Method for improving braking performance of microporous friction materials under wet conditions

Abstract

The invention relates to a method for improving braking performance of a microporous friction material under wet conditions. A hydrophobic agent is added into the components for preparing microporous friction material. The microporous friction material is prepared from the following raw materials in percentage by weight: 10%-20% of nano-silica modified phenolic resin, 4%-14% of butadiene-styrene rubber, 5%-15% of glass fiber, 2%-11% of aramid pulp, 4%-15% of aluminum borate whisker, 4%-10% of hydrophobic agent and 3%-8% of calcium silicate, 1%-8% of artificial graphite, 2%-8% of coke, 2%-7% of mica, 5%-10% of cryolite and 4%-10% of diatomite.

Claims

1. A method for improving braking performance of a microporous friction material under wet conditions, wherein a hydrophobic agent is added into components for preparing the microporous friction material, comprising the following steps: step 1, preparation of raw materials, including the following components and weight percentage: 10%-20% of nano-silica modified phenolic resin, 4%-14% of butadiene-styrene rubber, 5%-15% of glass fibre, 2%-11% of aramid pulp, 4%-15% of aluminum borate whisker, 4%-10% of hydrophobic agent, 3%-8% of calcium silicate, 1%-8% of artificial graphite, 2%-8% of coke, 2%-7% of mica, 5%-10% of cryolite, and 4%-10% of diatomite, wherein the hydrophobic agent comprises one or more of the following substances: paraffin, stearic acid or stearate, wherein the stearate includes magnesium stearate, calcium stearate, zinc stearate and iron stearate; step 2, preparation, including the following steps: adding the above components into a high-speed rake mixer and mixing the components, a mixture is obtained, and placing a steel back and the mixture in a shaping mold for compression molding, a blank is obtained; and the blank is put into an oven to be heated and cured, and machining is carried out to obtain a brake shoe, wherein during the compression molding, a mold temperature is 60-100° C., a molding pressure is 20-30 MPa, air is deflated 5-10 times within 10 min, and then the molding pressure is kept for 15-25 min, wherein conditions for the heating and the curing are: putting the blank in the oven for programmed heating and curing heat treatment, wherein a heating time of every two intervals is 60 min, wherein a specific curing temperature and a specific curing time are: the curing time is 2-3 h when the curing temperature is 200° C., the curing time is 2-3 h when the curing temperature is 220° C., the curing time is 3.5-4 h when the curing temperature is 240° C., the curing time is 3-4 h when the curing temperature is 260° C., the curing time is 1-2 h when the curing temperature is 280° C., and the curing time is 5-6 h when the curing temperature is 300° C., wherein during the curing of the microporous brake shoe and formation of micropores, the hydrophobic agent is heated and melted, molecules of the hydrophobic agent gradually migrate to an inner wall of the micropores by using a principle of surface tension, and a uniform, dense and stable film is formed on the inner wall of the micropores, so that a macroscopic surface of the microporous friction material has no capillary phenomenon and shows hydrophobic characteristics, wherein a friction coefficient of the microporous friction material under wet conditions is more than 0.30.

2. The method for improving the braking performance of the microporous friction material under wet conditions according to claim 1, wherein a particle size of the cryolite is 200-300 mesh.

3. The method for improving the braking performance of the microporous friction material under wet conditions according to claim 1, wherein a particle size of the artificial graphite is 20-60 mesh.

4. The method for improving the braking performance of the microporous friction material under wet conditions according to claim 1, wherein the components are added into the high-speed rake mixer according to a certain proportion, and a rotating speed is 2500 r/min, and a mixing time is 25-40 min.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIGURE is a graph of instantaneous friction coefficient-velocity curve of the brake shoe in the first embodiment of the present invention. When the brake shoe thrust is 22 kN and the brake shoe is in a stopping brake under wet conditions.

DESCRIPTION OF THE EMBODIMENTS

(2) The present invention is described in detail below with reference to attached drawings and specific embodiments.

Embodiment 1

(3) A method for improving a braking performance of a microporous friction material under wet conditions, wherein a hydrophobic agent is added into components for preparing the microporous friction material, specifically comprising the following steps.

(4) (1) Preparation of raw materials, including the following components and weight percentage: 10% of nano-silica modified phenolic resin, 10% of butadiene-styrene rubber, 12% of glass fibre, 2% of aramid pulp, 9% of aluminum borate whisker, 10% of hydrophobic agent, 8% of calcium silicate, 8% of artificial graphite, 8% of coke, 7% of mica, 6% of cryolite, and 10% of diatomite.

(5) (2) Preparation

(6) Adding the above components into a high-speed rake mixer and mixing the components, a mixture is obtained, and placing a steel back and the mixture in a shaping mold for compression molding, a blank is obtained; and the blank is put into an oven to be heated and cured, and machining is carried out to obtain a brake shoe.

(7) Mixing: The components are added into the high-speed rake mixer according to a certain proportion, and a rotating speed is 2500 r/min, and a mixing time is 25 min;

(8) Pressing: Placing the mixture and steel back in a shaping mold for compression molding, wherein during the compression molding, a mold temperature is 60° C., a molding pressure is 20 MPa, air is deflated 5 times within 10 min, and then the molding pressure is kept for 15 min.

(9) Curing heat treatment: Putting the blank in an oven for programmed heating and curing heat treatment, wherein the heating time of every two intervals is 60 min. See Table 1 below for specific methods.

(10) TABLE-US-00001 TABLE 1 Curing temperature and curing time of brake shoes Curing temperature/° C. Curing time/h 200 2 220 2 240 3.5 260 4 280 2 300 5

Embodiment 2

(11) A method for improving a braking performance of a microporous friction material under wet conditions, wherein a hydrophobic agent is added into components for preparing the microporous friction material, specifically comprising the following steps.

(12) (1) Preparation of raw materials, including the following components and weight percentage: 16% of nano-silica modified phenolic resin, 12% of butadiene-styrene rubber, 15% of glass fibre, 11% of aramid pulp, 15% of aluminum borate whisker, 4% of hydrophobic agent, 3% of calcium silicate, 7% of artificial graphite, 2% of coke, 6% of mica, 5% of cryolite, and 4% of diatomite.

(13) (2) Preparation

(14) Adding the above components into a high-speed rake mixer and mixing the components, a mixture is obtained, and placing a steel back and the mixture in a shaping mold for compression molding, a blank is obtained; and the blank is put into an oven to be heated and cured, and machining is carried out to obtain a brake shoe.

(15) Mixing: The components are added into the high-speed rake mixer according to a certain proportion, and a rotating speed is 2500 r/min, and a mixing time is 30 min;

(16) Pressing: Placing the mixture and steel back in a shaping mold for compression molding, wherein during the compression molding, a mold temperature is 80° C., a molding pressure is 25 MPa, air is deflated 10 times within 10 min, and then the molding pressure is kept for 20 min.

(17) Curing heat treatment: Putting the blank in an oven for programmed heating and curing heat treatment, wherein the heating time of every two intervals is 60 min. See Table 2 below for specific methods.

(18) TABLE-US-00002 TABLE 2 Curing temperature and curing time of brake shoes Curing temperature/° C. Curing time/h 200 2.5 220 2.5 240 3.5 260 4 280 2 300 5

Embodiment 3

(19) A method for improving a braking performance of a microporous friction material under wet conditions, wherein a hydrophobic agent is added into components for preparing the microporous friction material, specifically comprising the following steps.

(20) Preparation of raw materials, including the following components and weight percentage: 18% of nano-silica modified phenolic resin, 14% of butadiene-styrene rubber, 5% of glass fibre, 9% of aramid pulp, 4% of aluminum borate whisker, 9% of hydrophobic agent, 7% of calcium silicate, 6% of artificial graphite, 6% of coke, 6% of mica, 9% of cryolite, and 7% of diatomite.

(21) (2) Preparation

(22) Adding the above components into a high-speed rake mixer and mixing the components, a mixture is obtained, and placing a steel back and the mixture in a shaping mold for compression molding, a blank is obtained; and the blank is put into an oven to be heated and cured, and machining is carried out to obtain a brake shoe.

(23) Mixing: The components are added into the high-speed rake mixer according to a certain proportion, and a rotating speed is 2500 r/min, and a mixing time is 35 min;

(24) Pressing: Placing the mixture and steel back in a shaping mold for compression molding, wherein during the compression molding, a mold temperature is 100° C., a molding pressure is 30 MPa, air is deflated 7 times within 10 min, and then the molding pressure is kept for 25 min.

(25) Curing heat treatment: Putting the blank in an oven for programmed heating and curing heat treatment, wherein the heating time of every two intervals is 60 min. See Table 3 below for specific methods.

(26) TABLE-US-00003 TABLE 3 Curing temperature and curing time of brake shoes Curing temperature/° C. Curing time/h 200 3 220 2.5 240 4 260 3 280 1 300 6

Embodiment 4

(27) A method for improving a braking performance of a microporous friction material under wet conditions, wherein a hydrophobic agent is added into components for preparing the microporous friction material, specifically comprising the following steps.

(28) Preparation of raw materials, including the following components and weight percentage: 20% of nano-silica modified phenolic resin, 4% of butadiene-styrene rubber, 13% of glass fibre, 8% of aramid pulp, 12% of aluminum borate whisker, 8% of hydrophobic agent, 6% of calcium silicate, 1% of artificial graphite, 7% of coke, 2% of mica, 10% of cryolite, and 9% of diatomite.

(29) (2) Preparation

(30) Adding the above components into a high-speed rake mixer and mixing the components, a mixture is obtained, and placing a steel back and the mixture in a shaping mold for compression molding, a blank is obtained; and the blank is put into an oven to be heated and cured, and machining is carried out to obtain a brake shoe.

(31) Mixing: The components are added into the high-speed rake mixer according to a certain proportion, and a rotating speed is 2500 r/min, and a mixing time is 40 min;

(32) Pressing: Placing the mixture and steel back in a shaping mold for compression molding, wherein during the compression molding, a mold temperature is 90° C., a molding pressure is 28 MPa, air is deflated 8 times within 10 min, and then the molding pressure is kept for 22 min.

(33) Curing heat treatment: Putting the blank in an oven for programmed heating and curing heat treatment, wherein the heating time of every two intervals is 60 min. See Table 4 below for specific methods.

(34) TABLE-US-00004 TABLE 4 Curing temperature and curing time of brake shoes Curing temperature/° C. Curing time/h 200 2 220 3 240 4 260 3.5 280 1.5 300 5.5

(35) No hydrophobic agent is added, the rest of the formula composition and production process are completely the same as those in the embodiment 1, and the prepared brake shoe is denoted as X. According to CZJS/T 0013-2016 technical specification for composite brake shoes for urban rail vehicles, the physical and chemical properties of the brake shoe prepared in the embodiment and the brake shoe X are tested, and the results are shown in Table 5.

(36) TABLE-US-00005 TABLE 5 physical performance test data of brake shoes Embodi- Embodi- Embodi- Embodi- ment 1 ment 2 ment 3 ment 4 X Density 1.40 1.43 1.45 1.50 1.60 (g/cm.sup.3) Hardness 55 58 60 70 85 (HRR) Impact strength 2.0 2.5 2.8 3.0 1.8 (kJ/m.sup.2) compressive 50 55 60 70 62 strength (MPa) Compression 640 680 700 750 850 modulus (MPa)

(37) The physical and chemical properties of the brake shoe prepared in the embodiment completely meet the standard requirements.

(38) For the brake shoe prepared in the embodiment and the brake shoe X, the friction performances of the brake shoe are tested by using the scale bench MM-1000, and the results are shown in Table 6.

(39) TABLE-US-00006 TABLE 6 MM-1000 test data of the brake shoe Friction coefficient under wet conditions Test item Embodi- Embodi- Embodi- Embodi- Speed/km/h ment 1 ment 2 ment 3 ment 4 X 20 0.308 0.300 0.316 0.301 0.240 40 0.303 0.316 0.315 0.307 0.264 60 0.309 0.318 0.312 0.310 0.240 80 0.311 0.320 0.318 0.317 0.234 100 0.319 0.323 0.320 0.325 0.230 Average 0.310 0.315 0.316 0.312 0.242 friction coefficient Average 90 91 90 92 76 stability coefficient/% Average 0.04 0.05 0.06 0.07 0.13 wear rate/cm.sup.3/MJ

(40) From Table 6, it can be seen that the friction coefficient of the brake shoe prepared in the embodiment does not decrease with the increase of speed under wet conditions, but can still be kept above 0.30, and the stability coefficient can reach above 90%.

(41) Referring to CZJS/T 0013-2016 technical specification for composite brake shoes for urban rail vehicles, a 1:1 bench test is conducted in the Product Quality Supervision and Inspection Center of the Ministry of Railways, and the friction and wear performance test is conducted. The test results are shown in Tables 7-1 and 7-2.

(42) TABLE-US-00007 TABLE 7-1 The 1:1 bench test data of the brake shoe Test result Test condition Initial Maximum Braking Brake shoe Braking Braking Average tread tread Serial Inspection speed pressure distance time friction temperature temperature number item (km/h) (kN) (m) (s) coefficient/ (° C.) (° C.) 1 Primary 20 22 17.9 8.0 0.321 27.6 31.9 parking 40 67.3 14.8 0.341 28.8 49.8 brake 60 158.5 20.0 0.326 37.0 79.6 under dry 80 309.7 27.6 0.350 33.0 126.9 conditions 80 296.9 28.1 0.359 21.4 121.5 60 144.4 19.0 0.358 34.8 97.4 40 62.8 12.2 0.366 35.7 68.7 20 17.2 8.6 0.334 37.3 43.5 2 Dry state 20 44 9.1 6.7 0.318 22.3 35.0 of primary 40 33.3 9.2 0.347 24.6 83.1 parking 60 80.0 12.6 0.325 26.8 176.7 brake 80 152.2 15.9 0.335 32.7 146.4 80 157.6 17.8 0.330 15.6 162.7 60 84.5 12.5 0.307 32.7 148.6 40 36.4 10.0 0.317 28.7 56.5 20 9.1 6.7 0.318 36.2 42.1 3 Simulated 80 33 235.9 21.4 0.261 17.3 71.4 operation 80 230.9 21.1 0.265 34.6 143.3 test 80 224.3 21.0 0.273 57.5 171.3 under dry 80 214.9 21.9 0.285 71.2 191.8 conditions 80 217.8 20.8 0.282 79.4 233.5 80 223.1 21.8 0.275 103.4 250.5 80 225.7 21.3 0.272 104.5 245.6 80 222.5 21.6 0.276 126.6 235.3 80 218.0 20.8 0.281 131.8 265.3 80 221.2 21.7 0.277 141.0 255.9 80 211.6 20.7 0.290 145.0 265.5 80 219.1 20.7 0.280 151.7 276.0 80 209.6 20.5 0.293 157.3 275.5 80 219.6 21.0 0.279 161.4 280.0 80 213.1 20.0 0.288 164.1 275.2 80 210.6 19.6 0.291 144.2 276.8 80 205.9 19.7 0.298 163.1 274.6 80 206.0 19.6 0.298 169.5 277.0 80 205.3 19.5 0.299 174.7 275.6 80 214.4 21.2 0.286 171.5 280.5 Remarks: Parking interval 120 s in the “Simulated operation test under dry conditions”

(43) TABLE-US-00008 TABLE 7-2 The 1:1 bench test data of the brake shoe Serial Inspection numb item Test condition Test result 4 Static Brake shoe average value 0.548 friction test pressure 5.0 kN Braking Brake shoe Braking Braking Average Initial tread Maximum tread speed pressure distance time friction temperature temperature (km/h) (kN) (m) (s) coefficient/ (° C.) (° C.) 5 Primary 20 22 19.5 8.2 0.294 16.7 20.5 parking 40 76.7 14.6 0.299 17.5 31.4 brake 60 171.0 21.0 0.301 22.2 53.6 under wet 80 305.0 27.6 0.300 26.0 94.6 conditions 80 296.8 27 2 0.309 32.6 108.1 60 164.4 21.2 0.314 39.2 86.6 40 75.6 15.1 0.303 43.6 67.6 20 18.8 8.1 0.305 43.2 49.9 6 Wear of parking brake under 1.2 g the brake dry conditions shoe simulated operation test 7.2 g under dry conditions parking brake under 0.5 g wet conditions Remarks: average sprinkling amount 14 L/h in the “Primary parking brake under wet conditions”

(44) The friction coefficient of the brake shoe is relatively stable and there is no thermal decay phenomenon under different pressures of stopping brake and simulated operation test under dry conditions. Under wet conditions, the friction coefficient does not decrease, the average friction coefficient remained above 0.30, and the stability is high. During the whole test process, the brake shoe does not appear peeling, falling block and metal inlaying, and the brake is noiseless and less worn. The dual wheel tread is smooth without cracks.

(45) FIGURE is a graph of instantaneous friction coefficient-velocity curve of the brake shoe in the first embodiment of the present invention. When the brake shoe thrust is 22 kN and the brake shoe is in a stopping brake under wet conditions.

(46) According to the invention, the hydrophobic agent is added to carry out hydrophobic treatment on the inner wall of the microporous material, so that the friction coefficient of the microporous material under wet conditions does not decrease, and the microporous material has a high friction coefficient. By adopting the technology of the invention, the friction coefficient under wet conditions can be kept above 0.30 whether it is on a MM-1000 scale bench test or a 1:1 bench test, and the stability of the friction coefficient is higher, which can reach above 90% on the MM-1000 tester. The wear rate of materials is lower and the service life is longer.

(47) The above description of the embodiments is for the convenience of ordinary technicians in the technical field to understand and use the invention. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative labor. Therefore, the present invention is not limited to the above-mentioned embodiments, and the improvements and modifications made by those skilled in the art according to the disclosure of the present invention without departing from the scope of the present invention should be within the scope of the present invention.