GB2084915A - Apparatus for expanding metallic strip - Google Patents

Abstract

Apparatus for expanding metallic strip inwardly from its edges to leave an unexpanded selvedge at each edge e.g. in the manufacture of a battery plate, includes a lower fixed expander block whose edges converge in the direction of movement of the strip. An upper reciprocable expander block carries two lines of expander punches whose cutting edges cooperate with the edges of the fixed block to cut and expand those portions of the strip which extend over the edges of the fixed block. Feed means incrementally advances the strip through the apparatus. The cutting edge and underside surface of the upstream punch 20', and preferably the adjacent punch also has a rounded portion 18'. This reduces the distortion to which the selvedges are subjected thus facilitating their bending and reducing the incidence of broken mesh strands. <IMAGE>

Description

SPECIFICATION Apparatus for expanding metallic strip The present invention relates to apparatus for expanding metallic strip, in particular strips of lead or lead alloy for subsequent processing into electrode supports for lead acid electric storage batteries.

Such apparatus may be divided into two broad types, namely apparatus in which a plurality of slits is formed sequentially in a metallic strip which is subsequently stretched into a mesh structure which is usually of rectangular form, and apparatus in which two lines of punches arranged to converge in the direction of travel of the strip are reciprocated with respect to a fixed block with the edges of which the punches cooperate to simultaneously cut and expand the strip incrementally from its edges inwardly.The invention is concerned with the latter type of apparatus, one example of which is made by the German company Bender and will now be described with reference to Figs. 1 to 4 of the accompanying drawings in which: Figure 1 is a diagrammatic plan view of the fixed expander block; Figure 2 is a diagrammatic side elevation of the two upstream expander punches in one of the lines of punches; Figure 3 is a diagrammatic side elevation of part of the edge of an expanded lead strip; and Figure 4 is an end view of the downstream end of the expanding machine showing the shape of the expanded lead strip leaving it.

As shown diagrammatically in Fig. 4 the expanding machine includes an elongate lower fixed expander block 2 and an upper vertically reciprocable expander block 4 carrying two lines of expander punches 6. As seen in Fig. 1 the edges of the fixed expander block are convergent in the direction of travel of the metallic strip and comprise two sets of straight parallel edges 8 which converge on the central axis of the block, adjacent edges 8 of each set being interconnected by a respective short edge 10 extending substantially perpendicular to the axis of the block. The punches 6 are arranged in two corresponding converging lines so that the cutting edge of each punch cooperates with a respective edge 8 of the fixed expander block to cut a sheet of metal which extends over that edge.The upper block 4 is pushed downwardly by two counter-rotating shafts 12 positioned above it, each of which carries an eccentric cam 14, driven by a motor (not shown) via a spur gear (not shown). The apparatus also includes a pair of feed rollers (not shown) connected to one of the shafts 12 by a crank to feed a metallic strip incrementally through it. Thus, in use, the upper block is pushed downwardly by the cams 14, and each punch cooperates with a respective edge 10 of the lower block to cut a portion of the strip and pushes the cut portion downwardly to expand the strip.

The upper block is then returned to its rest position by springs (not shown), the feed rollers advance the strip one step or increment and the cycle repeats. The apparatus produces a diamond shaped mesh structure, and on each stroke each punch forms one side of two adjacent diamonds and two sides of one diamond alternately. The longitudinal dimension of the diamonds, point to point is referred to as the pitch of the mesh and the longitudinal dimension of that part of each punch which performs the cutting is therefore one pitch.

The punches are spaced 13 pitches apart centre to centre, and the increments by which the strip is fed through the apparatus are of exactly one pitch.

Thus, as the end of a metallic strip is advanced into the apparatus the two first or upstream punches are the first to contact the strip, and they each make a single cut adjacent and substantially parallel to the edges of the strip. The strip is then advanced one pitch, and the first punches then make a further cut whilst the two second punches also make a cut in the strip. After each successive increment two further punches contact the strip, until they are all in action, and the strip is thereafter cut and expanded sequentially along the two convergent lines defined by the cutting edges of the punches.

As mentioned above, the expansion of the strip occurs by virtue of the fact that the strands which are separated from the strip by the cutting action of the punches but whose ends are connected to the strip are pushed downwardly by the punches and thus caused to extend at an acute angle to the remaining uncut portion of the strip. As the strip is expanded inwardly, the expanded portion is progressively bent more and more, and when the expansion is finished the two expanded portions, which extend on either side of the downstream end of the expander block extend in a deformed "gulls-wing" configuration as seen diagrammatically in Figure 5. On each side of the expanded strip is an unexpanded selvedge 16, the width of which depends on the spacing of the upstream punches in relation to the width of the unexpanded strip, but is typically about twice the width of the mesh elements.It will be appreciated that these selvedges are subjected not only to bending, but also to twisting along their length.

As seen in Fig. 2 the cutting edge 18 of the upstream punches 20 is horizontal over most of its length with a short upwardly inclined portion 22 at each end, so as to produce a straight even inner edge to the selvedge. The remaining punches have a rather shorter horizontal portion to their cutting edge and rather longer upwardly inclined portions. When the outer cuts defining the selvedges 16 are made by the punches 20, the entire portion of the selvedges beneath the punches will be deformed into a shape corresponding to the profile of the underside of the punches 20.

The selvedges will thus be of sharply corrugated form as seen in Fig. 3.

In a typical embodiment the lead strip had an original width of 1 05mm and a thickness of 1 mm. It was expanded to have an overall width of about 250mm with a central unexpanded land 42mm wide (i.e. equal to the width of the downstream end of the fixed expander block). The mesh pitch is about 21mm, the mesh elements are 1.5mm wide and the selvedges are 2.sum wide. It was found that the selvedges were capable of being subjected to the corrugation, bending and twisting referred to above without substantial damage to themselves or to the mesh elements connected to them.

It is frequently desired to provide lead acid storage battery electrode grids with feet which in use, rest on mud ribs on the bottom of the battery container so as to define a mud space to accommodate active material which becomes dislodged from the plates during service.

It is a simple matter to provide such feet on cast grids, but on expanded grids it is necessary to provide the expanded strip with particularly broad selvedges from which portions are subsequently removed, the portions which remain constituting feet. For this purpose the selvedges may be between, say, 4 to 12 mm wide, and it has been found that the distortion to which these wider selvedges are subjected results in a substantial stress at the points where the mesh elements are connected to the selvedges and thus frequently to breakage of the mesh elements at these points.

After expansion the strip is flattened, and this is achieved by passing it under one or more plough-shaped plates and then through one or more sets of flattening rollers. It is found that the force that must be applied to the selvedges by the flattening rollers to substantially flatten them results in the outer edges of the selvedges becoming corrugated in the plane of the strip due to the tensional forces exerted on the selvedges by the mesh elements connected to them, and it is generally either at the stage that the selvedges are formed or at this flattening stage that many of the mesh elements connected to the selvedges fracture, due to the high tensile forces produced in them and the high degree of deformation to which they are subjected.

According to the present invention apparatus for expanding metallic strip inwardly from its edges to leave an unexpanded selvedge at each edge includes a lower fixed expander block whose edges converge in the intended direction of movement of the strip, an upper reciprocable expander block carrying two lines of expander punches whose cutting edges cooperate in use, with the edges of the fixed block to cut and expand those portions of the strip which extend over the edges of the fixed block and feed means adapted to incrementally advance the strip through the apparatus, the cutting edge and underside surface of the upstream punch in each line being at least partially of rounded section when seen in side view.

The inner edges of the selvedges are formed by the upstream punches, and during the cutting of these edges the selvedges are deformed to a shape which corresponds to the underside profile of these punches. By shaping the cutting edge and underside surface of the upstream punches so as to be rounded the selvedges will not be bent into a sharp angled corrugated form but into a rounded or rippled corrugated form. This reduces the angle through the which the selvedge are deformed by the upstream punches, and the deformation to which they must be subjected to flatten them again. In addition such rippled selvedges are more capable of bending and twisting.The resulting reduction of deformation and concomitant reduction of stress produced in the selvedges and the mesh elements connected to them substantially reduces the incidence of broken mesh elements.

In the preferred embodiment the cutting edge of the upstream punches have a central rounded portion when seen in side view with a linear portion on each side of the rounded portion. The rounded portion preferably has a radius of curvature of between 0.1 and 0.5 and preferably 0.3 of one mesh pitch. It will however be appreciated that it is not essential that the rounded portion of the cutting edge and underside surface of the upstream punches actually be of circular section, and other rounded shapes are possible since they too will reduce the deformation to which the selvedges are subjected. In an alternative embodiment the entire cutting edge of the upstream punches is of circular section.

Preferably the cutting edges and underside surface of the two punches adjacent the upstream punches are also at least partially of rounded section when seen in side view.

Preferably the rounded portion of the cutting edge of these punches is of circular section having a radius of curvature of between 0.4 and 0.8 and preferably 0.6 of one mesh pitch. Modifying the shape of the second punch in each line further reduces the distortion of, and stress induced in, the selvedges and the mesh elements connected to them.

Preferably each upstream punch is so constructed and/or positioned with respect to the punch adjacent to it that the length of the cut it forms is less than that formed by the punch adjacent to it.

The width of the selvedges is preferably 3 to 9 times e.g. 4 to 8 times and preferable 6 times that of the mesh elements.

Further features and details of the invention will be apparent from the following description of one specific embodiment which is given by way of example with reference to Figs. 5 to 7 of the accompanying drawings in which: Figures 5 and 6 correspond to Figs. 2 and 3; and Figure 7 is a plan view of part of a lead strip partially expanded by an expanding apparatus in accordance with the present invention.

The general layout of the expanding apparatus in accordance with the invention is similar to that described with reference to Figs. 1 to 4 and will therefore not be described again.

However, as seen in Fig. 5 the cutting edge 18' of the upstream punches 20' is radiused over its central portion when seen in side view, and on each side of this radiused portion is a flat portion 22' inclined upwardly to the sides of the punches. The cutting edge of the two adjacent punches is also radiused over its central portion (with a greater radius of curvature) and has upwardly inclined portions 22' at each end of the radiused portion.

Thus, in use, the selvedges 16' of the strip are deformed to correspond to the underside surface 22' of the upstream punches into a rippled form, and appears, as seen in side view, as shown in Fig. 6.

Fig. 7 shows a specific example of a partially expanded strip (whose direction of movement is to the right as seen in the drawing) in which the mesh pitch is 200mm. The axial length of each punch which actually performs the cutting is therefore about 1 9mm, the punches are spaced 30mm apart centre to centre and the strip is advanced 20mm at a time through the apparatus. The width of a mesh element 24' is about 1.5mum whilst that of the selvedge 1 6' is about 8mm.

The cuts 26' which define the inner edge of the selvedge 16' are formed by the upstream punches, whilst the cuts 28' are formed by the punches adjacent the upstream punches.

As may be seen the portions of the selvedges adjacent the cuts 26' are rippled, and their shape corresponds to the shape of the underside surface of the upstream punches. The upstream punches are dimensioned or positioned so as not to extend downwardly as far as the remaining punches, and the cuts 26' are therefore somewhat shorter than the other cuts, i.e. they are only 14mm long. This results in the meshes adjacent the selvedges being somewhat smaller, and the cross-sectional area of the metallic connection of the mesh elements to the selvedges being greater than that at the other nodes of the mesh structure. This increases the mechanical strength of the connection of the mesh structure to the selvedges, and thus reduces the risk of breakage at these points.

The cutting edge of the upstream punches has a radius of curvature of 1 2mm and the central portion of the cutting edge of the adjacent punches has a radius of curvature of 6mm. The rippling, twisting and bending of the selvedges which occurs is such that mechanical failure of the mesh elements at the points where they are connected to the selvedges is substantially eliminated.

Claims (7)

1. Apparatus for expanding metallic strip inwardly from its edges to leave an unexpanded selvedge at each edge including a lower fixed expander block whose edges converge in the intended direction of movement of the strip, an upper reciprocable expander block carrying two lines of expander punches whose cutting edges cooperate in use, with the edges of the fixed block to cut and expand those portions of the strip which extend over the edges of the fixed block and feed means adapted to incrementally advance the strip through the apparatus, the cutting edge and underside surface of the upstream punch in each line being at least partially of rounded section when seen in side view.

2. Apparatus as claimed in Claim 1 in which the cutting edge of the upstream punches have a central rounded portion when seen in side view and a linear portion on each side of the rounded portion.

3. Apparatus as claimed in Claim 2 in which the central rounded portion has a radius of curvature of between 0.1 and 0.5 of one mesh pitch.

4. Apparatus as claimed in any one of the preceding claims in which the cutting edge and underside surface of the two punches are at least partially of rounded section when seen in side view.

5. Apparatus as claimed in Claim 4 in which the rounded portion of the cutting edge and underside surface of the two punches adjacent the upstream punches is of circular section having a radius of curvature of between 0.4 and 0.8 of one mesh pitch.

6. Apparatus as claimed in any one of the preceding claims in which each upstream punch is so constructed and or positioned with respect to the punch adjacent to it that the length of the cut it forms is less than that formed by the punch adjacent to it.

7. Apparatus for expanding metallic strip substantially as specifically herein described with reference to Figs. 5 to 7 of the accompanying drawings.