No. A larger oil seal interference does not mean a better oil seal. Increasing interference increases the deformation of the sealing lip and can raise the contact force against the shaft. That may help maintain contact when the interference is insufficient, but beyond a suitable range it can create new problems such as higher friction, more heat and faster wear.
This is easier to understand from what happens after the machine starts.
Imagine an oil seal sitting on a shaft before the equipment begins to rotate. A certain amount of radial force is required to keep the lip pressed against the shaft. Once the shaft begins turning, however, the contact is no longer stationary. The lip and shaft move relative to each other, and friction is generated.
If the interference is increased, the lip generally has to deform more strongly around the shaft. Under otherwise comparable conditions, that can increase the radial loading at the contact zone. Research on radial lip seals has found that interference is an important parameter in friction torque, while practical sealing references also associate excessive interference with increased friction and heat generation.
The consequences become more obvious as shaft speed rises. More sliding
movement means that frictional energy is converted into heat at the lip area.
The lubricant helps control this condition, but the seal still has to operate
within a suitable thermal range. Excessive contact load can therefore be
counterproductive, especially when a seal is already working at relatively high
speed.
There is another point that is sometimes overlooked: an oil seal does not depend on maximum mechanical pressure to stop leakage. The sealing interface is a combination of lip geometry, contact pressure, material behavior and lubrication. During rotation, a very thin lubricant film can develop between the lip and shaft. The microscopic surface characteristics of the lip also contribute to the way fluid is transported through the contact zone.
This explains why simply making the lip tighter is not a universal solution to leakage.
For example, if leakage is actually caused by a damaged shaft surface, excessive runout or an unsuitable lubricant, increasing interference may not address the real cause. In some cases, it can make the situation worse by increasing friction and wear. Shaft surface characteristics have been shown to affect both the friction behavior and sealing performance of rotary lip seals.
The condition of the seal also changes during service. Elastomer properties can change with temperature and aging, while the sealing edge gradually experiences wear. The radial force at the lip therefore does not necessarily remain identical throughout the entire service period. A good design needs enough initial contact to accommodate these changes without creating excessive friction from the beginning.
For this reason, the goal of interference design is not to obtain the tightest possible fit. It is to establish a suitable contact condition for the actual application.
A properly designed oil seal should maintain sufficient lip contact while keeping friction, temperature and wear under control. In other words, more interference is only beneficial when the original interference is insufficient for the working conditions. Once the required sealing contact has been achieved, additional interference can become a disadvantage rather than an advantage.
