Oil seals or shaft seals are an integral part in any rotating and moving part assembly. Oil seals find great deal of usage in gearboxes, hydraulic cylinders, etc. The usage of the seals in areas concerned with motion also earns them a name of “Dynamic Oil Seals." The purpose of the oil seals is
· To act as a physical barrier retaining the lubricating oil where it is bound to be.
· To prevent thelubricating oil from leaking outside even under high pressure of the oil.
· To act as a barrier and prevent dirt, contamination and other external entities from entering the system containing the lubricating oil.
Constructional Aspects of an Oil Seal: (Click here to see the figure)
1. The oil seal consists of a metal ring as the inner skeleton which provides the structural stability to the oil seal.
2. The outer skin is made of nitrile rubber and various other materials which are used based on the requirement.
3. The spring on the lip of the oil seal tends to provide support to the lip and prevents the lubricant from leaking outside and also prevents the entry of contaminants from outside.
Based on the application of the oil seal, the outer skin layer tends to differ. Here are some types of the materials used for the outer skin of the oil seal.
1. Nitrile rubber - The commonly used material for oil seals
2. Silicone – Used in specific applications where only light loads are applied.
3. Poly acrylate
4. Fluroelastomer also popularly known as Viton. – The high temperature resistant material used in places where temperature is more than 120 Degree Celcius.
5. PolytetraFluroEthylene (PTFE)
The oils seals require certain prerequisites to be maintained for their proper working. They are as follows:
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.
b) The area where the oil seal is seated is to be plunge ground in order to prevent wear grooves that normally tend to wear out the lip of the oil seal at a faster rate.
c) The lip of the oil seal needs to be lubricated in order to prevent the direct contact of the oil seal lip to the shaft.