This type of PTFE was the first to be introduced to the market. This style is made from virgin or reprocessed PTFE resin, without fillers, which is then molded, compressed and sintered. As with any other type of plastic, PTFE has a high creep factor when compressed. The creep factor is detrimental and can lead to having to re-tighten the bolts to maintain seating pressure and prevent leakage. The higher the temperature in the application it is used for, the more the creep factor will increase. Even with these drawbacks, PTFE is affordable, easily available and highly chemical resistant.
Skived PTFE:This style is similar to molded and sintered PTFE as it is also make of virgin or reprocessed PTFE without fillers. Instead of molding an individual sheet, the sheets are taken from a billet of PTFE with a process called skiving. The skiving process was developed to overcome manufacturing deficiencies of the molding process. Skived PTFE shares the same creep characteristics as molded and sintered PTFE.
Molded or Skived Filled PTFE:In order to correct the creep characteristics of molded and skived PTFE, manufacturers started adding mineral fillers or fibers in order to reduce creep factor. This indeed reduced the creep characteristics but not by a significant amount.
Restructured Filled PTFE:Besause the addition of fillers in the molding process was not enough to significantly reduce creep, a new manufacturing process was developed to produce filled PTFE sheets. In this new process the material is laminated before being sintered, which yeilds a highly fibrillated structure with significantly less creep. The different fillers used in this process are as follow:
• Barite: Added for use in strong caustic service. Also FDA compliant.• Mineral Silica: Used for strong acidic service.
• Hollow Glass Microshperes: Used to increase compressibility.
• Synthetic Silica: Used as subsitute for glass microspheres.
Expanded PTFE:
This style of PTFE is made by heating and stretching PTFE before sintering it. Lke all PTFE it has strong chemical resistance, but unlike molded or skived PTFE, this material has a high compressibility and is good for use in flanges made from fragile materials. The only drawback to this material is that its floppy and difficult to install, especially if the flanges cannot be separated.
