PTFE is a polymer of tetrafluoroethylene, a white or off-white substance. It
is made by polymerizing chloroform and hydrofluoric acid under high pressure to
make PTFE. At 370°C, the obtained tetrafluoroethylene powder is molded and
sintered to produce a tough, non-thermoplastic and non-porous resin. Although
PTFE is mostly crystalline, it has no melting point. Its plasticity increases
with increasing temperature, while its mechanical properties deteriorate
sharply. And when it is higher than 327°C, it turns into a non-flowing amorphous
jelly.
Above 400°C, ptfe decomposes and emits toxic volatile fluoride gas. Its low temperature performance is also very good, and it can still maintain its toughness when the temperature is no stick bbq mat lower than -80℃. Since PTFE has a dense structure, it has excellent vacuum performance. Its permeability is very low, and its vapor pressure and outgassing rate at room temperature are very low, which is better than rubber and other plastics. Its vapor pressure is 10-4Pa at 25°C and 4×10-3Pa at 350°C.
The PTFE compression molding method basically includes four steps of mixing, preforming, sintering and cooling. Pre-forming is to add PTFE powder evenly into the mold and press it at room temperature to form a compact pre-form (ie rough); sintering is to heat the pre-form above the melting point, and cooling is to drop the sintering temperature to room temperature the process of. Some PTFE is pressurized once above the melting point temperature. This molding die is called a hot press die, and the corresponding PTFE die is called a cold press die. When molding PTFE, attention should be paid to the influence of compression ratio (a Yin PTFE is 4-6) and molding shrinkage rate (generally PTFE is 2.6-4.5%) on the product.
The raw material is best to polymerize resin by suspension method, and the soft fine powder with a particle size of 20-500 microns is best. The pressing process must be 'deflated', the preforming pressure is 17-35 MPa, and the holding time depends on the thickness of the blank. For example, a 100 mm thick blank should be held for 15 minutes.