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Rotary Lip Seals for Pressure
Published in Heinz K. Müller, Bernard S. Nau, Fluid Sealing Technology, 2019
Heinz K. Müller, Bernard S. Nau
PTFE lip seals: Figure 4 shows a typical commercial PTFE lip seal for pressurized applications. The seal flange together with an elastomeric gasket is clamped in a metal case. Compared to automotive PTFE lip seals, the distinguishing features are the short lip, which is plain where it contacts the shaft (no wind-back groove), and the metal case, which is extended close to the shaft to provide axial support. The short lip is radially stiff, which limits the allowed static eccentricity and shaft run-out. Unpressurized, the lip load is typically 0.6–1.2 N/mm, and at 150°C, after reduction in elastic modulus and the thermal expansion of the PTFE, 40–50% of the initial value remains. Unpressurized the contact width is approximately 0.5 mm, increasing to 1.5 mm at 1 MPa. Unfortunately, when pressurized, these seals do not meet the user’s expectation of the leak-free operation normal with elastomeric lip seals. At higher pressure, the lip is axially deformed, and the consequent sharp lip bending radius can cause “bell-mouthing” of the PTFE lip with lift-off at the contact, which increases leakage. Causes of leakage are discussed further in the next section. Where space is at a premium, PTFE lips are available without the metal case, for individual clamping. Figure 5 shows some commercial variants of PTFE lip seals, most of which have a comparatively large contact area and hence a relatively high friction torque.
Overview and introduction
Published in Tom Denton, Automobile Mechanical and Electrical Systems, 2018
The most common type of oil seal is the neoprene (synthetic rubber) radial lip seal. The seal is fitted into a recess and the soft lip rubs against the rotating component. The lip is held in place by a spring. Figure 1.98 shows this type of seal; note how the lip faces the oil such that any pressure will cause the lip to fit more tightly, rather than allow oil to be forced underneath. Figure 1.98 shows a valve stem oil seal, which prevents oil entering the combustion chamber past the inlet valves.
5 Rights of Successful RCFA
Published in Randy Riddell, Practical Root Cause Failure Analysis, 2022
All these patterns have time as a common factor so we must first understand how long this part should last if achieving full life. For example, full life for a V-belt might be 3 years while full life on a spherical bearing running on oil might be 25–40 years. A contact lip seal may reach full life at 6–12 months while a labryth seal may last a lifetime or 50 years. This can help us to understand whether the component failed due to wear out at end of life or because of infant mortality.
A Near-Frictionless Sealing Approach with Innovative, Gas-Lubricated Shaft Seals Made of Elastomer
Published in Tribology Transactions, 2021
Nino Dakov, Marco Gohs, Frank Bauer
In summary, the self-induced pumping structures of the back-structured elastomer lip seal are capable of pumping enough air from the air side into the sealing contact to generate a hydrodynamic pressure buildup (i.e., an air cushion that supports the entire radial load and separates the seal from the shaft). The liftoff effect is observed at shaft speeds of between 2000 and 4000 rpm. The effect allows a dynamic operation at near-zero friction without the need for liquid lubrication. The hydrodynamically active pumping structures ensure low-power-loss and low-wear dynamic operation comparable to state-of-the-art mechanical seals. Due to advantages such as the low manufacturing time and use of affordable materials, the back-structured elastomer lip seal shows great potential to serve as a low-friction sealing solution in various cost-sensitive applications. The functional principle of separating the sealing lip from the shaft by an air film and thus eliminating the friction losses is achieved with only a minimal lubricant supply. The potential of the new design can thus be fully exploited for partially flooded or mist-sprayed lubrication conditions, as well as for dry running of the sealing system.
Driveline Lubricant Impacts on Dynamic Seal Test Life
Published in Tribology Transactions, 2018
Hongmei Zhao, Jiatong Chai, Xiaoming Lin, Wei Wang, Jeanne Petko, Valerie Woodward, Monica Ford
A typical radial lip seal includes an elastomeric body with a lip that, in the application, is in contact with a rotating shaft, and this lip–shaft contact provides the sealing force preventing oil leakage. Sealing force is provided by the seal design, seal material, and interference fit between lip and shaft and is often enhanced by using a garter spring, which sits behind the seal lip. The elastomeric body is bonded to a metallic case. These basic components and the dynamic sealing zone formed between the seal lip and shaft are illustrated in Fig. 1.