IL43776A - Leak-proof dry cells - Google Patents

Abstract

1485426 Sealed cell casings TADIRAN ISRAEL ELECTRONICS INDUSTRIES Ltd 28 Nov 1974 [7 Dec 1973] 51669/74 Heading H1B A dry cell is enclosed in a plastics jacket 12 extending, 14, beyond the bottom of the can, a metal terminal having a central portion 41 spaced from the bottom of the can by a waisted wall portion 44 is push-fitted on to the bottom of the can and a plastics sealing ring 48 is injection moulded into the annular space between the jacket extension 14 and the waisted wall portion 44 of the terminal, fusion taking place between the ring and the jacket. [GB1485426A]

Description

LEAK PROOF DRY CELLS This, invention relates to leakproof sealed dry cells and batteries, particularly cylindrical Zinc-Carbon cells commonly known as ^Leclanche »s cells" or ^flashlight cells11 (hereinafter referred to as "the Cells").

Great efforts have been expended to devise a method for •wrapping the cells to eliminate any leakage of the eleBtro- hicn lyte/is corrosive and can cause great damage to the sometimes very expensive equipment in which the batteries are utilized. The problem is made most difficult to overcome due to the high degree of capillary flow that is characteristic of the electrolyte.

In Spanish Patent Application No. 171501 (Pilas Secas Jupiter 3.A, ) (corresponding to French Patent No. 2 ,150 ,683 and German Of enlegungssch ift 2 , 226,441) and Austrian Patent Application No. 082 (Telephon and Telegraph Fabric AG Kapsch & Sonne in Wien) (corresponding to French Patent No.1,523 , 887 , U.K. Patent No. 1,175 ,445 and U.G. Patent No. 3 ,301 ,351 ) fhere have been disclosed means for dry-cell leakproof sealing essentially comprising a metal dish-shaped closure member havin an upstanding peripheral flange for itting over the bottom of a tubular anode, a flat annular peripheral zone and a central bulge spaced from the bottom of the anode. The anode is enclosed by a jacket or coating made of thermoplastic material.

For sealing such cells, thermoplastic material was injected into the space between the said metal member and the bottom of the anode to fill such space as well as to form an annular covering layer above said peripheral zone which fuses with the lower periphery of said jacket. The metal member became therefore practically embedded in the plastic material.

The injection was performed through openings made at said peripheral zone or at the central bulging zone of the metal member. Alternatively, the plastics coverings of the inner -surface of the metal dished member, and of the outer surface of said peripheral zone thereof has been separately prepared by spraying, and the said fusing effected by ultrasonic or heat welding.

In practioe, however, none of the above described sealing methods have proved to be satisfactory, due to that no+ sufficient account has been taken of the contraction or shrinkage of the plastics after solidification, and of the that fac when injected on cold metal9 the plastics material is repelled from the surface of the metallic members.

Therefore, the combined effect of these phenomena caused the formation of a gap between the injected plastics and the metal member, which, of course, destroyed the desired sealing of the cell.

An Attempt to solve the problem has been desclosed in Spanish Patent Application No. 175654- (Pilas Secas Jupiter S.A. ) (corresponding to U.K. Patent No. 1 ,361 ,932 , German O fenle-gungsschrift 2 ,230,772 and U.S. Patent No. 3 ,823 ,039 ). The proposed method was similar to the prior art techniques regarding the fusing of injected plastics with the said thermoplastic jacket. However, the said dish-like member was characterized by an annular folded rib of zig-zag cross-section formed in the said peripheral (flat) zone and extending outwardly at an acute angle to said zone, the plasties covering, a closing force would be generated, < acting around and against the said inclined rib to grip same between the two eoncentrical parts of the said covering.

It has further been stated in the above mentioned Specification that the annula folded rib, which was anchored in the plastics material, constituted a circular sealing zone because it was subjected to a higher external pressure than the pressure formed internally during discharge of the cell, and that at moments of maximum formation of gas and liquid, the cylindrical baser would tend to swell slightly, so that its edges acting on the covering thickenedzone would J contracted, applying additional closing pressure to the annular folded rib* It has, however, been found, that this "folded ib9 concept Is not effective, being, on the one hand relatively expensive regarding the formation of the annular folded rib at the bottom closure and, on the other hand, the contraction forces do not really contribute to the sealing of the cell as represented in the above mentioned Specifica ion. n fact, One of the following results would occure: Should the folded rib project only a small distance above the said flat peripheral zone of the metal closure, then the active surface, available to be subjected t said shrinkage forces would be too small to attain the required amount of closing force; If, however,: the rib would be made to extend higher, it mAxii causalt the splitting of the annular plastics covering into two eoncentrical rings* each shrinking irrespective of the other, and again, insufficient contraction forces would be applied aga&a&t the folded rib to effectively seal the coll.

Furthermore, th inner ring migh hecome completely torn and would fall-off the metal member because of the inclined wall connecting the central projecting bottom and the inner surface of the zig-zag rib, forming with the latter a right-angle.

It is therefore the object of this invention to overcome the disadvantages of the above mentioned methods, Accorfling to the invention there is provided an electric dry cell comprising a cylindrical can enclosed within a Jacket made of mouldable plastics material having aimargineli portion extending around the periphery of the bottom of said ean a cup*shaped metal member having a flat circular bottom^ a first substantially upright portion extending from said bottom, an outwardly projecting portion extending from said first upright portion and a second upright portion adapted to be press-fitted around the bottom of said can, an annular body of injected plasties material covering the said outwardly projecting portion and fused with the said marginal portion of said Jacket characterised in that the outer diameter of said bottom is larger than the inner diamete of aQ%& w y projecting portion, Te said first upright portion ma be conical or of "S* like therein section, and openings may be providedfor admitting the plastics material inside of said flat bottom.

It wlHd be readily understood by those skilled, in the art* and in view of the foregoing analysis, that the ring of injected plastics material, when solidifying, will shrink against the said first uprigh portion. The upwardly tapering section of this portion will cause the ring as a whole , to exert substantial pressure thereagainst and against the said outwardly projecting portion amounting to the sum vector of the contraction forces in the direction perpendicular to said upright and said outwardly directed portions. These forces effectively neutralize and oveBcome the repellent forces between the plastics material and the metal, to complete the leakproof sealing of the cell.

The invention is illustrated, by way of example only, in the accompanying drawings, wherein: Fig. 1 is a cross#sectional view showing a cell placed within an injection mould to form the seal according to the present invention, the cell being provided with one form of said cup-shaped member; Fig. 2 shows a cell provided with another form of the metal member featuring the principles of the invention; Fig. 3 is a plan view of the metal member of Fig.2; Fig. 4 shows a cell provided with a third for$ of the metal member; Fig. 5 is a plan view of the metal member of Fig. 4; Fig. 6 shows a cell provided with fourth form of the metal member; Fig. 7 is a plan view of the metal member of Fig. 6, and Fig. 8 is an elevation of the metal member of Figs. 6 and 7· Referring to Fig. 1 of the drawings, a cell 2 is shown operation. The cell 2 which is a conventional Leolanche's type dry cell, comprises a zinc can 4 containing a depolarizer mixture 6 and a carbon rod 8 which is provided with a cap 10, A jace¾ct 12 made of plastics material envelopes the can 4· The jacket terminates at its lower end in a marginal portion 14 bein of thickness slightly reduced relative to the thickness of the Remaining wall. The top of the jacket is made more rigid and merges into a top portion 16 adapted to embrace the projecting end of the carbon electrode, thereby ensuring that no leakage will occur from the top end t the cell. The jacket 12 usually bears printed information such as the manufacturer's name, the battery designation, etc.

For sealing the lower side of the cell the following construction is employed. First,' a metal member 18 is affixed to the bottom of the can 4. This member is in the form of a cup having a flat bottom 19 with a small central bulge 21, a first upright portion 23, an outwardly projecting portion 23 and a second upright cylindrical portion 27. The diameter of the second upright cylindrical portion 27 is designed so that it may be press fitted (at 20 ) on the bottom of the can 4. The diameter of the bottom 19 is larger than the inner diameter of the outwardly projecting portion 23, the tfirst upright portion 23 tapering inwardly at an angle A, preferably of 3 to 15 degrees with respect to the vertical.

The assembly - comprising the cell, the jacket, and the die 26. Molten plastics material is injected through a runner 30 in the mould die 28 to fill the toroidal ©pace between the lower jacket end 14 and the portion 23 of the metal member 18, thereby forming a sealing ring 32· As a result of the contact between the injection molten plastics material and the marginal portion 14 of the jacket 12, the latter is partly melted, which results in a complete unification of the two component materials owing to their compatibility under the given conditions. This process is herein referred to as "fusion*.

Bheh the ring 32 solidifies and shrinks within the cavity or undercut . pfcace defined by the tapering portion 23 and the flange 23» the internal contraction forces firmly grip same to complete the sealing of the cell.

In Figs. 2 to 8, various modifications of the metal member l8 of Fig. 1 are shown. The member 40 of Figs. 2 and 3 has a planar bottom 41 with a bulged portion 42, an upright portion of *Sn section comprising a first circular radially inwardly directed bead 43 and a second outwardly directed bead 44, an outwardly directed portion 43 and a cylindrical portion 46. The metal member 40 is first forcibly fixed to the bottom of the can 4. The cell is placed within a mould (not shown), and molten plastics material is injected to fill the annular space provided for, to form the ring 48. As shown in Fig. 2, is this instance, the plas bics ring 48 is so shaped as to include a protruding portion 30 and an inwardly directed portion bearing the name of the Manufacturer as well as other date.

The metal member 60 of Figs. 4 and 5 has been designed to allow molten plastics material to fill also parts of the underside of the metal member, i.e. the space 62 between the circular bead 64 and the bottom portion 66. To this end, at least one opening 68 (the illustrated example has four openings) is provided as shown. Molten plastics material is forned, during the injection operation, to flow above as well as under the bottom 60. Two rings of plastics material, 70 and 72 are thus formed, interconnected through the openings 68· Consequently, the metal member 60 is partly embedded in the plastics material which contributes to the sealing effect provided by the fused external ring 70 and sleeve 12, and the grip of the ring 70 against the inwardly tapering portion 72 forming the angle A with respect to axis of the cell.

This concept of partly embedding the metal member is f rther developed in the example snwon in 'Figs. 6 to 8. The member 80 is embedded between an inner plastics body 82 and an outer ring 84. Appropriate openings 86 are formed in the inclined portion 88 for introducing the plastics material to the inner surface of the bottom 90* There may be provided a membrane 92 integral with ring 84 (or rings 32, 48 and 70 of the previously described embodiments), which covers the bottom 90 of the metal member 80.

This represents a furthei* improvement readily achieved by the method of this invention, namely, the provision of a protection against accidental short circuit of the cell, as well as an

Claims (1)

1. ϊ WHAT WE CLAIM 4 An electric dry cell comprising a cylindrical can enclosed within a jacket made of mouldable plastics material having a marginal portion extending the periphery of the bottom of said a metal member having a flat circular a first rim substantially extending from said outwardly projecting portion extending from said first upright and a second upright portion adapted to be around the bottom of said an annular body of injected plastics material covering the said outwardly projecting portion and fused with the said marginal portion of said flat characterised in that the outer diameter of is larger than the inner diameter of said outwardly projecting The dry cell as claimed in claim 1 further characterised rim in that said first The dry cell as claimed in claim 1 further characterised in that said first upright portion is of The dry cell as claimed in claim 1 wherein at least rim one opening is provided said first admitting said plastics material inside said flat The dry cell as claimed in claim 4 wherein said plastics also material forms a membrane covering the outer side of said flat An electric dr cell substantially as hereinbefore described with reference to accompanying For the Applicants DANIEL Advocate insufficientOCRQuality