Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Reexamination Certificate
1998-09-16
2001-01-30
Kalafut, Stephen (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
Reexamination Certificate
active
06180286
ABSTRACT:
This invention relates to lead-acid batteries and, more particularly, to grids and plates used in making such batteries and to the method of making such grids and plates.
BACKGROUND OF THE INVENTION
Over the last 15 to 20 years or so, there has been substantial interest in automotive-type, lead-acid batteries which require, once in service, little, or more desirably, no further maintenance throughout the expected life of the battery. This type of battery is usually termed a “low maintenance” or “maintenance-free battery”. The terminology maintenance-free battery will be used herein to include low maintenance batteries as well. This type of battery was first commercially introduced in about 1972 and is currently in widespread use.
A considerable amount of attention over the years has been given to the type of alloys used for manufacturing positive and negative grids in such maintenance-free batteries. When maintenance-free batteries were first commercially introduced, the conventional automotive lead-acid battery normally used grids made from antimony-lead alloys in which the antimony content ranged from about 3-4.5by weight of the alloy composition. Such alloys were capable of being commercially produced at acceptable rates into battery grids by the gravity casting production techniques then widely used. Moreover, the batteries made using grids of such alloy compositions had desirable deep discharge cycling characteristics.
However, such high antimony content lead-based alloys could not be used in grids in maintenance-free batteries. Thus, the use of such high antimony content alloys resulted in the batteries having undesirable higher gassing, higher self-discharge on stand, and higher attendant water loss characteristics. In other words, batteries with grids made from such alloys accepted high end of charge current during constant voltage overcharge so that excessive gas generation occurred. Accompanying this gas generation was loss of water from the battery electrolyte.
The assignee of the present invention and its predecessors in interest have been in the forefront of research relating to alloys and maintenance-free batteries. Among the patents relating to this subject are the following U.S. Pat. Nos. 4,006,035; 4,007,056; 4,166,155 and 4,456,579.
Much commercial interest has centered around the use of calcium-tin-lead alloys for use in making grids for maintenance-free batteries. The calcium content in such alloys for positive grids has varied generally from about 0.06 to about 0.1% by weight of the alloy while the tin has generally ranged from about 0.1 up to 0.8% and even more. More typically, the calcium content in such alloys when used for making maintenance-free battery grids has been at least about 0.08% by weight or more.
Other commercial interest for maintenance-free battery grids has been directed to the use of “low antimony” lead-based alloys, viz., alloys containing antimony contents of about 1 to about 2.5%, more typically about 1.5% or so. Use of such low antimony alloys generally required the need to add other alloying ingredients since such low antimony alloys were not capable of being made into grids at acceptable rates under normal production conditions.
Other approaches for grid alloys in maintenance-free batteries have included the use of “hybrid” alloy systems. Most typically, a low antimony, lead-based alloy is used as the alloy for the positive grids while an antimony-free alloy is employed for the negative grids. Often, the alloy of choice for the negative grids has been a calcium-tin-lead alloy or a calcium-aluminum lead alloy.
It has been well recognized over the years that lead-acid batteries are perishable products. Eventually, such batteries in service will fail through one or more of several failure modes. Among these failure modes are failure due to positive grid corrosion and excessive water loss. The thrust of maintenance-free batteries has been to provide a battery that would forestall the failure during service for a period of time considered commensurate with the expected service life of the battery, e.g., three to five years or so.
To achieve this objective, the positive grids used initially for maintenance-free batteries typically had thicknesses of about 60 to about 70 mils or so. The batteries were likewise configured to provide an excess of the electrolyte over that needed to provide the rated capacity of the battery. In that fashion, by filling the electrolyte to a level above that of the top of the battery plates, maintenance-free batteries contained, in effect, a reservoir of electrolyte available to compensate for the water loss, during the service life of the battery. In other words, while the use of appropriate grid alloys will reduce water loss during the service life of the battery, there will always be some water loss in service.
Over the past several years, the manufacture of such automotive lead-acid batteries, typically termed SLI automotive batteries (principally used for the starting, lighting and ignition requirements of an automobile), has become substantially more complex. Battery grids have typically been made by gravity casting (e.g., the molten alloy is fed into what is termed a book mold and is then allowed to solidify, the book mold providing either one or two side-by-side grids). Production equipment using an alternate method to fabricate grids is now commercially available by which battery grids can be continuously formed by expanded metal fabrication techniques. For example, a rolled or wrought alloy strip or a cast strip is slit and expanded using reciprocating dies or the like and then cut into the desired width and height dimensions to form the grid with a lug.
Automobile battery manufacturers thus have available a variety of techniques for forming battery grids in production. However, the effect on performance of the batteries when such techniques are used is not understood all that well. This lack of understanding is particularly evident in view of the factors complicating current SLI battery performance requirements.
One complicating factor in attempting to provide satisfactory service life is the seemingly ever-increasing power and energy requirements demanded in current SLI automotive batteries used in modern automobiles. Many factors have contributed to the need and/or desire for such higher power and energy for such batteries. One major measure of power currently in common usage is the rated number of cold cranking amps. The number of cold cranking amps is considered in the industry as some indication of the relative power of the battery to start an automobile in cold temperature conditions.
Yet another complicating factor is the “under-the-hood” space requirements. Automobile manufacturers have significantly decreased the overall space available for batteries in the engine compartment. Typically, this has required that battery manufacturers provide a lower profile battery, viz., a battery having less overall height than previously required so as to meet current aerodynamic styling needs in automobiles. Such lower profile batteries will have less acid above the plates.
These complicating factors (i.e., a need for increased power and energy with less available space for the battery) have required battery manufacturers to alter the battery internal design configurations to provide the needed power in a lower profile battery container. These internal alterations have typically involved increasing the number of plates used in each cell by employing battery grids with reduced thickness. For example, the number of plates in a BCI Group 24 battery has increased from about 13 to about 19 or so over the last few years while the thickness of the positive grids has decreased from about 65 to 75 mils or so down to about 45 mils and even less in some cases. The reduction in the thickness of the positive grids together with an increase in the number of plates has allowed battery manufacturers to provide Group 24 batteries having rated power output capabilities of 875 cold cranking amps or so. Battery manufacture
Rao Purushothama
Uhlemann Thomas F.
GNB Technologies, Inc.
Kalafut Stephen
Leydig , Voit & Mayer, Ltd.
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