Radial Shaft Seals
Radial shaft seals are used to seal rotary elements, such as a shaft or rotating bore. Common examples include strut seals, hydraulic pumps seals, axle seals, power steering seals, and valve stem seals. Early radial shaft seals utilized rawhide as the sealing element, and many elastomeric seal companies today once were tanneries. The advent of modern elastomers replaced rawhide, industry also added a garter spring which helps the sealing lip compensate for lip wear and elastomer material changes.
The seal construction will consist of a sprung main sealing lip which has a point contact with the shaft. The point contact is formed by two angles, with the air side angle usually less than the oil side angle. Depending on the seal type these two angles are varied to create a pressure distribution at the seal contact point which has a steeper slope on the oil side of the seal. The shallower the slope on the oil side of the seal the wetter the seal will run. The spring is positioned such that axially the centerline of the spring is biased to the air side of the lip contact point.
Basic types and main characteristics of DIN 3760 standards:
Type A
Metal pad is covered with a rubber layer, which ensures a safe position in the housing during the exploitation. Type A is proposed for widely usage.
Type AS
Is made with double sealing lips for serious conditions of exploitation, such as dust, humidity, water, etc. Sealing lip is filled with adequate lubricants during assembly.
Type B
Is made for small variations of temperature and higher axis oscillation .
Type BS
Is made for combined use in severe conditions.
Type C
Type CS
Type DUO
Is made for the separation of two different sealing media (water-oil, hydraulic and motor oil).
Extrenal diameter(d2)
External diameter of Radial Shaft Seals are measured in two places, with a turn of 90 degrees. The exact measure comes as the average value of the measures. Arithmetic difference between the two measurements gives the value of deviations from circular shape.Materials and labels of materials
Radial shaft seals production is most often made of the four basic material, on the basis of rubber:
Nitrile butadiene rubber (NBR)
Due to its outstanding characteristics (good performance and low cost) this
material is the broadest application in the production of Radial shaft seals.
NBR has a very good physical and mechanical properties, application in the exploitation of a wide range of temperature. However at the working
temperatures above 100 ° C, special attention should be paid to other
influential elements, such as the type or types of material and
axis rotation speed.
Gasket made of this material is installed in the automotive industry, the engines, Exchange boxes, wheels, etc.. Ne preporučuju se međutim, za ugradnju kod radilica i kod bregastih osovina motora. Not recommended, however, for the installation of crankshaft and engine shafts.
EPDM
EPDM is black, very resistant to the influence of water, ozone, chemical substances (acids, bases, and their solutions) and up to 150 ° C. Applied mainly in the food industry (milk, fat, juice, etc.). Should not get in contact with motor oils and fats.
Silicone rubber (Si)
Seals made of this material are marked Si. Chemical properties of material allow the application to a wide range of temperature. It is very resilient and resistant to the influence of various motor oils and at higher temperatures exploitation
It is desirable that seals can reach atmospheric air, otherwise the elastomer will collapse. Seals made of Si are more expensive than the NBR seals are
Fluoriune rubber (FP)
This material is closest to the concept of the ideal material for making seals. It has excellent chemical resistance even at low and high (from -30 ° C to +280 ° C) temperature. The most known Fluorine rubber on the market, made on the basis of Fluoride rubber is VITON, by USA's manufacturer Du Pont.
The largest obstacle in using FP for producting seals is high price elastomers.
