There are various challenges for designing polymer seals and bearings for the food industry, such as FDA regulations if the seal or bearing will be in contact with food products or the ability to withstand intensive cleaning and sterilization.
There are five polymers that have risen to the top as effective materials for use in food processing:
- Virgin PTFE
- Mineral-filled PTFE
- UHMW PE
#1 Virgin PTFE
Virgin PTFE has many excellent characteristics for food applications:
- Chemical resistance
- A wide range of operating temperatures
- Availability in FDA approved grades
It is extremely easy to clean and sterilize compared to other polymers because it is hydrophobic and has very low moisture absorption. PTFE also has a maximum operating temperature of 500°F — the lowest coefficient of friction of any metal or polymer in existence.
#2 Mineral-filled PTFE
There are mineral-filled PTFE grades that are FDA compliant which share properties similar or superior to virgin PTFE. The inclusion of minerals such as mica provide for excellent dimensional stability, better load bearing capabilities, and far superior wear resistance over virgin PTFE. Like virgin PTFE, is has very low moisture absorption, an extremely low coefficient of friction, and a maximum operating temperature of 500°F.
#3 UHMW PE
UHMW PE (ultra-high molecular weight polyethylene) is self-lubricating, has very low moisture absorption, offers good wear resistance, and has the highest impact resistance of any polymer in
production. It is also FDA, 3A-Dairy, and USDA compliant. In addition, UHMW PE absorbs virtually no moisture and has a coefficient of friction on the same order of PTFE, but with a lower operating temperature.
PEEK is known for its ability to withstand the type of chemical attack it would be subjected to during common cleaning and sterilization procedures (including repeated steam-cleaning). It can also handle high temperatures up to 480°F. Grades of PEEK are available which are FDA approved for contact with food. In addition, PEEK is flame-resistant and low friction. It also offers superior mechanical strength compared to the other polymers, and excellent wear resistence.
Acetal offers very good strength and toughness along with chemical resistance to commonly used solvents, oil, and grease. Acetal can handle temperatures up to 250°F and has a very low coefficient of friction. Acetal is available in grades that are USDA, 3A-Dairy, and FDA compliant. Acetal is commonly used as a bearing material and is an excellent replacement for metal bearings.
The polymers we just discussed are well adapted to the challenges of a food processing environment such as chemical and heat resistance, low friction, and low moisture absorption. In general, all the polymers we just discussed are easy to clean, resistant to corrosion, able to withstand rigorous cleaning regimens, and will result in longer mean time to failure because of their durability and extremely low maintenance. These materials are excellent choice for polymer bearings, bushings, and seals.
Interested in reading more about Seals and Bearings for the Food and Dairy Industry?
- Using PTFE and UHMW to Solve Big Problems in Food And Dairy Industry
- Food and Dairy Applications: 10 Reasons Why You Should Opt for Polymer Bushings