SOME EXPERIMENTAL RESULTS CONCERNING THE INFLUENCE OF SURFACE COATINGS ON THE WEAR OF POLY-ETHER-ETHER-KETONE (PEEK) POLYMERIC GEARS Dimitar PETROV, Karl DEARN, Doug WALTON, Richard BANKS Abstract: Gears made from general purpose Poly-Ether-Ether-Ketone (PEEK) polymeric material and coated on their flanks with thin layer of different solid lubricants MoS 2 , graphite (C), BN and PTFE are tested in relation to wear and mesh point temperature in conditions of prolonged running. The derived experimental results are shown graphically. Some conclusions are given (the order of wear increasing according to the type of coating (PTFE (least wear), uncoated, graphite, MoS 2 , BN); proportional correlations between wear and mesh temperature, etc.) Key Words: Wear; Polymer Gears; Solid (Dry) Lubricant Coatings 1. INTRODUCTION The applications of polymeric gears increase because of their most beneficial properties – low cost (when injected molded); light weight and low inertia; capability to absorb shock and vibration as a result of their elastic compliance; noiselessness; tolerances often less critical than for metal gears, due in part to their greater resilience; their ability to operate under dry un-lubricated conditions; etc [1, 2]. Their most perceived disadvantages are – lower strength leading to less load carrying capacity; sensitivity to temperature; sensitivity to post mould distortion and moulding complications such as shrinkage; polymeric gears are subject to greater dimensional instabilities due to their greater coefficient of thermal expansion and moisture absorption; etc. Connected with first two mentioned disadvantages the most common ways of fail of polymeric gears are thermal related tooth failures, tooth root and pitch point fatigue. The most common failure however is wear which has been extensively reported [3-8]. Various authors have investigated different parameters thought to influence wear. Akkurt [7] examined the effect of surface roughness of steel gears running against polymer (acetal) gears. Rao et el [8] using a twin disc rolling-sliding test rig looked at the effect of polytetrafluoroethylene (PTFE) as an internal lubricant on the friction and wear of filled and unfilled PA6/6 and polyacetal. The experimental results showed that the friction and wear performance of the PTFE filled polymers was superior to those of the unfilled polymers. In an attempt to increase the transmissible power levels still higher problems of surface temperatures arise due to the frictional losses between mating gear teeth. This leads to high wear rates and high surface temperatures resulting in the gear flanks melting and rapid failure. With an aim to investigate the influence of surface coating on dry running polymer gear wear a number of polymeric gears were coated with a thin coating of dry lubricants. Within the framework of one bigger project the authors investigated gears made from three polymeric materials - general purpose polyamide (PA 66), unreinforced Poly-Ether-Ether-Ketone (PEEK 450G) and a 30% carbon fiber reinforced Poly-Ether-Ether-Ketone (PEEK 450CA30). This paper reports only on the wear and temperatures of the (PEEK 450G) gears with the specified coatings and compares the wear with uncoated gears. As polymer gears are frequently run against a steel gear, coated polymer gears running with steel were also tested. The results described below were based on a pilot study of the influence of coatings on gear wear. 2. POLYMER GEAR WHEELS, THEIR COATINGS, TEST RIG AND LABORATORY EQUIPMENT All examined gears had 30 teeth, 2 mm module and 30 o pressure angle with a face width of 17.4 mm – fig. 1. The polymeric gear wheels were made from PEEK 450G by injection molding. In the experiment were used steel gears, too, with the same geometrical parameters. The investigated coatings were solid lubricants of molybdenum disulphide (MoS 2 ), graphite flake(C), boron nitride – hexagonal (BN) and PTFE powder. The coatings were laid by Indestructible Paint Ltd, Birmingham. The coating procedure included – substrate preparation (using grit blasting with 13-16 September, 2010 Sozopol, Bulgaria 26 th INTERNATIONAL SCIENTIFIC CONFERENCE 65 YEARS FACULTY OF MACHINE TECHNOLOGY