The seal is assured by a beading of elastomer fitted to the inside or the outside of the sheet. The shape of the beading and its attachment to the sheet are designed in such a way that the compression of the elastomer absorbs the faults in the flatness and deformation due to expansion while remaining within acceptable stress constraints.
When the fixing screws of a crankcase are being tightened, the reaction of the sealing element (paste or paper) can cause a deformation of the flatness of the seal. This deterioration of flatness often causes leaks when expansion occurs.
To solve this problem, Paulstra offers a metallic-elastomeric seal.
The metal part consists of a thin sheet. The fixing screws which act on this rigid material haven o effect on the flatness of the crankcase.
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.
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).
The mini-lip has many advantages:
– Reduced dimensions
The decrease in height and the difference between the internal and external diameters allow type IE seals to be used for applications where only type IO used to be possible. The reduced dimensions also mean less weight.
– Less energy loss due to friction
The radial load is smaller, which leads to a decrease of about 30% of the friction torque, which results in:
– a gain in power for the prime mover.
– less heating.
– Increased life
The decrease in heating due to friction results in a lower temperature, which:
– improves the life of the elastomer.
– slow carbonisation, which causes leaks by producing irregularities and stiffening the lip.
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.
