A sintering process and die for copper-based friction materials

Abstract

The present invention relates to the technical field of friction material sintering, in particular to a sintering process for copper-based friction materials. The sintering process includes the following steps: S1, batching: the mass ratios of the respective powder materials are as follows: copper powder 40-60%, iron powder 10-20%, ferrochrome powder 5-15%, graphite 5-15%, molybdenum disulfide 2-5%, ceramic particles 1-8%, nickel powder 1-5%, chromium powder 1-5%, and the sum of the components of the above powder materials is 100%; S2, mixing: putting the powder materials prepared in step S1 into a mixer and mixing and stirring for 3-5 h; S3, compacting: cold-compacting the mixed powder materials in step S2, with a forming pressure of 800-1000 MPa and a pressure holding time of 10-30 s; S4, sintering: putting the billet pressed in step S3 into a mold, placing the mold and the billet together in a mesh-belt sintering furnace, introducing a protective atmosphere and carrying out sintering, with a sintering temperature of 900-1000 °C and a sintering time of 60-180 min. Meanwhile, the present invention also provides a mold for the above sintering process. The technical solution of the present invention simplifies the processing technology, has less energy consumption, and has high precision of the processed products.

Description

Technical Field

[0001] The present invention relates to the technical field of friction material sintering, in particular to a sintering process for copper-based friction materials and a mold for sintering use. Background Art

[0002] Copper-based powder metallurgy friction materials are widely used in high-speed train brake pads due to their excellent thermal conductivity and mechanical properties. With the continuous development of China's high-speed rail industry, higher requirements are bound to be put forward for copper-based powder metallurgy brake pads for high-speed trains.

[0003] Traditional sintering processes are mainly divided into bell-type furnace sintering and mesh-belt furnace sintering. During the use of bell-type furnace sintering, in order to avoid excessive expansion of copper-based friction materials during sintering, a certain pressure is usually applied additionally through the hydraulic device of the bell-type furnace. This process method can effectively control the dimensional accuracy of the material, but has the disadvantages of low efficiency and high energy consumption, which is not conducive to large-scale production. When using a mesh-belt furnace for sintering, although the sintering process can operate continuously, avoiding problems such as low production efficiency caused by replacing cooling covers, heating covers, heating, and cooling, etc., it has no pressurizing device and cannot well control the dimensional accuracy of the sintered material. Summary of the Invention

[0004] The purpose of the present invention is to provide a sintering process for friction materials with a simpler process, capable of realizing pressureless sintering, high precision, and low energy consumption, so as to solve the problems raised in the above background art.

[0005] To achieve the above purpose, the present invention provides the following technical solution: A sintering process for copper-based friction materials, the sintering process includes the following steps:

[0006] S1, batching: The mass ratio of each powder is: copper powder 40 - 60%, iron powder 10 - 20%, ferrochrome powder 5 - 15%, graphite 5 - 15%, molybdenum disulfide 2 - 5%, ceramic particles 1 - 8%, nickel powder 1 - 5%, chromium powder 1 - 5%, and the sum of the above powder components is 100%;

[0007] S2, mixing: Put the powder prepared in step S1 into a mixer and mix and stir for 3 - 5 h;

[0008] S3, compacting: Cold-press the mixed powder in step S2 into a shape, with a forming pressure of 800 - 1000 MPa and a pressure holding time of 10 - 30 s;

[0009] S4, sintering: Put the blank pressed in step S3 into a mold, place the mold and the blank together in a mesh-belt sintering furnace, introduce a protective atmosphere and carry out sintering, with a sintering temperature of 900 - 1000 °C and a sintering time of 60 - 180 min.

[0010] Furthermore, in step S2, the mixing time is 4 hours.

[0011] Furthermore, in step S3 of pressing the embryo, the holding time is 20 seconds.

[0012] Furthermore, in the sintering step S4, the protective atmosphere is a nitrogen-hydrogen mixed gas, and the ratio of nitrogen to hydrogen in the nitrogen-hydrogen mixed gas is 1:1-5.

[0013] Preferably, in the sintering step S4, the ratio of nitrogen to hydrogen in the nitrogen-hydrogen mixed gas is 1:3.

[0014] Furthermore, in the sintering step S4, the sintering temperature is 980° C., and the sintering time is 120 minutes.

[0015] The present invention also provides a mold for sintering copper-based friction materials, comprising a shell and a cover plate, wherein the shell and the cover plate are fixed to form a sealed installation cavity, wherein a plurality of templates are stacked in the installation cavity, and a plurality of material troughs are evenly arranged on the templates, a first fixing hole is provided on the cover plate, and a second fixing hole corresponding to the first fixing hole is provided on the template, and a pre-tightening bolt passes through the first fixing hole and the second fixing hole to fix the cover plate and the template.

[0016] Further improved, the template includes a first template located at the top layer and several second templates located below the first template, the first template is provided with several third fixing holes, the second template is provided with fourth fixing holes corresponding to the third fixing holes, and the first connecting bolt passes through the third fixing holes and the fourth fixing holes to fix the first template and the second template.

[0017] As a further improvement, the radial cross-section of the third fixing hole is stepped, comprising a relief portion and a connecting portion arranged in sequence of height, and the relief portion is adapted to the screw cap of the first connecting bolt.

[0018] As a further improvement, a plurality of fifth fixing holes are evenly arranged at the outer edge of the cover plate, and a sixth fixing hole corresponding to the fifth fixing hole is provided on the shell. A second connecting bolt passes through the fifth fixing hole and the sixth fixing hole to fix the cover plate on the top of the shell.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] The present invention utilizes a mold in conjunction with a mesh belt furnace to achieve pressure-free, position-limited sintering of copper-based friction materials. A compacted green body is placed in the mold, and the mold cavity is used to limit the height expansion of the green body during sintering, eliminating the need for an additional pressurizing device, thereby achieving pressureless sintering. Furthermore, the mold containing the green body is placed in a mesh belt furnace, where it is sequentially sintered within the furnace, achieving continuous sintering of the green body. This avoids the problems of low production efficiency and high energy consumption associated with replacing heating and cooling hoods and heating and cooling the sintering furnace during traditional pressure sintering. Furthermore, it addresses the issues of poor product dimensional accuracy and low bonding strength caused by the lack of a pressurizing device during mesh belt furnace sintering.

[0021] The mold of the present invention uses a layered stacking method to set up templates, so that the template located on the upper part limits the material trough of the template located on the lower part, and the material trough of the topmost template is limited by the bottom surface of the cover plate of the mold. Each layer of template can be used for product processing, which saves more processing space and improves processing efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0023] Figure 1 This is a processing flow chart of the first embodiment of the present invention;

[0024] Figure 2 An exploded view of the mold structure according to the second embodiment of the present invention;

[0025] Figure 3 A cross-sectional view of a mold according to a second embodiment of the present invention;

[0026] In the picture:

[0027] 1. Shell;

[0028] 11. Sixth fixing hole;

[0029] 2. Cover plate;

[0030] 21. First fixing hole; 22. Fifth fixing hole;

[0031] 3. Template;

[0032] 31. Material trough; 32. Second fixing hole; 33. First template; 34. Second template; 331. Third fixing hole; 332. Giving way; 333. Connecting part; 341. Fourth fixing hole;

[0033] 4. Pre-tighten the bolts;

[0034] 5. First connecting bolt;

[0035] 6. Second connecting bolt. Specific embodiments

[0036] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed present invention, but merely represents the selected embodiments of the present invention.

[0037] In the description of the present invention, the terms "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present invention, "a plurality" means two or more, unless otherwise specifically defined.

[0038] Example 1:

[0039] Please refer to Figure 1 , a sintering process for copper-based friction materials, the sintering process comprising the following steps:

[0040] S1. Batching: The mass ratio of each powder is: copper powder 40 - 60%, iron powder 10 - 20%, ferrochrome powder 5 - 15%, graphite 5 - 15%, molybdenum disulfide 2 - 5%, ceramic particles 1 - 8%, nickel powder 1 - 5%, chromium powder 1 - 5%, and the sum of the above powder components is 100%.

[0041] S2. Mixing: Put the powders prepared in step S1 into a mixer and mix and stir for 3 - 5 h. Preferably, the mixing and stirring time is 4 h.

[0042] S3. Compacting: Cold-press the mixed powders in step S2 into a shape, with a forming pressure of 800 - 1000 MPa and a pressure holding time of 10 - 30 s.

[0043] When the pressure is lower than 800 MPa, the density of the compact is small and the dimensional deviation is large. When the pressure is higher than 1000 MPa, the density of the compact is too high and there are tiny cracks. Therefore, a pressure of 900 MPa and a pressure holding time of 20 s have a high yield rate and production efficiency.

[0044] S4, Sintering: Place the billet pressed in step S3 into a mold, place the mold and the billet together in a mesh belt sintering furnace, introduce a protective atmosphere and conduct sintering. The sintering temperature is 900 - 1000 °C, and the sintering time is 60 - 180 min. The protective atmosphere is a nitrogen-hydrogen mixed gas, and the ratio of nitrogen to hydrogen in the nitrogen-hydrogen mixed gas is 1:1 - 5. The sintering temperature is 980 °C, and the sintering time is 120 min. Preferably, in this embodiment, the ratio of nitrogen to hydrogen is 1:3.

[0045] In this embodiment, a reference example is established. The above copper-based friction material sintering process, traditional bell-type furnace sintering, and mesh belt furnace sintering are used to obtain their respective corresponding product parameters in a reference environment.

[0046] Experimental data:

[0047] Through actual testing of the parameters of the structure disclosed in Example 1, the experimental parameters are specifically as follows:

[0048] The mass percentages of each powder are respectively 40 - 60% copper powder, 10 - 20% iron powder, 5 - 15% ferrochrome powder, 5 - 15% graphite, 2 - 5% molybdenum disulfide, 1 - 8% ceramic particles, 1 - 5% nickel powder, and 1 - 5% chromium powder;

[0049] Stirring time: 4 h;

[0050] Molding pressure: 800 - 1000 MPa;

[0051] Pressure holding time: 20 s;

[0052] Protective atmosphere: A nitrogen-hydrogen mixed gas with a nitrogen-hydrogen ratio of 1:3;

[0053] Sintering time: 120 min;

[0054] Sintering temperature: 980 °C.

[0055] Comparison items: Bell-type furnace sintering, mesh belt furnace sintering.

[0056] Reference Example 1:

[0057] Mix the powders in a mixer for 4 h. After mixing evenly, put them into a molding die. The molding pressure is 800 MPa, and the pressure holding time is 20 s. Place the green compact on a small back plate and put them together into the mold. Then put the mold together with the green compact into a mesh belt sintering furnace, and sinter and form in a mixed atmosphere with a nitrogen-hydrogen ratio of 1:3. The sintering temperature is 980 °C, and the heat preservation time is 120 min.

[0058] Reference Example 2:

[0059] Mix the powder materials in a mixer for 4 h. After mixing evenly, put them into a forming mold. The forming pressure is 900 MPa and the pressure holding time is 20 s. Place the green compact on a small backboard and put them together into the said mold. Then put the mold together with the green compact into a mesh belt sintering furnace and sinter them into shape in a mixed atmosphere with a nitrogen-hydrogen ratio of 1:3. The sintering temperature is 980 °C and the heat preservation time is 120 min.

[0060] Reference Example 3:

[0061] Mix the powder materials in a mixer for 4 h. After mixing evenly, put them into a forming mold. The forming pressure is 1000 MPa and the pressure holding time is 20 s. Place the green compact on a small backboard and put them together into the said mold. Then put the mold together with the green compact into a mesh belt sintering furnace and sinter them into shape in a mixed atmosphere with a nitrogen-hydrogen ratio of 1:3. The sintering temperature is 980 °C and the heat preservation time is 120 min.

[0062] Comparative Example 1: (Sintering in a bell jar furnace)

[0063] Put the evenly mixed powder materials into a forming mold and cold press them into shape under a pressure of 500 MPa. The pressure holding time is 10 s. Then place the cold-pressed green compact on a small backboard and put them together into a bell jar sintering furnace. Sinter them into shape in a mixed atmosphere with a nitrogen-hydrogen ratio of 1:3. The sintering temperature is 980 °C, the sintering pressure is 4 MPa, and the heat preservation time is 120 min.

[0064] Comparative Example 2: (Sintering in a mesh belt furnace)

[0065] Put the evenly mixed powder materials into a forming mold and cold press them into shape under a pressure of 1000 MPa. The pressure holding time is 10 s. Then place the cold-pressed green compact on a small backboard and put them together into a mesh belt sintering furnace. Sinter them into shape in a mixed atmosphere with a nitrogen-hydrogen ratio of 1:3. The sintering temperature is 980 °C and the heat preservation time is 120 min.

[0066] Among them, in Reference Examples 1 to 3, a new sintering process is adopted. The pressed blank is placed in the corresponding mold, and the blank is limited and plastically deformed by the mold itself, so that there is no need for an additional pressing device to control the dimensional accuracy of the material, improving the processing efficiency, simplifying the process and reducing energy consumption. At the same time, since there is no need for a pressing device for plastic deformation, the blank is further sintered in a mesh belt furnace, making the sintering process operate continuously, avoiding problems such as low production efficiency caused by replacing the cooling hood, heating hood, heating up, and cooling. Comparative Example 1 and Comparative Example 2 are both processing technologies in the prior art and will not be elaborated here. Through the above five groups of experiments, five groups of corresponding different product parameters and processing efficiencies are obtained respectively. The test results are shown in the following table. Table 1 is the statistical table of the physical properties test and efficiency of the reference examples and comparative examples.

[0067] Table 1

[0068]

[0069] The experimental items include hardness, shear strength, bonding strength, height error, sintering efficiency, etc. As can be seen from Table 1, the performance of Reference Examples 1-3 is equivalent to that of Comparative Example 1, indicating that the sintering process of this embodiment can meet the product standard requirements of traditional pressure sintering. However, in the production process of 24 hours, the sintering efficiency of Reference Examples 1-3 using the sintering process of this embodiment is about 3,600 per day, while the sintering efficiency of the traditional bell jar furnace is about 2,000 per day. Compared with Comparative Example 1 using traditional bell jar furnace pressure sintering, the sintering efficiency is increased by about 80%. The sintering process of this embodiment greatly improves the production efficiency, does not require an additional pressure device to control the dimensional accuracy, has low energy consumption, and is conducive to large-scale production.

[0070] In Comparative Example 2 sintered by a traditional ordinary mesh belt furnace, the sintering efficiency is about 3,600 per day, which is the same as that of Reference Examples 1-3. However, the hardness, shear strength, and bonding strength of the products processed by the sintering process of this embodiment are significantly improved to varying degrees compared with Comparative Example 2, and the height dimension error is also smaller. Obviously, this embodiment has better product parameters and yield than Comparative Example 2 using traditional ordinary mesh belt furnace sintering.

[0071] The sintering process of this embodiment not only solves the disadvantages of low sintering efficiency and high energy consumption of the bell jar furnace, but also solves the problems of poor dimensional accuracy and low bonding strength of the products sintered by the mesh belt furnace. By restricting the expansion of the blank through the mold, the dimensional accuracy and bonding strength of the products are ensured. By sintering through the mesh belt furnace, the efficiency is improved and the energy consumption is reduced, realizing pressureless sintering.

[0072] Example Two:

[0073] Please refer to Figures 2-3 , a mold for the above-mentioned copper-based friction material sintering process, including a housing 1 and a cover plate 2. The housing 1 includes a bottom plate and a side wall provided around the outer edge of the bottom plate. The cover plate 2 covers the side wall to form a sealed installation cavity with the housing 1. A plurality of templates 3 are stacked in the installation cavity. A plurality of material grooves 31 are uniformly arranged on the templates 3 for placing blanks. The templates 3 are sequentially attached to each other, and the bottom surface of the lowermost template 3 is attached to the bottom surface of the installation cavity (the top surface of the bottom plate of the housing 1), and the top surface of the uppermost template 3 is attached to the top surface of the installation cavity (the bottom surface of the cover plate 2), so that the material grooves 31 form a closed processing die cavity to achieve the corresponding limiting effect.

[0074] Specifically, four first fixing holes 21 are arranged in a ring in the middle of the cover plate 2, and each of the templates 3 is provided with a second fixing hole 32 corresponding to the first fixing hole 21. The pre-tightening bolts 4 pass through the first fixing holes 21 and the second fixing holes 32 to fix the cover plate 2 and the template 3, and limit the position of the template 3 to avoid displacement of the template 3 during processing and affect the processing accuracy.

[0075] In this embodiment, the template 3 includes a first template 33 located at the top layer and several second templates 34 located below the first template 33. The first template 33 is provided with several third fixing holes 331, and the second template 34 is provided with fourth fixing holes 341 corresponding to the third fixing holes 331. The first connecting bolt 5 passes through the third fixing holes 331 and the fourth fixing holes 341 to fix the first template 33 and the second template 34.

[0076] Furthermore, the radial cross-section of the third fixing hole 331 is stepped, comprising a relief portion 332 and a connecting portion 333, arranged in ascending and descending order. The diameter of the relief portion 332 is larger than that of the connecting portion 333. The relief portion 332 mates with the head of the first connecting bolt 5, while the connecting portion 333 mates with the shank of the first connecting bolt 5. When the first connecting bolt 5 is installed, its head is completely located within the first template 33 and flush with the top surface of the first template 33. The top surface of the head mates with the bottom surface of the cover plate 2, allowing the trough 31 located in the first template 33 to cooperate with the cover plate 2 to form a closed processing cavity.

[0077] In this embodiment, a plurality of fifth fixing holes 22 are evenly arranged at the outer edge of the cover plate 2, and a sixth fixing hole 11 corresponding to the fifth fixing hole 22 is provided on the side wall of the shell 1. The second connecting bolt 6 passes through the fifth fixing hole 22 and the sixth fixing hole 11 to fix the cover plate 2 to the top of the shell 1.

[0078] In this embodiment, the thickness of the template 3 is 41 mm, and the depth of the material tank 31 is 31 mm. At least 10 mm of thickness needs to be set to ensure the strength and stiffness of the template 3, and at the same time, it has a larger bearing space and higher efficiency. In this embodiment, the volume of the material tank 31 is larger than the volume of the blank to be processed, and the volume ratio of the material tank 31 to the blank to be processed is about 1.3 - 1.1:1. A number of exhaust holes (not shown in the figure) are provided on the side wall of the material tank 31. Preferably, the exhaust holes are provided at the top of the side wall of the material tank 31, and the aperture of the exhaust holes is 0.03 - 0.06 mm. During the processing, the blank to be processed expands due to heat. At this time, the gas in the mold cavity is compressed and discharged from the exhaust holes. The discharge rate of the gas is slightly less than the expansion rate of the blank, so that the upper gas is first discharged from the exhaust holes, and the remaining gas forms a pressure in the mold cavity formed by the material tank 31 and the upper structure in the upward expansion direction of the blank, applying a downward pressure on the top surface of the blank, making its circumferential expansion more uniform during heating and fitting with the side wall of the material tank. As the processing time changes, all the gas in the mold cavity is discharged from the exhaust holes, and the blank expands to fit all sides of the mold cavity to form the final shape. Through the above settings, the blank can expand more uniformly during heating. Since this solution completely relies on the mold cavity formed by the material tank for the plasticity of the workpiece, a smaller exhaust hole is preset, so that the discharge amount of the gas forms a difference with the expansion amount of the blank, thereby forming a downward pressure and playing a limiting role on the upper top surface of the blank. The magnitude of the acting force and the limiting height change with the discharge of the gas state, making the blank tend to first expand circumferentially and fit, and then gradually expand axially to fit with the upper top surface as the gas continues to be discharged. This avoids the uncontrolled synchronous expansion of all directions of the blank, and there may be a difference in the expansion rate and expansion amount, which easily leads to insufficient precision of the finished product and affects the processing efficiency and yield.

[0079] Working principle: Place the pressed blank on the small back plate, and then place the blank and the small back plate together in the material groove 31. Overlap the first template 33 and the second template 34 in sequence and fix them with the first connecting bolt 5 to form a fixed whole. At this time, the material grooves 31 on the second template 34 have all become closed spaces. Place the fixed template connection body into the housing 1 and cover the cover plate 2, so that the first fixing hole 21 and the second fixing hole 32, and the fifth fixing hole 22 and the sixth fixing hole 11 are respectively aligned. The second connecting bolt 6 passes through the fifth fixing hole 22 and the sixth fixing hole 11 to fix the cover plate 2 on the top of the housing 1 to form a closed installation cavity. At this time, the top surface of the first template 33 is in contact with the bottom surface of the cover plate 2. The pre-tightening bolt 4 passes through the first fixing hole 21 and the second fixing hole 32 to tighten the cover plate 2 and the template 3. The cover plate 2 is used to limit the sintering material located in the material groove of the first template 33 to ensure the height of the blank after sintering is completed. At the same time, the template connection body is limited to prevent its movement relative to the housing 1 and the cover plate 2, which affects the processing accuracy.

[0080] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A mold for the sintering process of copper-based friction materials, characterized in that, It includes a housing (1) and a cover plate (2). The housing (1) and the cover plate (2) are fixed to form a sealed installation cavity. A number of templates (3) are stacked in the installation cavity. A number of material grooves (31) are evenly arranged on the template (3). A number of first fixing holes (21) are arranged on the cover plate (2). Second fixing holes (32) corresponding to the first fixing holes (21) are arranged on the template (3). A pre-tightening bolt (4) passes through the first fixing hole (21) and the second fixing hole (32) to fix between the cover plate (2) and the template (3). A number of exhaust holes are arranged on the side wall of the material groove (31). The exhaust holes are arranged at the top of the side wall of the material groove (31). The aperture of the exhaust hole is 0.03 - 0.06 mm. The template (3) includes a first template (33) at the topmost layer and a number of second templates (34) below the first template (33). A number of third fixing holes (331) are formed on the first template (33). Fourth fixing holes (341) corresponding to the third fixing holes (331) are arranged on the second template (34). A first connecting bolt (5) passes through the third fixing hole (331) and the fourth fixing hole (341) to fix between the first template (33) and the second template (34).

2. A mold according to claim 1, characterized in that, The radial cross-section of the third fixing hole (331) is stepped, including a yielding part (332) and a connecting part (333) arranged in sequence from high to low. The yielding part (332) is adapted to the head of the first connecting bolt (5).

3. A mold according to claim 1, characterized in that, A number of fifth fixing holes (22) are evenly arranged at the outer edge of the cover plate (2). Sixth fixing holes (11) corresponding to the fifth fixing holes (22) are arranged on the housing (1). A second connecting bolt (6) passes through the fifth fixing hole (22) and the sixth fixing hole (11) to fix the cover plate (2) on the top of the housing (1).

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