Brake pad and method of manufacture

Abstract

The application discloses a novel brake pad and a preparation method thereof, relates to the technical field of brake pads of brake systems, and aims to solve the problem of scratches of brake pads and brake discs caused by metal inlaying. One of the brake pads comprises a friction body (1), a steel back (2) and a dovetail block (3), the friction body (1) and the steel back (2) are integrally pressed and sintered to form a shape, the dovetail block (3) is fixed on the steel back (2), the edge of the friction body (1) is of an arc structure, and the steel back (2) is the same in shape as the friction body (1). In order to solve the problem of metal inlaying of brake pads and brake discs in rainy and snowy weather in high-cold regions and reduce the space for hidden hard foreign matters between and around the friction blocks of the brake pad, the gaps and the intermediate holes between the friction materials are cancelled, the friction body of the brake pad is integrally pressed and sintered, and the novel brake pad and the preparation method thereof are provided.

Description

Technical Field

[0001] This application relates to the field of brake pad technology for braking systems, and more particularly to a brake pad and its preparation method. Background Technology

[0002] Chinese invention patent application CN116447256A discloses a brake pad and its preparation method, comprising 65wt%-75wt% beryllium bronze powder or aluminum bronze powder, 3-5wt% metal powder, 15-25wt% ceramic whiskers, and 6-15wt% solid lubricant, used to solve the problem of brake pads generating a large amount of high-temperature wear debris and the brake pad friction coefficient declining during continuous braking under high speed and high load.

[0003] Chinese invention patent application CN105927686A discloses a friction material for high-speed train brake pads and its preparation method, comprising 13.2-23.2 wt% copper powder, 14.6-24.6 wt% bronze powder, 8.7-18.7 wt% copper fiber, 8.5-18.5 wt% reduced iron powder, 2-12 wt% iron oxide, 0.6-1.6 wt% chromium oxide, 1.3-2.3 wt% silicon carbide, 2.3-4.3 wt% titanium silicon carbon, 3.2-13.2 wt% antimony sulfide, and calcined oxygen. The composition includes 0.4-1.4 wt% aluminum hydroxide, 1.5-11.5 wt% flake graphite, 0.8-1.8 wt% zinc powder, 1.5-3.5 wt% petroleum coke, and 0.4-1.4 wt% aramid pulp. This technology addresses the problem of unstable friction coefficients in existing semi-metallic synthetic brake pads, which fail to meet the braking requirements of high-speed trains. The improved pads exhibit better impact resistance, do not crack, and have a thermal shock temperature up to 550℃. Under frictional heating conditions, the friction coefficient remains stable between 0.5 and 0.55, resulting in lower wear rates and a longer service life.

[0004] With the opening of several high-speed rail lines in the frigid regions of Northeast and Northwest my country, scratches on brake pads and discs caused by metal inlays are frequently observed in winter. Currently, there is no effective solution; the only recourse is to replace brake discs and pads after they are discovered, increasing the workload of maintenance personnel and operational costs. During high-speed operation, if metal inlays detach, they can easily damage bogies or other undercarriage equipment, potentially leading to derailment. The brake discs and pads used in high-speed trains operating in frigid regions are the same products used in high-speed trains in other regions, and their operation has been satisfactory. Scratches on brake pads and discs often occur before and after snowfall. The abnormal wear of brake discs on the Harbin-Dalian line in winter is primarily due to the extremely cold and freezing weather conditions, which exacerbate the abnormal wear. Therefore, developing a brake pad design suitable for use in frigid regions is urgently needed.

[0005] Two factors contribute to metal embedding: a humid environment and hard particles between the brake pads and discs. During high-speed train operation, localized pressure differentials and eddies are generated in the bogie area, easily causing ice and snow from the air and track to adhere to the bogie. This is especially true when the basic brakes are surrounded by ice and snow, creating a humid environment for the brake friction pairs, thus contributing to metal embedding. Sand particles and aluminum and silicon compounds in the friction material from the roadbed act as sources of hard particles, freezing in the gaps or on the surface of the brake pad friction blocks. The heat generated during braking melts the ice and snow, allowing the hard particles to reach the friction surface and rub against the brake disc, producing metal shavings or cutting metal wires. These metal cuttings continuously grind the brake disc surface, causing metal to accumulate on the brake pad surface, resulting in abnormal scratches on the friction surfaces of the brake pads and discs. To address the scratches on brake pads and brake discs caused by metal inlays, reducing the space between and around the brake pad friction blocks is one effective approach. Therefore, the existing split structure of the brake pad friction blocks can be eliminated, as can the gaps between the friction blocks and the central hole in the friction blocks. The brake pad friction body is integrally pressed and sintered. However, since the unit pressure required for pressing powder metallurgy materials is too high, which is generally unattainable by ordinary equipment, and the uniformity of pressing cannot be guaranteed, it is necessary to improve the existing powder metallurgy process and materials. Summary of the Invention

[0006] The purpose of this application is to provide a brake pad that solves the problem of metal embedding between the brake pad and the brake disc in rainy and snowy weather in cold regions, reduces the space between the brake pad friction blocks and around the friction blocks to hide hard foreign objects, and eliminates the gaps and intermediate holes between the friction materials.

[0007] To achieve the above objectives, this application provides the following technical solution:

[0008] A brake pad includes a friction body, a steel backing, and a dovetail block, wherein the friction body and the steel backing are integrally pressed and sintered, and the dovetail block is fixed on the steel backing.

[0009] To reduce the space for hard foreign objects to be hidden between and around the friction blocks, the brake pads are made of friction body and steel backing by integral pressing and sintering. The friction surface is flat and without gaps. The edge of the friction body is curved to reduce the hiding of hard foreign objects. The steel backing under the friction body plays a supporting role and has the same shape as the friction body.

[0010] As a preferred option, the dovetail block is cast integrally with the steel backing.

[0011] As a preferred option, the dovetail block is connected by rivets, a steel back, and a friction element.

[0012] As a preferred option, the steel back and dovetail block have six rivet holes.

[0013] As a preferred option, the steel backing thickness is 6mm. Attached Figure Description

[0014] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings:

[0015] Figure 1 This is a schematic diagram of the brake pad structure;

[0016] 1. Friction body; 2. Steel back; 3. Dovetail block; 4. Rivet. Detailed Implementation

[0017] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and are not intended to limit the scope of this application.

[0018] It should be noted that when a component is referred to as being "fixed to" or "set on" another component, it can be directly on or indirectly on that other component. When a component is referred to as being "connected to" another component, it can be directly connected to or indirectly connected to that other component.

[0019] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise expressly specified. "Several" means one or more, unless otherwise expressly specified.

[0020] In the description of this application, it should be understood that the terms "upper", "lower", "front", "rear", "left", "right", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0021] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0022] The structure of the brake pads is explained below with reference to the accompanying drawings.

[0023] like Figure 1 As shown, the brake pad consists of a friction element 1, a steel backing 2, a dovetail block 3, and rivets 4. To reduce the space between and around the friction elements where hard foreign objects may hide, the brake pad is integrally pressed and sintered from the friction element and steel backing. The friction surface is flat and without gaps. The edges of the friction element are curved to reduce the hiding of hard foreign objects. The steel backing under the friction element supports it and has the same shape as the friction element. For assembly with the dovetail block, the steel backing has six rivet holes. The dovetail block serves as the interface for mounting the friction pad and is connected to the steel backing and friction element via rivets. Alternatively, the dovetail block and steel backing can be integrally cast and then machined, eliminating the need for rivets. Tooling can be used during sintering and pressurization to prevent stress on the dovetail block. Whether the dovetail block and steel backing are riveted or integrally cast, the performance of the brake pad remains unaffected.

[0024] The friction body is composed of 50-60 wt% bronze powder, 5-15 wt% low-density iron powder, 2-6 wt% zinc powder, 1-5 wt% chromium oxide green, 8-12 wt% crystalline chromium carbide, 1-5 wt% crystalline tungsten carbide, 3-9 wt% artificial graphite, and 6-12 wt% chopped carbon fiber. To increase the adhesion during pressing, an additional binder is added: 1-3 wt% polyethylene wax powder of the total weight of the friction body. This binder will volatilize during pressing and sintering, creating voids between the friction body and the steel backing.

[0025] The bronze powder is 660 bronze powder, 325 mesh, containing 6% Zn and 6% Sn, with the balance being Cu. It acts as a matrix component in friction materials, possessing excellent processing performance, good hardness, strength, wear resistance, and superior anti-wear properties.

[0026] The low-density iron powder, 100 mesh, contains 98% iron and has an apparent density of 2.3 g / cm³. 3 The secondary hydrogen reduction process has good compatibility with the matrix in friction materials and can be used as a matrix reinforcing component to improve the matrix strength. Its porous structure is beneficial to reduce braking noise of friction materials in use.

[0027] The polyethylene wax powder, 325 mesh, melting point 120 degrees Celsius, is used as a binder during pressing. It is melted by heating the mold and can bond the components of the friction body together. It can also reduce material friction, reduce the loss of pressing pressure, increase the density of the pressed blank, improve formability, reduce the demolding force during demolding, and extend the service life of the mold. During pressing and sintering, the polyethylene wax powder volatilizes and forms voids in the friction body, which can adjust and stabilize the coefficient of friction, improve the condition of the friction surface, reduce the wear of the friction body and brake disc, and reduce braking noise.

[0028] The chromium oxide green, 325 mesh, has high wear resistance, corrosion resistance and high temperature resistance, and plays a role in increasing friction and stabilizing the coefficient of friction in friction bodies;

[0029] The crystalline chromium carbide (120 mesh) and crystalline tungsten carbide (200 mesh) are used as friction components. Metal carbides have higher compatibility with the matrix components. Crystalline carbides are grown from crystals, and their grain structure is very dense with few grain boundaries. Compared with ordinary carbides, they have better mechanical properties and high-temperature stability. They have excellent wear resistance, corrosion resistance and high-temperature resistance under extreme conditions such as high temperature, high pressure and high speed. When added to the friction body, they can increase the friction coefficient, improve thermal stability and reduce wear.

[0030] The short-cut carbon fibers have a specification of 3mm-12mm and possess properties such as high strength, low density, strong corrosion resistance, high temperature resistance, and high thermal conductivity. As a lubricating component, they play a role in the friction body by reducing the temperature friction coefficient, protecting the friction mating surfaces, and reducing wear on the mating surfaces.

[0031] Artificial graphite, 60-120 mesh, with a carbon content of 99%, serves as a lubricant component, playing a role in temperature friction coefficient, protecting friction surfaces, and reducing wear on the friction surfaces.

[0032] The friction body is supported by a steel backing with the same outer contour. The steel backing is 6mm thick and has 6 rivet holes. To increase the bonding strength, the steel backing is plated with copper. The steel backing and the dovetail block have 6 rivet holes at corresponding positions. During sintering, the rivets are sintered together with the friction body and the steel backing. After sintering, the rivets are riveted together with the friction body, the steel backing, and the dovetail block.

[0033] A method for preparing brake pads includes the following steps:

[0034] S1, Preparation of pressing material: Weigh bronze powder, low-density iron powder, zinc powder, chromium oxide green, crystalline chromium carbide, and crystalline tungsten carbide according to the formula and mix them in a high-speed mixer for 1 hour to obtain the mixture;

[0035] The chopped carbon fibers, artificial graphite, binder, and the mixture obtained in S1 are mixed in a double-motion horizontal mixer for 0.5 hours to obtain the pressed material, with a weight of 2-3 kg.

[0036] S2, pressing, using a double-cavity mold, the steel back and rivets are placed in the mold, the mold temperature is raised to 130-180℃, the pressing material is pressed for 15 minutes under 18-22MPa pressure to form a pressed blank, the upper mold is lifted for 5 seconds to release air at 0.5, 1, 3, 5 and 10 minutes of the pressing process;

[0037] A double-cavity mold is used. The temperature is heated to 130-180℃ by resistance wire. The steel back is placed in the mold cavity, and the rivets are placed in the rivet holes on the steel back. The pressing material is pressed for 15 minutes under a pressure of 18-22MPa to form a pressed blank. Since a small amount of gas will be discharged from the mixture during pressing, the upper mold is lifted for 5 seconds at 0.5, 1, 3, 5 and 10 minutes during the pressing process to release the gas.

[0038] S3, sintering: The pressed billet obtained in S2 is sintered in a bell-type pressure sintering furnace at a temperature of 850-950℃, with a holding time of 1-3 hours at the highest temperature. A pressure of 3-5 MPa is applied above the billet. After cooling, a friction block consisting of friction body, steel back, and rivets is obtained. The pressed billet is then sintered in a bell-type pressure sintering furnace with a protective gas of 15-25% hydrogen and 75-85% nitrogen. The heating rate is 5-10℃ / min. To exhaust the volatile gases from the friction body, a stepped heating process is used, reaching 200℃, 300℃, 500℃, and 700℃, holding for 20 minutes at each temperature. The sintering temperature is 850-950℃, with a holding time of 1-3 hours at the highest temperature, and a pressure of 3-5 MPa is applied. After holding, the billet is cooled in the furnace at a rate of 3-5℃ / min, with a pressure of 3-5 MPa applied during the cooling process.

[0039] S4. Rivet the friction block and dovetail block obtained in S3 together. The riveting pressure is 3-5 MPa and the riveting time is 5 seconds.

[0040] When the above technical solution is adopted, chopped carbon fiber and artificial graphite are added after other materials are mixed evenly. The purpose is to prevent other materials and blades from damaging the particle size of chopped carbon fiber and artificial graphite during high-speed mixing, and to reduce the mixing time.

[0041] By employing the above technical solution, under a reducing atmosphere, oxidation of the metal materials in the friction block is prevented at high temperatures. Controlling the heating rate and the step-heating method avoids uneven heating of the material's interior and exterior due to excessively rapid temperature increases, preventing the release of volatile gases and avoiding cracks and hollow areas in the friction block. Applying pressure above the friction block makes the friction body more compact, enhancing the strength of the brake pads and improving adhesion to the steel backing.

[0042] The rivets and dovetail blocks on the sintered friction block steel back are riveted together with a riveting pressure of 3-5 MPa for 5 seconds to obtain the brake pad.

[0043] The present invention will be further described in detail below with reference to the embodiments.

[0044] For a direct comparison, the weight ratio of brake pad friction element and adhesive provided in Examples 1-3 has been adjusted, while the process remains unchanged. The composition of the friction element is shown in Table 1 below.

[0045] Table 1

[0046]

[0047] Example 1

[0048] This embodiment 1 provides a method for preparing brake pads, including the following steps:

[0049] S1. Preparation of pressed material: Weigh 55wt% 660 bronze powder, 10wt% low-density iron powder, 4wt% zinc powder, 3wt% chromium oxide green, 10wt% crystalline chromium carbide, and 3wt% crystalline tungsten carbide, and mix them in a high-speed mixer for at least 1 hour to obtain a mixture;

[0050] 6 wt% artificial graphite, 9 wt% chopped carbon fiber and binder, the binder being 2 wt% polyethylene wax powder of the total weight of the friction body, are mixed with the material in a double-motion horizontal mixer for 0.5 h to obtain the pressed material;

[0051] S2. Pressing: A double-cavity mold is used. The steel back and rivets are placed in the mold. The mold temperature is raised to 160°C. The pressing material is pressed under 20MPa pressure for 15 minutes to form a pressed blank. During the pressing process, the upper mold is lifted for 5 seconds at 0.5, 1, 3, 5 and 10 minutes to release air.

[0052] S3. Sintering: The pressed billet obtained in S2 is sintered in a bell-type pressure sintering furnace at a sintering temperature of 900℃, with a maximum holding time of 2 hours. A pressure of 4MPa is applied above the friction body. After cooling, a friction block consisting of the friction body, steel back, and rivets is obtained. The pressed billet is then sintered in a bell-type pressure sintering furnace with a protective gas composition of 15-25% hydrogen and 75-85% nitrogen. The heating rate is 5-10℃ / min. To exhaust the volatile gases from the friction body, a stepped heating process is used, with temperatures raised to 200℃, 300℃, 500℃, and 700℃, and held for 20 minutes at each temperature. The sintering temperature is then 900℃, with a maximum holding time of 2 hours, and a pressure of 4MPa is applied. After holding, the billet is cooled in the furnace at a cooling rate of 3-5℃ / min, with a pressure of 4MPa applied during the cooling process.

[0053] S4. Riveting: Rivet the friction block and dovetail block obtained in S3 together. The riveting pressure is 4MPa and the riveting time is 5s.

[0054] Example 2

[0055] This embodiment 2 provides a method for preparing brake pads, including the following steps:

[0056] S1. Preparation of pressed material: Weigh 50wt% 660 bronze powder, 8wt% low-density iron powder, 4wt% zinc powder, 3wt% chromium oxide green, 12wt% crystalline chromium carbide, and 4wt% crystalline tungsten carbide, and mix them in a high-speed mixer for at least 1 hour to obtain a mixture;

[0057] 8 wt% artificial graphite, 11 wt% chopped carbon fiber and binder, the binder being 3 wt% polyethylene wax powder of the total weight of the friction body, are mixed with the material in a double-motion horizontal mixer for 0.5 h to obtain the pressed material;

[0058] S2. Pressing: A double-cavity mold is used. The steel back and rivets are placed in the mold. The mold temperature is raised to 160°C. The pressing material is pressed under 20MPa pressure for 15 minutes to form a pressed blank. During the pressing process, the upper mold is lifted for 5 seconds at 0.5, 1, 3, 5 and 10 minutes to release air.

[0059] S3. Sintering: The pressed billet obtained in S2 is sintered in a bell-type pressure sintering furnace at a sintering temperature of 900℃, with a maximum holding time of 2 hours. A pressure of 4MPa is applied above the friction body. After cooling, a friction block consisting of the friction body, steel back, and rivets is obtained. The pressed billet is then sintered in a bell-type pressure sintering furnace with a protective gas composition of 15-25% hydrogen and 75-85% nitrogen. The heating rate is 5-10℃ / min. To exhaust the volatile gases from the friction body, a stepped heating process is used, with temperatures raised to 200℃, 300℃, 500℃, and 700℃, and held for 20 minutes at each temperature. The sintering temperature is then 900℃, with a maximum holding time of 2 hours, and a pressure of 4MPa is applied. After holding, the billet is cooled in the furnace at a cooling rate of 3-5℃ / min, with a pressure of 4MPa applied during the cooling process.

[0060] S4. Riveting: Rivet the friction block and dovetail block obtained in S3 together. The riveting pressure is 4MPa and the riveting time is 5s.

[0061] Example 3

[0062] This embodiment 3 provides a method for preparing brake pads, including the following steps:

[0063] S1. Preparation of pressed material: Weigh 60wt% 660 bronze powder, 12wt% low-density iron powder, 4wt% zinc powder, 2wt% chromium oxide green, 8wt% crystalline chromium carbide, and 2wt% crystalline tungsten carbide, and mix them in a high-speed mixer for at least 1 hour to obtain a mixture;

[0064] 4 wt% artificial graphite, 8 wt% chopped carbon fiber and binder, the binder being 1 wt% polyethylene wax powder of the total weight of the friction body, are mixed with the material in a double-motion horizontal mixer for 0.5 h to obtain the pressed material;

[0065] S2. Pressing: A double-cavity mold is used. The steel back and rivets are placed in the mold. The mold temperature is raised to 160°C. The pressing material is pressed under 20MPa pressure for 15 minutes to form a pressed blank. During the pressing process, the upper mold is lifted for 5 seconds at 0.5, 1, 3, 5 and 10 minutes to release air.

[0066] S3. Sintering: The pressed billet obtained in S2 is sintered in a bell-type pressure sintering furnace at a sintering temperature of 900℃, with a maximum holding time of 2 hours. A pressure of 4MPa is applied above the friction body. After cooling, a friction block consisting of the friction body, steel back, and rivets is obtained. The pressed billet is then sintered in a bell-type pressure sintering furnace with a protective gas composition of 15-25% hydrogen and 75-85% nitrogen. The heating rate is 5-10℃ / min. To exhaust the volatile gases from the friction body, a stepped heating process is used, with temperatures raised to 200℃, 300℃, 500℃, and 700℃, and held for 20 minutes at each temperature. The sintering temperature is then 900℃, with a maximum holding time of 2 hours, and a pressure of 4MPa is applied. After holding, the billet is cooled in the furnace at a cooling rate of 3-5℃ / min, with a pressure of 4MPa applied during the cooling process.

[0067] S4. Riveting: Rivet the friction block and dovetail block obtained in S3 together. The riveting pressure is 4MPa and the riveting time is 5s.

[0068] For a direct comparison, the weight ratio of brake pad friction element and adhesive provided in Examples 4-5 is the same as that in Example 1, but the process has been adjusted. The adjustments are shown in Table 2.

[0069] Table 2

[0070]

[0071] Example 4

[0072] This embodiment 4 provides a method for preparing brake pads, including the following steps:

[0073] S1. Preparation of pressed material: Weigh 55wt% 660 bronze powder, 10wt% low-density iron powder, 4wt% zinc powder, 3wt% chromium oxide green, 10wt% crystalline chromium carbide, and 3wt% crystalline tungsten carbide, and mix them in a high-speed mixer for at least 1 hour to obtain a mixture;

[0074] 6 wt% artificial graphite, 9 wt% chopped carbon fiber and binder, the binder being 2 wt% polyethylene wax powder of the total weight of the friction body, are mixed with the material in a double-motion horizontal mixer for 0.5 h to obtain the pressed material;

[0075] S2. Pressing: A double-cavity mold is used. The steel back and rivets are placed in the mold. The mold temperature is raised to 130°C. The pressing material is pressed under 20MPa pressure for 15 minutes to form a pressed blank. During the pressing process, the upper mold is lifted for 5 seconds at 0.5, 1, 3, 5 and 10 minutes to release air.

[0076] S3. Sintering: The pressed billet obtained in S2 is sintered in a bell-type pressure sintering furnace at a sintering temperature of 860℃, with a maximum holding time of 2 hours. A pressure of 4MPa is applied above the friction body. After cooling, a friction block consisting of the friction body, steel back, and rivets is obtained. The pressed billet is then sintered in a bell-type pressure sintering furnace with a protective gas of 15-25% hydrogen and 75-85% nitrogen. The heating rate is 5-10℃ / min. To exhaust the volatile gases from the friction body, the temperature is increased in stages to 200℃, 300℃, 500℃, and 700℃, and held for 20 minutes at each stage. The sintering temperature is 900℃, with a maximum holding time of 2 hours, and a pressure of 4MPa is applied. After holding, the billet is cooled in the furnace at a cooling rate of 3-5℃ / min, with a pressure of 4MPa applied during the cooling process.

[0077] S4. Riveting: Rivet the friction block and dovetail block obtained in S3 together. The riveting pressure is 4MPa and the riveting time is 5s.

[0078] Example 5

[0079] This embodiment 5 provides a method for preparing brake pads, including the following steps:

[0080] S1. Preparation of pressed material: Weigh 55wt% 660 bronze powder, 10wt% low-density iron powder, 4wt% zinc powder, 3wt% chromium oxide green, 10wt% crystalline chromium carbide, and 3wt% crystalline tungsten carbide, and mix them in a high-speed mixer for at least 1 hour to obtain a mixture;

[0081] 6 wt% artificial graphite, 9 wt% chopped carbon fiber and binder, the binder being 2 wt% polyethylene wax powder of the total weight of the friction body, are mixed with the material in a double-motion horizontal mixer for 0.5 h to obtain the pressed material;

[0082] S2. Pressing: A double-cavity mold is used. The steel back and rivets are placed in the mold. The mold temperature is raised to 180°C. The pressing material is pressed under 20MPa pressure for 15 minutes to form a pressed blank. During the pressing process, the upper mold is lifted for 5 seconds at 0.5, 1, 3, 5 and 10 minutes to release air.

[0083] S3. Sintering: The pressed billet obtained in S2 is sintered in a bell-type pressure sintering furnace at a sintering temperature of 950℃, with a maximum holding time of 2 hours. A pressure of 4MPa is applied above the friction body. After cooling, a friction block consisting of the friction body, steel back, and rivets is obtained. The pressed billet is then sintered in a bell-type pressure sintering furnace with a protective gas of 15-25% hydrogen and 75-85% nitrogen. The heating rate is 5-10℃ / min. To exhaust the volatile gases from the friction body, the temperature is increased in stages to 200℃, 300℃, 500℃, and 700℃, and held for 20 minutes at each stage. The sintering temperature is 900℃, with a maximum holding time of 2 hours, and a pressure of 4MPa is applied. After holding, the billet is cooled in the furnace at a cooling rate of 3-5℃ / min, with a pressure of 4MPa applied during the cooling process.

[0084] S4. Riveting: Rivet the friction block and dovetail block obtained in S3 together. The riveting pressure is 4MPa and the riveting time is 5s.

[0085] Performance testing

[0086] Parking braking tests were conducted on Examples 1-5 to test the friction coefficient, maximum wear, density, hardness, and shear strength of the brake pads. The performance test data are shown in Table 3 below.

[0087] Table 3

[0088]

[0089] The test results above show that the brake pads prepared in Examples 1-5 all meet the standard requirements for average friction coefficient, wear rate, peak noise, metal inserts, density, hardness, and shear strength of the friction material. Example 2, based on Example 1, replaced some matrix components with friction and lubrication components. While this increased the friction coefficient, it reduced the strength of the friction material, posing a risk of chipping and breakage during use. Example 3, based on Example 1, replaced some friction and lubrication components with matrix components. While this increased the strength of the friction material, it reduced the friction coefficient. Example 4, based on Example 1, had lower pressing and sintering temperatures, leading to insufficient volatile matter release from the friction material, resulting in porosity and lower strength. Example 5, based on Example 1, had higher pressing and sintering temperatures, resulting in a denser brake pad friction material exceeding the optimal lower limit of porosity, thus causing larger fluctuations in the friction coefficient and higher noise. In summary, Example 1 demonstrates a more balanced performance across all aspects, representing the optimal combination of materials and processes. Furthermore, if the material ratio and process parameters exceed the allowable range, the brake pads may not meet the standard requirements.

[0090] Comparative Examples 1 and 2 were prepared using the method of Example 1. In Comparative Example 1, the matrix components exceeded the lower limit of the reasonable range, and the friction components exceeded the upper limit of the reasonable range. Although no metal inlays appeared, the coefficient of friction and wear rate exceeded the upper limit, and the strength of the friction material was too low, resulting in a high risk of flaking and chipping during use. In Comparative Example 2, the matrix components exceeded the upper limit of the reasonable range, and the friction components exceeded the lower limit of the reasonable range. No metal inlays appeared either, but the coefficient of friction exceeded the lower limit, and the strength of the friction material was too high, which could easily cause damage such as hot spots and scratches to the brake disc during use.

[0091] Use test

[0092] Altitude not exceeding 1500m; ambient temperature: -50℃~+40℃; monthly average maximum relative humidity not exceeding 95% (monthly average minimum temperature is 25℃).

[0093] Maximum wind speed: less than 15 m / s in normal years; occasionally up to 33 m / s.

[0094] Suitable environments: windy, sandy, rainy, and snowy weather, and occasionally salt spray, acid rain, sandstorms, etc.

[0095] Vehicle specifications: Operating speed: 250 km / h, maximum test speed: 275 km / h.

[0096] Maximum axle load: ≤17t, with brake discs installed on 2 wheels of each driving axle and brake discs installed on 3 axles of each tow axle.

[0097]

[0098] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A brake pad, characterized in that, It comprises a friction element, a steel back, and a dovetail block. The friction element and the steel back are integrally pressed and sintered, resulting in a smooth, seamless friction surface. The dovetail block is fixed to the steel back. The friction element comprises 50-60 wt% bronze powder and 5-15 wt% of an apparent density of 2.3 g / cm³. 3 The components include low-density iron powder, 2-6 wt% zinc powder, 1-5 wt% chromium oxide green, 8-12 wt% crystalline chromium carbide, 1-5 wt% crystalline tungsten carbide, 3-9 wt% artificial graphite, 6-12 wt% chopped carbon fiber, and 1-3 wt% polyethylene wax powder by weight of the friction body.

2. The brake pad according to claim 1, characterized in that, The friction body comprises 55 wt% bronze powder, 10 wt% low-density iron powder, 4 wt% zinc powder, 3 wt% chromium oxide green, 10 wt% crystalline chromium carbide, 3 wt% crystalline tungsten carbide, 6 wt% artificial graphite, 9 wt% chopped carbon fiber, and 2 wt% polyethylene wax powder by weight of the total friction body.

3. A method for preparing a brake pad as described in any one of claims 1-2, characterized in that, Includes the following steps: S1. Preparation of the mixture: Weigh bronze powder, low-density iron powder, zinc powder, chromium oxide green, crystalline chromium carbide, and crystalline tungsten carbide, and mix them using a high-speed mixer to obtain the mixture; S2. Preparation of pressed material: Artificial graphite, chopped carbon fiber and polyethylene wax powder are mixed with the mixture obtained in S1 using a double-motion horizontal mixer to obtain the pressed material; S3. Pressing: A steel backing and rivets are placed in the mold. The rivets are placed in the rivet holes of the steel backing. The mold temperature is raised to 130-180℃. The pressing material is pressed under a pressure of 18-22MPa. During the pressing process, the upper mold is lifted several times to release air. The pressed material is then formed into a pressed blank. S4. Sintering: The compact obtained in S3 is sintered under a protective gas mixture of hydrogen and nitrogen. Step heating is used, with each step held for 20 minutes. The sintering temperature is 850-950℃, and the holding time at the highest temperature is 1-3 hours. A pressure of 3-5 MPa is applied above the compact. After holding at the highest temperature for 1-3 hours, the compact is cooled to obtain a friction block. The cooling rate is 3-5℃ / min, and a pressure of 3-5 MPa is applied during the cooling process.

4. The preparation method according to claim 3, characterized in that, The friction block and the dovetail block are fixed together by riveting.

5. The preparation method according to claim 3, characterized in that, The mold is a double-cavity mold.

6. The preparation method according to claim 3, characterized in that, During the pressing process, the upper mold is lifted and vented several times at 0.5, 1, 3, 5 and 10 minutes respectively, and the upper mold is lifted for 5 seconds to vent.

7. The preparation method according to claim 3, characterized in that, The pressed blank is obtained by pressing for 15 minutes.

8. The preparation method according to claim 3, characterized in that, The sintering is carried out in a bell-type pressure sintering furnace.

9. The preparation method according to claim 3, characterized in that, The temperature is gradually increased to 200℃, 300℃, 500℃, and 700℃, and then held for 20 minutes each time.

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