Hydraulic rock hammers use hydraulic power to drive a sealed pneumatic hammer system. Seals are required to seal both the pneumatic and hydraulic systems. Traditional seal designs often fail prematurely due to the severity of the application. Rock hammer seals are exposed to high frictional heat, generated by the high-speed, short stroke reciprocating motion of the rod. The seals see this type of motion on both the hydraulic and pneumatic sides of the system, and at both low and high pressures. Urethane u-cups are traditionally used in this application for their excellent wear and extrusion resistance. The failure mode of the urethane seals is material degradation and lip set. The high frictional heat generated by the speed of the rod, short stroke length, and high pressures causes this failure mode. Various seal designs have been explored to resolve this problem. This presentation will cover some of these designs and their relative performance in testing. A rock hammer manufacturer tested three different seal designs on two hammer sizes. This report focuses on the heat damage to the seals and lip set percent. The lip set percent is found from seal measurements before and after the test and are represented graphically. Lip set is caused by excessive heat on the seals while under compression and can lead to leakage, i.e. seal failure. The test results will compare the different seal designs and their performance.
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