Cell-container and cell-lid for electric-accumulators particularly for those meant for traction

The cell-container, obtained by blow-forming, thus having a minor thickness, presents at the upper-rim a conformation in two steps (1) permitting the mating of the cell-lid to the cell-container remaining within unified overall-dimensions, as the welding-bead between the cell-lid and the cell-container forms itself on the inside instead of on the outside of the same. Furthermore, it becomes possible to increase the welding-surface according to one's need if the cell-container is cut in correspondence with the flat-part of the step. The cell-container presents, furthermore, horizontal-recessings at various levels permitting the modular-cutting of the product according to unified measures. The cell-lid's form is concave towards the exterior in order to follow the dilatations of the poles during the service-life of the battery. The cell-lid is also furnished with a molded ring, which has a circular profile around the electrolyte's inlet thus avoiding the application of a gasket onto the top-cover.

BACKGROUND AND SUMMARY OF THE INVENTION 
The present invention regards some improvements in construction of 
cell-containers for accumulators, especialy for those meant for 
construction. 
The above-mentioned improvements regard the construction-form of the 
accumulator's cell-container and of its lid and the way the cell-lid is 
welded to the cell-container itself. 
It is well-known that the overall-dimensions of accumulator's 
cell-containers have been standardized according to international 
specifications. This doubtlessly positive and necessary fact forces the 
constructors of accumulators to adopt construction solutions which, while 
keeping overall-dimensions in parity, enable an increase of useful volume 
of the electrolyte's flooding capacity, thus obtaining an increased 
energetic-capacity of the accumulator itself. 
Another problem of equal importance is to obtain perfect seal-tightness in 
welding the cell-lid to the cell-container. Furthermore, during the 
service-life, the cell-lid tends to crack due to the inevitable elongation 
of the positive pole caused by the well-known phenomenons of 
electrochemical nature; the connected problem is thus to obtain that both, 
the cell-lid and the cell-container, stand the above-mentioned elongation 
without damage. 
Constructors of industrial accumulators faced these problems and solved 
them in different ways. Regarding the overall-dimensions of 
cell-containers, for example, the usual technique provides 
parallelopiped-formed cell-containers obtained by molding in polypropylene 
or similar thermoplastic-materials. The standard thickness usually 
obtainable by this proceeding is of approx. 3 mm. 
To avoid exceeding the standard overall-dimensions, the cell-lid is joined 
to the cell-container by butt-welding, founding the contacting parts of 
the lid to the rim of the cell-container. However, as the above-mentioned 
welding generates a perimetric-bead, it is actually necessary to trim the 
same in order to be able to place one accumulator along the other without 
losing any space (like, for example, in batteries of accumulators for 
traction). This trimming-operation, aside from the cost of the operation 
in itself, can lead to uncovering of points lacking material caused by, 
for example, imprisoned air-locks or, anyway, by bad welding; 
consequently, there exists a possibility of electrolyte-leaks or, still of 
the impossibility of automatically topping-up through the pneumatic 
top-cover. 
The improvements object of the present invention solve all the problems 
related to the trimming of the bead, as the bead forms itself on the 
inside and not on the outside of the cell-container. This was made 
possible by two factors and precisely by (1) the particular conformation 
of the cell-lid and of the cell-container's rim provided with a 
male-female mating remaining with the standard overall-dimensions and (2) 
by the extremely reduced thickness of the cell-container's walls and that 
of the cell-lid's rim, reduced to more than a half in comparison to the 
generally used ones. 
It is obvious that, if there were no reduction of thickness, the said 
solution of the cell-lid having an external rim in respect to the walls of 
the cell-container, would lead to an increase of the overall-dimensions of 
the battery. Furthermore, the construction-method of the cell-container 
itself should be kept present, as it is generally made by 
injection-molding, usually in polypropylene, whereby in the present 
invention it is obtained by blow-forming. This process of blowing the form 
of the cell-container permits to obtain extremely reduced thickness of its 
walls, arriving up to 60% in comparison to the thermoplastic-molding 
process; it enables forms with undercuts otherwise not obtainable or 
prohibitedly expensive, due to the extremely complex molds needed in such 
a case. 
The above-mentioned blow-forming process permits the reduction of thickness 
of the cell-container's walls, as well as considerable savings of 
material. Another advantage is represented by the fact that the molds 
involved are very simple and made in easily-workable materials. 
Another element of basic importance deriving from the present invention is 
that it is possible to increase the welding-surface between the cell-lid 
and the cell-container, independently from the thickness. This is due to 
the special forming of the head of the terminal part of the cell-container 
obtained directly by the form of the blowing-mold. Not the least advantage 
of the present invention is, further, to have foreseen 
perimetric-horizontal recessings, obtained directly in forming and placed 
at various standardized levels so that by one and only blowing it becomes 
possible to obtain cell-containers with modular-systems, of various 
heights, depending on necessity. In this case the advantage for the 
constructor lies in the possibility to reduce the number of forming-molds, 
obtaining from one mold several cell-containers of different height and 
capacity; the constructor of industrial-batteries, on his part, can reduce 
his store, still having the possibility to assemble batteries of different 
capacities. Another function of said horizontal recessings is to avoid 
possible deformations of the cell-container, either in its terminal part 
where it is matched and welded to the cell-lid or in its central part, 
particularly in case of considerably high cell-containers. Said recessings 
have still another, not secondary, function of guiding and locking the 
iner cells of the battery. 
The last improvement, part of the present invention, regards the cell-lid 
of the accumulator, made in such a way to stand, without damage, the 
elongation of the poles. The known technique in this field regards 
performances using a plastic-type binder fitted-in between the cell-lid 
and the cell-container, this type permitting a certain elongation of the 
poles. Said solution is mostly used in accumulators for cars, but it 
doesn't solve the problem for industrial accumulators, especially those 
meant for traction, where the height of the cells may arrive to 650 mm and 
where the said elongations are consequently increased. Another known 
solution consists in having created, within the cell-lid and in the area 
around each of the poles a series of concentric-rings which, due to their 
form and construction, permit some elongation of the poles. 
The improvement regarding the cell-lid in the present invention solves the 
problem of deformation of the same and, thus, of its ability to stand the 
elongation of the poles, as said cell-lid is constructed in a special, 
externally concave form. By this extremely simple solution, which is at 
the same time extremely functional and economical, the elastic-tensions 
developed by the elongation of the poles are evenly distributed on the 
whole of the cell-lid's surface instead of being concentrated on a reduced 
area as it is generally the case. In this way the possibility of the 
cell-lid's cracking under the pressure of the differently distributed 
tensions is nullified or, in any case, drastically reduced. Another 
interesting characteristics of not secondary importance presented by this 
solution is that, due to its special convex-form, the cell-lid holds 
possible leaks of electrolyte caused by overflowing of the central 
top-cover when recharging distilled water. Thus the process of removal and 
cleaning-up of the overflown liquid, in case such a thing happens, is 
simplified and the chance that the liquid might run-down between the 
accumulators and settle at the bottom of the accumulator's box which, 
although usually constructed in plastified-iron, could be, at least in 
some weak-points, effected by the action of electrolyte, is avoided. 
Another characteristics of the present improvement is that the cell-lid is 
furnished with a ring molded around the inlet of the electrolyte, thus 
avoiding eventual leaks when recharging the battery while the top-cover is 
removed. In this way the application of a gasket on the top-cover becomes 
unnecessary, as said barrier, circular and deformable, acts as a 
sealing-element.

DETAILED DESCRIPTION OF THE INVENTION 
In reference to the improvements regarding the cell-container and in 
respect to FIG. 3, the plastic-material, usually polypropylene, is blown 
into a parallelepiped-form, as shown in FIG. 1 and in its terminal-part 
its conformation is "in steps", as shown in 1, thickness being "S". When 
the excess of material is removed, along the line A--A, the width of the 
cell-container's rim, represented in 2 on FIG. 5, will exceed the 
thickness "S" and it will depend exclusively on the depth one has foreseen 
for the mold. The surface 2 represents the area to be welded onto the 
cell-lid 3 of the FIG. 2. It is obvious that the bead will form itself in 
the area 4 and 5, along the perimeter of the rim between the 
cell-container and the cell-lid, not touching its exterior. 
The cell-lid's thickness finds its place in the re-entering space obtained 
in the step 6, thus there will be no projections on the unified shape of 
the battery. The welding-solution of increased-surface here described, 
assures in any case a major-security welding, whereby an already 
sufficient grade of security for welding the cell-lid to the 
cell-container is given by the solution evidenced in FIG. 4. It shows the 
welding between the cell-lid and the cell-container, when the 
cell-container from FIG. 1 is cut, for example, along the line 7, in order 
to obtain a lower battery, starting from the manufactured article itself. 
It is cut along one of the recessings, corresponding to a standard-height. 
In this case, as there is no double-step, it is possible to use the 
welding-surface of the cell-container's thickness, the surface in question 
being already sufficient in itself to assure a perfect seal, also because 
the bead, which forms itself and isn't removed, contributes to the 
increase of the surface of contact between the cell-lid and the 
cell-container. FIG. 5 shows a partial-section of the cell-container's 
terminal-part. In it, the recessing 8 is made in order to create a 
reinforcing-bead close to the terminal-part of the cell-container. This 
reinforcement avoids possible deformation at the top of the 
cell-container, due to tensions developed during the blowing-process which 
tend to be released after the cutting along the line A--A. FIG. 6 shows, 
in section, the described effect of what could happen without the 
reinforcement through recessings 8. Furthermore, if we indicate by SP in 
FIG. 6 the minimum possible thickness of the various containers obtained 
by the molding-process (generally running from 3.75 to 3 mm), one can 
immediately see how the blowing-process, the overall-dimensions remaining 
none-the-less within the thickness SP of the molding-process, permits a 
considerable increase of inner-volume, thus an increased quantity of 
electrolyte in the battery, while the inner and external 
overall-dimensions remain the same. The areas 9 and 10 represent, in fact, 
this increased space in comparison to that of the molding-process. It is 
well-known that increasing the quantity of electrolyte in parity of the 
overall-dimensions results in increased energetic-capacity of the battery 
with obvious advantages. FIG. 7 shows the form taken by a section of the 
battery at approx. half of its height and in very high batteries, without 
the reinforcement by perimetric-recessings 11, 12, 13, and 14 of FIG. 1. 
As already mentioned, these reinforcements are made corresponding in height 
to standardized measures, in order to be able to cut the cell-containers 
in modulars at desired height and thus obtain batteries of different 
capacities, in case this is required. Said perimetric-recessings act as 
well as guides at inserting of the inner-cells of the battery and locking 
them in place. 
Regarding the cell-lid of the accumulator, FIG. 9 shows the section (15) of 
the cell-lid with a concave-profile, which by lowering proceeds, in a 
nearly uniform manner, from the rims of the cell-lid to the central-area, 
where the poles and the central charge-inlet of the electrolyte and the 
topping-up are placed. The cell-lid's profile is obviously connected with 
the bush of the poles 16 and 17 of the FIG. 9 and with the outline-shape 
of the electrolyte's inlet 18. The section C--C on FIG. 12 shows, that the 
profile of the cell-lid is concave in both senses--longitudinal and 
transversal. The surface thus formed will be, therefore, elastic and able 
to stand the pressure produced by the dilatation of the positive pole, or 
poles, permitting the concave cell-lid to rise to a certain extent and, 
depending on the entity of dilatation, it will tend to flatten or even 
assume a convex-form. It is already well-known technique in this field, 
that the lead-bushes 16 and 17 are flooded into the plastics of the 
cell-lid by hot-molding. The cell-lid is then autogenously welded to the 
cell-container of the accumulator on the whole surface of its rim, 
assuring that way a perfect seal. 
The poles, inserted previously into the bush-holes, are then welded to the 
bushes, after the autogenous welding of the cell-lid to the cell-container 
has been done. This way a rigid lock between the cell-lid of the 
accumulator and the poles is assured, but--at the same time--as already 
mentioned, nonwithstanding the rigid connection, the elongation of the 
pole has been made possible due to the cell-lid's conformation permitting 
its deformation, while contemporaneously assuring a rigid joint between 
the pole and the bush flooded in the pole itself. 
On the cell-lid, object of the present invention, a ring, circular in form 
with a special section and concentrical at the inlet of the electrolyte 9 
FIG. 10, was made directly in the molding-process. This ring, projected in 
respect to the inlet's surface, has two functions: first, to prevent, 
acting as a barrier, eventual leaks of overflown electrolyte at 
recharging. This especially important, as such leaks may create channels 
of electric-discharge between the positive and negative pole of the 
accumulator; second, and as important, to act in place of a gasket, as 
said ring, circular and deformable, provides for a perfect seal when the 
top-cover is put in place. 
FIGS. 10 and 11 are shown two solutions of the profile for this 
containing-ring, both as solving the same function. In FIG. 10 the detail 
19 evidently shows the section of the circular ring projected in respect 
to the surface of the electrolyte's inlet 18. Said projection permits to 
avoid overflowing of the electrolyte at recharge. Furthermore, due to the 
minor thickness of the ring 19, it deforms under pressure of the top-cover 
locking the inlet 18, which, when locked, centers onto the conical-part 
21, assuring a perfect seal, as required. This avoids providing the 
top-cover with a gasket and is, therefore, in addition to the 
above-mentioned advantages, also particularly economical. FIG. 11 shows, 
in evidence, an equivalent solution with the ring 22, its profile 
converging towards the center of the inlet 18.