DESCRIPTION The present invention relates to a machine for the manufacture of lead grids intended to form the plates of electric accumulators, as well as to a method for forming said grids.

More clearly, the machine in question may advantageously be used for the production of a continuous lead grid from which it is then possible to obtain, by means of cutting operations, the plates to be inserted in electric accumulators.

At present, in accordance with the known art, various systems for the production of lead grids exist.

A first system envisages the incision and expansion of a strip by means of pressing means provided with a plurality of teeth.

As is known, different constructional solutions of machines which use this system for the manufacture of lead grids exist.

In greater detail, a first solution envisages the use of a feeding mechanism able to feed, in successive steps, a lead strip through a die provided with teeth for

forming the mesh of the grids.

In accordance with the known art, these machines envisage that the strip stops in the pressing zone so that it can be cut by the teeth of a movable head which is generally actuated by movement means suitably coupled to the feeding system, following which the strip advances by a predefined amount so as to allow pressing of a following section thereof.

These pressing machines have given rise to certain operational drawbacks associated in particular with the discontinuous feeding system which does not allow high production outputs to be achieved owing to the fact that the stepwise feeding movement of the lead grid is obviously subject to the mechanical strength limits of the lead.

Moreover, pressing machines of these type do not allow the production of grids with a high level of quality. This is due in particular to the fact that the stepwise movement of the lead strip results in a significant amount of imprecision with regard to correct positioning thereof in the pressing zone owing to the continuous stopping and starting.

In order to overcome these drawbacks, more recently a machine described in the patent US 6,145, 363 has been developed, whereby it is envisaged that the pressing

means are operationally actuated so as to cut the strip with a movement sequence which has a component oriented in the direction of continuous feeding of the strip and a component oriented in a substantially perpendicular direction. The first component allows the teeth to advance substantially in synchronism with the strip, while the second component allows the teeth to cut and expand the strip during a machine cutting step.

This latter machine, although improving significantly the performance characteristics of the previous commercially available machines, is suitable in particular for the production of grids intended for a sector distinguished by the need for an electrical performance which is not very high.

The performance limitations of the grids obtained with the systems described above are due to the material from which the strips forming the grids are made. This material must have specific mechanical characteristics such as to allow correct operation of the abovementioned machines and in particular must have a sufficient mechanical rigidity which, as is widely known, is obtained by the addition of additives such as antimony, tin, calcium, etc. The latter, although on the one hand they improve the mechanical response, in particular necessary in the pressing process, on the other hand may

give rise to self-discharging phenomena which, as is widely known, reduce the performance of the batteries.

Moreover, the abovementioned known machines allow, however, only the production of fairly strong grids, whereas alternatively, for certain applications, grids made using a smaller amount of material, i. e. with extremely thin filaments, would be more suitable.

In particular, for some applications, batteries with a high electrical performance, for example characterized by a very long life, fairly low self-discharging levels, absence of gassification and operation also at half- charge, may be required.

In order to obtain these performance features it would be advantageous to be able to use, for the manufacture of the grids, alloys which are optimised according to the electrical characteristics which are to be obtained and not constrained by mechanical production requirements. In particular, for example, the thickness of the grid filaments should be determined principally on the basis of the electrical resistance which must be obtained and not on the mechanical strength which must be imparted to the grid in order to allow the teeth of the pressing head to cut the strip without damaging it.

In greater detail, once the correct composition of the lead alloy able to withstand corrosion has been

determined, the thickness of the filaments should be determined solely according to the quantity of current to be conveyed. This fact may mean that the thickness of the grid must be chosen so as to be suitably thin for electrical reasons.

As is known, an optimum composition of the lead alloy does not correspond to optimum mechanical characteristics. In particular, a high grid quality is obtained with pure lead. On the other hand, it is known that lead has a high viscosity and plasticity and has a fairly irregular mechanical behaviour which cannot help ensure that the grid remains intact during the production processes. In fact, the lead mass behaves in the manner of a paste and tends to cling to the teeth of the pressing head instead of following the pressed strip leaving the pressing machine.

It must also be commented that, as is well known, the production process by means of which the lead strip is originally made is decisive for the definition of the mechanical and electrical characteristics of the grid.

In fact, in general the possibility of using a strip obtained with a lead alloy distinguished by particularly well-compacted granules, obtained for example by means of rolling processes which result in a reduction of the thickness down to a tenth of the initial thickness, would

allow the mechanical response to be improved, allowing the dimensions of the grid to be defined only on the basis of the desired electrical characteristics.

A second system, which is an alternative to that commonly represented by pressing and/or expansion, envisages the casting of a lead alloy inside a suitable mould. This production process requires the use of a lead alloy enriched with additives able to overcome the problems of castability. This fact results in the production of grids distinguished by a non-optimum electrical performance. Moreover, the said casting production process is characterized by a low productivity.

Grids with a high electrical performance obtained with fairly soft lead alloys are made, as is well known, also using punching systems which act cyclically only on a very small portions of the strip so as to cut only a few rows of the strip during each perforation cycle so as to allow extraction of the teeth from the said strip without damaging it.

Alternatively, grids which are stronger or produced with a very large mesh or produced with harder alloys allow larger regions to be punched, increasingly considerably the production speed. This occurs, however, once again to the detriment of the electric performance

which is poorer and dimensions of the grid filaments which are larger, to ensure extraction of the cutting teeth without breaking or damaging the said filaments which form the grid.

The main object of the present invention is therefore that of overcoming the drawbacks of machines of the known type by providing a machine for forming metal strips for the manufacture of grids for electric accumulators, which allows high production outputs to be achieved while ensuring a high level of quality.

Another object of the present invention is that of providing a machine able to process strips made from any type of lead alloy, or lead which is substantially pure or also has a low level of additives, without mechanical problems occurring during the forming of the grids in particular as a result of the composition of the material from which it is obtained.

Another object of the present invention is that of providing a machine which is able to process continuously lead strips which are particularly soft and the composition of which has been optimised substantially on the basis solely of the electrical characteristics which are to be obtained.

A further object of the present invention is that of providing a machine which is constructionally simple and

operationally entirely reliable.

The technical characteristics of the invention, in accordance with the abovementioned objects, may be clearly determined from the contents of the claims indicated below and the advantages thereof will emerge more clearly from the detailed description which follows, with reference to the accompanying drawings which show a purely exemplary and non-limiting embodiment in which: - Figure 1 shows schematically a general side view of the forming machine in question; - Figure 2 shows schematically a perspective view of a detail of the machine according to Figure 1, relating to a forming unit; - Figure 3 shows schematically a cross-section through the unit according to Figure 2; - Figure 4 shows an enlarged detail of Fig. 3, relating to two compression stations; - Figure 5 shows an enlarged detail of Fig. 3, relating to the first compression station; - Figure 6 shows an enlarged detail of Fig. 2 relating to the grid before, during and after passage through the forming unit.

With reference to the accompanying drawings, 1 denotes overall the forming machine according to the present invention.

It comprises a support structure 2 which rests on the ground and on which a forming unit 3 actuated by an electric motor 4 via drive means 5 is mounted.

Advantageously, in accordance with a preferred embodiment of the present invention, the machine 1 is provided with a feeding unit 6 and a drawing unit 7 which are arranged respectively upstream and downstream of the forming unit 3 and are intended to convey a metallic strip 8 composed of a material comprising lead through the machine 1 and in particular through the abovementioned unit 3.

The mechanical characteristics of the machine 1 according to the present invention allow, as will be explained in detail below, the use of any type of lead alloy intended to form the grids for electric accumulators. Owing to the machine 1 according to the present invention, it is in fact possible to use alloys which take account solely of the electrical characteristics which are to be obtained. Therefore the lead alloy may be distinguished by a high level of plasticity, by a limited hardness or may be composed almost exclusively of lead, without the material of the alloy, during the forming operations, clinging in an undesirable manner to the components which have the function of forming it in the form of a grid.

According to a main characteristic feature of the present invention, the forming unit 3 comprises three rollers-indicated below as first roller 9, second roller 10 and third roller 11-which are made to rotate by the electric motor 4 via drive means 5. All three rollers are arranged transversely with respect to the direction of feeding X of the strip 8. The second roller 10 and the third roller 11 rotate on the first roller 9 with the same tangential speed relative to the said first roller 9, but in the opposite direction to the latter.

In this way, the strip 8 advances from an entrance way 12 to an exit way 13 of the forming unit 3, passing between the first roller 9 and the second roller 10 at a first compression station 14 and then between the first roller 9 and the third roller 11 at a second compression station 15.

The second roller 10 is provided with first grooves 16 which are formed substantially in a meshwork according to the profile of the grid 17 to be defined.

These first grooves 16 are therefore formed in the form of a continuous cavity on the external surface of the second roller 10 and have substantially the form of the profile of the filament of the grid 17 which is to be obtained. As will be clarified below, the height H of the first grooves 16 may be greater or smaller than the

thickness S of the strip 8 at the entrance way 12 of the forming unit 3.

The pressure exerted on the strip 8 by the first roller 9 and by the second roller 10 at the first compression station 14 causes a displacement and a compression of the material of the strip 8 itself inside the first grooves 16. Upon leaving said compression station 14, the strip 8 is therefore provided with a modelled portion 18, which extends projecting from its surface and is counter-shaped with respect to the form of the first grooves, and a thinned portion 19 which is substantially flat and connected to the modelled portion 18.

The thinned portion 19 is obtained by means of the compression of facing flat surfaces 40, 40'which belong to the two rollers 9 and 10. In fact, owing to the plasticity of the lead alloy, a thinned portion 19 in the form of a thin sheet with a thickness preferably less than one tenth of a millimetre nevertheless remains inside the mesh of the modelled portion 18.

The abovementioned third roller 11 has a profile with a cutting edge 20 formed substantially according to the profile of the grid 17 to be defined and able to score and cut the strip 8, during the passage of the latter through the second compression station 15, in the

vicinity of the modelled portion 18 without however ever substantially cutting it. In this way, separation of the modelled portion 18 from the thinned portion 19 occurs with the formation of the continuous grid 17.

Mere drawing of the grid 17 by means of the unit 7 at the exit way 13 from the unit 3 causes separation of the two portions, the modelled portion 18 being raised from the first roller 9 and the thin layer 19 remaining in contact with the surface of the said first roller 9.

The strip 8 leaving the first compression station 14 is made to adhere against the first roller 9 by means of suitable retaining means 21 of the mechanical or pneumatic type.

In accordance with a preferred embodiment of the present invention, the retaining means 21 are obtained by providing first receiving pockets 22 formed on the first roller 9 as a continuation of the flat surfaces 40 so as to face the free portions 23 situated in the meshwork defined by the first grooves 16 on the second roller 10.

As can be clearly seen in Fig. 5, the mass of material which forms the strip 8 and which reaches the first compression station 14 forms partly the modelled portion 18 and partly the thin layer of the thinned portion 19, while the remaining excess portion 24 ends up inside the first receiving pockets 22, forming tablet-

shaped elements.

The entire mass of strip-like material 8 which reaches the entrance way 12 is necessarily formed into the various portions, i. e. modelled portion 18, thinned portion 19 and excess portion 24.

In this way, the situation is avoided where any portion of the material of the strip 8 which cannot be given a particular form is expelled from the first compression station 14.

The presence of the first pockets 22 results in the formation, on the strip 8, of several effective gripping points which allow all the portions 18,19 and 24 of the said strip 8 to be kept perfectly in contact with the first roller 9 upon leaving the first compression station 14, travelling above the remaining strip portions.

Moreover, the provision of the first receiving pockets 22 for recovery of the excess material 24 facilitates the operations involving adjustment of the machine 1.

In the example according to Figure 5, the volume of the first receiving pockets 22 is designed so as to have dimensions greater than the mass of the excess portion 24 which they are required to contain and correspondingly the height H of the first grooves 16 is designed so as to be slightly smaller than the thickness S of the strip 8

entering into the compression station 14. In fact, in accordance with this embodiment, the mass of material of the strip 8 could have difficulty in reaching, as a result of compression, heights greater than that of the thickness S of the strip 8 since it would always find an escape route into the first receiving pockets 22.

In order to be able to obtain grids 17 composed of filaments of various dimensions irrespective of the thickness of the strip 8 used, it is possible to envisage, in accordance with a further embodiment of the present invention, that the volume of the first receiving pockets 22 has dimensions such as to receive only partly the mass of the excess portion 24 which in this way would be compressed with a predefined force inside the first grooves 16.

As a result of this, it is possible, for example, to form first grooves 16 having heights H greater than the thickness S of the strip 8 entering the compression station 14. In this way, the mass of material which forms the strip 8, once the first receiving pockets 22 have been filled, is pushed inside the first grooves 16 to a height H which is greater than the thickness of the strip 8, allowing the manufacture of particularly strong grids.

Obviously, moreover, the form of the first grooves

16 may be of any kind depending on the different requirements for manufacture of the grids, the filaments of which will thus have a form counter-shaped with respect to that of the first grooves 16.

The shape of the first pockets 22 may be designed so as to allow easier extraction of the tablet-shaped excess portions 24 once the first roller 9 during its rotation conveys them beyond the second compression station 15.

Advantageously, the second roller 10 may also be provided, inside the meshwork defined by the first grooves 16, with second receiving pockets 25 having dimensions smaller than those of the first pockets 22 and intended to face the latter inside the compression station 14, as clearly shown in the accompanying Figure 5. The form of the second receiving pockets, however, must be such as not to adversely affect the adherence of the strip 8 leaving the first compression station 14.

Moreover, second grooves 26 may be formed on the first roller 9, said grooves being intended to face the first grooves 16 in the abovementioned first compression station 14. In this way, the second grooves 26 combine with the first grooves 16 to define the form of the filament and likewise the second pockets 25 combine with the first pockets 22 to define the form of the excess portions 24.

The depth and the form of the second grooves 26 will nevertheless be such as to favour the adherence of the strip 8 on the first roller 9 upon leaving the first compression station 14 without adversely affecting, however, the possibility of easy separation of the grid 17 from the first roller 9 upon leaving the second compression station 15.

The excess portion 24, which is still located inside the first receiving pockets 22 upon leaving the exit way 13 of the unit 3 after separation from the grid 17, needs to be removed from this position so as to allow the forming cycle to be started again.

For this purpose, suitable removal means 27 are provided downstream of the second compression station 15, for separating the thinned portion 19 from the first roller 9 and, if present, at the same time the excess portion 24 as well.

Once detached from the first roller 9, the thinned portion 19 and the excess portion 24 may be collected in suitable storage means indicated by 70 in Fig. 1.

Advantageously, the removal means 27 may be obtained by means of a forced-injection plant able to propel a fluid against the portions 19 and/or 24 to be removed.

In greater detail, this plant 27 may comprise a fixed supply source connected to a header 29 intended to

establish communication with the first receiving pockets 22 by means of connection ducts 30 formed inside the first roller 9 in at least a first segment 31 of the latter, as schematically shown in Figure 3.

The expulsion of the excess portion 24 from inside the first pockets causes the simultaneous separation also of the thinned portion 19 connected to the said excess portion 24.

Alternatively or in conjunction therewith, the removal means 27 may envisage one or more mouths for injecting a fluid 32 and/or for sucking air 32'which are arranged outside the first roller 9, in the vicinity of its surface and along at least one second segment 33 of the first roller 9 so as to cause separation of the thinned portion 19 and/or excess portion 24 from the first roller 9.

The first roller 9 and the second roller 10 are intended to produce on the strip 8 a notable compressive force and therefore are advantageously made of a single block of particularly hard steel.

Advantageously, the third roller 11 may instead have inside it a layer of resiliently yielding material 34 able to allow the cutting edge 20 to be kept pressed on the thinned portion 19 even in the presence of irregularities.

For a better distribution of the pressure, the said third roller 11 may advantageously be composed of numerous individual disks arranged coaxially alongside each other.

The present invention also relates to the forming unit 3, in particular as described in detail above.

This forming unit 3 may be arranged above a machine 1 of the type described above or in more complex plants which also envisage the simultaneous presence of other processing units arranged upstream and/or downstream of the said unit 3, such as, for example, a cutting unit for separation of the continuous grid 17 into individual plates and cutting of the lugs for the electrical connection.

The present invention also relates to a method for forming a strip for the manufacture of grids for electric accumulators, which can be obtained in particular by means of use of the machine 1 described above.

Therefore, with particular reference to the observations made above, this method comprises the operating steps described below.

First of all there is a step involving preparation of the strip 8 which is composed of a material comprising lead and is preferably obtained by means of rolling processes which, starting with the strip 8 produced using

casting processes, gradually reduce the thickness thereof down to as much as a tenth of the original thickness. In this way, the grains which form the material of the strip 8 are greatly compressed and consequently the mechanical elasticity and internal cohesion properties which favour the formation of the strip 8 are improved considerably.

Subsequently, the strip 8 undergoes a pressing step resulting in formation of the modelled portion 18, intended to form the grid 17, and the thinned portion 19.

This step may be performed in particular by means of the forming unit 3 described above.

At this point, firstly cutting of the thinned portion 19 in the vicinity of the modelled portion 18 is performed, followed by separation of the modelled portion 18 in the form of a grid 17 from the thinned portion 19.

Once the thinned portion 19 has been separated from the modelled portion 18, separation may occur by means of simple drawing of the modelled portion 18 alone.

The forming step and cutting steps may be performed continuously by means of the forming unit 3 described above.

However, in order to implement the method according to the invention, the same steps may also be achieved in a non-continuous manner by envisaging for example feeding of the strip 8 in successive steps firstly through a

machine designed to press the strip into a modelled portion 18 and a thinned portion 19 and then subsequently through a machine provided with a cutting edge so as to cut into the thinned portion 19, separating it from the modelled portion 18.

Advantageously, the method according to the present invention may envisage that, during the pressing step, formation and forming of the excess portion 24 may also occur, as described above, said portion being arranged as a continuation of the thinned portion 19 and intended also to be separated from the modelled portion 18 together with the thinned portion 19 during said cutting step.

The main advantage of the present invention is that of allowing the processing of strips 8 which are also particularly soft and have a notable plasticity without the consistency of the material representing a constraint during production and forming of the grids.

In particular, the composition of the material which forms the grid 17 and the dimensions of the latter may be chosen in a manner which is substantially independent of the production requirements and may therefore be optimised in accordance solely with the electrical characteristics which are to be obtained.

Obviously, the present invention may also assume, in

its practical embodiment, forms and configurations different from that described above, without thereby departing from the present scope of protection.

Moreover, all the details may be replaced by technically equivalent elements, and the dimensions, forms and materials used may be of any nature in accordance with requirements.