Tank formation

Tank formation means that the cured positive and negative raw plates are inserted alternately in special tanks filled with fairly dilute sulfuric acid (generally in the range 1.1 to 1.15gem ) and positive and negative plates are connected, a number of each, in parallel with a rectifier. The formation process means that the active material of the plates is electrochemically transformed into the final stage, namely  

Because of the porous material in the raw plate, both substances are produced in a spongy state with a porosity of about 50 vol%. Tank formation takes between 8 and 48 h, depending on the plate thickness and formation schedule. When the formation process is finished, the plates are washed and dried. They can be stored and later assembled in batteries. 

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The fundamental difference from tank formation is that the battery is assembled first, then filled with electrolyte, and finally the formation process is carried out with the complete battery. 

As explained in Chapter 11, it is unlikely that enemy tank formations wilt venture into built-up areas it is niore probable that infantry will be called upon to capture a town. 

The potential distribution of a state-of-the-art plate with a near-centre lug is shown in Fig. 12.7. This position of the lug became possible when manufacturing was changed from tank formation of individual electrodes, which did not allow for that lug position for handling reasons, to container formation with the whole battery being formed after complete assembly. 

Batteries intended to be used within 2 or 3 months after manufacture are produced with lead—ealeium—tin alloys, filled with electrolyte and ready for use. In this case, the technological scheme in Fig. 2.52 is modified. The tank formation and plate drying steps are eliminated and plate curing is followed by battery assembly, the formation process being completed in the battery itself. 

Figure 9.1 presents the technological steps involved in the two types of formation processes tank formation and container (jar) formation. 

Tank formation is usually conducted in H2SO4 solutions with concentrations between 1.05 and 1.08 rel. dens., most often 1.06 rel. dens. What is the criterion for selecting the appropriate acid concentration ... 

For VRLA batteries tank formation is preferred to jar formation (Fig. 9.4). The latter formation process should not be used for tall VRLA batteries, for battery applications requiring long... 

After flooding the cured plates with H2SO4 solution in the battery container (for jar formation) or immersing the plates into the tank filled with H2SO4 solution (for tank formation), reactions proceed between H2SO4 and the cured paste as a result of which new solid phases are formed at both plate surfaces. 

In the tank formation method, the heat capacity of the tank is great and the concentration of the H2SO4 solution is low (1.06 rel. dens.), so a small quantity of paste is sulfated and less heat is generated (and at a lower rate) during the formation process. Hence, the temperature reaches a maximum after the PbO and basic lead sulfates in the surface paste layers have reacted with most of the H2SO4 solution. 

In tank formation, the tank full of electrolyte has great heat capacity, so substantial amount of heat has to be generated for the temperature in the tank to rise (Fig. 12.1). This is not the case with container formation, however. There is a small volume of electrolyte in the battery and hence the latter s heat capacity is small. The heat capacity of a system is the measure of the heat energy required to increase the temperature of the system by 1 °C. The heat capacity of 1 g of mass is called specific heat. The electrolyte has the highest specific heat as compared to the specific heats of the other battery components. During soaking, the temperature in the battery increases rapidly... 

Chen et al. [7] propose an algorithm for tank formation of batteries including many steps of current increase and decrease. This algorithm (presented in Fig. 12.8) is assessed as optimum, in terms of energy consumption and battery performance, but the formation process is rather too long. 

Multi-step current profile for tank formation [7]. 

Once the plates have been cured, they need to be electrically formed or charged before they become functional positive and negative electrodes. During formation, the positive paste is converted to brownish black lead dioxide the negative paste is converted to a soft gray lead. The cured plates can be formed before (tank formation) or after assembly (case formation) into the battery case. 

In tank formation the cured plates are formed as doubles, with two to five plates stacked together in a slotted plastic formation tank and facing the counter-electrode in adjacent slots that are spaced 1 in. or less away. In addition, all positive plates are placed on the same side and aU negative plates are placed on the other side. All plates with the same polarity are connected to a low-voltage, constant-current power supply. The formation tank is fiUed with electrolyte with electric current passed until the plates are formed. 

During formation, both the pore radii and the porosity of the active mass increase. The formation can be carried out either through tank formation (prior battery assembly) or case formation (after battery assembly). 

The more usual method of formation is to completely assemble the battery, fill it with electrolyte, and then apply the formation charge. This method is used for SLI and most stationary and traction batteries. A variety of formation conditions are used, similar to those for tank formation. The two major formation processes are the two-shot formation process (used for stationary and traction batteries) and the one-shot formation process (used for most SLI batteries). In the two-shot formation, the electrolyte is dumped to remove the low-density initial electrolyte and refilled with more concentrated electrolyte, chosen so that when this is mixed with the dilute initial acid residue which is absorbed in the elements or trapped in the case, the cell electrolyte will equilibrate at the desired density (Table 23.11). Typical values of the electrolyte specific gravity at full charge after formation are given in Table 23.12. 

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