Thrust Washer Research Articles

Reliability Design of Mechanical Systems Such as Compressor Subjected to Repetitive Stresses

This study demonstrates the use of parametric accelerated life testing (ALT) as a way to recognize design defects in mechanical products in creating a reliable quantitative (RQ) specification. It covers: (1) a system BX lifetime that X% of a product population fails, created on the parametric ALT scheme, (2) fatigue and redesign, (3) adapted ALTs with design alternations, and (4) an evaluation of whether the system design(s) acquires the objective BX lifetime. A life-stress model and a sample size formulation, therefore, are suggested. A refrigerator compressor is used to demonstrate this method. Compressors subjected to repetitive impact loading were failing in the field. To analyze the pressure loading of the compressor and carry out parametric ALT, a mass/energy balance on the vapor-compression cycle was examined. At the first ALT, the compressor failed due to a cracked or fractured suction reed valve made of Sandvik 20C carbon steel (1 wt% C, 0.25 wt% Si, 0.45 wt% Mn). The failure modes of the suction reed valves were similar to those valves returned from the field. The fatigue failure of the suction reed valves came from an overlap between the suction reed valve and the valve plate in combination with the repeated pressure loading. The problematic design was modified by the trespan dimensions, tumbling process, a ball peening, and brushing process for the valve plate. At the second ALT, the compressor locked due to the intrusion between the crankshaft and thrust washer. The corrective action plan specified to perform the heat treatment to the exterior of the crankshaft made of cast iron (0.45 wt% C, 0.25 wt% Si, 0.8 wt% Mn, 0.03 wt% P). After these design modifications, there were no troubles during the third ALT. The lifetime of the compressor was secured to have a B1 life of 10 years.

Improving lifetime of domestic compressor subjected to repeated pressure loading

To enhance the lifetime of domestic refrigerator compressors subjected to repeated pressure loads, parametric accelerated life testing (ALT) as a reliability methodology is studied. It contains (1) ALT plan used on BX lifetime, (2) load analysis for the ALT, (3) parametric ALTs with action plans, and (4) assessment of the last compressor designs to make sure the targeted BX lifetime is achieved. To combine the design concepts of a compressor with parametric ALT, we have derived the approximated sample size equation, the life-stress model with an effort concept and acceleration factor. As a test case, a compressor with a newly designed crankshaft subjected to repetitive pressure loading was studied. Based on a mass and energy balance, the compressor loads were analyzed. In the 1st ALT, the failure mode was locking of the compressor due to crankshaft wear. The design fault of the crankshaft was the improper lubrication in the crankshaft. As a corrective action plan, the crankshafts were redesigned by: (1) changing the starting RPM from 1650 to 2050, (2) relocating the lubrication holes and adding a new groove, and (3) modifying the material of crankshaft from FCD450 to FCD500. In the 2nd ALT, wear on the surface of compressor crankshaft occurred. The minimum clearance between thrust washer and the crankshaft was then modified. After three parametric ALTs, the lifetime of the newly designed compressor was guaranteed to have B1 life 10 years.

Application of topological optimisation methodology to hydrodynamic thrust bearings

The bearing geometry has a big impact on the performance of a hydrodynamic thrust bearing. For this reason, shape optimisation of the bearing surface has been carried out for some time, with Lord Rayleigh’s early publication dated back to 1918. There are several recent results e.g. optimal bearing geometries that maximise the load carrying capacity for hydrodynamic thrust bearings. Currently, many engineers are making an effort to include sustainability in their work, which increases the need for bearings with lower friction and higher load carrying capacity. Improving these two qualities will result in lower energy consumption and increase the lifetime of applications, which are outcomes that will contribute to a sustainable future. For this reason, there is a need to find geometries that have performance characteristics of as low coefficient of friction torque as possible. In this work, the topological optimisation method of moving asymptotes is employed to optimise bearing geometries with the objective of minimising the coefficient of friction torque. The results are both optimised bearing geometries that minimise the coefficient of friction torque and bearing geometries that maximise the load carrying capacity. The bearing geometries are of comparable aspect ratios to the ones uses in recent publications. The present article also covers minimisation of friction torque on ring bearing geometries, also known as thrust washers. The results are thrust washers with periodical geometries, where the number of periodical segments has a high impact on the geometrical outcome.

Effects of thrust washer bearing surface characteristics on planetary gear train wear

Thrust washers in spur planetary gears are placed between the planet wheel and planet carrier and act as spacers and wear pads. Metal to metal sliding contact between the planet wheel – washer – carrier causes frictional power losses that, combined with starved lubrication, may cause high contact temperatures and thermo-mechanical effects that potentially trigger thermo-elastic instabilities and excessive local wear. The planetary gear system would benefit from a low-friction interface between the washer and the planet wheel. Five washers with different surface treatments were tested in a full-scale gear rig. These tests were also replicated as closely as possible in a pin-on-disc tribometer. The following types of finishing material treatments were studied: a chemical nickel coating plus polymer on a nitro-carburised surface, a combination of nitro-carburization and solid lubricant layers, electroless deposited chemical nickel coating plus polymer, nitro-carburizing, and manganese phosphating. The frictional results indicate that tribometer tests can be used to compare and classify new washer materials. Lab scale tests show that a new experimental self-lubricating tribomaterial that was applied with laser cladding has a promising potential to increase planetary gear train robustness and service life, especially if the surface is fine grinded.

자동차 엔진용 Thrust Washer 생산을 위한 판형 소재의 단조 공정기술개발 및 이를 위한 유한요소해석

In this paper, we present a study on the development of the manufacturing process of thrust washers for an automobile. The thrust washers are manufactured using the progressive cold forging method. The proposed progressive cold forging method requires less manufacturing cost and processing time compared with the previous conventional manufacturing method, through the elimination of some cutting and grinding processes. The proposed cold forging method uses the single plate material that is used in multi-step forging process (progressive method). In order to estimate the plastic deformation of the product due to cold forging, we conduct a finite-element analysis and compare the predicted deformation with the experimental results. The effectiveness of the proposed manufacturing process is verified by comparing the simulation and experimental results. Finally, we suggest a new stereotyped design of the single plate type cold forging process, based on the data obtained by performing simulation and experiments.

Tribological performance of differential gear end-face sliding on washer with a radial groove

Abstract Effects of a radial groove perpendicular to relative sliding direction on the tribological properties of the differential gear end-face on the corresponding thrust washer, were experimentally investigated under both sufficient and insufficient lubrication. A radial groove was artificially introduced into the thrust washer. The monitored friction force signals were analyzed by discrete wavelet transform. The wear scar of thrust washers were scanned with scanning electron microscope. The wear particles were collected and identified in the tests under insufficient lubrication. Results indicated that (i) the radial groove tended to decrease the friction force at the running-in period and to cause several fluctuation of approximate 5 (A5) of the friction force at the test beginning time, and the amplitudes of detail 5 signals reflected the performance deterioration of the thrust washer after a specific operating period under sufficient lubrication; (ii) the amplitude of the friction force was reduced and the values of the pulsation of A5 gradually increased before the friction failure time under insufficient lubrication; (iii) with the effect of the radial groove, non-contact area and smooth surface area were found in the groove regions of the washer under sufficient lubrication, and shallow and narrow plowing grooves on the washer's wear scar were the dominant wear morphologies and the percentages of irregular and elongated particles were significantly high under insufficient lubrication.

Effect of gamma radiation on graphite – PTFE dry lubrication system

An effect of gamma radiation on lubrication behavior of graphite -PTFE dry lubrication system has been studied using (TR-TW-30L) tribometer with thrust washer attachment in plane contact. Different compositions of graphite and PTFE were prepared and irradiated by gamma rays. Gamma radiation exposure significantly improves the tribological properties indicated by decrease in coefficient of friction and wear properties of graphite -PTFE dry lubrication system. SEM and XRD analysis confirm the physico-chemical modification of graphite-PTFE on gamma radiation exposure leading to a novel dry lubrication system with good slip and anti friction properties.

Modification of spider gear back to uniform the stress and improve the anti-wear performance of a real thrust washer

The maintenance cost of a heavy truck increases due to the severe damage of thrust washer in the differential. The wear was usually related to the contact stress concentration. In the study, the finite element analysis (FEA) was performed for identifying the source of the abnormal wear of thrust washer. An improved approach of modifying the surface profile of spider gear back was proposed. FEA simulations were further conducted to investigate the effect of different spider gear back parameters on the tribological behavior of thrust washer. The FEA simulation results were verified by tribological experiments. Results showed that: (i) the abnormal wear of thrust washer pairing the original gear was caused by the local stress concentration; (ii) the local stress concentration could be eliminated by modifying the surface profile of spider gear back; (iii) using the modified spider gear back, the wear mass loss of the thrust washer was reduced significantly; (iv) the promising surface radius of spider gear back was 73.15mm.

A comparison of the relative friction and wear responses of PTFE and a PTFE-based composite when tested using three different types of sliding wear machines

In this work, the tribological behavior of a commercially available polytetrafluoroethylene-based composite material filled with polyimide microparticles has been thoroughly investigated using different approaches. Specifically, two standard tribological tests, i.e., pin-on-disc and thrust washer measurements, have been compared with sliding tests performed on real components using a specially designed lab bench. The obtained results demonstrated that, despite the different testing methods (continuous rotation vs. reciprocating linear movement for the pin-on-disc/thrust washer and sliding tests, respectively), the different techniques provide highly comparable data within the adopted experimental conditions and can be successfully combined to assess the overall tribological features of this PTFE-based polymer composite.

Wear and friction characteristics of surface-modified aluminium alloys

This study investigates the wear and friction characteristics of surface–modified aluminium alloys of JIS AC4CH–T6 and A6061–T651. The aluminium alloys were individually treated with five surface modifications, including anodising, anodising/MoS2, electroless Ni, electorless PTFE and DLC. Dry wear tests of thrust–washer–type specimens were carried out at room temperature to evaluate the tribological behaviours of the coatings. The results indicate that coatings effectively enhanced specimen hardness and the surface roughness of the anodising coatings was affected by the choice of base materials. That is, the roughness of the anodised A6061–T651 aluminium alloy was superior to that of the anodised AC4CH–T6. The worn morphology shows wear mechanisms which vary with the coatings. Low–friction coatings of EN/PTFE and DLC exhibited higher wear resistance because of a lower level of material softening caused by the induced friction heat during the wear tests.

Effects of sintering temperature on the microstructural evolution and wear behavior of WCp reinforced Ni-based coatings

This article focuses on the microstructural evolution and wear behavior of 50wt%WC reinforced Ni-based composites prepared onto 304 stainless steel substrates by vacuum sintering at different sintering temperatures. The microstructure and chemical composition of the coatings were investigated by X-ray diffraction (XRD), differential thermal analysis (DTA), scanning and transmission electron microscopy (SEM and TEM) equipped with energy-dispersive X-ray spectroscopy (EDS). The wear resistance of the coatings was tested by thrust washer testing. The mechanisms of the decomposition, dissolution, and precipitation of primary carbides, and their influences on the wear resistance have been discussed. The results indicate that the coating sintered at 1175°C is composed of fine WC particles, coarse M6C (M=Ni, Fe, Co, etc.) carbides, and discrete borides dispersed in solid solution. Upon increasing the sintering temperature to 1225°C, the microstructure reveals few incompletely dissolved WC particles trapped in larger M6C, Cr-rich lamellar M23C6, and M3C2 in the austenite matrix. M23C6 and M3C2 precipitates are formed in both the γ/M6C grain boundary and the matrix. These large-sized and lamellar brittle phases tend to weaken the wear resistance of the composite coatings. The wear behavior is controlled simultaneously by both abrasive wear and adhesive wear. Among them, abrasive wear plays a major role in the wear process of the coating sintered at 1175°C, while the effect of adhesive wear is predominant in the coating sintered at 1225°C.

Temperature Distribution in Pocketed Thrust Washers

This article presents an experimental and numerical investigation of temperature distribution in a pocketed thrust washer. An experimental test rig was designed and developed to measure the temperature in the thrust washer contact under various operating conditions. To measure the temperature in the contact, a thin layer of thermochromic material was placed beneath the pocketed surface. The thermochromic material allowed temperature measurements across the contact through color contours displayed on the sheet. Video recording during operation showed the thermochromic sheet dynamically adapting to the rising temperature in the bearing. For the numerical investigation, the thermal Reynolds and energy equations were simultaneously solved subject to boundary condition to determine the pressure and temperature within the thrust washer. The thermal Reynolds equation was augmented with the Jacobsson-Floberg-Olsson (JFO) boundary condition to model cavitation and the energy equation was used to determine temperature and viscosity variations across the film. Experimental and numerical results showed significantly lower temperatures within the cavitation region due primarily to lower heat transfer from the gas to the solid. The temperature profile and corresponding operating conditions of the bearing obtained from the model correlated well with the experimental results.

Hydrodynamic Pressure Generation in a Pocketed Thrust Washer

The objective of this study was to experimentally investigate hydrodynamic pressure generation in surface-pocketed thrust washers. A novel method of pressure mapping was developed to allow for in situ measurement of the pressure generated by surface modifications. Thin-film pressure transducers, located just below the thrust washer surface, were used to measure pressure variations as a function of the operating conditions. Contour maps showing the cavitation region and the location of peak pressure were clearly displayed. The experimental work presented maps the pressure profiles with real-time, high-resolution sensors. The thin-film pressure transducers were used to investigate the pressure interactions between surface features. In addition to the experimental setup, a model of the contact was developed using ANSYS FLUENT. Cavitation, friction, film thickness, and load support were all compared with experimental results and the two were shown to be in good agreement. The model demonstrated an accurate prediction of the pressure profile but varied slightly with the predicted load support of the thrust washer. The simulation was then used to optimize the pocket density for the experimental operating conditions. The optimal bearing design had the highest load-carrying capacity with a low friction coefficient.

Flow Visualization in a Pocketed Thrust Washer

The objectives of this study were to experimentally and numerically investigate oil flow in surface-pocketed thrust washers. In order to achieve the experimental aspects of this investigation, a thrust washer test rig was designed and developed to visualize the lubricant flow at the contact interface. A novel approach for creating the pockets was developed to allow optical inspection of the lubricant during thrust washer operation. The thrust washers were fabricated using a glass disk with a thin layer of steel shim stock adhered to the surface. The micrometer-thick shim stock was machined using an Nd:YAG laser to create the circular pocket geometries and then glued to the glass disk. A mirror and camera were placed below the semitransparent washer to observe the lubricant flow in the pocket. The results obtained from this configuration illustrate a cavitation bubble forming on the leading edge of the pocket followed by a sharp transition back to liquid. The size of the cavitation area was found to be a function of rotational speed, nominal bearing pressure (NBP), viscosity, and pocket geometry. The cavitation area ratio (gaseous region divided by the pocket area) increased for greater speeds and higher viscosities and decreased for larger pocket diameters, deeper pockets, and higher NBPs. The friction force for various thrust washer designs was also measured as a function of load, speed, and lubricant. The results showed that shallower, wider pockets provided the lowest friction. It was found that, generally, the conditions that minimize friction also result in a stable cavitation region. ANSYS Fluent computational fluid dynamics software was used to develop a three-dimensional model of the pocketed thrust washer utilizing the full Navier-Stokes equations to investigate the cavitation and pressure distribution occurring at the contact and corroborate the experimental results.

The Influence of Silver Content on the Tribological and Antimicrobial Properties of ZrN/Ag Nanocomposite Coatings

ZrN/Ag nanocomposite coatings with varying silver contents were produced by co-deposition in a dual pulsed magnetron sputtering system. The coatings were characterised using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), scratch adhesion testing, thrust washer wear testing and nanoindentation. The hardness of the ZrN/Ag coatings and the friction coefficient running unlubricated against a steel counterface decreased with increasing silver content, whereas the coating-to-substrate adhesion increased for coatings with higher silver contents, compared to a 'pure' ZrN coating. The antimicrobial properties of the coatings were investigated using two well established microbiological assay techniques: zones of inhibition and a NBT (nitro-blue tetrazolium) redox dye. Zones of inhibition were used to determine the extent of silver ion release from the nanocomposite materials, and a NBT (nitro-blue tetrazolium) redox dye was used to determine the antimicrobial effectiveness of the surfaces following incubation. The microorganisms tested were Pseudomonas aeruginosa (P. aeruginosa), Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). Whilst no zones of inhibition were observed for S. aureus, on any of the surfaces, the diameter of the 'kill' zones generally increased with increasing silver content for the other microorganisms. For the NBT assays, after incubation, no P. aeruginosa colony forming units were observed on any surface and the number of viable cells of E. coli and S. aureus decreased with increasing silver content, compared to a 'pure' ZrN surface.

Comparison of the tribological and antimicrobial properties of CrN/Ag, ZrN/Ag, TiN/Ag, and TiN/Cu nanocomposite coatings

Nanocomposite coatings including CrN/Ag, ZrN/Ag, TiN/Ag and TiN/Cu with varying silver or copper contents were produced by co-deposition in a dual pulsed magnetron sputtering system. The compositions and structures of the coatings were characterised using energy dispersive X-ray spectroscopy (EDX) and scanning electron microscopy (SEM), and the physical and tribological properties were assessed by means of nanoindentation and thrust washer wear testing. Although increasing silver or copper content provided a reduction in the coefficient of friction, this was accompanied by reductions in hardness for all the coatings and wear resistance for some of the coatings. Zones of inhibition were used to determine the extent of silver ion release from the coating surfaces, and a NBT (nitro-blue tetrazolium) redox dye was used to determine the antimicrobial effectiveness of the coatings following incubation. The microorganisms tested were Pseudomonas aeruginosa and Staphylococcus aureus. For the NBT assays, significant reductions in the number of viable cells were observed with increasing Ag or Cu content, compared to the ‘pure’ nitride surfaces. Whilst no zones of inhibition were observed for S. aureus, on any of the surfaces, the diameter of the ‘kill’ zones generally increased with increasing silver content for P. aeruginosa.

A study of the antimicrobial and tribological properties of TiN/Ag nanocomposite coatings

TiN/Ag coatings with varying silver contents have been deposited by pulsed magnetron sputtering. The films were characterised in terms of structure and composition using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD). The tribological properties of the coatings were assessed by thrust washer wear testing, which showed a marginal reduction in friction coefficient with increasing silver content against a steel counterface. Zones of inhibition were used to determine the extent of silver ion release from the nanocomposite materials, and a NBT (nitro-blue tetrazolium) redox dye was used in an assay to determine the antimicrobial effectiveness of the surfaces following incubation. The microorganisms tested were Pseudomonas aeruginosa and Staphylococcus aureus. Whilst no zones of inhibition were observed on any of the surfaces, for the NBT assays, after incubation, the silver containing coatings revealed a significant reduction in the number of viable cells of both microorganisms, compared to a ‘pure’ TiN surface.

Effects of area ratio and nature of surfaces on scuffing in lubricated contacts

Heavily loaded moving machine components encounter severe tribological problems. Typical examples include piston and cylinder contacts in a hydraulic motor. Piston and cylinder bore contacts invariably operate in boundary lubrication regime and the risk for seizure of these contacts is high particularly when lubricated with low-viscosity lubricants. The piston assembly in a radial piston hydraulic motor has conformal (area) contact. In this work, these contacts have been simulated in the laboratory by using a thrust washer test configuration. The influence of area ratio, nature of contacting surfaces, and speed on scuffing has been investigated by using a factorial design of experiments approach. The influence of area ratio on wear at lower speed has also been studied. The results have revealed that the surface power, or μ pv-value, at scuffing varies by 3—4 times when the area ratio was increased from 8 to 72 per cent. The running-in wear tests have shown that running-in of the upper and lower specimens also varies with the area ratio. During the first 30 s the upper specimen is polished with low area ratio, whereas the lower specimen is polished with high area ratio. The surface temperature was estimated by using finite-element calculation and it was found to be similar prior to scuffing for both 8 and 72 per cent area ratios at 1.7 m/s sliding speed. The comparison of the results with the actual motor tests shows that an area ratio of 24 per cent seems to simulate the piston-cylinder contact better.

There’s the Rub

This article reviews the mechanical design and a set of practical guidelines for design engineers. Engineers have plenty of technology for controlling friction and wear, including naturally lubricious materials, high-performance lubricants, and rolling element bearings. But where friction is concerned, good mechanical design starts with guidelines. Friction changes with time, reflecting sliding-induced changes to the interface. The traditional single static and single dynamic coefficients of friction are misleading because they do not reflect fluctuations and transitions in friction. The friction coefficient, static or dynamic, has no single, unique value for a given material pair, but rather is a characteristic of those materials when rubbed together under specific conditions. Friction and wear are not material properties; they are system properties. So many test protocols, such as thrust washer tests, will give one result, but actual systems will have different results.

Reliability design and case study of a refrigerator compressor subjected to repetitive loads

A newly designed crankshaft of a compressor for a side-by-side (SBS) refrigerator was studied. Using mass and energy conservation balances, a variety of compressor loads typically found in a refrigeration cycle were analyzed. The laboratory failure modes and mechanisms were compressor locking and crankshaft wear. These were similar to those of the failed samples in the field. Failure analysis, accelerated life testing (ALT), and corrective actions were used to identify the key reliability parameters. The design parameters of the crankshaft included the hole locations and the groove of the crankshaft used for oil lubrication, crankshaft hardness, and thrust washer interference. Based on the analysis and design changes, the B 1 life of the new design is now over ten years with a yearly failure rate of 0.01 percent. A five step procedure is recommended for parts design.