László Zsidai

The tribological behaviour of engineering plastics during sliding friction investigated with small-scale specimens

Abstract For economical, ecological and even technical reasons for some years there has been a tendency to introduce self-lubricating materials for bearing applications. In this way external lubricants such as oil or grease can be excluded, the design can be simplified and maintenance cost can be reduced. Among the self-lubricating materials the so-called engineering plastics have increasing importance. Unfortunately, data on their friction and wear characteristics are very disparate and often there is a lack of general understanding of the physical phenomena involved. In the present paper some basic types of engineering plastics (PA, oil-filled PA PTFE-filled PETP, POM-H) are experimentally investigated by means of small-scale reciprocating tribotesting. The tribological behaviour is explained in correlation with the chemical and mechanical properties of the materials. The basic failure processes are described for mild wear conditions as well as for overload conditions.

Polymer structure and antimicrobial activity of polyvinylpyrrolidone-based iodine nanofibers prepared with high-speed rotary spinning technique.

Poly(vinylpyrrolidone)/poly(vinylpyrrolidone-vinylacetate)/iodine nanofibers of different polymer ratios were successfully prepared by a high-speed rotary spinning technique. The obtained fiber mats were subjected to detailed morphological analysis using an optical and scanning electron microscope (SEM), while the supramolecular structure of the samples was analyzed by positron annihilation lifetime spectroscopy (PALS). The maximum dissolved iodine of the fiber samples was determined, and microbiological assay was carried out to test their effect on the bacterial growth. SEM images showed that the polymer fibers were linear, homogenous, and contained no beads. The PALS results, both the o-positronium (o-Ps) lifetime values and distributions, revealed the changes of the free volume holes of fibers as a function of their composition and the presence of iodine. The micro- and macrostructural characterisation of polymer fiber mats enabled the selection of the required composition from the point of their applicability as a wound dressing.

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.

Temperature Effects on Friction and Wear of Thermoset Polyester Fabric Composites

ABSTRACT The tribological properties of unsaturated polyester with a plain weave polyester fabric and poly(tetrafluoro-ethylene) fillers are evaluated in reciprocating sliding at 23 to 220°C. Thermogravimetric analysis and differential scanning calorimetry show that poly(tetrafluoro-ethylene) restricts the thermostability, while the curing reaction becomes more pronounced in the presence of poly(tetrafluoro-ethylene). The pure polyester composites show continuously increasing friction and overload above 120°C, while the poly(tetrafluoro-ethylene)-filled composites indicate a regime of increasing friction up to 100°C, decreasing friction at 100–160°C, and increasing friction above 160°C. The infrared spectra of worn composites have absorption bands representing poly(tetrafluoro-ethylene), curing, and degradation of the matrix. GRAPHICAL ABSTRACT

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