By Joyce Laird, Contributing Editor

What is the primary function of a radial shaft seal?

Radial shaft seals are used retain to lubrication, exclude contamination and can also separate two fluids. The function that the seal will serve depends on the application conditions and thus the orientation of the seal lip. “Primary lip towards primary function is how proper seal orientation is determined,” explained Eric Phaneuf, Applications Engineer, Industrial Market for SKF USA Inc.

How do you match the proper radial shaft seal for a bearing?

First, Phaneuf notes that a seal is not necessarily matched to a bearing, but is rather selected for the machine. The seal is indifferent as to what bearing is being used. “What is important to the seal is the type of lubricant that will be used. What needs to be considered is will a grease or oil will be used?” he said.

Application conditions need to be considered include:
• What temperatures will the seal see?
• What is the speed of the shaft?
• Is it a dirty environment or are there any concerns of chemical compatibility of the seal and process fluid?

“Only after all of this information is gathered then a seal can be selected,” Phaneuf said.

Why is Proper Radial Shaft Seal important to System Operation?

Seals are important for retaining lubricant and excluding contaminants. If the seal doesn’t adequately retain the lubricant then the machine will fail prematurely. If contaminants are allowed to enter the machine then there will also be premature failure. In order to get maximum service life out of the system, a proper sealing arrangement is crucial.

How to Ensure Proper Installation

“The first step to ensure proper installation is to make sure that the shaft and housing bore are designed properly,” Phaneuf said.  “A critical design feature for ease of installation is having a proper lead-in chamfer of 15 to 30° and making sure they are free from burrs or sharp edges that might damage the seal during installation. It is also important that the seal is properly oriented, either for lubrication retention or contamination exclusion, so again think: primary lip to the primary function.”

Prior to installation it is suggested to wipe the shaft and/or seal sparingly with the selected bearing lubricant. Force should be applied as close as possible to the outside diameter of the seal and uniformly around the entire seal. Phaneuf adds that if there are any features on the shaft such as splines, keyways, or no lead-in chamfer, then installation sleeves should be used to protect the seal from damage.

“It is also important that seals be installed in a clean, controlled environment. If a seal is installed in a dirty environment then you are just allowing those contaminants into the machine and sealing them in which will have adverse effects on seal and bearing life. As stated, the seal is to exclude contamination during operation and therefore one does not want to introduce contamination into the system during installation. This could have adverse effects on the bearing service life,” he said.

Important: No “One Size Fits All”

In order to select the proper seal, all of the application conditions need to be considered. There is no one-size-fits-all sealing solution. Proper handling and installation techniques are crucial. Phaneuf warns, “If the seal is compromised in any way during storage, handling or installation then the seal will not effectively serve its purpose.”

SKF
www.skf.com