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.

Fluid Characteristics Analysis of the Lubricating Oil Film and the Wear Experiment Investigation of the Sliding Bearing

The sliding bearing is an important component in machines. The characteristics of the oil film fluid of the sliding bearing is the key factor affecting lubrication, which will affect the wear and reliability of the sliding bearing. Herein, the lubricating oil of the sliding bearing is studied, the oil film flow model considering the cavitation effect is established, the pressure and temperature distribution of the oil film under different rotational speeds is explored, and its influence on oil film pressure and temperature are analyzed. Furthermore, wear tests are carried out to measure the wear amount of the bearing bush under different rotational speeds, and the influence of the fluid characteristics of the lubricating oil film on bearing wear is explored. The simulation and experimental study in this paper can provide a reference for the design of sliding bearings.

Effects of Graphene on the Wear and Corrosion Resistance of Micro-Arc Oxidation Coating on a Titanium Alloy

In order to improve the wear and corrosion resistance of micro-arc oxidation (MAO) coating on a Ti-5Al-1V-1Sn-1Zr-0.8Mo alloy, 0–0.20 g/L graphene was added to the electrolyte to prepare micro-arc oxidation coating. The thickness, roughness, micro-morphology, and composition of the MAO coating were characterized, and the wear and corrosion resistance of the coating was tested and analyzed. The results show that with 0.05 g/L of graphene in the electrolyte, the roughness of the coating decreased from 56.76 μm to 31.81 μm. With the increase in the addition of graphene, the microstructure of the coating became more compact, the diameter of micro-holes and micro-cracks decreased, and the corrosion resistance of the coating improved. The wear tests showed that the mass loss of the coating at the early wear stage (0~100 revolutions) was greater than that at the later stage (100~250 revolutions), and the wear resistance of the coating obtained by the addition of 0.10 g/L of graphene was the highest. With 0.10 g/L of graphene, the adhesion force between the coating and the substrate alloy is the largest, reaching 57.1 N, which is 9.98 N higher than that without graphene. After salt spray corrosion for 480 h, the coating with graphene has better corrosion resistance than that of a graphene-free coating.

Influence of ultrasonic agitation on the abrasive wear characteristics of Al-Cu/ 2 vol.% Grp composite

In the present study, the abrasive wear behavior of Al-4.4 wt.% Cu composite reinforced with 2 vol.% graphite particle (Grp) has been investigated. In the preparation of composite, Ultrasonic Treatment (UT) is provided in the composite melt for the uniform distribution of reinforcement particles. Two bond abrasive wear tests are conducted for composites treated with ultrasound and without UT and base alloy. The results of abrasive wear studies indicate that at 5 and 10 Newton (N) loads, the composite with UT has a higher coefficient of friction (COF) and wear resistance than that of the base alloy (Al-4.4 wt.% Cu). Whereas, at 15 and 20 N load, the value of COF and wear resistance is lower for the composite. Two abrasive wear mechanisms micro-plowing and micro-cutting have been observed during the wear tests of base alloy and composites. The analysis of worn-out sample surfaces at higher load reveals that softened material layer due to localized elevation in temperature between two contact surfaces during wearing acts as a tribolayer in base alloy while in composites both softened material layer and graphite layer have worked together as tribolayer.

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.

Investigation of wear conditions of a composite material based on an anti-friction alloy AO20-1 reinforced with Ti particles

Сomposite material samples were obtained by the method of reaction casting by mixing titanium particles to obtain intermetallic phases Al3Ti. Dry sliding wear tests were carried out using a fixed sleeve (steel 45) against a rotating disk (sample) at sliding speeds from 0.25 to 0.75 m/s and loads from 0.5 to 3.5 MPa.There were constructed maps of wear rate, which determine the friction modes during testing. There were shown boundaries and conditions of changing wear modes.

Measurement of The Cycloidal Drive Sleeves and Pins

In the paper, an issue of CMM measurement strategy of the sleeves and pins designed for wear tests in the cycloidal drive. The measurement strategy was proposed, based on initial out-of-roundness measurement in scanning mode. Proposed approach ensured that the pin was measured along its entire 40 mm length with only small area of fixation ca. 5 mm left out, and all probing points for cylindricity deviation assessment were collected in one fixation. It was demonstrated that the cylindricity and roundness measurement results based on 8, 16 and 48 probing points provided sufficient data for further wear analysis. In some cases, the circles calculated from 4 points gave additional insights allowing to accept the part that otherwise might be possibly rejected.

Ceramic Inlay Bonded Interfaces in Minimally Invasive Preparations: Damage and Contributing Mechanisms in Sliding Contact

SUMMARY Background: In the preparation of inlay cavities, a choice must be made between conventional standard and minimally invasive preparation designs; in the long run, this choice can affect the integrity of the bonded interface. Purpose: To evaluate the effect of minimally invasive cavity preparation designs on the extent and contributing mechanisms of damage to ceramic inlay bonded interfaces. Methods and Materials: Tooth blocks with 90°, 120° and 75° marginal angles were prepared, representing tooth cavities with conventional standard and minimally invasive preparations with large divergence and convergence angles and bonded to monolithic ceramic (IPS e.max CAD). Vickers indentations were placed at various distances from the bonded interface. The indentation morphology and crack length were observed. Reciprocating wear tests were performed on the bonded interface with a 20-newton (N) vertical load. The wear depth and wear-scar morphology were characterized after increments of cyclic sliding contact. Results: The 120° group exhibited longer indentation cracks in the ceramic, whereas the 75° group showed larger indentations in the enamel when compared to the 90° group (p<0.001). Consistent with the weaker edge crack resistance, the 120° group experienced the greatest wear (p=0.008), and the wear depth in the enamel of the 75° group exceeded that of the 90° group (p<0.001) in the early stage (5×102 cycles). However, no significant difference in the wear depth (p>0.147) and morphology were found at the later wear stage among the three groups. Conclusion: Within the limitations of this study, minimally invasive preparations with 120° and 75° marginal angles can result in early sever damage at the ceramic inlay bonded interface but show comparable wear behaviors to the conventional 90° group at the later stage.

Galling wear between ASTM 6061 aluminum and grade D2 tool steel

In the automotive industry, galling is a huge problem either for the tool life or the quality of the stamping metal component. Galling is a severe form of scuffing associated with gross damage to the surface or failure. This work aims to carry out a series of experiments of galling tests at different loads and similar roughness with 6061 aluminum and D2 steel, common materials used in automotive components and tools respectively. A tribometer was employed to generate Galling wear, the button-on-button configuration, according to the ASTM G-196-08 standard. The results show the threshold of minimum load without galling wear. Post-test-surface analysis of the specimens was conducted by confocal microscopy to identify the damage generated during the wear tests. Additionally, a couple of friction tests were carried only to illustrate the friction coefficient behavior under galling conditions.

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.