GB2057920A - Producing lead acid electric storage battery electrodes - Google Patents

Abstract

A method of producing electrodes for lead acid storage batteries includes expanding a strip of lead or lead alloy to leave an unexpanded central land 14 and an unexpanded selvedge 12 on each edge of the strip. One or more lozenges of metal are sequentially removed from the land leaving holes 30 and 32 and simultaneously one or more portions of metal are removed from each selvedge leaving projecting portions 38. The strip is then separated into battery electrodes each of which has two or more feet constituted by the projecting portions 38. The invention also embraces an apparatus for carrying out the method. <IMAGE>

Description

SPECIFICATION Lead acid electric storage battery electrodes The present invention relates to electrodes for electric storage batteries and to a method and an apparatus for producing such electrodes.

According to one aspect of the present invention a method of producing electrodes for lead acid storage batteries includes the steps of expanding a strip of lead or lead alloy to leave an unexpanded central land, and an unexpanded selvedge on each edge of the strip, sequentially removing one or more lozenges of metal from the land and simultaneously removing one or more portions of metal from each selvedge to leave spaced portions of the selvedge projecting from the strip and separating the strip into battery electrodes each of which has two or more feet constituted by the spaced portions of the selvedge.

The invention also embraces an apparatus for producing electrodes for lead acid storage batteries including means for expanding a strip of lead to leave an unexpanded central land and an unexpanded selvedge on each edge of the strip, means for sequentially removing one or more lozenges of metal from the land, and means for simultaneously removing one or more portions of metal from each selvedge to leave spaced portions of the selvedge projecting from the strip and means for separating the strip into battery electrodes each of which has two or more feet constituted by two or more portions of the selvedge.

It is known to produce expanded lead acid battery electrodes by expanding a strip of lead or lead alloy leaving a central unexpanded land, removing a plurality of lozenges from the central land leaving a series of holes, spaced apart by transversely extending metallic lug portions, and then cutting up the strip to form a plurality of electrodes, each of which has a plate lug constituted by one of the lug portions. As described in more detail below the cutting mechanism is set to cut the strip at a predetermined spacing, and it is therefore essential that the spacing of the holes formed by removal of the lozenges be precisely predetermined otherwise the finished plates may have an incorrectly positioned plate lug, or even no plate lug at all.

For certain applications such as traction batteries, it is desired to produce lead acid battery electrodes having two or more feet which in the finished battery rest on suitably positioned mud ribs on the floor of the battery container to maintain a so-called mud space below the plates. The purpose of this mud space is to accommodate active electrode material that becomes dislodged from the plates and thereby to prevent the dislodged active material from forming a short-circuit between adjacent electrodes of opposite polarity.

We attempted to produce battery electrodes by expanding a lead strip leaving an unexpanded selvedge on each edge of the strip and an unexpanded central land, removing sequentially two lozenges of metal from the land, sequentially removing the major proportion of each selvedge by means of co-operating punches and dies to leave two portions which in the finished plates constitute feet, and subsequently cutting the strip to form the separate plates either before or after applying active electrode material to the expanded portion of each electrode.

It was however found to be extremely difficult to precisely synchronise the foot punches and the lozenge punches and that the position of the feet on the finished battery plates was therefore somewhat variable with respect to the edges and the plate lug of the plates. It will be appreciated that the mud ribs are provided at predetermined positions on the floor of the battery container and that the feet must therefore be provided at precisely corresponding positions on the plates otherwise they will be unable to rest on the mud ribs and will not perform their designed function.

Use of the method in accordance with the invention obviates this difficulty because the fact that the lozenge punches and the foot punches are mechanically coupled and in fact in the preferred embodiment are both part of the same punch means that the spatial relationship between the holes formed by the removal of the lozenges and the feet is precisely predetermined. As explained in more detail below the strip is cut into individual electrodes at positions which are set to be in a predetermined relationship to those of the holes, and thus the position of the feet in the finished electrodes can be precisely predetermined.

The invention may be put into practice in a number of ways but one specific embodiment will now be described by way of example with reference to the accompanying drawings in which Figure 1 is a plan view of an expanded lead strip with an unexpanded central land and selvedges; Figure 2 is a diagrammatic plan view of one layout of the die bed; and Figure 3 is a plan view of the strip of Fig. 1 after it has been punched.

The method of producing lead acid battery electrodes consists of firstly passing a strip of lead or lead alloy through an expander machine to expand the strip into the form shown in Fig. 1 in which the strip has an overall width of 1 50mm. with two expanded side portions 10, each having an unexpanded selvedge 12 about 5mm. wide. Between the two expanded side portions there is left an unexpanded central land 42mm. wide. The expanding machine may be of any convenient type, but in the preferred embodiment in a machine made by a German company called Bender. This machine has two rows of expander punches, and corresponding die blocks arranged one either side of the central line of the working path of the machine and converging in the direction of movement of the lead strip.The strip is therefore advanced incrementally through the expander machine, eåch step being equal to the pitch of the expanded mesh to be formed, in this embodiment about 21 mm. The strip is therefore incrementally expanded from its outer edge inwards.

The strip is then fed incrementally into a lozenge puch having a plurality of punches and corresponding die cavities. The lozenge punch is provided with an incremental feed system adapted to feed the strip in steps considerably larger than the feed mechanism of the expander machine. One arrangement of the die bed is shown in Fig. 2.

The principle purpose of the lozenge punch is to remove one or more lozenges from the central unexpanded land at each incremental step of the strip through the lozenge punch so as to leave the land with a series of holes separated by transversely extending lug portions. The strip is subsequently cut up into a number of separate battery electrodes in such a manner that each lug portion constitutes a plate lug on a finished electrode. The mechanism for cutting the strip up is set to operate at a predetermined spacing, in this case 147 mum. It will be appreciated that it is therefore extremely important that the holes formed in the central land be accurately positioned, otherwise the finished plates may have an incorrectly positioned plate lug or even no lug at all.For this reason the lozenge punch is provided with an incremental feed system which is extremely precise, but which forms no part of the present invention.

The lozenge punch feed system feeds the strip 1 47mm. at a time while the feed system of the expander machine feeds the strip about 21 mm at a time, and it will therefore be appreciated that the lozenge punch feed system operates at about one seventh of the frequency of that of the expander machine.

For this reason a tensioning device comprising one more spring loaded idler rollers is positioned between the expander machine and the lozenge punch to receive the expanded strip produced by the expander machine without kinking and then to release it to the lozenge punch.

As may be seen in Fig. 2 the lozenge punch die bed has two centrally disposed die cavities 20 and 22, 13 and 1 02mm long respectively, spaced apart by 1 6mm and each of a width of 35mm, i.e. slightly less than that of the central land of the strip. The dotted lines indicate the position occupied, in use, by the lead strip. On each side of the central cavities there are two sets of three further cavities, each set having two short cavities 24 between which is a long cavity 26, the cavities being spaced apart by 1 Ornnn. The inner edges of the three cavities of each set are colinear and arranged to be at a position just beyond the position where the inner edge of the respective unexpanded selvedge will be in use, as indicated by the dotted lines 28.It will be appreciated that for each die cavity the lozenge punch has a corresponding punch. All the punches are preferably part of a single multi-headed punch.

Thus, in operation the strip is advanced into the lozenge punch which is then actuated, and the strip will subsequently appear as shown in Fig. 3. The cavities 20 and 22 and their associated punches form alternating short and long holes 30 and 32 separated by lug portions 34, which are 16mum. wide. The cavities 24 and 26 and their associated punches remove the majority of the unexpanded selvedges leaving only a thin strip of metal 36 which ensures the mechanical integrity of the expanded portions of the strip and projecting feet 38 whose width is equal to that of the selvedge and whose length is equal to the spacing between adjacent die cavities 24 and 26.

Either before or after the application of active electrode material the strip is cut up into individual electrodes along the dotted lines shown in Fig. 2. That is to say a transverse cut is made right across the strip in the middle of each short hole 30, and adjacent lug portions 34 are severed at opposite ends.

There is thus produced a plurality of battery electrodes each of which has a plate lug, constituted by a lug portion 34, in a precisely determined position with respect to the edges of the electrode. In addition each electrode has two feet 38, the position of each of which is precisely determined with respect to the edges of the electrode by virtue of the fact that they are formed by punches which are mechanically linked to those which form the lug portions 34. Thus use of the method and apparatus in accordance with the invention facilitates the production of battery electrodes having feet whose position is reliably predetermined, so that the feet will precisely engage mud ribs formed on the floor of the battery container.

It will be appreciated that the number of punches and cavities used to produce the feet may be varied as described. Thus a single central cavity on each side of the strip will produce an electrode having two feet, one at each of its two edges. lf#more feet are required, correspondingly more punches and cavities are provided.

Claims (8)

1. A method of producing electrodes for lead acid electric storage batteries including the steps of expanding a strip of lead or lead alloy to leave an unexpanded central land, and an unexpanded selvedge on each edge of the strip, sequentially removing one or more lozenges of metal from the land and simultaneously removing one or more portions of metal from each selvedge to leave spaced portions of the selvedge projecting from the strip and separating the strip into battery electrodes each of which has two or more feet constituted by the spaced portions of the selvedge.

2. A method as claimed in Claim 1 in which the lozenges of metal and the portions of the selvedges are removed by a plurality of punches co-operating with a plurality of die cavities formed in a single die bed.

3. A method as claimed in Claim 2 in which each of the plurality of punches is a part of a multi-headed punch.

4. A method of producing electrodes for lead acid storage batteries substantially as specifically described herein with reference to the accompanying drawings.

5. Apparatus for producing electrodes for lead acid storage batteries including means for expanding a strip of lead to leave an unexpanded central land and an unexpanded selvedge on each edge of the strip, means for sequentially removing one or more lozenges of metal from the land, and means for simultaneously removing one or more portions of metal from each selvedge to leave spaced portions of the selvedge projecting from the strip and means for separating the strip into battery electrodes each of which has two or more feet constituted by two or more portions of the selvedge.

6. Apparatus as claimed in Claim 5 including a single punching device for removing both the lozenges from the land and the portions from the selvedges including a plurality of punches co-operating with a plurality of die cavities formed in a single die bed.

7. Apparatus as claimed in Claim 6 in which each of the plurality of punches is a part of a multi-headed punch.

8. Apparatus for producing electrodes for lead acid storage batteries substantially as specifically described herein with reference to the accompanying drawings.