Accuracy of determining the physical friction coefficient at cold rolling by methods of strip forced braking and torque moment

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The paper presents a comparative study of the accuracy of d mining the physical friction coefficient during cold rolling by the methods of forced strip braking f Q and torque f М , proposed by I.M. Pavlov and D. Bland together with G. Ford. The compared methods have a sufficient theoretical basis, which contributed to their widespread use. They are based on experimental measurement of the braking force of the rear end of the strip Q, the resultant of normal rolling forces N and torque M. It is shown that, because of the approximate determination of position of the point of resultant rolling force application on the contact arc, the friction coefficient values are always overstated when determined by the method of forced strip braking. The method of torque moment is devoid of this shortcoming. It provides more accurate and reliable data on the value of the physical friction coefficient at cold rolling and allows us to recommend it as the main method for the experimental determination of this parameter. A comparative experimental study of the physical friction coefficient was performed during cold rolling using technological lubrication under laboratory conditions. It is established that, other things being equal, the values of the friction coefficient found by the method of forced strip braking are 1.25 – 1.40 times higher than by the torque method, thereby confirming the validity of theoretical conclusions. It is shown that the torque method is more accurate than the method of strip forced braking and is one of the most reliable methods for determining the physical coefficient of friction during cold rolling.