Metal treatment – Process of modifying or maintaining internal physical... – Heating or cooling of solid metal
Reexamination Certificate
2000-05-26
2004-10-12
Ip, Sikyin (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
Heating or cooling of solid metal
C429S226000, C429S233000, C429S245000
Reexamination Certificate
active
06802917
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a process for improving the resistance to intergranular corrosion and cracking of perforated current collectors, in particular to the production of lead-alloy grids for use as the positive plates in a lead-acid battery. The process takes advantage of conventional processes employed to perforate flat metal sheet to form grid or mesh-type current collectors, to serve additionally as a bulk deformation treatment, which is then immediately followed by an applied heat-treatment and, optionally, subsequent quenching to yield a recrystallized microstructure in the metal which possesses significantly improved resistance to undesired corrosion and growth.
DESCRIPTION OF PRIOR ART
In the production of grid- or mesh-form current collectors of the kind used in electrochemical cell applications, e.g. for storage batteries, a flat metal sheet is typically perforated using a continuous process. An electrochemically active material is typically then pasted into the resulting perforated grid, the paste is flash cured using an in-line furnace and, subsequently, the continuous pasted grid structure is cut into individual battery plates.
A typical application of this conventional process is in the production of lead-acid batteries. For the purpose of simplification, the process specifically illustrated in what follows is directed to the production of lead-alloy grids for use in lead-acid batteries. However, similar methods are used in the manufacture of metallic current collectors for other electrochemical cells and batteries as well. Some of these are disclosed in the prior patents and applications described below, all of which are hereby incorporated by reference for their teachings relative to the manufacture of metallic current collectors.
Two-step processes are frequently used to prepare perforated current collectors using a continuous approach. In the first step, flat solid sheets are produced by a variety of strip casting or slab casting followed by rolling processes. The flat solid strips produced are typically wound into coils. Coils are typically stored until needed.
In the second step the strip coils are transferred to another process-line where the perforation and usually the active material pasting take place. This process generally starts with an uncoiler that unwinds the flat solid lead coils and feeds the strip into a perforation apparatus. Commonly used perforation techniques include reciprocating expanders, rotary expanders and grid punching systems. In the case of expanders the lead strip is slit and stretched to form a continuous expanded mesh. In the case punching is employed, typically rectangular coupons are punched out of the strip to create a continuous perforated grid-like sheet. The perforation processes apply mechanical stress to the lead foil by stretching and/or pressing the base material, but in all cases the overall strip deformation, as expressed by the ratio of the strip thickness before and after the perforation are kept under 10%, typically under 7.5%. The perforated strip created by any one of the listed processes travels downstream in the process to a paster, typically followed by a flash cure oven and is then cut into individual grids in tab blanker and plate dividers.
To enhance the longevity of non-consumable electrodes, current collectors and other metallic articles used in electrochemical cells, a variety of metal, metal alloys and composites have been developed. They include lead, copper, nickel, aluminum, iron, silver, zinc, lithium and their respective alloys. In many applications the environment in which the metallic articles are exposed to is highly corrosive and research is conducted to enhance the stability, e.g. by reducing the corrosion induced weight loss and growth experienced, particularly when the metallic article is exposed to oxidizing potentials and corrosive electrolytes. As many of the batteries in question are mass-produced at high speeds, continuous fabricating and processing of current collectors are becoming the manufacturing method of choice.
The prior art describes numerous methods for producing current collectors using continuous or semi-continuous processes:
Various technologies exist for producing a flat metal or metal alloy strip. They include horizontal casting processes as described by Geiger in U.S. Pat. No. 3,926,247 (1975) and Vincze in U.S. Pat. No. 5,462,109 (1995) in which a strip is cast on a chilled casting surface of a rotating drum from a pool of molten metal. Vertical casting processes, using a twin roll arrangement with an adjustable gap, are described by Folder in U.S. Pat. No. 6,003,589 (1999) and Romanowski in U.S. Pat. No. 5,518,064 (1996). Additional equipment suitable for the production of solid strips includes belt casters as described by Ashok in U.S. Pat. No. 5,131,451(1992). Numerous commercial processes exist where a slab or strip is reduced to size by sequential rollers. Prengaman in U.S. Pat. No. 3,953,244 (1976) describes stable wrought lead-calcium-tin alloy sheet which is prepared by casting, cold working the casting, preferably using rolling to one quarter of the original thickness, within two to three days after casting and heating aged work pieces sufficiently to dissolve the precipitated calcium phases.
Various processes have been described to perforate such a continuous strip to form a suitable current collector. They include reciprocating expanders such as described by Daniels in U.S. Pat. No. 3,853,626 (1974). In this process a solid ribbon or strip of lead is fed into a continuous, in-line, guillotine-type, dual expansion machine and therein expanded along its longitudinal edges to form two reticulated portions and leaving a central unexpanded portion from which a grid, header and lug are subsequently formed. The reticulated portions are uniformly stretched in a direction perpendicular to the central portion by embossed forming rolls and matched counter rolls. Finally, the reticulated portion is rolled to twist and flatten the nodes joining skeletal elements.
Tsuda in U.S. Pat. No. 3,959,016 (1976) describes a manufacturing method for a lead-antimony alloy-grid plate for batteries comprising the fabrication of a rolled lead-alloy foil, stepwise press-punching the foil to obtain a perforated plate and hardening the plate using heat-treatment. In this method, the hardening of the lead alloy is accomplished either by preparing the rolled lead-alloy plate through a hot rolling process or by carrying out a heat-treatment before or after the press-punching process to increase the hardness of the lead grid plate for the purpose of attaining an increased strength to facilitate the battery assembly and to enable a reduction of strip thickness while maintaining dimensional tolerance and strength. Tsuda goes through great effort to avoid or at least minimize any deformation of the remaining grid strands, typically induced by punching processes, and achieves his objective by employing a multi-step punching process. The rolled lead alloy plate is passed through a funnel furnace at 210 to 220° C. for between 30 and 90 minutes, optionally water quenched, and hardened by a subsequent natural aging process over 24 hours.
Hug in U.S. Pat. No. 4,151,331 (1979) discloses a lead-acid battery grid having a network of integrally connected strands of lead in which a portion of the strands are offset and project from one face of the grid while a second portion of strands projects and are offset to the other opposed face of the grid. The perforated structure is formed from a lead foil by a punching process. Hug indicates that it is known that lead-acid battery grids are formed from lead sheets by slitting and stretching to form an-expanded mesh. He indicates that the expansion process involves considerable cold-working of the lead which leads to corrosion of the grid, and is therefore undesirable. Hug goes further stating that perforated lead-grids, in which a flat lead sheet of substantially non-distortable thickness is perforated, stamped, rolled or slit to form a
Limoges David L.
Lin Peter K.
Palumbo Gino
Tomantschger Klaus
Integran Technologies Inc.
Ip Sikyin
Ridout & Maybee LLP
LandOfFree
Perforated current collectors for storage batteries and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Perforated current collectors for storage batteries and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Perforated current collectors for storage batteries and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3299395