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Home >> Shaft Seals >> Oil Seals >> Sealing Element Material Properties

 

Sealing Element (Rubber)

An oil seal normally consists of three basic components: Sealing Element, Metal Case, and Spring. The function of an oil seal is to prevent leakage along the shaft. This is mainly achieved by the sealing element. Materials normally used are Nitrile, Acrylic, Silicone, and Fluorinated Rubber.

Silicone Rubber (SI)

Silicone compounds operate effectively in a broad temperature range of -50 to 180° C. It is unsurpassed in its resistance to heat and low temperatures. The high lubricant absorbency of silicone minimizes friction and wear. It is usually used for crank shaft seals. Silicone has poor hydrolysis resistance. It should not be used in oxidized or hypoid oils.

Nitrile Rubber (NBR)

NBR is most commonly used material. It has good heat resistance properties, good resistance to oils, salt solutions, hydraulic oils, and gasoline. Operation temperatures are recommended from -40 to 120° C. It also functions well in dry environments, but only for intermittent periods. The disadvantage is poor chemical resistance.

Fluorinated Rubber (VI)

Fluorinated rubber is widely known under the DuPont trade name of Viton®. It has the best resistance to chemicals, and superior performance to high temperatures. Though Viton® provides so many good prospects, it has the highest cost.

Polyacrylate Rubber (PA)

Acrylic rubber has better heat resistance than Nitrile. It is recommended for high surface speed environments. The operation temperatures are recommended from -20° C to 150° C. It should not be used with water or in temperatures below -20° C.

Lubrication

Oil seals are designed to operate with either oil or grease lubrication. Insufficient levels of lubrication cause excessive heat build up and reduce the life expectance of the seal lip and the shaft.
When selecting a lubricant ensure that the lip material is compatible with the lubricant base materials. Before installation both the seal and shaft should be sufficiently lubricated.

 

MATERIAL PERFORMANCE

NITRILE PA SILICONE VITON
Temperature  Range (°C) -40 to 120 -20 to 150 -50 to 180 1-30 to 200
Hardness (Shore) 70/80 70/80 75/85 70/80
Wear Resistance O X XX X
Costs Most economical 3rd costly 2nd costly Highest
O: Applicable | X: Applicable but must be observed | XX: Applicable in a limited amount of time | XXX: Not Applicable

MATERIAL CHEMICAL RESISTANCE

NITRILE PA SILICONE VITON
Inorganic acids
Organic acids XXX XX XX
Alkali XX O O O
Salt O O O O
Alcohol XXX O O O
Esters XXX XXX XXX
Phenol XXX XXX O
Ketones XXX XXX XX
O: Applicable | X: Applicable but must be observed | XX: Applicable in a limited amount of time | XXX: Not Applicable

RPM and Surface Speed

The following table shows the permissible surface speed and RPM’s for various sealing element materials and shaft diameters.

DMR_RPMSurfaceSpeed
FPM = shaft diameter in inches X RPM X .262 | m/s = shaft diameter in millimeters X RPM X 0.0000523

 

 

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