Teflon has the following advantages:
– a very low coefficient of friction.
– resistance to aggressive products.
The life of this type of seal is much longer than that of elastomer lip seals. As teflon does not have elastomeric properties, the seal is ensured by the hydrodynamic effect of the ridges.
The static seal is ensured by the pressure of the teflon on a beading of elastomer. The use of this type of seal is limited to applications which do not need to be sealed at rest.
A moulded lip guarantees a better geometrical fit of the sealing lip by eliminating the machining tolerances on:
– the lip angle on the fluid side,
– the distance between the edge of the lip and the axis of the spring,
– the length of the lip (i.e. the distance between the fixing rim and the sealing edge).
In an automatic gearbox, the setting in motion and the changing of gears are done by clutches on which pistons, moved by oil pressure, act.
Up to the present, these pistons were in moulded aluminium alloy or steel. The sealing for aluminium pistons was done by elastomer seals of various shapes fitted into the grooves or, for steel pistons, kept in position by outer rings.
This type of seal has its own friction track.
Its main advantages are:
-reduces the need to grind the shaft,
-treatment of only one part,
-no shaft wear,
– protection of the lip in storage and handling,
– in a bearing, it can serve as a supporting element until it is fitted in the unit.
Instead of the metal plate, Paulstra offers a rubberised cover which has the following advantages:
– only a simple shape needs to be machined in the crankcase.
– only one part needs to be fitted to ensure the closure of the crankcase with a perfect seal.
