CN114672132B - High-performance copper-free resin-based braking material prepared from coal ash hollow microspheres - Google Patents

Abstract

The invention discloses a high-performance copper-free resin-based braking material prepared from fly ash hollow microspheres, which is prepared from the following raw materials in parts by weight: 10-20 parts of coal ash hollow microsphere, 10-20 parts of cashew nut shell oil modified phenolic resin, 5-10 parts of coconut fiber, 10-20 parts of alumina, 3 parts of graphite, 5 parts of rubber powder and 22-47 parts of barium sulfate powder. The invention uses the coal ash hollow microspheres to replace copper which is harmful to the environment and has higher cost in the braking material, thereby improving the friction performance of the braking material and simultaneously effectively reducing the cost of the braking material. The braking material does not contain heavy metal components such as copper, lead, zinc, antimony and the like, has excellent friction and wear properties, and solves the problem of poor high-temperature tribological properties of the copper-free braking material.

Description

A high-performance copper-free resin-based brake material prepared using fly ash hollow microspheres

Technical Field

The invention relates to the field of brake materials, and in particular applies fly ash hollow microspheres to brake materials to prepare a high-performance, copper-free and environment-friendly brake material.

Background Art

In the research on fly ash utilization, people found that the fly ash in thermal power plants contains 50-80% hollow glass microspheres, whose main components are silicon dioxide and aluminum oxide, which are fired at high temperature and have a diameter of 5-1000 microns. They are a loose, fluid inorganic non-metallic powder material. Hollow microspheres have sound insulation, heat insulation, low density, high temperature resistance, wear resistance and high compressive strength. They can be used as high-quality fillers for thermal insulation coatings, adhesives, engineering plastics, modified rubber, electrical insulation parts, fiberglass and other products.

With the rapid development of global industry and the enhancement of people's environmental awareness, the requirements for brake materials (brake pads) are also increasing. They are not only required to be safe and comfortable, but also environmentally friendly. The demand for high-performance friction materials is also more urgent. However, in recent years, people have found that the particles formed in the use of brake materials contain certain heavy metal elements, such as copper, lead, zinc, antimony, etc., and particles with a particle size of less than 10μm can be inhaled by the human body, thereby causing diseases and threatening the health of humans, animals and plants. Related studies have shown that copper-containing wear debris generated by braking is one of the sources of copper in the main runoff of highway rainwater. Copper can cause rapid death of aquatic organisms due to its neurobehavioral toxicity. Harmful particles generated by braking have become an increasingly serious environmental problem. In 2014, Washington State in the United States first passed a bill to restrict the use of copper powder and other harmful substances in brake materials, requiring that the copper content in brake materials be less than 5wt% in 2021 and less than 0.5wt% in 2023. Countries around the world have also gradually begun to restrict the use of copper in brake materials. Therefore, seeking alternative materials for copper in brake materials has become an urgent research topic in the current friction material industry.

Resin-based friction materials have the advantages of low cost, simple production process, wide application, and easy performance adjustment. They are currently the most widely used automotive brake materials. Copper has excellent thermal conductivity and plays a vital role in the high-temperature tribological properties of resin-based brake materials. For example, copper has excellent thermal conductivity and can effectively conduct the high temperature of the friction surface, so that the thermal decay resistance of the brake material can be improved; copper can play the role of high-temperature solid lubrication and reduce braking noise. For example, in patents CN112745802A and CN107461436A, single-layer thermally modified synthetic graphite and aluminum fiber are used in combination with other ingredients to replace copper powder, respectively, in an attempt to quickly conduct the friction heat during braking and reduce the occurrence of thermal decay; patent CN109929511B reduces the wear rate of friction materials by adding artificial graphite, aluminum alloy fiber, etc.; patent CN109931350A uses the friction synergy between graphene, aramid and zinc powder during braking to form a graphene-enhanced friction transfer film on the surface to replace copper and improve the wear resistance of the material. The high temperature friction performance of the copper-free brake materials obtained in the above research is inferior to that of copper-containing materials.

As mentioned above, the main components of fly ash hollow microspheres, waste materials from thermal power plants, are silicon dioxide and aluminum oxide, which are fired at high temperatures and have the characteristics of sound insulation, heat insulation, low density, high temperature resistance, and wear resistance. Using them to prepare resin-based brake materials can not only achieve high-value-added recycling of fly ash hollow microspheres, but also realize copper-free brake materials, which is of great significance to the green and sustainable development of my country's brake material industry.

Summary of the invention

In response to the above problems, this patent uses fly ash hollow microspheres as functional fillers in brake materials to replace the role of copper powder in brake materials. By studying the content of fly ash hollow microspheres and their interaction with resin and reinforcing fibers, a high-performance, copper-free, environmentally friendly brake material is prepared with excellent friction and wear properties. The friction coefficient is 0.55~0.65, and the high temperature friction coefficient of 350℃ is higher than the low temperature friction coefficient (100℃), which solves the problem of poor high temperature tribological performance of copper-free brake materials.

To achieve the above object, the present invention adopts the following technical solution:

The first aspect of the present invention provides a high-performance copper-free brake material prepared from fly ash hollow microspheres, comprising the following components: fly ash hollow microspheres, cashew nut shell oil-modified phenolic resin, coconut shell fiber, alumina, graphite, rubber powder, and barium sulfate.

Furthermore, the proportions of the raw materials are as follows, by weight: 10 to 20 parts of fly ash hollow microspheres, 10 to 20 parts of cashew nut shell oil-modified phenolic resin, 5 to 10 parts of coconut shell fiber, 10 to 20 parts of alumina, 3 parts of graphite, 5 parts of rubber powder, and 22 to 47 parts of barium sulfate powder.

Furthermore, the fly ash hollow microspheres are hollow microspheres in fly ash, a waste material of a thermal power plant, and have a mesh size of 60 to 200 meshes.

Furthermore, the coconut shell fiber is chopped coconut shell fiber with a length of less than 10 mm.

Furthermore, the cashew nut shell oil-modified phenolic resin is a cashew nut shell oil-modified phenolic resin produced by Jiangsu Nantong Sumitomo Bakelite Co., Ltd. or Shandong Laiwu Runda New Materials Co., Ltd., or a cashew nut shell oil-modified phenolic resin PF-221 produced by Huantai County Yonghui Chemical Co., Ltd.

In a second aspect of the present invention, the high-performance copper-free resin-based brake material provided does not contain heavy metal components such as copper, lead, zinc, antimony, etc.

In a third aspect of the present invention, the high-performance copper-free resin-based brake material provided has the following properties:

1) The friction coefficient is 0.55~0.65;

2) The friction coefficient at 350°C is not less than that at 100°C;

3) Wear rate is 0~1.0×10 ^-7 cm ³ /(N•m).

A fourth aspect of the present invention provides a method for preparing a high-performance copper-free brake material using fly ash hollow microspheres, comprising the following steps:

1) Fiber chopping: Coconut shell fiber is cut by a fiber cutting machine to obtain coconut shell fiber with a length of less than 10 mm.

2) Drying of raw materials: Cashew nut shell oil modified phenolic resin is dried at 50-60°C for 0.5 hour, coconut shell fiber is dried at 100-120°C for 1.5 hours, rubber powder is dried at 80-100°C for 0.5 hour, and other components (fly ash hollow microspheres, alumina, graphite, barium sulfate powder) are dried at 100-120°C for 1 hour.

3) Mixing: The dried raw materials (except coconut shell fiber) are mixed according to the experimental design formula and put into a mixer with multiple sets of high-speed rotary knives for 3 to 5 minutes. Then, the coconut shell fiber is put into the mixer and mixed for 1 to 2 minutes to obtain a uniform powdery mixture.

4) Hot pressing: Weigh the uniformly mixed mixture and perform hot pressing in a hydraulic press. The molding temperature is 165-170°C, the pressure is 25-35MPa, the pressure holding time is 6-8min, and the exhaust is performed 5-6 times during the process.

5) Heat treatment: The sample obtained by hot pressing is placed in an electric constant temperature forced air drying oven for heat treatment at 160° C. for 12 hours, and cooled in the oven to obtain the high-performance copper-free resin-based brake material.

The beneficial effects of the present invention are:

(1) The brake material does not contain heavy metal components such as copper, lead, zinc, and antimony, and has excellent friction and wear properties, especially outstanding thermal decay resistance. Specifically, the friction coefficient at 350°C is higher than the low-temperature friction coefficient (100°C), which solves the problem of poor high-temperature tribological performance of copper-free brake materials.

(2) The brake material uses fly ash hollow microbeads to replace the environmentally harmful and costly copper in the brake material, thereby improving the friction performance of the brake material while effectively reducing the cost of the brake material.

(3) The present invention makes efficient use of waste materials from thermal power plants and can provide a new approach for the high value-added recycling of fly ash. It is in line with the concept of green and sustainable development and has good application prospects and engineering application value.

(4) Adding fly ash hollow microspheres to friction materials can significantly improve the thermal stability of friction materials and increase the high-temperature friction coefficient of friction materials; cashew nut shell oil-modified phenolic resin can improve the shear strength and thermal decomposition temperature of the resin, and can effectively improve the wear resistance and mechanical properties of the sample; coconut shell fiber has the advantages of light weight, low cost, renewable and biodegradable. As a reinforcing fiber of friction materials, it can improve the friction and wear performance of materials; alumina, as a friction-increasing functional filler, can be added to brake materials to increase the medium and low temperature friction coefficient of friction materials; rubber powder, as an organic space filler, can be added to brake materials to help reduce the hardness and density of friction materials, stabilize the friction coefficient and reduce wear; barium sulfate, as an inorganic space filler, mainly functions to reduce the cost of brake materials; graphite, as a solid lubricant, can be added to friction materials to reduce the change of friction coefficient during braking, while stabilizing the friction coefficient and reducing the wear of the mating material.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a graph showing the thermal stability of fly ash hollow microspheres.

DETAILED DESCRIPTION

As introduced in the background technology section, copper tools play an important role in the high-temperature friction performance of resin-based brake materials. Fly ash hollow microspheres are mainly composed of silicon dioxide and aluminum oxide, and have the characteristics of sound insulation, heat insulation, low density, high temperature resistance, wear resistance, etc. Therefore, the present invention uses fly ash hollow microspheres to replace copper in brake materials, and obtains high-performance copper-free resin-based brake materials by studying the content of fly ash hollow microspheres and their interaction with resin and reinforcing fibers.

In order to more intuitively understand the thermal stability of fly ash hollow microspheres, TG/DSC was used to characterize the thermal stability of fly ash hollow microspheres, and the results are shown in Figure 1. As can be seen from Figure 1, the mass loss of fly ash hollow microsphere particles from room temperature to 1000°C in air atmosphere is only 1 wt%. It can be seen that fly ash hollow microspheres have good thermal stability, and adding them to friction materials can improve the thermal stability of friction materials.

The orthogonal optimization experiment was further used to optimize the component ratio of the brake material, analyze the synergistic effect between the components, and obtain the optimized formula of high-performance copper-free resin-based brake material. The orthogonal level table is shown in Table 1, and the effects of each component and its interaction on the friction coefficient of the brake material are shown in Table 2. In the low temperature stage (100-150℃), the fly ash hollow microsphere content has a highly significant effect on the friction coefficient of the sample; the resin content has a significant effect on the friction coefficient of the sample, and the effect is second only to the fly ash hollow microsphere; while the coconut shell fiber content, the interaction between the resin and the microspheres, and the interaction between alumina and the microspheres have a certain effect on the friction coefficient of the friction material. In the medium temperature stage (200-250℃), the best effect on improving the friction coefficient of the sample is alumina powder. At this stage, there is a large amount of alumina powder on the surface of the sample, which strengthens the plowing effect during the braking process and thus improves the friction coefficient of the material; the resin content, the interaction between the fly ash hollow microspheres and the resin have an effect on the friction coefficient of the sample; and the coconut shell fiber, the interaction between the fly ash hollow microspheres and the coconut shell fiber have a certain effect on the friction coefficient of the sample. At high temperature (300-350℃), the fly ash hollow microsphere content and resin content have the strongest influence on the friction coefficient of the sample; the interaction between the resin and microspheres has a significant effect on the friction coefficient of the sample; it is worth mentioning that at 300℃, the influence of alumina powder on the friction coefficient of the sample is equivalent to the effect of resin and microspheres; at 350℃, the fiber also has an effect on the friction coefficient of the sample, and the interaction between microspheres and coconut shell fibers has a certain influence on the friction coefficient. In general, it can be found that the factors that have a greater influence on the friction coefficient of the sample are mainly microspheres, resins and alumina.

Table 1 Orthogonal level table

Table 2 Effect of each component on friction coefficient

Note: *- has an impact, **- has a significant impact, ***- has a highly significant impact, △- has a certain impact, A×B- the interaction between the two

In order to enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present application is described in detail below with reference to specific examples. Preferably, according to the content of fly ash hollow microspheres and their interaction with resin and reinforcing fibers, the following preferred embodiments are obtained:

The coconut shell fiber is chopped to obtain fibers with a length of less than 10 mm; the cashew nut shell oil-modified phenolic resin is dried at 50-60° C. for 0.5 hour, the coconut shell fiber is dried at 100-120° C. for 1.5 hours, the rubber powder is dried at 80-100° C. for 0.5 hour, and the other components are dried at 100-120° C. for 1 hour; the dried raw materials (except the coconut shell fiber) are prepared according to the experimental design formula and put into a mixer with multiple sets of high-speed rotary knives for mixing for 3-5 minutes, and then the coconut shell fiber is put into the mixer for mixing for 1-2 minutes to obtain a uniform powdery mixed material; the uniformly mixed mixture is hot-pressed at a molding temperature of 165-170° C., a pressure of 25-35 MPa, a holding time of 6-8 minutes, and exhausting 5-6 times during the period; the sample obtained by hot pressing is placed in a heat treatment box for heat treatment at 160° C. for 12 hours, and cooled with the furnace to obtain the high-performance copper-free resin-based brake material.

Example 1

1) Composition of raw materials (by weight)

10 parts of fly ash hollow microspheres, 15 parts of cashew nut shell oil modified phenolic resin, 5 parts of coconut shell fiber, 20 parts of aluminum oxide, 3 parts of graphite, 5 parts of rubber powder, and 42 parts of barium sulfate powder.

2) Preparation method:

The coconut shell fiber is chopped to obtain fibers with a length of less than 10 mm; the phenolic resin is dried at 50°C for 0.5 hour, the coconut shell fiber is dried at 100°C for 1.5 hours, the rubber powder is dried at 80°C for 0.5 hour, and the other components are dried at 100°C for 1 hour; the dried raw materials (except the coconut shell fiber) are prepared according to the experimental design formula and put into a mixer with multiple sets of high-speed rotary knives for mixing for 3 minutes, and then the coconut shell fiber is put into the mixer and mixed for 1 minute to obtain a uniform powdery mixture; the uniformly mixed mixture is hot-pressed at a molding temperature of 165°C, a pressure of 25MPa, a holding time of 6min, and exhaust 5 times during the period; the sample obtained by hot pressing is placed in a heat treatment box for heat treatment at 160°C for 12 hours, and cooled with the furnace.

Example 2

1) Composition of raw materials (by weight)

15 parts of fly ash hollow microspheres, 15 parts of cashew nut shell oil modified phenolic resin, 5 parts of coconut shell fiber, 20 parts of aluminum oxide, 3 parts of graphite, 5 parts of rubber powder, and 37 parts of barium sulfate powder.

2) Preparation method:

The coconut shell fiber is chopped to obtain fibers with a length of less than 10 mm; the phenolic resin is dried at 55°C for 0.5 hour, the coconut shell fiber is dried at 110°C for 1.5 hours, the rubber powder is dried at 90°C for 0.5 hour, and the other components are dried at 110°C for 1 hour; the dried raw materials (except the coconut shell fiber) are prepared according to the experimental design formula and put into a mixer with multiple sets of high-speed rotary knives for mixing for 4 minutes, and then the coconut shell fiber is put into the mixer and mixed for 2 minutes to obtain a uniform powdery mixture; the uniformly mixed mixture is hot-pressed at a molding temperature of 170°C, a pressure of 30MPa, a holding time of 7min, and exhaust 6 times during the period; the sample obtained by hot pressing is placed in a heat treatment box for heat treatment at 160°C for 12 hours, and cooled with the furnace.

Example 3

1) Composition of raw materials (by weight)

20 parts of fly ash hollow microspheres, 15 parts of cashew nut shell oil modified phenolic resin, 10 parts of coconut shell fiber, 20 parts of aluminum oxide, 3 parts of graphite, 5 parts of rubber powder, and 27 parts of barium sulfate powder.

2) Preparation method:

The coconut shell fiber is chopped to obtain fibers with a length of less than 10 mm; the phenolic resin is dried at 60°C for 0.5 hour, the coconut shell fiber is dried at 120°C for 1.5 hours, the rubber powder is dried at 100°C for 0.5 hour, and the other components are dried at 120°C for 1 hour; the dried raw materials (except the coconut shell fiber) are prepared according to the experimental design formula and put into a mixer with multiple sets of high-speed rotary knives for mixing for 5 minutes, and then the coconut shell fiber is put into the mixer and mixed for 1 minute to obtain a uniform powdery mixture; the uniformly mixed mixture is hot-pressed at a molding temperature of 175°C, a pressure of 35MPa, a holding time of 8min, and exhaust 6 times during the period; the sample obtained by hot pressing is placed in a heat treatment box for heat treatment at 160°C for 12 hours, and cooled with the furnace.

Example 4

1) Composition of raw materials (by weight)

20 parts of fly ash hollow microspheres, 15 parts of cashew nut shell oil-modified phenolic resin, 10 parts of coconut shell fiber, 15 parts of aluminum oxide, 3 parts of graphite, 5 parts of rubber powder, and 32 parts of barium sulfate powder.

2) Preparation method:

The coconut shell fiber is chopped to obtain fibers with a length of less than 10 mm; the phenolic resin is dried at 50°C for 0.5 hour, the coconut shell fiber is dried at 110°C for 1.5 hours, the rubber powder is dried at 80°C for 0.5 hour, and the other components are dried at 120°C for 1 hour; the dried raw materials (except the coconut shell fiber) are prepared according to the experimental design formula and put into a mixer with multiple sets of high-speed rotary knives for mixing for 5 minutes, and then the coconut shell fiber is put into the mixer and mixed for 1 minute to obtain a uniform powdery mixture; the uniformly mixed mixture is hot-pressed at a molding temperature of 165°C, a pressure of 25MPa, a holding time of 6min, and exhaust 6 times during the period; the sample obtained by hot pressing is placed in a heat treatment box for heat treatment at 160°C for 12 hours, and cooled with the furnace.

Comparative Example 1

1) Composition of raw materials (by weight)

20 parts of copper powder, 15 parts of cashew nut shell oil modified phenolic resin, 10 parts of coconut shell fiber, 20 parts of aluminum oxide, 3 parts of graphite, 5 parts of rubber powder, and 27 parts of barium sulfate powder.

2) Preparation method:

The fly ash hollow microspheres in Example 3 were replaced with the same amount of copper powder, and the preparation method was the same as that in Example 3.

Comparative Example 2

1) Composition of raw materials (by weight)

5 parts of fly ash hollow microspheres, 15 parts of cashew nut shell oil-modified phenolic resin, 10 parts of coconut shell fiber, 20 parts of aluminum oxide, 3 parts of graphite, 5 parts of rubber powder, and 27 parts of barium sulfate powder.

2) Preparation method:

The preparation method is the same as Example 3.

Comparative Example 3

1) Composition of raw materials (by weight)

25 parts of fly ash hollow microspheres, 15 parts of cashew nut shell oil-modified phenolic resin, 10 parts of coconut shell fiber, 20 parts of aluminum oxide, 3 parts of graphite, 5 parts of rubber powder, and 27 parts of barium sulfate powder.

2) Preparation method:

The preparation method is the same as Example 3.

Test example:

The brake materials prepared in Examples 1-4 and Comparative Examples 1-3 were tested for friction and wear performance on an X-DM pressure-adjustable variable speed friction tester. According to the requirements for the fourth type of disc brake linings in the national standard for disc brake linings (GB5763-2008), the friction coefficient and wear rate of the disc at 100°C, 150°C, 200°C, 250°C, 300°C and 350°C during the heating and cooling process were measured. The results are shown in Tables 3 and 4, respectively. The national standard allowable values for disc brake linings are shown in Table 5.

Table 3 Friction coefficient test results of different samples

Table 4 Wear rate test results of different samples

Table 5 National standard allowable values for disc brake linings

^a The experimental temperature refers to the temperature of the friction surface of the testing machine disc

^b Friction coefficient range includes allowable deviation

It can be seen from the above experimental data that compared with the allowable values of the national standard, the friction coefficient and wear rate of the embodiments of the present invention are within the allowable value range of the national standard, and the friction coefficient is at a relatively high level. The friction coefficients of the embodiments of the present invention are all between 0.55 and 0.65, and the wear rate is between 0 and 1.0×10 ^-7 cm ³ /(N•m), and the friction coefficients of embodiments 1-4 at 350°C are all higher than the friction coefficients at 100°C, indicating that the brake material does not experience thermal decay at high friction temperatures and has excellent thermal decay resistance. Compared with comparative examples 1-3, the high-performance copper-free resin-based brake material of the present invention has a higher friction coefficient at both low and high temperatures. The main components of fly ash hollow microspheres are silicon dioxide and aluminum oxide. After high-temperature firing, they have the characteristics of sound insulation, heat insulation, high temperature resistance, and wear resistance. The addition of fly ash hollow microspheres can effectively improve the friction coefficient of the brake material, especially the high-temperature friction coefficient. It can be seen that replacing copper powder with fly ash hollow microspheres can not only improve the friction performance and thermal decay resistance of brake materials, solve the problem of copper-free and high-performance brake materials, but also realize the high added value recycling of fly ash hollow microspheres. Compared with comparative examples 2-3, Example 3 shows that the content of fly ash hollow microspheres has a significant effect on the friction coefficient and wear rate of brake materials.

The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention should fall within the scope of the present invention.

Claims (4)

1. The high-performance copper-free resin-based braking material prepared from the fly ash hollow microspheres is characterized by being prepared from the following raw materials in parts by weight: 10-20 parts of coal ash hollow microsphere, 10-20 parts of cashew nut shell oil modified phenolic resin, 5-10 parts of coconut fiber, 10-20 parts of alumina, 3 parts of graphite, 5 parts of rubber powder and 22-47 parts of barium sulfate powder;

the coal ash hollow microspheres are hollow microspheres in waste coal ash of a thermal power plant, and the mesh number is 60-200 meshes;

the coconut shell fibers are chopped coconut shell fibers, and the length of the chopped coconut shell fibers is smaller than 10mm.

2. The high-performance copper-free resin-based brake material prepared by using the fly ash hollow microspheres according to claim 1, wherein the preparation method of the brake material comprises the following steps:

1) Drying raw materials: drying cashew nut shell oil modified phenolic resin at 50-60 ℃ for 0.5 hours, drying coconut shell fiber at 100-120 ℃ for 1.5 hours, drying rubber powder at 80-100 ℃ for 0.5 hours, and drying other components at 100-120 ℃ for 1 hour;

2) Mixing: the dried raw materials except the coconut fibers are put into a mixer with a plurality of groups of high-speed rotary cutters according to the proportion to be mixed for 3-5 min, and then the coconut fibers are put into the mixer to be mixed for 1-2 min to obtain uniform powdery mixed materials;

3) Hot press molding: weighing uniformly mixed materials, carrying out hot pressing in a hydraulic press, wherein the molding temperature is 165-170 ℃, the pressure is 25-35 MPa, the pressure maintaining time is 6-8 min, and the exhaust time is 5-6 times;

4) And (3) heat treatment: and (3) placing the sample obtained by hot press molding into an electrothermal constant-temperature blast drying oven for heat treatment at 160 ℃ for 12 hours, and cooling along with the furnace to obtain the high-performance copper-free resin-based braking material.

3. The high performance copper-free resin-based brake material according to claim 1, wherein the brake material is free of copper, lead, zinc, antimony heavy metal components.

4. The high performance copper-free resin-based brake material according to claim 1, wherein the high performance copper-free resin-based brake material has the following properties: the friction coefficient is 0.55-0.65; a coefficient of friction at 350 ℃ of not less than 100 ℃; the wear rate is 0 to 1.0X10 ^-7 cm ³ /(N•m)。

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