Frictional behavior of marine lip seals: Sensitivity to operational parameters

Marine lip seals are a topic seldom studied in published literature compared with other types of lip seals. Marine lip seals are unique in their harder material compound and larger diameters, in addition to higher operational oil pressures. This paper explores the behavior of marine thruster lip seals with a nominal diameter of 300 mm under normal operating conditions. The counterface is a stainless-steel shaft liner coated with tungsten carbide. The lip seals and counterfaces studied are commonly used in marine applications. A test device was designed and constructed to study the effects of different parameters on the behavior of lip seals, namely the oil temperature, oil pressure, and rotational speed. For each parameter, three values were selected, which totaled 27 parameter combinations per seal, and the sample size was 3. The behavior was characterized by measuring the frictional torque and the subsurface temperature at a given test point for one hour. The measurements for each seal were taken after an initial running in period of at least 100 hours. Air bearings were used to support the seal housing, to allow for a more accurate measurement of the frictional torque. The subsurface temperature was measured 0.5 mm beneath the contact using a wireless temperature probe embedded in the liner. The contact pressure was measured before the start of test sequence and after its completion. The results showed that the speed had the most significant effect on the subsurface temperature, which increased with increasing speed. The oil pressure had the most significant effect on the frictional torque, which increased with increasing pressure. Increasing oil temperature resulted in lower frictional torque and higher subsurface temperature. The peak contact pressure was higher for new seals compared with used seals. This paper demonstrates the sensitivity of the lip seal frictional behavior to the operational parameters.