JPH07316542A - Production of copper-based sintered friction material - Google Patents

Abstract

PURPOSE:To obtain a copper-based sintered friction material useful for a brake friction pad or a clutch facing, having high frictional characteristics, firmly bondable to a core plate, by sintering a molded article of green compact having a specific composition under limited sintering conditions. CONSTITUTION:Mixed raw material powder comprising (A) (i) 3-8wt.% of Sn powder, (ii) 2-9wt.% of Zn powder, (iii) 4-10wt.% of SiO2 powder and (iv) 15-25wt.% of SiO2 and (v) the rest of electrolyzed copper powder is molded in green compact. The molded article is brought into contact with a bonding face of a core plate and thermally pressed in a reducing atmosphere preferably under 1-10MPa. After the molded article reaches 750-850 deg.C, preferably 790-830 deg.C, the reducing atmosphere is changed into a neutral atmosphere or a vacuum atmosphere and successively the molded article is retained in the above temperature range for a prescribed time (preferably 20 minutes to 5 hours). The molded article in green compact is sintered and simultaneously bonded to the core plate to give the objective frictional material.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention has friction characteristics suitable as a brake pad or a clutch facing,
The present invention relates to a method for manufacturing a copper-based sintered friction material that is firmly bonded to a core plate.

[0002]

2. Description of the Related Art Sintered metal-based friction materials have hitherto been mainly composed of Cu, Sn, Zn, Al, Al ₂ O ₃ , S
The mainstream is a copper alloy-based material obtained by adding and sintering iO ₂ , MoS _2, etc., but addition of graphite and other carbonaceous powders improves the lubricity and thermal and chemical stability. (For example, Japanese Patent Laid-Open No. 61-67736).

This type of copper-based sintered friction material is usually used by bonding it to a core plate having steel or the like as a backing metal, so that the friction member and the core plate member can be firmly adhered to each other. is necessary. Conventionally, as a means for joining a friction member and a core plate member, for example, a powder compact of a copper-based friction material containing Zn powder is combined with a joint surface of a steel backing metal and applied in a neutral or weak reducing atmosphere. A joining method has been proposed in which pressure molding is performed to sinter the powder compact and to join it to the backing metal (Japanese Patent Laid-Open No. S60-12065).
50-150656). Further, Japanese Patent Application Laid-Open No. 2-274802 discloses a powder molded product comprising Cu 5 to 70 parts by weight, S, FeS, ZnS and the like 0.2 to 3 parts by weight (S amount conversion), C 5 parts by weight or less, and the balance Fe. A method is disclosed in which an alloy layer mainly composed of Cu is formed at the contact interface portion by contacting with steel or the like and heating at 1000 to 1080 ° C. in a non-oxidizing atmosphere to bond the two.

[0004]

However, in these prior arts, the performance as a friction material, such as the porosity, the friction coefficient, the wear amount, etc., is not taken into consideration. Was not sufficient to achieve both the increase in strength.

The present inventors have made a detailed study of the conditions for sintering the Cu-Sn alloy system. As a result, when sintering is performed in a hydrogen atmosphere, the sintering proceeds and shrinks, resulting in a decrease in the open porosity. , The friction characteristics such as the reduction of the friction coefficient and the increase of the wear amount are reduced, while the joint with the core plate is strengthened,
In addition, it was confirmed that there is a trade-off relationship that volume expansion occurs when sintering is performed in a nitrogen atmosphere, the open porosity increases and friction characteristics are improved, but the bonding force with the core plate decreases.

The present invention has been made as a result of multifaceted research on optimum sintering conditions by paying attention to this relationship.
The purpose is to produce a copper-based sintered friction material that has a high friction property and can be firmly bonded to a core plate by sintering a green compact of a specific composition under limited sintering conditions. To provide a method.

[0007]

A method of manufacturing a copper-based sintered friction material according to the present invention for achieving the above object is as follows: Sn powder 3 to 8% by weight, Zn powder 2 to 9% by weight, SiO ₂ powder. 4-1
0% by weight, 15 to 25% by weight of graphite powder, and the remainder of the mixed raw material powder made of electrolytic copper powder are compacted, and the compact is hot pressed in a reducing atmosphere in contact with the joint surface of the core plate. After the heating temperature reaches 750 to 850 ° C., the atmosphere is switched to a neutral atmosphere or a vacuum atmosphere, and then the heating temperature is maintained for a certain period of time to sinter the powder compact and bond it to the core plate. And

The raw material component of the present invention is composed of Cu as a main component and a certain amount of Sn, Zn, SiO ₂ and graphite powder powder added thereto. As the Cu powder which is the main component, a dendritic electrolytic copper powder suitable for maintaining the material strength during powder compaction is used. Among the added components, Sn powder is a component that forms a solid solution with Cu during sintering to form a Cu—Sn alloy, promotes sintering, and functions to increase the open porosity,
It is compounded in the range of 3 to 8% by weight. If the content is less than 3% by weight, it becomes difficult to sinter Cu, and if it exceeds 8% by weight, solidification segregation of the Sn component is caused, which causes the friction characteristics to be deteriorated. As the Sn powder, it is preferable to use atomized powder or stamp powder of 200 mesh or less.

Zn powder also functions in the same manner as Sn powder, and the addition of this can reduce the amount of expensive Sn compounded.
The SiO ₂ powder is a component that imparts wear resistance and stabilizes friction characteristics by appropriately grinding the mating member to expose a new friction surface, and is compounded in the range of 4 to 10% by weight. It If the blending amount is less than 4% by weight, the wear resistance and the friction coefficient decrease, and if it exceeds 10% by weight, the abradability becomes too large and the strength of the sintered body decreases. Graphite powder is a component necessary to stabilize friction characteristics,
It is blended in a proportion of 15 to 25% by weight. This compounded amount is 1
If it is less than 5% by weight, the friction characteristics are unstable, and if it exceeds 25% by weight, the strength and friction coefficient of the sintered body are remarkably lowered.

These raw material powders are uniformly mixed using a mixing device such as a V-type blender, then filled in a predetermined mold and pressed to form a powder compact. The pressing force during powder compaction is preferably set in the range of 50 to 750 MPa, and if it is less than 50 MPa, a molded product that can withstand handling cannot be obtained. Next, the compact is hot pressed and sintered in a reducing atmosphere in a state of being in contact with the joint surface of the core material. As the core plate, one made of steel having a surface plated with Cu is used, and the reducing atmosphere is a gas atmosphere such as hydrogen gas and mixed gas thereof, propane-modified gas or ammonia decomposition gas.

The pressure during sintering is preferably set in the range of 1 to 10 MPa. If the pressure is less than 1 MPa, a strong bond with the core material cannot be obtained, and if it exceeds 10 MPa, the open porosity and the friction characteristics are deteriorated. The heating temperature at the time of sintering is raised to the range of 750 to 850 ° C. If the heating temperature is lower than 750 ° C., the sintering reaction does not proceed sufficiently, and if it exceeds 850 ° C., the open porosity of the sintered body is reduced, and the frictional characteristics are deteriorated such as the reduction of the friction coefficient and the increase of the wear amount. The preferred heating temperature is in the range of 790 to 830 ° C.

When the heating temperature reaches the range of 750 to 850 ° C., the atmosphere is switched to a neutral atmosphere or a vacuum atmosphere, and then the heating temperature range is maintained for a certain period of time. At this time, examples of the neutral atmosphere to be switched include nitrogen and argon, and the holding time for heating in a neutral atmosphere or a vacuum atmosphere is appropriately in the range of 20 minutes to 5 hours.

As described above, by switching the atmosphere system from reducing to neutral or vacuum in the hot pressing step, the green compact is sufficiently sintered and at the same time firmly joined to the core plate. The copper-based sintered friction material produced in this manner is processed into a predetermined shape, surface-polished and oil-grooved, etc., to obtain a product.

[0014]

In general, when the raw material powder of the present invention is heated in a reducing atmosphere such as hydrogen or ammonia decomposition gas, Sn powder melts out from its melting point during the temperature rising process, and the liquid phase becomes Cu--Sn phase diagram as the temperature rises. Liquid phase sintering of Cu particles proceeds while increasing the solid solution amount and the volume of Cu according to the liquidus line. Then, when it reaches the Cu-Sn peritectic temperature of 798 ° C, it starts to expand rapidly, and rapidly changes to contraction at about 820 ° C. Further, when the green compact of the mixed raw material powder is heated and heated in a reducing atmosphere, the melting point of Sn is 2
A liquid phase is generated from the temperature of 32 ° C., and if the temperature is further increased, the interface between the core plate and the powder compact is brought into close contact with each other to obtain a strong joined body. However, if the temperature exceeds 850 ° C., the open porosity of the sintered body decreases, and the frictional characteristics deteriorate, such as a decrease in the friction coefficient and an increase in the amount of wear. On the other hand, when sintered in a neutral atmosphere or a vacuum atmosphere, the porosity increases and the friction characteristics are improved, but the joining with the core plate becomes unstable. Further, when the temperature exceeds 850 ° C., a foaming phenomenon occurs due to a low melting point metal such as Sn and Zn, and distortion of the core plate also occurs.

According to the present invention, when the sintering temperature reaches the temperature range of 750 to 850 ° C., the sintering atmosphere is changed from a reducing atmosphere to a neutral atmosphere or a vacuum atmosphere.
It is intended to increase the open porosity of the sintered body and improve the frictional characteristics, and to enable strong and stable bonding with the core plate which is the backing metal. That is, according to the process of the present invention, a strong bond with the core plate is achieved by hot pressure sintering in a reducing atmosphere, and in this case, a decrease in open porosity and a decrease in friction characteristics are caused by a neutral atmosphere. Alternatively, it can be effectively suppressed by switching to sintering in a vacuum atmosphere. In addition, the destabilization of the bonding that occurs during sintering in a neutral atmosphere or a vacuum atmosphere is prevented by the strong bonding already formed by sintering in a reducing atmosphere.

The functions of the hot-pressing sintering process by switching the atmosphere as described above can be comprehensively operated to produce a high-performance copper-based sintered friction material having excellent friction characteristics and firmly bonded to the core plate. It will be possible.

[0017]

EXAMPLES Examples of the present invention will be specifically described below in comparison with comparative examples. However, the present invention is not limited to these examples as long as the constitutional requirements are satisfied.

Example 1 62% by weight of electrolytic copper powder (particle size 100 μm or less), 5% by weight Sn powder (stamping powder, # 200 or less), Zn powder (stamping powder, # 200 or less) 7% by weight, SiO ₂ Powder (silica powder, average particle size 17 μm) 6% by weight and graphite powder (particle size 100 μm or less)
The mixture was blended in a proportion of 20% by weight and mixed for 20 minutes by a V-type mixer to prepare a homogeneous mixed powder. This mixed raw material powder was filled in a ring-shaped mold having an outer diameter of 335 mm and an inner diameter of 280 mm, and was compacted at a pressure of 300 MPa to obtain an outer diameter of 335 m.
A molded product having an m, an inner diameter of 280 mm and a thickness of 1.5 mm was obtained. This molded body was heated in a hydrogen atmosphere while applying a pressure of 2 MPa in a state where it was in contact with both sides of an iron core plate having a surface plated with copper, and the temperature was raised to 830 ° C. for 2 hours, and then the nitrogen atmosphere. And the temperature was maintained for 1 hour for hot pressure sintering. The conditions are shown in Table 1. Then, both surfaces of the obtained sintered body were subjected to surface grinding, and spiral grooves and radial grooves (36 on both sides from the center to the outside) were processed and formed as oil grooves to manufacture a copper-based sintered friction material.

Examples 2 to 4 A copper-based sintered friction material was manufactured under the same conditions as in Example 1 except that the mixed raw material powder having the composition shown in Table 1 and the heat treatment conditions were applied.

Comparative Examples 1 to 6 Using mixed raw material powders having the compositions shown in Table 1, without changing the atmosphere as a heat treatment condition, the mixture was heated to a predetermined temperature only in a hydrogen atmosphere or a nitrogen atmosphere and kept for a certain time. And sintered, and a copper-based sintered friction material was manufactured under the same conditions as in Example 1 except for the above.

[0021]

[Table 1]

With respect to each of the above copper-based sintered friction materials, the open porosity, frictional characteristics and joint strength with the core plate were measured, and the results are shown in Table 2. The measured value is a value obtained by the following method.

Open porosity; Japan Powder Metallurgical Industry Association Standard, JP
The sintered body was impregnated with oil by MAM02-1992, and calculated from the impregnated amount.

Dynamic Friction Coefficient; Measuring Machine: Inertial Friction Tester (Tokyo Koki Co., Ltd.) Friction plate with outer diameter 340 mm, inner diameter 280 mm (friction area 292 cm
² , effective radius 0.1550m), 3 sheets each, S4 as mating material
The number of frictional surfaces was set to 6 by alternately using 4 sheets of 5C. Inertia moment of 10.5kgfms ² , engagement surface pressure of 2
The torque was measured by setting each to 0 kgf / cm ² and increasing the rotation speed from 1400 rpm to 2400 rpm in 200 rpm increments. The dynamic friction coefficient is calculated from each torque by [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), and the larger the value, the better the friction characteristics.

Wear rate; wear volume of friction material (A × d × Z)
Value divided by kinetic energy (1/2 × I × ω ² ) [V
= (A × d × Z) / (1/2 × I × ω ² )], and V
Is the wear rate, A is the area of one surface of the friction material, d is the wear thickness, Z is the number of friction surfaces, I is the moment of inertia, and ω is the rotational angular velocity. The smaller the wear rate V, the better the frictional properties.

Bonding strength: The back plate side of the core plate is fixed to a jig,
A shear strength was measured by applying a load in the thickness direction near the boundary line on the friction material side. The bonding strength is [F = f / A] formula (however, f
Is a shear load and A is a value calculated by a fracture area).

The proportions of the joined areas in the joined portion were 35% in Comparative Example 2, 45% in Comparative Example 4, 30% in Comparative Example 6, and about 100% in other cases. Further, in Comparative Example 6, the friction material peeled from the core plate during the friction test,
The test was canceled on the way.

[0028]

[Table 2]

From the above results, the friction materials according to the examples of the present invention show excellent friction characteristics having a high open porosity, a large dynamic friction coefficient, and a small wear rate as compared with the friction materials of the comparative examples. There is. Furthermore, it is recognized that the frictional property and the bonding strength are imparted in a good balance as a friction material having a large bonding strength with the core plate material.

[0030]

As described above, according to the present invention, as a sintering condition, the atmosphere at the time of temperature rise is a reducing atmosphere, and the atmosphere at the time of sintering after the temperature rise is changed to a neutral atmosphere or a vacuum atmosphere to reduce friction. It is possible to simultaneously improve the characteristics and firmly bond the core plate as the back metal. Therefore, it is extremely useful as a method for producing a copper-based sintered friction material for brake pads and clutch facings that require high performance.

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Claims (4)

[Claims] 1. A mixed raw material powder comprising 3 to 8 wt% Sn powder, _{2 to} 9 wt% Zn powder, 4 to 10 wt% SiO ₂ powder, 15 to 25 wt% graphite powder, and the balance being electrolytic copper powder. Powder molding, hot pressing the molded body in a reducing atmosphere in contact with the joint surface of the core plate, and after switching the heating temperature to 750 to 850 ° C, switch to a neutral atmosphere or a vacuum atmosphere, and continue to the above temperature range. A method for manufacturing a copper-based sintered friction material, which comprises holding the powder for a certain period of time to sinter the powder compact and joining it to a core plate. 2. The method for producing a copper-based sintered friction material according to claim 1, wherein the heating temperature is 790 to 830 ° C. 3. The pressing force is 1 to 10 MPa.
Or a method for producing a copper-based sintered friction material according to 2 4. The method for producing a copper-based sintered friction material according to claim 1, wherein the holding time in a neutral atmosphere or a vacuum atmosphere is set to 20 minutes to 5 hours.