Friction In Cold Rolling Research Articles

Contribution of viscous shear to friction in cold rolling of low-carbon steel

This work shows that for temperatures, pressures and shear rates that are common in cold rolling of low-carbon steel, viscous shear stress significantly contributes to the total friction force. Experiments were carried out to validate the theory on lubricant film formation and elasto-hydrodynamic lubrication, both with laboratory scale tribometers and a semi-industrial pilot mill facility. These experiments showed that at high shear rates, that are common in cold rolling, the lubricant does not behave as a Newtonian fluid anymore; moreover the viscosity at high pressure cannot accurately be described by a simple exponential law. With the correct relations implemented in a rolling model, both rolling force and forward slip are predicted with good accuracy for hydrodynamically lubricated cold rolling experiments.

Friction and Forward Slip in High-Speed Cold Rolling Process of Aluminum Alloys

Effects of process parameters on friction in cold strip rolling process have been studied in this article. The prime objective is to examine the major parameters affecting the metal working process. A varying coefficient of friction through the roll contact arc has been determined. A few formulae, commonly used to predict the coefficient of friction from forward slip measurements of a rolling process, have been evaluated according to forward slip measurements and coefficient of friction data. Essentially, this article bridges the industrial constant coefficient friction approach from forward slip measurements with the academic varying coefficient of friction strategy. A systems analysis has been made regarding the effects of potentially important parameters on friction in cold rolling. Based on this analysis, the effects of a few parameters have been identified of most importance.

A multi-scale model for friction in cold rolling of aluminium alloy

A simple and robust friction model is proposed for cold metal rolling in the mixed lubrication regime, based on physical phenomena across two length scales. At the primary roughness scale, the evolution of asperity contact area is associated with the asperity flattening process and hydrodynamic entrainment between the roll and strip surfaces. The friction coefficient on the asperity contacts is related to a theoretical oil film thickness and secondary-scale roll surface roughness. The boundary friction coefficient at the “true” asperity contacts is associated with tribo-chemical reactions between fresh metal, metal oxide, boundary additives, the tool and any transfer layer on the tool. The asperity friction model is verified by strip drawing simulations under thin film lubrication conditions with a polished tool, taking the fitting parameter of the boundary lubrication friction factor on the true contact areas equal to 0.1. Predicted values of average friction coefficient, using a boundary friction factor in the range 0.07–0.1, are in good agreement with measurements from laboratory and industrial rolling mill trials.

Friction in cold rolling of a low carbon steel with lubricants

Six commercial lubricants are tested during cold rolling of low carbon steel strips. The objectives are to test the ability of the oils to lower the loads on the mill; to determine the dependence of the coefficient of friction on the model used in inverse calculations and to establish the lubrication regimes during the rolling process. The roll separating forces, roll torques and the forward slip are monitored. The reduction and the speed of rolling are taken to be the independent variables. While the viscosities of the oils vary over a fairly large range, their effects on the roll forces, torques and the forward slip are not very pronounced. The oil, which caused the largest reduction of the loads on the mill is a synthetic one with no additives. The coefficients of friction are determined by two mathematical models. While both models show that the coefficients decrease with increasing speeds and reductions, their magnitudes are strongly dependent on the models. It is recommended that when the inverse technique is used to establish the friction coefficients, all three measured parameters: the force, torque and the forward slip be matched by the predicted ones. In all instances boundary or mixed lubrication regimes are in existence. The hydrodynamic region is approached but not reached.

The effect of lubricant additives on the coefficient of friction in cold rolling

Abstract The effect of four boundary additives—lauryl alcohol, stearyl alcohol, lauric acid and stearic acid—in mineral seal oil, on the roll separating forces, roll torques and the coefficient of friction was investigated. The independent variables were the rolling speed, reduction and the concentration of the additives. Lauryl alcohol was the most effective in reducing the roll separating force while stearyl alcohol caused the largest reduction of the roll torque. The coefficient of friction, obtained by the use of Hill's empirical relation, was the lowest when lauryl alcohol was used.

Influence of Rolling Speed Upon Friction in Cold Rolling of Foils

A theoretical model for simulation of the cold rolling process is presented. A characteristic part comprises the coupling of the bulk plastic deformation and the local plastic deformation of the strip due to impression of roll surface asperities into the work material. The lubricant, which in this case is a liquid, is modeled as a Newtonian fluid. The shear stresses at the roll/strip interface will he a function of the real area of contact, the shear stresses from boundary lubrication and internal shearing in the lubricant film. Simulations have been carried out for rolling with different speeds. The result is a diagram that can be interpreted as a Stribeck curve for cold rolling. The mean friction coefficient in the roll bite decreases with increasing speed to a minimum value i.e., mixed film lubrication prevails. For higher speeds the friction coefficient increases (hydrodynamic lubrication). The influence of roll surface roughness, thickness reductions, and viscosities of lubricant upon the Stribeck curve is also studied. It is concluded that the model can be used to find optimal combination of process parameters for the cold rolling process.

The effects of the reduction, speed and lubricant viscosity on friction in cold rolling

The effects of the reduction, roll speed, lubricant type and viscosity on the roll separating forces, forward slip and resulting specimen surface roughness during the cold rolling of aluminium are investigated. Increasing speed and/or viscosity are found to lower the forward slip and the coefficient of friction. The roll separating force is reduced when lubricants are used. Increased reduction results in increased forward slip. The surface roughness of the rolled strip tends toward that of the roll. The dominant mechanism affecting these changes appears to be the entrapment of the lubricant in the contact zone. The most significant attribute of a lubricant appears to be its viscosity. Both natural and synthetic lubricants affect the rolling parameters to approximately the same extent. The results should aid industry in decision making concerning the choice of natural or synthetic lubricants.

Friction in cold rolling : C. T. van Rooyen and W. A. Backofen. Iron and Steel Institute, journal, v. 186, June 1957, P. 235–244

Friction in cold rolling : C. T. van Rooyen and W. A. Backofen. Iron and Steel Institute, journal, v. 186, June 1957, P. 235–244