TANK, ESPECIALLY FIRE EXTINGUISHER CYLINDER, PROVIDED WITH INNER CORROSION PROTECTION, AND PROCESS FOR PRODUCING IT

Abstract: Tank, especially fire extinguisher cylinder, provided with inner corrosion protection, having a metal tank, preferably a metal tank made of steel plate and an inner surface made of corrosion resistant material bordering the inner space of the tank, the inner surface made of corrosion resistant material is the inner surface of an insertion tank made of thermoplastic synthetic material, especially polyethylene terephthalate, which insertion tank seats to the inner surface of the metal tank and lines the mouth opening of the metal tank.

Description: Tank, especially fire extinguisher cylinder, provided with inner corrosion protection, and process for producing it The object of the invention is a tank, especially fire extinguisher cylinder, provided with inner corrosion protection, which tank has more efficient corrosion protection as compared with the known tanks due to its construction, as a result of which it can be used as a tank for fire extinguishers filled with especially aggressive material, e.g. fire foam solution composition. The tank according to "the invention comprises a metal tank, preferably made of steel plate, and an inner surface made of corrosion-resistant material bordering the inner space of the tank. /Another object of the invention is a process for producing " the "tank provided "with " this kind of inner corrosion protection, which process is simpler and cheaper than the known methods for similar purpose. There are several methods for inner corrosion protection of tanks. At a widespread solution used with metal tanks of 0.5 - 100 litres, especially tanks used with fire extinguishers, thermoplastic synthetic powder is brought into the metal tank, usually made of steel plate, the powder in the tank is fused via heating the tank, lately via induction heating of the tank, and the inner surface of the tank is covered with the fuse via moving the tank. When the tank cools down the fuse solidifies and forms a protective coating adhering to the inner surface of the tank. The continuity and the homogeneity of the protective coating is checked by high tension combed sounding electrode. In addition to the fact that an expensive moving device is requixed so as to move the tank, the disadvantage of this solution is that, in order to achieve the required adhesion of the protective coating, pre-treatment of the inner surface of the tank is necessary, further, in spite of the automated manufacturing, the protective coating formed by this method is porous at certain places and its thickness is not uniform. As a result, when the tank is used, and the tank is filled with some aggressive, corrosive (acidic) material, e.g. fire foam composition, and it is stored in the tank for longer time, in certain cases stored under pressure, the material stored in the tank soaks through the pores and gets between the protective coating and the wall of the tank. As a result, the protective coating gradually gets off the wall of the tank, the filling material destroys the wall of the tank, damaging the tank this way, making it weaker, the material of the tank gets into solution and it changes the chemical composition of the solution, as a consequence of which the durability, efficiency and this way the serviceability of the fire foam solution composition changes. It is a further disadvantage of this solution that covering the tank using such a method requires an expensive apparatus. At a second solution liquid varnish, especially phenol- formaldehyde varnish, is brought into the inner space of the tank, and the inner surface of the tank is covered with the liquid varnish via moving the tank, and the varnish is burned into the surface via heating the tank. At a third solution multicomponent synthetic resin is brought into the tank also in liquid form, and a protective coating is formed by the solidified synthetic resin via moving the tank. A common disadvantage of these solutions is that the technological time required for producing the protective coating is long, which makes the manufacturing expensive, and further, expensive special machines are required for supplying and for moving the tank. A further common disadvantage of the presented methods is that the filling under overpressure in th-e tank locally getting between the protective coating and the wall of the tank can remove the protective coating from the wall of the tank when the overpressure in the inner space of the tank ceases, e.g. if it is a fire extinguisher, when it is used or discharged so as to be recharged for warranty or safety reasons, and this way the tank, e.g. the fire extinguisher, becomes unserviceable. It is a further common disadvantage that in every case the entire mass of the tank must be warmed or heated to a certain temperature so as to produce the protective coating, which, taking into consideration that the tank must be cooled or let cooled down after the protective coating has been formed, requires significant unnecessary use of energy. It is a further significant disadvantage especially with tanks to be used for long period of time, e.g. fire extinguishers, that if the tank is repainted in the course of a reg-eneration, which usually requires burning down the outside paint coat, the inner protective coating is also damaged, and it can only be renewed by producing a new protective coating using the original production machine, it can not be reproduced subsequently. The disadvantages of the above described solutions made it necessary to develop a tank which is not only of the required mechanical strength and pressure tightness, but has a reliable corrosion protection and can be produced in a simple, easy, cheap and economic way. It was a further requirement to develop a construction where, if supplied with a suitable intermediate piece, it can be ensured that if the tank is connected to a unit, e.g. a valve, the filling can not contact the less corrosion resistant surface of the tank -even when flowing out from the tank, and this way a continuous corrosion-protected surface is achieved, and further, the tank can keep t e high pressure for a long period of time. When developing the invention we started out from the fact that the problem with the above described tanks and the production method thereof is how to solve the adherence of the protective coating to the internal surface of the tank made of steel, and that the disadvantages of the known solutions originate from the fact that the imporosity and the adherence of the protective coating are not satisfactory. The fundamental idea of the invention is that the corrosion resistance should not be achieved by a forming a protective coating adhering to the wall bordering the inner space of the tank, but the mechanical strength and pressure tightness required from such tanks and the requirement of resistance against aggressive fillings can only be met if producing a tank where these two requirements are separated, and the tank consists of two parts, one part meeting one requirement and the other part meeting the other. Therefore the tank, especially fire extinguisher cylinder, provided with inner corrosion protection being a solution for the problem according to the invention has a metal tank preferably made of steel plate and an inner surface made of corrosion resistant material bordering the inner space of the tank. The essence of the tank is that the inner surface made of corrosion resistant material is the inner surface of an insertion tank made of thermoplastic synthetic material, which insertion tank seats to the inner surface of the metal tank and lines the mouth opening of the metal tank from the inside. At a preferred embodiment of the invention the material of the insertion tank is polyethylene terephtalate. At a preferable embodiment of the tank the insertion tank projects over the mouth opening of the metal tank and overlies the rim of the mouth opening. The insertion tank suitably has a collar, with this collar the insertion tank fits to the rim of the mouth opening of the metal tank. At another preferable embodiment the metal tank has a neck extension piece welded to its mouth opening, which neck extension piece has a thread on its inner and/or outer surface. The neck extension piece can be fixed to the metal tank by welding. At an advantageous embodiment of the tank the metal tank has air channel (s) near its mouth opening leading to the free atmosphere. At another preferable embodiment the metal tank has ducts near its mouth opening, mainly groove (s) and/or hole(s) forming the air channel. It is a very favourable embodiment where there is (are) hole(s) in the wall of the metal tank, preferably in the arched part of the wall, leading to the free atmosphere. The assembly of the tank according to the invention is made easier with the embodiment where there is a threaded intermediate piece made of corrosion-resistant material connected to the neck via screw joint, in its screwed-on position the intermediate piece fits to the insertion tank. With this solution the section leading out from the inner space of the tank is prevented against corrosion. If the tank is used as a fire extinguisher cylinder the threaded intermediate piece has a threaded part to be connected to the valve mechanism ot the fire extinguisher via screw joint. The thread can be either internal or external. It is an especially favourable embodiment where, in its position connected to the neck via screw joint, the threaded intermediate piece forms a sealed joint to the insertion tank. At this embodiment, in its position connected to the neck extension piece via screw joint, the threaded intermediate piece closes the channels leading to the free atmosphere . Another object of the invention is a process for producing tanks, especially fire extinguisher cylinders, provided with inner corrosion protection. The essential idea of the process is that a pre-product, mainly female pre-product, made of thermoplastic synthetic material, is inserted in the internal space of the metal tank, especially made of steel plate, joining at least to a part of the mouth opening "fro the inside, while, if necessary, we leave air channels leading from the inner space of the metal tank to the free atmosphere, we ensure the required deformation temperature for the pre-product, and using the metal tank as a mould, the pre-product is formed to be an insertion tank via blow moulding applying the method known in itself, and than the insertion tank is left in the metal tank. At a favourable realisation of the process the pre-product made of thermoplastic synthetic material is made of polyethylene terephtalate. We note that instead of the phrase "pre-product", in certain references they use the phrase "pre-form". In what follows, the essence of the invention is described in detail by presenting its favourable embodiments, used for fire extinguishers as an example, with reference to the accompanying drawings in which: Figure 1 is a sectional view of a tank according to the invention, the dashed line showing the position of the pre-product at the beginning of the production process, Figure 2 is a detail of the sectional view of an embodiment of the tank according to the invention with a neck piece with internal thread, Figure 3 is a detail of the sectional view of an embodiment of the tank according to the invention with a neck extension piece with external thread, Figure 4 is a magnified sectional view of a part of the tank shown in figure 3, Figure 5 is a detail of the sectional view of an embodiment of the tank according to the invention with a sleeve insert with an internal thread, Figure 6 is a detail of the sectional view of another embodiment of the tank according to the invention with a sleeve insert with an internal thread, Figure 7 is a detail of the sectional view of an embodiment of the tank according to the invention with a neck extension piece with an internal thread, Figure 8 is a detail of the sectional view of an embodiment of the tank according to the invention with a neck extension piece with internal thread and with a sleeve insert, Figure 9 is a detail of the sectional view of another embodiment of the tank according to the invention with a neck extension piece with internal thread and with an intermediate piece. It can be seen in figure 1 that at this embodiment shown as an example the tank 10 is to be used as the cylinder of a 3 kg fire extinguisher has a metal tank 20 and an insertion tank 30 seating to the inner surface of the metal tank 20. The metal tank 20 is usually made from steel sheet plate, while the material of the insertion tank 30 is polyethylene terephtalate, which is a thermoplastic synthetic material. The outer surface of the tank 10 the outer surface 21 of the metal tank 20, while the inner surface of the tank 10 is the inner surface 31 of the insertion tank 30, which is resistant to aggressive agents due to its material. The outer surface of the insertion tank 30 is seating to the inner surface of the metal tank 20, the neck part of the insertion tank 30 projects over, lining the mouth opening and the neck of the metal tank from the inside, and its collar 32 overlies the rim 22 of the mouth opening of the metal tank 20. This way the two tanks form a unit that can not be detached without being damaged, where the required mechanical strength and pressure tightness is ensured by the metal tank 20, while the insertion tank 30 connected to it in tight fit practically acts as only the corrosion protection layer for the metal tank 20. For the sake of the description of the production process to be discussed later, dashed line indicates in the figure the pre-product 15, and the position of it in relation to the metal tank 20, which pre-product 15 will be used for forming the insertion tank 30 as an insert for the metal tank 20. Figure 2 shows the sectional view of an embodiment of the tank 10, where the wall of the neck part 33 of the insertion tank 30 is thicker than that of the other parts, and there is a thread 34 formed in this part with thicker wall, to which the valve of the fire extinguisher (not indicated in the figure) can be connected via screw joint directly or with a threaded intermediate piece inserted. It can clearly be seen in the figure that if a valve or an intermediate piece is screwed into the thread 34, its edge bears up on the collar 32 of the insertion tank 30, this way the corrosive medium, e.g. corrosive fire foam solution, stored in tank 10, can have no contact with the metal tank 20, neither in the disused position of the tank 10, nor when flowing out from the tank 10. Figure 3 shows a detail of the sectional view of an embodiment of the tank 10 with a neck extension piece 41 with external thread. A neck extension piece 41 is mounted by welding to the neck of the metal tank 20 part of the tank 10. There is a thread 42 formed on the curved surface of the neck extension piece 41, a valve can be connected to the tank 10 using it. It can be clearly seen in the figure that the insertion tank 30 projects over the mouth opening of the metal tank 20 and the neck extension piece 41, and with its collar 32 it overlies the free-standing end surface of the neck extension piece 41. This embodiment can be assembled with suitable valve with internal thread or intermediate piece, and it can be seen that in the assembled position the corrosive agent flowing out from the tank 10 can contact the wall of neither the metal tank 20 nor the neck extension piece 41 at any place, this way the protection of the tank 10 against corrosion is ensured, hence it can be safely filled several times, and can be used for a long time. For the sake of the description of the production process to be discussed later, dashed line indicates the initial position of the pre-product 15 in this figure, too. Figure 5 shows a detail of the sectional view of an embodiment of the tank with a sleeve insert with an internal thread. As it can be seen in the figure, the insertion tank 30 projects over the mouth opening of the metal tank 20, and with its collar 32 it fits to the rim 22 of the mouth opening of the metal tank 20. The tank 10 has a sleeve insert 45 made of corrosion resistant material, at this embodiment it is made of copper, situated in the mouth opening lined with the neck part of the insertion tank 30. The sleeve insert 45 is prevented from displacement in the opening partly by the solution that its end 47 penetrating in the inner space of the tank 10 is bent so as to bear up to the neck part of the tank, and partly by the solution that the rim on the other end 48 fits to the collar 32 of the insertion tank 30. The sleeve insert 45 is provided with internal thread 49, a valve can be connected to it directly or with an intermediate piece inserted. Figure 6 shows a detail of the sectional view of another embodiment of the tank 10 with a sleeve insert 50 with internal thread. It can. be seen in. the figure that the insertion tank 30 projects over the mouth opening of the metal tank 20, and with its collar 32 it fits to the rim 22 of the mouth opening of the metal tank 20. The tank 10 has a sleeve insert 50 made of corrosion resistant material, it is made of copper at this embodiment, too. The sleeve insert 50 has an external thread 51 on its curved surface and it also has an internal thread 52, and it is fixed in the thread 34 formed in the neck part of the insertion tank 30 via its external thread 51. The screwed-in position of the sleeve insert 50 is limited by the butt on of the rim of the sleeve insert 50 on its outer end 53 on the collar 32 of the insertion tank 30. The sleeve insert 50 is provided with internal thread 54, a valve can be connected to the tank 10 directly or with an intermediate piece inserted.- It can be seen at this embodiment as well that in the position assembled with the valve the corrosive agent flowing out from the tank 10 can contact only surfaces made of corrosion resistant material. Figure 7 is a detail of the sectional view of an embodiment of the tank according to the invention with a neck extension piece with an internal thread. As it can be seen in the figure, there is a neck ring 25 fixed to the neck of the metal tank 20 by welding so as to increase mechanical strength. There is a groove 27 running around the outer surface of the neck ring 25. The insertion tank 30 joins the inner surface of the metal tank 20 and the inner surface of the neck ring 25 welded to its neck, and it bears up on the rim of the neck ring 25 with its collar 32. At this embodiment the neck extension piece 55 has a part provided with a thread 57 so as to be connected to a valve directly or with an intermediate piece inserted, and has a part embracing the neck ring 25 of the tank, and there is a groove running round in its curved surface. In the position of the neck extension piece 55 fitted on the tank its groove 5£ is positioned opposite to the groove 27 running around the outer curved surface of the neck ring 25, and the two grooves together form a groove for snap ring 60. When it is assembled with the snap ring 60, the snap ring 60 fitting into the grooves lying opposite to each other fixes the neck extension piece 55 in its position slid on the tank. There is a neck extension piece 55 slid on the curved surface -of the neck ring 25, and there is a grove 56 in the inner surface of the neck extension piece 55. It can be seen at this embodiment as well that the corrosive agent flowing out from the tank can contact only surfaces made of corrosion resistant material. Figure 8 shows a detail of the sectional view of an embodiment of the tank according to the invention with a neck extension piece 65 with internal thread connected to the metal tank 20 by welding and with a sleeve insert 70 with internal and external thread. The insertion tank 30 fits to the shoulder 67 formed in the internal surface of the neck extension piece 65 with internal thread connected to the mouth of the metal tank 20 by welding, in which position it is fixed by the sleeve insert 70 made of corrosion resistant material connected to the thread of the neck extension piece 65 with its external thread. At the presented embodiment there is a gasket ring 78 in the surface of the sleeve insert 70 facing the tank suitable for sealing the position of the sleeve insert 70 in its position connected to the tank. The internal thread 72 of the sleeve insert 70 is suitable for connecting and fixing a valve to the tank directly or with an intermediate piece inserted. At the tank shown in figure 9 the insertion tank projects over the mouth opening of the metal tank and its collar overlies the rim oϋ the mouth opening. There is a neck extension piece with internal thread welded on the month opening of the metal tank, which neck extension piece surrounds the collar of the insertion tank, there is an intermediate piece with internal and external thread screwed in the neck extension piece, and the hole in the intermediate piece is opening into the mouth opening of the insertion tank. The valve mechanism is screwed in the intermediate piece, this way it is ensured that when the filling flows out, it will not contact unprotected surface of the tank. In the course of the favourable production process of the tank according to the invention a pre-product 12 is placed on the mouth opening of the metal tank 20 projecting in the inner space of the metal tank 20. The fitted position is indicated with dashed line in figures 1 and 3. The deformation temperature required tor the plastic shaping of the pre-product is ensured as occasion requires, either by pre-heating or by any other known method, and the moulding is realised by the known method via blow moulding using moulding gas, preferably moulding air, using the metal tank as a mould. When the pre-product is inflating, it reaches the wall at the middle of the metal tank first, and it approaches the shoulder and the neck part afterwards. In order to ensure that no air should remain in the shoulder and the neck of the metal tank used as mould hindering the insertion tank to take its final shape, air channels and holes leading to the free atmosphere are formed in the metal tank. Figure 4 shows the grove 28 acting as air channel and the hole 29 leading from the middle of the groove to the free atmosphere applied at the embodiment shown in figure 3, through which the air remained in the neck part of the metal tank can exit when the insertion tank is blew. We let the insertion tank blew to the required size using the metal tank as a mould cool down in the metal tank, or, if it is necessary, it can be cooled down by the known methods , The tank according to the invention meets the specified requirements in full. The metal tank part ot the tank is acting as a mould for the insertion tank, the insertion tank somewhat lays out the metal tank via bearing up on the inner surface of the wall of the metal tank acting as its place of application, the metal tank acts only as a part of " the tank according to the invention providing the required mechanical strength and pressure tightness, while the insertion tank acts as a part separating the material filled in the tank from the wall of the metal tank, preventing the wall of the metal tank from contacting the filling, that is, providing the required corrosion protection. This way there is no requirement for corrosion resistance of the metal tank, and there is no requirement for mechanical strength and pressure tightness of the insertion tank, so many kind of materials can be chosen as material of these tanks, always adjusted to be the best for the given purpose. The major advantage of the tank provided with inner corrosion protection according to the invention is that it has a void-free, continuous protective surface resistant to corrosion to the required extent depending on the material of the insertion tank. It is a further advantage of the tank that the insertion tank providing the corrosion protection can be manufactured easily, economically, with low material costs and short technological time, there is no need for moulder's tools in the course of the manufacturing as it is the metal tank itself, and there is no need for unnecessary energy either. It is a further significant advantage that the part of the tank providing the corrosion protection can be repaired without damaging the other part of the tank or its outside paint coat, and similarly, the outer part of the tank can be renewed without damaging the part of the tank providing the corrosion protection or without causing any change in its quality. It is a further advantage that the insertion tank providing the corrosion protection can be formed even after the tank has been painted and/or the paint coat has been burned in the surface.

Claims: CLAIMS : 1. Tank, especially fire extinguisher cylinder, provided with inner corrosion protection, having a metal tank, preferably a metal tank made of steel plate and an inner surface made of corrosion resistant material bordering the inner space of the tank, ch a r a ct er i s e d in t h at the inner surface made of corrosion resistant material is the inner surface of an insertion taτik made of thermoplastic synthetic material, which insertion tank seats to the inner surface of the metal tank and lines the mouth opening of the metal tank. 2. Tank according to claim 1 ch a r a ct eri s e d i n tha t the material of the insertion tank is polyethylene terephtalate. 3. Tank according to claim 1 or claim 2 c h a r a c te r i s e d i n t h a t the insertion tank projects over the mouth opening of the metal tank and overlies the rim of the mouth opening. 4. Tank according to any of claims 1 - 3 ch a ra c t e r i s e d i n tha t the insertion tank fits to the rim of the mouth opening of the metal tank with its collar. 5. Tank according to any of claims 1 - 4 ch a r a c t e r i s e d i n th a t tne metal tank has a neck extension piece welded to its mouth opening. 6. Tank according to any of claims 1 - 5 cha r ac t e r i s e d i n t h a t there is an inner thread in the neck part of the insertion tank. 7. Tank according to any of claims 1 - 6 cha racte r ised i n t hat the metal tank has a neck extension piece and an external thread on it. 8. Tank according to any of claims 1 - 6 char a ct eri s e d in that the metal tank has an external thread on its neck part. 9. Tank according to any of claims 1 - 8 cha r a c t e r i s e d in tha t the metal tank has vent holets) in the wall of its neck part and/or its shoulder and/or its bottom part and/or its neck extension piece leading to the free atmosphere. 10. Tank according to any of claims 1 - 9 cha r a c t e r ise d in t h at it has a threaded intermediate piece made of corrosion-resistant material connected to the neck extension piece or to a sleeve insert via screw joint, and in its screwed-on position the intermediate piece fits to the insertion tank. 11. Tank according to any of claims 1 - 10 cha r ac t e r i s e d i n tha t it has air channel (s), suitably groove (s), in the wall of the metal tank and/or the neck extension piece, leading to the vent hole (s) . 12. Tank according to any of claims 1 - 11 cha-r a c t e r i s ed i n t h a t the threaded intermediate piece has a threaded part to be connected to the valve mechanism via screw joint. 13. Tank according to any of claims 1 - 12 ch a r a c t e r i s e d i n th a t in the position of the threaded intermediate piece connected to the neck via screw joint, the threaded intermediate piece forms a sealed joint to the insertion tank. 14. Tank according to any of claims 1 - 13 ch a r a c te r i s e d i n t ha t in its position connected to the neck via screw joint, the threaded intermediate piece closes the channels leading to the free atmosphere. 15. Tank according to any of claims 1 - 14 ch a r a c t e r i s e d i n t h a t the insertion tank projects over the mouth opening of the metal tank and its collar overlies the rim of the mouth opening, and there is a neck extension piece with internal thread welded on the month opening of the metal tank, which neck extension piece surrounds the collar of the insertion tank, there is an intermediate piece with internal and external thread screwed in the neck extension piece, and the hole in the intermediate piece is opening into the mouth opening of the insertion tank. 16. Process for producing tanks, especially tanks according to any of claims 1-15, mainly fire extinguisher cylinders, provided with inner corrosion protection, c h a r a c t er is ed in t h. a t a pre-product made of thermoplastic synthetic material is inserted in the internal space of a metal tank, especially metal tank made of steel plate, fitting at least to a part of the mouth opening of the metal tank from the inside, while leaving air channels leading from the inner space of the metal tank to the free atmosphere, the required deformation temperature for the pre-product is ensured, and using the metal tank as a mould, the pre-product is formed to be an insertion tank via blow moulding using moulding gas, preferably moulding air, applying the method known in itself, and than the insertion tank is left in the metal tank and let cooled down, or it. is cooled down using a method known in itself. 17. Process according to claim 16 ch a r a c te r i s e d i n tha t the pre-product made of thermoplastic synthetic material is a pre-product made of polyethylene terephtalate.

Inventors: SZOECS ISTVAN, SZ&ODBLAC
Applicants: SZOECS ISTVAN, SZ&ODBLAC
Application year: 2000
Main classification: B65D
IPC codes: F17C1, F17C3