Plate curing

Laminates are pressed in steam-heated, multiple-opening presses. Each opening may contain a book of as many as ten laminates pressed against pohshed steel plates. Curing conditions are 20—30 min at about 150°C under a pressure of about 6900 kPa (1000 psi). 

After the reactions of paste sulfation start, plates that have been partially carbonated during the paste preparation, and especially during the plate-curing process, release CO2. 

Fig. 9.6 Profile of sound velocity V as a function of position d inside an epoxy plate cured and post-cured in a Silgel cuvette. The left and right sides of the graph correspond to the top and bottom of the horizontal cuvette, respectively.

Fig. 9.10 Sound velocity profiles v(d) for the RT-cured and for the post-cured state of two independently prepared EP plates on polished Cu alloy (open squares and triangles) as well as for an EP plate cured on polished Al alloy at ambient temperature (black squares). The metal is positioned at d = 0 mm.

Plate curing. Pallets with plates are placed in a high humidity chamber and left to cure at 35 °C for 48—72 h. During the curing process, lead in the paste is oxidized, the basic lead sulfates recrystallize and the plates are then dried to moisture content <0.5%. 

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. 

The basic components of the paste are crystal phases of 3BS or 4BS, small amounts of orthorhomb-PbO, tet-PbO and Pb. These are detected by X-ray diffraction methods. If a paste is prepared from crystal phases of 3BS and tet-PbO in the same proportion as in the paste prepared from leady oxide and H2SO4, and then grids are pasted with this paste and set to curing and formation, the obtained PAM is mechanically unstable and difficult to form, and hence the plates have low capacity. Valeriote has found that one of the reasons for the low energetic characteristics of positive plates is the lack of amorphous components in the paste [17]. The content of amorphous phases should amount to 15—10%. Such amorphous components in the paste are most often hydroxides. Some of the amorphous hydroxides are obtained as a result of oxidation of Pb in the leady oxide during paste preparation and plate curing. And the content... 

A sample scheme of the successive technological procedures involved in the process of 3BS paste preparation is presented in Fig. 6.32. An example of a formulation for 3BS paste preparation could be LO (78% PbO) — 500 kg, H2O — 65 L, H2SO4 (1.4 g cm ) — 39 L, fibres — 0.35 kg. For the conversion of the 3BS paste into 4BS during the plate curing procedure, some 6—7 kg of tetrabasic lead sulfate nucleants should also be added to the initial paste mix. 

The process of plate curing has been investigated both for practical purposes, with the aim to improve the performance parameters of battery plates, and for purely fundamental purposes, namely to disclose the mechanism of the elementary processes involved [1—15]. Based on the results of these investigations the essence of the curing process can be summarised as follows. 

The following basic processes take place during plate curing ... 

The plate curing processes are influenced by two types of parameters ... 

External, i.e. characteristics of the surrounding medium air temperature, relative humidity (RH) and air flow rate the processes of plate curing are atmosphere dependent. 

Depending on the temperature of paste preparation and plate curing two types of cured pastes are obtained ... 

During plate curing, the pore distribution in the paste changes due to recrystallization and chemical conversion processes. Figure 8.8 illustrates the pore volume distribution by... 

Amount of residual unoxidized lead as a function of curing time for plates cured at 25 °C and different relative humidity in the curing chamber [14]. 

The rate of lead oxidation is influenced also by the moisture content of the paste prior to curing. The amount of water in the paste pores should be reduced so as to open the pores for access of oxygen from the air needed to oxidize the residual free lead in the paste. The rate of water evaporation from the paste pores depends on the RH in the curing chamber. This dependence is illustrated in Fig. 8.17 for plate curing at 25 °C and various relative humidities [14]. 

Oxidation of lead during plate curing proceeds through two mechanisms a chemical and an electrochemical one with formation of local microelements involving conjugated reactions. 

It can be assumed that breaking of oxygen bonds in the O2 molecule during plate curing proceeds through a similar mechanism, where electrons come from Pb oxidation and lead peroxide forms. 

Corrosion of PbSnCa Grids During Plate Curing and Formation of Corrosion Layer... 

Segregation of Sn and Ca during plate curing and its effect on grid corrosion... 

Figure 8.19 presents micrographs of the surface of a concast grid from 3BS plate cured at 40 °C for 48 h. The oxidized intergrain layer was dissolved using a solution of glucose and NaOH. 

Bonding of 3BS particles to the CL2 layer for plates cured at 40 C for 48 h. (a) and (b) SEM images of the CL macrostructure with bonded particles from the cured paste at different magnifications [16]. 

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