FIELD OF THE INVENTION

[0001 ] The invention relates generally to methods of making battery plates for lead- acid batteries, and more particularly to methods of making battery plates for lead-acid batteries that improve paste adhesion and the service life of the batteries.

CROSS REFERENCE TO RELATED APPLICATION

[0002] This application claims priority to co-pending US provisional application No. 61 /569,816, filed 13 December 201 1 , entitled "A METHOD OF MAKING BATTERY PLATES FOR LEAD-ACID BATTERIES", which is entirely incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0003] It is well known that formation efficiency can be improved by increasing the adhesion between the paste and the grid. The increased adhesion between the grid and the paste provides for improved interfacial contact between the grid and the paste, thereby improving current flow between the grid and paste. Accordingly, certain efforts to improve battery formation efficiency have focused on improving the adhesion between the battery grids and the paste.

[0004] When applying battery paste to a grid, an oval-shaped wire such as that in a book mold cast grid allows the paste to flow around the wire. The rough surface and the sharp angle of the wires provide a mechanical graft and interlock of paste particles. Efforts have been made to create similar results of a book mold cast grid in a punched grid by performing a second operation to deform the cross-section of the wire after the punch operation. In this punch/deformation process, material is first punched from a strip of material to form a grid comprising a plurality of wires. The wires are then deformed such that the wire has a non-rectangular cross-section. While this punch/deformation process can help with paste adhesion, it requires additional equipment and additional unit operations compared to, for example, a punch process. [0005] Accordingly, a need continues to exist for methods of punching and reforming openings in battery plates for lead-acid batteries with a single punch that improve paste adhesion.

SUMMARY OF THE INVENTION

[0006] Disclosed herein are methods of punching and reforming openings in battery plates for lead-acid batteries with a single punch that improve paste adhesion.

[0007] In one embodiment, a method of making battery plates for lead-acid batteries comprises providing a strip of material comprising lead; and punching material out of the strip to form a grid comprising wires having a non-rectangular cross-sectional shape by utilizing a die set comprising a plurality of male die components and female die components, wherein each of the male die components comprises a first cross-sectional shape in a first portion and a second-cross sectional shape in a second portion.

[0008] In one embodiment, a method of making battery plates for lead-acid batteries comprises providing a strip of material comprising lead; punching material out of the strip to form a grid comprising wires having a non-rectangular cross-sectional shape by utilizing a die set comprising a plurality of male die components and female die components, wherein each of the male die components comprises a first cross-sectional shape in a first portion and a second-cross sectional shape in a second portion, the first cross-sectional shape is generally rectangular and the second cross-sectional shape has a sloping outer surface; and applying paste to the strip.

[0009] The above-described and other features will be appreciated and understood by those skilled in the art from the following detailed description, drawings, and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Referring now to the figures, which are exemplary embodiments, and wherein like elements are numbered alike: [001 1 ] Fig. 1 is a perspective view of a punch die set of the present invention;

[0012] Fig. 2 is a cross-sectional view of the punch die set of Fig 1 ;

[0013] Fig. 3 is a front view of one male die component and a corresponding female die component in the open position;

[0014] Fig. 4 is a perspective view of the male and female die components in the open position;

[0015] Fig. 5 is a perspective view of the male and female die components in the closed position;

[0016] Fig. 6 is a cross-sectional view of the male and female die components in the closed position;

[0017] Fig. 7 is a top view of a continuous strip of material where a first plurality of holes have been punched in a first stage, a second plurality of holes have been punched in a second stage, and where non-rectangular wire segments are formed between adjacent first and second holes; and

[001 8] Figs. 8A and 8B are cross-sectional views of non-rectangular wire segments taken along lines A-A and B-B, respectively.

DETAILED DESCRIPTION OF THE INVENTION

[0019] Referring now to Figs. 1 -5, a punch die set generally designated as 100 is illustrated. The punch die set 100 is used to make battery grids that when pasted with active materials are used as battery plates in lead acid batteries. The upper male die portion 102 and the lower female die portion 104 of the punch die set 100 function with one another to punch and reform holes in a strip of lead that is cut into a plurality of grids. The punch die set 100 comprises a plurality of male die components 1 12 and female die components 1 14. One male die component 1 12 and one female die component 1 14 of the male and female die portions 102, 104, respectively, form one hole or opening in the grid.

[0020] Further, as is readily understood in the art, the grid pattern design varies widely depending on the application and is not intended to limit the invention disclosed herein. The punch die set 100 is advantageously used to form a non-rectangular cross sectional shape on the grid wire or segment that aids with paste adhesion. The resulting plates (when pasted and cured) can be used in any number of lead-acid batteries including, but not limited to, flooded batteries, absorbed glass mat (AGM) batteries, and gel batteries.

[0021 ] The male die component 1 12 has a first portion 121 with a first cross- sectional shape and a second portion 122 with a second cross-sectional shape. The first portion 121 of the male die component 1 12 cooperates with the female die component 1 14 to form a hole in the lead strip by punching out material. During a punch, a gap 1 1 8 is defined between opposing surfaces of the male and female die sets 1 12, 1 14 based on the thickness of the strip of material passing though the die set 100. The second portion 122 of the male die component 1 12 cooperates with the female die component 1 14 to shape the material in the gap 1 18 corresponding with the inner perimeter or edges of the hole. During a punch of a hole, part or all of the hole itself is substantially simultaneously shaped by the male and female die components 1 12, 1 14. In one or more embodiments, the female die component 1 14 may have a complementary positive or raised portion 144 to shape the side of the strip of material in the gap 1 18 defined between the male and female die component 1 12, 1 14.

[0022] In one or more embodiments the continuous strip of lead is feed into a progressive die press having multiple stages of operation. As best shown in Fig. 6, a first plurality of holes 132 is punched into the continuous strip of lead. The first plurality of holes 132 are sufficiently spaced apart from one another so that when the portion of the lead strip is advanced to the next stage a second plurality of holes 134 is punched such that holes 132 and holes 134 are intermixed or alternately spaced from one another. A hole 132 adjacent to a hole 134 defines a grid wire 136 there between. The shape of each grid wire 136 is formed by the shape of the gaps 1 18 defined between a pair of adjacent die components 1 12, 1 14. The punch die set 100, in a single step, both removes material and shapes the material to form a grid with a plurality of wires 136 having non-rectangular cross-sectional shapes.

[0023] Cross sections A-A and B-B of grid wires 136 are shown in Figs. 7A and 7B, respectively. The cross sections A-A and B-B are the same although each of the grid wires 136 shown in Figs. 7A and 7B are oriented differently. The cross sections are preferably the same but may be different based on the shapes of the male and female die components 1 12, 1 14. The sizes of the wires 136 may be different as well. [0024] As illustrated in Fig. 3, for example, a grid wire 200 with a generally rectangular cross sectional shape can be formed utilizing the first portion of the die component 12. The second portion of the die component 12 can then be used to deform the rectangular cross-sectional shape into any number of cross-sectional shapes (e.g., grid wires 202 and 204 in Fig. 3). In one embodiment, the second cross-sectional shape 16 can have a sloping outer surface. The angle of the slope can vary depending on the desired application. In one embodiment, the slope is 30 degrees to 60 degrees, more particularly 30 degrees to 45 degrees. In other embodiments, the second cross-sectional shape 16 has a curvilinear outer surface.

[0025] The use of the punch die set 100 to form plates for a battery as described above constitutes an inventive method of the present invention in addition to the punch die set 100 itself. In practicing the method of punching a hole in a strip of material and forming the inner edge or perimeter of the hole with the male and female die components 1 12, 1 14 described above, the steps include providing a strip of material comprising lead, punching material out of the strip, and forming an edge to define wires having a non-rectangular cross- sectional shape. The method may also include applying paste to the punched strip. It is to be understood that additional operations may be performed between the process steps mentioned here or in addition to those steps.

[0026] The provided strip of material comprises lead, but as will be appreciated by those skilled in the art, the material can be 99.99 percent pure lead or it can be an alloy comprised of other metals. Suitable metals that can be alloyed with lead include, but are not limited to, calcium, tin, silver, and bismuth to name j ust a few. It is believed that the punch die set 100 works particularly well when the material is "soft." The lead alloy can have a microhardness, as measured by a Vickers hardness test, Hv value of 10 to 30. A person of skill in the art can readily determine the optimum hardness of the alloy for use in this method without undue experimentation. Additionally, it is to be noted that the strip of material may be formed by a continuous casting process or a rolling process depending on which yields the best grain structure for the particular application.

[0027] In one embodiment or more embodiments, material is punched out of the strip to form a grid comprising wires having a non-rectangular cross-sectional shape. The grids are punched to shape while maintaining a continuous strip. The grid shapes result from a progressive punching operation, i.e., features will be added to the grid through several punching operations.

[0028] The punched strip is processed to add active material (paste) and a pasting substrate (e.g., paper, glass, polymeric, etc.) to keep plates from sticking together during subsequent stacking operations. The strip is cut into individual grids. In an alternative embodiment, the punched strip can first be cut into individual grids and then processed to add active material (paste). The pasting and cutting operation is not intended to limit the disclosed invention.

[0029] Additionally, to further increase paste adhesion, the grids themselves can optionally be shot blasted to provide a desired surface roughness. In one example, the grids may be shot blasted according to any material removing or deforming process. More particularly, the grids may be shot blasted after the grid is formed but before the paste is applied. As an example, any suitable shot blasting equipment may be used to provide the controlled surface roughness on any of the grid surfaces with any suitable particles, such as particles composed of lead oxide, silica or sand, metal or glass balls, granules of silicon carbide or the like. In another example, the grids may be sprayed according to any material deposition process. More particularly, the grids may be processed according to plasma processing technology.

[0030] While the invention has been described with reference to an exemplary embodiment, it will be understood by those skilled in the art that various changes can be made and equivalents can be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications can be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.