, it is necessary to disperse hard particles on the friction surface. It is necessary for the particles to be retained in the base metal matrix and not fall off, but generally these hard particles are themselves brittle and furthermore, they have poor sinterability with the metal matrix. They easily fall off from the metal matrix, and the addition of hard particles alone does not necessarily provide sufficient frictional properties.On the contrary, the hard particles that fall off significantly increase the wear of the friction material itself due to the abrasive abrasive action, and cause damage to the mating friction surface. This also has a large impact on wear and tear.

In order to improve these drawbacks, the present invention has been made as a result of various researches.
Kokichi has discovered that the addition of phosphorus is extremely effective in causing a reaction between iron in the metal matrix and silicon nitride in the hard particles.

In powder metallurgy, phosphorus is often added in small amounts for the purpose of improving sinterability, strength, and wear resistance, but in the present invention, phosphorus is also added to a part of the Si3N4 particle surface to strengthen the matrix.
Formation of the e-8i alloy layer has the effect of significantly improving the bonding between the matrix and Si3N.

If the amount of P added is less than 0.3%, the effect will be small; 1.
If it is added in a ratio of 5 or more, phosphorus compounds will precipitate at the grain boundaries and the material will become brittle, so the range should be 0.3 to 1.5.

The sintering temperature of the present invention material is 1050°C (preferably 108°C
0°C) to 1230°C.

When the sintering temperature is below 1050°C, the reaction between the matrix and Si3N4 is insufficient, and when the sintering temperature is above 12300°C, a liquid phase of Fe-8i, which is the main reaction product, is generated, so the decomposition of 5iaN+ is significantly accelerated. This is not preferable since the abrasion resistance is rather reduced and the dimensional accuracy is also deteriorated.

The optimum particle size of the Si3N4 powder is in the range of 160 mesh to +350 mesh.

If the mesh is more than 60, excessive friction will be produced between the mating friction surface and the mating friction surface will be worn out.

In addition, if the mesh is less than 350, Fe -8i during sintering
It is difficult to control the 3N4 reaction.

This tendency becomes more pronounced as the amount of Si3N4 added increases or as the sintering temperature increases.

C dissolves in solid solution in iron and increases matrix strength, and a portion of it precipitates as cementite to improve wear resistance.

If it is less than 0.2%, the effect is insufficient, and if it is more than 1.5, network-like cementite is formed and the material becomes brittle, so the range is set to 0.2 to 1.5%.

Pb has low shear strength, I n , B 1 t S n
It is a metal that has lubricating properties along with Cd, Se, etc., but as a result of friction, some of the lead on the friction surface becomes molten or oxidizes into the form of PbO, which further increases its lubricity and improves the friction material. It has the effect of preventing adhesion between the friction surface and the mating friction surface, stabilizing the coefficient of friction, and reducing wear and tear on the mating friction surface.

If it is less than 1%, the effect will be small, and if it is more than 6%, the friction coefficient will decrease and the material strength will also decrease, so the range is set to 1 to 6%.

In addition to lead, which has a melting point of 329°C, bismuth, which has a melting point of 271°C, and 23
Tin at 1°C, indium at 150°C, cadmium at 3200°C, and selenium at 220°C exhibit the same effect as lead.

Therefore, one or more of these may be added in a total amount of 1 to 6.

Addition of a lubricious fluoride such as CaF2, BaF2, or LsF has the effect of stabilizing the coefficient of friction and reducing wear on the mating friction surface, similar to low melting point metals such as Pb.

CaF2 and BaF2. Since LiF exhibits very similar behavior during friction, it may be added alone or two types may be added at the same time.

If the amount added is less than 3% in total, the effect will be small, and if it is more than 8%, the material strength will decrease, so the preferred range is 3 to 8% in total.
It was hot.

Next, an example will be described.

Example 1 -10o+3so mesh Si3N4 powder and -3
Red phosphorus powder of 00 mesh, graphite, and iron powder of -150 mesh were blended into the composition shown in Table 1, molded at 5 t/cni pressure, and then sintered at 1000°C or 1150°C for 30 minutes in a reducing atmosphere. The obtained sintered body was subjected to a friction and wear test under the test conditions shown in Table 2.

In addition, the heat-treated SCM-21 steel (JIS standard) currently in use and the well-known sintered Cu-based friction material (70% Cu7
%5n-7%C-7%Pb-9%5iO7 composition) was also tested for comparison.

These test results are summarized in Table 3.

As is clear from the above results, the material of the present invention has excellent frictional properties that combine high frictional force and excellent wear resistance.

Example 2 A sample obtained by blending the composition shown in Table 4 in the same manner as in Example 1, molding at 5 t/m pressure, and sintering at 1150°C for 30 minutes was prepared in Example 1.
Similarly, a friction and wear test was conducted under the test conditions shown in Table 2,
The results are shown in Table 5.

As is clear from the above results, P in the composition range of the product of the present invention
Those containing b or CaF2 have high frictional force and wear resistance, and also exhibit the effect of improving the wear of the mating material and increasing the stability of the frictional force as shown in the figure.

[Brief explanation of the drawing]

The figure shows representative friction force measurement diagrams of comparative materials and invented materials among the friction force measurement diagrams obtained by friction and wear tests under the conditions shown in Table 2. (The frictional force on the vertical axis is 6m=I5Kf-α)

Claims (1)

[Claims] 1 Si3N4 in terms of weight: 8 to 25 inches, P: 0.3 to 1
．． Article 5, C: Sintered alloy friction material consisting of 0.2 to 1.5 pieces and the remainder substantially iron. 2 Weight: 3i3Nt; 8-25%, P; 0.3-1
．． 5%, C; 0.2-1.5% plus lead, indium,
At least 1 to 6 types of low melting point metals such as bismuth and tin
Sintered alloy friction material containing weight ratio. 3 Weight: 3 i3N458~25%, P; 0.3~
1.5%, C; 0.2-1.5% further CaF
A sintered alloy friction material containing at least 3 to 8 parts by weight of at least one of 2 or BaF2°LiF.