Peerless-Winsmith: Shaft & Seal Topics

Engineering Information

SHAFT AND SEAL TOPICS

SHAFT OIL SEAL LEAKAGE
One of the most annoying maintenance problems is a leaking oil seal. If unattended it can cause damage to your product, the machinery it operates not to mention the unit from which the oil is leaking. Repair of the unit and clean-up is messy and often involves costly down time. Once the seal has been replaced, it is not uncommon to find that the equipment is still leaking oil. Why? Because in most cases the seal is not the problem, it’s the shaft.

CR Industries, an internationally respected oil seal manufacturer, has done extensive research on the causes of shaft leakage. They have found that the shaft surface on which the seal rides is critical to seal performance. If the shaft finish is too rough, or if the material used is incorrect for the operating environment, the seal cannot do its job: to retain lubricants and exclude contaminants.

CR has published some industry guidelines to assist manufacturers who incorporate oil seals in their products. Some of the major shaft problems are:*

SHAFT ECCENTRICITY

Shaft-to-bore misalignment
Dynamic run-out

SHAFT SPEED

Maximum speed for effective seal operation depend on shaft finish, pressure, temperature, eccentricity, lubricant or fluid being retained, seal type and other conditions.

RECOMMENDED SHAFT FINISH

Shaft finish should fall between 10 to 20 mircro inches AA. Shafts should be ground with mixed number RPM ratios. There should be no machine lead—spiral marks that can cause lip damage and augering out of the lubricant.
• Plunge Grinding—the best known method for meeting these requirements and obtaining optimum shaft finish.

Other methods of shaft finishing might produce the correct finish, but they do not remove machine lead. This includes all of the following methods.

• Surface honing	• Rotopeening
• Transverse grinding	• Tumbled stone finishing
• Paper polishing	• Roller burnishing
• Glass bead blasting	• Diamond burnishing

TESTING FOR THE PRESENCE OF MACHINE LEAD

The most effective method requires a 36 inch length of cotton quilting thread, a one ounce weight, and silicone oil. Suspend the weight on the thread over the oiled shaft. Rotate the shaft at approximately 60 rpm. If the thread moves along the shaft, machine lead is present.

*Portions Reprinted from C R Services Publication 457542. Used with permission.

SHAFT QUALITY AT WINSMITH
WINSMITH has a long standing reputation for quality in the speed reducer industry. And we continually strive to maintain that quality by keeping abreast of the newest advances in technology and methodology. That’s why the D-90 TYPE SE shafts, that are centerless ground, are all plunge ground to provide the best possible seal surface to minimize the potential of costly down time. In addition, we test every SE shaft for machine lead. Who else but WINSMITH would take these extraordinary measures to insure the quality of every unit and all its components.

This is just one more reason to specify WINSMITH quality speed reducers for all your gearing applications. For harsh environments such as high humidity, dusty or chemical laden atmospheres, where a completely sealed unit is required, use the new S-EQUALIZER®. This option, available on all D-90 TYPE SE Units provides an internal diaphragm, that adjusts to prevent internal pressures that can cause premature seal wear and thus oil leakage.