The present invention relates to plates for lead-acid batteries and, more particularly, to grid plates used in making such batteries and to the method and apparatus for making such grid plates. Background art

Lead-acid storage batteries typically comprise several cell elements which are encased in separate compartments of a container containing sulphuric acid electrolyte. Each cell element includes at least one positive plate, at least one negative plate, and a porous separator positioned between each positive and negative plate. The positive and negative plates each comprise a lead or lead alloy grid that supports an electrochemically active material. The active material is a lead based material that is pasted onto the grid.

Grids constituting the paste material support part usually have a reticular configuration and end frame bars with a contact lug that forms part of an end bar. They provide an electrical contact between the positive and negative active materials which serves to conduct current and they also serve as a current collector during discharge and a current distributor during recharge.

Accordingly, grid designs generally seek to optimise the amount of active material supportable by the grid to increase current collection and distribution characteristics while minimising weight and improving the resistance characteristics of the grids.

It is well known that lead-acid batteries will eventually fail in service through one or more of several failure modes.

Among these failure modes is the electrical short due to the sharp end parts of the grids that may snag and tear the separator material between the positive and negative plates.

Another failure mode is failure due to corrosion of the grid surface. Electrochemical action corrodes the grid surface, particularly for positive grid structures, and reduces the adhesion between the active material and the grid. Corrosion has been also found to be promoted by fabrication cracks forming up mainly at the junctions or nodes of the grid ribbing.

It is highly desirable to manufacture grids from high purity Pb (99.99% ) since such construction would avoid intergranular corrosion and would greatly improve internal conductivity and, eventually, the life cycle and the shelf life of the battery, by virtue of very low current losses. Pure Pb however has low physical resistance and is difficult to work.

Efforts have been made to improve the service life of a lead-acid battery by increasing the quantity of active paste material fixable on the grids and also the adhesion of the grid material to the active paste material by depositing layers or coatings of various materials on the grid surfaces before pasting.

While this coating method may provide satisfactory solutions to the problem of inadequate paste adhesion, it has certain disadvantages. For example such a method requires the incorporation of an additional material into the grid manufacturing process, additional process steps and materials that can significantly increase the cost of manufacturing the battery grids.

It has also been discovered that another source of the problem of inadequate paste adhesion both during forming and service life may be the configuration of the grid. Consequently, the effect of different battery grid making processes on paste adhesion has been further examined. Known arts of lead acid battery grid making include: (1) batch processes such as mould gravity casting; and (2) continuous processes such as strip expansion, strip expansion followed by coining, strip stamping/cutting, continuous casting, continuous casting followed by rolling.

Grids made by way of these processes have unique features characteristic of the process and behave differently in lead acid batteries,

especially with respect to the pasting process.

In the batch mould casting process, molten lead (alloy) is poured into a grid mould and cooled to form a grid. The grid so made has rough surfaces, pores and large grain structure that promote intergranular corrosion. The geometric shape of the cross-section of the grid wires is usually oval with a sharp angle formed at the plane where the mould closes that provide unsuitable cutting edges. The batch process also has low productivity.

In the strip expansion process, a cast or wrought lead strip is pierced, stretched above and below the strip plane, and then pulled or expanded to form a grid with a diamond pattern. The surface of the wires perpendicular to the plane of the strip is smooth and the cross-section of the wires is rectangular. Cracks in the material form however at the junctions or nodes of the grid forming wires.

Additional coining working was also envisaged to be performed subsequent to the expansion, in order to ensure a re-shape of the expanded reticulated strip by eliminating sharp edges and corners of the wire-node structure and to break continuous grain boundary configuration formed during expansion.

Stamped or die cut grids also have smooth surfaces and a rectangular cross-section in the wires.

For continuous casting, the surface of the grid can be rough on the mould side and is smooth on the belt/air side. The geometry of the cross- section of the wires produced by continuous casting can be a triangle, a trapezoid, a section of an arc or a semi-circle, depending on the mould design. If the grids are rolled after casting, the surfaces become smooth and the cross-section of the grid wires becomes rectangular.

When applying battery paste to a grid, an oval-shaped wire, such as that in a mould cast grid or in an expanded and coined grid, allows the paste to flow around the wire. The rough surface and/or the sharp angle of the wires provide a mechanical graft and interlock of paste particles. Therefore,

the contact between the grid and the battery paste is good and the plate is strong.

With rectangular wires, on the other hand, it is much more difficult to make good contact between the battery paste and the surface of the wire moving in a direction perpendicular to the direction in which the paste is applied because the flow of paste must change direction in a 90 degree step.

When the battery paste is cured and dried, it will shrink and generate tensile force at the paste/grid interface. The tensile force at the paste/grid wire interface is at a maximum when the wire surface is perpendicular to the grid surface and at a minimum when the wire surface is parallel to the grid surface. As a result, a gap is formed between the grid wire and the paste at the location where the tensile force is the maximum. This type of plate is weak and the paste will fall off easily. Because of a lack of contact between the paste and the grid, a battery made with this type of plate is much more difficult to form, performs poorly in certain reserve capacity tests, and does not exhibit satisfactory cycle life.

Mechanical working methods, such as expansion or stamping and die cutting can successfully be carried out on Pb alloy materials, such as Pb-Ca alloys and the like, that have high mechanical strengths. Therefore, it appears that there is still a need in the battery grid plate manufacturing field for new grid structures obtained with new methods that improve uniform spreading over, and the adhesion of battery paste active material to the grid, and allow substantial increase of the quantity of such material that it is possible to fix thereto. The method should also be suitable to allow working and obtaining of grids made from high purity Pb material .

More particularly, there is a need for a method that can increase the adherence of battery active material to a battery grid produced by a continuous process, that yields high productivity and has a low cost. It is therefore an object of the present invention to provide a method

for grid manufacturing that allows obtaining of grids that increases the shelf life and life cycle of a battery by enhancing uniform spreading of, and the adhesion between the battery active material and the battery grid, and the quantity of paste active material that may be fixed to the grid. It is a further object to provide a method for grid manufacturing that allows obtaining of grids with low weight, made of a high purity Pb material, that still show good mechanical strength.

It is yet another object to provide a method for grid manufacturing that allows obtaining of grids from a continuous process with a configuration such that the paste can flow around the grid wires to arrange in a continuous, consistent layer that improves the plate strength, and such that it may indeed ensure high current density achievement.

It is yet another object of the present invention to provide a method of making battery grids that allows a battery manufacturer to take advantage of a low cost and high productivity continuous grid making process without the drawbacks associated with inadequate paste adhesion, reduced formation efficiency, continuous, straight-through grain boundaries, and reduced life cycle.

Still another object of the invention is to provide a method of making battery grids with a low scrap production rate and efficient scrap salvage. Disclosure of the Invention

The foregoing needs in the art and the foregoing objects are achieved by a method of continuously making grid plates provided with a grid mesh for lead-acid batteries, according to the invention, that comprises: providing an electrically conductive strip; feeding said strip into a coining unit assembly; coining working said strip for forming impressions on opposite surfaces thereof; and subsequently performing a cutting working of said coined strip consistent with the formed impressions for conversion of the coined strip into a continuous sequence of grid mesh plates. In one version of the invention, a grid plate for lead-acid batteries is

formed, according to the invention, with a continuous manufacturing method that comprises: a plurality of ribs constituted by cold formed profiled protrusions that have a convex, smoothed, rounded edge cross- sectional shape; cold formed thinner plate regions with openings, forming a grill mesh, cut formed therein so as to separate said profiled protrusions; and head, lug and end frame members that enclose the grill mesh.

This embodiment of the invention is particularly useful in improving the paste adhesion to individual battery grids formed by the continuous process that produces grid ribs and nodes with smooth surfaces and no cracks and suitable grain size and grain boundary configuration.

The preform battery grid includes a grid mesh bordered by frame members on at least one side. The top frame member has a current collector lug.

The invention also provides for the grid plates for lead-acid batteries to be made on an apparatus provided with a coining unit assembly that comprises: a feeding unit for continuous feeding of an electrically conductive strip; a coining working unit adapted for cold forming in said continuous strip of impressions consisting of a plurality of ribs constituted by profiled protrusions that are separated by thinner plate regions that have dedicated peripheral regions formed so as to correspond to head, lug and end frame members of grid plates; and a cutting unit adapted for forming of cuts on the coined strip, that are consistent with the formed impressions and dedicated peripheral region arrangement and such as to form grill mesh openings and peripheral contours of , said frame members and to convert the strip in a continuous sequence of grid mesh plates. Brief Description of the Drawings

Further characteristics and advantages of the present invention will become better apparent from the following detailed description of a preferred but not exclusive embodiment of the method and of an apparatus for the manufacturing of a grid plate for lead-acid batteries, illustrated by way of

non-limiting example in the accompanying drawings, wherein:

Figure 1 schematically illustrates the various steps and equipment utilised in the preferred embodiment of making the battery grid plates according to the invention; Figure 2 is a perspective, partial view, showing a continuously worked strip provided with coined impressions as obtained after the coining working of the strip, according to the invention;

Figure 3 is a perspective, partial view, showing a double row grid sequence cut in a coined strip in agreement with the coined impression configuration, obtained according to the invention;

Figure 4 is a perspective view of a finished grid plate of an embodiment made according to the invention;

Figure 5 is a cross-sectional, enlarged, partial view, taken along the line V-V of Figure 4, showing the cross-section configuration of a grid obtained in accordance with the present invention;

Figure 6 is a cross-sectional, enlarged, partial view, of a grid as shown in Figure 5, made in accordance with the present invention with further illustrated a paste material deposition;

Figure 7 is a perspective view showing a pair of coining rollers suitable for coining a single row grid sequence according to the invention;

Figure 8 is a perspective view showing a pair of coining rollers suitable for coining a double row grid sequence according to the invention;

Figure 9 schematically illustrates the various steps and an equipment for the preliminary strip making in the coining method and with the apparatus for making the battery grid plates according to the invention. Ways of carrying out the Invention

With reference to the figures 1-9, there is provided, in accordance with the invention an apparatus for continuously making grid plates for lead-acid batteries including a coining unit assembly, generally designated in Figure 1 with the reference numeral 1. The coining assembly comprises a feeding

unit 40 (Fig. 9) that continuously feeds an electrically conductive strip S to a coining working unit 2 adapted for cold forming in the continuous strip of impressions consisting of a plurality of ribs constituted by profiled protrusions 13 that are separated by thinner plate regions 14 (Fig. 2) with dedicated peripheral regions formed so as to correspond to the head 18, lug 21, and end 19 frame members of grid plates 20 (Fig. 4).

A cutting unit 4 is provided downstream of the coining working unit 2, which is adapted for forming of cuts on the coined strip, that are consistent with the formed impressions 13, 14 and dedicated peripheral region arrangement . The cuts are performed in a configuration such as to form grill mesh openings 17 and peripheral contours of the frame members 18, 19, 20 and to convert the strip in a continuous sequence of grid mesh plates P.

The apparatus, further comprises a trimming unit 3, arranged downstream of the coining working unit 2 and upstream of the cutting unit 4 and is adapted for trimming edge regions of the coined strip S and frame members 18, 19, 20.

A cleaning unit 5, arranged downstream of the cutting unit 4 is also provided that is adapted for cleaning, preferably through brushing, for example with suitable rotating brushes, the continuous sequence of grid mesh plates P.

Arranged downstream of the cutting unit 4, a rolling unit 6 is provided for rolling up the continuous sequence of grid mesh plates P and for forming rolls of grid mesh plate P sequences that may be either stored for later transport and use or delivered to a pasting unit 8, that may also be provided as part of the apparatus and which is adapted for applying paste active material 22 on the surfaces of the continuous sequence of grid mesh plates P.

The coining working unit 2 comprises at least one or more suitably arranged pairs of opposed coining rollers 10 that have mating, active

forming surfaces 11 provided with coining indents 12, with a shape adapted to form in cooperation, through pressing-coining action that involves migration of controlled masses of the worked material in said indents 12 and related thinning in selected zones of the material of the strip S, the impressions 13, 14.

The indents 12 are shaped concave with a form adapted to form on the strip S the profiled protrusions 13, provided in corresponding opposite arrangement on each of the opposite surfaces 15, 16 of the strip S, preferably having a convex, smoothed, rounded edge cross-sectional shape. The pairs of rollers 10 may be either shaped and arranged for working the strip S so as to eventually obtain sequences of single row grid plates 20 (Fig. 7), or sequences of grid plates 20 that are connected to each other, in a side- by- side arrangement, at the lugs 21 (Figures 8 and 3).

The cutting unit may be a die cutting pressing unit 4 adapted to operate with step- by- step feeding of the coined strip S and die cutting of the cuts, or may comprise a roller cutting unit 4 adapted for continuous feeding of the coined strip S and roller cutting.

The dies of the die cutter press or those provided at the surface of the roller cutters 4 may be so shaped as to cause slitting of the coined lead strip. While a variety of shapes can be used for the top of the dies to effect the cutting, the rectangular shape is preferred to obtain the grid configuration shown in the Figures 3 and 4.

The dies may include two identical cutting configurations to provide series of two, paired grid plates 20 such as shown in Fig. 3, but also only a series of cutting profiles for the working of the one row series of grid plates 20 .

The apparatus may also be provided, in a more complex configuration thereof, with a strip forming unit 30 of a type that is presently available on the market, adapted to continuous form electrically conductive strip S. The strip forming unit 30 comprises a continuous furnace 31, provided with

either a continuous casting or an extrusion device 32, and with a rolling device 33.

It is also envisaged to provide the apparatus, in a preferred embodiment thereof, with a scrap salvage unit 9 for salvaging scrap that is mainly produced at the cutting unit 4 and also at the trimming unit 3.

A scrap conveyor 7 is provided so that it preferably extends at least from the salvage unit 9, to the cutting 4 and trimming 3 units and up to a recycling unit, for conveying scrap produced during the working/machining operations. The recycling unit may be constituted by the continuous furnace 31 of the strip forming unit 30 (Fig. 9) or by any other recycling unit that is suitable to recycle the scrap.

The method of continuously making grid plates for a lead-acid battery, according to the preferred but not exclusive embodiment of the invention comprises providing an electrically conductive strip S, feeding the strip S into the coining unit assembly 1, coining working the strip for forming impressions 13, 14 on opposite surfaces 15, 16 of the strip, and subsequently, performing a cutting working of the coined strip consistent with the formed impressions 13, 14 for conversion of the coined strip into a continuous sequence of grid mesh plates P.

The coining working step comprises cold forming of the impressions 13, 14 on opposite surfaces 15, 16 of the strip S. The impressions made in the strip surfaces consist, in particular, of a plurality of ribs having the shape of profiled protrusions 13 that are separated by thinner plate regions 14.

The impression cold forming step is carried out by cold rolling, by way of the at least one pair of opposed coining rollers 10 with the active forming surfaces 11 provided with the indents 12 shaped complementarily to the shape of the profiled protrusions 13 to be formed in the strip S. The cold forming step comprises forming, on the opposite surfaces 15, 16 of the

strip S, of the profiled protrusions 13 that have the convex, smoothed, rounded edge cross-sectional shape, with the convex protrusions 13 provided in corresponding opposite arrangement on each of the opposite surfaces 15, 16 of the strip S and also of the dedicated peripheral regions arranged so as to correspond to head 18, lug 21 and end 19 frame members for the grid plates 20 that are produced.

The cold forming coining working is usually carried out, when rather soft lead based material is used, at the environment temperature, and preferably at about 2O ⁰ C. The coining rollers 10 work the strip S such that the metal thereof flows to assume the shape of the roller surface pattern, thereby avoiding formation of any sharp edges, corners and of any cracks which are typically rapid corrosion sites, and such as to reorient and break up any continuous, straight-through grain boundaries. This greatly lowers the rate of intergranular corrosion inwardly via these grain boundaries.

It has been indeed practically ascertained that coining significantly cold works the metal, especially at the surface but also in depth through material migration, thereby reducing the grain size and reorienting the grain boundaries to minimise the number of grain boundaries otherwise extending directly through the metal. Moreover, the coining operation prevents formation of sharp edges and corners.

The method further comprises a trimming step, carried out after the coining working step for trimming edge regions of the coined strip S and frame members 18, 19, 20. The strip cutting working step is carried out after the trimming step and comprises forming of cuts on the strip, that are consistent with the formed impressions 13, 14 and with the dedicated peripheral region arrangement, and are such as to form grill mesh openings 17 and the peripheral contours of the frame members 18, 19, 20 on the coined strip S and to convert the strip in a continuous sequence of grid mesh plates P.

Moreover, the cutting working step may comprise a step- by- step feeding of the strip S to a die cutting pressing unit 4 and die cutting of said cuts on said strip S or a continuous feeding of the strip S to an alternative roller cutting unit 4 and roller cutting of said cuts on the strip S. A strip cleaning step, preferably a brushing cleaning step, may preferably be carried out, at the cleaning unit 5 after the cutting working step for cleaning the surfaces 15, 16 of the cut strip.

The cutting working step can be completed by an additional scrap salvage step for salvaging scrap obtained during cutting that is performed through collection of the scrap and transport thereof on the conveyor 7, from the scrap salvage unit 9 to a recycling unit, such as the continuous furnace 31 of the strip forming unit 30.

A further rolling step for rolling the continuous sequence of grid mesh plates P may eventually be carried out. The rolled plates can either be stored for ageing and deferred, final working, or transported right away to the appropriate installations for carrying out subsequent, required operations.

Such subsequent operation, that may be carried out either immediately after the rolling step, or even before the rolling step, directly on the sequence of mesh plates P, or at an independent and later moment, on an aged rolled plate sequence, is the pasting step. This step consists in applying paste active material 22 on the surfaces of the continuous sequence of grid mesh plates P.

Following cleaning or later , the grid sequences P may be continuously pasted, for example on a continuous belt or support passing under a paste dispensing apparatus, drying the paste, with the headers 18, the end frame members 19 and with lugs 21, separating the pasted strips and finally segmenting each strip into individual plates. Forming of the shape of the headers 18 of the frame members 19 and of lugs 21, these last being formed at the centre portion or offset (Fig. 4), according to requirements, is accomplished in the coining step, the profile cutting being performed in the cutting step.

As illustrated in the Figures 5 and 6, coining cold forms cross- sectionally to the strip, ribs 13, that after cutting of the openings 17, will generally have ellipsoidal or anyway round edged, lobed shapes in two mutually perpendicular directions. The rounded edge, oval-to-round shaped ribs 13 constituting the grill mesh of the plates allow, during the pasting step, an optimal paste spreading with the paste 22 flowing around the surface of each individual rib 13 and through the openings 17 to eventually cover both faces 15, 16 of the plate 20 and to solidify in thick, consistent and even layers (Fig. 6). The rib shape provides a mechanical graft and interlock of the thick paste material 22 to the grid. Therefore, the contact between the grid and the solidified battery paste is intimate and the plate is eventually strong, even if soft pure lead material is used.

The electrically conductive strip S may be preferably obtained by way of a continuous process, consisting in a continuous casting or by a continuous process consisting in an extrusion step followed by a rolling step. Such steps are optionally followed by an ageing of the strip obtained, before its feeding and introduction into the coining unit assembly 1.

Highly pure lead material, with a purity of up to 99.9% was advantageously used, that along with the grid design (square grid mesh opening instead of rhomboid as in the prior art) helped achieving in practice grid plates with much higher electrical conductivity and higher current density. Also the closed perimeter configuration of the grid plates made in accordance with the invention formed by the header 18 and end frame members 19 provides no sharp angles as the prior art grid plates and thus avoids short circuits due to charge concentrations and _. puncturing of the isolation.

The new coining technology, according to the invention, was also found out to provide substantial production cost savings with respect to the expanded and cast grid plates, due to material savings obtained through the

lower plate thickness obtainable with the new method high productivity and low equipment investment.

It was found possible, for example, to start from a strip with a thickness of 0.7mm and obtain through coining with material migration vertical ribs 13 of 1-1.3mm thickness connected by horizontal ribs, parallel to the header 18, of 0.4-0.6mm. The lesser thickness dimension is obtainable with pure lead (99.9% by weight) and the higher one with Pb-Ca alloys.

Also the quantity of scrap produced with the method according to the invention, and which is entirely recyclable, was found to be with up to 40- 50% lower than in the expanded and cut or stamped/cut plates.

Tests were carried out in sulphuric acid, under equal conditions of acid concentration and temperature, with the same alloy characteristics and electric charge, involving coined grid plates made in accordance with the invention and also expanded grid plates made according to the known art. A minor loss of weight for the coined plates, measured in rng/cm ² .day of up to 50% has thus been ascertained.

While this invention has been disclosed in terms of specific embodiments thereof, it is not intended that it be limited thereto, but rather only to the extent set forth hereafter in the appended claims. The disclosures in Great Britain Patent Application No.0425343.1 from which this application claims priority are incorporated herein by reference.