Patent Application
20140224811
The invention relates to a pressure tank, comprising a hollow body of thermoplastic material with at least one outlet, into which one connector each is inserted, which has at least one aperture each to the interior of the hollow body.
In the prior art tanks for holding gases or liquids are known, which are under high pressure, such as liquefied petroleum gas (LPG) or compressed natural gas (CNG). These tanks are manufactured inter alia of thermoplastic material in a blow moulding or injection moulding process. In order to increase the compressive strength, these tanks are covered in a second step with an outer layer of resilient fibers, which are generally embedded in a resin, which bonds the fibers to each other and fixes them to the inner plastic layer.
Regardless of the embodiment, such a tank has to be provided in any case with at least one connector, to which a valve, a hose or a tube is coupled in order to fill or to empty the tank. These elements have in most cases as an interface a metal tube socket with a thread or a bayonet, which must be connected pressure-resistant and tightly with a complementary shaped counterpart in the connector of the tank.
In the prior art plastics with sufficient tensile strength are known for the connectors, which can be produced also as a hollow body with sufficient wall thickness and suitable threads or bayonet guides.
As the wall thickness and the accuracy requirements of the connectors differ considerably from the wall thickness and the tolerances of the pressure tank, it is in practice neither reasonable nor economically, to manufacture the connectors and the tanks all of a piece.
Rather, it is common to provide a hollow plastic container after its completion in a further step with a separately produced and in most cases multi-part connector. For example, patent application U.S. 2011/010/1002 describes a plastic tank with two outlets. Onto these outlets from the outside and from the inside each an approximately cylindrical connector is placed, which is widened at one end with a collar-like flange. These two parts are screwed together with a thread and thus pressed together, so that they lie planely from the inside and from the outside on the area around the outlet of the tank. By corresponding pressure and by additionally inserted sealing rings in the tank or the flange, the required pressure strength is obtained.
A significant disadvantage of this and other similar approaches is that the connectors are configured rotationally symmetrical. If a screw coupling has to be made for connection with a hose, a tube or a valve, the connector has to transfer a torque to the tank. With rotationally symmetrical connectors, however, only the value of the tightening torque can be achieved, resulting from the pressing force of the two flanges to the tank and the coefficient of static friction of the two surfaces pressing on each other.
Since the surface of the plastic tanks is generally even and smooth, only a limited torque peak value is the result if this is exceeded, it becomes difficult to establish a sufficiently tight connection. Additionally there is the risk that due to the rotating of the connector against the tank this connection is leaking quickly and the fluid, which is actually to be discharged, is continuously leaking and that with tendency to rise.
On this background, the present invention has tackled the task to develop for composite pressure tanks a connector, which transfers also peak values of a torque occuring during tightening of a screw or a bayonet, safely and permanently to the hollow body of plastic.
As a solution, the invention teaches that a sealing flange is integrally formed around the aperture to the connector. This sealing flange is visible to the outside and is welded and/or bonded to the hollow body and at least one torque coupling is integrally formed to it, whose cross-section is polygonal or non-circular and which is inserted into a complementary coupling socket in the hollow body, which is running around the outlet.
It is also an essential idea of the invention to separate the function of the sealing between the connector and the hollow body from the function of the torque transmission from the connector to the hollow body. In contrast to the prior art, in which these two functions are combined in one element, the present invention provides clearly separated areas of the connector:
The first, sealing area is the “sealing flange” The second, the torque transmitting area is the “torque coupling”.
The sealing flange is visible to the outside when mounted. In the simplest case it has the shape of a disc, which is flange-mounted on the central body of the connector around the outlet. If the front edge of this disc is round, the disc does not have a torque coupling and serves only as sealing. The area of the flange facing the hollow body can be bonded to the hollow body.
Additionally or alternatively, the marginal area of the sealing flange can be welded to the hollow body, i.e. both the hollow body in the contact area of the sealing flange and the sealing flange itself in its marginal area are liquefied at the contact areas, by heating these areas beyond the melting temperature of the material and then pressing both parts on each other so that the liquids are mixed together. When the heating is completely revolving and uniformly, the connection between the sealing flange and the hollow body is sealed during cooling and solidification of the liquid.
As mentioned before, it is the essential idea of the invention that the connector comprises at least one further, the torque transmitting area, namely the “torque coupling”. Such a torque coupling can either be formed on the side of the sealing flange which is facing the interior of the hollow body and/or on the front side of the sealing flange.
In both embodiments its function is similar to a wrench, which is placed on the head of a screw to transfer a torque. In a similar manner, the cross section of the torque coupling and the complementary coupling socket is formed:
In the most general case, a torque is transmitted by each non-circular cross-section, by pressing of all different from a circular line shaped areas of the outside area of the torque coupling to the complementary area of the coupling socket.
For the cross section simply to construct variants are polygons, i.e. polygons that consist of interconnected lines. The simplest polygon is a triangle. It has in principle the largest extension in the radial direction with respect to the central axis of the torque coupling. Applicable are of course also all other polygons, such as a rectangle, a hexagon (hexagon), an octagon (octagon), a nonagon (Neuneck), a decagon (decagon), a dodecagon (dodecagon) or another quantity of areas.
In the most general case, this polygon has a random shape. Since in practice, however, the connector usually has only one single circular outlet, it makes sense to choose a regular polygon, which surrounds the circular outlet with a regularly repeated variation of the wall thickness to the outlet. That is, all lines have the same lengths and form with each proximate line the same angle. With an increasing number of corners such a regular polygon approaches more and more the circle. Thus also the effective ratio of the area for transmitting the torque decreases in the longitudinal section. This effect is illustrated best by the fact that in the cross-section a circle is drawn inside the polygon, that touches all edges tangentially. A second circle is defined through the edges of the polygon, which is then concentric to the inner circle. The distance of the two circles from each other limits the area ratios that are effective for the torque transmission. With a regular triangle the area ratios are the largest, therefor there are however only three of these areas. With a regular dodecagon for example, these areas are significantly smaller, but are also present twelve times.
Typically for each polygon is that during the transmission of a torque it is loaded the most heavily in the area of its edges. This effect will be particularly visible when there is a small play between the coupling torque and the torque socket. Then the two parts each touch at the first moment only punctiformly. Only by the elasticity of the material the dot becomes an area with increasing force.
This limitation of all polygonal profiles, that in the area of the corners the pressure rises abruptly, can be avoided by the fact, that the outline is a waved line. Then the force load across the outer areas of the torque coupling and the coupling socket doesn't change abruptly but steadily.
As an alternative to polygonal cross-sections the outline of the torque coupling and the coupling socket can also be a star or another jagged line. Compared to a polygon, thus the area is increased, which transmits the force from one element to the other.
In a very simple illustrative embodiment of the torque coupling, it is integrally formed to the front edge of the sealing flange, When assuming theoretically a circular disc as sealing flange, the area of this disc is extended by the “corners” of a polygon. Of course a corresponding counterpart to these “corners” has to be created in the hollow body. In this variant, the diameter of the torque coupling is larger than the sealing area of the connector.
When the area of the sealing flange merges into the area of the torque coupling, there is no precisely defined border between the two areas visible at first glance.
In this embodiment, the area of the sealing flange contributes with its bonding of course also to the transmission of torque. If this area, however, starts to deform already slightly under the load of a torque, which is too high for it, then further torque is transmitted above the outside margin of this area onto the so-called “second torque coupling” and from there to the “second coupling socket”. In this way, the connection between the sealing flange and the slot is protected against overload.
The areas for sealing and for transmission of the torque are to be distinguished very clearly in another embodiment of the torque coupling. In this variant, the torque coupling is integrally formed on the side of the sealing flange, which is facing to the inside area of the sealing flange—that is closer to the centre of the tank. Here the torque coupling—e.g. as a polygonal profile—is attached to the inside area of the sealing flange and is therefore to be seen at first glance as pure torque coupling.
In a further stage of the torque coupling at the inside of the sealing flange, it is proposed for the outline of the cross section of the torque coupling and of the coupling socket, that to a core area at least one strip-shaped area is integrally formed, facing outwards approximately radially. The strip-shaped area is then directing from the core area approximately similar as the blades from the hub in a propeller.
The two embodiments of the torque coupling described above can be used either alone or also in a combination. In the last-mentioned variant the connector of the invention has even two torque couplings: one on the front face of the sealing flange and the other on the area facing towards the tank.
In a more refined embodiment, a further, annular slot is placed beneath the sealing flange in the complementary slot, in which a seal such as an O-ring is inserted. In the case that the welding or bonding of the sealing flange is not perfectly sealed, the O-ring seal performs this function.
In another variant, elongate welding rings are integrally formed to the sealing flange and/or the torque coupling. In a first variant the material of these welding rings projecting the proximate areas will liquefy when welded and will spread on the proximate areas of the sealing flange and the coupling socket and/or the slot on the surface of the hollow body and thus ensure a tight connection.
This effect can thereby be amplified that the welding rings rest on same extending second welding rings, which are also melted during the welding process, so that even more liquid material is available.
Alternatively, the welding rings join into complementary shaped welding grooves in the slot or in the coupling socket. When welding the sealing flange, the liquefied material of the welding rings flows into the welding Grooves and liquefies there the top layer.
In all three variants, the profile of welding rings and welding grooves can be curved or angular. In their course rings and grooves can be continuously straight or waved. However a dotted or dashed course is also possible and reasonable.
In the simplest case, the sealing flange lies on the surface of the hollow body around the outlet. Alternatively, for an even better connection of the sealing flange with the hollow body, the sealing flange can be inserted into a complemetary slot of the hollow body, which surrounds the coupling socket.
The hollow body of a pressure tank of the present invention is in practice usually made of a thermoplastic, which receives its shape by blow moulding or by injection moulding in a corresponding counterpart. Advantages of this method are the relatively short processing time and comparatively low processing costs in the production of each single exemplar. A limitation is however, that such a hollow body can only withstand a very limited pressure. Therefore, the compressive strength is increased by appyling fibres such as glass fibres or carbon fibres or aramid fibres or dyneema fibres. These fibres are laid in rings or in waved lines around the hollow body and are bonded with resins to each other and on the hollow body. These resins may then be crosslinked thermally or by radiation with UV light and thus cured.
In the simplest case, the connector contains for the connection of the therewith linked valve or hose or tube an internal thread, a bayonet or the counterpart of another coupling. For very filigree couplings or higher claims, a further coupling for example of metal, can be inserted or embedded in the outlet, which fits exactly to the connecting profiles. So that this additional profile itself is not rotating towards the connector during a torque transmission, it meaningfully has on its outside area a polygonal or other non-circular profile.
If this coupling is embedded in the connector, thus an exactly complementary counterpart is generated. Between the connector and the coupling the torque is then transmitted in the same way as between the connector and the hollow body.
Below further details and features of the invention shall be explained more detailed by means of an example. This shall however not limit, but only explain the invention it shows a schematic illustration:
In the front side of the hollow body 1, the outlet 11 is visible through which a view to the interior 12 of the hollow body is released.
The embodiment of a pressure tank of the invention shown here, comprises a connector 2, which transmits a torque from connector 2 to the hollow body 1 through the two—different from each other—torque couplings 23 and 25.
The first torque coupling 23 comprises a central octagonal area and on two opposite edges integrally formed strips, which is designed complementary to the first coupling socket 13 in the hollow body 1. This extends around the outlet 11. In the shown embodiment, it comprises an octagon, to which on two opposite edges strip-shaped extensions are formed integrally, which extend radially to the outlet 11. The first coupling socket 13 is the level which is countersunk the most into the surface layer in the area of the outlet 11.
The second torque coupling 25 is in the illustrated embodiment also a polygon, which is designed here as an octagon, that continues without further outlet directly from the sealing flange 22.
In
For torque transmission from the connector 2 to the hollow body 1 serves in the embodiment shown in
By four double arrows it is illustrated how the connector 2 has to be rotated and lowered so that it can be inserted into the slot 14 and the two coupling sockets 13 and 16.
In
As an additional variant is in the illustrated embodiment a further e.g. metallic coupling inserted in the middle of the connector 2 around the outlet 21. It offers a thread on its internal side, with which a valve, a tube or a hose can be connected. Alternatively the guides of a bayonet or other elements can be formed integrally.
In
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2011 111 406.1 | Aug 2011 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/DE2012/000824 | 8/16/2012 | WO | 00 | 4/25/2014 |
