Failure of lead-antimony alloy sheathing for tele-communication cables during extrusion - a case-study

Abstract

Alloy 'B' (PB--0.85 Sb) is one of the standard alloys used in telecommunication cable sheathing on account of its excellent mechanical properties. However, during extrusion this alloy is prone to develop cracks/defects if the parameters are not closely controlled. This paper deals with the metallurgical investigation carried out on some typical defects in alloy 'B' sheaths, that had developed during extrustion. Metallographic examination has revealed that the oxide inclusions in the ingot had acted as nucleation sites for the development of cracks during extrusion. Moreover, cracking had also been caused by the (i)prevalence of high temperature gradient in the die-block, and (ii) ineffective cooling of the dieto inadequacy in the control of extrusion parameters. Measures to overcome the problem by reducing the oxide inclusion during melting and for the control of the above extrusion parameters have been suggested