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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 a subsequent conversion of the lead peroxide to "spongy” lead, which constitutes the active material for these plates. Finally, the plates are subjected to a special treatment to remove any impurities. An advantage of the spinning process is that the ribs are not cut and subsequently bent, as in some of the other methods of producing Planté plates. It is said that bending, because of the crystalline properties of lead, opens up pores for the penetration of electrolytic action, and that such ribs may be eventually cut off by the chemical action after the battery has been in use
for a time. It is also stated that cast lead is not equal to the rolled or spun lead for battery plates on account of its porosity. The parts of a typical Gould cell used for train-lighting service and the method of grouping two of these cells in trays to make for easy handling is clearly shown at Fig. 11.
Manufacture of Faure Type Plates.—Most of the lead plate type storage batteries now used have “pasted” plates instead of the more expensive formed plates. The foundation of a Faure type plate consists of a skeleton or plate grid, such as shown in Figs. 13 and 14, made from an alloy of antimony and lead, to which the active material is mechanically applied. The original Faure cell had both the positive and negative plates coated with red lead. But a comparatively short time was required to change the red lead to lead peroxide on the anode or to metallic lead on the cathode. The great advantage of this construction was the high capacity for unit weight. There is a disadvantage, and that is that if the plates are not very carefully made the active material may drop away from the grid pockets and fall to the bottom of the cell. These have been largely overcome at the present time by forming the grids to hold the applied material more firmly. The reason that pure lead is not used to make grids is that it does not have enough rigidity or strength for use when the active material is applied by mechanical means. The soft lead grids might be bent, which would tend to loosen the active material. This is true to a certain degree of Planté plates, but inasmuch as the active material is generally formed on small surfaces separate from each other, and as it is much thinner than in the applied types, there is not so much danger of the material fall
In order to increase the strength of the lead grid it is necessary to add some substance that will make a stiffer skeleton, but of course this material should not change the electrical characteristics of the grid to any extent. Antimony is the material ordinarily added, and the proportions of the resulting alloy may vary from 88% lead and 12% of this metal to 98% lead and but 2% of antimony. It is stated that the usual mixture is 1% antimony and 96% lead. Positive grids should have more lead in their composition than the grids intended to be made into negative plates. While in many cases the active material is applied to the plates by hand, it is advanced that machine-pasted plates make more enduring batteries.
Combination Planté and Faure Types.-The "Chloride” battery, which was manufactured for a time by the Electric Storage Battery Company, is a compromise between the two types. In this cell the positive plate is a Planté type, and the negative follows the Faure principle of construction. Finely divided lead is produced by blowing a stream of air against a stream of molten