Receptacles – High-pressure-gas tank
Reexamination Certificate
1995-09-01
2001-06-05
Shoap, Allan N. (Department: 3727)
Receptacles
High-pressure-gas tank
C220S089200, C220S601000, C220S608000, C220SDIG001
Reexamination Certificate
active
06241116
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a metal container which is capable of withstanding internal overpressure and whose hollow vessel containing the contents is composed of an essentially cylindrical wall and two outwardly curved end walls, wherein at least one of the end walls has a bulge which protrudes as a cup-shaped bottom from the curved end wall, wherein at least one container connecting pipe is provided which is preferably seated in the bulge or cup-shaped wall, and wherein an intended breaking point formed as a notch at the outer surface is integrated in at least one of the end walls.
DESCRIPTION OF THE RELATED ART
Containers of this type are primarily used for the transport and storage of liquids and are predominantly utilized in the beverage industry for containing beer or alcohol-free beverages. They are intended for operating pressures which are usually between 0 and 7 bars overpressure. These containers are either equipped only with standing rings or gripping rings of metal, of synthetic material or also of rubber, or they are provided with a complete shell of these materials which then forms the standing ring and gripping ring and additionally surrounds the cylindrical wall of the container.
The containers of this type are increasingly equipped with an integrated overpressure protection which in certain cases of application is even required by regulations.
The overpressure protection has the purpose of preventing the internal pressure of the container from rising to very high values up to bursting when the container is incorrectly handled or when pressure reduction devices are incorrectly operated or fail to operate. In other words, when the internal pressure of the container reaches a defined value below the maximum bursting pressure of the container, the existing overpressure is to be discharged safely by an automatic opening of the intended breaking point in the wall of the container. In accordance with the prior art, this intended breaking point is provided as a defined reduction of the thickness of the container wall at various points of the container; preferably, the reduced thickness points have the form of a notch, as already mentioned above.
When producing this intended breaking point in the form of a notch, it must be ensured that the remaining thickness of the container wall is selected with a dimension that is technically sound, while not reducing the long-term strength of the container under operating conditions.
For the above reasons, the previously known solutions still have a relatively high opening pressure of the intended breaking point in relation to the bursting pressure of the container without intended breaking point.
In accordance with DE-OS 35 33 406, a container of this type has an intended breaking point in the cup-shaped bottom, wherein the opening pressure is approximately 50 to 70% of the bursting pressure of a container without intended breaking point. As a general requirement, the technically controllable minimum residual thickness of the container wall without impairing the long-term strength of the container during operation is approximately 25 to 30% of the normal wall thickness of the surrounding wall.
In a variation of this embodiment used millions of times, DE-OS 35 33 406 starts from a container which has an inner shell of metal and a casing of synthetic material which surrounds and is fixedly connected to the inner shell, wherein the intended breaking point serves its function even when the casing is provided. In this case, the influence of the casing of synthetic material which increases the response pressure of the intended breaking point is 50 to 70% of the bursting pressure of the container and, thus, is relatively small, especially in view of the fact that the thickness of the casing is as small as possible in the area of the cup-shaped bottom in order to save material costs. The casing of synthetic material provides the advantage that a corrosion influence (crevice corrosion) on the intended breaking point mechanically produced in the form of a notch and also mechanical damage are prevented, and that undesired manipulations of the externally not visible intended breaking point are practically excluded.
In accordance with DE-OS 37 37 977, another container is known in which an intended breaking point is supposed to discharge the impermissible overpressure, wherein the intended breaking point is arranged in the transition area between the curvature of an end wall and the cylindrical container wall, i.e., in the area of the bottom rim. The response pressure of the intended breaking point is still at approximately 60 to 70% of the bursting pressure of a container without an intended breaking point, when the minimum remaining thickness in the area of the notch forming the intended breaking point still is to have a technically controllable dimension of at least 20 to 25% of the initial wall thickness and the intended breaking point is to additionally have a sufficient strength with respect to alternating pressure for the normal operating pressures of the container. However, DE-OS 37 37 977 generally starts from a container without casing, i.e., from an intended breaking point which is not at all covered. However, when the intended breaking point according to this embodiment is covered by a casing, for example, in the form of a casing of synthetic material or by a standing ring or gripping ring of rubber which is integrally formed or vulcanized, the response pressure increases by approximately 5 to 10 bars depending on the type of cover. Of course, this pressure increase is directly dependent on the stability or the thickness of the cover.
In containers with integrated overpressure protection in the form of an intended breaking point, there is a certain residual risk that the container can rupture as a result of a material defect or production defect before the intended breaking point has assumed its safety function. This residual risk increases in direct dependence on the ratio of the response pressure of the intended breaking point relative to the nominal bursting pressure of the container. In other words, the existing residual risk increases with increasing response pressure of the intended breaking point.
In the previously known configurations of intended breaking points, the minimum residual thickness of the wall in the area of the notch is already so small that it cannot be further reduced for reasons of technical control of the manufacture and the long-term strength of the container under operating conditions. A further reduction of the residual thickness is also not possible because of the danger of failure resulting from external mechanical damage.
SUMMARY OF THE INVENTION
Therefore, the invention is based on the object, for further reducing the above-described risk and for certain uses of the container, to provide an intended breaking point which is integrated in an end wall and is constructed as a notch, wherein the response pressure is approximately 25% of the nominal bursting pressure of a container without intended breaking point, wherein the intended breaking point still has a technically controllable residual metal thickness of about 25% of the thickness of the surrounding metal wall, and wherein the maximum bursting pressure is adhered to even when the intended breaking point is covered by a casing or by standing rings or gripping rings of synthetic material or rubber.
In accordance with the invention, this complex object is basically met by providing the notch of the intended breaking point with varying depths, wherein the maximum depth of the notch is provided in that area of the end wall which is subjected to the greatest deformation when a defined internal pressure exceeding the permissible operating pressure acts on the intended breaking point.
It has been found particularly useful, in accordance with the invention, if the maximum depth of the notch is located in the area of the maximum extension of the end wall and the location of the notch is arranged transversely of the direction of
Reichmann Hans-Helmut
Schrepfer Bernd
Eloshway Niki M.
Kueffner Friedrich
Schafer Werke GmbH
Shoap Allan N.
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