Experimental investigation of friction phenomena on the roll–material contact surface

A conceptual framework for investigations performed is a thesis on relationship of unit friction forces (tangential stresses) on the tool and metal contact surface with the relative velocity and material displacement, normal stresses stress field and the magnitude of yield stress. According to a premises assumed point measurements (taken at a small contact area) provide an inference basis. This is an objective of tangential and normal unit force measurements taken with point contact sensors. They can be classified into two systems. In the first one, the measurement of a component of metal thrust against a needle face, parallel to the sensor centre line, is taken; and a second one is based on measurements of two components, i.e., the tangential and normal to the needle face. The first system requires the measurement to be taken at two different points of the bite region of the work rolls. Conforming to the assumption of the point measurement a transducer type suitable for taking measurements of both tangential and normal to the needle face force has been employed. The sensors were housed in the work roller with a 198 mm diameter. As a test material, aluminium and lead strips were used. Samples were rolled applying various drafts. Among results obtained confirmed occurrence of the friction coefficient hold (local minimum of the absolute value) in the delay zone and of the curve asymmetry with respect to the neutral point deserves the particular mention. Unit force curves provide an evidence for the asymmetry in specimen material flow conditions. Thus, one can admit that the local minimums occurring in the unit pressure courses, revealed in numerous investigations, reflect a real regularity but not a measurement error.