WO1999058920A1

WO1999058920A1 - Method of manufacturing a curved container wall

Info

Publication number: WO1999058920A1
Application number: PCT/NL1999/000176
Authority: WO
Inventors: Willem Frederik Jense
Original assignee: Omega Engineering Holding B.V.
Priority date: 1998-05-12
Filing date: 1999-03-26
Publication date: 1999-11-18
Also published as: AU3058999A; NL1009138C2

Abstract

A method of manufacturing a curved tank wall comprises of: providing a first (1) and a second (2) flat metal plate; placing the two plates flat against each other; mutually connecting the plates by laser (3) welding such that a weld contour is created which forms two side boundaries of a space corresponding with a channel for forming, on the two respective ends of which are situated openings, for instance continuous holes (9) in at least one plate (1, 2) or an interruption in the weld contour, which openings serve as medium passage opening; bending the mutually connected plates (1, 2) to the desired general shape; admitting medium under pressure via an opening into the space bounded by the contour such that at least one of the plates (1, 2) undergoes a plastic deformation whereby the contour with the plates (1, 2) bounds a channel through which can flow heat transfer medium; performing the welding operation such that the space possesses the general form of a meander; and that on the end of a non-continuous weld seam a sub-weld seam (8) in the form of a closed sub-contour is formed connecting onto this weld seam, which sub-contour has a smooth rounded form.

Description

METHOD OF MANUFACTURING A CURVED CONTAINER WALL

The invention relates to a method of manufacturing a curved tank wall or part thereof, which method comprises the following steps, to be performed successively, of: a) providing a first flat metal plate; b) providing a second flat metal plate; c) placing the two plates flat against each other and holding the plates temporarily in mutually fixed position, for instance by clamping; d) mutually connecting the plates by laser welding such that a weld contour is created which forms two side boundaries of a space corresponding with a channel for forming, on the two respective ends of which are situated openings, for instance continuous holes in at least one plate or an interruption in the weld contour, which openings serve as medium passage opening; e) bending the thus mutually connected plates to the desired general shape; f) admitting medium under pressure via at least one opening into the space bounded by the contour such that at least one of the plates undergoes a plastic deformation such that the contour with the plates bounds a channel through which can flow heat transfer medium; 1) performing step d) such that the space possesses the general form of a meander, wherein substantially parallel meander parts are separated by a single of double weld seam; and m) performing step 1) such that on the end of a non-continuous weld seam a sub-weld seam in the form of a closed sub-contour is formed connecting onto this weld seam, which sub-contour has a smooth rounded form.

In the known art a heat-exchanging tank wall is made by first rolling the tank wall to a round shape from a flat plate. On this cylindrical wall a half pipe is then welded spirally against the tank wall. The mutual distance of two successive windings of the pipe is a minimum of 20 mm. This distance is the space required for the welding torch during welding.

It is also possible according to the prior art to make a heat-exchanging tank wall by welding a profiled plate onto a flat plate and subsequently bending the plate in the direction of the profile. The drawback of this method is that the plate can only be rolled in the direction of the profile and that only a profile with parallel elevations can be applied.

It is further known art to profile a plate in a desired pattern by means of moulds. This profiled plate is then welded onto a flat plate and the assembly subsequently rolled to a desired shape. A drawback is that expensive moulds and high pressure forces are required to profile the plate.

The above stated drawbacks are obviated with a method according to the invention.

The general meander shape as according to step (1) is per se known from DE-A-44 16 645. However, when the structure is "inflated" to form a channel through which heat-transfer medium can flow, the problem occurs in said prior art that great material stresses can occur at the end of the transverse weld seams, whereby there is the danger of cracks. Step (m) according to the invention ensures that such stresses cannot occur according to the invention. It should be understood that the described aspect can only be implemented by making use of laser welding as according to step (d) . As is apparent from DE-A-44 16 645, the technique described therein is wholly based on the use of seam welding. Such a standard technique for this type of structure does not permit the arranging of said smooth, rounded forms of sub-contours. According to a specific embodiment the method according to the invention comprises the step of (q) performing step (1) such that the meander form is defined by two for instance continuous edge weld seams and substantially mutually parallel weld seams in intertwined, mutually staggered relation extending in substantially transverse direction relative thereto.

A particular embodiment hereof comprises the step of

(r) performing step (q) such that the edge weld seams have a smooth round form in each zone between adjacent transverse weld seams.

With this structure a channel is obtained which is free of dead zones and in which the flow of the medium through the or each channel is unobstructed and can substantially take place in wholly predictable manner. With the method according to the invention any desired pattern of the channels for the coolant can be made in simple manner on the tank wall, wherein the tank wall can be deformed in any desired manner, such as for instance by means of rollers, by rolling or bending. It is likewise possible herein to apply the pattern to both the inside and the outside of the tank wall.

It is moreover possible to form the pattern such that the channels lie against each other, whereby a maximum cooling surface area is obtained. In one embodiment both plates are of practically equal thickness, preferably 0.8 mm, whereby after hydraulic deformation they strengthen the tank wall considerably. Because both plates are equally thick they will bulge uniformly towards the inside and the outside of the tank. In combination with the form of the pattern, a strong and stable wall is obtained.

According to the invention welding of the plates is performed by means of a laser. An advantage is that the laser welds the plates to each other from only one side and that the usual protective foil on the underside of the plate thereby remains undamaged during the welding. It is further possible to weld any random pattern with a laser. It is hereby possible to place the 4 channels against each other and to apply stress-reducing geometries in the pattern in order to reduce the local tensile stresses in the plates during the hydraulic deformation. Such a pattern is for instance a droplet shape or circle shape which can be arranged on the end of a non-continuous weld seam. As pattern can be chosen a pattern with a plurality of parallel channels, whereby the pressure drop over the channels is limited.

A tank wall can be manufactured by making use of p) mutual connection of the free end edges of a tank wall, a part or parts thereof.

In a particular embodiment the method has the step of h) performing steps (a) and (b) such that the plates have thicknesses differing substantially from each other, whereby in step (f) the thicker plate undergoes no or only negligible plastic deformation.

In order to form a tank with smooth inner surface on the basis of the thereby obtained tank wall or part thereof, use can advantageously be made of the step of i) performing step (e) such that the thicker plate becomes the inside of the tank wall or the part thereof.

For reasons of hygiene use can further be made of the step of j) performing steps (a), (b) and (e) such that the inner plate of the tank wall or the part thereof consists of stainless steel.

The invention also relates to a curved tank wall comprising two metal plates mutually connected via a closed weld contour, wherein the weld contour bounds a medium flow channel and connects at both ends to a medium passage opening.

These and other features will be further elucidated with reference to the annexed drawings . Figure 1 shows very schematically a method according to the invention.

Figure 2 shows the assembly of a tank with tank wall parts manufactured with a method according to the invention.

Figure 3 shows a piano of a plate part with which a cone-shaped heat-exchanging tank bottom can be manufactured with a method according to the invention.

Figure 4 shows the plate of figure 3 rolled to form a heat-exchanging cone-shaped tank bottom.

Figure 5 is a perspective view of a preferred embodiment of a tank wall part which is drawn in plane view for the sake of clarity.

Figure 6 shows a top view of the detail VI of figure 5.

Figure 7 is a partly broken-away perspective view of a part of a tank wall with a relatively thick and a relatively thin plate.

Figure 1 shows very schematically a method according to the invention. In accordance with this method a thin steel plate 1 is placed onto a thick steel plate 2. Thin steel plate 1 is provided at a suitable chosen position with a hole for arranging a feed opening. For a tank wall the ratio of the thickness of thin steel plate 1 and the thickness of thick steel plate 2 preferably equals 1:3. Thin steel plate 1 is then welded fixedly via a chosen pattern onto thick steel plate 2 by means of a laser 3. For a heat-exchanging tank wall this pattern 4 is preferably meander-shaped as in this embodiment. In this pattern a droplet-shaped weld seam 8 is arranged on the end of a non-continuous weld seam in order to reduce the stresses.

Once thin steel plate 1 has been welded onto thick steel plate 2 the assembly is rolled into a desired shape. To this end the assembly of plates 1, 2 is carried between the main roller 5 driven by a drive (not shown) and the counterpressure rollers 6. In this embodiment this results, as shown, in a cylindrical tank wall. 6

Subsequently arranged on thin steel plate 1 in the hole is a feed opening 7 along which a fluid can be introduced between thin plate 1 and thick plate 2. By supplying this fluid at high pressure the two plates will, depending on the pressure and the thickness and type of material thereof, deform due to the. hydraulic pressure. A channellike structure thereby results between thin steel plate 1 and thick steel plate 2. After arranging of a drainage opening downstream of the feed in the channel formed by the hydraulic pressure, the heat-exchanging tank wall part is complete.

Figure 2 shows the assembly of a tank with a heat-exchanging wall. The tank is assembled from four semi-cylindrical tank walls 10 manufactured according to the method which are placed one on top of another and welded together along connecting seam 20. Two heat- exchanging sections 11 are formed on each tank wall . Each section is provided with a feed 12 and a discharge 13. The channels of section 11 run substantially horizontally so that air can readily escape via discharge 13, and the channel parts are mutually separated by a single weld having a droplet-shaped weld 14 on the outer end. Tank wall 10 is divided into a number of sections 11 in order to keep the pumping losses in the channels as low as possible and to keep the temperature variation of the coolant in the channels as small as possible.

Figure 3 shows a plate formed as according to the method which can be assembled to form a cone-shaped tank bottom by welding along connecting seam 21 as shown in figure 4. Formed on plates 15 is a channel 16, the bends of which are very wide, so that flow losses in channel 16 are low. Channel 16 is further provided with a feed opening 17 and a discharge opening 18.

Figure 4 shows a conical tank wall bottom manufactured by bending the panel of figure 3 in for instance a rolling process.

Figure 5 shows a panel 31 comprising two stainless steel plates 32, 33 which are welded fixedly to 7 each other via two continuous weld contours designated 34 and 35 respectively in the drawing. Panel 31 is drawn in plane view for the sake of clarity but has a curved form according to the invention such that it can be used as tank wall or part thereof. In the shown situation the channel 36 bounded by weld seams 34 and 35 has already been formed by "inflating" via a hydraulic process. For this purpose an opening is initially made on both ends 37 and 38 respectively of channel 36. Plates 32 and 33 are plastically deformed by admitting medium under pressure. The openings through which heat-exchanging medium can be admitted respectively drained in the operational situation are designated 39 and 40.

Figure 5 shows that channel 36 has the general shape of a meander. It is important that edge weld seam parts, which for the sake of convenience are all designated 41, have a smooth round form. On the inner side of the bend defined thereby is situated the more or less droplet-shaped weld contour 8. This connects with its ends onto the respective two portions of the double weld seam 42, 43 which extend in mutually parallel relation in transverse direction relative to the edges 44, 45 of panel 31.

Figure 6 shows the described structure in detail.

Figure 7 shows a cut-away perspective view of a panel 51 which can serve as part of a tank wall. Inner plate 52 is relatively thick, while outer plate 53 is relatively thin. Plates 52, 53 are fixedly welded to each other via weld seams 54, 55. In the same manner as described with reference to for instance figure 5, channels 56 are formed by plastically deforming under hydraulic pressure the spaces bounded by weld seams 55, 54.

Claims

1. Method of manufacturing a curved tank wall or part thereof, which method comprises the following steps, to be performed successively, of: a) providing a first flat metal plate; b) providing a second flat metal plate; c) placing the two plates flat against each other and holding the plates temporarily in mutually fixed position, for instance by clamping; d) mutually connecting the plates by laser welding such that a weld contour is created which forms two side boundaries of a space corresponding with a channel for forming, on the two respective ends of which are situated openings, for instance continuous holes in at least one plate or an interruption in the weld contour, which openings serve as medium passage opening; e) bending the thus mutually connected plates to the desired general shape; f) admitting medium under pressure via at least one opening into the space bounded by the contour such that at least one of the plates undergoes a plastic deformation such that the contour with the plates bounds a channel through which can flow heat transfer medium;

1) performing step d) such that the space possesses the general form of a meander, wherein substantially parallel meander parts are separated by a single or double weld seam; and m) performing step 1) such that on the end of a non-continuous weld seam a sub-weld seam in the form of a closed sub-contour is formed connecting onto this weld seam, which sub-contour has a smooth rounded form.

2. Method as claimed in claim 1, comprising the step of

(q) performing step (1) such that the meander form is defined by two for instance continuous edge weld 9 seams and substantially mutually parallel weld seams in intertwined, mutually staggered relation extending in substantially transverse direction relative thereto.

3. Method as claimed in claim 2, comprising the step of

4. Method as claimed in claim 1, comprising the step of h) performing steps (a) and (b) such that the plates have thicknesses differing substantially from each other, whereby in step (f) the thicker plate undergoes no or only negligible plastic deformation.

5. Method as claimed in claim 4, comprising the step of i) performing step (e) such that the thicker plate becomes the inside of the tank wall or the part thereof.

6. Method as claimed in claim 1, comprising the step of j) performing steps (a), (b) and (e) such that the inner plate of the tank wall or the part thereof consists of stainless steel.

7. Method as claimed in claim 1, comprising the step of n) performing step (m) such that the sub- contour acquires a general droplet shape or circle shape and connects smoothly to said end.

8. Method as claimed in claim 1, comprising the step of o) performing step (e) by a bending process, by means of rollers or by rolling.

9. Method as claimed in claim 1 for manufacturing a tank wall, which method comprises the step of 10 p) mutually connecting the free end edges of a tank wall, a part or parts thereof.

10. Tank wall or tank wall part obtained by applying a method as claimed in any of the foregoing claims, which tank wall or tank wall part comprises: two curved metal plates mutually connected via a closed weld contour, wherein the weld contour bounds a medium flow channel and connects at both its ends to a medium passage opening.