Effect of calcium, tin and silver contents in the positive grids of automotive batteries with respect to the grid manufacturing process

A study has been undertaken in order to compare the properties of grids pro duced by rolling expansion and by gravity casting in some specific test con ditions. In both types of grids, the effects of calcium, tin and silver con tents have been investigated. After bare grid study, a series of electrical tests has been carried out followed by thorough tear down analysis. The me chanical properties of rolled expanded grids have been found to be improved by an increase of tin content from 0.8% to 1.2%, silver and calcium conten t having no significant effect. The resistance to corrosion of bare grids a t equilibrium potential is strongly dependent on the acid density. At low a cid density corresponding to the most severe condition, grid corrosion is L imited by a high tin content (1.2%) and by a low calcium content (0.04%). T here is no effect of silver. In hard conditions of use such as storage and overcharge at high temperature, battery life is increased with a higher tin content for all technologies, and by a smaller extent by the addition of s ilver on gravity casted grids. A high tin content improves the battery rech argeability after a deep discharge. In conclusion, the addition of silver h as only a poor impact on the behaviour of rolled expanded grids. On gravity casted grids, in the same conditions, the addition of silver associated wi th a low calcium content has been found to improve the battery life slightl y. In high temperature conditions of overcharge and storage, the battery Li fe obtained with rolled expanded grids is higher than that with gravity cas t, whatever the alloy. (C) 1999 Elsevier Science S.A. All rights reserved.