JPH0753947A - Wet friction material - Google Patents

Abstract

PURPOSE:To obtain the material made of a metallic sinter which material has an excellent energy absorption performance and always retains stable high- friction characteristics. CONSTITUTION:The material is obtained by sintering a bronze mixture comprising 20-35wt.% C, 2-8wt.% Sn, 4-10wt.% SiO2, up to 8wt.% Zn as an optional component, and Cu as the remainder, the C being in the form of a graphite powder having an average particle diameter of 20-60mum, a content of particles with diameters of 5-100mum of 90% or greater, and a graphite crystal plane distance, C0, of 0.672nm or shorter. The sinter is highly effective when it has a porosity of 15-20vol.% and a strength of 20MPa or greater.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sintered metal-based wet friction material suitable for a brake pad or a clutch facing and having excellent energy absorption and high friction performance.

[0002]

2. Description of the Related Art Wet friction materials used with a liquid such as lubricating oil interposed between opposing friction surfaces are useful as brake pads and clutch facings. There are paper-based and rubber-based wet friction materials, but at present, mainly sintered metal-based materials having excellent heat resistance and mechanical strength are used.

As a wet friction material of a sintered metal type, conventionally, Cu, Sn, Zn, Al, Al ₂ O ₃ ,
Copper alloy-based materials obtained by sintering composition components containing SiO ₂ , MoS _2, etc. are mainly used. Attempts to add graphite and other carbonaceous powders as effective components in addition to these metal and ceramic powders. Has been done. That is, since graphite has inherently excellent lubricity and thermal / chemical stability, it has been conventionally used as a filler for friction materials (for example, Japanese Patent Laid-Open No. 61-67736). as aimed at the further material improvement by addition of a portion of the friction modifier or all crystal lattice constant C ₀
No. 6.75 to 6.85 of semi-graphite to eliminate the effect of temperature on lubricity (Japanese Patent Laid-Open No. 64-49726), and a highly elastic friction material containing expanded graphite as a filler ( JP-A-3-282028), graphite powder 10
3 wt% of coke powder with 30 wt% and porosity of 10-20%
There has been proposed a wet friction material (Japanese Patent Laid-Open No. 5-32955) having a stable high friction coefficient, which is composed of a sintered body of a metal component powder containing 15 wt% and the balance being copper.

[0004]

DISCLOSURE OF INVENTION Problems to be Solved by the Invention As a result of intensive studies conducted by the present inventors, in the friction material made of a bronze-based sintered material, focusing on the relationship between the energy absorption capacity during friction and the added graphite powder, It was confirmed that a friction material exhibiting excellent energy absorbing ability can be obtained by setting the composition ratio of the filler components to a specific range and adding graphite powder having specific properties.

The present invention was developed on the basis of the above-mentioned findings, and an object thereof is to provide a metal-sintered wet friction material exhibiting an excellent energy absorption ability and always having stable high friction performance. To do.

[0006]

Means for Solving the Problems The wet friction material according to the present invention for achieving the above object is C: 20 to 30% by weight, Sn: 2 to 8% by weight, SiO ₂ : 4: 10% by weight,
The balance is made of Cu, and the C has an average particle diameter of 20 to 60 μm.
Grains having a particle size of 5 to 100 μm in m have a particle property of 90% or more, and the interlayer distance between graphite crystal planes C ₀ is 0.67.
A structural feature is that a bronze-based component having a composition of 2 nm or less of graphite powder is sintered.

The wet friction material of the present invention is mainly composed of Cu, and has a filler composition in which C, Sn and SiO ₂ in a specific range are added and blended. Among the added components, Sn is solid-dissolved in Cu at the time of sintering to promote sintering, and 750 to 850
It is a component that enables sintering in the range of ° C and increases the open porosity of the sintered body. The blending amount is required to be 2 to 8% by weight, and if it is less than 2% by weight, it becomes difficult to sinter Cu, and if it exceeds 8% by weight, solidification segregation of the Sn component occurs to cause deterioration of friction performance. . SiO ₂ is a component that imparts wear resistance and at the same time stabilizes the friction performance by appropriately grinding the mating member to expose a new friction surface, and is added in the range of 4 to 10% by weight. To do. If the added amount is less than 4% by weight, the wear resistance and the friction coefficient decrease, and if the added amount exceeds 10% by weight, the abradability of the counterpart member increases too much and the strength of the sintered body decreases.

If necessary, the bronze-based component may include Zn.
Can be added in an amount ratio of 8% by weight or less. Similar to Sn, Zn is a component that functions as a sintering aid and an open porosity forming agent. Therefore, when the amount of Sn is increased, no addition may be made, but the amount of expensive Sn added is reduced to
Is a good compounding means. However, Zn
If the amount of addition of Al exceeds 8% by weight, solidification segregation occurs, which causes a decrease in friction performance.

The C component has an average particle size of 20 to 60.
The particle size is in the range of μm, the content of particles having a particle size of 5 to 100 μm is 90% or more, and the interlayer distance between C ₀ planes constituting the graphite crystal is 0.672 nm or less. Graphite powder is selectively used and added in an amount ratio of 20 to 35% by weight. The reason why the particle properties are limited to the above range is that when the average particle size of 20 to 60 μm and the particle size of 5 to 100 μm satisfy the condition of 90% or more, excellent energy absorbing ability is imparted and stable friction performance is obtained. This makes it possible to maintain high material strength. For example, if the amount of fine graphite powder of less than 5 μm increases, the bond of the Cu alloy matrix will be broken and the strength of the sintered body will decrease, and conversely, if the amount of particles exceeding 100 μm increases, the friction coefficient will decrease. The graphite powder having an interlayer distance of C ₀ between graphite crystal planes of 0.672 nm or less is used because this high graphitization property is an essential element for stabilizing the friction characteristics. Further, the addition amount of the graphite powder is set in the range of 20 to 35% by weight when the above effects are not exhibited below 20% by weight, and the strength of the sintered body is exceeded when it exceeds 35% by weight. In addition, the friction coefficient is reduced.

In addition to the above filler requirements, the open porosity of the sintered body is 15 to 20% by volume and the transverse rupture strength is 20.
It is preferable to maintain the characteristics of MPa or more. Open porosity is a property effective for impregnating and supporting intervening oil,
If this is less than 15% by volume, the impregnating and carrying capacity of oil is insufficient,
If it exceeds 20% by volume, the strength will be reduced. In addition, the transverse rupture strength is a requirement to maintain practical material strength, and is 20 MPa.
As described above, in practical use, the pressure is adjusted within the range of 20 to 60 MPa. These characteristics of open porosity and transverse rupture strength can be imparted by controlling the conditions such as molding pressure and firing temperature when obtaining a sintered body.

The wet friction material of the present invention is formed by sintering the above-mentioned bronze-based filler component, and this sintered body can be manufactured as follows. First, preferably Cu powder such as electrolytic copper powder, graphite powder of 2 to 35 wt% as a blending ratio to the total amount of filler, 2 to 8 wt%
Sn powder, 4-10 wt% SiO ₂ powder, and if necessary, 8 wt% or less Zn powder are added. The graphite powder is a graphite material graphitized until the interlayer distance between the graphite crystal planes C ₀ becomes 0.672 nm or less, and the average particle size is 20 to 60.
What is pulverized and classified so that the content of particles having a particle diameter of 5 to 100 µm is 90% or more is used. As the Sn powder and the Zn powder, atomized powder or stamp powder having a particle size of 200 mesh or less is preferably used, and as the SiO ₂ powder, it is desirable to apply fine powder of 5 to 50 μm.

The filler component having the above composition is uniformly mechanically mixed, powder-molded, and then sintered under pressure.
In powder compacting, the mold is filled with a filler component, and 100 to 10
The pressure is applied in consideration of the open porosity of the sintered body obtained within the range of 00 MPa. Sintering process is 1-10
It is carried out in a temperature range of 750 to 850 ° C. under a reducing or inert atmosphere while applying a pressure of MPa. At this time, the applied pressure and the sintering temperature range are set in consideration of the open porosity and the range of material strength of the obtained sintered body. The resulting sintered body is finally processed into a product in accordance with the shape of the friction material.

[0013]

According to the wet friction material of the present invention, C: 20
˜35% by weight, Sn: 2 to 8% by weight, the balance being Cu, or Zn: 8% by weight or less if necessary, and a filler composition of a bronze-based component having appropriate pores in the sintered body. Rate and a material strength within a practical range, and at the same time functions to impart excellent wear resistance, stable friction performance, and appropriate abradability to the mating material. In particular, the C component has an average particle size of 20 to 60 μm, a particle size of 5 to 100 μm and a particle content of 90% or more, and has a graphite crystal plane C ₀
By selectively blending graphite powder having an interlayer distance of 0.672 nm or less, the energy absorption capacity at the time of friction is increased, and it becomes possible to maintain a more stable and high level friction characteristic.

Further, the open porosity of the sintered structure is 15 to 20.
The characteristic that the capacity is 20% and the transverse rupture strength is 20 MPa is that the liquid such as the intervening lubricating oil is impregnated and carried inside the pores to enhance the energy absorption capacity at the time of friction, while at the same time maintaining the practical material strength. Stable friction performance is given.

In combination with such an action, stable high friction performance is always exhibited in the case of a brake pad or clutch facing.

[0016]

EXAMPLES Examples of the present invention will be specifically described below in comparison with comparative examples.

Examples 1 to 11 and Comparative Examples 1 to 12 Sn powder (stamp powder, 20 powder) to Cu powder (electrolytic copper powder)
(0 # or less), Zn powder (stamp powder, 200 # or less), SiO
C powder composed of ₂ powders (silica stone powder, average particle size 17 μm) and graphite powder having specific properties was blended at the ratio shown in Table 1, and dry mixed by a V-type mixer for 20 minutes to prepare a homogeneous mixed powder. did. A mixed powder of these bronze-based fillers was filled in a ring-shaped die having an outer diameter of 335 mm and an inner diameter of 280 mm, and then a predetermined pressure was applied to perform powder compacting to obtain a disk molded body having a thickness of 1.5 mm. Next, each molded body was placed on both sides of the iron core plate and heated and sintered at a predetermined temperature in a reducing atmosphere while applying a predetermined pressure to produce a friction material. The friction material was subjected to surface grinding, and then spiral grooves and radial grooves (38 on both sides from the center to the outside) were processed as oil grooves to obtain a friction plate.

The open porosity and transverse rupture strength of each of the obtained friction materials (sintered body) were measured and shown in Table 2 together with molding and sintering conditions. The open porosity was measured by impregnating the sintered body with water in a vacuum and calculating the amount of impregnation. In addition, the transverse rupture strength was measured by cutting a test piece having a width of 15 mm and a length of 35 mm from the sintered body, and using a 3-point bending method with a span of 25 mm (test speed: 2 mm
/ min breaking load measurement).

[0019]

[Table 1]

[0020]

[Table 2]

Next, a friction test was conducted on each of the above friction plates by an inertial tester under the following conditions, and the peripheral speed, the stop time, the limit value, the friction coefficient and the abnormality occurrence condition at the time of the limit condition ( (Except for baking) is shown in Table 3. Friction test conditions: Friction plates (friction area 292.2 cm ² , effective radius 0.1550 m) were used for each 3 sheets, and 4 sheets of S45C were used as mating materials to alternately combine them to obtain 6 friction surfaces. 1 moment of inertia
Set 0.5kgfms ² and the engaging surface pressure to 20kgf / cm ² , respectively, and increase the peripheral speed from 6.5m / s by 0.8m / s to rub until a critical situation such as abnormal torque waveform occurs. The test was done. Engine oil [Mitsubishi Oil Corp.]
Manufactured by SAE # 30], oil temperature 70 ° C, oil supply 20ml / c
m ² .min. The peripheral speed is the peripheral speed at the time of seizure, and the larger the value, the higher the load can be used. The limit value is indicated by the rotational kinetic energy of the inertial body per apparent friction area, and the energy absorption rate obtained by dividing the energy absorption amount by the stop time is the energy absorption amount (kgfm / kgfm / cm ² ) × energy absorption work rate (kgfm / cm ² / s)], which corresponds to the load when seizure occurs. Therefore, the larger the value is, the more it can be used under high load condition without seizure.
The friction coefficient is calculated from the torque at a peripheral speed of 10 m / s [μ = T
/ P × Z × R] (where T is torque, P is total pressing force, Z is the number of friction surfaces, and R is effective radius). The larger the value, the higher the friction performance. .

[0022]

[Table 3]

As is clear from a consideration of Tables 1 to 3, the friction materials according to the examples all have high absorption energy limit values and relatively excellent friction coefficients. However, in Examples 10 and 11, since the open porosity of the sintered body was less than 15% by volume, the friction characteristics tended to deteriorate. On the other hand, in the comparative examples that deviate from the conditions of the present invention, the limit value and the coefficient of friction were relatively low, and many abnormalities other than the seizure phenomenon were recognized.

[0024]

As described above, according to the present invention, Cu containing C, Sn, and SiO ₂ (Zn) in a specific mixing ratio is used.
The composition is mainly composed of a bronze-based component as a filler, and the C component as a graphite powder having a specific particle property and a specific graphitization degree. The sintered body has excellent energy absorption and high friction performance. A wet friction material can be provided. Therefore, it is extremely useful as a brake pad or clutch facing that requires high performance.

Claims (3)

[Claims] 1. C: 20 to 35% by weight, Sn: 2 to 8% by weight, SiO ₂ : 4 to 10% by weight, the balance being Cu, said C having an average particle size of 20 to 60 μm and a particle size of 5 to 5. 1
A bronze-based component having a composition, which is a graphite powder having a particle content of 00 μm of 90% or more and an interlayer distance between graphite crystal planes C ₀ of 0.672 nm or less, is sintered. Wet friction material. 2. The wet friction material according to claim 1, wherein Zn: 8 wt% or less is added as a bronze-based component. 3. The wet friction material according to claim 1, which has an open porosity of 15 to 20% by volume and a transverse rupture strength of 20 MPa or more.