Background of the Invention Traditionally, metal rainwater tanks have been made from corrugated metal panels which are formed with a circular cross section. The use of this cylindrical form is beneficial as it well suited to accommodate the hoop tension induced in the tank by the hydrostatic pressures of the water. Whilst the cylindrical water tanks are suited to resist the hydrostatic pressures, they are not particularly well suited for domestic applications because of aesthetic reasons and also because of space requirements.

In view of these limitations, in recent times, new designs of water tanks have been developed primarily for domestic use. The designs are generally of a rectangular cross section where the major front and back faces are significantly wider than side walls which interconnect the front and back faces. These designs are ideally suited to be located against building walls where they may be more easily accommodated and also where they will be less intrusive.

In the past, difficulties have been encountered in

producing tanks, either in the original cylindrical form, or in the generally rectangular form, that are easy to manufacture and well suited to accommodate the hydrostatic pressures induced in the tank. Traditionally, prior art metal circular water tanks are assembled by hand thereby limiting the opportunity to reduce the cost of manufacture of such tanks. Plastic versions of these tanks are not self supporting and therefore require separate support and frames to be provided. These frames typically require extensive bridging which extend intermediate the tank and as such, the frames not only significantly increase the cost of manufacture of the tank, but can substantially reduce its storage capacity.

Summary of the Invention In a first aspect, the invention provides a water storage tank having a base, and a tank wall upstanding from the base and extending about a central axis of the tank, the tank wall being formed from one or more lengths of sheet material, each sheet being helically wound about the tank axis, the wall further comprising at least one seam extending helically about the tank axis that interconnects adjacent longitudinal edges of the or each sheet and forms a watertight joint along those edges.

Accordingly, the water storage tank is characterised in that the tank wall is formed from a helical wound length of one or more sheets of material. This approach has substantial practical benefits as it enables the wall of the tanks to be formed in a continuous process whereby the sheet strip is initially formed into a continuous cylinder by helically winding the sheet strip about a central axis, forming a joint at the longitudinal edges of the or each sheet strip, and then cutting the cylinder into discrete lengths to form the individual tank walls.

Accordingly, by providing the tank wall in this construction it is possible to produce at least a major

portion of the water tanks in a production line fashion.

If the tank wall is formed from one length of sheet material, then the wall is formed as a single helix.

Alternatively, if the tank wall is formed from two lengths of sheet material then the tank wall forms a double helix.

To simplify the manufacturing process of the water tanks, the tank wall is formed from a single length of metal sheet strip. However, forming the wall from more than one length of sheet material enables the introduction of materials of different characteristics (ie. materiel thickness, strength, material type) so as to optimise the performance of the tank relative to the costs of material.

In addition, as the water tanks may be used in areas where they are quite visible, it is possible to create tanks that have more visual impact by making the tank wall from more than one length of sheet material. For example, the tank wall can be two toned by making it from two lengths of sheet strip that are of different colours.

In one form, at least one stiffening formation is formed in the tank wall. The stiffening formation may be formed intermediate the longitudinal edges of the sheet, or at least one of the sheets, and/or may be formed at the seam interconnecting adjacent ones of the longitudinal edges. Further, where the stiffening formation is formed intermediate the longitudinal edges of the sheet, it may be incorporated into the sheet either before or after, or during formation of the lockseam.

In one form, the or at least one of the stiffening formations is a rib that extends helically about the tank axis. In one form of this arrangement, the stiffening formation is preformed in the sheet strip and extends longitudinally in the direction of the sheet strip. If the rib is formed at the joint, then in this arrangement, the rib may be preformed by profiling each of the longitudinal edges of the sheet into respective rib parts.

In another form where the stiffening formation is formed after, or during, formation of the lockseam, the

stiffening formation may be rolled formed into the sheet typically in a helical path that follows the pitch of the lockseam.

In one embodiment, the or each rib is interspaced by pans. In that arrangement, in one form the rib (s) extends inwardly into the water tank so that the pans form the outer limit of the external face of the tank wall. In another form, the rib (s) extends outwardly. In another form, a plurality of stiffening formations are provided that are in the form of corrugations or a plurality of ribs or pleats, such that cross sectional profile of the sheet strip displays a regular wave form with crests and troughs displacing from the centre plane of the sheet.

The wave form may be smoothly curved throughout or it may comprise straight portions meeting at relatively abrupt angles, or a combination of both these possibilities.

If the stiffening formations are formed after the formation of the lockseam, it is beneficial to introduce a corrugated or similar undulating profile as it places less stress on the lockseam as a result of forming the metal sheet than would occur if an angular rib profile is introduced.

In the embodiment where each stiffening formation is generally linear in the longitudinal direction of the sheet, the pitch angle of each formation is relatively low. In one form, the pitch angle is between 0.1 to 5°.

The advantage of a low angle of pitch is that it enables the tank wall to better accommodate the hydrostatic pressures in the tank.

In another form, the stiffening formations include a plurality of ribs or corrugations that extend generally in the direction of the tank axis. The stiffening formations may be used in conjunction with the helical stiffening formations or possibly in place of those stiffening formations. The advantage of the generally vertical stiffening formations is that they can minimise bulging of the tank wall. These stiffening formations may be in the

form of microflutes or may take the form of other larger ribs.

In one form, the sheet material, or at least one of the sheets if the tank wall is formed from a plurality of sheets, is sheet metal. In one form, sheet steel is used that incorporates a corrosion resistant coating that is typically a metal coating.

In one form, a protective coating is applied to the sheet metal to act as a moisture barrier and to enhance chemical resistance of the tank wall. In one form, the coating is in the form. of a film that is laminated onto the sheet metal.

In one form, the sheet metal is profiled to include the stiffening formation (s) in any form described above.

An advantage of using a profiled metal sheet is that the metal sheet strip can be profiled through a continuous cold roll forming process. As such, the use of metal profiles of this type can be included in a continuous production process whereby the metal strip is initially cold roll formed then helically wound to form the cylinder and cut into tank walls of discrete length in a single production line.

In one form, the seam is in the form of a lock seam that results from folding the longitudinal edges together under pressure. Again this lock seam can be formed as part of a continuous production process through a roll forming, pressing and/or clinching operation.

In one form, the lock seam forms the watertight joint without requiring a sealant to be applied to the joint.

In one form, a gasket may be incorporated in the lock seam to make the joint watertight. In another from, the sheet material incorporates a coating configured to act as the gasket thereby obviating the need for a separate gasket.

In one form, the coating is polymeric or formed from a synthetic or natural rubber. Examples of coatings for this purpose include polyethylene, PVC, polypropylene and synthetic rubbers such as neoprene. In one form, the

coating used to form the gasket in the lock seam is also applied to the major surface of the strip material to provide the moisture barrier as discussed above.

In a further aspect, the invention relates to a tank wall incorporating a lock seam according to the above form. The tank wall may include at least one helically wound sheet in accordance with the earlier aspect of the invention. Alternatively, the tank wall may be formed of interconnected panels with the lock seam being used to interconnect the panels.

A lock seam in accordance with this latter form is the subject of a co pending International application by the Applicant entitled"Watertight Joint", the contents of which are herein incorporated by cross-reference.

In one form, the tank wall of the water tank is circular in cross section perpendicular to the tank axis.

However, in another form, the cross section of the tank wall may be non-circular and may be either generally elliptical or obround (ie having substantially parallel front and back faces and generally semi-circular or arcuate sides). This latter arrangement is ideally suited to domestic use where the water tank can be mounted against a building wall or the like.

In one form, the tank wall may be formed in its final cross sectional shape. In such an arrangement, each metal sheet strip may be helically wound to provide a continuous cylinder of either circular or non circular cross section.

In an alternative arrangement, the tank wall is originally formed to have a particular cross section (typically circular) and is then post formed into its final shape. This may be achieved through the use of mandrels or the like which are inserted within the cylinder. The mandrels include outer engaging surfaces and are movable relative to each other to force a change of shape on the tank wall. Where the tank wall has its shape changed as part of its manufacture, this change may occur whilst the individual tank walls are in the form of

a continuous cylinder or alternatively may occur once the cylinder is cut at the discrete intervals to form the individual tank walls.

In a particular embodiment, the lower edge at least of the tank wall is generally planar and disposed perpendicular to the tank axis. Typically this lower edge is formed on cutting the cylinder at the discrete intervals. A similar arrangement may also be formed at the upper edge of the tank wall.

In one form, the base is formed from sheet material and may be metal, and is interconnected to the lower edge of the tank wall by a seam connection. In a particular form, the seam joining the base with the tank wall comprises a roll formed lock seam. The advantage of this arrangement is that the interconnection of the base with the tank wall can also form part of a continuous production process. To adequately seal the base to the tank wall, particularly in the vicinity of where the rib intersects the seam, the seam may need to be completed through a crimping or similar operation at these regions.

In one form, internal spacers are disposed within the tank wall. These spacers interconnect portions of the tank wall and are operative to resist outward bowing of the tank wall. In one form, the spacers comprise a plurality of metal ties.

Reinforcing elements may be provided adjacent the base of the water tank where the hydrostatic pressures are at their greatest. In one form, these reinforcing elements are in the form of metal flanges or gussets that abut the outer surface of the tank wall and the base of the tank.

In a further aspect, the invention relates to a tank wall for use in a storage tank as described in any form above.

In a further aspect, the present invention relates to a method of manufacturing a water storage tank having a base and a tank wall upstanding from the base, the method

comprising the steps of: - helically winding at least one length of sheet material about a central axis to form a cylinder; - forming a watertight joint interconnecting adjacent longitudinal edges of the or each helically wound sheet; -cutting the cylinder transverse to the central axis to separate the tank wall from the cylinder; - locating a base at one end of the tank wall; and joining the base to the tank wall.

In one embodiment wherein one of the lengths of sheet material is sheet metal strip, the method further comprises roll forming the sheet metal strip to incorporate at least one stiffening formation in the sheet.

In one form, the roll formed sheet is used in forming the cylinder. In another form, the at least one stiffening formation is introduced during, or after formation of the cylinder.

In one form, the method according to this aspect of the invention is carried out in a production line facility wherein the steps are repeated to produce a plurality of water tanks. In particular, the cylinder may be formed in a continuous process from sheet coil.

In yet a further aspect, the invention relates to a production line facility to manufacture the water storage tanks.

In yet a further aspect, the present invention relates to a method of manufacturing water storage tanks having a base and a tank wall upstanding from the base, wherein the tank wall of a plurality of tanks is formed in continuous process by helically winding at least one length of sheet material about a central axis to form a cylinder, forming a watertight joint interconnecting adjacent longitudinal edges of the or each sheet strip, and cutting the cylinder at discrete intervals to form the individual tank walls.

Brief Description of the Drawings It is convenient to hereinafter describe embodiments of the present invention with reference to the accompanying drawings. Particularly of these drawings and the related description is to be understood as not superseding the generality of the preceding broad description of the invention.

In the drawings: Fig. 1 is a perspective view of a water tank according to an embodiment of the present invention; Fig. 2 is a planar view of the tank of Fig. 1; Fig. 3 is a perspective view of a sheet metal strip including a ribbed profile for use in the water tank of Fig. 1.

Fig. 4a is an alternative metal strip profile for the tank of Fig. 1; Fig. 4b is a further alternative profile of the metal strip for use in the tank of Fig. 1; Figs. 5a to 5c are schematic illustrations of the manufacture of the join at the base of the water tank of Fig. 1 ; Fig. 6a is a detail of the helical seam in the tank wall of the tank of Fig. 1; Fig. 6b is alternative design of helical seam for the tank wall of the tank of Fig. 1; Fig. 7 illustrates a cross section of a tank wall incorporating a mandrel used in construction of the tank of Fig. 1; Fig. 8 is a cross sectional profile of the tank wall of the tank of Fig. 1 using the mandrels of Fig. 7; Fig. 9 is an alternative cross sectional to the profile of the tank of Fig. 8; Fig. 10 is a side view of the tank of Fig. 1 incorporating stiffening flanges ; Fig. 11 is an end elevation of the tank of Fig. 10; Fig. 12 is a schematic cross sectional view of the

tank of Fig. 1 incorporating internal ties; Fig. 13 is a variation on the tank illustrated in Fig. 12; and Fig. 14 is a schematic view of a production facility for manufacturing water tanks.

Detailed Description of the Drawings Turning firstly to Figs. 1 and 2, a rain water storage tank 10 is disclosed which is generally obround in cross section. The tank includes a base 11 and tank wall 12 which extends upwardly from the base. The tank wall 12 includes opposite generally parallel sides 13 and 14 and generally semi-circular ends 15 and 16.

The tank 10 is made from sheet metal, with the tank wall 12 being formed by a single length of metal sheet 17, which is helically wound around a central axis (CA) of the tank. To ensure that the tank wall 12 is continuous, a lock seam 20 is provided which interconnect the opposing longitudinal edges 18, 19 (see Fig. 3) of the sheet metal strip 17 that locate adjacent one another when the strip 17 is wound in a helix. The lock seam 20 similarly extends helically about the tank axis CA.

As best illustrated in Fig. 3, the sheet metal strip 17 may be profiled to include a plurality of ribs 21 which extend in the longitudinal direction of the sheet metal strip 17. In the illustrated form of Fig. 3, the sheet metal strip is profiled to include three ribs 21 which are in close proximity to each other and pans 22 located adjacent the ribs 21.

The ribs 21 are provided to stiffen the sheet strip 17 so that it is better able to accommodate the hydrostatic pressures induced in use of the tank 10.

These ribs are typically formed from a cold roll form operation. It needs to be appreciated however that other profiles may be used as will be appreciated by those skilled in the art. Examples of other profiles are

illustrated in Figs. 4a and 4b. In the embodiment of Fig.

4a, the pan sections 22 disposed between the ribs 21 incorporate a series of transverse flutes 23 that are inclined both to the longitudinal ribs 22 and to the lateral axis of the sheet 17. These flutes, which are typically microflutes, are inclined in this way so that when the sheet 17 is helically wound to form the tank wall 12, the microflutes extend substantially vertically (ie. in the direction of the tank axis CA). The purpose of the flutes is to further increase the strength of the sheet metal strip so as to resist bulging of the sheet intermediate the ribs 21. In a further form, the flutes may extend laterally across the sheet so that when the sheet is wound on to form the tank wall 12, they extend at an angle to the central axis.

A further alternative arrangement is illustrated in Fig. 4b where the sheet metal strip is formed from a regular corrugated profile having a series of spaced crests 24 and troughs 25.

Turning back to the form as illustrated in Fig. 1, the sheet 17 is helically wound so that the pitch angle a as illustrated in Fig. 1, is relatively low and is typically in the range of 0.1 to 5°. Further, in the illustrated form, the ribs 21 project outwardly from the tank. However it is to be appreciated that the tank may be wound so that the ribs extend inwardly. This latter option has the advantage as it provides a smoother exterior surface with the outer surface of the pans 22 forming the outer margins of the tank wall 12.

The sheet metal strip 17 is formed from a high tension or mild steel which typically has thickness of 0. 35-3. Omm and incorporates a protective coating which is formed from zinc or a zinc mixture. The sheet steel may also be laminated with a protective polymer based film which provides superior chemical resistance and enhanced moisture barrier. One such polymer film is sold under the trade mark TRENCHCOAT LG which is a trade mark of the Dow

Chemical Company. The thickness of the coating is preferably in the range of 100 to 400 microns.

Whilst not shown, the tank 10 typically also includes a lid 16 which incorporates an inlet pipe 17 to the tank 10. An outlet (also not shown) is also typically provided adjacent the base 11.

Figs. 5a to 5c illustrate a connection detail of the base 11 to the tank wall 12. As illustrated, the lower end of the tank wall 12 includes an outwardly extending flange 26. Similarly the base includes a main body portion 27 and a turned lip 28. Initially, the tank wall 12 is located on the main body portion 27 within the turned end 28. A gasket 29 is disposed between the tank wall 12 and the base 11.

A lock seam is formed at the juncture between the base and the tank wall 12 by a roll forming operation wherein the turned end 28 is rolled back onto the laterally extending flange 26 as best illustrated in Fig.

5b. This formation of the lock seam illustrated in Fig.

5b is effected by a roll former which proceeds around the perimeter of the water tank. However, the roll former is typically not suitable to provide an adequate seal at those regions where the rib 21 extends to the base 11. In those regions, a further clinching operation is required to form a more effective seal and this is illustrated in Fig. 5c.

Fig. 6a illustrates the lock seam 20 which is provided in the tank wall and joins the longitudinal edges 18 and 19 of the metal strip. The lock seam 20 is formed by folding overlapping portions 18 and 19. A gasket 30 is disposed within the lapped portion prior to folding so that it is captured within the locked seam 20. The lock seam is designed so that outward hydrostatic pressure forces the seam into tighter engagement thereby improving the seal between the longitudinal edges 18 and 19.

Fig. 6b illustrates a variation in the lock seam 20.

In this arrangement, the steel strip 17 includes a

laminated polymer film 40. The film 40 is compressible and is designed not only to provide a moisture barrier on. the inner surface of the tank, but is also designed to make the lock seam watertight, thereby obviating the need for a separate gasket. Examples of films for this purpose include the protective polymer film used to provide a moisture barrier to the metal strip. Other coatings that could be applied along the relevant edge margins include polyethylene, PVC, polypropylene and synthetic rubbers such as neoprene.

The lock seam is arranged so that the edges overlap with the film coatings of one edge being in facing relation with the coating of the other edge. Further, the lapping edges are forced together under pressure to thereby compress the coating 40. In tests conducted by the Applicant, adequate seals were formed at the lock seam in a tank that had a water head of 2.6m with an overlap of between 3-10mm and with the film coating compressed in the range of 10-50%.

As discussed in further detail below with reference to Fig. 14, the tank wall is initially formed in a circular cylinder as illustrated in Fig. 7. The tank wall is then able to be reshaped into different configurations such as the elliptical form as shown in Fig. 8 or the obround shown in Fig. 9. The advantage of this arrangement is that the tanks of different shape can all be made from a common stock. To reshape the tank wall 12 mandrels 50 (as illustrated in Fig. 7) are inserted within the tank wall 12 prior to connecting of the wall with the base 11. Each mandrel 50 includes mandrel parts 51 and 52 which are movable relative to each other. Each of the mandrel parts 51,52 include an engagement surface 53 which in the illustrated form is arcuate. Through outward displacement of the mandrel parts 51 and 52 it is possible to reform the circular cylindrical wall to the elliptical shape illustrated in Fig. 8 or the obround shape of Fig.

9.

Figs. 10 to 13 illustrate various reinforcing elements which can be used in conjunction with the water tank 10 so that it can be fully self supporting and able to accommodate the hydrostatic pressures induced in the tank in use. In one form illustrated in Fig. 10, the tank incorporates a series of metal flanges which each include an inner engagement edge 32 which is designed to abut a lower margin of the tank wall 12. In the illustrated form, the inner edge 32 of the flanges 31 is profiled to match the profile of the tank 10. A lower edge 33 of the flanges 31 engages a support structure 34 which is connected to the base 11 or separately formed thereto.

The flanges 31 are designed to resist outward bowing of the tank wall and are disposed in regions where these pressures are at their highest and where the wall is at its most susceptible. In the particular arrangement where the tank is formed as an obround, the reinforcing flanges are spaced along the generally parallel surfaces 13 and 14.

Another form of reinforcing element is illustrated in Figs. 12 and 13 where internal ties 35 are disposed within the tank 10. The ties 35 are arranged to interconnect portions of the tank wall 12 so as to resist outward bowing of the tank wall 12 under hydrostatic pressures.

In use, a plurality of the ties maybe disposed within the tank 10 between its upper and lower ends. The spacings between the ties 35 may vary along the tank and in particular, be more closely spaced towards the bottom of the tank 10 where the hydrostatic pressures are at their highest.

The tank 10 is designed so that it can be manufactured in a production line fashion. This has distinct advantages as it can substantially reduce the cost of manufacture of the tanks as compared with tanks of comparable size and performance which were hand assembled.

A particular advantage of the tank design is the manufacture of the tank wall 12 from helically wound sheet

metal strip. Incorporation of this feature enables the tank walls to be formed from a continuous length of metal tubing. The process of manufacture is schematically represented in Fig. 14.

As disclosed in Fig. 14, the tank 10 is manufactured in a production line fashion from flat sheet metal strip.

The sheet metal strip is provided in a coil 100 and is pre-coated with the polymer film. In a first stage, the sheet is fed through a roll former 101 wherein the appropriate stiffening formations are formed in the sheet to produce the profiled sheet 17. The profiled sheet is then helically wound to form a continuous cylinder 103 at step 102. The cylinder wall 103 is continuous with the lock seam 20 interconnecting the longitudinal edges 18 and 19 of the sheet 17. The cylinder 102 then progresses to a shearing station 104 which cuts the cylinder into discrete lengths to thereby form the individual wall sections 12 of the tank. In an alterative form (not shown), the metal strip is profiled during, or after, formation of the cylinder wall 103.

At stage 105, one or more mandrels 50 is inserted into the tank wall 12 so as to reshape it into its desired configuration. The reshaped tank wall 12 is then passed to a subsequent station 106 wherein the base is located over one end of the tank wall 12. The base is supplied from a store 107. The flange 26 is formed at the outer edge of the tank wall 12 and thereafter, a roll former 108 folds over the turned end 28 of the base to form the lock seam. A crimping apparatus 109 then traverses around the base to seal the base to the tank wall 12 in those regions where required, particularly where a rib 21 extends into the bottom lap seam.

In accordance with the present invention, an improved water tank is provided which can be produced in a production line fashion thereby significantly reducing the costs of manufacture over prior art water tanks that are hand assembled. The water tank may be formed in any

height and various cross sectional profiles and include different strengthening rib configurations as required.

In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word"comprising"is used in an inclusive sense, i. e. the features specified may be associated with further features in various embodiments of the invention.

Variations and or modifications may be made to the parts previously described without departing from the spirit or ambient of the present invention.