Ramiro C. Martins

Gear power loss performance of biodegradable low-toxicity ester-based oils

Environmental issues are leading to a growing interest in bio-lubricants, which can have similar or even better performance than mineral and synthetic oils. In this work, the power loss performance of two biodegradable, low toxicity, ester-based gear oils was evaluated and compared with a commercial mineral oil and an ester-based fluid containing zinc dialkyl dithio phosphate (ZDDP) additives. Power loss tests were performed on the FZG test rig, using type C carburized gears and the different lubricants under evaluation. The operating temperatures of the oil and of the FZG gearbox wall were measured for different values of the input torque and speed and lubricant samples were periodically collected and analysed by direct reading ferrography. At the end of the tests, the gear mass loss and the oil viscosity were measured, the teeth flanks were inspected, looking for typical surface failure mechanisms, and the tooth flank surface roughness was measured. An energetic model of the FZG test gearbox, which took into account the power loss mech-anisms inside the gearbox and the heat flow mechanisms from the gearbox to the surrounding environment, was used to calculate the friction losses between the gear teeth, knowing the oil, gearbox wall, and room temperatures, in steady-state conditions. Using this model, it was poss-ible to analyse the influence of lubricant formulation on the average friction coefficient between gear teeth. The results obtained showed that one of the biodegradable, low-toxicity, ester-based gear oils generated significantly lower mass loss than all the other lubricants, presenting almost no degradation, even when operating at very high temperature for long periods. These bio-lubricants generated friction coefficients between gear teeth up to 27 per cent smaller than the commercial mineral oil, promoted significant reductions of the power loss inside the FZG gearbox, increasing the overall efficiency up to 0.25 per cent.

Evolution of tooth flank roughness during gear micropitting tests

Purpose – The purpose of this paper is to get a better understanding of roughness evolution and micropitting initiation on the tooth flank, as well as the evolution of surface topography during the test load stages in a modified DGMK short micropitting test procedure.Design/methodology/approach – A modified DGMK short micropitting test procedure was performed, using an increased number of surface observations (three times more) in order to understand the evolution of the surface during each load stage performed. Each of these surface observations consists in the evaluation of surface roughness, surface topography, visual inspection and also weigh measurements as well as lubricant analysis.Findings – This work showed that the larger modifications on surface took place in the beginning of tests, especially during load stage K3 (lowest load, considered as running‐in) and on the first period of load stage K6, that is, during the first 200,000 cycles of the test. The 3D roughness parameters (St and Sv), obtain...

Micropitting performance of mineral and biodegradable ester gear oils

Purpose – This papers aim is to present the gear micropitting performance of two industrial gear oils: a standard mineral lubricant (CM) containing a special micropitting additive package and a biodegradable ester with low toxicity additivation.Design/methodology/approach – Gear micropitting tests were performed on the FZG machine, using type C gears made of case carburized steel. Lubricant samples were collected during the tests for analyzing the wear particles generated during operation. Post‐test analysis included the visual inspection of the teeth flanks and the assessment of the micropitting area, the mass loss of the gear, the ferrometric analysis of the lubricant samples and the surface roughness measurement of the teeth flanks, below and above the pitch line.Findings – The micropitting performance of the two lubricants was very similar, confirming the advantage of using the ester lubricant (CE) as an industrial gear oil, now that it is an environmentally friendly product.Research limitations/impl...

Power Loss in FZG gears lubricated with industrial gear oils: Biodegradable Ester vs. Mineral oil

ABSTRACT Two industrial gear oils, a reference paraffinic mineral oil with a special additive package for extra protection against micropitting and a biodegradable non-toxic ester, are compared in terms of their power dissipation in gear applications [ [1] , [2] ]. The physical properties, wear properties and chemical contents of the two lubricants are characterized. The viscosity-temperature behaviors are compared to describe the feasible operation temperature range. Standard tests with the Four-Ball machine and the FZG test rig characterize the wear protection properties. Biodegradability and toxicity tests are performed in order to assess the biodegradability and toxicity of the two lubricants. Friction and wear tests have been performed with a configuration that combines rolling/sliding in a line contact simulating the working conditions on gears. The results for the ester oil presented a lower friction coefficient and operating temperature throughout tthe test in relation to mineral oil. Power loss gear tests are performed on the FZG machine using type C gears, for wide ranges of the applied torque and input speed, in order to compare the energetic performance of the two industrial gear oils [ 3 ]. The results of the power loss gear tests show that the operating temperature of the ester oil is always smaller than that of the mineral oil. Lubricant samples are collected during and at the end of the gear tests [ 4 ]. The lubricant samples are analyzed by Direct Reading Ferrography (DR3) in order to evaluate the wear particles concentration (CPUC) and the index of wear particles severity (ISUC). Both parameters indicate that the gear lubricated with the mineral oil suffered more flank tooth wear than the one lubricated with the biodegradable ester. The influence of each lubricant on the friction coefficient between the gear teeth is discussed taking into consideration the operating torque and speed and the stabilized temperature.

Carbon/chromium low friction surface coating for gears application

Purpose – Provide tribological information about the applicability of multi‐layer carbon‐chromium composite coatings to gears. Discuss the protection provided against scuffing failures, wear and the influence on gear power losses.Design/methodology/approach – Several screening tests, such as Rockwell indentations, ball cratering, pin‐on‐disc and reciprocating wear tests, were performed in order to evaluate the adhesion to the substrate and the tribological performance of the carbon/chromium composite coating. Afterwards, twin‐disc tests were performed at high contact pressure and high slide‐to‐roll ratios to confirm the good adhesive and tribological properties of the coating under operating conditions similar to those found in gears. Gear tests were performed in the FZG machine in order to evaluate the anti‐scuffing performance of the carbon/chromium coating using additive free gear oils. Finally, the carbon/chromium composite coating was also applied to the gearing in a gearbox and its influence on the ...

Influence of tooth profile on gear power loss

Purpose – The purpose of this paper is to develop innovative geometry for gears aiming low power loss and easy manufacturing.Design/methodology/approach – New gear profiles were developed and studied, and gears were built accordingly and then tested using an FZG machine.Findings – Results from the experimental tests revealed the influence of the profile modifications on the operating temperature, thus on the efficiency of gears (in terms of power loss).Research limitations/implications – Studied cases were limited to experimental gear models compliant to the FZG machine.Practical implications – Low‐loss gears can be produced using common technologies and tools. Its design includes power loss minimization besides mechanical strength. The new gears are more environmentally friendly and can operate with lower power consumption, lower temperature, increasing gear and gear oil life.Originality/value – This work contributes to the development of the “low‐loss gears” concept, adapting it to low‐cost manufacturin...

Load Distribution in Spur Gears Including the Effects of Friction

Friction losses between meshing gear teeth are amongst the most influential loss sources in a gearbox at nominal or near nominal operating conditions. Gear friction losses are influenced by speed, load and coefficient of friction. These factors and their variation along the path of contact must be taken into account in order to obtain accurate power loss predictions. Understanding how the power loss develops along the path of contact certainly helps in the development of more efficient and reliable gear designs. The aim of this work is then to introduce a formulation to calculate the load distribution along the path of contact taking into account elastic effects and friction.

Surface damage prediction during an FZG gear micropitting test

A numerical simulation of an actual FZG spur gear micropitting test was performed. The simulation was based on a model that takes into account: overpressure effects due to mixed or boundary film lubrication, in turn caused by the interaction of roughness features of the contacting gear teeth, represented in the simulation by actual roughness profiles measured on the teeth; residual stresses in the gear teeth; a high-cycle, multi-axial fatigue criterion to evaluate the fatigue damage on the surface. The simulation was applied to the four load stages that constitute an FZG gear micropitting test and actual gear meshing was simulated. It was additionally possible to ascertain the adequacy of the model to shorter load durations because the load stages of the original micropitting test had been periodically interrupted for intermediate monitoring.

Influence of oil formulation on gear micropitting and power loss performance

This study presents a study of the influence of oil formulation on the protection against gear micropitting and also its influence on gear efficiency. The study had both components because a well-balanced product is necessary and its behaviour must be demonstrated in dedicated tests. The industrial gear oils studied combined polyalphaolefin with ester base oils and had different additive packages. FZG gear power loss tests were performed using 20MnCr5 carburized gears under a wide range of operating conditions. During the tests, the oil and gearbox temperature were continuously recorded and gear oil samples were collected. After the tests, the gear mass loss was measured and oil samples were analyzed by ferrography. Using an energetic model of the FZG test gearbox, it was possible to quantify the influence of lubricant formulation on the average friction coefficient between gear teeth, which will provide a quantitative comparison of lubricants. The gear micropitting protection provided by the oxidized lubricant samples was evaluated in a FZG test rig according to DGMK short micropitting test procedure. During the tests, lubricant analysis, mass loss measurements, surface observation, and topography measurements were performed to evaluate the micropitting evolution along the tests as well as severity of micropitting. The results obtained show that the base oil, the additive package, as well as their combination can have a very significant influence on the efficiency and micropitting performance of industrial gear oil.

Micropitting of carburized gears lubricated with biodegradable low-toxicity oils:

Abstract Environmental issues are leading to a growing interest in bio-lubricants, which can have similar or even better performance than mineral and synthetic oils. In this work, the biodegradability and toxicity characteristics of ester-based gear oils are presented and their physical, chemical, and wear properties are compared with those of a commercial mineral oil. In an earlier work, power loss tests were performed on the FZG test rig, using carburized gears and several different lubricants. The operating temperatures of the oil and of the FZG gearbox wall were measured for different values of the input torque and speed. An energetic model of the FZG test gearbox was developed, taking into account the power loss mechanisms inside the gearbox and the heat flow mechanisms from the gearbox to the surrounding environment. Using this model it was possible to quantify the influence of lubricant formulation on the average friction coefficient between gear teeth. Gear micropitting tests were performed on the FZG test rig, using carburized gears and different oils. Post-test analysis included the mass loss measurement of the gear, the ferrometric analysis of lubricant samples collected during the tests, and the visual inspection of the gears. The tooth flanks were inspected using surface topography measurements to assess the number and depth of micropits. In comparison with the gear lubricated with mineral oil, the gears lubricated with ester-based oil showed significantly higher mass loss (3—4 times higher), smaller number of micropits, and less deep micropits. If carefully formulated, biodegradable low-toxicity ester-based gear oils, beside their environmental advantages, enhance gear performance when compared with the mineral lubricant providing (a) lower friction coefficients and lower operating temperatures of gearboxes and (b) lower number of micro-pits (with depths greater than 4 μm). One of the ester-based gear oils passed the FVA gear micropitting criterion.