Tribological behavior of UHMWPE in water lubrication: the effect of molding temperature

Purpose Ultra-high molecular weight polyethylene (UHMWPE) is adopted in water-lubricated bearings for its excellent performance. This paper aims to investigate the tribological properties of UHMWPE with a molecular weight of 10.2 million (g mol‐1) under different molding temperatures. Design/methodology/approach The UHMWPE samples were prepared by mold pressing under constant pressure and different molding temperatures (140°C, 160°C, 180°C, 200°C, 220°C). The friction and wear tests in water were conducted at the RTEC tribo-tester. Findings The friction coefficient and wear loss decreased first and rose later with the increasing molding temperature. The minimums of the friction coefficient and wear loss were found at the molding temperatures of 200°C. At low melting temperatures, the UHMWPE molecular chains could not unwrap thoroughly, leading to greater abrasive wear. On the other hand, high melting temperatures will cause the UHMWPE molecular chains to break up and decompose. The optimal molding temperatures for UHMWPE were found to be 200°C. Originality/value Findings are of great significance for the design of water-lubricated UHMWPE bearings.

A Novel Reciprocating Tribometer for Friction and Wear Measurements with High Contact Pressure and Large Area Contact Configurations

There are many moving machine assemblies with conformal tribological contacts at very high contact pressures, e.g., sliding bearings, propeller shaft bearings and machine guideways. Furthermore, applications such as trunnion and guide vane bearing in Kaplan turbines have very low sliding speeds and oscillatory types of motion. Although there is a vast selection of tribology test rigs available, there is still a lack of test equipment to perform friction and wear tests under high contact pressure, reciprocatory sliding and large area contact. The aim of this work is thus to develop a novel reciprocating tribometer and test method that enables friction and wear tests under low-speed reciprocatory sliding with contact pressures up to 90 MPa in a flat-on-flat contact configuration. First, a thorough description of the test rig design is given. Secondly, the influence of contact pressure and stroke length on the tribological properties of a stainless steel and polymer composite material combination is studied. The significance of considering creep, friction during the stroke and contact temperature is specifically highlighted. The novel tribometer can be used to screen different bearing and shaft material combinations and to evaluate the friction and wear performance of self-lubricating bearings for the specific operating conditions found in Kaplan turbines.

Friction and wear of polyetheretherketone (PEEK) samples with different melt flow indices

Polyetheretherketone (PEEK) is a promising polymer material for tribological applications. Friction and wear tests of PEEK samples vs. steel with different melt flow indexes (MFI) were studied. The results showed dependencies of the friction force on the sliding velocity, either decreasing or increasing depending on whether the normal load exceeds the yield strength of the polymer. The data can be well fitted with the assumption of the two-component friction law involving the Amontons component and an adhesional component. With a decrease in MFI, i.e. with an increase in viscosity of polymer. The adhesive component of friction increases with increasing viscosity while the abrasive wear decreases. At high loads, the plastic displacement increases with an increase in the viscosity and plasticity of the polymer. The wear does not show a clear correlation with the viscosity.

Tribological Analysis of novel Apricot oil based Biolubricant against 15W40 oil tested on High Temperature Tribometer

Nowadays, petroleum products have become an integral part of day-to-day life. Lubricants made from petroleum products were widely used as automobile lubricants. But the use of petroleum-based lubricants has significantly damaged the environment. The concern of environmental damage caused by petroleum-based lubricants has increased the search for environmentally friendly lubricants. The vegetable oil-based lubricants proved to be environmentally friendly. In the present work, a bio lubricant is produced from the apricot oil, scientifically known as Prunus Armeniaca, using the trans-esterification method. The tribological behavior is analyzed for pure bio-lubricant, 15W40 oil, and also for the blend of apricot oil and 15w40 at different volume percentages. A high-temperature Pin on disc tribometer is used to perform friction and wear tests at 40oC and 100oC. It was found that the blend of apricot oil-based biolubricants and 15W40 lubricant showed better tribological behavior as compared to the pure bio-lubricant and 15W40 oil alone.

Research on the Effect of Texture on Wear Performance of High-Pressure Piston Pump Valve Pair

In this paper, the surface wear performance of the valve pair of a high-pressure axial piston pump is improved. Firstly, the friction and wear tests are carried out for different materials of the axial piston pump valve pair. Moreover, the friction and wear behavior of the valve pair contact is studied. A valve pair material that is more suitable for processing surface texture is chosen. Friction and wear models of a valve pair based on degradation coefficient are proposed and wear conditions of different textures are calculated. Lastly, the texture with the best anti-wear effect is selected. Finally, the selected textures are experimentally validated by laser processing. The results show that a long strip with a diameter of 400 μm, a depth of 20 μm, and an area ratio of 2% can effectively reduce wear. Through comparative analysis, it is concluded that the texture shape has the least influence on the wear of the valve pair. On the other hand, the area ratio of the texture has the greatest effect on the wear of the valve pair. As the diameter of the texture increases, the wear of the valve pair gradually decreases. As the texture depth increases, the wear amount of the valve pair shows a downward trend.

Microstructure and Wear Resistance of Laser Cladding of Fe-Based Alloy Coatings in Different Areas of Cladding Layer

In this study, laser cladding technology was used to prepare Fe-based alloy coating on a 27SiMn hydraulic support, and a turning treatment was used to obtain samples of the upper and middle regions of the cladding layer. The influence of microstructure, phase composition, hardness, and wear resistance in different areas of the cladding layer was studied through scanning electron microscopy (SEM), X-ray diffractometry (XRD), friction and wear tests, and microhardness. The results show that the bcc phase content in the upper region of the cladding layer is less than that in the middle region of the cladding layer, and the upper region of the cladding layer contains more metal compounds. The hardness of the middle region of the cladding layer is higher than that of the upper region of the cladding layer. At the same time, the main wear mechanism of the upper region of the cladding layer is adhesive wear and abrasive wear. The wear mechanism of the middle region of the cladding layer is mainly abrasive wear, with better wear resistance than the upper region of the cladding layer.

Catecholated graphene-filled polyimide with enhanced mechanical, thermal, and tribological properties

In order to achieve good dispersion of graphene in polyimide (PI), catecholated graphene (G-Cat) was prepared by 1,3-dipolar cycloaddition reaction of N-methylglycine and 3,4-dihydroxybenzaldehyde with graphene sheets. G-Cat/PI composites were prepared by in situ polymerization with pyromellitic dianhydride and 4,4-oxydianiline in the presence of G-Cat. The successful modification of graphene was proved by infrared spectroscopy, Raman spectroscopy, and transmission electron microscopy. The comprehensive properties of G-Cat/PI composites were studied by tensile, dynamic mechanical analysis, thermogravimetric analysis, and friction and wear tests. By observing the morphology of wear marks, the friction and wear properties of the composites were emphatically analyzed. Therefore, graphene/PI composites were expected to have broad application prospects in lubrication and wear resistance.

UV/Ozone-Assisted Rapid Formation of High-Quality Tribological Self-Assembled Monolayer

UV/ozone (UVO)-assisted formation of self-assembled monolayer (SAM) of 1H,1H,2H,2H-perfluorodecyltriethoxysilane (PFDS) was prepared on a glass surface. The effect of UVO exposure time on surface roughness and hydrophilicity was investigated through goniometer and atomic force microscope (AFM), and deposition time-dependent SAM quality was detected by AFM and X-ray photoelectron spectroscopy (XPS). The glass surface became smooth with UVO radiation after 10 min, and the hydrophilicity was also improved after the treatment. Confirmed by surface topography detection and chemical composition analysis, a high-quality SAM can be formed rapidly on glass with 10 min UVO treatment followed by 2 h deposition in PFDS solution. Excellent tribological performances of SAM coated with UVO treatment glass were demonstrated by friction and wear tests on AFM compared to film-deposited glass without UVO treatment and original glass. The study sheds a light on preparing high-quality lubrication and antiwear self-assembled films on the surface of engineering materials.

Anti-Friction and Anti-Wear Mechanisms of Micro Textures and Optimal Area Proportion in the End Milling of Ti6Al4V Alloy

To solve the problems of low efficiency, poor surface quality, and short tool life in the milling of titanium alloys, this study took the micro-textured ball-end milling tool as a starting point and established a platform for friction and wear tests. Based on a new method of external friction theory, the anti-friction and anti-wear mechanisms of the micro-textured tool were analyzed. According to these mechanisms, the optimal area proportion of the micro textures in the contact area between the chip and tool was theoretically investigated considering the milling force, and the proportion was verified experimentally. This work provides a reference for improving the cutting performance of hard metal tools.

Tribological behavior of Ti6Al4 V alloy swing against UHMWPE under different lubrication

Friction and wear tests were performed in this study between the Ti6Al4 V socket and ultrahigh molecular weight polyethylene (UHMWPE) ball on swinging friction tester to clarify the wear mechanism of Ti6Al4V/UHMWPE friction pair under different conditions, including dry condition, simulated body fluid (SBF), and fetal bovine serum (FBS). Results showed that there are many scratches in different depths on the edge of the Ti6Al4 V socket, which reveals the characteristic of swinging friction, and the wear severity of the scratches was the worst under dry friction. What is more, the wear mechanism models under different lubrication conditions have been established. The wear mechanism of Ti6Al4 V alloy is mainly a combination of abrasive and oxidation wear, whereas the wear mechanism of UHMWPE is a combination of adhesive and abrasive wear. Compared with the dry friction condition, the friction coefficient and wear rate decreased under SBF and FBS lubrication conditions, and the wear mechanisms presented primarily adhesive wear combined with minimal oxidation wear. Among the three conditions, the effects of reducing friction and improving lubrication showed the following tendency: FBS > SBF > dry condition.