Note: Descriptions are shown in the official language in which they were submitted.
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Background of the Invention
For many years it has been pop~lar to add antimony
to lead alloy which is eventually cast to produce battery
grids. These grids essentially consist of a lattice of
thin lead structs which are textured on their surfaces
to subsequently engage and hold lead oxide pastes which
are applied thereto. In the past, it has been known that
approximately 3% antimony in a lead alloy is suitable to
increase the strength of that alloy and to provide certain
other characteristics which are desirable in battery grids.
One of the disadvantages of utilizing such a percentage of
antimony is that the antimony itself is an impurity with
respect to the chemical reactions which take place in the
battery, and therefore, the antimony content of the lead
grids is respohsible for numerous chemical or electro-
chemical side effects which are undesirable.
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In particular "high" percentages ti.e. about 3 wt-%)
of antimony in lead alloys used to cast hattery grids are be-
lieved to directly effect the amount of "gassing" which is ex-
perienced when a battery is subjected to overcharge conditions.
Once a battery which has been discharged is charged to approach
a "full charge" condition there will be a tendency for water
in the sulfuric acid solution to disassociate through elec-
trolysis into hydrogen (H2~) and oxygen (`2~) gas. This elec-
trolysis is belie~ed to be catalyzed directly in proportion to ~ -
the amount of antimony, i.e. the percentage of antimony, which
is contained in the grid alloy material.
Recently, attention has been directed by the battery
industry to reducing the tendency of a battery to "gas" during
overcharge conditions so that water need not be added to that
battery during the normal operating life thereof. These bat-
teries are now commonly referred to by the battery industry as
"maintenance free" batteries.
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Since the above described phenomena relating to anti-
mony and its effects on "gassing'l is well documented in the
~! 20 prior art, one common approach of the battery industry to re-
duce the '!gassing" of a battery is the reduction or elimination
of antimony from the battery grid alloy. For example, it has
long been known that alloys with antimony contents in the range
of 2.25 - 2.75 wt~% will reduce gassing while retaining other
properties which produce suitable battery grids, particularly
in lead alloys with other amounts of standard battery grid ma-
terials such as tin (0.25 - 0.50 wt-~), arsenic (0.01 - 0.5
wt-%), copper (0.01 - 0.08 wt-%), and sulfur (0.003 - 0.01
wt-%3, (the remainder being lead). These alloys are ~enerally
known as "low-antimony" grid alloys and have experienced
limited success in the battery industry.
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One of the problems which is encountered in casting
with a relatively lower antimony battery grid alloys is
that the surface tension of such an a]loy is somewhat
greater than the surface tension normally encountered
with the higher antimony - containing lead alloys. Since
surface tension is an important factor in filling the
molds for relatively thin lattice - like grids, the use
of low-antimony grid alloys, while reducing somewhat the
degree of "gassing" of the battery, brings with it other
difficulties which may adversely affect the manufacturing
cost of the resultant grids and the equality of the end
product produced therefrom.
Summary of the Invention
According to the invention there is provided a method
of treating a ~ow-antimony battery grid lead alloy prior
to casting comprising the steps of: (a) bringing said
alloy into a molten state; and (b) adding between 0.001
to 0.010 wt-~ of phosphorus to said molten alloy.
The present invention provides a novel method for
overcoming many of the problems which have plagued the use
of relatively low-antimony grid alloys. Accordingly, the
method of the present invention improves the castability
and resultant grain structure and resistance to cracking
of grids made from such alloys. According to the preferred
embodiment, a conventional low-antimony lead alloy having
between 2.25% and 2.75% antimony (with minor amounts of
other standard battery grid materials) is pretreated in
the molten condition prior to casting by adding small
amounts of red phosphorus to the molten alloy. This
treating is believed to have the effect of refining
the grain structure of the resultant battery grid, of
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providing better resistance to cracking, and o~ ceducing
the surface tension of the battery grid alloy so that upon
casting the battery grid alloy will more easily fill all
of the interstices o a conventional battery grid mold.
Accordingly, the primary advantage of the present inven-
tion is the provision of a treating method wherein red
phosphorus is utilized to increase the castability of a
low-antimony lead battery grid alloy. Another advantage
of the present invention, at least in the preferred forms,
is the provision of a method of treating a low-antimony
battery grid alloy to refine the grain structure of the
resultant battery grid, and to provide better resistance
to cracking of the resultant battery grid.
Description of the Preferred Embodiments
:
Although specific forms of the invention have been
selected for illustrations and the following description
is drawn in specific terms for the purpose of describing
these forms of the invention, this description is not in-
tended to limit the scope of the invention which is defined
; 20 in the appended claims.
In the preferred embodiment, an amount of phosphorus,
and preferably red phosphorus, is introduced into molten
battery grid alloy, preferably by introducing said phos-
phorus across the surface of said alloy. The amount of
phosphorus preferred is approximately five pounds to a
standard fifty ton kettle of molten battery grid alloy.
While five pounds is preferred, the amount of red phos-
phorus which may be added ranges from between one to ten
pounds per fifty ton kettle. Higher amounts may be in-
troduced into the alloy to obtain the above describedeffects, but are not necessary or preferred due to
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possible interference with other battery grid character-
istics, and particularly those produced by the minor
amounts of other standard battery grid materials present
in such alloys such as tin, arsenic, copper and sulfur.
Somewhat more than ten pounds
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per fifty ten kettle may, therefore, be utilized provided the
amount of red phosphorus introduced is sufEicient to produce
superior castability (i.e lower surface tension), better grain
refinement or a greater resistance to cracking of the final
battery grid, without adversely affecting the aforementioned
characteristics imparted by other grid alloy additives. In
any event, it is believed that at the time of addition the
amount of red phosphorus added should preferably represent
0.001% to 0.010% by weight of the alloy to which said phos-
phorus is added, and more preferably the amount of phosphorusto be added is approximately 0.005 wt-% of said alloy. In the
event standard battery processes are not conducted which have
the effect of mixing said phosphorus into said alloy, auxiliary
mixing should be employed to agitate the molten alloy to ensure
complete dispersion of the phosphorus through the alloy. Cast-
ing of the battery grids is then conducted utilizing convention-
al molding or castinq equipment~ which need not be modlfled to
handle this relatively low-antimony alloy. Grids are produced
with refined grain structures and superior resistance to
cracking.
While the amounts indicated above represent the a-
mount of phosphorus added to the molten battery grid alloy, it
is not presently known whether or not any of the phosphorus
actually remains in and is incorporated in the lead alloy, or
whether the red phosphorus acts only as a catalytic or cleaning
agent which is not incorporated in the final alloy structure.
In any event, due to the small percentages of phosphorus util-
ized in the method of the present invention, and the difficulty
- of determining the existance of such amounts of phosphorus
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in the final elld product, it is not anticipated by the
present invention that any measurable amount of phos-
phorus need be obtained in the final battery grid,
provided the method of the present invention has been
followed to treat the alloy prior to the casting of said
battery grids.
It will be understood that various changes in the
details, materials and arrangement of parts which have
been herein described and illustrated in order to explain
the nature of this invention may be made by those skilled
in the art within the principle and scope of the invention
as expressed in the following claims.
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