This article presents an analytical model for predicting friction in mixed lubrication regime. The calculations consider load shared between roughness asperities and the lubricant film, as well as the appearance of thermal effects in the contact and the influence of the lubricant rheology. Tests using tribometers have been performed to measure the friction coefficient in non-conformal surfaces for both point and line contacts. This allows verifying the results of the model under a broad range of experimental conditions with an influence on the lubrication conditions. Reasonably good precision has been found in the results obtained, which combined with a simplicity of use confers the model a high practical utility for rough estimates of the friction coefficient under mixed lubrication.
This article presents thermal EHL calculations for line contacts using a new analytical form of the Reynolds equation for lubricants whose rheological behaviour follows a modified Carreau model proposed by Bair. The isothermal calculation process was presented in: de la Guerra (Tribol Int 82:133-141, 2015). A new parametric formula is hereby developed using the aforementioned Reynolds-Carreau equation and adding the thermal effects to the solving process. The accuracy of this formula is discussed by comparing the estimates with the experimental and numerical results available. This analytical formula provides a fast and easy calculation methodology with good accuracy within a reasonably wide range of operating conditions.
This article presents a thermal resistances-based approach for solving the thermal-elastohydrodynamic lubrication problem in point contact, taking the lubricant rheology into account. The friction coefficient in the contact is estimated, along with the distribution of both film thickness and temperature. A commercial tribometer is used in order to measure the friction coefficient at a ball-on-disc point contact lubricated with a polyalphaolefin base. These data and other experimental results available in the bibliography are compared to those obtained by using the proposed methodology, and thermal effects are analysed. The new approach shows good accuracy for predicting the friction coefficient and requires less computational cost than full thermal-elastohydrodynamic simulations.
This paper presents an alternative to the materials traditionally used in the manufacture of coal mills for coating wedges. For this purpose, we designed and tested ten new austenitic steels with medium manganese content. The thermal structural stability and hardness were evaluated after different heat treatments. The steels were subjected to hyperquenching and tempering between 100 and 900 °C. A metallographic analysis of each sample was then performed to determine their thermal stability, and the Brinell hardness was measured. Later, wedges of two alternatives and reference-material alloys were manufactured and installed in three types of mills. Their mass loss was determined after 25 months and at an intermediate time during that period. One steel was selected as an alternative material.
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