Helix Lip Design for Rotary Shaft Oils Seals

Tracy Decker & Shiv Sabaree

Colonial Seal Company

Oil seals for use on a rotating shaft have a primary function of preventing oil leakage. There are several factors that influence the sealing performance of the lip of the seal against the shaft: the distance between the lip and the seal back face; the strength of the flex section; the angle of the lip; and the tension of the spring. Here is a profile of a standard seal:

The style of the seal and the configuration of the lip are dependent on the application. The radial shaft seal must also have low torque on the lip contact with the shaft; otherwise the friction of the lip on the shaft will result in excessive heat which would in turn cause premature failure of the seal. In order to overcome this friction and reduce the torque the shaft could be lubricated by a thin film of oil from the sump. This thin film between the rotating shaft and the stationary rubber lip is also a source of leakage. While the shaft is static there is enough pressure from the lip to the shaft to prevent oil leakage. Once the shaft starts to rotate, the sealing lip will continue to maintain contact on the shaft unless there is a mechanism to lubricate the shaft. A helix design on the lip will continue to prevent leakage and provide reduce friction between the shaft and the sealing lip. The helix design permits the pumping of the leaked oil back into the sump.

Helical Ribs on the seal lip work the same way as the vanes of a pump by forcing liquid caught between the lip and the shaft to flow in a particular direction. The rotating shaft creates shear forces in the oil film which drag the oil along the shaft perimeter. Depending on the application, the helical ribs are angled to deflect this oil flow and pump it back to the sump side and at the same time exclude contaminants. The helix maintains an even flow of oil around the shaft which is evenly distributed resulting in increased seal performance. While each application will determine which helix would work best, these helical designs are most commonly used to solve some of these issues: load support; friction force; temperature rise; and attitude angle.

Here are some of the standard types of helix designs:

UNIDIRECTIONAL

The most commonly used helix is a Right Helix or Left Helix. You would determine which helix to use based on the rotation of the shaft. Is the shaft clockwise or counter clockwise? If it is clockwise, you will use a left helix, if it is counter clockwise, a right helix is used. The only way to determine this is to view the seal from the AIR SIDE. This is most commonly used in the automotive industry in high performance engines.

BIDIRECTIONAL

The bidirectional Helix has a wave design that is used more for shafts that rotate in both directions. The ribs on this helix are designed in a triangular shape for this purpose. SKF has a “Wave Seal” which is suitable for rotation in both directions. The Wave Seal pumps lubricants back into a bearing arrangement and expel contaminants. This sinusoidal form of helix reduces the pressure at the sealing lip contact point on the shaft. It is estimated that this design reduces friction by 20% resulting in 30% lower temperature than conventional lip designs. These designs are recommended where there is a higher demand for seal reliability and long service life.

There are many other helix designsthat customers have used in a variety of applications. Of course, each application has its own requirements and seal engineers/designers can determine which design is best for your application. The sealing ability is based on the pumping rate of the lubricating oil over the shaft. If this pumping rate is measured, then designers can determine the effect on performance of a given application. Measuring this pumping rate is rather complicated and involves many variables, calculations, and formulas. Here is an illustration of other designs:

Colonial Seal has provided helix design recommendations for customers since 1994. Most shaft seals sold today do not have a helix design, so designing a seal with a helix on the sealing lip would usually require additional tooling. If you have an application that might benefit from the use of a helix on the seal lip, then contact our on-staff engineer to determine the feasibility and potential results from the use of a helix design. Contact us anytime at Sales@Colonialseal.com or 856-432-0012.

Founded in 1994, Colonial Seal Co. is headquartered in Westville, New Jersey. Colonial Seal specializes in oil & grease seals, hydraulic seals, rotary shaft seals, mechanical seals, rubber molded products and gaskets. Through a global network of manufacturers, Colonial Seal can produce custom seals designed for a client’s unique sealing applications.

Colonial Seal Company is ISO 9001:2008 certified.