INTRODUCTION:
The two main parts of a rotary shaft seal are a rigid outer case and the flexible sealing lip (typically made of an elastomeric material). The outer case provides the stiffness and structure needed to keep the seal stable, and protects the lip during installation.
A popular choice for the sealing lip is PTFE, better known as Teflon. Its chemical compatibility, low friction, and outstanding performance at high speeds have made it a favorite among engineers. However, what is the best case material to combine with a PTFE lip for rotary shaft seals?
Metal Seals VS Polymer Seals
The first issue that arises with metal cases is the need to fasten the lip to the case. This is done through crimping or bonding. Bonding can pose a problem with seals made of an advanced plastic such as PTFE, and may require additional assembly to attach the seal lip to the metal case. However, non-metal cases can be made as a one piece mold that reduces the chances of a leak path developing.
Non-metal cases are usually polymer-based composites, and include Neoprene/Aramid and Flouroelastomer/Aramid. Here are the benefits to using a non-metal case:
- Provides a rust-proof gasket type seal at the outer diameter
- Reduces machining costs fills slight imperfections in the bore housing
- Fits a considerable range of bore tolerances
- Softer exterior prevents damage to the housing
- Excellent for applications that require regular seal removal
- Resist corrosion better
- Can be molded as one piece with the PTFE flexible lip
- There are some applications where a metal case simply cannot be used
Metal cases are made of heat treated cold rolled steel (including zinc-plated), stainless steel, brass, aluminum, or Hastelloy. Many of the metal cases are subsequently coated in a polymer or elastomeric material. Use of a metal case provides its own set of benefits:
- Provides more rigidity than most polymer cases
- Performs well in extreme high pressure applications
- Has an unlimited shelf life
- Excels in a wider temperature range than non-metal cases
CONCLUSION:
After reviewing the application parameter, the conclusion is that either a metal case or a non-metal case could be applicable. Contact Advanced EMC Technology for further highly qualified reccommendaitons.
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