Compression springs of oil seals
As the original radial force exerted by the rotary shaft seal decreases because of the loss of mechanical and/or chemical properties due to its exposure to heat, the compression spring tends to maintain said force. The standard spring is prestressed by having tight coils. The thermal resistance of the spring is generally speaking much higher than the one of the seal rubber so that its force is more stable.
Usually, the steel used for the springs production follows the DIN 17223, SAE 1074 guidelines. However, in some specific applications and whatever is the oil material, the original Steel spring can be replaced by one in EN 1.4301 AISI302 or AISI304 Stainless steel.