A method for preparing graphite-modified polytetrafluoroethylene pre-sintered material

Abstract

The present invention belongs to the field of pipe processing, and provides a method for preparing a graphite-modified polytetrafluoroethylene pre-sintered material, comprising: uniformly mixing polytetrafluoroethylene powder and graphite, and pre-granulating; drying the material, sintering into blocks, cooling, and crushing to obtain uniform particles; wherein the amount of graphite is 5-30% of the polytetrafluoroethylene powder; the mixing comprises: low-speed mixing and high-speed crushing; the specific steps of the mixing include: mixing the materials in a low-speed mixer for 5-8 minutes. Compared with the traditional process, the preparation process of the present invention first granulates into uniform particles, and then sintering and crushing are performed, so that the obtained particles are uniform in size, and are evenly heated during extrusion, which greatly improves the strength and toughness of the pipe fittings.

Description

Technical Field

[0001] The invention belongs to the field of pipe processing, and particularly relates to a method for preparing a graphite-modified polytetrafluoroethylene pre-sintered material. Background Art

[0002] The information disclosed in this background technology section is only intended to enhance the understanding of the overall background of the invention, and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art.

[0003] Graphite can improve the wear resistance, thermal conductivity, self-lubrication, electrical conductivity, heat deformation resistance, etc. of polytetrafluoroethylene. At the same time, graphite is suitable for use in environments such as high temperature resistance, wear resistance, and corrosion resistance. After polytetrafluoroethylene is modified with graphite, the application environment of existing polytetrafluoroethylene can be broadened, so that it is not limited to food, insulation, and oxidant environments. In the traditional application fields of polytetrafluoroethylene (food, insulation, oxidants), there are fewer restrictions on the size and shape of products. Generally, products with large sizes or thick walls can be directly molded using polytetrafluoroethylene powder or granules filled with graphite. After sintering the blank, it can be processed into a finished product. However, in special environments (high temperature resistance, wear resistance, and corrosion resistance), the finished gasket is required to have small size and thin wall characteristics. Small-sized blanks are prone to cracking during molding, so the molding process cannot meet its needs. Summary of the invention

[0004] In order to solve the above problems, the present invention provides a method for preparing a graphite-modified polytetrafluoroethylene pre-sintered material, which adopts an extrusion process instead of molding. At the same time, the preparation process of the graphite-modified polytetrafluoroethylene pre-sintered material is improved to better meet the extrusion process and prepare a small-sized thin-walled tube with better quality.

[0005] In order to achieve the above object, the present invention adopts the following technical solution:

[0006] The first aspect of the present invention provides a method for preparing a graphite-modified polytetrafluoroethylene pre-sintered material, comprising:

[0007] The polytetrafluoroethylene powder and graphite are mixed evenly and pre-granulated;

[0008] The material is dried, sintered into blocks, cooled, and crushed to obtain uniform particles;

[0009] The amount of graphite used is 5-30% of the polytetrafluoroethylene powder;

[0010] The mixing includes: low-speed mixing and high-speed crushing;

[0011] The specific steps of the low-speed mixing include: mixing the materials in a low-speed mixer for 5-20 minutes.

[0012] The second aspect of the present invention provides a graphite-modified polytetrafluoroethylene pre-sintered material prepared by the above method.

[0013] The third aspect of the present invention provides the use of the above-mentioned graphite-modified polytetrafluoroethylene pre-sintered material in the preparation of pipes.

[0014] Beneficial effects of the present invention

[0015] (1) Due to the low friction coefficient and high lubricity of graphite, it requires higher technical skills in molding. To address the problem of difficulty in molding thin-walled products, the present invention uses graphite-modified polytetrafluoroethylene, whose pre-sintered particles can pass the extrusion process well to achieve the expected finished product processing.

[0016] (2) The traditional pre-sintering material production process is to directly pressurize the powder into blocks, sinter and crush the particles, and the resulting particles are uneven in size. During the subsequent extrusion process, the uneven particle size causes different degrees of heating, and the resulting extruded pipes have different strengths and toughnesses, which will cause problems such as reduced yields. Compared with the traditional process, the preparation process of the present invention first forms uniform particles through granulation, and then sinter and crush them. The resulting particles are uniform in size, and are evenly heated during extrusion, which greatly improves the strength and toughness of the pipe fittings.

[0017] (3) The preparation method of the present invention is simple, practical and easy to promote. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention, and the exemplary embodiments of the present invention and their description are used to explain the present invention and do not constitute improper limitations on the present invention.

[0019] Figure 1 It is a process flow chart of the present invention. DETAILED DESCRIPTION

[0020] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0021] A method for preparing a graphite-modified polytetrafluoroethylene pre-sintered material, comprising:

[0022] The polytetrafluoroethylene powder and graphite are mixed evenly and pre-granulated;

[0023] The material is dried, sintered into blocks, cooled, and crushed to obtain uniform particles;

[0024] The amount of graphite used is 5 to 30% of the polytetrafluoroethylene powder;

[0025] The mixing includes: low-speed mixing and high-speed crushing;

[0026] The specific steps of the low-speed mixing include: mixing the materials in a low-speed mixer for 5-20 minutes.

[0027] In some embodiments, the weight of each mixing is between 25-50KG.

[0028] In some embodiments, after the materials are mixed in a low-speed mixer, they are frozen at -20°C to -10°C for 2-3 hours.

[0029] In some embodiments, the frozen material is sent to a high-speed crushing barrel and mixed and crushed for 1-15 minutes before discharging.

[0030] In some embodiments, the specific conditions of the sintering are sintering at 300° C. to 320° C. for 5 to 7 hours.

[0031] In some embodiments, the sintered material is cooled to room temperature.

[0032] In some embodiments, the pulverizing is performed using a hammer mill.

[0033] In some embodiments, the average particle size of the graphite-modified polytetrafluoroethylene pre-sintered material is 480-900 microns.

[0034] In some embodiments, the graphite-modified polytetrafluoroethylene pre-sintered material is made into a thin-walled tube by an extrusion process, wherein the extrusion process can adopt a currently common process, and the present application does not make any special limitation on this. Those skilled in the art can select corresponding equipment and processes according to the production requirements of the tube.

[0035] The present invention will be further described in detail below in conjunction with specific embodiments. It should be noted that the specific embodiments are intended to explain the present invention rather than to limit it.

[0036] In the following embodiments, the low-speed mixer, high-speed crushing barrel, and hammer mill are all commercially available equipment.

[0037] Example 1

[0038] like Figure 1 As shown in the preparation process flow chart of the present invention, the specific implementation steps are as follows:

[0039] 1. Process polytetrafluoroethylene powder and graphite in a certain proportion. Here, 15% graphite is used for filling. After weighing on a scale, mix and add them into the material barrel. Then mix the prepared materials in a low-speed mixer for 6 minutes. Control the weight of each mixture at 28KG.

[0040] 2. Send the low-speed mixed materials to the cold storage, control the temperature to -15℃, and freeze for 2.5 hours. Send the frozen materials to the high-speed crushing barrel, crush for 1.5 minutes, and discharge. After the materials are discharged here, particles have been formed, which optimizes the difficulty of implementing the later crushing and makes it easier to form particles.

[0041] 3. Put the material in step 2 into a material tray and put it into an oven. First, it needs to be dried. The dried material is then loaded into a sintering furnace. The sintering temperature is controlled at 300° C. and the sintering time is 5 hours to obtain a sintered graphite-modified polytetrafluoroethylene pre-sintered material.

[0042] 4. Use a clean material cart to remove the sintered material from the oven. After the material cools to room temperature, it can be seen that the particles sintered at this temperature are connected to each other. Finally, the present invention uses a hammer mill to crush and separate the connected particles into separate smooth particles, and finally samples are taken to test the performance and package for shipment.

[0043] Finally, through monitoring data, it is found that the test results obtained by the preparation process of the present invention are better than those of the traditional process, as shown in Table 1 below.

[0044] The present invention aims to overcome the problem of great difficulty in molding graphite-modified polytetrafluoroethylene, and realizes the processing of thin film tubes used in special environments through a new preparation process granulation pre-sintering method. The present invention is simple to operate, has uniform particles, improves product performance, is suitable for automated production, and has high output.

[0045] Example 2

[0046] like Figure 1 As shown in the preparation process flow chart of the present invention, the specific implementation steps are as follows:

[0047] 1. Process polytetrafluoroethylene powder and graphite in a certain proportion. Here, 5% graphite is used for filling. After weighing on a scale, mix and add them into the material barrel. Then mix the prepared materials in a low-speed mixer for 5 minutes. Control the weight of each mixture between 25KG.

[0048] 2. Send the low-speed mixed materials to the cold storage, control the temperature at -10℃, and freeze for 3 hours. Send the frozen materials to the high-speed crushing barrel, crush for 1 minute, and discharge the materials. After the materials are discharged here, particles have been formed, which optimizes the difficulty of implementing the later crushing and makes it easier to form particles.

[0049] 3. Put the material in step 2 into the material tray and put it into the oven. First, it needs to be dried. The dried material is then loaded into the sintering furnace. The sintering temperature is controlled at 310° C. and the sintering time is 6 hours to obtain the sintered graphite-modified polytetrafluoroethylene pre-sintered material.

[0050] 4. Use a clean material cart to remove the sintered material from the oven. After the material cools to room temperature, it can be seen that the particles sintered at this temperature are connected to each other. Finally, the present invention uses a hammer mill to crush and separate the connected particles into separate smooth particles, and finally samples are taken to test the performance and package for shipment.

[0051] Example 3

[0052] like Figure 1 As shown in the preparation process flow chart of the present invention, the specific implementation steps are as follows:

[0053] 1. Process polytetrafluoroethylene powder and graphite in a certain proportion. Here, 30% graphite is used for filling. After weighing on a scale, mix and add them into the material barrel. Then mix the prepared materials in a low-speed mixer for 8 minutes. Control the weight of each mixture between 30KG.

[0054] 2. Send the low-speed mixed materials to the cold storage, control the temperature to -20℃, and freeze for 2 hours. The frozen materials are sent to the high-speed crushing barrel, crushed for 2 minutes, and discharged. After the materials are discharged here, particles have been formed, which optimizes the difficulty of implementing the later crushing and makes it easier to form particles.

[0055] 3. Put the material in step 2 into the material tray and put it into the oven. First, it needs to be dried. The dried material is then loaded into the sintering furnace. The sintering temperature is controlled at 320° C. and the sintering time is 7 hours to obtain the sintered graphite-modified polytetrafluoroethylene pre-sintered material.

[0056] 4. Use a clean material cart to remove the sintered material from the oven. After the material cools to room temperature, it can be seen that the particles sintered at this temperature are connected to each other. Finally, the present invention uses a hammer mill to crush and separate the connected particles into separate smooth particles, and finally samples are taken to test the performance and package for shipment.

[0057] Comparative Example 1

[0058] The difference from the embodiment is that the material after low-speed mixing is molded into a block blank, and the molding pressure is 60 MPa.

[0059] Table 1, Comparison of experimental data

[0060]

[0061]

[0062] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. 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 method for preparing a graphite-modified polytetrafluoroethylene pre-sintered material, characterized in that: include: The polytetrafluoroethylene powder and graphite are mixed evenly and pre-granulated; The material is dried, sintered into blocks, cooled, and crushed to obtain uniform particles; Among them, the amount of graphite is 5~30% of the polytetrafluoroethylene powder; The mixing includes: low-speed mixing and high-speed crushing; The specific steps of the low-speed mixing include: mixing for 5-20 minutes using a low-speed mixer; The weight of each mix is ​​between 25-50KG; The specific conditions of the sintering are 300°C~320°C and sintering time of 5-7 hours; The average particle size of graphite-modified polytetrafluoroethylene pre-sintered material is 480~900 microns; After mixing at a low speed, the material is frozen at -20℃~-10℃ for 2-3 hours.

2. The method for preparing a graphite-modified polytetrafluoroethylene pre-sintered material according to claim 1, characterized in that: The frozen materials are sent to a high-speed crushing barrel and mixed and crushed for 1-2 minutes.

3. The method for preparing a graphite-modified polytetrafluoroethylene pre-sintered material according to claim 1, characterized in that: The sintered material is cooled to room temperature.

4. The method for preparing a graphite-modified polytetrafluoroethylene pre-sintered material according to claim 1, characterized in that: The crushing is carried out using a hammer mill.

5. A graphite-modified polytetrafluoroethylene pre-sintered material prepared by the method according to any one of claims 1 to 4.

6. Use of the graphite-modified polytetrafluoroethylene pre-sintered material according to claim 5 in the preparation of pipes.

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