Polytetrafluoroethylene board products can only be made […]
Polytetrafluoroethylene board products can only be made with simple molding and extrusion processes. It is difficult to form and complex products must be processed by later machine tools. This limits the production efficiency of the product and wastes too much material during the processing.
Polytetrafluoroethylene board products have "cold flow". That is, the plastic deformation (creep) of the material product under long-term continuous load, which brings certain restrictions to its application. For example, when PTFE is used as a gasket, the bolts are tightened very tightly for a tight seal, so that when the specified compressive stress is exceeded, the gasket will produce "cold flow" (creep) and be crushed. These shortcomings can be overcome by adding appropriate fillers and improving the structure of the parts.
Polytetrafluoroethylene has a high melt viscosity and does not flow at high temperatures. It is above the melting point (327℃) and the melt viscosity reaches 1 010 Pa.s. It does not flow even if heated to the decomposition temperature, which makes it impossible to use general thermoplastic molding methods, but to use sintering similar to powder metallurgy. Method of molding.
Polytetrafluoroethylene board products have outstanding non-stick properties, which limits their industrial applications. It is an excellent anti-sticking material, and this performance makes it extremely difficult to bond with the surface of other objects.
PTFE board products have low thermal conductivity and poor thermal conductivity, which not only prevents it from being used as a bearing material, but also makes it impossible to quench when manufacturing thick-walled products.
The linear expansion coefficient of polytetrafluoroethylene board products is 10-20 times that of steel, which is larger than most plastics, and its linear expansion coefficient changes very irregularly with the change of temperature. In the application of PTFE, if insufficient attention is paid to this aspect, it is easy to cause losses.
When heated above 400℃, the cracking rate of PTFE gradually increases, and the decomposition products are mainly tetrafluoroethylene, perfluoropropylene and octafluorocyclobutane. Above 475°C, the decomposition product has a very small amount of highly toxic perfluoroisobutene. Note that the heating temperature should not exceed 400°C, and the laboratory should have a good ventilation system to help eliminate toxic gases.