A method for preparing polytetrafluoroethylene-coated aluminum powder

Abstract

The application discloses a preparation method of polytetrafluoroethylene coated aluminum powder, which comprises the following steps: (1) preparing materials: according to the mass percentage, 93-99% aluminum powder and 1-7% coating material are weighed, the coating material is polytetrafluoroethylene and fluxing agent, and the fluxing agent is polyethylene wax and wax-based auxiliary agent; (2) coating treatment: the weighed aluminum powder is firstly put into a kneader, the oxygen concentration in the kneader is controlled to be lower than 5%, then the weighed polytetrafluoroethylene, polyethylene wax and wax-based auxiliary agent are put into the kneader together, and the materials are stirred and kneaded at a temperature of 110-120 DEG C for 30-60 min; (3) cooling and discharging: when the temperature of the materials in the kneader is lower than 45 DEG C, the materials can be discharged to obtain the polytetrafluoroethylene coated aluminum powder. The application simplifies the process, reduces the melting point of the polytetrafluoroethylene, makes the coating more easily completed, improves the wrapping quality of the aluminum powder, and makes the prepared polytetrafluoroethylene aluminum powder have perfect sphericity.

Description

Technical Field

[0001] This invention belongs to the technical field of industrial aluminum powder production, specifically relating to a method for preparing polytetrafluoroethylene-coated aluminum powder. Background Technology

[0002] Polytetrafluoroethylene (PTFE)-coated aluminum powder is a composite powder material. Its core consists of aluminum powder particles coated with a layer of PTFE material through a specific process, forming a core-shell structure. PTFE-coated aluminum powder has applications in many fields. It can be developed into a new, highly efficient damage unit, significantly increasing air defense and anti-light armor capabilities. It can also be used as a rocket propulsion system or a micro-propulsion system for space satellites. In the petroleum industry, it can be used in perforated projectiles to increase oil extraction efficiency. In thermal conductive materials, it can be used as a filler for silicone oil. Currently, the mainstream method for preparing polytetrafluoroethylene-coated aluminum powder is liquid-phase mixing-ball milling-sintering. For example, in patent CN201910308376.1, an aluminum powder / polytetrafluoroethylene composite material and its preparation method, the aluminum powder / polytetrafluoroethylene composite material is composed of 26.5%-95% by mass of micron-sized aluminum powder and 5-73.5% by mass of polytetrafluoroethylene. The steps for preparing the aluminum powder / polytetrafluoroethylene composite material are: (1) weigh aluminum powder and polytetrafluoroethylene according to the proportion, add a polar dispersant, mix and then ultrasonically vibrate to form a uniform suspension; (2) dry the suspension until the polar dispersant completely evaporates. (2) Transfer to vacuum drying at 50°C for 2 hours and allow to cool naturally; (3) Under vacuum, ball mill the cooled sample, with a ball-to-material ratio of 6:1 to 12:1, a ball milling speed of 150 to 500 r / min, and a ball milling time of 15 to 2 hours; (4) Take out the ball-milled sample and sinter it at 310 to 340°C under a nitrogen atmosphere, keep it warm, and allow it to cool naturally; (5) After sintering, mechanically crush it and collect it by sieving to obtain the composite material. The process of this patent is simple, with little environmental pollution, and is suitable for industrial production. By enhancing Al-F bonding through mechanochemical action, the uniformity and performance of the composite material can be improved. For example, the literature "Composite Polytetrafluoroethylene Materials, Their Preparation Methods and Applications" relates to the field of polytetrafluoroethylene materials technology, disclosing composite polytetrafluoroethylene materials, their preparation methods and applications. The preparation method of the composite polytetrafluoroethylene materials includes: mixing PFA and filler at a mass ratio of 100:150-200 to coat the surface of the filler with PFA to obtain modified PFA filler; mixing the modified PFA filler with a modification solution to obtain a mixed slurry, and then evaporating the solvent in the mixed slurry to obtain a modified composite filler with a network structure coating layer on the surface; mixing polytetrafluoroethylene and modified composite filler at a mass ratio of 100:20-30 to obtain a mixture; and molding the mixture into a billet and then sintering it. The finished rods prepared by this method have good wear resistance and good mechanical properties.While the above-mentioned preparation methods can yield coating materials with relatively good performance, they have the following drawbacks during production: First, during the coating process, a certain amount of dispersant needs to be added to dissolve the aluminum powder into a suspension. The mixing process must be carried out in a solvent, followed by filtration and drying, making the process complex. Second, the dissolved and dried suspension needs to undergo high-intensity extrusion to force the polytetrafluoroethylene (PTFE) and aluminum powder to bond together, such as ball milling and impact. High-intensity extrusion alters the original morphology of the aluminum powder, affecting some of its properties, such as flattening the spherical shape, which reduces its filling capacity. Third, because PTFE has a high melting point of 327°C, the molten PTFE will carbonize at this temperature, leading to impurity formation and PTFE modification. At this temperature, the aluminum powder will soften to some extent. During the continuous stirring of the coating process, the spherical shape of the aluminum powder will change, resulting in a significant decrease in the high filling capacity of the aluminum powder and uneven and unstable PTFE-coated aluminum powder. Therefore, it is objectively necessary to develop a method for preparing polytetrafluoroethylene-coated aluminum powder that is simple to produce, can effectively improve the coating quality of products, and can ensure the performance of products. Summary of the Invention

[0003] In order to solve the technical problems of complex production process, altered product performance and uneven aluminum powder coating in the background technology, the purpose of this invention is to provide a simple production process that can effectively improve the coating quality of the product and ensure the performance of the product by preparing polytetrafluoroethylene coated aluminum powder.

[0004] This invention discloses a method for preparing polytetrafluoroethylene-coated aluminum powder, comprising the following steps: (1) Material preparation: Weigh out 93-99% aluminum powder and 1-7% coating material according to the mass percentage. The coating material is polytetrafluoroethylene and flux. The amount of polytetrafluoroethylene added accounts for 65-70% of the total amount of the coating material. The flux is polyethylene wax and wax-based additives. The amount of polyethylene wax added accounts for 18-25% of the total amount of the coating material. The amount of wax-based additives added accounts for 8-15% of the total amount of the coating material. (2) Coating treatment: First, put the aluminum powder weighed in step (1) into the kneader. After the feeding is completed, remove the air in the kneader and fill the kneader with nitrogen to control the oxygen concentration in the kneader to be less than 5%. Then, put the polytetrafluoroethylene, polyethylene wax and wax-based additive weighed in step (1) into the kneader together. Heat the material in the kneader under stirring and let the material be stirred and kneaded at a temperature of 110-120℃ for 30-60 minutes. The stirring and kneading speed of the kneader is 40-60 r / min. (3) Cooling and discharging: After the mixing and kneading are completed, stop heating the material and continue mixing. When the temperature of the material in the kneader is below 45°C, discharge the material to obtain polytetrafluoroethylene-coated aluminum powder.

[0005] Compared with existing technologies, the advantages of this invention are as follows: First, the raw materials used in the production of polytetrafluoroethylene aluminum powder according to this invention, besides aluminum powder, only use a coating material, without the addition of other solvents or elements. It eliminates the need for dissolving, filtering, and drying operations, simplifying the production steps and making the production process simple and easy to operate. Second, this invention directly mixes and kneads the weighed coating material and aluminum powder in a kneader, avoiding the problem of forcibly bonding PTFE and aluminum powder through high-intensity extrusion. This effectively prevents structural damage, deformation, or flattening of the aluminum powder, ensuring that the aluminum powder possesses excellent properties. Mechanical properties; thirdly, this invention optimizes the production process of polytetrafluoroethylene aluminum powder, reducing the temperature of mixing and kneading the coating material and aluminum powder. The polytetrafluoroethylene coating material is less likely to melt at low temperatures, and the aluminum powder will not soften at low temperatures. By reducing the heating temperature to achieve the coating of aluminum powder with polytetrafluoroethylene, deformation during the coating process can be avoided. It can significantly increase the filling amount of aluminum powder in polytetrafluoroethylene, and make the resulting coated polytetrafluoroethylene aluminum powder spherical, uniform and intact, without the phenomena of flakes, irregular shapes, cracks, clumps or lumps. It can effectively improve the coating quality of the product and is easy to promote and use. Attached Figure Description

[0006] Figure 1 This is a schematic diagram of the overall structure of the present invention; Figure 2 This is a side view excluding the metering feed assembly 8 in this invention; Figure 3 for Figure 1 Enlarged schematic diagram of the middle shock absorber bracket 2; Figure 4 Images showing the morphology of the products produced in Examples 1-3 after being bathed in a water bath at 80°C for 24 hours; Figure 5 Images showing the morphology of the products produced in Examples 1-3 after immersion in a pH 2 hydrochloric acid solution for 24 hours. Figure 6 Images showing the morphology of the products produced in Examples 1-3 after being subjected to pH 2 hydrochloric acid solution and heated to 80°C for 24 hours. Figure 7 Electron microscope images of the product produced in Example 1; Figure 8 Electron microscope images of the product produced in Example 2; Figure 9 Electron microscope images of the product produced in Example 3; In the diagram: 1-Frame, 2-Shock-absorbing bracket, 21-Support column, 22-Telescopic rod, 23-Seat body, 24-First spring, 25-Second spring, 26-Guide rod, 27-Slide plate, 28-Third spring, 3-Kneading box, 4-Box cover, 5-Agitator, 6-Transmission mechanism, 7-Feed pipe, 8-Quantitative feeding assembly, 81-Aluminum powder storage tank, 82-PTFE storage tank, 83-Polyethylene wax, 84-Wax-based additive storage tank, 85-Weight sensor, 86-Upper positioning plate, 87-Lower positioning plate, 88-Feeding pipe, 89-Guide inclined pipe, 8 10-Intermediate conduit, 811-Screw conveyor shaft, 812-Drive motor, 9-Dust collector, 10-Discharge pipe, 11-Heating jacket, 12-First temperature sensor, 13-Second temperature sensor, 14-Nitrogen storage tank, 15-Nitrogen filling pipe, 16-Temperature control component, 161-Heat transfer oil buffer tank, 162-Circulation pipe, 163-Circulation valve, 164-Circulation pump, 165-Third temperature sensor, 166-Electric heater, 167-Fourth temperature sensor, 168-Heat exchanger, 169-Return pipe, 1610-Heat transfer oil conveying pipe. Detailed Implementation

[0007] The present invention will be further described below with reference to the embodiments and accompanying drawings, but this does not limit the present invention in any way. Any changes or substitutions made based on the teachings of the present invention are within the protection scope of the present invention. Example 1

[0008] The method for preparing polytetrafluoroethylene-coated aluminum powder described in Example 1 includes the following steps: (1) Material preparation: Weigh 93% aluminum powder and 1% coating material according to the mass percentage. The particle size of the aluminum powder is 150μm. The coating material is polytetrafluoroethylene and flux. The amount of polytetrafluoroethylene added accounts for 65% of the total amount of the coating material. The flux is polyethylene wax and wax-based additive. The amount of polyethylene wax added accounts for 18% of the total amount of the coating material. The amount of wax-based additive added accounts for 8% of the total amount of the coating material. The wax-based additive is stearic acid or paraffin wax. In addition to aluminum powder, the raw materials used in the production of polytetrafluoroethylene aluminum powder in this invention are only coating materials. No other solvents or elements are added. The coating material only needs to be used to coat the aluminum powder during the kneading and stirring process. There is no need to dissolve, filter and dry. The production process is simple and easy to operate. (2) Coating treatment: First, put the aluminum powder weighed in step (1) into the kneader. After the feeding is completed, remove the air from the kneader and fill the kneader with nitrogen to control the oxygen concentration in the kneader to be less than 5%. Then, put the polytetrafluoroethylene, polyethylene wax and wax-based additive weighed in step (1) into the kneader together. Heat the material in the kneader under stirring and let the material be stirred and kneaded at 110°C for 30 minutes. The stirring and kneading speed of the kneader is 40 r / min. In this invention, the weighed coating material and aluminum powder are directly stirred and kneaded in the kneader, avoiding the use of high-strength extrusion to promote the reaction between polytetrafluoroethylene and metal powder. The forced bonding effectively prevents the aluminum powder structure from being damaged, deformed, or flattened, ensuring excellent mechanical properties. It also lowers the mixing and kneading temperature of the coating and aluminum powder. The PTFE coating is less prone to melting at low temperatures, and the aluminum powder does not soften under low-temperature conditions. By reducing the heating temperature to coat the aluminum powder with PTFE, deformation during the coating process is avoided. This significantly increases the amount of aluminum powder filling the PTFE, resulting in spherical, uniform, and intact PTFE-coated aluminum powder, preventing flaky, irregular, broken, clumped, or agglomerated phenomena, thus effectively improving the coating quality of the product. (3) Cooling and discharging: After the mixing and kneading are completed, stop heating the material and continue mixing. When the temperature of the material in the kneader is below 45°C, discharge the material to obtain polytetrafluoroethylene-coated aluminum powder. Example 2

[0009] The preparation method of polytetrafluoroethylene-coated aluminum powder described in Example 2 includes the following steps: (1) Material preparation: Weigh 96% aluminum powder and 4% coating material according to the mass percentage. The particle size of the aluminum powder is 100μm. The coating material is polytetrafluoroethylene and flux. The amount of polytetrafluoroethylene added accounts for 72% of the total amount of the coating material. The flux is polyethylene wax and wax-based additive. The amount of polyethylene wax added accounts for 20% of the total amount of the coating material. The amount of wax-based additive added accounts for 10% of the total amount of the coating material. The wax-based additive is stearic acid or paraffin. In addition to aluminum powder, the raw materials used in the production of polytetrafluoroethylene aluminum powder in this invention are only coating materials. No other solvents or elements are added. The coating material only needs to be used to coat the aluminum powder during the kneading and stirring process. There is no need to dissolve, filter, or dry it. This simplifies the production steps and makes the production process simple and easy to operate. (2) Coating treatment: First, put the aluminum powder weighed in step (1) into the kneader. After the feeding is completed, remove the air from the kneader and fill the kneader with nitrogen to control the oxygen concentration in the kneader to be less than 5%. Then, put the polytetrafluoroethylene, polyethylene wax and wax-based additive weighed in step (1) into the kneader together. Heat the material in the kneader under stirring and stir and knead at 115°C for 45 minutes. The stirring and kneading speed of the kneader is 50 r / min. In this invention, the weighed coating material and aluminum powder are directly stirred and kneaded in the kneader, avoiding the use of high-strength extrusion to promote the reaction between polytetrafluoroethylene and metal powder. The forced bonding effectively prevents the aluminum powder structure from being damaged, deformed, or flattened, ensuring excellent mechanical properties. It also lowers the mixing and kneading temperature of the coating and aluminum powder. The PTFE coating is less prone to melting at low temperatures, and the aluminum powder does not soften under low-temperature conditions. By reducing the heating temperature to coat the aluminum powder with PTFE, deformation during the coating process is avoided. This significantly increases the amount of aluminum powder filling the PTFE, resulting in spherical, uniform, and intact PTFE-coated aluminum powder, preventing flaky, irregular, broken, clumped, or agglomerated phenomena, thus effectively improving the coating quality of the product. (3) Cooling and discharging: After the mixing and kneading are completed, stop heating the material and continue mixing. When the temperature of the material in the kneader is below 45°C, discharge the material to obtain polytetrafluoroethylene-coated aluminum powder. Example 3

[0010] The preparation method of polytetrafluoroethylene-coated aluminum powder described in Example 3 includes the following steps: (1) Material preparation: Weigh 99% aluminum powder and 1% coating material according to the mass percentage. The particle size of the aluminum powder is 1μm. The coating material is polytetrafluoroethylene and flux. The amount of polytetrafluoroethylene added accounts for 70% of the total amount of the coating material. The flux is polyethylene wax and wax-based additive. The amount of polyethylene wax added accounts for 25% of the total amount of the coating material. The amount of wax-based additive added accounts for 15% of the total amount of the coating material. The wax-based additive is stearic acid or paraffin. In addition to aluminum powder, the raw materials used in the production of polytetrafluoroethylene aluminum powder in this invention are only coating materials. No other solvents or elements are added. The coating material only needs to be used to coat the aluminum powder during the kneading and stirring process. There is no need to dissolve, filter, or dry it. This simplifies the production steps and makes the production process simple and easy to operate. (2) Coating treatment: First, put the aluminum powder weighed in step (1) into the kneader. After the feeding is completed, remove the air from the kneader and fill the kneader with nitrogen to control the oxygen concentration in the kneader to be less than 5%. Then, put the polytetrafluoroethylene, polyethylene wax and wax-based additive weighed in step (1) into the kneader together. Heat the material in the kneader under stirring, and stir and knead the material at a temperature of 110-120°C for 60 minutes. The stirring and kneading speed of the kneader is 60 r / min. In this invention, the weighed coating material and aluminum powder are directly stirred and kneaded in the kneader, avoiding the use of high-strength extrusion to promote the bonding of polytetrafluoroethylene with metal. The forced bonding of powder effectively prevents the aluminum powder structure from being damaged, deformed, or flattened, ensuring excellent mechanical properties. It also lowers the mixing and kneading temperature of the coating and aluminum powder. The PTFE coating is less prone to melting at low temperatures, and the aluminum powder does not soften under low-temperature conditions. By reducing the heating temperature to coat the aluminum powder with PTFE, deformation during the coating process is avoided. This significantly increases the amount of aluminum powder filling the PTFE, resulting in spherical, uniform, and intact PTFE-coated aluminum powder, preventing flakes, irregular shapes, breakage, clumping, and lumps, thus effectively improving the coating quality of the product. (3) Cooling and discharging: After the mixing and kneading are completed, stop heating the material and continue mixing. When the temperature of the material in the kneader is below 45°C, discharge the material to obtain polytetrafluoroethylene-coated aluminum powder.

[0011] like Figures 1-3The kneading machines used in Examples 1-3 have the same structure. Each kneading machine includes a frame 1 and a body. The body is mounted on the frame 1 via multiple sets of shock-absorbing supports 2. These supports reduce vibration and extend the machine's lifespan. The body includes a kneading box 3 and a cover 4 mounted on top of the box 3. In this example, the cover 4 can be connected to the kneading box using snap-fit ​​or flange connections. Two parallel stirring paddles 5 are rotatably mounted inside the kneading box 3. A transmission mechanism 6 connected to the stirring paddles 5 is mounted on the frame 1. The two cooperating stirring paddles inside the kneading box 3 are arranged in parallel. In this example, the stirring paddles can be any type of blade used in existing kneading machines. The transmission mechanism 6 is located outside the kneading tank, and its connection with the transmission mechanism 6 adopts the existing connection method, which will not be improved here and will not be described in detail. A feed pipe 7 is installed on the box cover 4, and a feed valve is installed on the feed pipe 7. A quantitative feeding component 8 connected to the feed pipe 7 is installed above the frame 1. The quantitative feeding component 8 is used to quantitatively add aluminum powder and coating material to the kneading box 3. A manhole and an exhaust pipe are also provided on the box cover 4. The manhole facilitates access to the kneading box 3 for cleaning and maintenance of its internal components. A dust collector 9 connected to the exhaust pipe is installed on the frame 1. A discharge pipe 10 is installed at the bottom of the kneading box 3, and a discharge valve is installed on the discharge pipe 10. The exhaust pipe and dust collector 9 work together with the discharge pipe 10 to discharge... When discharging material through the material pipe 10, the exhaust pipe can be opened, and the generated dust enters the dust collector 9, avoiding environmental pollution. Heating jackets 11 are spaced apart on the outer side of the kneading box 9. The heating jacket 11 has a heat transfer oil inlet at the top and a heat transfer oil outlet at the bottom. A temperature regulating component 16 is installed between the heat transfer oil inlet and outlet. A first temperature sensor 12 and a second temperature sensor 13 are respectively installed on the kneading box 3 and the heating jacket 11. The first temperature sensor 12 facilitates real-time monitoring of the material temperature inside the kneading box 3, and the second temperature sensor 13 facilitates real-time monitoring of the heating temperature inside the heating jacket 11. High-temperature heat transfer oil enters the heating jacket 11 to heat the material inside the kneading box 3. The high-temperature heat transfer oil flows through the heating jacket 11. The material flows downwards, entering the temperature control component 16 through the heat transfer oil outlet. After the temperature control component 16 adjusts the temperature of the high-temperature heat transfer oil, it returns to the heating jacket 11 for circulation. This ensures the uniformity of the material's heating temperature. A nitrogen storage tank 14 is installed on the frame 1, and a nitrogen filling pipe 15 is installed on the nitrogen storage tank 14, which is connected to the kneading box 3. A pressure regulator, a flow meter, and an inlet valve are sequentially installed on the nitrogen filling pipe 15 along the airflow direction. Nitrogen holes are provided on the side wall of the kneading box 3. In actual use, when the aluminum powder in the kneading box 2 needs to expel or isolate oxygen during the wrapping process, the nitrogen valve is opened, and the nitrogen in the nitrogen storage tank 14 supplies inert nitrogen gas to the material inside the kneading box 3 through the nitrogen filling pipe 15.Inert nitrogen gas is discharged through the nitrogen vent to remove and isolate oxygen during the reaction process, ensuring its proper operation. To enhance automation, the kneader can be equipped with a controller similar to those used in existing technology to automatically control the feeding of the quantitative feeding component, the heating temperature of the temperature control component, and the nitrogen charge.

[0012] Furthermore, to facilitate the metering and weighing of aluminum powder, polytetrafluoroethylene (PTFE), polyethylene wax, and wax-based additives, and to improve the accuracy and efficiency of feeding, the quantitative feeding assembly 8 includes an aluminum powder storage tank 81, a PTFE storage tank 82, a polyethylene wax storage tank 83, and a wax-based additive storage tank 84. The aluminum powder storage tank 81 is used to weigh aluminum powder, the PTFE storage tank 82 is used to weigh PTFE, the polyethylene wax storage tank 83 is used to weigh polyethylene wax, and the wax-based additive storage tank is used to weigh wax-based additives. Multiple weight sensors 85 are evenly distributed around the outer side of the wax 83 and wax-based additive storage tank 84 along the circumferential direction. An upper positioning plate 86 is installed above the weight sensors 85 and is mounted on the outer side of the tank wall. A lower positioning plate 87 is installed at the bottom of the weight sensors 85 and is mounted on the top of the frame 1. The weight sensors 85 are the structure used in the prior art. Finished products are purchased according to the usage requirements. The weight is measured by multiple weight sensors 85, and the average weight value is taken as the weight of the raw materials stored in each storage tank. To facilitate the temporary weighing of raw materials in each storage tank and improve feeding efficiency, a discharge pipe 88 is installed at the bottom of each of the following storage tanks: aluminum powder tank 81, polytetrafluoroethylene tank 82, polyethylene wax tank 83, and wax-based additive tank 84. A discharge valve is installed on each discharge pipe 88, and a guide pipe 89 is installed below the discharge pipe 88. The guide pipe 89 is mounted on the frame 1, and sealing plates are installed at both ends. A middle conduit 810 connected to the feed pipe 7 is installed at the lower end of the guide pipe 89. When material needs to be added to one of the storage tanks, the discharge pipe 88 connected to it is opened, and the material in the storage tank will enter the guide pipe 89. The material enters the kneading box 3 through the intermediate conduit 810 and the feed pipe 7. Preferably, to avoid material blockage in the guide tube 89, a spiral feeding shaft 811 is rotatably installed in the guide tube 89 along its axial direction. A drive motor 812 is installed on the frame 1. The output shaft of the drive motor 812 is connected to one end of the spiral feeding shaft 811. The drive motor 812 is a structure used in the prior art, and finished products can be purchased according to the needs of use. In use, the drive motor 812 drives the spiral feeding shaft 811 to rotate. The rotation of the spiral feeding shaft 812 will convey the material in the guide tube 89, avoiding material blockage in the guide tube 89.

[0013] Furthermore, to reduce the vibration of the kneading box 3 and extend its service life, the shock-absorbing bracket 2 includes a support column 21, a telescopic rod 22, and a base 23. The base 23 has a hollow internal structure and is installed at the bottom of the frame 1. A guide hole is machined on the top of the base 23. The telescopic rod 22 is installed inside the base 23, and a first spring 24 is fitted on the telescopic rod 22. The lower end of the support column 21 is installed on the upper end of the telescopic rod 22, and the upper end of the support column 21 passes through the guide hole and is fixedly connected to the bottom of the machine body. A second spring 25 is fitted on the support column 21 between the base 23 and the machine body, and multiple guide rods 26 are evenly distributed inside the base around the telescopic rod 22. A sliding plate 27 is installed at the lower end of the support column 21. The sliding plate 27 is slidably mounted on the guide rods 26. A third spring 28 is fitted on the guide rods 26 on the lower side of the sliding plate 27. The first spring 24, the second spring 25 and the third spring 28 can alleviate the vibration generated by the stirring paddle 5 during the stirring process, which can improve the stability of the device operation and extend the service life of the kneader.

[0014] Furthermore, to ensure the uniformity and stability of the material heating temperature within the kneading chamber 3, the temperature control assembly 16 includes a heat transfer oil buffer tank 161 and a circulation pipe 162. One end of the circulation pipe 161 is connected to the heat transfer oil outlet, and the other end is connected to the heat transfer oil inlet. Along the flow direction of the heat transfer oil, a circulation valve 163, a circulation pump 164, a third temperature sensor 165, an electric heater 166, a fourth temperature sensor 167, and a heat exchanger 168 are sequentially installed on the circulation pipe 161. The heat exchanger 168 is equipped with a cold water inlet and a cold water outlet. The circulation pipe 162 connects the circulation valve 163 to the heat transfer oil outlet. A return pipe 169 connected to the heat transfer oil buffer tank 161 is installed on the 62, and a return valve is installed on the return pipe 169. A heat transfer oil delivery pipe 1610 connected to the heat transfer oil buffer tank 161 is installed on the circulation pipe 162 between the circulation valve 163 and the circulation pump 164, and a delivery valve is installed on the heat transfer oil delivery pipe 1610. The buffer tank 161 is equipped with a heat transfer oil inlet. In use, if the high-temperature heat transfer oil is used to heat the material in the heating jacket 11, the return pipe 169 and the heat transfer oil delivery pipe 1610 need to be closed, and the circulation valve 163 and the circulation pump 164 need to be opened to heat the high-temperature heat transfer oil in the heating jacket 11. The high-temperature heat transfer oil will flow within the circulation pipe 161. During the circulation process, the third temperature sensor 165 and the fourth temperature sensor 167 can monitor the temperature of the high-temperature heat transfer oil in real time. When the temperature of the high-temperature heat transfer oil is lower than the set heating temperature, the electric heater 166 needs to be turned on to reheat the high-temperature heat transfer oil. The electric heater 166 is a structure in the existing technology, and finished products are directly purchased based on the usage. If the temperature of the high-temperature heat transfer oil is detected to be higher than the set heating temperature, the heat exchanger 168 needs to be used to cool down the high-temperature heat transfer oil to ensure that the heating temperature entering the heating jacket 11 is maintained. The heat exchanger 168 can adopt the shell-and-tube heat exchanger structure used in the existing technology, ensuring uniformity and stability. If the material does not need to be heated but needs to be cooled and discharged, the circulating pump 164 and the circulating valve 163 are turned off, and the return pipe 169 is opened to transport the high-temperature heat transfer oil to the heat transfer oil storage tank 161. When heating is required again, the return pipe 169 is turned off again, the circulating pump 164 and the circulating valve 163 are turned on, and the heat transfer oil delivery pipe 1610 is opened to send the high-temperature heat transfer oil into the circulating pipe 161 through the heat transfer oil delivery pipe 1610. The kneading box can be heated again according to the above heating steps.

[0015] Examples 1-3 only require stirring and kneading to coat the coating material and aluminum powder, which simplifies the process and reduces the difficulty of production. Furthermore, since the stirring and kneading are carried out at low temperatures, this avoids the melting of PTFE and softening of the aluminum powder, ensuring excellent mechanical properties of the aluminum powder. It also improves the filling rate and coating quality of the aluminum powder within the PTFE, achieving a filling rate of >95%. The resulting PTFE aluminum powder exhibits no flaky, irregular, broken, or clumped characteristics; it has good sphericity and relatively uniform size, with a tap density ≥1.55 g / cm³. 3 The active aluminum content is ≥94.5%.

[0016] The inventors conducted the following verification on the polytetrafluoroethylene-coated aluminum powder obtained in Examples 1-3 above. The verification revealed that the polytetrafluoroethylene-coated aluminum powder possesses excellent mechanical properties and product quality. Details are as follows: like Figures 4-6 As shown, the inventors mixed the polytetrafluoroethylene-coated aluminum powder prepared in Examples 1-3 and subjected it to tests including 80°C water bath, pH2 hydrochloric acid solution immersion, and pH2 hydrochloric acid solution immersion and heating to 80°C. After 24 hours of observation, the polytetrafluoroethylene-coated aluminum powder did not react in any of the water bath, acid immersion, or water bath + acid immersion tests. It did not produce bubbles or boil. After 48 hours of stability, no bubbles were observed. The test showed that the aluminum powder had excellent mechanical properties.

[0017] like Figures 7-9 As shown, the inventors took electron microscope images of the polytetrafluoroethylene-coated aluminum powders prepared in Examples 1 to 3. The electron microscope images showed that the polytetrafluoroethylene-coated aluminum powders prepared in Examples 1 to 3 were well dispersed, their morphology did not change from the original aluminum powder, and there were no free irregularities between the aluminum powder particles. The polytetrafluoroethylene could completely coat the aluminum powder, and the coated polytetrafluoroethylene aluminum powder had good sphericity and uniformity, resulting in good product quality.

Claims

1. A method for preparing polytetrafluoroethylene-coated aluminum powder, characterized in that, Includes the following steps: (1) Material preparation: Weigh out 93-99% aluminum powder and 1-7% coating material according to the mass percentage. The coating material is polytetrafluoroethylene and flux. The amount of polytetrafluoroethylene added accounts for 65-70% of the total amount of the coating material. The flux is polyethylene wax and wax-based additives. The amount of polyethylene wax added accounts for 18-25% of the total amount of the coating material. The amount of wax-based additives added accounts for 8-15% of the total amount of the coating material. (2) Coating treatment: First, put the aluminum powder weighed in step (1) into the kneader. After the feeding is completed, remove the air in the kneader and fill the kneader with nitrogen to control the oxygen concentration in the kneader to be less than 5%. Then, put the polytetrafluoroethylene, polyethylene wax and wax-based additive weighed in step (1) into the kneader together. Heat the material in the kneader under stirring and let the material be stirred and kneaded at a temperature of 110-120℃ for 30-60 minutes. The stirring and kneading speed of the kneader is 40-60 r / min. (3) Cooling and discharging: After the mixing and kneading are completed, stop heating the material and continue mixing. When the temperature of the material in the kneader is below 45°C, discharge the material to obtain polytetrafluoroethylene-coated aluminum powder.

2. The method for preparing polytetrafluoroethylene-coated aluminum powder according to claim 1, characterized in that: In step (1), the particle size of the aluminum powder is 1 to 150 μm.

3. The method for preparing polytetrafluoroethylene-coated aluminum powder according to claim 1, characterized in that: In step (1), the amount of polyethylene wax added accounts for 20% of the total amount of the coating, and the amount of wax-based additives added accounts for 10% of the total amount of the coating.

4. The method for preparing polytetrafluoroethylene-coated aluminum powder according to claim 1, characterized in that: In step (1), the wax-based additive is stearic acid or paraffin.

5. The method for preparing polytetrafluoroethylene-coated aluminum powder according to claim 1, characterized in that: In steps (2) and (3), the kneader includes a frame (1) and a body. The body is mounted on the frame (1) via multiple sets of shock-absorbing brackets (2). The body includes a kneading box (3) and a box cover (4) mounted on top of the kneading box (3). Two parallel stirring paddles (5) are rotatably mounted inside the kneading box (3). A transmission mechanism (6) connected to the stirring paddles (5) is mounted on the frame (1). A feed pipe (7) is mounted on the box cover (4), and a feed valve is provided on the feed pipe (7). A quantitative feeding assembly (8) connected to the feed pipe (7) is provided above the frame (1). A manhole and an exhaust pipe are also provided on the box cover (4). An exhaust valve is provided on the exhaust pipe. A dust collector (9) connected to the exhaust pipe is mounted on the frame (1). A discharge pipe (10) is provided at the bottom of the kneading box (3), and a discharge valve is installed on the discharge pipe (10). A heating jacket (11) is provided at intervals on the outside of the kneading box (9). A heat transfer oil inlet is provided at the upper part of the heating jacket (11), and a heat transfer oil outlet is provided at the lower part. A temperature control component (16) is provided between the heat transfer oil inlet and the heat transfer oil outlet. A first temperature sensor (12) and a second temperature sensor (13) are respectively provided on the kneading box (3) and the heating jacket (11). A nitrogen storage tank (14) is provided on the frame (1). A nitrogen filling pipe (15) connected to the kneading box (3) is provided on the nitrogen storage tank (14). A pressure regulator, a flow meter and an air inlet valve are arranged sequentially along the airflow direction on the nitrogen filling pipe (15). A nitrogen hole is provided on the side wall of the kneading box (3).

6. The method for preparing polytetrafluoroethylene-coated aluminum powder according to claim 6, characterized in that: The quantitative feeding assembly (8) includes an aluminum powder storage tank (81), a polytetrafluoroethylene storage tank (82), a polyethylene wax (83), and a wax-based additive storage tank (84). Multiple weight sensors (85) are evenly distributed along the circumference on the outer sides of the aluminum powder storage tank (81), the polytetrafluoroethylene storage tank (82), the polyethylene wax (83), and the wax-based additive storage tank (84). An upper positioning plate (86) is installed above each weight sensor (85), and the upper positioning plate (86) is installed on the outer side of the tank wall. A lower positioning plate (87) is installed at the bottom of each weight sensor (85). The position plate (87) is installed on the top of the frame (1). The bottom of the aluminum powder storage tank (81), polytetrafluoroethylene storage tank (82), polyethylene wax (83) and wax-based additive storage tank (84) are respectively equipped with a discharge pipe (88). A discharge valve is installed on the discharge pipe (88). A guide pipe (89) is installed below the discharge pipe (88). The guide pipe (89) is installed on the frame (1). Sealing plates are installed at both ends of the guide pipe (89). An intermediate guide pipe (810) communicating with the feed pipe (7) is installed at the lower end of the guide pipe (89).

7. The method for preparing polytetrafluoroethylene-coated aluminum powder according to claim 5, characterized in that: A spiral feeding shaft (811) is rotatably installed inside the guide tube (89) along its axial direction. A drive motor (812) is installed on the frame 1. The output shaft of the drive motor (812) is connected to one end of the spiral feeding shaft (811).

8. The method for preparing polytetrafluoroethylene-coated aluminum powder according to claim 5, characterized in that: The shock absorber bracket (2) includes a support column (21), a telescopic rod (22), and a base (23). The base (23) has a hollow internal structure and is installed at the bottom of the frame (1). A guide hole is machined on the top of the base (23). The telescopic rod (22) is installed inside the base (23). A first spring (24) is fitted on the telescopic rod (22). The lower end of the support column (21) is installed on the upper end of the telescopic rod (22). The upper end of 21) passes through the guide slide hole and is fixedly connected to the bottom of the machine body. A second spring (25) is installed on the support column (21) between the seat (23) and the machine body. Multiple guide rods (26) are evenly installed inside the seat around the telescopic rod (22). A slide plate (27) is installed at the lower end of the support column (21). The slide plate (27) is slidably installed on the guide rod (26). A third spring (28) is installed on the guide rod (26) on the lower side of the slide plate (27).

9. The method for preparing polytetrafluoroethylene-coated aluminum powder according to claim 5, characterized in that: The temperature control assembly (16) includes a heat transfer oil buffer tank (161) and a circulation pipe (162). One end of the circulation pipe (161) is connected to the heat transfer oil outlet, and the other end is connected to the heat transfer oil inlet. A circulation valve (163), a circulation pump (164), a third temperature sensor (165), an electric heater (166), a fourth temperature sensor (167), and a heat exchanger (168) are sequentially installed on the circulation pipe (161) along the flow direction of the heat transfer oil. The heat exchanger (168) is provided with a cold water inlet and a cold water outlet. A return pipe (169) connected to a heat transfer oil buffer tank (161) is installed on the circulation pipe (162) between the circulation valve (163) and the heat transfer oil outlet. A return valve is installed on the return pipe (169). A heat transfer oil delivery pipe (1610) connected to a heat transfer oil buffer tank (161) is installed on the circulation pipe (162) between the circulation valve (163) and the circulation pump (164). A delivery valve is installed on the heat transfer oil delivery pipe (1610). A heat transfer oil addition port is installed on the buffer tank (161).

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