New cooling system with hollow mandrel in cold pilgering

In cold pilgering, tube lubrication is critical to obtaining a high surface quality of the finished tube, long tool life, and high productivity, and addressing environmental concerns. To enhance lubrication, a new cooling system for the working tool was studied. The thermal balance between the heat generated and that removed during working was investigated, which is important for cooling the mandrel. The cooling system with a hollow mandrel and a coolant for the inner surface, which should have mechanical integrity and good cooling performance, is presented. The inner dimensions of the hollow mandrel were determined on the basis of mechanics of materials to prevent fissures on its inner surface. A fully developed turbulent flow in the inner coolant can remove the heat from the mandrel. The design procedure for the cooling system is described, including the determination of parameters, mechanical calculation, the calculation of heat transfer, and the determination of optimal designs. The mechanical integrity of the hollow mandrel was investigated by the finite element analysis of stress. The heat generated was calculated on the basis of the plastic deformation theory and the kinetics of cold pilgering, and heat transfer was calculated on the basis of the thermal conduction of the mandrel as well as the thermal convection of the inner coolant. The design results for a type 304 stainless steel tube indicated the feasibility of cold pilgering at mandrel temperatures below 100 °C. These findings indicate that the cooling system can be installed inside the tube for cold pilgering.