Radial shaft seals with one or more PTFE sealing lip(s) are designed to withstand aggressive environments, high temperatures, high pressures and dry running that traditional radial shaft seals made of elastomeric sealing lip materials cannot withstand. Many of the PTFE compounds are FDA approved. Main advantages of PTFE seals include:
- High chemical resistance
- Withstand speeds up to 30 m/s (5 900 ft/min)
- Wide operating temperature range, –70 to +250 °C (–95 to +480 °F)
- Withstand pressures up to 3,5 MPa (500 psi)
- Withstand dry running
The profiles shown are a selection of the most commonly used SKF seal designs with sealing lips made of PTFE. They can be installed in existing housing grooves where traditional radial seals are used, provided that the grooves are manufactured in accordance with international standards.
There are two main executions of PTFE seals: those with a metal case SL (fig 1), SLX (fig 2), SLS (fig 3), SLA (fig 4), DL (fig 5) and DLA (fig 6) and those without a metal case (YSLE (fig 7), YNSLE (fig 8) and YSL (fig 9). The metal case can be made of steel, aluminium or any of the stainless steel materials SS 304, SS 316 and SS 316 TI. The PTFE material should be selected based on the needs of the application.
PTFE seals without a metal case can be designed with an O-ring in the outside diameter groove to provide static sealing ability. Both the PTFE and O-ring material can be selected to meet the demands of different operating conditions, e.g. in the food industry to enable disassembly of the equipment for cleaning.
The selection of seal materials typically requires a compromise between advantages and disadvantages. There are hundreds of different PTFE materials with a variety of fillers. Common fillers include glass fibre, carbon, graphite, molybdenum disulphide, metal oxides and various polymers. Each possesses different properties, appropriate for different applications and service conditions. Common to all filled PTFE materials are their improved resistance to wear and deformation.
Unfilled PTFE provides, in most cases, a lower coefficient of friction than a filled PTFE material and the lowest degree of wear of the seal counterface. However, a sealing lip made of an unfilled PTFE material has limited resistance to wear and deformation under load.
Selecting the appropriate material for the metal case and the O-ring(s) is also of significant importance to achieving satisfactory sealing performance. Contact SKF for additional information.
Special care must be taken during handling and installation of PTFE seals. For detailed information, refer to the section PTFE seals.
Size range and availability
The majority of PTFE radial shaft seals from SKF are made to order to meet the demands of each application. There are, however, certain standard sizes within the ranges of approximately 6 to 200 mm (0.250 to 8 in.) shaft diameter and approximately 16 to 230 mm (0.630 to 9 in.) bore diameter. Contact SKF for detailed information regarding designs and sizes.