JP2003145568A - Degassing method in process for thermoforming friction material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a degassing method for preventing the occurrence of defective molding such as cracks and blisters and a method for thermoforming a friction material which can obtain the friction material excellent in quality at a high temperature in a short time. SOLUTION: In a method for producing the friction material in which the preliminary molding of the friction material is thermoformed by using a mold for thermoforming the friction material comprising a press mold, a middle mold, and a pressurization mold, in a degassing method in a process for thermoforming the friction material, the middle parts of the press mold and the middle mold are manufactured from a material having heat conductivity higher than that of the other parts. During the thermoforming, the preliminary molding is heated so that a part to be finally cured is concentrated to the side contacting the middle mold, and gas generated from the preliminary molding by the thermoforming is discharged outside the mold from a position contacting the final curing part of the preliminary molding through a degassing passage opened to the inner surface of the middle mold.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a degassing method in a thermoforming process of friction materials, and particularly to industrial machinery,
The present invention relates to a degassing method in the thermoforming process of friction materials used in railway vehicles, luggage vehicles, passenger cars, etc., and more specifically to thermoforming of brake pads, brake linings, clutch facings, etc. used for the above-mentioned applications. It relates to a degassing method in the process.

[0002]

2. Description of the Related Art Conventionally, friction materials mainly used for brakes of automobiles, railway vehicles, industrial machines, etc., generally include various fillers, various fibers for reinforcement, abrasives, graphite and metals. Various resins are blended with a friction adjusting material such as powder as a binding material for binding these materials. In the manufacturing process of a brake pad for a disc brake, which is one example of a conventionally known method for manufacturing a friction material, it is molded into a predetermined shape by a sheet metal press, subjected to degreasing treatment and primer treatment, and then coated with an adhesive. Pressure plate, heat-resistant organic fiber, inorganic fiber, fiber base material such as metal fiber, inorganic / organic filler,
Mixing powder materials such as friction modifiers and binders (thermosetting resins such as phenolic resins), and thoroughly homogenizing the raw materials by stirring and molding at room temperature at a predetermined pressure (preforming)
In the thermoforming step, the preformed body produced in this way is thermoformed at a predetermined temperature and pressure so that both members are integrally fixed, aftercured, and finally finished.

Generally, in the method of manufacturing a friction material, it is preferable that the time of thermoforming is as short as possible in order to reduce the manufacturing cost. To shorten the molding time, it is most effective to raise the molding temperature to accelerate the curing reaction of the organic binder. By the way, in the conventional thermoforming process, as shown in FIG. 6, the pressure plate (P / P) is used.
1 and the preform 2 of the friction material raw material, the metal middle mold 3,
Upper die 4 which is a pressing die and lower die (punch) 5 which is a pressure die
The space between the upper, middle and lower molds is inserted and filled, and the material preform 2 is pressed by the upper mold 4 and the lower mold 5 together with P / P1. The heating plate 7 provided on the lower die 5 is used to heat the preform 2 together with P / P1.

[0004]

In the thermoforming process of the preform 2 of the friction material raw material, gas is generated along with the thermosetting reaction of the organic binder (thermosetting resin) in the friction material raw material. Then, when the generated gas is confined inside the thermoformed friction material, the generated gas with a high gas pressure trapped inside the friction material is released at a dash during depressurization of the press pressure, causing cracks and blisters. Becomes However, in the conventional thermoforming die shown in FIG. 6, since it is made of the same material without paying particular attention to the thermal conductivity,
Heat is easily transferred from the middle mold 3 and the lower mold 5, and as a result, the surface of the friction material in contact with the middle mold 3 that contacts P / P1 and the friction surface that contacts the lower mold 5 are rapidly hardened, so that the gas is used as a friction material. There is a problem that it is trapped inside and causes the cracks and blisters mentioned above.

That is, when the molding temperature is raised by the conventional molding method, the curing reaction is promoted, gas is concentrated, and molding defects frequently occur. Since the above problems have not been solved, the conventional molding method has a low molding temperature and a long molding time. Therefore, if there is a degassing method capable of quickly discharging the gas accumulated inside the friction material, molding defects can be prevented and molding at high temperature and in a short time becomes possible.

The present invention has been made in view of the above-mentioned conventional problems, and a method of degassing for preventing the occurrence of molding defects such as cracks and blisters, and a friction material excellent in quality at high temperature for a short time. An object of the present invention is to provide a thermoforming method for a friction material obtained in 1.

[0007]

[Means for Solving the Problems] The inventors of the present invention have made various studies on a thermoforming mold and a molding method that do not cause molding defects such as cracks and blisters, and have found that in the friction material raw material during the thermoforming process of the friction material. It was found that the gas generated by the curing reaction of the thermosetting resin, which is the binder, is not smoothly degassed, which is the main cause of cracks and blisters. Then, the present inventors have completed the present invention based on the above findings.

That is, the present invention has solved the above problems by the following constitution. (1) In a method of manufacturing a friction material in which a preform of a friction material is thermoformed using a thermoforming die for a friction material, which includes a pressing die, a medium die, and a pressure die, It is made of a material with higher thermal conductivity than the part, and the preform is heated so that the part that cures last during thermoforming is concentrated on the side that contacts the middle mold, and the gas generated from the preform by thermoforming is From the position in contact with the final cured part of the preform,
A method for degassing a friction material thermoforming process, characterized in that the material is discharged to the outside of the thermoforming mold through a degassing passage opening to the inner surface of the middle mold.

(2) The pressing die and the pressure die have a central portion as a split die, and the split die is made of beryllium copper alloy.
The degassing method in the friction material thermoforming process according to (1) above, wherein the other die body portion is made of hot work tool steel. (3) The degassing method in the friction material thermoforming process according to (1) or (2), characterized in that a heater is built in the split mold of the central portion. (4) Any of the above (1) to (3), characterized in that a member for forming a gas vent passage is incorporated in the middle mold, and this member is made of a material having a thermal conductivity smaller than that of the preform. 2. A method of degassing a friction material thermoforming process according to item 1.

That is, the essence of the present invention is that in the method of manufacturing a friction material, thermoforming having both means for controlling the position of the final hardened portion to collect gas and means for removing the gas collected in the final hardened portion. It is to thermoform a preform of the friction material using a die.

In the normal thermoforming process, the temperature distribution of the friction material is high at the outer periphery and low at the inner portion as shown in FIG. Usually, the friction material is integrally formed with an iron plate called a pressure plate (P / P). P / P absorbs heat from the mold and delays heat conduction to the friction material. Therefore, the lowest temperature part is slightly closer to the upper mold side from the center of the friction material. The coldest parts are voided because the organic binder is the last to cure. Therefore, the gas moves and collects in the “part where the organic binder is finally cured” (hereinafter, referred to as “final curing part”). When the press pressure is released in this state, the high-pressure gas in the final hardening portion expands. As a result, the surrounding hardened part is destroyed and cracks occur, resulting in defective molding. Since the temperature distribution shown in FIG. 6 is obtained in normal thermoforming, cracks are generated in a portion having a thickness of about 2/3 of the friction material. From the above, it is understood that defective gas can be prevented by promptly releasing the gas from the final cured part.

Therefore, in the present invention, the principle that "gas generated in the thermoforming process is collected in the final hardening portion" is utilized.
That is, the point of the present invention is a degassing method in a thermoforming method that is configured by "controlling the position of the final cured portion and collecting and degassing gas." In short, the present invention uses the following two means. 1) A means for collecting the gas by controlling the position of the final curing part. 2) A means for removing the gas collected in the final curing section.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The degassing method in the thermoforming process of the friction material of the present invention will be described in detail with reference to FIGS. The components having the same functions as those shown in FIG. 6 are designated by the same reference numerals. Each of the above-mentioned two means will be described in detail below.

1) Means for collecting gas by controlling the position of the final hardened part The amount of heat given from the mold to the friction material is made different so that the gas is collected at the lowest temperature. By controlling the temperature distribution of the friction material as shown in FIG. 1, the final hardened portion can be located on the side surface of the friction material. Since the gas collects on the side surface of the friction material, a gas venting mechanism is provided on the inner surface of the middle die to vent the gas. In order to obtain the temperature distribution as shown in FIG. 1, the following methods may be combined and used. The temperature of the pressing die (upper die) 4 and the temperature of the pressure die (lower die) 5 are set high, and the temperature of the middle die 3 is set low.・ The upper mold 4 and the lower mold 5 are made of a material having high thermal conductivity, and the middle mold 3 is used.
Use a material with low thermal conductivity. -A porous material is used for the middle mold 3 to reduce the contact area with the friction material 2 and reduce heat conduction. The portion of the upper die 4 and the lower die 5 that is in contact with the center of the friction material 2 is the split die 8, and the split die 8 is made of a material having a high thermal conductivity. A heater 9 is built in the split mold 8 to raise the temperature of the split mold 8 to 10 to 100 ° C. higher than the temperature of the parts other than the split mold 8.

2) Means for degassing from the final hardened part The gas is collected on the side surface of the friction material 2 by the above means, and the degassing mechanism 11 is provided on the inner side surface of the middle mold 3 to degas the gas. That is,
A gas vent passage 10 such as a gas vent hole or a gas vent groove 10A is provided on the inner surface of the middle die 3 to exhaust gas to the outside of the molding die. In addition, a decompression suction device may be connected to the gas venting mechanism 11 to forcibly vent the generated gas. Examples of the structure of the degassing mechanism 11 are shown in FIGS. FIG. 2 shows a gas vent groove 10A in the shape of a lateral groove provided on the inner surface of the middle mold 3 and is connected to a gas vent path 10 communicating with the outside of the mold. FIG. 3 shows a gas vent groove 10B in the shape of a zigzag groove. It is connected to the gas vent passage 10 communicating with the outside of the mold.
It is explanatory drawing which provided only several places in the inside mold, (a) is a horizontal sectional view of a middle mold, (b) is a longitudinal sectional view of a shaping die.

Here, the thermal conductivity of the degassing mechanism must be equal to or less than that of the friction material. This is because when the thermal conductivity of the degassing mechanism 11 is higher than that of the friction material 2, the organic binder around the degassing mechanism 11 is hardened first. As a result, the periphery of the gas venting mechanism 11 becomes dense and gas venting is hindered. When the thermal conductivity of the degassing mechanism 11 is made equal to or lower than that of the friction material 2, the organic binder around the degassing mechanism 11 is cured last. Then,
A void can be secured around the degassing mechanism 11 in the thermoforming process,
Can easily escape gas.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. However, the present invention is not limited to this embodiment.

Examples 1 and 2 and Comparative Examples 1 to 10 FIG. 5 shows the structure of the mold used in the examples. The features of the mold are described below. (Molding die) ・ The part of the upper die and the lower die that hits the center of the friction material is a split die. Beryllium copper alloy (thermal conductivity: 174W
/ MK) was used. A heater was embedded inside the split mold. -A zigzag-shaped gas vent groove was provided on the inner surface of the middle mold.・ For members other than the split mold and the gas vent groove, hot tool steel (SK
D61, thermal conductivity: 74 W / mK) was used.

(Medium-sized) Medium-sized having different thermal conductivity of the degassing mechanism was manufactured by using various materials. In the examples, the material of the degassing mechanism was made of fiber reinforced plastic (FRP). Plastic: Polyimide resin. Reinforcing fibers: carbon fiber, glass fiber. Filler: barium sulfate, calcium carbonate, magnesia. Venting grooves with different thermal conductivity were prepared by changing the type and amount of filler and reinforcing fiber mixed in plastic. -In Example 1, the gas venting mechanism used was a gas venting channel constituent member made of FRP having a thermal conductivity of 1 W / mK. -In Example 2, the gas venting mechanism was made of FRP having a thermal conductivity of 5 W / mK. -Comparative example 1 has a gas venting mechanism with S having a larger thermal conductivity than a semi-metallic friction material (thermal conductivity: 12 W / mK).
It was made of a gas vent passage constituent member made of US304 (heat conductivity: 15 W / mK). -Comparative example 2 used a conventional medium type without a degassing mechanism. This middle mold was used in combination with the upper mold / lower mold prepared in the above process and the conventional upper mold / lower mold (having no split mold).

(Friction Material) Table 1 shows the composition of the friction material used.

[0021]

[Table 1]

The friction material agitated product was placed in a preforming mold and pressure-molded at room temperature under a pressure of 40 MPa to prepare a preform. The preform was placed in a thermoforming mold to perform thermoforming.
The molding conditions were set to the two conditions described below. (Figures in parentheses are molding time for semi-metallic compound) (1) Conventional molding conditions: upper mold temperature 155 ° C, lower mold temperature 1
55 ° C, molding time 420 seconds (410 seconds). (2) High temperature and short time molding conditions: Upper mold temperature 175 ° C,
(Temperature of split mold: 210 ° C.), lower mold temperature 175 ° C., molding time 90 seconds (75 seconds). -Comparative Examples 3 to 6 are examples in which the above-mentioned middle mold and the conventional upper mold and lower mold are combined and thermoformed under the molding condition (2). -Comparative examples 7 to 10 are examples in which the above-mentioned middle mold and the conventional upper mold and lower mold are combined and thermoformed under molding condition (1).

(Inspection Result of Molded Product) After the thermoforming, an appearance inspection and a tapping sound inspection were performed to compare the defective molding rate. The test results are shown in Table 2 as experimental results.

[0024]

[Table 2]

[0025]

[Table 3]

Under the molding conditions of high temperature and short time, the molding die provided with the split mold had less molding defects. In particular, when a gas venting mechanism was provided and the thermal conductivity thereof was smaller than that of the friction material, no molding failure occurred. According to the present invention, it becomes possible to significantly shorten the molding time and mold with a high yield.

[0027]

According to the present invention, the central portion of the presser die and the pressurizing die is made of a material having a higher thermal conductivity than the other portions, and the final cured portion at the time of thermoforming is set to the middle die. I was able to concentrate on the side that touches. As a result, the gas generated from the thermoformed product can be discharged to the outside from the final curing section through the medium-sized gas vent passage, preventing defective molding such as cracks and blisters caused by insufficient degassing during the thermoforming process. Then
Product yield can be improved. Further, the molding can be performed at a high temperature in a short time, and the manufacturing cost can be reduced.

[Brief description of drawings]

1A and 1B are diagrams illustrating a position control method of a final curing portion according to the present invention, in which FIG. 1A is a top view of a presser die, FIG. 1B is a longitudinal sectional view thereof, and FIG. Is.

2A and 2B are explanatory views of a molding die in which a horizontal groove is provided as a degassing groove in a middle die, FIG. 2A is a plan view, and FIG. 2B is a longitudinal sectional explanatory view.

3A and 3B are explanatory views of a molding die in which a zigzag groove is provided as a gas vent groove in the middle die, FIG. 3A is a plan view of a middle die portion, and FIG.

4A and 4B are explanatory views of a molding die in which a gas vent hole is provided as a gas vent groove in a middle die, FIG. 4A is a plan view of a middle die portion, and FIG.

FIG. 5 is an explanatory view of a molding die used in Examples,
(A) is a top view, (b) is a longitudinal sectional view, and (c) is a top view.

FIG. 6 is a vertical cross-sectional view illustrating a temperature distribution of a friction material in a conventional thermoforming process.

[Explanation of symbols]

1 Pressure plate (P / P) 2 Preform of friction material 3 medium 3A Medium size (low thermal conductivity, porous) 3B Medium size (high thermal conductivity) 4 Presser type (upper type) 5 Pressurized type (lower type) 6 Final curing part 7 hot plate 8 division type 9 heater 10 degassing path 10A degassing groove 10B Zigzag groove 11 Degassing path component (gas venting mechanism) 12 cracks

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Katsuo Arai             Saitama Prefecture Hanyu City East 5-4-71 Co., Ltd.             Akebono Brake Central Technology Research Institute (72) Inventor Satoshi Kusaka             Saitama Prefecture Hanyu City East 5-4-71 Co., Ltd.             Akebono Brake Central Technology Research Institute (72) Inventor Kurihara             Saitama Prefecture Hanyu City East 5-4-71 Co., Ltd.             Akebono Brake Central Technology Research Institute (72) Inventor Koichi Miyagi             Akebonobu 19-5 Koamimachi, Nihonbashi, Chuo-ku, Tokyo             Rake Industry Co., Ltd. F term (reference) 3J058 BA61 FA01 FA11 FA21 FA31                       FA35 GA20 GA28 GA33 GA37                       GA55 GA64 GA87 GA92 GA93                 4F202 AC03 AE08 AH81 AJ12 AK09                       CA17 CB01 CK42 CN01 CN18                       CP05                 4F204 AA37 AB07 AB11 AB16 AE08                       AH05 AH17 AJ02 AJ12 FA01                       FB01 FF01 FN12 FN15

Claims (4)

[Claims] 1. A method of manufacturing a friction material in which a preform of a friction material is thermoformed using a die for thermoforming a friction material, which comprises a holding die, a medium die and a pressure die, and a center portion of the holding die and the pressure die is formed. It is made of a material with higher thermal conductivity than other parts, and the heat that the preform lastly hardens during thermoforming is concentrated so that it concentrates on the side that contacts the middle mold, and the gas generated from the preform by thermoforming Is discharged to the outside of the thermoforming mold from a position in contact with the final cured portion of the preform through a gas vent passage opening to the inner surface of the middle mold. 2. The pressing die and the pressurizing die have a central portion as a split die, the split die is made of beryllium copper alloy, and the other die main body is made of hot work tool steel. The degassing method in the friction material thermoforming process according to claim 1. 3. The degassing method in the friction material thermoforming process according to claim 1, wherein a heater is built in the split mold of the central portion. 4. A member for forming a gas vent passage is incorporated in a middle mold, and this member is made of a material having a thermal conductivity smaller than that of the preform. A method of degassing a friction material thermoforming process according to item 1.