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of lead gives an increase in voltage, the normal 2.2 augmenting to 2.5 volts. A reduction-of weight is also possible, because zinc plates can be lighter than lead one of the same capacity.
The disadvantage is the formation of zinc deposits during charging in the shape of clusters or "trees,” which may short-circuit the cell by extending across to the positive element or increase the sediment by dropping to the bottom. Another disadvantage is that the solution will vary in density, at different lieights. The zinc sulphate is taken from the top of the liquid during charging. Attempts have been made to prevent this by placing the plates horizontally and thus having practically the same density electrolyte surrounding each plate. The fault of this arrangement is that gas bubbles polarize the cell by collecting between the plates. In a vertical plate cell the bubbles rise to the top of the electrolyte and burst, liberating the confined gas, which reaches the atmosphere easily in an open-type cell and through a vent in the sealed types.
Another cell has a negative plate consisting of thin sheet copper amalgamized with zinc. The positives are made of lead leaves perforated with numerous small holes and riveted together, and are formed by the Planté process. The copper-alkali-zinc battery of Lalande and Chaperon and improved by Edison is reversible in action and can be used as a storage battery. When discharged, the positive plate is porous copper; on charging, the decomposition of the electrolyte follows, metallic zinc is deposited on the regative plate, while the porous copper becomes oxidized on the positive. The electrolyte becomes potassium hydrate. This cell may really be considered the ancestor of the modern Edison cell. This storage battery has been used commercially in a limited way, but is not really practical because of its low voltage, that of one cell being but seven-tenths of a volt. That means that three times as many cells would be needed to obtain a certain voltage given by the smaller number of lead plate cells. The weight factor is a serious one that militates against the wide commercial use of low voltage cells. The lead plate type has many practical advantages, but its ability to stand rapid discharge, its great efficiency and its high E.M.F. are among the most important ones,
Making Planté Process Plates. It is evident that even with the present low cost of electric current makers of storage batteries employing Planté elements must have a more commercial method of forming these than the repeated charge and discharge processes followed by the originator of this type of plate. It is also apparent that the electro-chemical action would form but a very thin layer of active material on plain lead sheets. In order to have a sufficient volume of it to generate an appreciable current it is necessary to provide a larger surface than prevails on an ordinary sheet of lead. To provide more surface, the usual process is to groove the lead plates in order to provide a sufficiently large area so that the forming process will produce an element of sufficient capacity to be commercially practical. The lead peroxide formed on such plates is positively hel in the spaces between the ribs or laminations designed to increase the surface.
Various systems of increasing the surface of lead sheets to increase the available area are by grooving, swedging, laminating, scoring or casting the pockets or retaining ribs integrally. A typical Planté process plate used in the Gould battery, with sectional views showing the structure if the plate is cut on lines A-B or C-D, is shown at Fig. 9, and the method of forming clearly outlined at Fig. 10. In the manufacture of these plates the "spinning" process is followed, as this is said to give the greatest possible increased surface and least modification in form of rim and groove. The blank plate, including the lug, is stamped from chemically pure rolled lead and placed in a steel frame, which reciprocates between two revolving mandrels, on which thin circular steel discs and spacing washers are placed. It is on the form and thickness of the discs that the width and shape of the grooves depend, and the thickness of the rib is regulated by the width of the spacing washers. The travel of the frame obviously determines the length of the section to be spun.
The pressure of the “spinning” rolls against the surface of the lead blank is maintained at a uniform point by compressed air, and the ridges and grooves begin to appear as soon as the operation is started. At the start the section is as shown at Fig. 10, B-1. As the spinning discs progress further and further into the
lead they displace it and cause it to flow in the form of ribs in the spaces between the cutting discs. The first action is to groove the surface of the lead plate as shown at Fig. 10, B-2, this section becoming more and more like 3 and 4, as the pressure of the disc causes more metal to be displaced. The blank is merely changed in form, as no lead is removed, and there is not cutting and subsequent bending to open up pores in the metal. The discs leave an
Fig. 9.-Gould Storage-Battery Plate Made by Planté Process.
unspun portion at the end of travel of the frame, in which each individual rib terminates, thus forming a main cross bar at each extremity. The two bars unite at the junction of two spun sections in a single cross bar of diamond section, solid metal, extending the width of the plate. By limiting the depth that the rolls penetrate the blank, it is possible to provide a web of metal that remains as a central conductor and current equalizer.
On the surface of plates thus produced a thin layer of lead peroxide, which is the active material of the positive plate, is formed by the electrolytic process. Negative plates are formed by