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

Increased temperatures at the sealing interface between the seal and shaft can reduce the work-ing 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 sys-tem. 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 in-crease 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 car-bide and Chrome oxide coatings remain within the expected temperature rise. Lastly, micro-scopically ‘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.密封件与轴之间的密封界面温度升高，会通过弹性体老化、溶胀以及摩擦力增大等途径缩短密封件的工作寿命。温度升高引发的密封件劣化，还会导致其过早失效、磨损与泄漏。不存在完美的密封件，每一种应用场景都需要适配对应系统的需求。针对直升机变速箱中的径向油封（radial oil seals），密封界面的接触温度是需要重点考量的关键参数。本研究旨在通过探究影响密封界面接触温度的各类因素，明确引发接触温度升高的运行参数。实验针对5~25 m·s⁻¹范围内的不同滑动速度，设置4种轴表面涂层与3种密封弹簧载荷进行测试，以复现直升机变速箱的实际工况。研究结果表明，当密封弹簧载荷为12 oz、圆周载荷达3.34 N时，密封界面温度最低，为最优参数。载荷为14 oz的高负载弹簧与8.5 oz的低负载弹簧，均会导致密封界面温度升高。此外，通过对比光面不锈钢轴与3种表面涂层轴的界面温度，实验数据进一步验证了轴表面涂层的必要性。镀铬轴并不适用，因为其表面会出现“抛光”效应。本研究结果进一步证实了这一点：镀铬轴的密封界面温度更高，会加剧该表面的磨损与抛光效应。采用碳化钨（Tungsten Carbide）与氧化铬（Chromium Oxide）涂层的轴，其接触温度均处于预期温升范围内。最后，相较于符合DIN 3760/61/ISO 6194标准规定粗糙度范围的表面涂层轴，微观上更粗糙的表面会导致密封界面温度升高。