An Experimental Study of Contact Temperatures at Sealing Interface against Varying Shaft Surfaces

Abstract

Increased temperatures at the sealing interface between the seal and shaft can reduce the working life of a seal through elastomer aging, swelling and increased friction. Degradation of the seal due to increased temperatures can cause pre-mature failure, wear and leakage. There is no such thing as a perfect seal; each application has requirements to cater to the needs of each system. For radial oil seals in helicopter gearboxes, the contact temperatures at the sealing interface are a critical parameter to consider. In this manuscript, investigating the factors that influence the temperatures at the contact interface shed light on the operating parameters that cause an increase in contact temperatures. Four varying shaft coatings are tested against three seal spring loads for a range of sliding velocities between 5–25 ms−1 to reproduce conditions of the gearbox. The study reveals an optimum seal spring of 12 oz, with a circumferential load of 3.34 N for lowest temperatures at the interface. Higher springs of 14 oz and lower springs of 8.5 oz both cause increased temperatures at the interface. Additionally, the need for surface coatings on the shaft is re-enforced through experimental evidence demonstrated by comparing temperatures reached between a plain stainless steel shaft and three surface coated shafts. Chrome plating shafts are undesirable due to the ‘polishing’ in effect they experience. The results of this study build on this by showing that chrome plated shafts have higher temperatures at the interface, aggravating any wear or polishing in of that surface. Contact temperatures with Tungsten carbide and Chrome oxide coatings remain within the expected temperature rise. Lastly, microscopically ‘rougher’ surfaces result in increased temperatures in contrast to surface coatings within the specified range of roughness as provided by DIN 3760/61/ISO 6194.