JPH0532955A - Wet friction material - Google Patents

Abstract

(57) [Abstract] [Purpose] To obtain a wet friction material having a stable and high friction coefficient by increasing the amount of pores without lowering the strength of the metal friction material. [Constitution] The friction material is 10 to 30 wt% graphite powder, and the porosity is
A friction material is obtained by forming a sintered body containing 10 to 20% of coke powder in an amount of 3 to 15% by weight and the balance mainly consisting of copper as a metal component powder. [Effect] By containing the coke having a high porosity, the amount of pores of the entire friction material is increased and the decrease in strength is suppressed.

Description

Detailed Description of the Invention

[0001]

The present invention has a high coefficient of friction,
The present invention relates to a wet friction material having excellent seizure resistance.

[0002]

2. Description of the Related Art Conventionally, a friction clutch has been used as a mechanical element for transmitting and cutting off power, and a friction brake has been used as a mechanical element for braking a moving body. These friction clutches or friction brakes perform their functions by mainly converting kinetic energy into heat energy, and it is the friction material that is used for the friction plate that functions as a place for the conversion.

There are two types of friction materials, dry type and wet type. In the case of a dry friction material, the solid surfaces forming the opposing friction plates directly rub against each other, but in the wet friction material, a liquid such as oil is interposed between the solid surfaces forming the friction plate. Then, the friction plate is rubbed under the boundary lubrication condition. The heat generated at that time is transferred to the liquid by being interposed between the solid surfaces to be released to the outside. Wet friction materials are roughly classified into non-metallic friction materials and metallic friction materials.

As the non-metallic friction material, a paper friction material called paper facing formed of pulp and an organic binder such as phenol resin, or rubber friction in which nitrile rubber is adhered to a metal core plate is used. Materials are known. Although these non-metallic friction materials have a high friction coefficient, they are not sufficient in terms of heat resistance and oil resistance.

The metal-based friction material is represented by a sintered body obtained by adding graphite powder, ceramic powder, etc. to a metal powder mainly composed of copper and sintering it. In general, metal-based friction materials have excellent heat resistance, but have a drawback of low friction coefficient.

[0006]

As described above, it is difficult for a wet friction material to have both heat resistance and friction characteristics at the same time. In particular, it is an important issue to increase the friction coefficient of a metal friction material. It was Here, let us consider the mechanism by which the frictional resistance of the metallic friction material is formed.

The structure of the metallic friction material is generally composed of a matrix phase, a lubricating phase, and a hard particle phase, and is present in the matrix phase and at the boundary between the matrix phase and the lubricating phase together with the properties of these phases. Porosity is also an important component of the friction characteristics of metallic friction materials. Friction forces are formed in each of these phases.

First, in the matrix phase which occupies the main part of the sintered metal, the adhered portion is sheared through the process of adhering with the mating material to be rubbed, and the frictional resistance force as a stress against the shearing force is generated in this shearing process. Occurs.

The lubricating phase is made of a solid lubricant, and a frictional resistance works when the solid lubricant extends to the surface of the friction material due to friction with the mating material.

In the hard particle phase, the cutting resistance force generated when the hard particles directly act on the mating material to grind it becomes the frictional resistance force.

Further, in the pores, an oil film shear resistance force when the oil film produced by the oil retained in the pores is sheared by the mating material is generated by friction with the mating material. Thus, the pores play a large role in the formation of the frictional resistance force.

The pores serve as a movement route of the oil supplied to the friction surface to change the lubricating behavior of the oil, thereby changing the boundary lubrication to have a larger friction coefficient than that of the fluid lubrication. Therefore, as the amount of pores increases, boundary lubrication is promoted and the friction coefficient increases.

However, when the amount of pores is increased, the friction coefficient is increased, but the strength of the friction material itself is lowered. Further, the amount of pores of the sintered metal depends on the sintering conditions. Normally, hot pressing for joining the friction material to the core plate is performed simultaneously with the sintering of the friction material. There is a problem that the amount cannot be easily controlled, and it is often disadvantageous especially to increase the pore amount.

On the other hand, in the metal-based friction material, the friction surface is often grooved. This groove facilitates drainage of the oil film generated on the friction surface and promotes boundary lubrication. As a result, the coefficient of friction can be improved and stabilized, and the efficiency of oil cooling can be improved. The function of this groove becomes more remarkable as the groove portion is enlarged. However, the larger the groove, the smaller the area of the land portion in contact with the mating material, and the higher the average surface pressure applied to the land portion, which causes the problem that the structure is easily broken.

In view of the above problems, the present invention provides a metal-based friction material having improved friction characteristics by increasing the amount of pores of the metal-based friction material and suppressing the decrease in strength to the minimum. With the goal.

[0016]

As described above, regarding the pores formed in the matrix phase and at the boundary between the matrix phase and the lubricating phase, the correlation that the strength is reduced if the amount thereof is simply increased. There is.

In this case, as a method of increasing the amount of pores while avoiding a decrease in strength, a specific material having a high porosity is dispersed in the matrix phase to maintain the strength and the pores of the entire friction material. By increasing the amount, the above-mentioned object is achieved. It is desirable that the material having a high porosity is a material that does not have a remarkable attack property with respect to the mating material and does not cause adhesion or the like. The present invention has been completed by finding coke as a material satisfying these conditions.

That is, according to the present invention, the granular graphite powder is
Coke powder with 30wt% and porosity of 10-20% is 3-15wt%
A gist of the wet friction material is characterized in that it comprises a sintered body containing a metal component powder mainly containing copper as a balance.

According to the present invention, the metal powder mainly composed of copper of the friction material is composed of a copper alloy such as bronze or brass, and a metal powder such as tin or zinc which produces such an alloy together with copper and a copper powder. The main part of the matrix phase of the friction material of the present invention is formed in the form of a mixed powder of the above or a sintered metal produced by sintering a copper alloy powder such as bronze or brass.

The graphite powder used to form the lubricating phase comprises 10-30 wt% of the total friction material. This graphite powder has the effect of preventing wear of the friction material, but if its content is less than 10 wt%, the desired wear preventing effect cannot be obtained,
On the other hand, if it exceeds 30 wt%, the strength of the graphite decreases due to the softness of the graphite, and in addition, the friction coefficient decreases due to the lubricating action of the graphite. The particle size of this graphite powder is preferably in the range of 325 to 100 mesh. The reason is that in order to disperse without causing segregation in the metal component powder mainly composed of copper forming the matrix phase and to express the desired lubricity at the above-mentioned addition amount, it is within the range of 325 to 100 mesh. The granular graphite in 1 is preferred.

The friction material of the present invention contains coke powder as a material having a high porosity for increasing the amount of pores. Coke is partially graphitized in the process of carbonization and has pores in the tissue. The coke powder used in the present invention has a porosity of 10 to 20 wt%.

If the porosity of the coke powder is less than 10%, it is not much different from the porosity of the friction material which is itself a porous sintered body, and the effect of increasing the porosity of the friction material is small. If the porosity exceeds 20%, the coke becomes brittle and the strength of the friction material as a whole is reduced.

The effect of increasing the amount of porosity by the coke powder is effective when the content of the coke powder is 3 wt% or more, but when the content of the coke powder exceeds 15 wt%, the strength of the friction material decreases. Therefore, the content range of the coke powder is set to 3 to 15 wt%.

In addition to the above-mentioned components, it is possible to add hard particles such as alumina, silica and mullite as a friction modifier to the friction material of the present invention.

[0025]

By adding coke powder having a relatively high porosity, the porosity of the entire friction material is increased. The liquid such as oil supplied to the friction surface of the friction material flows into the pores contained in the tissue of the coke and is discharged, like the pores formed in the sintered body.

At this time, an oil film shear resistance force works, but a large amount of pores are present on the friction surface, so that a large oil film shear resistance force is produced. This greatly contributes to the increase of the friction coefficient. At the same time, the increase in the amount of pores allows the oil to be smoothly discharged and promotes boundary lubrication.

As a result, the reduction of the friction coefficient due to the liquid such as oil is suppressed. In this way, stable friction characteristics can be obtained by the two factors of the oil film shear resistance and the boundary shear lubrication.

Further, since the coke is thermally stable and partially graphitized as described above, the lubricating action of the graphite prevents the coke from sticking to the mating material, that is, seizure. Moreover, since the coke is soft, it will not attack or damage the mating material.

[0029]

【Example】

[Examples 1 to 4] Copper powder, tin powder, zinc powder, silica powder, graphite powder and coke powder were mixed in the weight ratio shown in Table 1, and then uniaxially compression molded at a pressure of 3 t / cm ² .
Furthermore, under a pressure of 20 kg / cm ² , in a nitrogen atmosphere, 750 ℃
The temperature was maintained for 60 minutes for sintering to obtain a friction material of the present invention. The coke powder used had a porosity of 15%.

[Comparative Examples 1 to 5] The same materials as in Examples 1 to 4 (not used in Comparative Example 5) were used in the weight ratios shown in Table 1 except that coke powder having a porosity of 7% was used. A friction material for comparison was obtained in the same manner as in Examples 1 to 4.

[Table 1]

[Examples 5 and 6 and Comparative Example 6] Example 5
Coke powder having a porosity of 10.5%, coke powder having a porosity of 19.3% in Example 6, and porosity of 25.2 in Comparative Example 6.
% Coke powder was used, and the other materials were used in the weight ratios shown in Table 2 in the same manner as in Examples 1 to 4 to obtain the friction material of the present invention and the friction material for comparison.

[Table 2]

Next, each friction material obtained in Examples 1 to 6 and Comparative Examples 1 to 6 is subjected to a friction test by a rubbing test between a test disk and a mating disk to measure the friction coefficient of each. At the same time, the seizure situation was investigated by measuring the load that led to transfer.
The test conditions adopted are as follows. The test results are also shown in Tables 1 and 2. Peripheral speed: 55m / sec Load: per rotation of 200 times starting from 6kg / cm ² 2kg / cm ²
I raised each. Oil temperature: 80 ℃ Absorbed energy: 14kg ・ m / cm ² Clutch frequency: 12sec / oil flow rate: 8cc / cm ²・ min

As a result of the friction tests shown in Tables 1 and 2, when the friction materials of Examples 1 to 6 according to the present invention were used, the coefficient of friction was higher than that of the comparative example, and up to a high surface pressure. It was confirmed that seizure did not occur.

[0034]

In the friction material of the present invention, the pore volume is increased without depending on the increase in the pore volume of the metal sintered body itself.
The conditions of sintering and hot pressing are not particularly limited, and sintering and hot pressing can be performed under optimum conditions. The porosity can be controlled easily by selecting the amount of coke powder and the porosity.

Further, if the number of pores formed directly at the matrix phase of the metal sintered body or at the boundary between the matrix phase and the lubricating phase is excessively increased, the structure of the sintered body may be weakened, but in the present invention, the coke powder is used. The technique of addition of C is effective in increasing the amount of pores, and since the coke itself is soft and easily absorbs stress, a decrease in strength can be avoided even if the amount of pores is increased. Therefore, the present invention provides an excellent wet friction material applicable to industrial machines that require high friction coefficient and heat resistance.

Claims (2)

[Claims] 1. A graphite powder having a porosity of 10 to 30 wt% and a porosity of 10 to 20.
% Of coke powder, and the balance is composed of a sintered body composed of a metal component powder mainly composed of copper, the wet friction material. 2. The wet friction material according to claim 1, wherein the graphite powder has a particle size in the range of 325 to 100 mesh.