Pressure tank for a water heating device made of stainless steel and method for manufacturing a pressure tank

Abstract

Pressure tank for a water heating device made of stainless steel, wherein the tank is a hollow body with a circular-cylindrical central section and hemispherical end sections, wherein the length of the cylindrical central section is greater than the diameter of the cylindrical central section, characterized in that it comprises two identical deep-drawn tank halves (14), each comprising one half of the cylindrical central section and one half of each hemispherical end section, such that the common parting plane (7) of the tank halves coincides with a longitudinal axis (26) of the tank, wherein the tank halves are welded together in the common parting plane (7), and wherein the two tank halves are provided with a surrounding flange during deep drawing, the flange providing welding material for fusing the two tank halves by melting the flanges as a whole during welding;and forms a surface that is essentially flush with the tank wall on both the inside and outside, thus preventing weld cracks on the inside of the tank.

Description

[0001] The present invention relates to a pressure tank for a water heating device made of stainless steel. The invention also relates to a method for manufacturing the pressure tank.

[0002] The principles of the most commonly used technology today for manufacturing stainless steel pressure tanks are set out in the attached document. Fig. 1 shown.

[0003] Fig. Figure 1 shows a stainless steel pressure tank comprising a rolled sheet, which is welded lengthwise in a weld 1 to form a tube S and bent over at both ends. Two caps (P1 and P2) are deep-drawn to form an upper and lower part, respectively. Holes are punched for connections, and bent surfaces are provided for welding between the tube and the upper part P1. A winding 28 is inserted through the connections in the upper part P1, and the upper part P1 and the lower part P2 are then welded to the tube S along its circumference in welds 2 and 3. In a 200-liter tank with a diameter of 50 cm, approximately 4 m of welds are distributed among welds 1, 2, and 3. Since the welds are butt welds (see the sections on the underside in Figure 1), the required length of welds is approximately 4 m. Fig. 1) High precision is required, and the sheets need a material thickness of approximately 1.2 mm for laser welding, without additional material to avoid holes in the weld joints. Furthermore, the tank comprises a relatively large number of parts, requiring a significant amount of welding and material.

[0004] P1 and P2 can also be welded together, but due to limitations regarding how deep they can be drawn, the volume of the tank is limited to approximately 100 l, with a diameter of approximately 50 cm.

[0005] US 4,779,757 A relates to a container for chemically aggressive liquids and gases, with an inner lining comprising a coating of wire mesh or expanded metal welded to at least part of the inner surface of the container, and a layer of synthetic resin putty applied to this coating.

[0006] US 2008067179 describes a water tank made of plastic. This tank comprises two identical end sections and a possible intermediate section. Because the tank sections are made of plastic, there are relatively few limitations regarding their depth. However, a plastic tank is not suitable for use as a water heating device when the temperature and pressure are relatively high. According to this known solution, the tank sections are joined using a clamping ring and seals. DK 200600284U3 describes a spherical hot water tank. This tank is made of two halves. How the two halves are joined is not described.

[0007] JP 2002211558 describes a fuel tank. This tank is made of two separate parts joined together to form a relatively flat tank suitable for positioning in a vehicle. The joint appears to have been achieved by welding flanges onto the two halves. The flanges are intact after welding, and a distinct slot is formed on the inside of the tank. Since the tank is intended to be filled with fuel, corrosion problems are not as relevant for this tank as they would be for a hot water tank. Furthermore, the relatively flat shape is not suitable for a pressure tank.

[0008] US 2001 / 0054613 also describes a fuel tank. This tank is made of plastic. It is manufactured by placing two halves with their respective flanges against each other and joining them. The flanges remain intact after joining.

[0009] WO 2013 / 055433 describes a method for adding an aerogel coating to the inside of a tube or sphere, wherein the sphere is rotated about two axes to distribute the coating. Objectives of the invention

[0010] One objective of the invention is to use fewer and essentially identical parts. Another objective is to create a shorter weld path and a weld joint with sufficient material to join the two parts without the need for additional material. A further objective is to enable welding with a higher current and at a higher welding speed by employing laser welding without additional material. A desired result of this is the ability to use thinner sheets for the tanks. This allows for a weld joint that provides a reliable weld without burn-through, even when using sheets that are approximately 20% thinner.

[0011] This reduces the weight, and the thickness of the sheets is limited only by the required test pressure, which does not cause permanent deformation. The welded joint is therefore not the limiting factor. The present invention is particularly suitable for use in conjunction with connections that can be inserted into the tank without welding, as described in the simultaneously filed patent application NO 20140171 entitled "Pipe end piece for a tank made of stainless steel, steel or plastic and method for attaching the end piece to the tank". With the aid of these two inventions, rapid assembly of the parts within the tank is made possible, while at the same time the tank is not weakened by the heat load during welding.A further consequence of this invention and the invention in the aforementioned parallel application is that the number of work steps is reduced, resulting in a shorter cycle time and a better tank at a lower price.

[0012] These and other objectives of the invention are achieved with a pressure tank for a water heating device, characterized in that it has two identical deep-drawn tank halves which are welded together in a common parting plane, and that the tank has a longitudinal axis which lies in the parting plane, so that a cylindrical, elongated tank with a circular cross-section is provided.

[0013] Since the tank halves are formed or deep-drawn metal sheets with a surrounding flange, and the flange is used to join the two tank halves by welding the flanges together without additional material; since the flange as a whole is melted during welding and forms a surface that is essentially flush with the tank wall on both the inside and outside, thus leaving no weld gap on the inside of the tank, a good weld is obtained with a relatively small wall thickness for the tank.

[0014] The tank halves preferably include planar sections for connecting pipe ends, as these planar sections are formed in the same process as the forming or deep drawing. This allows the tank to be manufactured in fewer steps. The pipe ends will also be partially protected beneath the surface of the tank wall.

[0015] The object of the invention is further achieved by a method for manufacturing a pressure tank, characterized in that two identical tank halves are produced by deep drawing and that the two tank halves are welded together in a common parting plane, whereby the resulting longitudinal axis of the tank lies in the common parting plane, thus providing a cylindrical, elongated tank with a circular cross-section, and in that the two tank halves are formed with respective enclosing flanges. The flanges are used as the joining material during the welding of the two tank halves without the further addition of any material. The flange material melts to form a weld seam that is essentially flush with the tank wall on both the inside and outside, thus preventing any weld gap from forming on the inside of the tank.

[0016] The flanges preferably protrude approximately 3 mm beyond the tank wall, with a sheet thickness of approximately 1 mm. It has been found that this achieves optimal welding without requiring additional or excess material.

[0017] In a preferred embodiment, the tank is clamped after welding so that it can rotate about an axis of rotation extending perpendicular to the parting plane. A limited quantity of pickling fluid (acid) is poured into the tank, and the tank is rotated at least one full turn about the axis of rotation. This allows the pickling fluid to flow along the weld seam on the inside of the tank, and the remaining fluid is then drained from the tank. The amount of pickling fluid is adjusted to be sufficient to cover the weld seam, thus minimizing the application of pickling fluid outside the weld seam. This ensures that the pickling fluid is applied only where needed and reduces the amount of pickling fluid required to a minimum.

[0018] By forming flat sections in the tank wall during the formation of the tank halves for connecting pipe ends through the tank wall, the number of work steps in the manufacturing process is reduced.

[0019] By fitting the internal pipes in the tank, such as coils and inlet and outlet pipes, into at least one of the two tank halves before joining them, the manufacturing process is further simplified. This also provides better access during the fitting process. It will also be easier to verify internally that the fitting has been carried out satisfactorily.

[0020] With the present invention, the tank volume can be easily adjusted by shortening or lengthening the longitudinal axis, while the depth remains the same during deep drawing, e.g., approximately 250 mm. This results in a tank with a diameter of 500 mm, which is suitable for constructing a water heating device with an outer diameter of 600 mm. By varying the longitudinal axis, the tank can be manufactured with any volume between 50 l and at least 400 l. Drawings Fig. Figure 1 shows, as mentioned above, a method for manufacturing a tank according to the state of the art. Fig. Figures 2a-2f show the production of a tank according to the invention step by step: Fig. Figure 2a shows a sample sheet for the production of one tank half. Fig. Figure 2b shows the sample sheet after deep drawing one tank half. Fig. Figure 2c shows the tank half after the removal of excess material on the flange. Fig. Figure 2d shows one half of a tank with a fitted coil. Fig. 2e shows two tank halves immediately before they are joined together. Fig. Figure 2f shows a completed tank. Fig. Figures 2g-2i show welding flanges and weld seams for welding the two tank halves together: Fig. Figure 2g shows a section of the tank halves immediately before they are joined. Fig. Figure 2h shows a section of the tank halves in a connected arrangement. Fig. 2i shows a section after the two tank halves have been welded together. Fig. Figure 3 shows a composite tank in a more detailed view.

[0021] Fig. Figure 4 shows a possible framework for rotating the tank during internal pickling of the weld.

[0022] Fig. Figures 2a-f schematically show an imaginary production chain, where Fig. 2a a sheet 12, or possibly a sheet roll, which is to be fed into a large deep-drawing press (not shown) with a forming tool (not shown) that corresponds to the desired shape. In Fig. 2b The sheet metal is drawn into a desired shape to form one tank half 14. Deep drawing can, for example, produce half a tank section corresponding to a tank with a diameter of 500 mm, but the length can be variable to achieve the desired volume. The mold also includes sheet metal recesses 30, 32, 34, 36, 38, for example, for connections. The necessary clamping of the sheet metal takes place in area 20, which lies in the parting plane of the mold, and a sheet metal flange is thereby formed in the parting plane around the opening of the tank half 14.

[0023] Fig. Figure 2c shows the same tank half 14, in which almost the entire sheet metal flange 20 has been removed, for example by being burned away using a laser. However, a weld flange 22 with a height of, for example, 3 mm and a sheet thickness of approximately 1 mm remains around the entire edge of the tank half 14. This provides an adequate height for the weld flange 22 and an optimal amount of material for the weld, as will be explained later.

[0024] Fig. Figure 2d shows the same tank half 14, now designated 14a. Cutouts are punched in surface areas 30 and 32, with an inwardly bent cylindrical flange with a depth of, for example, 6 mm. Subsequently, a winding 28 with two end pieces 40, which are welded and thus bolted firmly to the flanges in surface areas 30 and 32, is inserted. End pieces are inserted in the other surface areas 34, 36, 38 in the same manner, if necessary. Preferably, pipe end pieces and the method described above in connection with the parallel application are used.

[0025] Fig. Figure 2e shows a second tank half, designated 14b. This was deep-drawn in the same process as the first half, 14a. The first and second halves, 14a and 14b, are identical. This reduces the number of different parts. Holes for attaching the end-piece connections are also punched into the flat sections 30, 32, 34, 36, and 38 in the second half, wherever necessary. The inlet and outlet pipes (not shown) are fitted into the tank through openings in the top, corresponding to the fitting of the coil 28.

[0026] Fig. Figure 2e shows that the second half 14b is arranged over the first half 14a in order to be welded together in the welding flanges 22a, 22b (see Fig. 2g). Subsequently, the two halves are joined in connection 24 to form a complete tank with a circular cross-section, as in Fig. 2f shown, welded together. The tank is now complete in terms of its contents, e.g. with a coil, inlet and outlet pipes and pipe ends.

[0027] The welding itself is in Fig. 2g-i shown. In Fig. 2g are the two halves immediately before they are joined together. Fig. 2h the halves are placed next to each other and the flanges 22a and 22b are held firmly together using suitable means. In Fig. In section 2i, flanges 22a and 22b are welded together to form a weld 24 by welding without additional material, e.g., by tungsten inert welding. Of course, other welding processes without additional materials can also be used. With a relatively small sheet thickness, flanges 22a and 22b, with a height of approximately 3 mm, can still provide a sufficient amount of material to be melted into a proper weld. By adjusting the available amount of material for the weld, a complete weld can be obtained on both the inside and outside of the tank, e.g., without any weld cracks, but with the weld being essentially flush with the tank wall. Therefore, there are no cracks that could lead to corrosion when the tank is filled.

[0028] Fig. Figure 3 shows the welded tank in more detail. It consists of two identical tank halves 14a and 14b, welded together with a common parting line 7. The parting line coincides with a longitudinal axis 26 to provide an elongated tank. Similarly shown are the required recesses 30, 32, 34, 36, 38 in the tank to provide connecting elements, and a welded joint 24 formed by the flanges 22a and 22b.

[0029] Fig.Figure 4 shows a tank according to the invention, made from two halves 12a and 12b. After welding, the tank is clamped in a frame 44 around a pivot axis 4c. To pickle the weld 24 inside the tank, approximately 1 liter of pickling fluid is poured in through a pipe end 40. The pickling fluid flows down to the center of the bottom. When the tank is rotated around the pivot axis 4c, the fluid flows along the weld 24, which is always located on the bottom of the tank. Thus, the fluid covers the entire inner weld. The fluid does not flow to other parts of the tank but is only applied where required. After a 360-degree rotation, the pickling fluid flows out through the same pipe end 40, and any remaining pickling fluid is removed by pressure testing with water.

[0030] With the present invention, the tank has one-third fewer parts, and the welding distance is approximately 30% to 60% shorter. The amount of material used can be reduced by approximately 20%, particularly with regard to the possibility of reducing the sheet thickness. Furthermore, it is easier to insert pipe ends, windings, etc., since this can be done before the halves are welded together. Pipe ends and windings are fitted by screwing them in instead of welding. A 100% more reliable pickling of the inner weld is achieved without covering other parts of the tank with pickling fluid. Using the welding flanges, a very reliable and strong weld is obtained, even though thin material is used.

Claims

[1] Pressure tank for a water heating device made of stainless steel, wherein the tank is a hollow body with a circular-cylindrical central section and hemispherical end sections, wherein the length of the cylindrical central section is greater than the diameter of the cylindrical central section, characterized by, that it comprises two identical deep-drawn tank halves (14), each comprising one half of the cylindrical central section and one half of each hemispherical end section, such that the common parting plane (7) of the tank halves coincides with a longitudinal axis (26) of the tank, the tank halves being welded together in the common parting plane (7), and that the two tank halves are provided with a surrounding flange during deep drawing, the flange providing weld material for fusing the two tank halves by melting the flanges as a whole during welding; and forming a surface that is substantially flush with the tank wall on both the inside and outside, thereby avoiding weld cracks on the inside of the tank. [2] Pressure tank according to claim 1, characterized bythat the two tank halves include planar sections for inserting pipe ends, the planar sections being formed in the same step as the deep drawing. [3] Pressure tank according to claim 1 or 2, characterized by that the flanges protrude approximately 3 mm from the tank wall before welding and that the sheet thickness is approximately 1 mm. [4] Pressure tank according to any of the preceding claims, characterized by , that it further includes internal pipes in the tank, such as windings and inlet and outlet pipes, which have been fitted into at least one of the two tank halves before the tank halves were joined. [5] Method for manufacturing the pressure tank according to any one of claims 1 to 4, characterized bythat after welding the tank is firmly clamped so that it can rotate about an axis of rotation (4c) perpendicular to the parting plane; that a limited quantity of pickling fluid (acid) is poured into the tank; that the tank is rotated at least one full revolution about the axis of rotation (4c) so that the pickling fluid runs along the weld seams on the inside of the tank; and that the remaining fluid is then drained from the tank; that the quantity of pickling fluid is adjusted to be sufficient to cover the weld seam, but that the application of pickling fluid outside the weld seam is avoided as much as possible. [6] Method for manufacturing a plurality of stainless steel pressure tanks according to any one of claims 1 to 4, wherein each of the tanks is a hollow body with a circular-cylindrical central section and hemispherical end sections, wherein the length of the cylindrical central section is greater than the diameter of the cylindrical central section, characterized by , that each tank comprises two identical deep-drawn tank halves, each tank half comprising one half of the cylindrical central section and one half of each hemispherical end section, such that the common parting plane (7) of the tank halves coincides with a cylinder longitudinal axis (26), wherein the tank halves are welded together in the common parting plane (7), the plurality of tanks having the same diameter and different lengths, such that the volume of each tank depends on the length of the cylinder axis.

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