FI96390C - Ways of freezing liquid used in bending double-walled tubes - Google Patents

Description

96390

Freezing method for liquid used in bending a double wall pipe

The invention relates to a method for bending 5 nested tubes to a desired shape so that the air gap between the tubes remains uniform. The method utilizes a phase change of a liquid, most preferably water, by freezing it in the air gap between the tubes and performing bending of the tube while the liquid is frozen. Liquefied gas is used for freezing.

The use of catalysts to clean vehicle exhaust has created a large market for double-walled tubular exhaust. For this reason, manufacturing methods that would be suitable for series production in a simple and inexpensive manner have been quite intensively researched and developed recently. Thus, a wide variety of tools have been developed for bending double-walled pipes in addition to the traditional mandrel. In double-walled exhaust pipes, the air gap is usually left so small that it is very problematic and difficult to manufacture the tool required for bending. In particular, there are difficulties with small bending radii. Various materials have been tried for the manufacture of mandrels, but organic materials such as plastics or the like do not withstand the stresses of cold forming of metal due to their strength and toughness. Various fillers such as sand and balls have also been used in bending pipes. However, the problem with these has been that after bending, some of the filling material has remained in the air gap.

30 Due to its incompressibility, the liquid has also been used as a filler in the air gap during the shaping step. When the liquid is frozen, it forms a very well-shaped solid in the air gap. However, the slowness of the process has been problematic in freezing, and the process becomes difficult if the freezing of the liquid is carried out by conventional methods with refrigeration machines or the like. In this case, long freezing times are required and in most cases several workpieces have to be placed in a freezer or the like.

It is an object of the present invention to provide a flexible method of bending a double-walled pipe using a liquid and a phase change solid to keep the pipes apart during the bending step. The method according to the invention is suitable for the production of mass-10 and does not cause any separate buffer storage, but the freezing can be carried out at approximately the same time as the bending of the pipe.

The invention is based on the fact that the liquid placed in the air gap is rapidly frozen by means of a liquefied gas which is sprayed on the surface of the double-walled tube to freeze the water in the air gap or a similar liquid. More specifically, the method of freezing a liquid used in bending a double-walled pipe according to the invention is characterized by what is stated in the characterizing part of claim 1.

The method according to the invention achieves considerable advantages. In mass production, the manufacturing method is made flexible without separate buffer stocks at different stages and the entire line can be automated. The equipment used to process the water required to freeze the water is simple and inexpensive to purchase. Savings in manufacturing costs are achieved by thermally insulating the equipment and piping in which the liquid, cooling gas is dispensed. The device can be thermally insulated from thermos 30 vials by known techniques or using other effective isolation methods. The dosing of the cooling liquid gas can also be adjusted in advance, in which case the desired cooling effect is achieved on a unit-by-piece basis. Liquid cooling gas storage production at the site 35 can be performed with the prior art in a variety of ways: Hill 1 1 i.Hk; . i 3 96390 way depending on gas demand and consumption. For example, various portable container tanks and centralized gas storage can be used.

In the following, the invention will be explained in more detail with reference to the accompanying drawings.

Figure 1 schematically shows the bending process of a double wall pipe.

Figure 2 shows a schematic of the freezing method.

Figure 3 shows a top view of the cooling chamber used in the method at section I-I.

In Figure 1, the number 1 refers to the cutting of the outer tube and the number 2 to the cutting of the inner tube. In step 3, an expansion or contraction of the base of the pipe is performed. Step 3 is performed with the pipes nested. The ring can also be used to connect and connect pipes. In step 4, the pipes are welded together at their lower ends in a gas-tight manner. In step 5, a liquid is introduced into the air gap between the pipes, and in step 6, the liquid in the air gap is frozen. In step 7, the pipe is bent and in step 8, the liquid in the air gap is melted and allowed to drain out. In Figures 2-3, the number 9 refers to the outer tube and the number 10 to the inner tube. The extension at the end of the pipe 10 is marked with the number 11 and the joint of the pipes nu-25 with the number 12. The space between the pipes 9 and 10 is marked with the number 13 and the liquid inside it with the number 14. The cooling chamber is marked with the number 15, its walls with the number 16 and the bottom at number 17. The chamber 15 is placed on legs 18. To place the nested tubes 9 and 10 in the cooling chamber 15, the inner edges have guide pins 19 at the inner edges. The inner tube 10 is closed at the top by a plug 20. The through the base 17 to a nozzle 24 with holes 25, 4, 96390 through which liquid gas is led to the inner surface of the tube 10. In the lower part of the cooling chamber 15 there are cross support ribs 26, which form a gap between the bottom 17 and the lower end of the nested tubes 9 and 10. From this gap, the cooling gas can flow freely into the outside air along the passage 27. The insulation of the pipe 23 is marked with the number 28.

The method according to the invention is used in the following way. The nested tubes are cut in steps 1 and 2, after which in step 3 the other end of the inner tube is expanded into the outer tube or the outer tube is contracted against the inner tube or a centering sealing ring is used, after which the nested tubes 9 and 10 are welded together at one end. gas tight. Liquids 15 are then introduced into space 13 and nested tubes 9 and 10 are placed in cooling chamber 15. Liquid gas is dispensed through valve 22 from tank 21 to nozzle 24, from where it is injected through holes 25 onto the inner cylindrical surface of the inner tube and the resulting gas is released into the atmosphere or 20 are recovered. The inner tube 10 is closed by a plug 20 which prevents gases from entering the outside air directly. The resulting gas is forced to flow through the lower part of the chamber 15 along the passage 27 to the outside air, whereby the cooling effect of the gas can be fully recovered for cooling the ul-25 tube. As it flows down the surface * of the inner tube 10, liquid nitrogen or the like gasifies and freezes the water 14 in the space 13.

In experiments, it has been found that, for example, a nested tube about 70 cm long with a diameter of 60 and 50 mm requires about 4 kg of liquefied nitrogen to cool and freeze the liquid between them. Since the temperature of the liquid nitrogen is below -190 ° C, a fairly efficient and rapid freezing is achieved. The use of nitrogen also has the advantage that the gas can be freely released into the atmosphere.

•. i «t« 4 «i i · n 5 96390 This application discloses an embodiment of the method according to the invention. However, it will be clear to a person skilled in the art that the invention according to the method can also be used differently from what has been illustrated above. The cooling gas used can be chosen other than nitrogen and the equipment itself can be implemented in another way. Thus, for example, it is possible to spray the cooling gas in liquid form in one way and in another place, for example on the outer circumference of the pipe. The preparation and storage of the liquefied gas used can also be performed in several different ways. Additional advantages can be achieved in the method by also enhancing the thermal insulation of the cooling chamber 15 and the thermal insulation 28 of the pipe 23.

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Claims (5)

9 6 3 9 Γ A method of freezing a liquid used in bending a double-walled pipe, wherein water or a similar liquid 5 is introduced into the space (13) between the walls of the pipes (9) and (10) and cooled and frozen during shaping, said pipes being bent to the desired shape. ) is achieved by passing a gas jet in the liquid state 10 onto the cylindrical surfaces of the double-walled tubes (9, 10 or the like) and then allowing the liquid to gasify and pass through the gate (27) or the like in gaseous form to cool the tube 15 (15). A method according to claim 1, characterized in that the liquid gas is injected by means of a nozzle (24) or the like onto the surface of the inner cylinder of the tube (10) and the liquid gas is allowed to drain by gravity and freeze the liquid (14). A method according to claim 1, characterized in that the mouth of the inner tube (10) is closed with a plug (20) and the generated gas is circulated under the double wall tube on the support fins (26) to the wall of the outer tube (9) and the cooling chamber (15). form • · along the ground passage (27). Method according to Claim 1, characterized in that the cooling chamber (15) is insulated from its jacket (16), the base (17) and the jacket of the tube (23) in order to reduce heat loss. A method according to claim 1, characterized in that the double-walled pipe is placed in the cooling chamber (15) by means of guide pins (19) centering the double-walled pipe and that the space for gas discharge at the bottom of the cooling chamber (15) is provided by cross-support straps (26) or the like. ! l 1 Itf i 3-121 I i} st! • · 96390