« НазадПродовжити »
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 falling off.
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
metal, which result in the production of a lead spray, which falls as a powder when cooled. Nitric acid is used to dissolve this powder, which precipitates as lead chloride when hydrochloric acid is added. After this material is washed and dried it forms the basis of the filling of the negative plates. A mixture of this lead chloride and zinc chloride is melted in crucibles and poured into moulds, which produce small tablets about 34 of an inch square and of a thickness varying from 14 to 5/16 of an inch, depending upon the thickness of the negative plate. These tablets are then assembled in special moulds and held in place by recesses, into which they fit and which prevent movement. They are kept at a distance of about .2 inch from each other and from the mould edges. Molten antimonious lead is then poured in to fill the spaces between the tablets, and to insure a proper flow of metal it is forced into the mould under approximately 75 pounds pressure. Upon cooling, the result is a solid lead grid, in which the small squares of active material are imbedded. The next step is to reduce the lead chloride by placing the plates in a dilute solution of zinc chloride, each plate being separated from its neighbor by a slab of zinc. By assembling the plates in this manner the equivalent of "short circuiting” a cell is obtained, and the lead chloride is reduced to metallic lead. The zinc chloride is removed from the plates by thoroughly washing them.
A new form of negative plate which is now manufactured to replace the chloride type just described consists of a pocketed grid, the openings of which are filled with litharge paste and afterward covered with perforated lead sheets, which are formed by casting integrally with the grid. The grid used for the positive plate is composed of a 5% antimony-lead alloy and is about 7/16 inch thick, having circular holes about 34 of an inch in diameter, staggered so that the nearest points are about 3/32 of an inch apart. Close spirals are rolled up of corrugated lead ribbon of the same width as the plate thickness, and these are forced into the circular holes of the plate. The spirals are formed into active material by the electro-chemical process, and during this the spirals expand sufficiently so they fit closer to the grid sides. This form of positive is known as the Manchester plate