Some aspects on lubrication and roll wear in rolling mills

Abstract: The thesis is focused on lubricants and roll wear in striprolling.Regarding lubricants, the possibility of introducing newones, which are less detrimental towards environment, isstudied in laboratory scale. This is done for cold rolling,both of an Al- alloy and a low carbon steel. The lubricationperformance of such newly developed?water-based?synthetic lubricants is compared with currently used mineraloils and emulsions. By using the experimental method of"forward slip" measurements combined with slab methodcalculations and FE- simulations, friction coefficients areevaluated for different single pass reductions. Lubricantsbearing capacity and the product surface roughness are alsoevaluated. The results are encouraging.A synthetic water-based lubricant, used in the cold rollingof an Al- alloy, showed good lubrication capability, betterthan the mineral oil but worse than the emulsion. The rolledAl- strip finish was found to be finest for the syntheticlubricant followed by the mineral oil and the emulsion. Similarresults were obtained from the steel rolling. Here foursynthetic lubricants were compared with two mineral oils andone emulsion. The best lubricant was found to be one of thewater-based synthetics, showing the lowest value of thefriction coefficient and a smooth product surface.The aim of the wear study is to develop an accurateroll-wear prediction for hot strip finishing mills, which takesmore influential parameters into account. A new model of higheraccuracy is presented. This model is based on a large amount ofproduction campaigns. The strategy of the work is describedbelow.After a comprehensive literature study a promising modelstructure was found. The corresponding equation is tested ontwo hot strip mills. Predicted wear is found to be inqualitative agreement with industrial experience and measuredwear. Thus the structure?taking the influence of back-uprolls into account?was chosen for further development.This was done on behalf of results obtained from one mill builtup by six stands and three different work-roll materials.Campaigns of "mixed" and "similar" strip grades were used. Theobtained model is tested successfully in two other hot stripmills.Contradictory to the currently used on-line model, the newmodel takes the work roll flattening and back-up rolls contactarea into consideration. Also the influence of strip- and workroll grades is included. The model enables increased rolledstrip length and prolonged lifetime of the rolls, because ofimproved process control. Further more, grinding cost and timefor roll changing can be minimized. Of course thesepossibilities should result in considerable energy saving.Keywords:Strip rolling, lubricants, environment, rollwear modeling, production campaigns, regression analysis