PTFE Shaft seals

Where High-Speed Seals Are Found

High speed rotary shaft seals are found in many applications.  Examples would include cryogenic deflashing equipment, vacuum pumps, torpedo shaft seals, gas turbine engine starters, and submersible dredge pumps.  AC/DC motors often require high speed shaft seals, and can be found in items like CNC tool spindles and dental or surgical instruments.

Smooth Operation

Another key issue with high speed seals is the need for smooth operation, which means avoiding problems like stick-slip.  PTFE is an ideal material for avoiding stick-slip, and supports smooth, quiet operation.

Friction

Friction can make or break a high-speed seal.  At high speeds, the effects of friction have a greater impact on seal performance.  Shaft seals need to have extremely low friction, and since some applications may prohibit the use of lubricants, there is a good chance that the ideal polymer material for a high-speed seal will be self-lubricating.  

PTFE is ideal for addressing this challenge because it has the lowest coefficient of friction of any material known to man, and is also self-lubricating.  

Elevated Temperatures

One of the main challenges in high speed shaft seals is controlling temperatures.  High speed leads to increased heat generation.  Heat generation leads to dimensional changes, which means that a high-speed seal needs to have a small coefficient of thermal expansion to ensure dimensional stability.  

Another goal is to conduct heat away from seal, which means that along with a small coefficient of thermal expansion the seal material needs to have a high coefficient of thermal conductivity.  Not all heat can be conducted away, however.  A high-speed seal needs to be made of a material that can handle higher temperatures.  

PTFE can perform well in temperatures up to 500°F.  It has good thermal conductivity which can be greatly improved using carbon fillers, and has a low coefficient of thermal expansion which can be enhanced through fillers such as glass and carbon.

Efficiency

As already mentioned, high speed shaft seals are often used with AC/DC motors.  These are often small and may be battery powered, making efficiency a very important factor.  If losses can be minimized, efficiency can be maximized and have a positive effect on battery life.  A low friction material that promotes smooth operation is vital for these types of applications, and PTFE certainly fits that bill.