MODIFIED SAFETY VENTED COVER FOR SEALED CONTAINER AND METHOD OF MANUFACTURING SAME

Abstract: A method of making a safety vent in a cover (2) for a hermetically sealed container and a product comprising a unique container cover for a hermetically sealed container including printing a material strip with a masking resist pattern having an uncovered channel (7) area corresponding to a safety vent area for the container cover, etching the uncovered area to a preselected material thickness, and press forming (7l) the etched area to provide a safety vent membrane in the cover capable of withstanding a preselected pressure before rupture.

Description: The present invention relates to sealed container covers and, more particularly, to a method of making safety vents in covers for hermetically sealed containers and a novel cover for such a container including a safety vent membrane. This patent application constitutes a continuation-in-part of patent application Serial No. 782048, filed September 30, l985, both applications being assigned to common assignee, Emerson Electric Company, 8000 West Florissant, P.0.Box 4000, St. Louis, Missouri 63l36. It is generally well known to provide hermetically sealed containers with a rupturable safety vent membrane in the container body so that if gas pressures develop within the container beyond a predetermined limit, the membrane ruptures to permit release of gas, avoiding uncontrollable container explosion or disintegration and possible personal and property damages occasionally associated therewith. Several such arrangements as taught by the prior art include: a pressure frangible safety device as disclosed in U.S. Patent No. 3,6l7,386 issued to Robert J. Bosben on November 2, l97l; a reduced area of container wall thickness designed to rupture in response to predetermined circumferential stresses occurring within the container, as disclosed in U.S. Patent No. 4,l75,l66, issued to M.G. Rosansky on November 20, l979; a cruciform shaped incision in a sealed container of V-shaped cross-section as disclosed in U.S. Patent No. 4,256,8l2, issued to K. Tamura, et al, on March l7, l98l; and, pressure relief safety membranes as disclosed in U.S. Patent No. 4,476,200, issued to C. Markin, et al, on October 9, l984. The formation of such safety vents in the past has generally been accomplished by mechanical means such as by the single step of stamping. Such past forming means have caused stress corrosion and non-uniformity in metal thickness and metal gain structure which, in turn, has resulted in non-uniform pressure sensitivity and limited pressure responsively characteristics because of stress corrosion, metal crystallization and work hardening problems. The present invention recognizing the importance of such uniformity in thin safety membranes in potentially explosive sealed containers and further recognizing the importance of carefully controlling the dimension and pressure sensitive characteristics of such membranes so as to be uniformly responsive to predetermined low pressures provides a unique and novel method of manufacturing safety vent membranes in covers for hermetically sealed containers in an efficient, straightforward and economical manner to permit mass production of a novel and inventive product without sacrifice of desired very low critical pressure responsive uniformity and without excessive metal crystallization and work hardening that would occur through stamping alone. Although the broad use of producing tearing lines in containers by etching is old, as disclosed in U.S. Patent No. 3,723,269, issued to E. Hofling on March 27, l973, the present invention, recognizing the desirability and importance of uniformity in low pressure sensitivity and low pressure responsiveness of safety vent membranes for sealed containers without excessive work hardening and crystallization of material provides a new and novel method and a unique product which affords such low pressure sensitivity and responsiveness in a manner previously unknown in the art. Various other features of the present invention will become obvious to one skilled in the art upon reading the disclosure set forth herein. More particularly, the present invention provides a method of making a safety vent in a cover for a hermetically sealed container comprising: feeding a container cover blank into a first groove forming zone to etch a first grooved area therein of a uniform preselected remaining material thickness capable of with standing a first preselected mean pressure; and, feeding the etched cover blank into a second groove forming zone to pressure form a second grooved area within the etched groove area of uniform preselected remaining material thickness capable of withstanding a second preselected mean pressure below the mean pressure limitation of the etched grooved area. In addition, the present invention provides a cover for a hermetically sealed container, the cover having a first grooved area etched therein to extend in spaced relation from the surrounding peripheral edge thereof with a preselected remaining material thickness and breadth to provide a first safety vent membrane capable of withstanding a first preselected mean pressure before rupturing; and a second grooved area formed in the etched grooved area to provide a safety vent groove capable of uniformly responding to and withstanding a preselected mean pressure lower than the first preselected mean pressure before rupturing. It is to be understood that various changes can be made by one skilled in the art in the several steps of the method and in the several parts of the product disclosed herein without departing from the scope of spirit of the present invention. For example, the etching step, the pressure forming step, the container cover material, the rupture limits and geometry of the safety vent, all can be changed by one skilled in the art to obtain desired results without departing from the inventive scope or spirit of the disclosure herein. Referring to the drawing which discloses one advantageous embodiment of the present invention: Figure l is a flow diagram setting forth schematically the several steps involved in carrying out the inventive process; Figure 2 is an enlarged plan view of a portion of a strip of material which has been subjected to the inventive process of Figure l; Figure 3 is a further enlarged cross-sectional view of the material of Figure 2 taken in a plane passing through line 3-3 of Figure 2; and, Figure 4 is a perspective view of an inventive cover for a hermetically sealed container, further disclosing a central aperture therein. Referring to Figure l of the drawing, a strip 2 of material is fed from a supply zone 3 where it can be stored in the form of a coil to a printing zone 4. The strip 2 of coiled material can be any one of a number of known materials used in the manufacture of covers for hermetically sealed containers, which is responsive to the hereinafter described controlled etching and press forming process and, in the manufacture of battery covers such as those utilized for hermetically sealed batteries of the button type, a suitable metallic alloy such as cold rolled alloyed carbon steel (for example "Cl0l0") having a thickness in the range of 0.008 to 0.06 inches and, advantageously, approximately 0.0l0 inches plus or minus 0.00l inches can be used. It is to be understood that prior to carrying out the etching and press forming process, an appropriate cleaning and degreasing of the metallic alloy can be accomplished in a satisfactory cleansing and degreasing bath (not shown). In the event a metallic steel alloy strip is used, as in the example hereinafter described, a suitable bath using a caustic cleansing agent would suffice. In printing zone 4, opposed printing rolls 6, frequently or continuously treated with a suitable masking resist agent or etching ground which can be selected from appropriate chemical materials in accordance with the material to be etched and the subsequent chemicals to be used in the etching process, mask all surfaces of the strip of material not to be etched with an appropriate etching resist coating, for example, a synthetic resin capable of resisting the particular etching step to be employed. The unmasked portion of the strip of material to which no resist coating has been applied in printing zone 4 by rolls 6 can be in any one of several geometric pattern forms in accordance with the present invention. In the embodiment of Figures 2 and 3, the geometric pattern includes spaced uncovered channel areas in the form of circular arcs 7 of less than 360 degrees and of preselected breadth, with a portion of each otherwise complete circle being masked to provide a retention portion. In the embodiment of Figures 2-4, each of the circular or horse-shoe shaped arcs 7 surrounds an uncovered hole defining central area 8, the arcs 7 being on opposite surfaces of material strips 2 in opposed mirror image relationship, as described in detail in parent application Serial No. 782,048 and as can be noted in the cross-sectional view of Figure 3. It of course is to be understood that the present invention can be adapted to other configurations, such as, but not limited to, those which are set forth more fully in the parent application. In accordance with the inventive process and again referring to Figure l, after strip 2 has been suitably masked with a resist coating in the manner above discussed, strip 2 is fed along spaced idle rollers l0 through an etching zone l2, to etch the first grooved areas 7 thereon of uniform preselected remaining material thickness and breadth capable of withstanding a first preselected mean pressure, a rinsing zone l3, a lubricating zone l4, then into a press forming zone, such as coining zone l5 where second grooves 7′ are press formed or are formed by working the material into plastic flow within etched grooves 7, the grooves 7′ being of preselected remaining material thickness and breadth capable of withstanding a preselected mean pressure below the mean pressure limitation of grooves 7. It is to be noted that grooves 7′ can be formed in any one of a number of cross-sectional shapes and in Figure 3, the grooves 7′ are shown in "V"-cross-section on one side of strip 2 and of trunca ted cross-section on the other side of the strip. Once grooves 7 have been properly formed with grooves 7′ in zone l5, strip 2 is fed to a further stamping or forming zone l6 where individual container covers l7, such as disclosed in Figure 4, are formed. It is to be understood that strip 2, after passing through rinsing zone l3, could be again coiled for subsequent treatment elsewhere. It, also, is to be noted that various types of rims 20 can be formed on covers l7 or rims can be eliminated, if so desired. In passing through zones l2,l3 and l4, strip 2 is fed along suitable idle rollers l0, as above noted. In etching zone l2, strip 2 can be fed through a suitable acid etching bath, such as ferric chloride if the material to be etched is a steel alloy. The density and temperature of the etching bath and even the number of baths can be controlled to avoid gas bubbling. Also, such parameters as the rate of feed or residence time of the strip within the bath or baths, the acidity concentrations of the bath and bath temperatures are all carefully controlled so that the etching depth and thus the thickness of the material is carefully predetermined and maintained uniform along the unmasked surfaces. For example, when a steel alloy in the range of 0.008 to 0.06 inches thickness and advantageously of 0.0l0 inches is used, the etching of the first grooves 7 is controlled to provide a uniform remaining material thickness in the range of 0.0025 to 0.0035 and advantageously 0.003 inches. The press forming of said second grooves 7′ is controlled to provide a uniform remaining material thickness within grooves 7 in the range of approximately 0.0005 to 0.002 inches. It is to be understood that advantageously, when battery covers for hermetically sealed containers are being processed, the depth of etching of said first grooved area is so controlled as to leave a preselected remaining material of thickness capable of withstanding a preselected pressure up to 500 pounds per square inch within the sealed containers of which such cover s form a part. Forming the second grooved area within the first groove is so controlled to leave second safety groove within the first membranes so as to be capable of uniformly responding to and withstanding a preselected pressure in a range up to 400 pounds per square inch. As previously described, once strip 2 has been properly etched in etching zone l2, it is then fed through rinsing zone l3. In the inventive embodiment of Figure l, rinsing zone l3 can include three stages, namely, a neutralizing stage l8, a resist stripping stage l9 and a washing stage 2l. The neutralizing stage l8 can include a bath of suitable caustic or alkaline solution such as sodium hydroxide. The stripping stage can include an appropriate acidic bath depending upon the chemistry of the mask resist coating applied to printing rolls 6 in printing zone 4 and the washing stage 2l can be a plain tap water bath. From the last stage of rinsing zone l3, strip 2 can be fed to a suitable oil lubricating zone l4 before it is fed into press forming zone, such as coining zone l5 and then to an overall stamping zone l6 to form covers l7 from strip 2. As in etching zone l2, the residence times and bath concentrations in the rinsing zone l3, stages l8,l9 and 2l can be controlled in accordance with the results desired. As aforenoted, it is to be understood that various changes can be made in the several steps of the method and product disclosed without departing from the invention. For example, other covers besides those for hermetically sealed containers can be so manufactured and other container materials besides steel alloys can be used in the inventive process and the etching and press forming treatments and channel geometrics can be varied to provide safety membranes which will accommodate other predetermined pressures for containers.

Claims: 1. A method of making a safety vent in a cover for a hermetically sealed container comprising: feeding a container cover blank into a first groove forming zone to etch a first grooved area of uniform preselected remaining material thickness capable of withstanding a first preselected mean pressure; and, feeding said etched cover blank into a second groove forming zone to pressure form a second grooved area within said first etched grooved area of uniform preselected remaining material thickness capable of withstanding a second preselected mean pressure below the mean pressure limitation of said etched first grooved area. 2. The method of claim l, wherein said second grooved area is press formed by a coining step. 3. The method of claim l, wherein said first grooved area is formed by a series of etching steps including mask printing a preselected resist pattern with an uncovered area corresponding to said first grooved area and control etching said uncovered area to uniform preselected breadth and remaining material thickness. 4. The method of claim l, wherein said first grooved area and said second grooved area therein are formed in said cover to be on the outer side of said container. 5. The method of claim l, the forming of said first grooved area including forming mirror image grooves on both faces of said cover blank. 6. The method of claim l, wherein said first grooved area and said second grooved area therein are formed in said cover to be on the inner side of said container. 7. The method of claim l, said container cover blank comprising a steel alloy in the range of approximately 0.008 to 0.06 inches thickness with the formation of said first grooved area being controlled to provide a uniform remaining material thickness in the range of approximately 0.0025 to 0.0035 inches and the formation of said second grooved area being controlled to provide a uniform remaining material thickness in said first grooved area in the range of approximately 0.0005 to 0.002 inches. 8. A method of making a safety vent in a cover for a hermetically sealed container comprising: feeding a container cover blank of steel alloy material in the range of approximately 0.008 to 0.06 inches thickness into a first groove forming zone including a printing subzone, an etching subzone and a rinsing subzone; printing said container cover blank while in said printing subzone on both surfaces therein with a masking resist pattern having an uncovered channel area to correspond to a safety vent membrane area; feeding said masked printed container cover blank to said etching subzone; subjecting said container cover blank while in said etching zone to a controlled etching process to etch said uncovered channel area on both surfaces to form a first grooved area and to leave a uniform preselected remaining material thickness in the range of approximately 0.0025 to 0.0035 inches which serves as a first safety vent membrane in said cover capable of withstanding a first preselected mean pressure before rupturing; feeding said etched grooved cover through said rinsing subzone to remove said resist and etching materials; feeding said grooved cover blank into a second groove forming zone; and, coining said etched area on both surfaces of said cover of said container to form a second grooved area in said first grooved area providing a uniform remaining material thickness in said first grooved area in the range of approximately 0.0005 to 0.002 inches. 9. A cover for a hermetically sealed container having a first grooved area etched therein to extend in spaced relation from the surrounding peripheral edge thereof with a preselected remaining material thickness to provide a first safety vent membrane capable of withstanding a first preselected mean pressure before rupturing; and, a second grooved area pressure formed in said etched grooved area with a preselected remaining material thickness to provide a safety vent membrane capable of uniformly responding to and withstanding a second preselected mean pressure lower than said first preselected mean pressure before rupturing. l0. The container cover of claim 9, said first grooved area being chemically etched in said cover in mirror image relation on both surfaces thereof. 11. The container cover of claim 9, said second grooved area within said first grooved area being coined therein on both surfaces of said cover. 12. The container cover of claim 9, said container cover being a steel alloy in the range of approximately 0.008 to 0.06 inches thickness with said first safety vent membrane having a uniform remaining material thickness in the range of approximately 0.0025 to 0.0035 inches and said second safety vent membrane having a uniform remaining material thickness in the range of approximately 0.0005 to 0.002 inches. 13. A circular steel alloy battery cover for a hermetically sealed lithium battery container, said cover having a thickness in the range of approximately 0.008 to 0.06 inches and having opposed chemically etched grooves therein in the form of mirror image circular arcs of less than 360° spaced from the peripheral edge of said cover to provide a first safety membrane of uniform preselected remaining material thickness in the range of approximately 0.0025 to 0.0035 inches capable of uniformly responding to and withstanding a first preselected mean pressure in the range of up to 500 pounds per square inch before rupture, said arcs surrounding an aperture therein sized to receive an eyelet and terminal pin assembly to be fused therein; and, a coin punched groove in said etched mirror image arc on both surfaces of said cover of the container to provide a second safety vent membrane within said first safety vent membrane having a uniform remaining material thickness of approximately 0.0005 to 0.002 inches capable of uniformly responding to and withstanding a preselect mean pressure in a range approximately up to 400 pounds per square inch before rupture.

Inventors: BURROWS, LARRY GENE, WILSON, EDWARD EUGENE
Applicants: EMERSON ELECTRIC CO.
Application year: 1987
Main classification: H01M2
IPC codes: F16J13, B65D83, F16K17, H01G9, F17C13, H01M2