What happens when the Teflon sheet is at a temperature above 19 °C

- Jul 17, 2019-

When the polytetrafluoroethylene sheet is at a temperature of 19 ° C or more, the lattice distance thereof becomes large, and the preformed article is deformed, eventually causing cracking inside the sintered product. 327 ° C is the melting point of polytetrafluoroethylene. Strictly speaking, above this temperature, the crystal structure disappears and changes to a transparent amorphous gel state with a specific volume increase of 25%. This gel-like melt viscosity, up to 1010 ~ 1011 Pa.s at 360 ° C, still does not flow. This property determines that the polytetrafluoroethylene cannot be subjected to the same method (for example, melt extrusion) as a general thermoplastic resin, and is subjected to a molding process, but is processed by a combination of pressure metallurgy pressurization and sintering. Since the thermal conductivity of polytetrafluoroethylene is low and the volume changes greatly at the upper and lower temperatures of the melting point, during the sintering process, the heating rate must be slow near the melting point to make the temperature inside and outside the product uniform; otherwise, the stress inside the product may be caused. Even cracking. The crystallinity of polytetrafluoroethylene has a certain influence on the physical properties and mechanical properties of the wire. Generally, the degree of crystallinity is large, the density of polytetrafluoroethylene is also large, and the physical and mechanical properties are improved; otherwise, it is small. Therefore, the crystallinity of polytetrafluoroethylene should be controlled during processing. The crystallinity of polytetrafluoroethylene is related to the size of the molecular weight and the cooling rate after sintering. At the same cooling rate, the PTFE plate has the smaller molecular weight, the easier it is to crystallize, and the higher the crystallization rate. Under the same molecular weight, the extremely slow cooling rate contributes to the recrystallization of macromolecules. High crystallinity. Up to 75% or so, if it is cooled rapidly, it can prevent the recrystallization of amorphous gel, and the crystallinity is small, but even the fastest cooling rate, its crystallinity is generally about 50%. Therefore, the cooling rate is different, and the crystallinity of the sintered polytetrafluoroethylene is usually between 50% and 70%, and the maximum crystallization rate is in the temperature range of 310 °C to 315 °C. PTFE sheet PTFE is a tough, soft, non-elastic, moderately tensile material with good low temperature properties. When the temperature is as low as (-269 ° C), PTFE is still ductile under pressure. 4.2 Polytetrafluoroethylene electrical insulation properties 4.2.1 Electrical properties of PTFE insulated wires Teflon has excellent electrical insulation properties over a wide range of temperatures and frequencies. Since the fluorine atoms in the polytetrafluoroethylene molecular chain are symmetric and evenly distributed, there is no inherent dipole moment, and the dielectric loss tangent tgδ and the relative dielectric constant ε r vary little in the power frequency 109 HZ range. From room temperature to 300 ° C, the actual change in the tg δ value of polytetrafluoroethylene is small, and εr decreases with increasing temperature.www.yihaoptfe.com