Investigation of the effective parameters of scuffing failure in gears

This study investigates the effective parameters of scuffing failure in gears using the integral temperature method. For this aim, the mass temperature, integral temperature and scuffing safety factor are calculated for a given parameters. Then, integral temperatures are simulated based on various geometrical, operational and lubrication parameters. Obtained results are presented graphically. The obtained results show that increasing the module mn results in a decrease in the integral temperature ϑint. Similarly, increasing the pinion teeth number zp results in a decrease in the integral temperature ϑint. Increasing the module and tooth number positively affects the scuffing failure in gears. In contrast, increasing the transmitted torque MT1T results in an increase in the integral temperature ϑint. Similarly, increasing the pinion speed np increases the mass temperature ϑM, and increasing the lubricant (oil) ϑÖ temperature increases the integral temperature ϑint. Increasing the transmitted torque, lubricant temperature and the pinion speed negatively affects the scuffing failure in gears. Finally, increasing the nominal kinematic viscosity v40 decreases the integral temperature ϑint. Increasing the nominal kinematic viscosity positively affects the scuffing failure in gears. By considering the effective parameters of scuffing failure such as geometrical, operational and lubrication, one can design and manufacture the desired gears without scuffing failure.

Tribological behavior of chrome-deposited SAE9254 grade steel top compression piston ring under lubrication starvation and mild extreme pressure lubrication

This article reports tribological studies of piston ring/cylinder liner tribo-contact to evaluate the scuffing failure under dry sliding conditions and its minimization with mild extreme pressure lubrication. The tribological conjugation tested employs a piston ring of SAE9254 grade steel substrate with plasma-sprayed chromium coating of 42 µm and ISO R185220 grade gray cast iron cylinder liner. A conformal, cylinder inscribed in cylindrical cavity contact was ensured to simulate actual dead center reciprocating between piston ring–cylinder liner interface. Tribotests were conducted under dry sliding, simulating lubrication starvation and sliding in extreme pressure additivation blend at a temperature of 200 °C with 10 mm stroke length and reciprocating velocity of 0.2 m s–1. The friction characteristics of the piston ring and cylinder liner samples in cited test conditions were studied as a function of load and continuously monitored throughout the tests. Optimal profilometry was employed for evaluating wear attributes. For surface morphology and allied surface characterization, energy-dispersive X-ray spectroscopy integrated scanning electron microscopy was used. For tribo-chemical interactions and film formation, the tribo-surfaces were further investigated with Raman spectroscopy. ASTM E-384 standard Vickers indentation microhardness and its precedence to tribological characteristics were evaluated. The extreme pressure lubrication is intended to potentially improve the scuffing résistance and optimization of coating material in achieving superior tribological characteristics. Superior lubricity, scuffing resistance and enhanced load-bearing capacity attributes were manifested by EP-PAO10 blend lubrication contrasting the surface deteriorations and scuffing failure ascribed to dry sliding.

A scuffing model considering additive depletion in boundary lubrication

Purpose This paper aims to propose a new scuffing model caused by the depletion of additives in boundary lubrication condition. Design/methodology/approach The differential equation governing the distribution of additive content in the fluid film was used. This formula was derived from the principle of mass conservation of additives considering the consumption due to surface adsorption of wear particles. The occurrence of scuffing was determined by comparing the wear rate of the oxide layer with the oxidation rate. Findings If the additive becomes depleted while sliding, the scuffing failure occurs even at a low-temperature condition below the critical temperature. The critical sliding distance at which scuffing failure occurred was suggested. The experimental data of the existing literature and the theoretical prediction using the proposed model are shown to be in good agreement. Originality/value It is expected to be used in the design of oil supply grooves for sliding bearings operating under extreme conditions or in selecting the minimum initial additive concentration required to avoid scuffing failure under given contact conditions.

The Effect of Starvation on a Thermal Mixed EHL Line Contact

To investigate the effect of the inlet starvation severity on the flash temperature, which dictates the scuffing failure, a thermal mixed elastohydrodynamic lubrication model is developed for line contacts operating under the starved lubrication condition. The scuffing failure of high speed gearing applications is commonly associated with the very high sliding condition occurring in the vicinity of either the root or the tip, where the shear thinning effect that decreases the lubrication film thickness and increases the contact pressure is significant. Utilizing a generalized Newtonian Reynolds equation, the lubricant viscosity dependence on the shear rate, as well as on the pressure and temperature, is incorporated for the proper and accurate modeling of the tribological behavior under the high sliding condition. A film fraction parameter is employed in the Reynolds equation to include the starvation and cavitation description, eliminating the need for the measured or assumed meniscus location in the inlet zone. Considering different operating and surface roughness conditions, a parametric study is performed to show an asymptotic relationship between the flash temperature and the inlet starvation severity.

A temperature measurement method for testing lubrication system or revealing scuffing failure mechanism of spur gear

In order to meet the needs of temperature measurement for testing lubrication system or revealing scuffing failure mechanism of spur gear, a temperature measurement method analysis is carried out. This method shifts the high temperature region to a position convenient for measurement. And the measurement target including the highest temperature of gear and its location are also shifted to the new position. Considering the change of gear temperature field caused by thermal barrier covering the end face, the temperature difference of the target measurement position and the direct measurement position is analyzed by finite element method. Taking a spur gear pair as an example, its temperature field is obtained in the thermal steady state before and after shifting of temperature. The results show that temperature of the target measurement position and the direct measurement position is same in distribution, and temperature of the direct measurement position is higher than the temperature in the target measurement position. The highest temperature of the direct measurement position increases by 2.5%. As a result, considering the increment as the safety margin, it is not conservative to estimate the temperature in the target measurement position by the measured temperature data in the direct measurement position. And the measured temperature data also will help to find out the location of the highest temperature of gear in the target measurement position. Meanwhile, the accidental risk of scuffing failure can be avoided during experimental research in testing lubrication system or revealing scuffing failure mechanism by this temperature measurement method. And the comparison of the analytical results with the experimental measurement data shows good agreement.

Influence of Surface Roughness Lay Directionality on Scuffing Failure of Lubricated Point Contacts

The influence of roughness lay directionality on scuffing failure is studied considering different roughness lay direction combinations of the contacting surfaces of a ball-on-disk contact. Using a recently developed scuffing model Li et al., (2013, “A Model to Predict Scuffing Failures of a Ball-On-Disk Contact,” Tribol. Int., 60, pp. 233–245)., the bulk temperature and flash temperature are predicted for each roughness lay combination within the load range from 0.76 GPa to 2.47 GPa in a step-wise manner under the rolling velocity of 10 m/s and slide-to-roll ratio of −0.5 to show substantial impacts of roughness lay directionality on scuffing resistance performance (SRP). It is found (i) the lay direction combination that results into contacts of asperities with small contact radii leads to increased local contact pressures and frictional heat flux, reducing SRP; (ii) the continuous asperity contact along the sliding direction leads to continuous surface temperature rise and lowers SRP; and (iii) the lubricant side leakage caused by the pressure gradient in the direction normal to the sliding direction leads to reduced SRP. With these main mechanisms in effect, the SRP of a contact decreases as the deviation between the roughness texture orientations of the two surfaces increases. The surfaces with their roughness lay directions both perpendicular to the sliding direction exhibits best SRP. The surfaces with one roughness lay direction positioned in line with the direction of sliding and the other positioned perpendicular to the sliding direction shows worst SRP.