Battery grids casting

FIGURE 7.2 Battery grid casting mold (bookmold). (From Wirtz Manufacturing. Available at http //www.wirtzusa.com.)... 

Wrought lead—calcium—tin alloys contain more tin, have higher mechanical strength, exhibit greater stabiUty, and are more creep resistant than the cast alloys. RoUed lead—calcium—tin alloy strip is used to produce automotive battery grids in a continuous process (13). Table 5 Hsts the mechanical properties of roUed lead—calcium—tin alloys, compared with lead—copper and roUed lead—antimony (6 wt %) alloys. 

Selenium acts as a grain refiner in lead antimony alloys (114,115). The addition of 0.02% Se to a 2.5% antimonial lead alloy yields a sound casting having a fine-grain stmcture. Battery grids produced from this alloy permit the manufacture of low maintenance and maintenance-free lead—acid batteries with an insignificant loss of electrolyte and good performance stability. 

Battery grid metal 92-88. 25 8-12 SOLDERS Cast battery grids. 

Figure 4.1 presents schematically the basic properties of lead alloys which are essential for their applicability for casting battery grids. These alloy characteristics and their influence on battery performance parameters will be discussed in more detail in this chapter. 

Key properties of lead alloys to be used for casting battery grids. 

The use of grids cast from the above multi-component alloys did reduce the need for battery maintenance but did not eliminate it altogether. So the battery industry chose two basic approaches to achieve the goal set by the automobile industry, i.e., to devise maintenance-free... 

The above results indicate clearly that, through the introduction of small amounts of alloying additives (Sn, As, Se, Cu and S) and a simple thermal treatment, grids cast from Pb—1.5 wt% Sb alloy may acquire a hardness level that meets fully the requirements of the battery industry. 

Grain refinement of Pb—2.5 wt% Sb chill cast battery grids by means of Se and S additions. Casting temperature 500 °C, mould temperature 135 °C [34]. 

Besides the requirements for adequate electrical, mechanical and corrosion properties of the grids, the grid pattern should allow easy casting with no defects. The process of double-grid casting provides high productivity and has therefore been widely adopted in the battery industry. 

After such pre-treatment, the connections of the battery poles to the power source terminals are reversed and formation proper starts. Test results for batteries that have been formed employing an algorithm that includes reverse polarization prior to formation are given in Fig. 12.23. The capacity curve is similar to that for batteries with cast grids with rough surfaces. 

As evident from Fig. 4.41 in Chapter 4 of this book, when Pb—Ca—Sn positive grids contain up to 1.8 wt% Sn, no tet-PbO layer forms in the corrosion layer. That is why the positive grids for all types of maintenance-free valve-regulated lead—acid batteries are cast from lead alloys with 0.05—0.07 wt% Ca and 1.5—1.7 wt% Sn content. 

Figure 9 0 Components of a lead acid battery, (a) Cast lead alloy grid, (b) separator, (c) positive electrode, (d) negative plate, (e) negative plate group, (f) positive plate group, (g) plate block with separator, and (h) the complete battery. (Reproduced with permission from Ref. [25], 1985, Wiley-VCH.)...

Positive grid corrosion can be caused by the grid alloy, grid casting conditions, and active material composition. Shedding of positive active material can be caused by battery construction, active material structure, battery cycles, DOD, and charge... 

Initially most lead antimony grids were produced from a eutectic alloy of 11% antimony, which has a single freezing point at 273°C, making grid casting relatively simple. Antimony as an alloying elanent was very expensive and battery... 

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