Study on preparation process parameters and tribological properties of porous PI materials

Purpose Previously, the effect of pore-forming agents on the properties of pore size and morphology was studied. In this paper, we determine the optimal combination of parameters by tensile strength and perform tribological tests with optimal combination of parameters. Design/methodology/approach In this paper, porous polyimide (PI) materials were fabricated using vacuum hot molding technology. The orthogonal experiment was designed to test the mechanical properties of porous PI materials with the process parameters and the content of pore-forming agent as the changing factors. The porous PI oil-bearing materials were obtained by vacuum immersion, and tribological test were carried out. Findings The results showed that porous PI oil-bearing materials are suitable for low-speed and low-load conditions. The actual value of the friction coefficient basically match with the theoretical value of the regression analysis, and the errors of the friction coefficient are within 10% and 3%, respectively, which proves that the method used in the study is feasible for the friction coefficient prediction. Originality/value In this paper, we have produced a new porous oil-bearing material with good tribological properties. This study can effectively predict the friction coefficient of PI porous material.

EFFECT OF HUMIDITY ON TRIBOLOGICAL PROPERTIES OF SELECTED FRICTION JUNCTIONS WITH AN EVALUATION OF ACOUSTIC EMISSION

The study aimed to compare the effect of humidity on the operation of tribological systems. The tested friction and wear are external properties; therefore, their values may differ significantly depending on the operating parameters of the friction junction and environmental conditions. Tribological tests were carried out on a TRB3 tribometer in a dry sliding mode at a relative humidity of 50% ± 5% and 90% ± 5% in the ball-on-disc configuration with a load of 15 N. The friction junction consisted of a sample made of 100Cr6 steel, and three counter-samples were made of 100Cr6, SiC, and Al2O3 steel. The geometric structure of the surface was examined with an optical profiler. The tribological test results showed reduced linear wear and friction coefficient at a relative humidity of 90% ± 5% compare to its 50% ± 5%. The paper also presents the results for the sound recorded in the 16-bit linear PCM standard and analysed in a Spectra-Plus program.

Mechanical and tribological behaviour of PA6 and short aramid fiber composites

This paper presents the results of mechanical and tribological characteristics for two composites: PA6 as matrix and 5% aramid whiskers as additive material and PA6 + 10% aramid whiskers, comparing them to those made of PA6 (polyamide 6). To improve the mechanical and thermal properties of polyamide (PA6), the composites were prepared via the Brabender lab mixer and mould forming under given pressure and temperature conditions. Test specimens made of pure PA6 and PA6 mixed with 5 wt.% and 10 wt.% aramid whiskers were subjected to mechanical tests (three-point bending and impact), thermo–mechanical test (HDT - heat deflection temperature), tribological test (block-on-ring) and analyzed from morpho-structural point of view. Compared to the PA6 samples, the mass concentrations of aramid whiskers improved the HDT deflection temperature values. In the case of samples with 5% aramid whiskers, the absorbed energy increased by 13% and for those with 10% aramid whiskers they increased by 30%. Aramid whiskers-doped materials performed much better on severe tribological testing as compared to PA6 samples. Increasing the deflection temperature, also improved their resistance from a tribological point of view.

Spheroidization Behavior of Nano-Primary Silicon Induced by Neodymium under High-Current Pulsed Electron Beam Irradiation

The spheroidization behavior of the nano-primary silicon phase induced by Nd under high-current pulsed electron beam (HCPEB) irradiation was investigated in this study. The study results revealed that, compared to the Al–17.5Si alloy, spheroidized nano-primary silicon phase emerged in the alloy’s HCPEB-irradiated surface layer due to the presence of Nd. Because Nd was abundantly enriched on the fast-growing silicon crystal plane, its surface tension was reduced under the extreme undercooling caused by HCPEB irradiation, causing the growth velocity of each crystal plane to be the same and spherical nanometers of silicon to appear. The spheroidization of nano-primary silicon phases occurred in the remelted layer. The microhardness test revealed that Nd could depress the microhardness of the Al matrix at the same number of pulses, but conversely increase the microhardness of the primary silicon phase, compared to the Al–17.5Si alloy. The tribological test showed that the presence of spherical nano-primary silicon could significantly improve the alloy’s tribological property.

Qualitative and Quantitative Evaluation of Different Types of Orthodontic Brackets and Archwires by Optical Microscopy and X-ray Fluorescence Spectroscopy

The wear behaviour and chemical composition of orthodontic components influence the mechanical characteristics of a fixed orthodontic treatment. The purpose of this paper is to evaluate the surface alterations of different types of brackets (aesthetic, metallic, and conventional self-ligating) and archwires (superelastic and thermal) subjected to wear tests through optical microscopy and, subsequently, to identify the chemical elements of accessories by X-ray fluorescence. The cycles (5000 for each bracket and 10,000 for each wire) of the tribological test were carried out in dry conditions inside a machine that allows alternating sliding. The results of the study highlighted different wear behaviours even within the same type of brackets and archwires. The monocrystalline sapphire brackets maintain their aesthetic properties despite traces of wear inside the slots and contain minimal amounts of nickel. Superelastic NiTi archwires have a better overall rating than thermal wires, as they do not show significant surface wear alterations.

High Temperature Tribological Performance of Steel/Copper Friction Pairs Lubricated With a Modified C-WS2-(Fe3O4+TiN) Nanoadditives in Non-Copper Coated Solid Wires

In this study, four kinds of nanoparticles: graphite, WS2, Fe3O4 and TiN were used as lubricating additives for steel/copper friction pairs to solve the problem of welding contact tube wear with non-copper-coated solid wire at high temperature. The single and composite nanoparticles have excellent dispersion stability in absolute ethanol under the action of the compound surfactant NaSTA+OA+PVP. The tribological test results showed that the maximum decrement with reference to the average coefficient of friction and wear volumes were measured with nanoparticle concentration in 1:1:1 ratio at 300℃. Compared with dry friction, the average friction coefficient and wear volume are reduced by 74.3% and 84.8%, respectively, which may be attributed to the formation of a stable tribo-film mainly composed of C-O, Fe2O3, WO3, TiO2, TiNxOy composite on the worn surface. Therefore, it is considered that the combined lubrication effects of the ball-bearing effect, repairing of worn surfaces and the tribo-film resulted in the lowest friction and wear.

METHODOLOGY FOR TESTING A JOINT CARTILAGE

A research method was developed to analyse the tribological properties of cartilage tissue. Based on the literature data and the possibility of obtaining samples of appropriate dimensions, the frequency and amplitude of friction tests were adopted. Based on the previously conducted preliminary tests, other test parameters were proposed, such as the frictional contact load and the number of test runs. It was assumed that the results of the research will be the friction coefficient and the wear intensity of the tribological system. According to the developed method, a series of verification tests was carried out in which the friction contact was lubricated in various ways with the selected lubricants. The results of tests of animal cartilage in nonlubricated contact were used as the reference basis for all the tested associations. The friction tests showed good method resolution and satisfactory repeatability. In the case of wear characteristics, a greater scatter of test results was observed. It is probably related to the varied geometrical structure of the cartilage surface as well as the elastic properties of the bone on which the tissue was placed. The correctness of the obtained results and a relatively good resolution of the tribological test method were found.

Effect of zirconium silicate and mullite with three different particle sizes on tribo performance in a non-asbestos brake pad

This work aims to examine the effect of two different abrasives: zirconium silicate and mullite with three different particle sizes (5, 44 and 149 µm) on the frictional characteristics of brake pads. Six brake pads were developed using these two abrasives with three different sizes. The effect of the abrasives towards fade, recovery and wear was investigated by carrying out a tribological test in a Chase tester following SAE J661 standards. Results indicated that brake pads with coarser particles generated good fade resistance and acceptable recovery rate. This effect was explained based on the formation of a stable friction film observed through the field emission scanning electron microscopy and testing the microhardness at the surface of the samples after dry sliding. However coarser particles exhibited poor wear resistance. In comparison, smaller abrasive particles exhibited poor friction stability with excellent wear resistance. Detailed examination of the wear surfaces was conducted to identify the possible wear mechanism.