Oil Seal Function and Working Principle

The area between the sealing edge and the shaft is the most important. The sealing effect is obtained by preloading the sealing lip, making its inner diameter slightly smaller than the diameter of the shaft. The garter spring ensures constant mechanical pressure and maintains the radial force on the shaft and extends the sealing edge to the defined width. Sealing is guaranteed by the surface tension of the hydrodynamic oil film between the flattened area of the seal and the shaft. The oil thickness must be between 1 and 3 mm to avoid leakage. The meniscus acts as an interface between the outside air and the fluid. Any rupture of the meniscus will cause a leak. This can occur if the shaft contains scratches along the path of the joint. Oil Seal Applications

OIL SEAL APPLICATIONS IN FARM TRACTORS

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The John Deere Waterloo Tractor Works, as manufacturers of farm tractors, does not manufacture oil seals. We rely on the manufacturers of oil seals for design assistance. After establishing the initial design, laboratory and field tests are required for verification.

One of the seal applications is on the crankshaft which must keep crankcase and transmission lubricants separated. Reliability and long life are imperative. Alertness as to the effect of detail changes on seal life is necessary to maintain long service life.

The front wheel bearing seals may be subjected to submersion in water and mud. Packing, lip and face type seals have been tested with the face type proving the most rugged, although the most costly of the three types.

A problem of design and space which was encountered in a hydraulic pump was overcome by design changes in the seal and in the pump.

Constant vigilance on assembly methods and tool maintenance is a requirement to keep quality level high.

The causes of oil seal failures in the field have been itemized by the authors of these papers. In the case of Beer, who deals with the case of a Model C Tournapull, which is a 20 ton machine on the 200 + class with a tourmatic drive consisting of a six speed transmission with a single stage torque converter, and on which there are fifteen shaft type oil seals, he states as follows :—Providing transmission shafts are correct hardness and finish and bore concentricities and shaft run‐outs meet the minimum requirements, the seals failed because (1) Incorrect spring tension held the sealing lip too tightly against the shaft causing increased frictional heat which hardened the material and with existing shaft run‐out did not permit the seal to follow the shaft resulting in leakage. The grooves in the shafts could also be associated with tight springs. (2) High operating temperatures exceeded the temperature limits of the seal material thus causing it to harden and lose its sealing effectiveness.