METHOD AND DEVICE FOR PREVENTING OR REDUCING TRUMPET-SHAPED EXPANSIONS AT THE TUBE END IN THE SLOPED ROLLING OF THIN-WALLED TUBES

摘要

The prevention or reduction of the trumpet like expansion of the pipe end during rolling of thin walled pipes on an Assel mill comprises reducing the degree of radial forming of the blank as the front end of the hollow blank enters into the mill, in comparison to the stationary state of rolling, and/or increasing the resistance torque of the blank cross section at the front end by reduction of the tangential material flow. At least one roll and preferably all rolls (A) are provided quick acting hydraulic closing and opening units which allow the rolls to be set radially against the rolled material (C, D), in a short time interval and also against the rolling force. The maximum closure distance of each movable roll is equal to the corresponding shoulder height or to the maximum wall thickness reduction.