GB2076583A - Electric Storage Batteries - Google Patents

Abstract

A battery is economically produced by blanking a thermoplastics sheet to produce a cover 13 of a size to close the open top of a thermoplastics battery box 11 housing a pack 12 of positive and negative battery plates with positive and negative terminals posts 10 projecting from the open top of the box 11. Apertures 14 and 15 are produced in the cover for receiving the terminal posts 10 and for allowing introduction of electrolyte into, and the escape of gases from, the finished battery. The cover 13 is welded onto the open top of the box 11 using a heater 16. <IMAGE>

Description

SPECIFICATION Electric Storage Batteries This invention relates to electric storage batteries and particularly, but not exclusively, single cell lead-acid batteries used for vehicle traction.

It is well known to use a thermoplastics material, such as polypropylene, for the box and lid of an electric storage battery, particularly a lead-acid battery. In the finished battery, the box and lid are normally secured together by contact butt welding. Since a lead-acid battery box must have sufficient depth to accommodate the battery plates and separators, it is conveniently produced by a moulding operation. To date, however, a moulding operation has also been employed to produce the thermoplastics lid, even in the case of a single. cell traction battery where the lid construction is relatively simple and no provision for intercell sealing is required.The use of moulding to produce battery lids not only leads to significant cost penalties, particularly in view of the high capital cost of moulding tools, but also means that the battery manufacturer is required to stock a variety of lid sizes to cater for the range of batteries he manufactures.

An object of the present invention is therefore to overcome or alleviate the above mentioned disadvantages by providing a simplified method of manufacturing electric storage batteries and particularly, but not exclusively, single cell leadacid batteries.

Accordingly, the invention resides in a method of manufacturing an electric storage battery comprising the steps of: (a) starting with an open-topped, thermoplastics battery box housing a plurality of electrochemically active elements, with positive and negative terminal posts being connected to respective sets of said elements and projecting from the open top of the box, (b) blanking a sheet of therrnoplastics material to produce a cover of dimensions sufficient to close the open top of the box, (c) producing apertures in the cover for receiving the terminal posts and for allowing introduction of electrolyte into, and the escape of gases from, the finished battery, and (d) welding the cover onto the open top of the box.

In the method described in the preceding paragraph, a strip of thermoplastics material blanked to the required shape and size is used in place of the moulded lid used in the prior art. The strip of theremoplastics material is conveniently a generally planar strip which can be produced simply and inexpensively without the use of costly moulding tools, while the use of a blanking operation to produce the size and shape of cover required avoids the necessity for the battery manufacturer to stock a large number of lid shapes.

Preferably, the strip of thermoplastics material is in the form of a generally planar, extruded sheet.

Conveniently, the cover is blanked from a continuous roll of the thermoplastics material.

Preferably, step (c) is effected simultaneously with the blanking step (b).

Conveniently, the blanked cover produced in step (b) is subjected to a vacuum forming operation to recess the cover. Conveniently, the vacuum forming operation is effected prior to said apertures being produced in the cover by step (c).

Preferably the welding step (d) is effected by placing a heater in physical contact with the top peripheral edge of the box to effect localised melting thereof, placing a heater in physical contact with a region of the cover which is to engage the top peripheral edge of the box to effect localised melting of said region, and pressing the cover onto the box.

Alternatively, the welding step (d) is effected by friction welding.

Preferably, the battery is a single cell battery and the battery box is free of internal partitions.

In the accompanying drawings, which illustrate one example of the invention; Figure 1 is a plan view of a cover produced by blanking a strip of thermoplastics material, Figure 2 is a plan view of a battery box, Figure 3 is a sectional view which illustrates welding of the cover shown in Figure 1 to the box shown in Figure 2, and Figure 4 is a sectional view of the assembled battery.

Referring to the drawings, in the example shown it is required to produce a single cell leadacid battery of the type normally used for traction purposes. To produce the battery, an open-topped battery box 11 is injection moulded in a thermoplastics material, preferably polypropylene, so as to have a generally rectangular configuration without internal partition walls. A pack 12 of positive and negative battery plates having insulating separators interposed therebetween is then assembled into the box 11.

The pack 12 also includes positive and negative terminal posts 10 (only one shown) which are connected to the positive and negative battery plates respectively and which project from the open end of the box 11.

To seal the box 1 1, a flat cover 13 is produced by blanking a strip of thermoplastics material, preferably extruded polypropylene, to the same rectangular dimensions as the open end of the box 1 The thermoplastics strip is at least 0.06 inch thick, preferably 0.1 inch thick, and is conveniently stored in the form of a roll.

Alternatively, the strip may be stored as flat sheets or as extrusions of various shapes (for example, an extrusion with a pair of parallel, upstanding walls on one surface such that the walls define therebetween a manifold in the finished lid). The blanking operation is arranged to produce a central aperture 14 and two outer apertures 15 and, after blanking, a cover 13 is welded to the open top of the box 11 using the heater shown diagrammatically at 16 in Figure 3.

The heater 16 includes a first, generally planar heating element 17 against which the free end surface of the box 11 is pressed for a sufficient time to cause localised melting of said end surface. The element 17 is provided with apertures (not shown) for receiving the projecting ends of the terminal posts 10 respectively. At its opposite surface, the heater includes a second heating element 18 which is in the form of a generally rectangular upstanding wall having sides of length substantially equal to those of the cover 1 3 and a thickness greater than the wall thickness of the box 11. One major surface of the cover 13 is pressed against the heating element 18 to produce localised melting of a peripheral region of said surface, the inside edge of the element 18 preferably being undercut to avoid melting of the remainder of said surface.When melting is complete, the box 11 and cover 13 are moved out of engagement with the heater 1 6 and are pressed together to weld the cover 13 to the box 1 The apertures 15 are positioned to receive the terminal posts 10 respectively when the cover 13 is correctly located on the box 1 1.

Welding the flat cover 13 to the box 1 1 tends to produce a solidified bead of displaced thermoplastics material around the joint between the box and cover. Such a welding bead not only detracts from the visual appearance of the finished battery but can also lead to problems when it is required to produce an assembly of closely packed batteries. It may therefore be desirable to remove the welding bead from the finished battery or alternatively provide a space between the lid and the box for receiving the bead. Such a space could be provided by chamfering the top peripheral edge of the box to define a triangular section between the box and lid or by shaping the top peripheral edge of the box to define inner and outer walls having a trough therebetween for receiving the welding bead.

In the assembled battery, the aperture 14 permits topping-up of the battery with electrolyte and also allows gases generated in the battery to escape to atmosphere. The aperture 14 is normally closed by a removable ment plug 19 (Figure 4) which is provided with a bleed hole (not shown) through which the required gas venting occurs. Preferably, the aperture 14 is key shaped and a complimentary portion 21 is provided on the region of the vent plug 19 which, in use, is located within the box 11. Thus, by inserting the portion 21 through the aperture 14 and rotating the vent plug through 900, it is possible to locate the vent plug in position relative to the cover 13. Preferably, the arrangement of the vent plug 21 is such that this rotation urges the vent plug into sealing engagement with the upper surface of the cover 13.

During assembly of the battery described above, it is to be appreciated that the sulphuric acid electrolyte of the battery can be introduced into the box 1 1 before or after the cover 13 is welded to the box.

In the battery described above, the flat cover 13 leads to the disadvantage that any electrolyte and/or water which may be deposited on the cover tends to remain in place so resulting in a danger of electrical tracking across the cover. In order to avoid this problem, a separate retaining wall may be welded to the external surface of the cover around the aperture 14. Alternatively, the blanked cover may be subjected to a vacuum forming operation, prior to welding to the lid so as to impart thereto a concave shape (so that any deposited electrolyte and/or water runs into the aperture 14) or a convex shape (so that any deposited electrolyte and/or water runs off the cover 14). In this case, the top of the box would have to be shaped complementarily with the curved lid. In addition, production of the apertures 14, 15 could be effected separately from the blanking step and after the vacuum forming operation.

As a further alternative, the blanked cover may be produced over-size and then subjected to vacuum forming or deep drawing to define a depending skirt such that the cover is recessed. In this case again, the apertures 14, 15 could be produced separately from the blanking step and after the vacuum forming operation. As yet a further alternative, the blanked, flat cover formed with the apertures 14, 15 formed therein could be hot pressed into a recessed shape.

In modification of the above example, the cover 13 is friction welded to the box 1 1 by urging the cover against the box and then subjecting the box and lid to relative vibrational movement.

Claims (15)

Claims

1. A method of manufacturing an electric storage battery comprising the steps of: (a) starting with an open-topped, thermoplastics battery box housing a plurality of electrochemically active elements, with positive and negative terminal posts being connected to respective sets of said elements and projecting from the open top of the box, (b) blanking a sheet of thermoplastics material to produce a cover of dimensions sufficient to close the open top of the box, (c) producing apertures in the cover for receiving the terminal posts and for allowing introduction of electrolyte into, and the escape of gases from, the finished battery, and (d) welding the cover onto the open top of the box.

2. A method as claimed in Claim 1 , wherein the strip of thermoplastics material is in the form of a generally planar, extruded sheet.

3. A method as claimed in Claim 1 or Claim 2, wherein the cover is blanked from a continuous roll of the thermoplastics material.

4. A method as claimed in any preceding claim and including the further step of subjecting the blanked cover produced in step (b) to a shaping operation so as to produce a peripheral skirt extending around the cover and thereby recess the cover.

5. A method as claimed in Claim 4, wherein the shaping operation is a vacuum forming operation.

6. A method as claimed in Claim 4 or Claim 5, wherein recessing of the cover is effected prior to step (c).

7. A method as claimed in any one of Claims 1 to 5, wherein step (c) is effected simulataneously with with the blanking step (b).

8. A method as claimed in any preceding claim and further including the step joining an electrolyte retaining wall to the cover around the aperture provided in the cover for introduction of the electrolyte into the battery.

9. A method as claimed in any preceding claim, wherein the cover welded to the box in step (d) is curved so that, in use, any liquid deposited on the cover runs into the electrolyte introduction aperture or off the edge of the cover, the top of the box being curved complementarily with the cover.

10. A method as claimed in any preceding claim, wherein the welding step (d) is effected by placing a heater in physical contact with the top peripheral edge of the box to effect localised melting thereof, placing a heater in physical contact with a region of the cover which is to engage the top peripheral edge of the box to effect localised melting of said region, and pressing the cover onto the box.

1 A method as claimed in any one of Claims 1 to 9, wherein the welding step (d) is effected by friction welding.

12. A method as claimed in Claim 10 or Claim 1 1, wherein the cover and/or the top peripheral edge of the box are shaped to accommodate any bead of molten material generated during the welding operation so that the bead is not visible at the exterior of the finished battery.

13. A method as claimed in any preceding claim, wherein the battery is a single cell battery and the battery box is free of internal partitions.

14. A method as claimed in Claim 1, of manufacturing an electric storage battery substantially as hereinbefore described with reference to the accompanying drawings.

15. An electric storage battery manufactured by a method as claimed in any preceding claim.