Stock material or miscellaneous articles – All metal or with adjacent metals – Having aperture or cut
Reexamination Certificate
2002-02-21
2004-09-28
Zimmerman, John J. (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Having aperture or cut
C148S400000, C148S706000, C029S006100, C429S226000
Reexamination Certificate
active
06797403
ABSTRACT:
BACKGROUND OF THE INVENTION
(i) Field of the Invention
This invention relates to the continuous production of lead alloy strip and, more particularly, relates to the continuous high-speed extrusion of lead alloy strip for use as positive and negative electrodes of a lead-acid battery. The strip has a highly controlled microstructure which increases battery life by reducing the rate of vertical growth in the positive plate and reduces the rate of corrosion when compared with plates produced by other continuous processes. By reducing growth in the positive plate and by minimizing and forming a desired strip profile (e.g. by varying or tapering thickness from top to bottom of the strip) for the positive and negative alloy strip, the mass of both the positive and negative plates can be reduced, thereby reducing the overall weight and cost of batteries.
(ii) Description of the Related Art
In the production of lead-acid batteries there are several methods to produce the positive and negative grids used in the battery. In the continuous production of grids for lead-acid batteries these processes are limited to the production of either a rolled or cast strip which is punched or expanded by either reciprocating or rotary expansion processes or to the direct casting of grids, such as by the Concast™ process.
The production of lead alloy strip for use as positive battery plates having limited plate growth is extremely important because plate growth can cause cell short circuits.
This is a leading factor in shortening battery life in batteries made by continuous processes. The strip produced by conventional method such as rolling or continuous casting typically have a highly heterogenous microstructure with non-uniform grain sizes and shapes leading to undesirable plate growth and to corrosive attack from the battery electrolyte.
The production of strip for negative plates also is commonly done by either continuous cast or rolling processes. The negative electrode is not subjected to corrosive attack due to the electrochemical characteristics of the electrode, and therefore the main focus of the negative strip is reducing the weight of the negative plate, while maintaining adequate conductivity. This is done by simply making the strip thinner; however if the lug is too thin there are problems in battery manufacturing, related to melting of lugs into the top lead.
The extrusion of lead and lead alloys to provide a protective sheath on submersible cables to protect the cables from the corrosive effects of seawater, by means of extruding machines, has been done extensively in the past in the cable industry. Electrical cable is passed through the machine and a layer of lead alloy tube is extruded onto the cable. H. F. Sandelin is a world leader in the production of this type of machine. Other manufacturers include Pirelli, which produced a machine which is similar to the older Henley Extruder™ in utilizing a large horizontal screw. This type of apparatus has problems with alloy segregation and contamination of the screw.
U.S. Pat. No. 4,332,629 describes the production of lead-antimony alloy strip by ram-press extrusion. This process is limited to certain thicknesses and aspect ratios. Also, the process has limitations on production speed, this patent disclosing production rates of 6-10 ft/min. (1.9-3.2 kg/min.). Strip produced by ram press extrusion has had negative results regarding corrosion and grid growth in laboratory testing. Also this process does not provide control of microstructure and grain size and is limited to alloy selection.
SUMMARY OF THE INVENTION
The objective of the present invention is to provide an extrusion method and apparatus that can economically produce superior extruded lead alloy strip of a desired profile for the production of positive and negative battery plates that are resistant to both vertical grid growth and weight loss through corrosion in lead-acid batteries. The strip is produced at a speed that is competitive with continuous cast and rolled strip, the extruded strip having superior qualities in any of the following areas; corrosion induced growth, corrosion weight loss, shape, grid weight, cost, and automation compared to conventional technologies.
The preferred use of the invention is in the production of lead-alloy strip to be coiled for use in a continuous battery manufacturing line. This strip can be used to produce battery mesh by continuous reciprocating expansion of the strip into expanded mesh or by continuous rotary expansion of the strip into expanded mesh, such as disclosed in U.S. Pat. No. 4,315,356 issued Feb. 16, 1982, U.S. Pat. No. 4,291,443 issued Sep. 29, 1981, U.S. Pat. No. 4,297,866 issued Nov. 3, 1981, U.S. Pat. No. 5,462,109 issued Oct. 31, 1995, and U.S. Pat. No. 5,896,635 issued Apr. 27, 1999 to Cominco Ltd., incorporated herein by reference. The expanded mesh is then pasted and divided into individual battery plates that can be placed in a battery.
The minimum and maximum grain sizes of the extruded strip will vary with the thickness of the strip but can be controlled by means of rapid cooling with water spray after the strip exits the extruder die. The microstructure of extruded alloy strip is homogenous, stable and can be easily controlled through machine parameter adjustments. With the correct choice of alloy and grain size, the vertical growth of positive grids in the lead-acid battery, made with extruded strip, can be greatly reduced. When compared with the current continuous processes for strip production, the growth of the positive grid is reduced by 50-75% in common laboratory testing. Weight loss caused by corrosion of the grid is similar to that of grids produced from continuously cast strip, and is less than that of rolled strip or bookmold grids. In extrusion, the strip can have different grid thicknesses over the width of the strip by control of the strip profile. This allows plates to be made with very thin wires, while still having a lug thickness sufficient to overcome manufacturing problems associated with thinner lugs. This leads to a significant weight savings in the negative plate and reduces the overall weight and cost of the battery. It has been found that by modifying the die block to allow for strip production rather than tube production, planar high-quality lead alloy strip can be produced of a desired profile. By introducing a novel strip cooling system, which preferably is a water spray system outside of the extruder dieblock, the strip can be optimized in alloy composition, grain size and thickness for fabrication of battery plates for use in lead-acid batteries.
The main advantage of the extrusion strip production method is the absolute control over the grain size and grain structure of the material. This allows for the optimization of these parameters for reducing corrosion, limiting corrosion induced growth, increasing strength, and manipulation of the aging process of the alloy.
Specifically, there are eight areas for optimizing strip and the resultant grids in a battery.
1. Grain Size: Extrusion offers the possibility of controlling the actual grain size of the final product over a wide range, from 20 microns to 500 microns. It should be noted that the minimum grain size will be further influenced by strip thickness and strip alloy composition. While it is possible to produce grain sizes anywhere in this range by modifying the cooling distance from the dieblock exit or the cooling rate, it should be noted that for battery performance it is preferred that the grain size for positive electrodes be in the range of 100-500 microns, most preferably in the range 100-300 microns. This is because at very small grain sizes of less than 100 microns, e.g. 20-100 microns, the grain boundary path for corrosive attack is almost straight through the material along the boundaries of very many grains. At very large grain sizes of greater than 100 microns, the path is also quite straight along the path of only one or two grains. Negative electrodes, however, are not subjected to corrosive attack and small grain s
Clark Douglas G.
Gustavsson Kenneth Henning Runo
Russell Derek William
Vincze Albert M.
Fors Arne I.
Teck Cominco Metals Ltd.
Zimmerman John J.
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