DK159629B - CONTAINER ROAD WITH A PRESSURE LIMITING MECHANISM IN THE WALL - Google Patents

Description

in

DK 159629 B

The invention relates to a container wall with a pressure-limiting mechanism in the wall of the kind specified in the preamble of claim 1.

Prior art pressure reducing mechanisms include safety valves, breakage diaphragms, shear plugs, sharp tips forced through plates, etc. One problem with all these mechanisms is that it is difficult to combine low cost, accurate release at a certain pressure, sufficient sealing of the pressure vessel. , and a certain degree of strength against unintended effects of mechanical abuse or error handling. Eg. is a safety valve adapted to open when the force on the valve exceeds the force of a spring sufficiently accurate to open at a particular pressure. However, this valve is unsuitable due to the cost of the additional parts which are also susceptible to mechanical accidents and the exact fit required in the case of hermetic closure, which can lead to 20 increased costs. Furthermore, such mechanisms rely on the stability of a seal for hermetic closure, and the corrosive components within a container can render this seal ineffective.

Rupture membranes consist of a weakened portion of a container or container wall which forms a hermetic closure until the container pressure is sufficiently large to tear the membrane to pieces. Although less complicated with regard to the material than the safety valve, its curvature, thickness and material condition require closer control because the pressure at which the membrane is torn is not determined by the stable elastic properties of the membrane, but its last plastic deformation behavior, which is dependent on the composition and the mechanical and thermal history of the material. Thus, although this seal is sufficient, the expense of ensuring the accuracy of the release pressure becomes high. Any cost savings that

DK 159629 B

2 is achieved by requiring less accuracy in the release pressure, overridden by the need for additional strength and weight of the container to absorb higher pressure. In addition, the membrane for smaller openings must be so thin that it will also be necessary to protect it from puncture and corrosion, which further increases the cost. Simple grooves in the container wall, as used with capacitors, have further disadvantages with respect to longer crack propagation and the lack of valve closure 10 after the overpressure has been released, unless an expensive spring container is used. These defects can be particularly damaging if the container contains caustic materials.

Other methods of venting, such as displacing the periphery of a plug, or forcing a sharp tool through a plate, are inaccurate in the sense that the release pressure depends on varying physical properties of the material used to initiate the venting process. In addition, shear plugs depend on low shear stress applied to the wall, and these materials must be selected so that they are compatible with the container contents.

It is therefore an object of the invention to provide a container wall with a pressure limiting mechanism of the kind which is inexpensive to manufacture, has good accuracy in venting and a hermetic seal against the pressure vessels.

30

This is achieved according to the invention in that the pressure limiting mechanism initially stated is characterized by the characterizing part of claim 1.

Such a mechanism may be manufactured to open at a predetermined slow or fast course and to substantially close the vent to thereby prevent the

DK 159629 B

3 prevent further penetration of container materials or penetration of impurities.

The pressure limiting mechanism can be manufactured inexpensively by molding, is exactly within acceptable limits and requires no materials other than the walls of the container to be vented.

The effect of the pressure limiting mechanism is based on the predictable behavior of a bending voltage rather than a tensile stress. Specifically, the predetermined ventilation area is located between channels formed by deformation of the container wall.

Voltage caused by excessive internal pressure is concentrated and directed to a preselected portion of the container wall, causing this preselected portion to break, thereby forming a discharge opening for releasing the pressure. The stress concentration is obtained because the normal contour of the container wall has been altered to form two deformed and more extensible portions between which a small undeformed or less deformed and relatively unstretchable portion of the wall resides. This undeformed part, in the predetermined ventilation area, is arranged to break when the pressure inside the container reaches a predetermined value. As the internal pressure grows, the end wall or side walls of the container are forced outward, and the deformed portion of the container wall will seek to unfold while undergoing a relatively low bending stress. However, this unfolding can only be achieved by stretching the undeformed part of the wall between the two deformed parts. This part, which is hereafter referred to as a "bridge", with "bridge area" cannot be stretched in the same way as the deformed parts and is therefore subjected to high tensile stress which inevitably leads to breach of the bridge area, which thus forms a vent opening.

DK 159629 B

4

The deformed parts are preferably elongated and formed as channels which are arranged such that one end of one is aligned with one end of the other with a bridge therebetween. The container material may be metal, e.g.

5 steel or nickel-plated steel or plastic or rubber which may contain constituents under pressure and has a predictable voltage expansion. The most suitable materials are those which are capable of undergoing a substantially inelastic elongation for fracture.

10

The invention is particularly suitable for use in an electrochemical cell which, due to its content, is either in a pressure state or subject to a large pressure increase.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described in more detail with reference to the drawing, in which: FIG. 1 is a top view of the end wall of a container whose wall contains a pressure limiting mechanism according to the invention; FIG. 2 is a perspective view of FIG. 1 with a portion along line 2-2 of FIG. 1 is a sectional view; this figure shows the container used for an electrochemical cell; 3a is an enlarged sectional view taken along line 3-3 of FIG. 1, FIG. 3b is a section on a larger scale similar to FIG.

.30 3a, but showing another embodiment of the container wall according to the invention, in which a further reinforcing section is provided; FIG. 4 shows the part of the container wall where the vent 35 takes place, in another embodiment, in which the shape of the vent area differs from that of FIG. 1,

DK 159629 B

5 FIG. 5 is a perspective view of a further embodiment of the container wall according to the invention, wherein the pressure limiting mechanism is built into a cylindrical container wall; 6 shows a perspective view of a further embodiment of the container wall according to the invention, wherein the pressure limiting mechanism is built into a cylindrical container wall, and FIG. 7 is a graph showing the general relationship between end wall deformation in the embodiment of FIG. 1 and the release pressure.

FIG. 1 shows the end of a container 10 which has been molded and / or deep-drawn, so that its wall contains annular duct portions 11, 12 which form deformed areas within which a center disc 19 is provided. The ends 61a-d, edges 62a-d and the bottoms 63a-b of the channels are preferably rounded; thereby the ducts can be made by drawing and stretching processes without producing attenuated parts which could be subject to corrosion or mechanical breakage. However, other forms can also be used.

The deformed areas formed by channels 11, 12, 25 are able to unfold under pressure by being subjected to bending stress. It does not matter much if the ducts extend inwards into containers (as shown) or from it, as long as extensibility due to internal pressure is possible. The bridges 13, 14 between the ends of the ducts 11, 12 are 30 points at which venting takes place because the bridge under pressure is subjected to tensile stress beyond its breaking point, while the ducts still have substantial extensibility. Grooves 15, 16 are cut or pressed as curved grooves extending across the bridges and down 35 across the ends of the corresponding channels, as these are transition regions from the high voltage at the unformed portions of the bridges to the low voltage. do they know

DK 159629 B

6 fully deformed portions of the ducts. The grooves 15, 16 on the bridge areas 13, 14 are relatively small, but nevertheless provide sufficient venting in contrast to the simple grooves used in venting means of the prior art which must be larger in order to be effective and therefore have disadvantages. that it is more susceptible to mechanical or corrosion damage and to the formation of wide openings.

When excessive pressure occurs in the container, the tensile stress is concentrated in the grooved portions 15, 16 in the bridge areas 13, 14 and not in the adjacent areas such as the outer ring 65 in the vicinity of the bridge areas.

The depth of the groove is essentially determined by the degree of this concentration and a groove having a depth of at least half of the original wall thickness is usually sufficient.

The width of the base of each groove is designed such that the breakage occurring in the groove takes place during the portion of the outward displacement of the disc 19 in which the excessive internal pressure varies the least. In order to obtain moderately uniform tension across the groove base, and thus to avoid premature breaking, it is preferred that the transitions between the groove bottom and the groove walls are rounded and that the material thickness of the groove base between these transitions is approximately constant. The desired bottom width depends on and is a function of the characteristic fracture elongation of the container materials under tensile stress and the structural tensile portion of the groove walls as the expanding internal pressure grows. The material in the groove bottom is tensioned in direct relation to the displacement which extends the groove, and vice versa in relation to its original width. Thus, e.g. the preferred groove bottom width for the more stretchable annealed soft steel has been made smaller than for the same steel which has become workable.

DK 159629 B

7 hardened. A material that allows for multiple extensions before fracturing, such as an annealed pure copper or fine silver, lead, rubber or some plastics, requires a much narrower groove for the same structure than soft steel.

5

If the grooves of a metal have been made by cold pressing, the base material is hard and relatively stretchable, but by a simple annealing, its extensibility and its mechanical and chemical properties are stabilized. The grooves can be annealed with the adjacent areas containing bridges and the ends of the channels by supplying sufficient heat to make the entire area 15, 16 red-hot for about 1 second. It has been found that by annealing the metal in the area where fracture is desired, it is possible to provide a more accurate control of the venting moment, counteracting the effects of the cold working of the metal container. The annealing also produces the groove area which is the weakest point of the container construction and the surrounding area which has been subjected to forming stresses, with a degree of resistance to corrosion and attack from materials contained in the container, of which the groove is a part, and also reduces the susceptibility to mechanical damage.

In the FIG. 1-4, channels 11, 12 have a center disc 19 therebetween. When the pressure in the container exceeds a normal working pressure, the center disc 19 will be pressed outwards. In turn, they will bring both the channels 11, 12 under bending stress and the bridge areas 13, 14 under tensile stress. FIG. 2 shows the movement of the channels 11, 12 under this voltage with a dotted line 20. The compressive force in the container is shown by arrows. The dashed line 20 shows that the ducts have been partially unfolded, but not completely at the time of venting. Once the vent pressure has been reached, the groove is stretched to a shape as in the embodiment in which the container is formed.

DK 159629 B

8, made of soft steel, is shown by a dotted line 21, which is roughly 35-50% larger than the original, and is broken or flanged to form a vent opening. It is desirable that the groove be broken while the deformed parts are still expandable because this allows further opening of the vent opening if the overpressure does not disappear. However, these tear-offs are limited to the bridge area because the windings of the ducts, when unfolded, are not subjected to the mentioned tensile stresses. The tensile load triggered by the broken bridge does not propagate the crack in the channel regions, as the area near the crack has maintained its strength even when the channels are not fully unfolded. Simple grooves do not have these properties, since the areas near the ends of the groove have been subjected to full tensile stress, which causes weakening, and when the groove breaks, the adjacent area does not have sufficient strength to contain the crack. Limiting the cracks to the selected vent regions is generally achieved by the greater thickness of the duct material. Thus, the groove 16 of FIG. 3a, a limited vent opening in any metal sufficiently flexible to allow deep drawing, even when the internal pressure after venting remains high enough to fully unfold the ducts 25. The duct material should, of course, preferably be of such thickness as to allow unfolding without bending breaking. For homogeneously rigid materials, including those materials in which reinforcement is impractical, means are needed to reduce tensile stresses across the ends of a vent crack to prevent further breakage. Such means are shown in FIG. 3b, where the end of the groove 35 goes below the lowest level of the other portion of the channel. The thinner portions 38, 39 below the groove become compressed as the channel unfolds, 35 displacing the tension which would otherwise extend the crack of the groove. Thus, there will generally be a difference in voltage between the vent area and the desired end of the vent opening obtained by these or other similar means.

DK 159629 B

9

With the movement of the ducts recovered due to the elasticity after venting, the opened vent opening will be closed sufficiently to prevent the container material from escaping and contaminant from entering the container. This is particularly important for electrochemical cells containing constituents which are incompatible with ambient atmospheric materials. This latter property is not present in vent openings which consist only of a thin groove in the wall of a container.

The disc 19, in its movement, as shown by the 15 dotted line 20, exerts traction on both the channels and the bridge area. This force produces small, preferably bending stresses in the channels, with the resultant large outward displacement of the disc, and on the groove 15 in the bridge area 13 a large tensile stress which is increased until the groove 20 is eventually broken.

FIG. 2 shows the container 5 with a pressure limiting mechanism according to the invention built into its wall used in a typical electrochemical cell, which at some moments can develop very large internal pressures. The cell shown is a cell in which the anode 22 is lithium and the cathode depolarizer is SC> 2. Separator mats 23 separate the anode 22 from the cathode current collector 24. After the cell has been made hermetically, SO2 is introduced into it. An insulating disk 25 separates the cell components from the outer cell wall and the pressure release mechanism; however, this disk is not a hermetic separator and excess fluid and the accompanying pressure may pass around this disk and act on the pressure release device in the cell wall.

35

FIG. 4 relates to an embodiment similar to that of FIG. 1. and showing the ends 31, 32 of adjacent channels 71,

DK 159629 B

10 72 and the bridge area 73 therebetween. In this embodiment, the groove 30 has a lens shape with its width approaching zero, at the end of the most deformed portion of the channels 71, 72. Various forms of the groove change the venting process. A groove of uniform width shown in FIG. 1, is first broken at the center of bridge area 33, forming a lens-shaped slot whose outer portions continue down the canal calendar, with continued outward movement of the disc 19 until they reach the ends of the heavier (or stretchable) material at the bottom of the groove.

The FIG. 4 is tensioned roughly to the same extent throughout its length and broken into a roughly full length, but at first very narrow slits extending the full length of the weakened bottom of the groove. The resulting partial reduction of the clamp on the disc 19 allows more steep vent opening than at the uniform width groove at the time of fracture, which means a faster pressure reduction. Thereby, the vent effect can be varied or controlled from a slow, pressure-regulating release to a sudden opening of a substantial vent opening.

FIG. 5 shows another embodiment of the invention in which a cylindrical container 2 is provided with a pressure-limiting mechanism in the form of circumferential deformations 40, 41 in the side wall thereof. Although the deformations 40, 41 are shown facing outwards, the direction has little effect on the operation of the pressure limiting mechanism. In this embodiment, the direction of the operating voltage 30 is axial as shown by the arrows, and the deformations can be unfolded to increase the axial length of the container. In this way, the tensile stress is concentrated on the bridge area 42, and especially in the groove 43, which is pulled under this tension, while the deformations 40, 41 are still able to further straighten as previously explained.

DK 159629 B

11

FIG. 6 shows another embodiment of a structure in which the channels 51, 52 are formed in the cylindrical side wall of a container 3, but which are not circumferential. In contrast, channels 51, 52 are arranged parallel to the cylinder axis. Excessive pressure in the container spans its circumference and channels 51, 52 are unfolded with just a bending stress, while bridge area 53 is subjected to high tensile stress, causing its wall to break by a groove 54. It should be noted that the construction of FIG. 1-4 10 have two properties not found in the embodiments of FIG. 5 and 6. First, the vent opening in the former is formed as a bridge between two completely different parts, a center disc 19 and an outer annular ring 65, instead of between two identical parts. The outer ring 15, with the adjacent portion of the container wall, is subjected to a contraction force along the diameter passing through the bridges as the disc is pressed outwardly by the internal overpressure. As desired, the width of this ring is sufficient to support the contracting force 20 without being subjected to plastic deformation, so that the force can continue to grow and tighten the bottom material of the groove until it breaks. Second, when the disc is displaced outwardly from the outer ring plane as a result of the internal overpressure, the bridges are rotated 25 degrees from their original plane but subjected to little initial elongation, thereby providing a degree of protection against accidental release by pressure vent formation in the bridge area.

FIG. 7 shows the displacement D of the disc 19 in FIG. 1 as a function of the internal pressure P. The provision of the channels in the end wall of the container permits a substantial outward movement of the disc with less tension in the channel material. As the disk is moved outward, the internal pressure changes only gradually, so that a pressure level is reached as shown between points A and B, followed by a faster increase in pressure when the channels are unfolded in it.

DK 159629B

12 degrees, where further unfolding becomes difficult. Although substantial movement of the disc 19 continues within the pressure level, the pressure within the cell varies slightly. In this way, the bridge area is strongly tensioned during this movement as previously explained and is broken below this predictable pressure level, which allows to predict with sufficient accuracy the internal pressure at which the vent opening is formed. To ensure breakage of the groove within a predetermined desired pressure range, such as the pressure level, the width of the groove can be varied; a greater width causes fracture to occur near the upper end of the curve and a smaller width causes fracture to occur toward the lower end of the same curve. Due to the relative sizes of the grooves and the ducts, most of the force exerted by excessive internal pressure is used to unfold the deformations or ducts, while only a minor portion of the force is used to bring the grooves under tension. Once the groove has been extended beyond its proportionality limit, both the smaller force which extends this section to fracture and the larger force which causes the deformation are slightly altered. In this way, the bridge section becomes tensioned for use while the inner container pressure remains substantially constant during unfolding of the deformations. It is therefore the reproducible movement of the deformations that determines the pressure at which the vent opening is formed. The position of the plateau which is related to the vent pressure is to a large extent dependent on the thickness of the container wall at the ducts. In this way, the container can be made to ventilate at a higher pressure if the thickness of the duct wall is increased and a lower pressure if it is reduced. Similarly, if the channels are annealed, the pressure plate is obtained faster and at a lower internal pressure. In this way, the venting will occur at a lower pressure. The following examples indicate the properties of a particular container type.

DK 159629 B

13

Cell containers of standard size D as shown in FIG. 2, was formed by deep drawing of soft steel to an outer diameter of 33 mm and a container thickness of 0.5 mm, channels of 23 mm edge diameter and 2 mm depth with channel 5 sides forming an angle of 80 ° with each other . The grooves connecting the bridges between adjacent channel edges were pressed about 0.25 mm deep and had a maximum width of about 0.6 mm at the center of the bridges. After local annealing of the bridges and connection of the duct ends, the vents of the containers opened at a 2.

pressure of 31.6 τ 1.75 kg / cm. Release pressure above these limits was obtained by inserting 0.53 mm stiffening of the ducts to increase the vent pressure to 34.1 2 t 1.75 kg / cm. Of course, such variables are controlled by fabrication to maintain certain dimensions and state of material. These pressure ranges for venting are sufficiently accurate and in the applicable range of working pressures for use in hermetically sealed electrochemical cells in which there is an overpressure.

20 25 30 35

Claims (5)

A container wall with a pressure limiting mechanism in the wall 5 in the form of a predetermined ventilation area, which breaks down by the effect of an overpressure, characterized in that the pre-fixed ventilation area (13, 14; 42; 53; 73) of the container wall is located between the ends of one or more adjacent ducts (11, 12; 40, 41; 51, 52; 10 71, 72) formed by deformation of the wall, the ventilation area (13, 14; 42; 53; 73) being arranged to stretch and thereby burst , when the channel or channels straighten out due to overpressure. Container wall according to claim 1, characterized in that in the predetermined ventilation area there is a narrow groove (15, 16; 30) extending over the venation area (13, 15; 73) and into the adjacent canals (61a , 61b, 61c, 61d; 31, 32). 20 Container wall according to claim 2, characterized in that the groove (15, 16; 30) has a depth of at least half the material thickness in the ventilation area. Container wall according to claim 2 or 3, characterized in that the width of the groove (15, 16; 30) has a shape which is between the lens shape (30, Fig. 4) and a shape due to the width of the groove being the same. throughout its length. Container wall according to any one of claims 1-4, characterized in that at least one of the following: a) said ventilation area, b) the groove or c) the adjacent canal calendar, are annealed.