Industry News

How to distinguish between PTFE gaskets

2018-06-15
PTFE, abbreviated as F4 (PTFE), is known as the plastic king. It is a plastic material with excellent performance in the world today. It has excellent corrosion resistance, except fluorine at high temperature and alkali metals in the molten state and chlorine trifluoride. In addition, almost all kinds of chemicals on the earth can resist corrosion; good temperature resistance, can work at -180-250 °C temperature; good electrical insulation, the product can withstand 15,000 volts per mm thickness The above; good oxidation resistance, will not age in the earth environment for decades; its surface friction coefficient is very low, and has a rare surface non-fouling advantages; does not absorb water and other properties, but is widely used in chemical industry , petroleum, textile, pharmaceutical, metallurgy, machinery, electronics, electrical appliances, dyes, electricity, food, paper, water treatment, environmental protection, aviation, military and scientific research and other industries have a wide range of uses.

So to distinguish it from the good we must look from the appearance, good quality PTFE gasket surface is very clean and smooth, poor quality will generally have impurities. The appearance and color of the fine point can not be seen, especially when the increase is less than 30% of the following as long as there is no black spot is invisible, and others add back to the sale of more than 180 is not impossible. That kind of added too much, there are impurities too low.

If you want to really find out, cut the sample to do the tensile test, the domestic pure can have more than 20MPa, and it is very likely to add back the material. The reason for the low stretch is also the problem of the sintering process and the temperature rise is too fast.

PTFE gasket quality is mainly reflected in the thickness tolerance, PTFE is not a good sealing material, of course, with the exception of expanded PTFE, ordinary PTFE gasket, whether it is recycled materials or pure raw materials, there is cold flow, That is, the thickness will change in the long term, and the screws will be tightly pressed for a period of time. Therefore, the thickness tolerance is the preference for the quality of the PTFE gasket.

Non-metallic ring corrosion
1, graphite ring corrosion. Impervious graphite ring impregnated with resin, its corrosion has three reasons: First, when the end surface is overheated, the temperature is greater than 180oC, the impregnated resin to break away from the graphite ring, so that the ring wear resistance decreased; Second, the impregnated resin Improper selection, so the establishment of sealed cooling system, this is mainly caused by material selection error. The corrosion of the film, the passivation film usually has the protective effect, but the material used in the metal seal ring, such as stainless steel, cobalt, chromium alloy, etc., the surface of the passivation film is damaged in the friction of the end surface, in the absence of oxygen, the new The film is difficult to produce. It is necessary to select the corrosion-resistant impregnating resin and use high pressure impregnation to increase the impregnation depth.

2, oxidation of graphite rings. In an oxidizing medium, when the end surface is dry or poorly cooled, a temperature of 350 to 40oC is generated to cause the graphite ring to react with oxygen, and CO and gas are generated to make the end surface rough or even broken. Non-metallic rings can also rupture under the simultaneous action of chemical media and stress.

3, corrosion of seal ring of PTFE gasket manufacturer's products. Chemical changes occur in the medium and the wear resistance also decreases. Third, the impregnation depth of the resin is not enough. When the impregnation layer is worn away, the wear resistance decreases. F4 is filled with glass fibers, for example, cracks are first generated in the weak areas, and then develop to deeper depths, resulting in cracks. The cracks in the seal ring are generally radially divergent and may be one or more. Graphite powder, metal powder, etc. to improve its temperature resistance, wear resistance. Corrosion of filled F4 rings mainly refers to the selective corrosion, dissolution or deterioration of the filling. As in hydrofluoric acid, glass fiber molecules are hot-etched, so what should be filled depends on the circumstances.