Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D25/00—Special casting characterised by the nature of the product
  • B22D25/02—Special casting characterised by the nature of the product by its peculiarity of shape; of works of art
  • B22D25/04—Casting metal electric battery plates or the like
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C11/00—Alloys based on lead
  • C22C11/02—Alloys based on lead with an alkali or an alkaline earth metal as the next major constituent
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C11/00—Alloys based on lead
  • C22C11/06—Alloys based on lead with tin as the next major constituent
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/64—Carriers or collectors
  • H01M4/82—Multi-step processes for manufacturing carriers for lead-acid accumulators
  • H01M4/84—Multi-step processes for manufacturing carriers for lead-acid accumulators involving casting
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/10—Energy storage using batteries

Definitions

• the present invention relates to strip material of a lead alloy, and to a method of making such strip material for use in the manufacture of electrode grids for lead acid storage batteries.
• BACKGROUND ART The lead acid battery industry is currently beginning to make greater use of expanded lead electrodes and this technology permits the use of a continuous line in which lead strip is expanded, punched, pasted and then cut up into individual plates.
• a number of methods of producing lead alloy strip is known, such as casting followed by rolling, however none of these is ideally suited to continuous production of strip in a line producing battery electrodes.
• a strip of lead or lead alloy has a thickness of at least 0.25mm and a grain structure which is substantially homogeneous across its width and which is elongate in a direction through the thickness of the strip. It has been found that such strip material is particularly suitable for making lead acid battery electrode grids in that it may be easily handled and expanded, and its tensile strength is such that growth of the positive plates in service is not excessive.
• the invention also embraces a method of producing such a strip and thus according to a further aspect of the present invention a method of producing a strip of lead or lead alloy comprises the steps of casting, e.g. centrifugally casting, a substantially circular section billet of lead alloy such that the grain structure of the resultant billet is substantially homogeneous across its width at any particular radius and peeling a strip of at least 0.25mm thickness from the circu rence of the Billet.
• the billet is formed by centrifugal casting it may be ensured that the grain structure is substantially homogeneous across its width, by introducing molten metal into the mould at an appropriate rate and rotating the mould at an appropriate speed.
• th.e lead alloy contains not more than 0.13%, e.g. 0.06 - 0.1% e.g. 0.08 - 0.09% calcium by weight, and preferably also contains not more than 0.99%, e.g. 0.5 - 0.9%, e.g. 0.6 - 0.8% tin by weight and optionally also up to 0.015%, e.g. 0.007 to 0.01% aluminium by weight.
• the cast cast billet has a thickness substantially less than its diameter.
• the strip material desirably has a tensile strength of more than 35 Newtons/mm 2.
• the billet may have a diameter of between 50 and 100 cms, e.g.
• the billet may have a thickness approaching or even exceeding its diameter.
• the billet may have an uneven surface coated with dross when removed from th.e mould thus the method preferably includes the step of removing a layer of material for instance by machining off 1 to 5mm or even more e.g. 3mm from each planar face so as to expose clean metal.
• the billet be cast such that its grain structure is substantially homogeneous across its width at any particular radius otherwise even satisfactory peeling of the strip is not possible.
• the billet is formed by centrifugal casting
• molten lead alloy is introduced into the mould in a number of separate charges each of which is added before the previous charge has fully solidified and the total casting operation may last between 10 and 30 minutes. If the mould is rotated too slowly voids may occur and molten metal may "run back" and the grain structure may not be sufficiently homogeneous,
• the mould is, therefore preferably rotated at at least 100 r.p.m.. e.g. at between 150 and 250 r.p.m.
• Centrifugal casting basically involves gradually pouring molten metal into the centre of a mould rotating at high speed about a vertical axis. The metal is forced against the outer wall of the mould by the centrifugal force and it is from this wall that the metal solidifies. Any voids that occur during solidification. will do so at the solid/liquid interface and are immediately forcibly filled by fresh liquid. Thus all the shrinkage appears at the inner face of the annular billet.
• the rapid rate of solidification of the metal coupled with the high, degree of turbulence ensures that the solid metal has a fine substantially homogeneous grain structure.
• the forces generated also accelerate the separation of non-metallic inclusions and precipitated gases.
• the strip When the strip is peeled from the billet it is the peeling operation itself which distorts the grain stuct ⁇ re and leads to the grains being elongated in a direction having a component through, the thickness of the strip. The reason for this is that the strip decreases in length, as it is being peeled.
• two marks that were placed 60cms apart on the peripheral surface of the billet were only 37 cms apart on the peeled strip.
• the shrinkage or compression of the strip at the point of peeling leads to similar shrinkage or compression of the grain structure in the plane of the plate.
• the net effect in the peeled strip is that the grain structure appears elongate in a direction perpendicular to the plane of the strip, though in truth it is compressed in the plane of the strip. It will be appreciated that for this reason if the cutting tool is set to cut about 1mm into the billet the peeled strip actually obtained will be thicker e.g. of the order of 2mm thick.
• the peeled strip has a smooth surface on the side which was contacted by the cutting tool, but has ripples or corrugations extending in a direction transverse to its length on the side remote from the cutting tool caused by the contraction of the strip which occurs at the point of peeling.
• a strip having one rough side does not lend itself to easy mechanical handling, and it is also more prone to failure during expansion into a grid. Furthermore the rough surface leads to increased corrosion of the battery plates, and a greater likelihood of grain Boundary cracking.
• the method preferably includes the step of rolling the peeled strip from a thickness of say 2 to Hmm down to 0.5 to 1.5mm in one or more passes. This distorts but does not radically alter the grain structure and renders the strip moresatisfactory for use in batteries.
• the rolling operations lead to an increase of between 10 and 30% typically 20% of the tensile strength, of the strip, e.g. to in excess of 45 Newtons/mm 2 .
• the reason for this is not fully understood, however it is believed that the rolling induces either work hardening or an accelerated age hardening, process.
• FIGURE 1 is a plan view at X 80 magnification of the grain structure of a strip peeled from a centrifugally cast billet in accordance with the present .invention; and FIGURE 2 is a cross-sectional elevation at X
• the mo ⁇ ld When the mo ⁇ ld was cooled it was disassembled and the annular billet, having a central hole whose diameter was between 15 and 30cms, was removed. It will be appreciated that the hole has no particular importance and it is therefore made as small as possible.
• the billet was void-free and had a substantially homogeneous grain structure across its width.
• a centre-piece for securing the billet to a chuck of a lathe was then secured in the central hole by any convenient means, such as forcing a square section rod into the round hole or bolting on a face plate or inserting an expanding mandrel into the hole. Dross and surface irregularities were then removed from each of the end faces of the billet until clean metal was reached. Typically about 2mm of material was removed from each face and the amount should not exceed 3.5mm.
• the billet was secured to the chuck of a lathe by means of the central bar and rotated at such a speed that its linear peripheral speed was between 0.1 and 0.5m/s, typically 0.25m/s.
• a cutting tool having a width, of about 19 cms was then presented to the peripheral edge of the rotating billet and set to move radially inwards at a constant speed such. that the thickness of the peeled strip remains constant, for instance between 1 and 4mm.
• the angular speed of the lathe was steadily increased as its diameter decreases so as to maintain its linear peripheral speed substantially constant.
• the peeled strip had one smooth side and one rough side, and was heated up to a temperature of about 80°C by the shearing action of the cutting tool.
• the peeled strip was withdrawn at a speed substantially equal to the linear peripheral speed of the billet and wound onto a take-up reel.
• the take-up tension used was 11 kg force, and it was found that this tension can slightly change the grain structure of the strip. However the change produced was not significant and the take-up tension was found not to be critical.
• the strip had a grain structure which was substantially homogeneous across its width as seen in Figure 1 and which was elongate through the thickness of the strip as seen in Figure 2, and had a tensile strength of between 40 and 45 N/mm 2 .
• the tensile strength (which largely correlates with the growth of the positive battery plates in service) at this stage would be satisfactory for battery plates since it has been found that a strength in excess of 35 N/mm 2 is adequate.
• Such strip cannot be handled very easily in the preferred subsequent expanding process and is subject to an increased rate of corrosion in the battery environment..
• the strip. was therefore subsequently rolled in one or more operations to reduce its thickness to between 10 and 80% of its original thickness, typically to 0.9mm. The rolling smooths the roughened side of the strip rendering it easier to handle and less subject to corrosion.
• the tensile strength was increased by about 20%, typically to between about 50 and 55 N/mm 2 .
• the strip was now expanded into a grid, punched pasted with active electrode material and cut into individual battery plates.
• the lead alloy of a Battery electrode desirably has a tensile strength of 35 N/mm 2 or more, and the method described above produces a strip having such a tensile strength, even Before the rolling step.
• the strip may nevertheless have an adequate tensile strength and corrosion resistance in the Battery environment to Be immediately processed into Battery electrodes.
• the strip according to the invention finds applicaBility as a material from which lead acid battery electrodes may be made by punching to perforate form or slitting and expanding to mesh. form.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• General Chemical & Material Sciences (AREA)
• Cell Electrode Carriers And Collectors (AREA)

Priority Applications (9)

Applications Claiming Priority (5)

Publications (1)

Family

ID=27423321

Family Applications (1)

Country Status (9)

Cited By (1)

Citations (4)

• 1979
  • 1979-06-29 DE DE792953733A patent/DE2953733A1/de not_active Withdrawn
  • 1979-06-29 WO PCT/GB1979/000108 patent/WO1981000068A1/en unknown
  • 1979-06-29 JP JP50095679A patent/JPS56500787A/ja active Pending
  • 1979-06-29 AU AU48540/79A patent/AU4854079A/en not_active Abandoned
  • 1979-06-29 ZA ZA793247A patent/ZA793247B/xx unknown
  • 1979-06-29 GB GB8105731A patent/GB2069002A/en not_active Withdrawn
• 1981
  • 1981-01-26 EP EP79900680A patent/EP0031320A1/en not_active Withdrawn
  • 1981-02-20 SE SE8101152A patent/SE8101152L/sv unknown
  • 1981-02-27 DK DK91181A patent/DK91181A/da unknown

Patent Citations (4)

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