Video Transcript
Hello and welcome to another installation of white papers on whiteboards. My name is Keith Flaherty, Validation Engineer at Engineered Seal Products. Today, we will be talking about lubrication and its effects in the sealing system.
Does Lubrication Effect The Radial Shaft Seal Sealing System?
Yes, lubrication minimizes the frictional losses within a system.
Lubricants are used in a wide variety of applications, such as gear boxes, for several different reasons:
- They reduce the friction and wear in the system
- They protect metal parts from corrosion
- They clean the system to remove by-products such as sludge and carbon buildup
- They reduce temperature by dissipating the heat in the system.
Most lubricants start with a base oil and additives are used to further improve upon its properties.
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A thickener can be added in order to turn oil into grease.
- Some performance improving additives include friction modifiers, rust inhibitors among others.
In all applications a seal is used to create a barrier to:
- keep the lubricant in the system
- keep contaminants such as dirt out of the system
Grease can be added to sealing lips to reduce friction, decrease seal temperature and help prevent contaminants from entering the system. Grease is used in applications where the lubricant needs to stay in its original position.
Lubrication is very critical in the performance of a real shaft seal. In general, lubrication reduces the wear of the elastomeric sealing lip and reduces the under-lip temperature of the sealing lip.
Some of the things to keep in mind are material compatibility, viscosity of the lubricant and lubricant fill level.
Lubrication & Radial Shaft Seal Material Compatibility
Most lubricants used today use additives to improve performance as I mentioned earlier. However, the chemicals in the additives can cause adverse reactions to the elastomers of the seal. Some additives can cause the elastomeric lip to further cure or harden.
Some additives cause elastomeric lips to break down and fall apart. The additives can reduce the life of the seal and cause costly maintenance repairs. Care must be taken in order to know the compatibility of the lubricant and of the seal elastomer material.
Lubrication Viscosity
Viscosity is a fluids resistance to flow. Applications require the use of fluids with different viscosities. Fluids with high viscosity generate more friction and therefore will result in a higher torque of the sealing system.
Lower viscosity lubricants will have a higher pump rate compared to high viscosity lubricants. Viscosity is temperature dependent. An increase in temperature will decrease a fluids viscosity. This can be a concern with cold starts. The lubricant will start with a higher visocosity which may result in inadequate lubrication at the sealing lip, causing excess wear. Eventually as the system temperature increases the viscosity will lower, and provide proper lubrication to the sealing lip.
Lubrication Fill Level
Elastomer lips of seals should never run without lubrication. This results in a higher wear of the sealing lip. As fill levels decrease, seal life will decrease. The reduction in life is not due so much to excess wear of the seal lip, but due to an increase in underlip temperature. The lower the quantity of oil, the harder it is to remove frictional heat from the system. Seal torque increases within an increase in lubricant fill level due to the increase of internal friction of the motion of the lubricant.
In some applications an elastomeric seal lip is not ideal. This could be due to the compatibility issue, constraint of low lubricant fill level, or excessive heat.
The solution to this problem is to use a PTFE bonded elastomer lip or a PTFE seal.
PTFE provides better compatibility with lubricants and has better wear properties and can operate in a wide range of temperatures. One drawback though is that PTFE in seals are more expensive than elastomeric seal lips.
Lubrication Radial Shaft Seal Installation Tip
Before installing the seal, make sure to add a thin film of oil or grease to the main sealing lip if not already present. Also add a thin film of the same lubricant to the shaft where the seal will contact. This not only eases the installation but help lubricate the seal when initially started and will avoid any dry running scenarios.