The extrusion of bimetallic strip from two containers

• Main Author: Whitlock, Bernard Cecil
• Published: Imperial College London 1968
• Subjects: 620.1
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.623162

The possibility of extruding dissimilar metals from two containers through a single die to form a bi-metallic strip has been investigated. Tin was extruded with lead at 20°C and copper was extruded with silver at approximately 750°C. The metals were pressure welded together within the extrusion die and simple bend tests on the extruded strips showed that the strength of the bonds were equal to the strength of the weaker parent metals. Within limits, adjustments to the speeds of the extrusion rams produced corresponding changes in the relative proportions of the component metals in the extruded strip without impairing the strength of the bond. Methods have been developed for predicting the operating conditions beyond which a composite strip cannot be extruded. Certain of these limiting conditions are associated with the state of stress on the bi-metallic interface within the die whilst others are related either to the load capacity of the extrusion tools or to the danger of incipient melting. The techniques of limit analysis were used to find approximate solutions for the extrusion pressures. Slip-line field solutions and a more approximate method of analysis using force polygons were developed to determine the state of stress on the bi-metallic interface within the die. Good agreement was obtained with the experimental results. In any commercial development of the process for metal combinations such as copper and silver a close control over the temperatures of the metals during extrusion will be essential.