Improvements in Plates. for Accumulators or Secondary Batteries.
Year: 1896

page_text: Date of Application, 18th June, 1896-Accepted, 16th Jan., 1897
COMPLETE SPECIFICATION.
Improvements in Plates. for Accumulators or Secondary Batteries.
I, CHARLES POLLAK, of 253, Mainzer Landstrasse, Frankfort-on-the-Main,
in the German Empire, Director of the Accumulatorenwerke System Pollaki
do hereby declare the nature of this invention and in what manner the same is to
be performed, to be particularly described and ascertained in and by the following
statement :-
This invention relates to improvements in plates for accumulators or secondary
batteries.
All known plates for electrical accumulators or secondary batteries as hitherto
made belong to one of three principal classes. which may be shortly distinguished
as follows,
1. Plates in which the porous mass is carried on a core of any suitable shape.
2. Plates in which the porous mass is produced by an electro-chemical process,
for instance, electrolysis.
.
.
3. Plates manufactured directly from porous lead, for instance, lead. dust.
In order to give plates of any one of the above classes the necessary amount of
cohesion and the requisite strength, and in order to cause a sufficient current to
pass to the active mass the said plates are usually provided with a core of good..
conducting material. As, however, the cohesion between the core and porous
mass in plates as hitherto constructed is not very good, the said plates possess
certain disadvantages.
In plates manufactured according to the first of the above classes the active
mass; for instance, crumbles away with time because the cohesion between the said
mass and the core carrying it, is comparatively slight; further the plate is often
warped and bent in consequence of the inequality of the current distribution, and
in some cases lead sulphate is formed between the two parts of the plate.
Plates of the second kind or class require a large expenditure of time and
electrical energy during their preparation particularly in consequence of the
dropping off of the outer layer, when it has reached a thickness of over
occasioned by the unequal coefficients of expansion of the metallic lead and of the
peroxide formed by the action of the current.
In plates of the third kind the same disadvantages mentioned in connection with
plates of the first kind occur to a great extent.
Now, my invention relates to a novel kind of plate which has for object to
remedy the above described disadvantages by effecting such an intimate connection
between the core and the porous layer that the two parts really consist of one
metallic piece. My plates are obtained by simultaneously casting the solid lead
core and the porous layer surrounding it. The solid core and the porous lead
layer form, as they are obtained in one casting, a cohesive whole connected
together in the best and safest manner which can be attained with this material.
The manufacture of these plates, by simultaneously casting the solid core and the
porous layer in one mould, over a finely grained or powdered body forms the
characteristic feature of my invention as distinguished from the methods heretofore
adopted. The peroxide on the positive plates is formed in a thoroughly homogeneous
manner and cannot drop off in consequence of the perfect cohesion of the particles
obtained in casting. The current flows equally over the whole surface of the core
aud porous part and prevents by its uniform distribution any warping or bending.
of the plates..
In carrying out my invention I avail myself of the fact, that certain metals; such

page_text: for instance as lead possess in molten condition the property of cohesion to a great
degree, so that when cast on any finely grained or powdered body, they without
special preparations therefor cannot penetrate into the small spaces between the
particles of such a body.
In order to enable such a metal to completely fill the spaces between the particles
of the powder it is necessary to first remove the air contained in the said spaces
and also to cast the metal under pressure, the pressure being continued until the.
metal solidifies, for the molten metal is otherwise drawn out of the small spaces as
soon as the pressure is removed. I, therefore proceed as follows. Finely divided
common salt or any. similar substance, which can withstand the heat of the molten
metal and can be easily removed by dissolving or in any other suitable way, when
the process of casting is finished, is introduced into a mould. The necessary space
for the solid core is obtained by placing a pattern or core in the mould, the said
pattern being removed before the casting operation is commenced.
The mould is now heated to the melting point of lead, and is then filled with
molten lead, suitable means, such as a runner being employed for keeping the lead
under pressure until it solidifies.
After the plate has been taken from the mould the salt may be removed by
dissolving or otherwise, and the plate formed by means of an electric current.
As it is not always easy to leave a space for the core, the process may be slightly
modified, that is to say, a solid lead cure may be first introduced into the mould,
and then surrounded with the powdered substance. The mould is then warmed and
filled with molten metal which melts the core, whilst a fresh supply of molten
metal poured in fills the space occupied by the core retaining in this way the shape
of the solid lead core originally placed in the mould.. At the same time the molten
metal is pressed, together with the molten portions of the said solid lead core, into
the small pores of the powdered body.
The result of this process is the formation of a plate the core and the porous part
of which consists of a continuous mass of metal.
It will be obvious, that my process of casting porous plates with solid cores in
one single operation may be modified in various ways, for instance, that instead of
lead any other suitable metal may be used, but the principal feature of the invention
will remain unaltered, that is to say, the casting of the porous and solid parts of
the plate simultaneously under pressure until the metal solidifies, together with
means for the production of the solid core of any desired shape.
Experiments made with my improved plates have shewn that the above statements
are correct and that the plates thus obtained possess considerably greater durability
and strength, than those hitherto in use.
These plates possess, weight for weight, much greater capacity than those
heretofore manufactured when the porous portion is finely grained, whilst on the
other hand discharge currents of great strength can be obtained owing to the
cohesion and the large surface of the porous mass which is a considerable
advantage in connection with the employment of accumulators for road cars and
the like.
In the accompanying drawings:
Figures 1, 2, 3 and 4 are sections of different forms of plates made according to
my invention and shewn here as examples.
a is the core and b the porous portion of the plate. In Figure 1 the core is
represented as a plate of uniform strength throughout. In Figure 2 the core is in
the form of lattice work of any desired shape. In Figure 3 the core is provided
with teeth and ribs, and in Figure 4 the plate is formed with the porous part
enclosed in a solid frame.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed, I declare that what I
claim is :-
1. Plates for accumulators or secondary batteries produced by casting together

page_text: a solid core of any desired shape to serve as the current conductor and a porous.
portion serving as the active substance, substantially as described.
2. The improved plates for accumulators or secondary batteries manufactured
by casting simultaneously and under pressure a solid core of any desired shape and.
a porous portion in a suitable mould over a finely grained or powdered body until
the metal solidifies, means being provided for producing the solid core either by
forming a space of the desired shape in the mould with the aid of a removable.
pattern or by placing inside the mould a suitable metal core, which is melted.
and cast together or soldered with the porous portiou by the casting operation,.
substantially as described.
G. F. REDFERN & Co.,
4, South Street, Finsbury, London, Agents for the Applicant..