Temperature In Contact Zone Research Articles

A Simplified Thermal Analysis of Elastohydrodynamic Contacts

Under elastohydrodynamic (EHL) conditions, the temperature in the contact zone determines the load resistance of the lubricant film. Therefore, an efficient assessment of the scuffing risks requires accurate contact temperature predictions. The work presented in this paper develops a simple and prompt temperature model exploitable within any thermal EHL modeling approach. The model incorporates a multilayer lubricant film representation for the heat equation solution. The developments also include an original heat repartition factor expression and a simple formula for handling intermediate values of the Peclet number. The rolling/sliding conditions in the inlet cause temperature rises that also affect the film resistance in the contact zone; this study proposes an inlet temperature rise equation. This formula offers temperature predictions in agreement with reference values. The contact zone temperature predictions for the line of contact problem under sliding/rolling conditions agree remarkably well with published numerical results; for the evaluations presenting the higher absolute difference, the correspondence remained over 94% and 95% for the maximum and mean temperatures, respectively. Both line and elliptical contact conditions were tested and compared to experimental data available in the literature. The analysis evidenced the precision of the estimates; thus attesting to the accuracy of the model under any contact conditions. Finally, the results indicate that, depending on the pressure and speed combination, the shearing zone may occupy around 30% of the film thickness.

Two Cases of Rapid Contact on a Coupled Thermoelastic Half-Space: Sliding Ellipsoidal Die, Rolling Sphere

In one case, a rigid ellipsoidal die translates over the surface of a coupled thermoelastic half-space under compression, and because of sliding friction, shear. In the other, a rigid sphere rolls on the surface under a compressive force. Both motions occur along a straight path at constant sub-critical speed. A dynamic steady state is treated, i.e., the contact zone and its traction remain constant in the frame of the die or sphere. Robust asymptotic expressions in analytic form for contact zone traction, temperature and geometry are derived. Axial symmetry is not required in the solution process. Instead Cartesian coordinate formulations are used, but a system of quasi-polar coordinates is introduced that allow problem reduction to integral equations similar in form to those found in 2D contact.

Temperature and energy partition in minimum quantity lubrication-MQL grinding process

An investigation is reported of the temperature and energy partition in grinding with minimum quantity lubrication (MQL) technique. Temperature distributions were determined in the subsurface of a hardened 100Cr6 steel workpieces through measuring by means of an embedded thermocouple during grinding in dry, MQL and fluid environments. The experiments were carried out with Al2O3 and CBN wheels. The energy partition to the workpiece was estimated using temperature matching. It is shown that the energy partition, and consequently the contact zone temperature, depends on the type of abrasives and coolant–lubricant conditions. For MQL grinding with Al2O3 abrasive wheels, the energy partition varies in the range 73%–77%. However, the energy partition is about of 82% for dry grinding. In fluid grinding with Al2O3 wheels, cooling by the fluid at the contact zone reduces the energy partition to less than 36%. For dry and MQL grinding with CBN superabrasive wheels, the energy partition is respectively about 52% and 46% due to the high thermal conductivity of the CBN abrasive. However, this can be reduced to 14% for grinding with CBN wheel and cooling by the fluid.

Research on Workpiece Surface Temperature and Surface Quality in High-Speed Cylindrical Grinding and its Inspiration

The temperature in cylindrical grinding contact zone is difficult for measurement. Relative to the fixed workpiece in surface grinding, the workpiece rotation in cylindrical grinding brings challenges to the temperature measurement. In grinding titanium alloy, more heat will be generated, and due to the poor thermal conductivity of this material, it is easy to make the high temperature rise in the grinding zone. The high surface temperature and its distribution along the depth of the workpiece have great impacts on the grinding burn, metamorphic layer and residual stress. In order to improve the surface quality of machined parts, based on the undeformed chip thickness, this paper proposed a quadratic curve heat flux distribution model to predict the surface temperature distribution in the grinding of titanium alloy (TC4). Experimental results showed that the quadratic curve model under the condition of the measured grinding power, can predict the temperature distribution in the cylindrical grinding zone. Meanwhile, it specifically discussed the impact of the wheel speed on the TC4 surface roughness and the stress distribution, and found the "high-speed" definition in high-speed grinding should be distinguished from the traditional way only judged by the wheel speed, different workpiece materials should be with different "speed" ranges for acquisition of better machining quality.

The Grinding Temperature of Alumina Ceramic in High Speed Deep Grinding (HSDG)

The grinding temperature in wheel-workpiece contact zone in HSDG of alumina ceramic was measured using the grindable K type thermocouple. Effects of the grinding conditions, including wheel velocity, feed rate and depth of cut, on the temperature were investigated. The results indicate that the grinding temperatures measured under different grinding conditions varied from 100 to 300 °C. The grinding zone temperature exhibits a reasonably linear relationship with the average energy flux, i.e. the higher the energy flux, the higher the corresponding grinding zone temperature will be.

Temperature in contact zone during shot hardening

Shot hardening is simulated by the single impact of a rigid spherical particle on a flat steel surface (an elastic halfspace). The corresponding results of thermophysical analysis are presented. Formulas are derived for the temperature at any point in the impact zone and the time for the shot to reach a minimal depth in hardening.

Thermal finite element analysis of high efficiency deep surface grinding

The study of grinding contact zone temperature and temperature distribution in the workpiece during high efficiency deep surface grinding (HEDSG) is important for the quality of the product and wheel wear. As a consequence of the high temperatures present in HEDSG, not only wheel wear increases, but large residual stresses may also develop in the workpiece resulting in surface cracks. Even microstructural changes occur if the temperature is sufficiently large. The present work aims to develop a two-dimensional (2D) thermal finite element method (FEM) model for the simulation of temperature in the contact zone as well as in the whole workpiece during HEDSG. The present model has been used for the calculation of temperature distribution in the workpiece during a deep grinding scenario and the results compared with the available results in literature. The effect of temperature dependent thermal properties and heat flux profile on temperature distribution in the workpiece has also been investigated. Parametric studies were carried out to study the effect of different input parameters such as depth of cut, work feed rate, material of grinding wheel and type of cutting fluid on temperature distribution, in the contact zone and in the workpiece.

Field Equations and Surface Convection with Thermal Relaxation: Illustration for Rapid Sliding Contact

A rigid cylinder slides without friction at constant speed on a thermoelastic half-space. Surface convection occurs, and both it and half-space exhibit thermal relaxation. An analytical solution valid near the contact zone center and for high sub-critical speeds is obtained. Its form resembles that for a half-space with surface friction but no convection. Calculations show that contact zone temperature is sensitive to sliding speed, the relaxation model for the half-space and a dimensionless convection layer constant. In particular, a half-space with one relaxation time predicts decreases in temperature; a double-relaxation time model can give increases as well.

Thermal Model's Building and Experimental Research in Grinding Contact Zone for Plunge Grinding Process

During the process of plunge grinding, a test piece can be axially grooved with thermocouple embedded, thermo-electromotive force will be conducted through collecting ring and then after A/D converting, data will be digitally acquired and online test will be realized. Based on the thermal theories, this paper presents a simple model to calculate the workpiece’s contact zone temperature during plunge grinding process. This model can be used to predict and calculate the grinding temperature easily. An empirical formula calculating the temperature of the grinding contact surface had been obtained through multivariate linear regression analysis experiments. The thermometric system showed in this paper had solved the knotty problem that the grinding temperature was very difficult to measure for plunge grinding. Compared with traditional method, the testing method adopted by the author will give more accurate result and more closely represent the test piece situation. The results of the computer simulation and the experiments proved the exactitude of the thermal model and the feasibility of the thermometric system.

Rolling without Slip on a Transversely Isotropic Thermoelastic Half-space

Rolling without slip by a rigid cylinder on a transversely isotropic, coupled thermoelastic half-space at constant subcritical speed is studied. The cylinder is of infinite length, surface heat convection is neglected, and a dynamic steady state of plane strain is treated. The unmixed problem of traction applied to a translating surface strip is addressed first. A robust asymptotic form of the exact transform solution, valid when Fourier heat conduction dominates any thermal relaxation effect, is extracted, and inverted analytically. Use of material characterization and identification of parameters that vanish in the isotropic limit or are invariant under an isothermal–thermoelastic transformation result in compact full-field solutions. These expressions are used to construct analytical solutions that satisfy the mixed boundary value problem and auxiliary conditions of rolling contact. For the hexagonal material zinc, calculations are made for contact zone width and temperature increases near onset of zone yield.

Rapid sliding indentation with friction on a transversely isotropic thermoelastic half-space

A rigid insulated die slides at a constant sub-critical speed on a transversely isotropic half-space in the presence of friction. In a two-dimensional analysis of the dynamic steady-state, the coupled equations of thermoelasticity are invoked. All elements of the Coulomb friction model are strictly enforced, thus giving rise to auxiliary conditions, including two unilateral constraints. Robust asymptotic forms of an exact solution to a related problem with unmixed boundary conditions lead to analytical solutions for the sliding indentation problem. The solution expressions, abetted by calculations for zinc, show the role of frictional heating on the half-space surface. The effects of friction and sliding speed on contact zone size and location and average contact zone temperature are also studied. The analysis is aided by factoring procedures that simplify the complicated forms that arise in anisotropic elasticity. A scheme that renders expressions for roots of certain irrational functions analytic to within a single quadrature also plays a role.

Workpiece Burn and Its Prediction in Creep Feed Grinding — Experimental Research of the Temperature Variance Process in Contact Zone

Summary On the basis of improving the experimental technique, the authors have obtained a set of experimental curves by developing uniquely designed experiments. The temperature distribution and its variance characteristics in contact zone during entire creep feed grinding process can be fully explored. According to the newly discovered experimental results, it was confirmed that the heating state of continuously renewed grinding surface during film boiling of coolant in creep feed grinding is quite different from that of boiler tubes. There exists a gradually developing process from low surface temperature in normal condition to burning temperature in contact zone during creep feed grinding. Therefore the prediction of workpiece burn can be realized. At the end of this paper, a scheme is proposed for in process prediction of workpiece burn during creep feed grinding used in production.

An Evaluation of Starting-Load Capacity and Static Friction in Babbitt-Lined, Hydrodynamic Journal Bearings

A recent application called for starting 127-mm (5-in) diameter, babbitt-lined hydrodynamic journal bearings under unit loads of about 10.34 MPa (1500 psi). In this application, the load was imposed only a few seconds before rotation could be started and hydrostatic jacking was not permitted. This paper presents the results of a test effort in which one full-size bearing was subjected to several hundred starts under unit loads ranging from 3.4 to 15.5 MPa (500 to 2250 psi). The dwell time between load application and start of rotation was varied in the test from less than one second to more than one hour. The paper also provides a review of the relevant literature, as well as calculations of the contact zone temperature during starts under boundary lubrication conditions. Presented as an American Society of Lubrication Engineers paper at the ASLE/ASME Lubrication Conference in New Orleans, Louisiana, October 5–7, 1981

The Relation Between Pressure and Temperature in Rolling-Sliding EHD Contact

A surface pressure/temperature transducer has been used to measure contact zone pressure and temperature distribution between a pair of steel disks. In addition, traction/slip curves have been generated for the same conditions. Data for oils representing a broad range of lubricant types are presented. They are (1) Synthetic paraffinic lubricant (2) Traction fluid (synthetic hydrocarbon) (3) Polyphenyl ether (4) MIL-L-23699 lubricant. The experimental conditions include two loads (0.7 and 1.1 GPa), one speed (220 inls; 5.6 m/s), and a range of slip conditions from 0–23 percent. Very large peak temperatures, up to 200°C above ambient, were observed during the experiments. The highest peak temperatures were observed for rolling-sliding conditions with the traction fluid, but even for pure rolling conditions, temperature rises of 30°C were measured. Presented at the 34th Annual Meeting in St. Louis, Missouri, April 30–May 3, 1979

A Method for Measuring Surface Temperature Between Rolling/Sliding Steel Cylinders

A special bisignal transducer has been developed which allows pressure and temperature measurements to be made (essentially) simultaneously. With this technique, it is possible to locate the contact zone temperature relative to pressure and evaluate the relationship between heat generation and pressure. Temperature and pressure data obtained using a synthetic mineral oil as the lubricant have been obtained for rolling and rolling-sliding contact in a disk apparatus. The temperature rise through the contact zone has been shown to be on the order of 20–40 C.

Elastohydrodynamic Lubrication of Involute Gears

A criterion is suggested for the application of the steady state elastohydrodynamic theories to the analysis of involute gear contacts. The criterion is based on a comparison of two physical time scales characterizing the system. It is found that for heavily loaded gears the unsteadiness effect may be important. A mean-viscosity method using a composite pressure-viscosity model for the lubricant is introduced for contact zone temperature calculation. An example of involute gears is given for the computation of elastohydrodynamic contact variables based on quasi-steady state assumption. It is found that the surface temperature rise in the tooth tip contact is much higher than that in the pitch line contact.