Seal materials

Seals integrated in SKF bearings are typically made of sheet steel reinforced elastomers. The type of material can depend on the series and size of the bearing as well as the application requirements. SKF seals are generally made of the materials listed below.
Acrylonitrile-butadiene rubber

Acrylonitrile-butadiene rubber (NBR) is the “universal” seal material. This copolymer, manufactured from acrylonitrile and butadiene, has good resistance to the following media:

  • most mineral oils and greases with a mineral oil base
  • normal fuels, such as petrol, diesel and light heating oils
  • animal and vegetable oils and fats
  • hot water

The permissible operating temperature range is –40 to +100 °C (–40 to +210 °F). The seal lip can tolerate dry running within this temperature range for short periods. Temperatures up to 120 °C (250 °F) can be tolerated for brief periods. At higher temperatures, the material hardens.

Hydrogenated acrylonitrile-butadiene rubber

Hydrogenated acrylonitrile-butadiene rubber (HNBR) has appreciably better wear characteristics than NBR so that seals made of this material have a longer service life. HNBR is also more resistant to heat, ageing and hardening in hot oil or ozone exposure.

The upper operating temperature limit is 150 °C (300 °F), which is appreciably higher than that of NBR.

Fluoro rubber

Fluoro rubbers (FKM) are characterized by their high thermal and chemical resistance. Their resistance to ageing and ozone is very good and their gas permeability is very low. They have exceptionally good wear characteristics even under harsh environmental conditions and can withstand operating temperatures up to 200 °C (390 °F). The seal lip can tolerate dry running within this temperature range  for short periods.

FKM is resistant to oils and hydraulic fluids, fuels and lubricants, mineral acids and aliphatic as well as aromatic hydrocarbons which would cause seals made of other materials to fail. FKM should not be used in the presence of esters, ethers, ketones, certain amines and hot anhydrous hydrofluorides.

Seals made of FKM exposed to an open flame or temperatures above 300 °C (570 °F) are a health and environmental hazard! They remain dangerous even after they have cooled. Read and follow the safety precautions below.

Polytetrafluoroethylene

Polytetrafluoroethylene (PTFE) is a thermoplastic polymer that is characterized by it's high thermal and chemical resistance. PTFE seals provide exceptionally good wear characteristics even under harsh environmental conditions and can accommodate high circumferential speeds. The permissible operating temperature range is –70 to +200 °C (–90 to +390 °F). The seal lip can tolerate dry running within this temperature range for short periods. Temperatures up to 250 °C (480 °F) can be tolerated for brief periods.

Seals made of PTFE exposed to an open flame or temperatures above 300 °C (570 °F) are a health and environmental hazard! They remain dangerous even after they have cooled. Read and follow the safety precautions below.

Polyurethane
Polyurethane (PUR) is a wear-resistant organic material which has good elastic properties. It withstands operating temperatures from –20 up to +80 °C (–5 to+175 °F). It has good resistance to mineral oil-based greases, mineral oils with no or a low proportion of EP additives, water and water-oil mixtures. It is not resistant to acids, alkalis or polar solvents.

WARNING: HAZARDOUS FUMES

Safety precautions for fluoro rubber and Polytetrafluoroethylene


Fluoro rubber (FKM) and Polytetrafluoroethylene (PTFE) are very stable and harmless up to normal operating temperatures of 200 °C (390 °F). However, if exposed to temperatures above 300 °C (570 °F), such as fire or the open flame of a cutting torch, FKM and PTFE give off hazardous fumes. These fumes can be harmful if inhaled, as well as if they contact the eyes. In addition, once the seals have been heated to such temperatures, they are dangerous to handle even after they have cooled. Therefore, they should never come in contact with the skin.

If it is necessary to handle bearings with seals that have been subjected to high temperatures, such as when dismounting the bearing, the following safety precautions should be observed:
  • Always wear protective goggles, gloves and appropriate breathing apparatus.
  • Place all off the remains of the seals in an airtight plastic container marked with a symbol for “material will etch”.
  • Follow the safety precautions in the appropriate material safety data sheet (MSDS).

If there is contact with the seals, wash hands with soap and plenty of water and, if contact has been made with the eyes, flush eyes with plenty of water and consult a doctor immediately. If the fumes have been inhaled, consult a doctor immediately.

The user is responsible for the correct use of the product during its service life and its proper disposal. SKF takes no responsibility for the improper handling of FKM or PTFE, or for any injury resulting from their use.
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