When Should I Use Braided PTFE Packing, and In What Form?
Manufacturers of braided packings are often asked to simply supply "A PTFE packing." Though this may seem a straightforward request, it generates questions that must be answered to ensure the correct PTFE packing for the application. A clear understanding of the differences between the various forms of PTFE braided packing will enable a selection of reliable sealing for the pump or valve. Get more news about Ptfe Gland Packing,you can vist our website!
Of the many forms of PTFE braided packing, the right choice takes advantage of its strengths and minimizes its limitations. If selected and applied incorrectly, poor performance and increased maintenance can result. To apply PTFE effectively, one must understand the properties of the material. A few unique properties of PTFE make it an excellent ingredient for braided packings:
While PTFE has its strengths, certain properties of PTFE are not so desirable in many pump packing applications. Problems encountered with PTFE packings are usually the result of its poor thermal and mechanical properties:
Many manufacturers produce packing styles that use PTFE as the base fiber. These styles may be supplied as dry fibers, fibers coated with PTFE dispersion, or fibers coated with various lubricants. Good practice uses these products only where there is no other PTFE alternative for the service, including applications with very aggressive chemicals, such as strong oxidizers, or those requiring materials suitable for use in food or pharmaceutical processes. Consult a packing manufacturer to determine what specific styles are suitable for these services.
With PTFE fiber packing it is particularly important to follow the manufacturer's limits for temperature, speed, and pressure. When used in rotating equipment, these packings can be very sensitive to adjustment. Typically, lower gland pressure is needed and higher leak rates are experienced than with other packing styles.
Expanded PTFE (ePTFE) Packings
ePTFE yarns are similar in appearance to a twisted PTFE tape. The most common form is an ePTFE impregnated with graphite to increase its thermal conductivity and speed rating. ePTFE braids are less sensitive to heat buildup than PTFE fiber packings. They tolerate higher speeds and provide lower leak rates. ePTFE packings may exhibit cold flow and extrusion under higher pressures.
When the superior chemical resistance of pure PTFE is not required, many fiber materials can be coated with PTFE to improve packing performance and take advantage of PTFE's strengths. These fibers can also help to reduce or eliminate some of the weaknesses of a pure PTFE braid.
Blended synthetic and fiberglass yarns can be coated with PTFE to produce economical, general service packings that exhibit higher resilience, greater extrusion resistance, and less sensitivity to adjustment than a PTFE fiber braid. They can also be coated with a dispersion mixture of PTFE and graphite to further increase the speed capability and heat dissipation characteristics of the braid.
Aramid fiber packings with a PTFE coating can be used in applications requiring extreme abrasion resistance. Novoloid fiber packings with PTFE coatings can be used in mild caustic services, and also exhibit better resilience and extrusion resistance than a PTFE fiber braid.
Carbon and graphite fiber braids with PTFE coatings are among the most versatile packing materials. They have excellent chemical resistance (with the exception of strong oxidizers), high speed capability, high temperature capability, and very good resilience. They are not prone to softening or extrusion at high temperature, and also exhibit good abrasion resistance.
