The effects of geometrical and process variables on the quality of cast-on-strap joints

An automated laboratory-scale, cast-on-strap joining process for lead/acid batteries has been developed. This allows tight control of relevant casting parameters such as strap mould and metal temperature, lug immersion speed, and the time between strap filling and lug entry into the molten strap. The joining of lead-antimony or lead-tin strap alloys with lead-antimony or lead-calcium-tin lugs is studied. It is found that lead-tin is not suitable as a strap alloy for the alloy combinations and joining conditions that have been investigated. Penetration depth of the lug into the strap is found to be critical and may be optimized for a given lug thickness under fixed process conditions. The joint quality improves with a deeper penetration of the thicker lugs for the geometrical configurations studied in this work. It is far easier to form a sound joint with thin lugs as these are not as sensitive as thick lugs to variations in the joining conditions.