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).
It avoids “irregularities” in the sealing ridge which could be caused by the machine tool.
Nowadays, the moulded lip has become a standard technique, thanks to:
– more accurate machining of the mould,
– suitable means of testing,
– improved vacuum moulding techniques.
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.
The efficiency of the ridge increases with its size.
Teflon has the following advantages:
– a very low coefficient of friction.
– resistance to aggressive products.
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.
