Technology of preparation of sleeve ends before pilgrims rolling

Abstract

The paper considers the issues of improvement of hot pilgrim rolling of pipes by means of preparation of front and rear ends of sleeves. The presence of a gap between the sleeve and mandrel increases transverse variance and reduces pipe accuracy during pilgrim rolling. In the present article the issues of preparation of the front and rear ends of the sleeves to ensure the alignment of the sleeve and mandrel in the process of Pilgrim rolling are comprehensively considered. The preparation of the front ends of the sleeves is proposed to be carried out on a slant-rolling piercing mill by idle rollers of the swaging device located on the output side of the piercing mill. In the work a new technology of preparation of front ends of sleeves providing their reduction by idle rollers without compression along the thickness of the sleeve wall is proposed. The concept of a running-in device characterised by lower metal intensity and, accordingly, capital expenditures is proposed. By means of the sliding line method the forces acting on the idle rollers during reduction of the front ends of the sleeves are determined. The questions of preparation of back ends of sleeves before pilgrim rolling of pipes are considered. The back end of the sleeve after piercing has reduced outer and inner diameters, which makes it difficult to charge the mandrel into the sleeve, increasing the gap between them, which adversely affects the deformation of metal by rolls during pilgrim rolling, increasing the differentiality of pipes. To facilitate loading of the mandrel into the sleeve, the piercing technology is used with the mandrel moving in the direction opposite to the sleeve movement when the rear end of the workpiece approaches the rolls. As a result, it is possible to provide thinning of the sleeve wall in the direction towards its rear end with an increase in the internal diameter at the rear end, which facilitates the conditions of mandrel loading into the sleeve. Thinning of the wall of the rear end of the sleeve due to the convergence of the rolls of the piercing mill can reduce the volume and mass of the separated pilgrim head. To facilitate the loading of the mandrel into the sleeve with the prepared front end at the out-of-station charging section of the piercing mill, the calibration of the front end of the mandrel with a cylindrical shape is proposed, while ensuring the minimum tension between the front end of the sleeve and the mandrel for centring between them. The proposed technology of centring the rear end of the sleeve on the mandrel, which provides for the presence of a conical belt adjacent to the head of the mandrel. The parameters of the conical belt of the mandrel are determined taking into account the gap between the mandrel and the sleeve with its constant value along the length of the sleeve. Charging of the mandrel with a new calibration of the front end and a conical belt adjacent to the head with the help of a hydraulic cylinder of the priming press at the section of off-stage charging ensures centring of the front and rear ends of the sleeve on the mandrel.