Maintenance and Replacement of Gaskets
NBR rubber is above all resistant to oils, especially hydraulic oils, lubricants, petrol and other aliphatic hydrocarbons, diluted acids and lyes. Good physical values such as high friction resistance and ruggedness and good temperature resistance (-25 °C up to +120 °C, in part to -40 °C) give this natural rubber a wide range of uses.
Advantages of Silicone and Rubber Gaskets
When the bore and shaft centers are misaligned, seal life will be shortened because the wear will be concentrated on one side of the sealing lip.
The seal shown in Fig. 14.2 is a relatively simple design; most automotive seals are more complex. Dust lips are often used to keep outside contaminants away from the oil lip seals; such seals thus have undercuts that make demolding more difficult. Fluoroelastomer compounds used for such undercut shapes must have reasonably high elongation at break at molding temperatures to avoid tearing the part during demolding. The metal insert is often U-shaped, and stock may be molded to form a thin layer over the outside of the insert. Since both compression and injection molding methods are used, suppliers of fluoroelastomers for shaft-seal applications often must provide different versions of the same polymer composition-medium to high viscosity for compression molding, and low to medium viscosity for injection molding. Different precompounds may be necessary to accommodate relatively long compression-molding times at low temperature and very short injection-molding times at high temperature.
a) The shaft on which the oil seal is to be mounted should be ground with the surface finish or surface roughness between 0.2 to 0.8 Microns. It is best for the shaft to be hardened atleast to 40 – 45 HRc in order to prevent groove formation on the shaft due to the pressure exerted by the spring.
Rubber covered