ABSTRACT

Applications of Lead 435

grid. The electrode porosity also makes allowance for the increase in volume that occurs when Pb02 is converted to PbS04 • Figures 4a and 4b show a schematic cross section of lead-acid positive plate in the presence and absence of conducting additive, and the redistribution of lead dioxide during cycling that leads to its eventual breakdown [357]. The paste is more readily applied to an open-grid support, rather than to a lead sheet. The use of grids require lead alloys with superior mechanical properties. Grid design takes into account a number of parameters such as weight, corrosion resistance, strength. and current distribution. Grids are designed to ensure a low internal resistance for the cell and to minimize shedding of active material on cycling. There are four different processing techniques that have been used in the production of grids: (I) gravity or pressure die casting using book molds, (2) mechanical working of lead strips (Plante and Manchester design), (3) continuous casting on a shaped drum surface, and (4) expansion from wrought strip or cast slabs, slit to width, followed by progressive die expansion, precision expansion, rotary expansion, and diagonal slit expansion. Some of these processing aspects were discussed in Chapter 3.