Experimental determination of the friction forces in the deformation zone at roller forming of large-diameter pipes

In roller molding of blanks for large diameter pipes all the work of deformation is realized by friction forces that transmit the drive power to the strip across the surface of the contact interaction with the rolls. In a typical process of forming the specificity of the contact boundary is the contact between clean polished surface of tempered roll with a roller surface of the workpiece coated with a layer of mill scale. Almost no data are available in the literature on the coefficients of friction in such conditions. Since the active forces of friction determine the resource of expansion process capability without slipping of rolls relative to strip, reliable data on the frictional forces are required for calculation of technological regimes and evaluation of loads on the elements of transmission. The paper presents experimental data on determination of the coefficient of friction obtained under conditions as close as possible to the conditions of forming pipe billets on a triple roll bending machine. Experimental technique and the description of the laboratory setup with the necessary means of measurement are described. The impact of major technological factors on the coefficient of friction is estimated.