KR100682278B1 - Friction material and manufacturing method of the same - Google Patents

Abstract

A manufacturing method of friction materials is provided to manufacture friction materials having excellent high temperature strength, abrasion resistance and friction coefficient. The manufacturing method of friction materials comprises the steps of: preparing mixed powder of 7~25 weight percent iron powder, 4~15 weight percent silica powder, 5~30 weight percent graphite powder, 0.5~5 weight percent carbon nano-tube, and 58~76 weight percent copper-nickel alloys(S100); immersing the prepared mixed powder in a mixing solution containing coatings and a solvent(S200); volatilizing the solvent and mixing the mixed powder(S300); manufacturing a molded body by inputting the mixed powder in a mold applied with zinc stearate as a lubricant and applying a single pressure type vertical pressure of 4~8 ton/cm^2(S400); and completing friction materials by sintering the molded body at 850~925‹C for 1~3 hours(S500).

Description

Friction material and manufacturing method thereof {FRICTION MATERIAL AND MANUFACTURING METHOD OF THE SAME}

1 is a flow chart showing a method of manufacturing a friction material according to an embodiment of the present invention.

 The present invention relates to a friction material and a method for manufacturing the same, and more particularly, to a sintered copper-based friction material including carbon nanotubes and improved high temperature strength, heat resistance, wear resistance and coefficient of friction and a method of manufacturing the same.

Generally, friction materials mounted in the braking system of transportation machinery are classified into organic materials, sintered alloys, and carbon-carbon composites.

Double organic friction materials are most commonly used as brake system friction materials for automobiles, trucks and railroad cars. The organic friction material is a composite material which is fired by mixing an additive and a friction control agent on an organic substance base of a thermosetting resin system. When such an organic friction material is used as a braking friction material of a high load, high speed vehicle such as a high-speed train, the heat generated at the contact surface of the counterpart during braking far exceeds the decomposition temperature of the thermosetting resin. As a result, mechanical properties of the entire friction material are rapidly deteriorated to cause problems in durability, and thus there is a problem that it cannot be used for high speed trains.

Carbon-carbon composite friction material has excellent braking properties, and many researches have been conducted on it. However, due to its high manufacturing cost, it is widely used as a friction material for aircraft.

For this reason, metal sintered materials are used as friction materials for high-speed trains. The characteristics required for the metal sintered friction material are to have sufficient strength even at high temperatures, to have high specific heat and thermal conductivity, to have a constant coefficient of friction regardless of the use conditions, and to have excellent wear resistance. Among the metal sintered materials that will satisfy these characteristics, the use of copper-based sintered materials with much higher thermal conductivity than iron-based sintered materials is common, and development studies for satisfying higher properties have been conducted.

The mainstream of copper-based sintered materials is a copper alloy powder alloyed with a hardening element such as tin (Sn) or nickel (Ni) as a main raw material, and an iron-based intermetallic compound or oxide powder as a friction modifier, and graphite or MoS as a solid lubricating component. ₂ powders and the like, which are mixed and sintered at a predetermined ratio, are described in Japanese Patent Application No. 97-48468, Japanese Patent Application No. 97-98943, Japanese Patent Application No. 96-99512, and the like.

Graphite used as a solid lubricating component has an oxidation temperature of about 450 ^o C (G. Jintang: Wear, 24, (2000) 100-106, HE Sliney: ASLE Transations, 29-3, 370-376), MoS ₂ The maximum service temperature is about 400 ^o C (S. Hwang: Journal of the Korean Welding Society, 21 (2) (2003), 157-164). For this reason, there is a problem that the oxidation proceeds under high load and high speed friction conditions at which the friction surface temperature is 400 ^° C. or higher, thereby increasing the variation of the friction coefficient and deteriorating the mechanical properties.

Accordingly, an object of the present invention is to provide a friction material having excellent high temperature strength, wear resistance and friction coefficient.

In addition, another object of the present invention is to provide a method for producing a friction material excellent in high temperature strength, wear resistance and friction coefficient.

The object is by a friction material consisting of 7 to 27% by weight of iron, 4 to 15% by weight of silica (SiO 2), 5 to 30% by weight of graphite, 0.5 to 5% by weight of carbon nanotubes and 58 to 76% by weight of copper-tin alloy. Can be achieved.

The tin content in the copper-tin alloy is preferably 5 to 15% by weight.

Another object of the present invention is iron powder 7 to 27% by weight, silica (SiO 2) powder 4 to 15% by weight, graphite powder 5 to 30% by weight, carbon nanotubes 0.5 to 5% by weight and copper-tin alloy powder 58 to Immersing a mixed powder comprising 76% by weight in a mixing solution containing a coating agent and a solvent; Mixing the mixed powder while evaporating the solvent; Molding the mixed mixed powder into a predetermined form; It can be achieved by a method of manufacturing a friction material comprising the step of sintering the molded mixed powder.

It is preferable that the average particle size of the said iron powder is 10-44 micrometers.

It is preferable that the average particle size of the said silica powder is 100-350 micrometers.

It is preferable that the average particle size of the said graphite powder is 44-200 micrometers.

It is preferable that the average particle size of the said copper- tin alloy powder is 10-70 micrometers or less.

The coating agent is preferably paraffin.

The amount of the coating agent is preferably 0.5 to 5% by weight of the mixed powder.

The volume of the solvent is preferably 50 to 100% of the volume of the mixed powder.

In the copper-tin alloy powder, the tin content is preferably 5 to 15% by weight.

The sintering is preferably carried out in either a vacuum atmosphere or an inert gas atmosphere.

The sintering is preferably performed for 1 to 3 hours at 850 to 925 ℃.

Hereinafter, the present invention will be described in more detail.

The friction material according to the present invention includes iron, silica (SiO 2), graphite, carbon nanotubes, copper-tin alloy, these components are mixed uniformly.

Iron is used 7 to 27% by weight as friction modifier. If the amount of iron used is less than 7% by weight, the effect on the increase of the strength of the finished friction material is insignificant. If it is 27% by weight or more, the strength is increased more than necessary, and the wear of the friction counterpart may be severe. The content of iron is preferably 12 to 20% by weight, more preferably about 17% by weight.

Silica is used 4 to 15% by weight as a friction control agent. If the content of silica is less than 4% by weight, the sintering reaction is suppressed due to the increase in volume due to the small specific gravity, and the strength of the friction material is lowered.If the content of silica is more than 15% by weight, the particles fall out during friction, thereby acting as a friction regulator. Because you lose. The content of silica is preferably 7 to 11% by weight, more preferably about 9%.

Graphite is used 5 to 30% by weight as a friction lubricant. If the content of graphite is less than 5% by weight loses the inherent role of the friction lubricant, at 30% by weight or more, the density of the friction material is sharply lowered, causing problems in mechanical strength. The content of graphite is preferably 18 to 22% by weight, more preferably about 20% by weight.

Carbon nanotubes are used in 0.5 to 5% by weight. If carbon nanotubes are used less than 0.5% by weight, they have little effect on securing the thermal stability of the friction material. When the carbon nanotubes are more than 5% by weight, the volume of carbon nanotubes rapidly increases, so that the mixing of each component is extremely difficult in the manufacturing process of the friction material. This is because it becomes difficult and the strength of the friction material to be completed by suppressing the sintering reaction is sharply lowered. The content of carbon nanotubes is more preferably 1 to 4% by weight.

Carbon nanotubes have the highest thermal conductivity in nature and are similar to diamond. The tensile strength is about 30Gpa, which is 100,000 times that of steel, and the oxidation temperature is about 550 ℃. By using carbon nanotubes, the friction material can ensure good thermal conductivity, high temperature strength, wear resistance and coefficient of friction.

Carbon nanotubes are produced in five to six ways, including electric discharge, laser deposition, thermochemical vapor deposition, and plasma chemical vapor deposition. Any carbon nanotubes produced by any method can be used. On the other hand, if carbon nanotubes are produced by thermochemical vapor deposition (Republic of Korea Patent Application Nos. 2002-0011838, 2002-0011839, and 2003-0096325), which have recently established low-cost mass production methods in consideration of their relatively high points. It is also more economically desirable.

The copper-tin alloy is used at 58 to 76% by weight. The content of tin in the copper-tin alloy is 5 to 15% by weight, with about 10% being preferred.

Hereinafter, a method of manufacturing a friction material according to the present invention will be described with reference to FIG. 1.

1 is a flowchart illustrating a method of manufacturing a friction material according to an embodiment of the present invention.

First, iron powder 7 to 27% by weight, silica (SiO 2) powder 4 to 15% by weight, graphite powder 5 to 30% by weight, carbon nanotubes 0.5 to 5% by weight and copper-tin alloy powder 58 to 76% by weight Prepare a mixed powder (S100).

In order to increase the strength of the friction material without forming a solid solution with the copper-tin powder, the iron powder may be smaller than the copper-tin alloy powder and may have an average particle size of 10 to 44 µm, and preferably about 34 µm.

The average particle size of the silica powder may be 100 to 350 μm. If the particle size is less than 100㎛, the sintering reaction is suppressed by increasing the volume due to the small specific gravity, which lowers the strength of the final friction material.It is more than 350㎛ and the particles fall out during friction with the counterpart to lose the role of the friction regulator. Because. The average particle size of the silica powder is preferably about 250 μm.

The average particle size of the graphite powder may be 44 μm to 200 μm. This is because if the average particle size of the graphite powder is 44 µm or less, the density of the friction material is drastically lowered, which causes a problem in mechanical strength, and at 200 µm or more, the particles fall out during friction. The average particle size of the graphite powder is preferably about 100 mu m.

The particle size of the copper-tin alloy powder may be smaller to increase the density of the friction material and may be about 10 to 70 μm.

Next, the prepared mixed powder is immersed in the mixing solution (S200).

In the mixed powder, silica powder, graphite powder, and carbon nanotubes other than the metal powder are very small in density, and uniform mixing is not possible due to the density difference with the metal powder. In order to solve this problem, the mixed powder is immersed and mixed in a mixing solution containing a coating agent and a solvent for the purpose of uniform mixing and strength increase.

The coating agent may be paraffin or wax or the like as a binder or binder for uniform mixing of each component of the mixed powder and increasing strength of the molded body. The amount of the coating agent may be 0.5 to 5% by weight of the mixed powder. If the amount of coating agent is 0.5% by weight or less, the molding strength is significantly reduced after molding, and handling of the molded body becomes very difficult. If it is 5% by weight or more, the sintering time for the same sintering density at the sintering temperature is prolonged. This is because the density is increased.

The solvent may be used as long as it is a substance capable of dissolving the coating agent, and a low boiling point may be used, but nucleic acid may be used. The volume of the solvent may be 50 to 100% of the volume of the mixed powder. If the volume of the solvent is 50% or less, it is difficult to secure the time required for the dough for uniform mixing of each powder due to the fast volatilization speed of the solvent, and if it is more than 100%, the time required for the volatilization of the solvent becomes longer than necessary. to be. The amount of the solvent used is preferably about 70% of the volume of the mixed powder. The amount of the solvent used may be adjusted in consideration of the volatility of the solvent used.

The preparation of the mixed powder and the immersion in the mixing solution described above may be variously modified. For example, the method of putting each component of a coating agent and mixed powder into a solvent one by one is possible.

Next, the mixed powder is mixed while the solvent is volatilized (S300).

In this process, the solvent is removed by natural drying and / or heating, increasing the viscosity of the mixed powder. Meanwhile, in the process, the components of the mixed powder are uniformly mixed with each other under the action of the coating agent. This process is performed until substantially all of the solvent is removed.

Thereafter, the mixed powder is molded into a predetermined shape to produce a molded body (S400).

Molding is carried out by charging the mixed powder into a die coated with zinc stearate, a lubricant, and applying a pressurized vertical pressure of 4 to 8 ton / cm ² . Through this process, the friction material is formed, but each component is physically combined only.

It is desirable to increase the molded body density as much as possible to increase the sintered density. The applied pressure of the press is preferably 4 to 8 ton / cm ² , because it is not possible to obtain a high molding density at 4 ton / cm ² or less, and at 8 ton / cm ² or more, it is formed by strong friction between the mold and powder. This is because there is a limit to the increase in density, so that no molding pressure is required, and a large press must be operated to form a friction material having a cross-sectional area of 10 cm ² or more.

After sintering the molded body to complete the friction material (S500).

Sintering is carried out in a vacuum atmosphere or inert gas atmosphere at a temperature of 850 to 925 ^° C. for 1 to 3 hours. In the case of a vacuum atmosphere, the degree of vacuum may be 10 ⁻⁵ torr or less.

If the sintering temperature is 850 ℃ or less and less than 1 hour, the sintering density is lowered. If the sintering temperature is more than 925 ° C and more than 3 hours, the sintering temperature may be undesirable due to the change of the shape of the friction material due to the poor wettability of the metal surface and graphite. Because. Sintering is preferably performed at 900 ^° C. for 1.5 hours.

Experimental Example

A friction material was prepared according to the method described above, and the friction materials of Examples 1 to 3 and Comparative Examples 1 to 3 were prepared by controlling the content of graphite powder and carbon nanotubes.

The friction material manufacturing conditions are as follows.

The mixed powder consisted of iron powder having a particle size of 34 μm, 17 wt% of iron powder, silica powder of 250 μm average particle size, 9 wt% of silica powder, and copper-10% tin alloy having an average particle size of 50 μm. And the contents of carbon nanotubes were changed according to the conditions.

Paraffin was used as a coating agent by weight of 2% by weight of the mixed powder and nucleic acid was used as the solvent by 70% of the volume of the mixed powder. The molding pressure was 8 kg / cm 2 and the sintering was carried out at about 900 ° C. under vacuum conditions for 1.5 hours.

The finished friction material was donut-shaped, and the outer and inner diameters were 26 mm and 20 mm, respectively, and the same height was 20 mm. The counterparts were made of 3.62% by weight of carbon, 2.26% by weight of silicon, 1.13% by weight of manganese, and 0.034% by weight of phosphorus. 30 mm x 30 mm, thickness 5 of a spheroidal graphite cast iron comprising 0.01% by weight or less of sulfur, 0.027% by weight or less of copper, 0.024% by weight or less of chromium, 0.039% by weight of magnesium, and iron and other unavoidable impurities. The sheet was processed into mm and used.

In the friction test, a tester configured to fix the counterpart and contact and rotate the friction material on the surface of the counterpart was used. It was designed to apply a constant load to the cross section of the friction material during the test. The rotational speed of the friction material was fixed at 1000 rpm and the magnitude of the load was 20 kg / cm ² .

Table 1 shows the experimental results for the Examples and Comparative Examples.

TABLE 1

As shown in Table 1, when carbon nanotubes are not included (Comparative Example 1) or when only 0.4 wt% is included (Comparative Example 2), as the friction time increases, the coefficient of friction, the amount of wear and the temperature of the friction surface are increased. It can be seen that the increase rapidly. This phenomenon is judged to be the result of the lubrication function of the graphite is lowered after the friction surface temperature rises to 450 ℃ or more, the use temperature of graphite after 600 seconds from the test.

On the other hand, in Examples 1, 2, and 3, wherein the contents of the carbon nanotubes are 1% by weight, 3% by weight, and 4% by weight, respectively, it was found that the friction surface temperature increase was not large. This shows that carbon nanotubes have a significant contribution to heat dissipation. Accordingly, there was no significant change in the friction coefficient and the amount of wear. In particular, in Example 2, in which the amount of use was 3% by weight, almost no change in the friction surface temperature, the wear rate, and the amount of wear showed optimum friction characteristics.

On the other hand, in the case of Comparative Example 3 in which the amount of carbon nanotubes used is 6%, a breakdown of the specimen started at 1500 seconds, the friction test was stopped, and it was confirmed that there was a problem in the friction material strength.

The friction material according to the present invention described above is excellent in high temperature strength, wear resistance and coefficient of friction, but is not limited thereto, and may be applied to high speed trains.

As described above, according to the present invention, a friction material having excellent high temperature strength, wear resistance, and friction coefficient is provided.

In addition, according to the present invention there is provided a method for producing a friction material excellent in high temperature strength, wear resistance and friction coefficient.

Claims (13)

In the friction material, A friction material comprising 7 to 27% by weight of iron, 4 to 15% by weight of silica (SiO 2), 5 to 30% by weight of graphite, 0.5 to 5% by weight of carbon nanotubes and 58 to 76% by weight of a copper-tin alloy. The method of claim 1, Friction material, characterized in that the tin content in the copper-tin alloy is 5 to 15% by weight. In the manufacturing method of the friction material, 7 to 27 wt% iron powder, 4 to 15 wt% silica (SiO 2) powder, 5 to 30 wt% graphite powder, 0.5 to 5 wt% carbon nanotube and 58 to 76 wt% copper-tin alloy powder Immersing the powder in a mixing solution comprising a coating agent and a solvent; Mixing the mixed powder while evaporating the solvent; Molding the mixed mixed powder into a predetermined form; Method for producing a friction material comprising the step of sintering the molded mixed powder. The method of claim 3, Method for producing a friction material, characterized in that the average particle size of the iron powder is 10 to 44㎛. The method of claim 3, Method for producing a friction material, characterized in that the average particle size of the silica powder is 100 to 350㎛. The method of claim 3, Method for producing a friction material, characterized in that the average particle size of the graphite powder is 44 to 200㎛. The method of claim 3, Method of producing a friction material, characterized in that the average particle size of the copper-tin alloy powder is 10 to 70㎛ or less. The method of claim 3, The coating agent is a method of producing a friction material, characterized in that the paraffin. The method of claim 3, Method for producing a friction material, characterized in that the amount of the coating agent is 0.5 to 5% by weight of the mixed powder. The method of claim 3, The volume of the solvent is a method of producing a friction material, characterized in that 50 to 100% of the volume of the mixed powder. The method of claim 3, Tin content in the copper-tin alloy powder is a manufacturing method of a friction material, characterized in that 5 to 15% by weight. The method of claim 3, The sintering method of producing a friction material, characterized in that carried out in any one of a vacuum atmosphere and an inert gas atmosphere. The method of claim 3, The sintering method of producing a friction material, characterized in that carried out for 1 to 3 hours at 850 to 925 ℃.

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