AU2006216070B1

AU2006216070B1 - Liquid Storage Tank and Method for Manufacturing Liquid Storage Tank

Info

Publication number: AU2006216070B1
Application number: AU2006216070A
Authority: AU
Inventors: Jared Hinkley; Wayne Hinkley; Wayne Schroter; Terry Styles
Original assignee: ASCENT BUILDING SOLUTIONS Pty Ltd
Current assignee: ASCENT BUILDING SOLUTIONS Pty Ltd
Priority date: 2006-09-15
Filing date: 2006-09-15
Publication date: 2008-02-14
Anticipated expiration: 2026-09-15
Also published as: AU2006252134A1

Description

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION Invention Title: Applicants: Liquid Storage Tank and Method for Manufacturing Liquid Storage Tank Wayne Hinkley and Ascent Building Solutions Pty Ltd The invention is described in the following statement.

-2- LIQUID STORAGE TANK AND METHOD FOR MANUFACTURING LIQUID STORAGE TANK FIELD OF THE INVENTION The present invention relates to a liquid storage tank. In another aspect, the present invention relates to a method for forming a liquid storage tank.

BACKGROUND TO THE INVENTION Rainwater storage tanks are being subject to increasing demand in Australia.

Rainwater storage tanks are typically made from steel or other metal, polypropylene or fibreglass. Metal rainwater tanks are normally made from corrugated metals, such as zinc-coated corrugated iron, a material sold under the trade name AQUAPLATE by Bluescope Steel, or corrugated steel.

Metal rainwater tanks typically have generally cylindrical side walls, with a flat bottom and a flat or domed top. Cylindrical side walls provide a strong structure that does not require any reinforcement.

Although generally cylindrical metal rainwater tanks provide a strong structure, they suffer from the disadvantage that they occupy a large amount of room. This can be disadvantageous in situations where room for a rainwater tank is restricted.

Consequently, there have been some efforts to manufacture metal rainwater tanks having generally straight sides. Such rainwater tanks are restricted to relatively small sizes as the straight sides of the tank represent potential areas of weakness when the tank is filled with water. Alternatively, larger size tanks having straight sides are provided with internal bracing to strengthen the tanks. Internal bracing typically requires many penetrations through the walls of the tank to fix the bracing to the tank. Further, if the internal bracing comprises metal bracing (such as metal rods) there is a risk that corrosion will occur where the bracing contacts the walls of the tank. The bracing itself may also deteriorate over time.

BRIEF DESCRIPTION OF THE INVENTION -3- In a first aspect, the present invention provides a tank for storing liquids 0 comprising side walls and a bottom, characterised in that the side walls include end portions and at least one intermediate portion between the end portions, the at least one intermediate portion having a width that is less than a maximum width of the end portions, wherein the end portions of the side wall include a curved portion.

N In one embodiment, the end portions of the side walls are curved end portions.

IND The at least one intermediate portion may include opposed curved side wall Sportions, with the opposed curved side wall portions moving towards each other with increasing distance from one of the end wall portions until a minimum distance between the opposed curved side wall portions is reached.

In some embodiments of the tank in accordance with the present invention, the end portions are formed with a radius of curvature and the intermediate portions are formed with a radius of curvature and the ratio of the radius of the curvature of an end portion to the radius of curvature of an intermediate portion falls within the range of 2:1 to 1:1:1, more suitably 1.5:1 to 1.3:1, even more suitably 1.45:1 to 1.4:1. In such embodiments, it will be appreciated that the intermediate portion has a tighter radius of curvature than the radius of curvature of the end portions.

In some embodiments, the tank may have a ratio of a maximum width of an end portion to a minimum width of the tank that falls within the range of 1.5 to 2, more suitably 1.6 to 1.9, even more suitably 1.7 to 1.8, and even more suitably 1.7 to 1.75.

In some embodiments, the radius of curvature of the intermediate portions falls within the range of 200 to 450mm, more suitably 250 to 350 mm, even more suitably about 300mm. A small radius of curvature in the intermediate regions is believed to enhance the strength of the tank.

In one embodiment, the tank in accordance with the first aspect of the present invention is made from a metal, especially corrugated metal, most suitably corrugated steel. The corrugated steel may be galvanised or otherwise treated to minimise corrosion.

-4-

O

In one embodiment, a tank in accordance with the first aspect of the invention may O include two curved end portions and one curved intermediate portion between the two curved end portions.

In another embodiment, the tank may comprise two curved end portions, two intermediate portions of reduced width (when compared to the maximum width of the end O portions) located adjacent the respective end portions and a further intermediate portion of larger width than the two intermediate portions of reduced width.

O

In yet a further embodiment, a tank in accordance with the present invention may comprise first and second curved end portions and a concave portion extending from one side of one end portion to one side of the other end portion, the tank further including a further convex portion, a second concave portion extending between another side of one of the first or second curved end portions and the further convex portion, and a third concave portion extending between the other end of the other of the first and second curved end portions and the further convex portion. In this embodiment, the tank may be positioned around or within a corner of a structure or building.

In another aspect, the present invention provides a tank for storing liquids comprising side walls and a bottom, characterised in that the side walls include end portions and at least one intermediate portion between the end portions, the at least one intermediate portion having a width that is less than a maximum width of the end portions, the end portions including a curved portion, wherein the tank is configured to extend around a corner of a building or to sit in an internal corner of a building.

In some embodiments, the tank of the present invention has a strength sufficiently high to not require any bracing. Alternatively, the tank may be provided with bracing that extends across at least one of the at least one intermediate portions. The bracing is suitably in the form of external bracing. The external bracing may take the form of an external strap extending around the intermediate portion of the tank. Alternatively, the external bracing may take the form of hollow sections extending along the side walls of the intermediate portion with spigots fitted to the upper part of the hollow portions said spigots being tied together with a transversely extending member. Suitably, the lower parts of the hollow sections on either side of the intermediate portion are also connected together. As the intermediate portion is a region of reduced width, the material requirements for the external bracing are thereby reduced.

In the description of the tank in accordance with the present invention, the terms "convex" and "concave" are used to describe the tank from the viewpoint of looking at the tank from the exterior of the tank.

The tank suitably has generally vertical walls. It will, of course, be appreciated that the material from which the side walls are manufactured may be a corrugated material. However, the person skilled in the art will readily understand what is meant by a tank made from a corrugated material having generally vertical side walls.

The tank will also have a bottom. The bottom may comprise a metal bottom that is joined to the lower edge of the side walls. The bottom may be joined to the side walls by roll forming, seam joining, "Pittsburghing", welding or the like. Alternatively, the bottom may comprise a plastic material that is sealingly joined to the side walls.

The tank is suitably provided with a top. The top may be joined to the upper edge of the side walls. For example, the top may be made from a metal material, such as steel sheet, and the top may be roll joined, welded or otherwise joined to the side walls.

Alternatively, the top may be made from a plastics material or a fibreglass material.

The tank will suitably be provided with an inlet for admitting liquids thereto and at least one outlet for allowing the outflow of liquids therefrom.

In a further aspect, the present invention provides a method for forming a side wall for a liquid storage tank comprising providing a sheet of metal material, rolling a first curve into the sheet of metal material, and rolling a second curve into the sheet of material, the second curve being of opposite orientation to the first curve.

In one embodiment, the method may further comprise the step of rolling a third curve into the sheet of material, the third curve having the same orientation as the first curve. The third curve may be spaced from the second curve. The third curve may be rolled into the sheet before the second curve is formed.

In another embodiment, the method may further comprise rolling a fourth curve into the sheet of material, the fourth curve being of opposite orientation to the first and third curves.

The first and third curves (if a third curve is present) are suitably of smaller radius of curvature than the second and fourth curves (if a fourth curve is present). In this embodiment, the first and third curves correspond to the intermediate or concave portions and the second and fourth curves correspond to the end portions.

In all embodiments of the present invention, the sidewall of the tank may be completed by joining ends of the sheet of material together or by joining the ends of the sheet of material to one or more other sheets of material. It is preferred that the tank is formed by joining one end of a sheet of material to another end of the sheet of material as this then only requires a single vertical join to be made.

In one embodiment of the method of the present invention, the ends of the sheet of material are joined together to form a tank having two curved ends and a waist region of reduced width, when compared to the maximum width of the curved ends of the side wall.

In another embodiment, the rolled sheet of material is joined to another rolled sheet of material.

The sheet of metal material is suitably rolled by passing the sheet through a roller arrangement comprising three rollers arranged in a triangular layout.

In the method of the present invention, the first curve may be rolled into the sheet of metal material by passing the sheet through the rollers, bringing one roller into contact with the sheet material and removing the roller from contact with the sheet material. The third curve (if required) may be formed by further passing the sheet of material through the rollers and subsequently engaging a forming roller with the sheet of material.

The sheet of material may then be removed from the rollers and inverted or turned around and passed back into the rollers form the other end. The sheet of material may then be again passed through the rollers, with a forming roller contacting the sheet of material at the desired position to form the second curve and the forming roller contacting the sheet of material again at the desired time to form the fourth curve (if required). As -7the sheet of material has been inverted, the second and fourth curves are of opposite orientation to the first and third curves.

In order to complete the side wall of the tank, the ends of the sheet of material are joined to themselves or to the ends of other sheets of material. The ends may be joined by way of riveting. Suitably, a sealant is positioned between the joints.

In some embodiments of the present invention, the side wall of the tank may be made from two or more overlapping sheets of material that are joined together along generally horizontal joining lines or joining regions.

In yet another aspect, the present invention provides a tank for storing liquids having a side wall that defines a first curved end portion, a second curved end portion and a waisted region having a smaller width than the maximum width of the end portions.

DESCRIPTION OF THE DRAWINGS Figure 1 shows a plan view of a tank in accordance with one embodiment of the present invention; Figure 2 shows a perspective view of the tank shown in figure 1; Figure 3 shows a plan view of a tank in accordance with another embodiment of the present invention; Figure 4 shows a perspective view of the tank shown in figure 3; Figure 5 shows a plan view of a tank in accordance with yet another embodiment of the present invention; Figure 5A shows a three dimensional view of the tank of Figure 5 positioned against a building to extend around a comer of the building; Figure 6 shows a perspective view of the tank shown in figure Figure 7 shows an end view of a roller arrangement used in the manufacture of tanks in accordance with embodiments of the present invention; Figure 8 shows a schematic view of the rolling operations of a sheet of metal used to fabricate a tank in accordance with an embodiment of the present invention; Figure 9 shows a schematic view of the rolling operations used to fabricate a tank in accordance with another embodiment of the present invention; Figure 10 shows another schematic view of the rolling operations used to fabricate a tank in accordance with a further embodiment of the present invention; Figure 11 shows another schematic view of the rolling operations used to fabricate a tank in accordance with a further embodiment of the present invention; Figures 12A and 12B show another schematic view of the rolling operations used to fabricate a tank in accordance with a further embodiment of the present invention; and Figure 13 shows a plan view of a tank in accordance with another embodiment of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS It will be appreciated that the attached drawings have been provided for the purposes of illustrating preferred embodiments of the present invention. Thus, it will be understood that the present invention should not be considered to be limited solely to the embodiment shown in the drawings.

Figure 1 shows a water tank 10 in accordance with the present invention. The water tank 10 includes a first curved end portion 12 and a second curved end portion 14.

The side walls of the tank include intermediate portions 16, 18 that interconnect end portions 12 and 14. Intermediate portions 16 and 18 define a region of the tank that has reduced width, when compared to the maximum dimension of the end portions 12 and 14.

For example, the end portions 12 and 14 may be formed with a radius of curvature of 425mm. The intermediate portions 16 and 18 may be formed with a radius of curvature of 300mm and the minimum width W of the intermediate region defined between intermediate portions 16 and 18 of the side wall of the tank may be 495mm. It will be appreciated that these dimensions may be varied.

-9- Figure 2 shows a perspective view of the tank 10 shown in plain view in figure 1.

As shown in figure 2, the side walls of the tank 10 are generally vertical, for example, as shown by reference numeral The tank 10 shown in figures 1 and 2 is suitably made from a rolled metal sheet material. The metal sheet material is suitably a corrugated material. For clarity, figure 2 does not show the corrugations in the material. However, the person skilled in the art will readily appreciate that corrugated sheet material, such as galvanised iron with a material sold under the trademark ZINCALUME by Bluescope Steel of Australia may be used in the manufacture or fabrication of tanks in accordance with the present invention.

In the embodiment shown in figure 2, the water tank may have a height of 1,850mm, for example.

Figure 3 shows a plan view of an embodiment of the tank in accordance with the further aspect of the present invention. The tank 30 shown in figure 3 includes curved end portions 32 and 34. End portion 32 blends into intermediate portions 36 and 38.

Intermediate portions 36 and 38 define a region of the tank of reduced width, when compared to the maximum width of the end portion 32.

Similarly, end portion 34 blends into intermediate portions 40, 42. Again, intermediate portions 40, 42 define a region of reduced width, when compared to the maximum width of end portion 34.

The tank 30 shown in figure 3 differs from the tank 10 shown in figure 1 and the tank 30 of figure 3 also includes a further intermediate region 46, which is defined by side wall portions 48, 50. Intermediate region 46 is of increased width when compared to the intermediate regions generally defined by side wall portions 36, 38 and 40, 42.

As will be appreciated, the tank 30 shown in figure 3 is a larger volume tank than the tank 10 shown in figure 1, for a given height of tank.

The tank shown in Figure 3 may have end regions that have a diameter of 850mm and the width of the intermediate regions may be 495mm, with the walls in the intermediate regions having a radius of curvature of 300mm. The tank may have an overall length of 2750mm.

As shown in figure 4, the tank 30 also has generally vertical side walls as shown by reference numeral 52.

Figure 5 shows a tank 60 in accordance with yet another embodiment of the present invention. The tank 60 includes end portions 62, 64. End portion 62 blends into intermediate side wall portions 66, 68. As shown in figure 5, intermediate portion 66 interconnects one side of end portion 62 to one side of end portion 64.

The other side of end portion 64 blends into intermediate portion The tank also includes a further intermediate portion 72 that presents a generally convex outer face. Intermediate portions 68, 70 blend into further intermediate portion 72.

The tank 60 shown in figure 5 includes generally convex portions 62, 64 and 72 and generally concave portions 66, 68, 70. In this regard, the expressions "convex" and "concave" are used to described the general shape presented by the external side walls of the tank when viewed from the outside of the tank.

The tank 60 shown in figure 5 may be positioned to extend around a corner of a building or structure. For example, a building or structure may have side walls as shown in dotted lines 74, 76 and the tank 60 can be positioned such that the comer of the side wall 74, 76 is positioned close to the intermediate portion 66. A three dimensional view of this is shown I Figure 5A. This enables a tank of reasonably large volume to be provided that makes effective use of space. This is particularly desirable in instances where the tank is to be used to collect rainwater in an urban environment. Similarly, the tank 60 may be positioned in an internal corner of a building to take advantage of the space-saving shape of the tank.

Alternatively, the tank 60 may be positioned against an internal corner of a building, as shown by dotted outline 77.

In the tank 60 shown in figure 5, the end portion 62 and 64 may have a radius of curvature of 425mm. Similarly, the further intermediate portion 72 may also have a radius of curvature of 425mm. The intermediate portions 66, 68 and 70 have opposed curvature to the portions 62, 64, 72. The intermediate portions 66, 68, 70 may have a -11radius of curvature of 300mm. The minimum width W of the tank may be 455mm. The tank may have a height of 1,850mm, although it will be appreciated that the tank heights may vary. Similarly, the tank capacities may also vary. The tank may have generally vertical side walls, for example, as shown by reference numeral 78 in figure 6.

The tank 60 shown in Figures 5 and 6 is especially suitable for use in urban areas or in dwellings having restricted space around a building. In these cases, there is often restricted room to place a water storage tank. Slimline tanks are available for purchase and positioning in areas where a boundary fence is located close to a dwelling. However, to obtain a reasonable storage volume in such slimline tanks, the tanks often have a significant length. If the tank is to be placed adjacent the dwelling, the tank may overlie a window, which is undesirable. In contrast, the tank 60 shown in Figures 5 and 6, in being able to extend around a corner or into a corner, is able to provide a reasonable storage volume without extending for undesirably long distances along a wall. It will also be understood that windows of most dwellings are positioned a distance away form the corners of the dwelling and the tank 60 can occupy that region of the walls without blocking any windows. When compared to round tanks of similar volume, the tank 60 has a significantly lesser width extending out form any wall, thus reducing the intrusion of the tank into walkways or other accessways next to the dwelling. For example, a tank having a height of 1800mm and a volume of 3500 litres may have a maximum width extending away from any wall of 850mm. In contrast, a round tank of the same height and volume will have a diameter of approximately 1500mm and hence will extend 1500mm away from the wall.

In the embodiment shown in figures 1 to 6, the tanks have intermediate regions of reduced width. Preferably, the side walls of the intermediate regions are curved.

Similarly, the side walls of the end portions are curved.

The intermediate portions of reduced width are believed to increase the strength of the side walls of the tank and thereby increase the resistance of the side walls of the tank from bowing outwardly or failing under the weight of water (or other liquid) that may be stored inside the tank. For smaller tanks, it is believed that the strength in the side walls of the tank formed by the waisted regions of reduced width will be sufficient to not -12require bracing of the tank to be used. However, in larger tanks, it may be necessary to C) provide some bracing.

Figure 3 shows a possible example of bracing that may be used. In figure 3, external bracing is used. The external bracing may comprise a vertical galvanized rectangular tube or section. This may be covered with a sleeve of plastic profiled material Sto match the corrugated profile of the tank wall. A strap or tie member 39 that extends i across the top of the tank to tie together the vertical members 35, 37. The lower ends of vertical members 35, 37 are also tied together or joined by a member that passes underneath the tank. The external bracing effectively acts to provide additional support to the side walls of the tank. As shown in figure 3, the external bracing is positioned such that it extends across an intermediate region of reduced width of the tank. In this fashion, the amount of material required in the external bracing is minimised, thereby minimising the material costs of the tank.

The tie member 39 is suitably a metal member, such as 316 stainless steel. It may be a tensioned member.

Use of external bracing, or being able to completely avoid bracing, also provides significant advantages over prior art tanks that included internal bracing. In particular, internally braced prior art tanks made from metal typically exhibited problems with leakage around the bracing points and corrosion at points where the internal bracing struts exited through the tank. Further, the internal bracing is also exposed to a moist or wet environment and this can also cause deterioration of the internal bracing.

The tanks shown in figures 1 to 6 may suitably be manufactured by rolling of sheet metal. Figure 7 shows one possible apparatus for manufacturing the tanks. The apparatus shown in figure 7 is effectively a roller apparatus. It includes three rollers 82, 84 mounted to a roller body 86. As can be seen in figure 7, the rollers 80, 82 and 84 are arranged in a triangular layout. The rollers are preferably oriented in a generally vertical direction. The roller body is cradled at bearing points 88, 90 to enable the roller body 86 to pivot in a support frame 92. In use, a sheet of metal is fed in between the rollers and the roller 80 is moved relatively towards the rollers 82, 84 to thereby engage the metal and roll form the metal sheet. When it is desired to stop roll forming the metal 13sheet, the roller 80 is moved relatively away from the rollers 82, 84. The apparatus shown in Figure 7 suitably has little or no parts that extend beyond the lateral-most extent of the rollers. This allows tight curves to be formed into the sheet material without the sheet fouling on the supporting parts for the rollers. The ability to form curves of tight radius is also enhanced by the generally vertical orientation of the rollers (that is, the longitudinal axes of the rollers are generally vertical). Orienting the rollers in a horizontal could open the possibility of the curved sheet material contacting the floor underneath the roller apparatus.

The ability to form tight curves in the sheet material allows curves of tight radius to be formed in the intermediate portions of the tank. This provides two advantages: i) For a given spacing between the centre points of the end portions (or adjacent portions of larger diameter), using a tight curve in the intermediate portion allows for the curvature of the end portion to close to a greater extent. For example, in a tank having end portions having a diameter of 1200mm and a radius of curvature in the intermediate portions of 600mm, the end curves trace out an arc covering 2460. If the radius of curvature of the intermediate portion is 300mm, the end curves trace out an arc covering 2760. For a tank having an end portion diameter of 850mm, having a radius of curvature in the intermediate portions of 425mm will see the end portions tracing out an arc covering 2400 whereas if the radius of curvature in the intermediate portion is 300mm, the end portions trace out a curve of 2560. In this regard, the end portion curve is taken to end where the end portion blends into the intermediate portion. In both of these examples, the spacing between the end portions is determined by closing an imaginary circle having the diameter of the end portions and being centred on the centre of the end portions and the closest that the imaginary circles come to each other is 100mm. It will be appreciated that providing an effective smaller "opening" of the end portions (this "opening" being represented by the gap between the respective ends of each one end portion at the positions where the end portions blend into the intermediate portions) results in a -14stronger tank. It is well understood that a smaller opening has less detriment to strength than a larger opening.

ii) The minimum width of the tank in the intermediate portions is also reduced by using a tighter radius curve in the intermediate portions. For example, with an end portion diameter of 1200mm and a radius of curvature in the intermediate portions of 600mm, the tank will have a minimum width of 800mm. With an end portion diameter of 1200mm and a radius of curvature in the intermediate portions of 300mm, the tank will have a minimum width in the intermediate portion of 620mm.

These figures are given for tank having the end portion spacing as described in above. Again, this assists in strengthening the tank.

Figure 8 shows a schematic view showing the various roll forming operations used on a sheet of metal in one embodiment of the present invention. In step of figure 8, a sheet of metal 100 is provided. In step a first rolled portion 102 is rolled into the sheet.

In step a second rolled portion 104 is rolled into the sheet. Rolled portions 102 and 104 may correspond to intermediate portions 16 and 18 of the tank 10 shown in figure 1.

In step the sheet of material having rolled portions 102, 104 is removed from the roller apparatus. The rolling machine modifications allows for tank body sheets to be passed back into the machine for further curving. It is then fed back into the roller and roll formed portion 106 is formed. Portion 106 may correspond to end portion 12.

In step rolled form metal portion 108 is formed. In step two portions 108 may be joined together along lines defined at joining lines 110, 112. The joins may be achieved by sandwiching a sealing material between the rolled form sheets 108 and riveting the sheets together along lines 110, 112.

Figure 9 shows an alternative way of forming a tank in accordance with the present invention. In step of figure 9 a sheet of metal 120 is provided. In step roll form portions 122, 124 are rolled into a metal sheet.

In step the roll formed sheet from step is removed from the roller apparatus and inverted. Convex rolled portion 126 is then rolled into the sheet. At this stage, the only straight portion of the metal sheet remaining is portion 128. In step portion 128 is roll formed into convex portion 130. The end 132 overlaps the end 134.

The roll formed sheet is removed from the rolling apparatus and overlapping ends 132, 134 are joined to form a tank. This forms a tank similar to that shown in figure 1.

Figure 10 shows a further schematic diagram for manufacturing a tank. In figure 10, step a straight piece of sheet metal 150 is provided. In step sheet 150 is roll formed to form curved regions 152, 154. The metal material is then removed from the rolling apparatus and inverted. In step the convex roll formed portions 156, 158 are formed. This leaves a roller formed sheet 160. In step two sheets 160 are joined along joining lines 162, 164 to form a tank similar to that shown in figure 3.

Figure 11 shows an alternative method for forming a tank as shown in Figure 3. In Figure 11, a sheet of material 170 has small curve A formed therein. Curves BI, B2, B3, and B4 are then formed in the material. Curves C1 and C2 are then formed between B1 and B2 and B3 and B4, respectively. It will be understood that the sheet of material is removed and either inverted or turned around to form curves C1 and C2. Curves D1 and D2 are then formed in the remaining straight parts of the sheet of material and the overlapping ends of the sheet of material are joined together.

Figures 12A and 12B show one possible forming method for forming a tank similar to that shown in Figure 6. In Figure 12A, a sheet of material 180 has a curve B formed in it, followed by curve C and then curve D. The sheet is then inverted and curve E formed between curves B and C. Curve F is then formed between curves C and D. The straight portion G (Figure 12B) is then curved to form curve G1 and the overlapping ends of the sheet of material are joined together.

Figure 13 shows another embodiment of a tank in accordance with the present invention. In Figure 13, the tank 200 has a first end region 202 of a first radius and a second end region 204 of a second radius, with the second radius being larger than the first radius. An intermediate region 206 is located between the first and second end portions. The radius of the first end portion may be 425mm, the radius of the second end -16portion may be 600mm and the radius of curvature of the walls of the intermediate portion 206 may be 300mm. The tank 200 may have an overall length of 2125mm.

As will be appreciated by those skilled in the art, sheets of corrugated iron or Zincalume type materials are typically provided with sheet widths of around 600mm.

Therefore, in order to construct a tank that is taller or higher than that, separate sheets must be roll formed, for example as shown in figures 8 to 12, and joined together along a horizontal joining lines. Again, this will be well understood by persons skilled in the art.

The tank in accordance with the present invention will suitably have a top and a bottom. The top and the bottom may be fabricated separately to the side walls. The top and bottom may be fabricated from metal and then may be formed by cutting or stamping.

The top and the bottom may be joined to the side walls of the tank using roll joints, or by welding, or by placing a sealing material between the top and the side wall and the bottom and the side wall and fastening the top and the bottom to the side wall. In this regard, the top and the bottom may also be provided with depending flanges or lips to enable attachment to the side walls.

Those skilled in the art will appreciate that the present invention may be susceptible to variations and modifications other than those specifically described. It will be understood that the present invention encompasses all such variations and modifications that fall within its spirit and scope.

Claims

2. A tank as claimed in claim I wherein the end portions of the side walls are IND curved end portions. S3. A tank as claimed in claim I or claim 2 wherein the at least one intermediate portion includes opposed curved side wall portions, with the opposed curved side wall portions moving towards each other with increasing distance from one of the end wall portions until a minimum distance between the opposed curved side wall portions is reached.
4. A tank as claimed in any one of the preceding claims wherein the end portions are formed with a radius of curvature and the intermediate portions are formed with a radius of curvature and the ratio of the radius of the curvature of an end portion to the radius of curvature of an intermediate portion falls within the range of 2:1 to 1.1 :1. A tank as claimed in claim 4 wherein the ratio of the radius of the curvature of an end portion to the radius of curvature of an intermediate portion falls within the range of 1.5:1 to 1.3:1.
6. A tank as claimed in claim 5 wherein the ratio of the radius of the curvature of an end portion to the radius of curvature of an intermediate portion falls within the range of 1.45:1 to 1.4:1.
7. A tank as claimed in any one of the preceding claims wherein the tank has a ratio of a maximum width of an end portion to a minimum width of the tank that falls within the range of 1.5 to 2.
8. A tank as claimed in claim 7 wherein the tank has a ratio of a maximum width of an end portion to a minimum width of the tank that falls within the range of 1.6 to 1.9. 18 O O U 9. A tank as claimed in claim 8 wherein the tank has a ratio of a maximum width of an end portion to a minimum width of the tank that falls within the range of 1.7 to 1.8. 00 A tank as claimed in any one of the preceding claims wherein the radius of curvature of the intermediate portions falls within the range of 200 to 450mm.
11. A tank as claimed in any one of the preceding claims wherein the tank Sincludes two curved end portions and one curved intermediate portion between the two (N I curved end portions. r, 12. A tank as claimed in any one of claims I to 10 wherein the tank comprises two curved end portions, two intermediate portions of reduced width (when compared to the maximum width of the end portions) located adjacent the respective end portions and a further intermediate portion of larger width than the two intermediate portions of reduced width.
13. A tank as claimed in any one of claims 1 to 10 wherein the tank comprises first and second curved end portions and a concave portion extending from one side of one end portion to one side of the other end portion, the tank further including a further convex portion, a second concave portion extending between another side of one of the first or second curved end portions and the further convex portion, and a third concave portion extending between the other end of the other of the first and second curved end portions and the further convex portion.
14. A tank for storing liquids comprising side walls and a bottom, characterised in that the side walls include end portions and at least one intermediate portion between the end portions, the at least one intermediate portion having a width that is less than a maximum width of the end portions, the end portions including a curved portion, wherein the tank is configured to extend around a corner of a building or to sit in an internal corner of a building.
15. A tank for storing liquids having a side wall that defines a first curved end portion, a second curved end portion and a waisted region having a smaller width than the maximum width of the end portions.
16. A tank as claimed in any one of the preceding claims wherein the tank is made from a metal. 00 OO
17. A tank as claimed in any one of the preceding claims wherein the tank has a strength sufficiently high to not require any bracing.
18. A tank as claimed in any one of claims 1 to 16 wherein the tank is provided with external bracing that extends across at least one of the at least one intermediate portions. (N
19. A method for forming a side wall for a liquid storage tank as claimed in any Sone of the preceding claims comprising providing a sheet of metal material, rolling a first curve into the sheet of metal material, and rolling a second curve into the sheet of material, the second curve being of opposite orientation to the first curve. A method as claimed in claim 19 wherein the method further comprises the step of rolling a third curve into the sheet of material, the third curve having the same orientation as the first curve.
21. A method as claimed in claim 19 or claim 20 wherein the method further comprises rolling a fourth curve into the sheet of material, the fourth curve being of opposite orientation to the first curve.
22. A method as claimed in claim 21, when appended to claim 20, wherein the first and third curves are of smaller radius of curvature than the second and fourth curves.
23. A method as claimed in any one of claims 19 to 22 wherein the ends of the sheet of material are joined together to form a tank having two curved ends and a waist region of reduced width, when compared to the maximum width of the curved ends of the side wall.
24. A method as claimed in any one of claims 19 to 22 wherein the ends of the sheet of material are joined to themselves or to the ends of other sheets of material to complete the sidewall of the tank. A tank substantially as hereinbefore described with reference to the accompanying drawings. O O
26. A method of forming a sidewall of a tank substantially as hereinbefore described with reference to the accompanying drawings. 00 NO OD O- (N