Polytetrafluoroethylene is used in many fields with its excellent characteristics, but no matter what product it is, it has corresponding good aspects, and naturally there are shortcomings. The disadvantages of pure PTFE in application are poor mechanical properties and bearing capacity, creep resistance, and thermal conductivity are not very ideal. In addition, we also noticed that the size of processed products often changes after a period of time. .
This is because the thermal expansion coefficient (linear expansion coefficient) of polytetrafluoroethylene itself is large, which leads to dimensional changes under the influence of the external environment. The dimensional instability of polytetrafluoroethylene after processing and secondary processing often affects its popularization and use.
The production of suspended PTFE products is carried out by the method of molding. At present, most of the powder adding methods are manual operations. Regardless of the processing of PTFE plates, PTFE rods, PTFE tubes or other products, it is necessary to calculate the products. The weight of the raw material is uniformly poured into the finished mold manually, and the raw materials are evenly dispersed in the mold by combing, vibrating, stirring and other methods, and then pressurized and formed. Due to the poor fluidity of PTFE powder, in order to maintain the uniform density of the product, a skilled operation is very important. Only uniform powder distribution and consistent density can ensure consistent product size shrinkage after heating and sintering. In addition, the molding process of the product will have a process of pressure control and pressure maintenance. According to the size of the specification, it is very important for us to choose an appropriate press with a certain pressure. A key is the holding time. Generally, the holding time of large products is long, and the holding time of corresponding small products is shorter. This is related to product quality, but we also need to consider the output factor of production.
Molded products have certain limitations, and many complex products must be realized through secondary processing. The cutting temperature should not be too high, because the thermal conductivity of tetrafluoroethylene is not good, and the deformation is large due to temperature changes, so it is best to use coolant to cool down when cutting. The cutting amount should not be too large, and it can be divided into fine turning or multiple turning, which can also effectively avoid the deformation of the workpiece. In short, the heat generated during the machining process should be minimized and the temperature generated by turning should be controlled to maintain dimensional stability. But for now, the processed PTFE materials still have thermal expansion and contraction, such as the size will change slightly in winter and summer, this is because of the large thermal expansion coefficient, so pay attention to control the tolerance range.
In order to solve the problem that the size of the parts after processing is not easily affected by temperature, the method of heating the PTFE blank product to about 200 °C at a constant temperature, keeping it for a period of time, and letting it cool down in the furnace slowly, in order to eliminate the internal stress of the material, This is the same as the heat treatment of metal. Let it cool for a few days, and the purpose is to relieve internal stress, and then cut it into a product.
Adding fillers to PTFE to enhance performance is also a frequently used method. On the one hand, because the added material has a small thermal expansion coefficient, it has a good effect on the dimensional stability of PTFE products. On the other hand, it can also increase the wear resistance, creep resistance and lubricity of tetrafluoro products. Commonly used fillers are: copper powder, glass fiber, carbon fiber, polystyrene resin, polyimide, graphite, molybdenum disulfide, silicon dioxide, barium sulfate, para-polyphenylene, ceramics, etc.
The basic material of the filled composite material is polytetrafluoroethylene powder, which is sintered by mixed molding. The filler is added to the PTFE powder suppliers in india to stabilize the product size. It should be noted here that the filled composite material is added according to the performance requirements, and the added amount occupies a certain proportion. Too much filler material may cause composite cracking and performance degradation; too little may not achieve the desired effect. Only filling in the proper proportion can not only enhance the performance of the product, but also ensure the stability of the product.
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