Róbert Keresztes

Design of a tribotester for evaluation of polymer components under static and dynamic sliding conditions

Abstract Coefficients of friction and wear lifetime for machine elements are usually estimated from pin-on-disc tests under fixed test conditions. The experimental design of a tribotester with variable sliding path, dynamically changing normal loads, and sliding velocities is presented in this paper together with a preliminary evaluation of sliding properties for engineering polymers. The design of a dynamic loading mechanism and control of the sliding motion are detailed. The importance of dynamic testing is illustrated for polyamides and polyacetals under pure, internally lubricated and glass fibre-reinforced conditions. Dynamic tests induce lower friction compared with static tests because of influences of visco-elastic deformation, inertia forces, and possibly molecular orientation on the sliding surface. Internal lubricants efficiently reduce friction and wear both under static and dynamic conditions. Glass fibres more effectively reduce wear rates on dynamic tests indicating different wear debris mobility in the interface.

Global Approach of Tribomechanical Development of Hybrid Aluminium Matrix Syntactic Foams

Hybrid syntactic foams with AlSi12 aluminium matrix were produced by pressure infiltration. The volume ratio of iron to ceramic hollow sphere reinforcement (in the same size range) was varied, and hybrid syntactic foams were also produced with bimodal size ceramic reinforcement. Previously, a very detailed analysis of the mechanical properties of the composites was made with quasi-static compression tests, and their tribological properties were investigated by pin-on-disc method in dry and lubricated conditions. The present article establishes and clarifies the correlations between mechanical and tribological properties. The coefficient of friction, height loss of the specimens and specific wear showed good correlation with different mechanical parameters, e.g. density, structural stiffness and yield strength. The established trends and correlations between mechanical and tribological behaviour enable a better understanding of materials design and selection for further applications of mechanically loaded sliding machine parts.

Extruded and Injection Moulded Virgin PA 6/6 as Abrasion Resistant Material

Polyamide (PA6/6) is often used as a tribological pair in abrasion prevalent applications such as hinges and sliders. PA6/6 is frequently processed by injection moulding and extrusion process. It is known that these processes influence the polymers mechanical behaviour, but their influence on the polymers wear response has not been studied. Hence the present research attempts to study the influence of different manufacturing processes on tribological behaviour for PA6/6. Wear tests were performed on a pin abrading tester (DIN 50322). Abrasion resistance of both extruded and injection moulded PA6/6 were tested at different loads (20 and 35 N). Single-pass (nonoverlapping mode) and multipass testing (overlapping mode) were used to understand the influence of clogging of wear debris. It is evidenced that with increasing load the specific wear rate decreases; moreover, fine abrasives tend to reduce the wear rate. In multipass testing a transfer layer clogged on the counterface that acted as a protective agent and lowers wear rate. Poor mechanical strength of injection moulded polymers is apparently compensated by microstructural response for having a similar wear behaviour between extruded and injection moulded PA 6/6. Hence a proper balance between microstructural and mechanical characteristics is an absolute must in PA 6/6 for better wear performance.

Friction and Wear of Engineering Polymer Gears

Technical polymers are widespread in the machinery owing to their beneficial properties against metals as operation without lubrication, low friction and wear, light weight, corrosion resistance, low manufacturing costs etc. There are many sorts of technical polymers available of which sliding elements can be produced. To choose proper polymers for a given tribological application is not a simple task owing to many different parameters influencing the performance of a polymer sliding element. We launched a broad research project to clarify the friction and wear phenomena of plastic gears.Copyright