Receptacles – High-pressure-gas tank – Multilayer container
Reexamination Certificate
2000-05-15
2001-05-15
Moy, J. (Department: 3727)
Receptacles
High-pressure-gas tank
Multilayer container
C220S592000, C220S592250, C220S589000
Reexamination Certificate
active
06230922
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a composite pressure vessel with a plastic liner for storing gaseous media under pressure.
2. Discussion of the Prior Art
EP European reference 0 753 700 A1 discloses a composite pressure vessel forming the generic type. It comprises a plastic liner having two neck pieces arranged in the neck region, and having a winding of a fiber composite material that reinforces the liner. At least one neck piece is designed in such a way that it can accommodate a screw-in valve having a cylindrical or conical thread. Both neck pieces are provided, in the end region facing the pressure vessel, with a flat, frustoconical collar which is surrounded on the inside by the liner and on the outside by the reinforcing winding. In the region facing the liner, both neck pieces have an internally threaded section which interacts with an externally threaded section arranged on that region of the liner which is designed as the neck. The neck piece that accommodates a valve has, on the inside in the thread-free region adjacent to the internally threaded section, an annular groove to accommodate a sealing element. This is adjoined by a further internally threaded section to accommodate the valve. As a safeguard against rotation, the neck piece that accommodates the valve is provided with a wrench attachment on the outside.
This design is only partially suitable to meet the special requirements which are placed on pressure vessels having a filling pressure up to 300 bar. This applies in particular to the sealing in the neck region and to impact stressing of this region.
SUMMARY OF THE INVENTION
The object of the invention is to provide a composite pressure vessel with a plastic liner for storing gaseous media under pressure which, at a test pressure of up to 450 bar, for example, satisfies the licensing requirements with regard to leakage even following impact stressing.
The core of the invention is the specific improvement of the sealing in the critical neck region. This includes the arrangement of a screw-in clamping ring, whose frustoconical section interacts with that end region of the liner that projects into the neck piece. This end region of the liner preferably has a bevel corresponding to the frustoconical section of the clamping ring. If required, this section can also be cylindrical. The entire section is produced by boring out the neck, accommodating the valve, of the plastic liner. When delivered, this neck generally has only a small venting hole, which is kept open during the production of the liner. Selecting the angle in the range between 3 and 5° means that the screwing-in force is subdivided into a very low axial component and, for this purpose, a radial component which is all the larger. The result of this is that the end region of the liner is pressed into the threaded contour of the screwed-on neck piece. In this case, it is advantageous that the critical end region of the liner makes contact under tension not only at high internal pressures but also at a low filling pressure. The magnitude of the prestress can be adjusted by screwing in the clamping ring to a greater or lesser depth. The prestress generated in this way counteracts the thermal expansion or contraction of the liner in relation to the neck piece. In order to be able to screw the clamping ring in a straightforward way, it has an internal hexagon, so that defined torques can be applied and, by calculation, the necessary flank pressure of the clamping ring can be reproduced.
Depending on the type of gas filling and, in particular, on the filling cycles, the arrangement of a modified clamping ring has proven to be advantageous. During daily filling with natural gas, as is customary in the case of city buses with natural-gas propulsion, large quantities are forced into the vessel in a short time in order to keep the filling operation short. Because of the energy of compression, this leads to the filling duct being heated. In order to protect the sensitive plastic liner from this heating, a cylindrical section, which extends into the interior of the vessel, adjoins the frustoconical section of the clamping ring. This prevents the heated gas in the narrow filling duct coming directly into contact with the liner, and the plastic liner connected to the neck piece is protected against the action of heat. If necessary, during such a filling operation, the valve connection can be cooled from the outside.
For valves with an upstream ceramic filter cartridge, such as is provided, for example for air to be breathed, the clamping ring has a clear width of at least 6 mm. As a rule, a clear width of 8-10 mm is necessary in order that the sometimes bent filter cartridge can be screwed in without difficulties.
A further aspect of the invention relates to arranging a sealing element in the neck region. In the known design from the prior art, the sealing element is arranged on the front side of the end region of the liner. However, a large number of trials and investigations have shown that the matching of the tolerances between the neck region of the liner and that of the neck piece is to be viewed as critical. The production of the liner is possible with only a large tolerance, because of the process, so that in the least favorable case a gap between the liner and neck piece has to be bridged. The screw-in clamping ring certainly provides a certain degree of compensation, but on the other hand limits are placed on the screwing-in force, otherwise the neck region of the liner would be destroyed. For this reason, it is proposed to arrange, in the thread-free section of the neck region of the liner, a sealing ring which is anchored in a groove which extends radially into the neck piece. For particularly critical cases, it has proven to be beneficial if a further sealing ring is additionally arranged on the underside of the collar of the neck piece. This has the advantage that, in the event of superimposed thermal and mechanical stressing, in particular impact stressing in the axial direction, possible leakage as a result of loosening the joint between the liner and neck piece in the collar region can be counteracted by the sealing ring. In order to improve the attachment between the neck piece and the plastic liner further, it is additionally proposed to make provision to arrange an adhesive between the underside of the collar of the neck piece and that region of the liner which makes contact with it.
With regard to impact stressing, arranging an external bead in the region adjacent to the collar has proven to be advantageous. This bead ensures that a large part of the impact stress which is incident on the neck piece is led into the winding, and only a remainder reaches the liner region via the collar. Otherwise, it is possible that the liner region will be so severely stressed, by the impacting neck piece, that it will tear locally. The arrangement of an impact-absorbing layer on both polar caps of the pressure vessel also acts with the same effect. Preferably, a rapidly curing polyurethane foam is used for this purpose. This can also be used to form a standing surface in the polar cap opposite the valve, so that the vessel can be placed upright without aids. This standing surface can be designed as a flat disk or as a foot ring.
Depending on the application, it may be necessary to screw in a valve with a standardized conical thread. In order for it to be possible to continue to screw in the clamping ring, the upper internally threaded section is subdivided into two sections. The first section is a cylindrical fine thread to accommodate the clamping ring, and this is adjoined, with an offset, by the standardized conical thread to accommodate the valve.
Overall, the result of the measures proposed is that the developed pressure container satisfies the licensing conditions at a test pressure up to 450 bar and can optionally be used for filling with a very wide range of gases, be it air to be breathed, natural gas, hydrogen or any other.
REFERENCES:
patent: 54761
Rasche Christian
Rau Steffen
Cohen & Pontani, Lieberman & Pavane
Mannesmann AG
Moy J.
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