Abstract:
A method for manufacturing a circular metal tank, from an elongated sheet of metal. The upper and lower longitudinal edges of the metal sheet are bent to produce a first “L” bend and a second “chair” bend, respectively. The sheet of metal is moved in a helical trajectory such that the second bend comes into proximity above the first bend. The second bend and the first bend are welded together such that the wall of the cylindrical tank is formed. Welding of the bends serves to stress relieve or anneal the bent metal, thereby preventing cracks in the metal which may result in leaks and/or compromise the structural integrity of the tank. The first and second bends additionally cooperate to form a helical roller track on the outside of the tank. The tank is supported and rotated about its longitudinal axis on a plurality of rollers that engage the roller track.

Description:
RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Patent Application 60/560,981, filed on Apr. 12, 2004. 
    
    
     FIELD OF THE INVENTION 
     This invention relates generally to the manufacture of circular metal tanks from steel coils shipped to site straight from the steel mill. 
     BACKGROUND OF THE INVENTION 
     The prior art describes a variety of methods for the construction of circular metal tanks used in storage of solids or liquids. For instance, U.S. Pat. No. 2,751,672, issued to Reed, describes the fabrication of circular tanks from a series of metal sheets which are bolted together. This method of assembly requires a large amount of manual labour, a complicated tank support structure, and is unsuitable for producing tanks for storage of liquids due to the massive number of bolt holes requiring hydraulic seals to prevent the leakage of any stored liquid. 
     U.S. Pat. No. 4,121,747, issued to McFatter, describes the construction of circular storage tanks from strip metal wound in a helical path in which the tank is built upwardly. The metal strip is fed to a support assembly arranged circularly on a base, and the upper edge of the strip that is fed to the support assembly is aligned with the lower edge of the helical turn immediately thereabove so that the edges are spaced apart in a vertical plane from each other and then “butt” welded together. This invention teaches away from the bending of metal strip edges and sees no potential advantage in doing so. This technique for tank fabrication suffers from the following disadvantages:
         a) satisfactory alignment of metal strips ahead of a butt welder is difficult;   b) slight misalignment of the metal strips, especially for thinner metal thicknesses, can cause weak welds and/or leaks due to insufficient metal-to-metal contact; and   c) there is no provision for reinforcement of metal strips to prevent their deformation (e.g. bulging due to pressure on lower metal strips in a tall liquid storage tank.       

     U.S. Pat. No. 3,863,479 to Lipp describes the fabrication of metal tubes and tanks from helical metal coils using severe folded bends from adjacent coils. Lipp suffers from the following disadvantages:
         a) the tanks are unsuitable for storage of liquids since perfect hydraulic seals at the mechanical bends cannot be guaranteed;   b) the method is unsuitable for hard-to-bend metals, especially for higher carbon steels, due to the severity of the bends and lack of stress relief (e.g. annealing) after bending resulting in potential metal cracking and subsequent loss of strength and hydraulic seals;   c) the thickness of usable metal is limited due to the severity of the bends, which may result in cracking and subsequent loss of strength and hydraulic seals; and   d) there are no reinforcing corrugations in the coils to prevent bulging, which is especially problematic since the thickness of the metal that may be used is limited, as discussed in point (c) above.       

     SUMMARY OF THE INVENTION 
     The invention relates to a method for manufacturing a circular metal tank, from an elongated sheet of metal. The upper and lower longitudinal edges of the metal sheet are bent to produce a first “L” bend and a second “chair” bend, respectively. The sheet of metal is moved in a helical trajectory such that the second bend comes into proximity above the first bend. The second bend and the first bend are welded together such that the wall of the cylindrical tank is formed. The first and second bends cooperate to form a helical roller track on the outside of the tank. The tank is supported and rotated about its longitudinal axis on a plurality of rollers that engage the roller track. As the tank is rotated and the metal sheet is welded to the bottom thereof, the tank moves upwards on said rollers. 
     The metal sheet can optionally be corrugated to reinforce the walls of the tank and to prevent bulging. 
     The bending of the longitudinal edges of the metal sheet achieves the following:
         easier alignment of adjacent portions of the metal sheet which results in stronger welds and therefore improved hydraulic seals and increased structural strength;   the first and second bends cooperate to form roller tracks that allow the tank to be supported and positioned on rollers as the tank is being manufactured;   the bends themselves also act to reinforce the tank walls;   welding of the bends serves to stress relieve or anneal the bent metal, thereby preventing cracks in the metal which may result in leaks and/or compromise the structural integrity of the tank.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention itself both as to organization and method of operation, as well as additional objects and advantages thereof, will become readily apparent from the following detailed description when read in connection with the accompanying drawings, wherein: 
         FIG. 1   a  shows a small circular tank production system according to the present invention; 
         FIG. 1   b  show a medium size circular tank production system according to the present invention; 
         FIG. 1   c  shows a large size circular tank production system according to the present invention; 
         FIG. 2  shows inclined adjacent loops of the metal strip supported on rollers; 
         FIGS. 3   a ,  3   b  &amp;  3   c  show a bender/corrugator; 
         FIGS. 4   a ,  4   b  &amp;  4   c  show cross sections of alternate embodiments of the metal strip after it has been bent and/or corrugated; 
         FIG. 5   a  shows a welding pre-aligner; 
         FIG. 5   b  shows a motorized double roller with adjustable top wheel; 
         FIGS. 6   a  &amp;  6   b  show a roller track formed by adjacent unwelded second and first bends of the metal strip; 
         FIG. 7  shows a roller track formed by adjacent second and first bends of the metal strip in combination with a double roller with adjustable bottom wheel; 
         FIG. 8   a  shows a welding positioner; 
         FIG. 8   b  shows a motorized double roller with adjustable bottom wheel; 
         FIGS. 9   a  &amp;  9   b  show a welder; 
         FIG. 10  shows a weld between adjacent loops of the metal strip as viewed from the inside of the tank; 
         FIGS. 11   a  &amp;  11   b  show a roller track engaged by a single roller; 
         FIG. 12  shows a single free roller assembly; 
         FIG. 13  shows a decoiler assembly; and 
         FIGS. 14   a  &amp;  14   b  show the wall of a tank formed according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF INVENTION 
       FIGS. 1   a ,  1   b  &amp;  1   c  show a top view of the cylindrical tank  10  being constructed according to the present invention. The major components are identified as follows:
         The Decoiler  20  unravels a coiled metal sheet  30  and feeds it into a Bender/Corrugator  40 .   The Bender/Corrugator  40  creates first and second bends to the longitudinal edges of the metal sheet and optionally imparts single or multiple waveform reinforcing corrugations along the length of the decoiled metal sheet  30 .   Welding Pre-aligner  50  “gross” positions adjacent edges of metal sheet  30  after it exits the Bender/Corrugator  40  and ahead of the Welding Positioner  60 .   Welding Positioner  60  “fine” positions adjacent edges of the metal sheet  30  after it exits the Welding Pre-Aligner  50  and before it enters the Welder Assembly  70 .   Welder Assembly  70  welds (e.g. by fillet weld) adjacent edges of the metal sheet  30 .   Support System  80  which is a structure having rollers and positioners (e.g. Welding Pre-aligner  50  and Welding Positioner  60 ) that guide and support the metal sheet  30 , before and after it is welded, along a helical trajectory.   Single Rollers  100  make up part of the Support System  80 . They may be motorized or un-motorized rollers and operate to support and position the metal sheet  30  that forms the wall of the tank  10  while it is being constructed.   Motorized or un-motorized double rollers  110  and motorized double rollers  111  also make up part of the Support System  80 . Double rollers  110  &amp;  111  operate to support and position the metal sheet  30  that forms the wall of the tank  10  while it is being constructed.   Vertical Coil Seam Welder  120  may be manual or automatic and is operative to join (e.g. butt weld) adjacent ends of metal sheets  30  in order to connect two consecutive metal sheets  30 .       

       FIG. 2  illustrates a typical sequence of single rollers  100  and double rollers  110  &amp;  111  showing adjacent portions of the metal sheet  30  inclined so that the sheet  30  follows a helical path. The image of  FIG. 2  is drawn as if it they were flat and unwound (e.g. “Mercator” projection) seen from the interior view. The ends  32  and  34  of the metal sheet  30  are connected to one another although they appear on opposite sides of the Figure. 
       FIG. 3   a  illustrates a bender/corrugator  40  which creates a first “L” bend  42  along the upper longitudinal edge  36  and a second “chair” bend  44  along the lower longitudinal edge  38  of the metal sheet  30 . In the preferred embodiment of the invention the first bend  42  forms what will be termed in the document an L-shaped bend with an angle of between 45 and 135 degrees with the metal sheet  30  and has a width of between 5 and 100 mm, (depending on the thickness of the metal, the type of metal, and the size of the tank  10 ). In the preferred embodiment the second bend  44  has a horizontal portion  46  that is between 5 mm and 100 mm wide and a vertical portion  48  that is between 5 mm and 150 mm. 
       FIG. 3   b  illustrates a bender/corrugator  40  which creates a first “L” bend along the upper longitudinal edge  36  and a second “chair” bend along the lower longitudinal edge  38  plus a single corrugated bend  130  on the metal sheet  30 . 
       FIG. 3   c  illustrates a bender/corrugator  40  which creates a first “L” bend along the upper longitudinal edge  36  and a second “chair” bend along the lower longitudinal edge  38  plus a double corrugated bend  135  on the metal sheet  30 . 
       FIG. 4   a  illustrates the cross section of the metal sheet  30  after it is output from the  FIG. 3   a  bender/corrugator  40 . 
       FIG. 4   b  illustrates the cross sections of the metal sheet  30  at various stages as it passes through the bender/corrugator  40  of  FIG. 3   b.    
       FIG. 4   c  illustrates the cross sections of the metal sheet  30  at various stages as it passes through the bender/corrugator  40  of  FIG. 3   c.    
       FIG. 5   a  illustrates the welding pre-aligner  50 , which is operative to gross position adjacent edges of the metal sheet  30 . The pre-aligner  50  has horizontal adjustable rollers  140 —roller  150  pushes the upper edge  36  of the lower unwelded part of the metal sheet  30  (not shown) in the exterior direction (i.e. from the inside of the tank  10  towards the outside) whereas roller  145  pushes both the upper edge  36  of the lower part of the metal sheet  30  and the lower edge  38  of the upper part of the metal sheet  30  in the exterior direction. The pre-aligner  50  additionally has horizontal roller adjustors  165  and  166  to regulate the horizontal positioning of rollers  145  and  150 . The pre-aligner  50  operates in conjunction with a double roller  110  described in more detail below. 
       FIG. 5   b , shows double roller  110  in isolation. The double roller  110  may be used alone or as part of a welding pre-aligner  50 . The double rollers are also used at other points during the construction of the tank  10 , as shown in  FIGS. 1 and 2 . Generally, the double rollers  110  may be motorized or free-rolling. In the preferred embodiment of the present invention the double rollers  110  of the welding pre-aligner  50  and the double rollers  111  of the welding positioner  60  are motorized to aid in the accurate positioning and welding of the metal sheet  30 . In addition, in the embodiment in  FIG. 5   b , the double roller  110  has rollers  115  and  117  that are adjustable. Rollers  115  and  117  can be simultaneously horizontally adjusted while the upper roller  115  can also be vertically adjusted upwards or downwards. 
       FIGS. 6   a  and  6   b  illustrate the roller track  160  formed by an adjacent “L” bend  42  and chair bend  44  of the unwelded upper and lower edges  36 ,  38  of metal sheet  30 . As shown in these figures, the roller track  160  has two opposing roller track sides. The first roller track side is formed by the portion of metal sheet  30  that is continuous with bend  42  and upper edge  36 . The opposing second roller track side is formed by an opposing vertical portion  48  that is continuous with the chair bend  44 . As shown in  FIGS. 11   a  and  11   b  and as discussed below, the space between the roller track sides accommodates one or more rollers that engage the roller track. By engaging the roller track these rollers support and rotate the tank wall as it is being constructed. In the preferred embodiment of the invention the first bend  42  forms an angle of between 45 and 135 degrees with the metal sheet  30  and has a width of between 5 and 100 mm, (depending on the thickness of the metal, the type of metal, and the size of the tank  10 ). In the preferred embodiment the second bend  44  has a horizontal portion  46  that is between 5 mm and 100 mm wide and a vertical portion  48  that is between 5 mm and 150 mm. 
     Referring to  FIG. 5   b , the roller track  160  (shown in isolation in  FIGS. 6   a - b ) is supported underneath by roller  119  (on which the “L” bend along the upper longitudinal edge rests) while roller  118  pushes downwards (on the chair bend along the lower longitudinal edge). 
       FIGS. 7 &amp; 8   b  show double roller  111  in isolation. Double roller  111  may also be used as part of a welding positioner  60 . Double rollers  111  are motorized. In the preferred embodiment of the present invention the double rollers  110  (see  FIGS. 1 ,  2  and  5   b ) of the welding pre-aligner  50  are also motorized to aid in the accurate positioning and welding of the metal sheet  30 . In addition, in the embodiment in  FIGS. 7 &amp; 8   b , the double roller  111  has rollers  115  and  117  that are adjustable. Rollers  115  and  117  can be simultaneously horizontally adjusted while the lower roller  117  can also be vertically adjusted upwards or downwards. Referring to  FIGS. 7 and 8   b , the roller track  160  (shown in isolation in  FIGS. 6   a - b ) is supported underneath by roller  117  (on which the “L” bend along the upper longitudinal edge rests) while roller  115  pushes downwards (on the chair bend along the lower longitudinal edge). 
     Engagement of the track  160  by motorized double rollers  110  and/or  111  provides both support for the tank  10  as it is being constructed and means to advance the metal sheet  30  in a helical fashion. 
       FIG. 8   a  illustrates the welding positioner  60 , operative to fine position the adjacent edges of the metal sheet  30  (not shown) for welding. Horizontal adjustable roller  170  pushes the lower edge of the upper part of metal sheet  30  in the exterior direction (i.e. from the inside of the tank  10  towards the outside) and roller  175  pushes the upper edge of the lower part of metal sheet  30  in the exterior direction. Adjustors  180  regulate the horizontal positioning of rollers  170 ,  175  and therefore the edges of the metal sheet. 
     Referring to  FIGS. 4 ,  6   a - b ,  7 ,  9   a - b  and  11 , it will be clear to those skilled in the art that the upper and lower longitudinal edges  36 ,  38  of the metal sheet  30  can be bent in a variety of configurations to create alternate track  160  shapes (e.g. non-right angle bends) which still permit the tank  10  to be moved and supported by, for example, engagement with double rollers  110  and/or  111 , or single rollers  100 . In addition, a variety of corrugation configurations may be used. 
       FIGS. 9   a  and  9   b  illustrate a welder  70  applying a continuous weld  200  (e.g. fillet weld) to the groove between the “L” bend along the upper longitudinal edge  36  and a second “chair” bend along the lower longitudinal edge  38  of the metal sheet  30 .  FIG. 10  illustrates the weld  200  as viewed from the interior of the tank  10 . 
       FIGS. 11   a  and  11   b  illustrate a welded roller track  160  engaged by a single roller  100 . Single rollers  100  are used throughout the support system  80  (see  FIG. 1 ) to support the tank  10  while allowing it to be easily rotated as the metal sheet  30  is welded and advanced in a helical fashion to produce the tank wall. As seen in the figures, the roller  100  is received between the roller track sides. Referring again to  FIGS. 1   a ,  1   b  and  1   c , the support system  80  may comprise as many or as few single rollers  100  and double rollers  110  &amp;  111  as are deemed necessary depending on the height and size of the tank  10 , and the size and thickness of the metal sheet  30 . 
     Referring again to  FIGS. 1   a ,  1   b  and  1   c , the support system  80  may comprise as many or as few single rollers  100  and double rollers  110  &amp;  111  as are deemed necessary depending on the height and size of the tank  10 , and the size and thickness of the metal sheet  30 . 
       FIG. 12  illustrates a single roller  100  supported by a support member  210  of the support system  80 . Support members  210  and rollers  100 ,  110  and  111  such as these are arranged in a circular fashion (see  FIG. 1 ) to support the tank  10  as it is being built. In the preferred embodiment of the invention the single rollers  100  are tiltable (i.e. the roller  100  can be tilted away from vertical alignment towards the centre of the tank  10  while maintaining contact with the roller track  160  (see  FIG. 11 ) to maintain fine control of tank diameter. Further, in the preferred embodiment, the height of the single rollers  100  is adjustable (e.g. by a double threaded height adjuster  220 ) in order to provide control of the shape and incline of the helical winding of the metal sheet  30 . 
       FIG. 13  illustrates a decoiler  20  that unwinds the coiled metal sheet  30  so that it can be incorporated into the tank. 
       FIGS. 14   a  and  14   b  show the wall of a tank  10  produced according to the present invention from one or more helically wound metal sheets  30  welded continuously longitudinally and at vertical sheet-to-sheet seams. As more of the metal sheet  30  is added to the bottom of the tank  10 , the tank is rotated about its longitudinal axis such that it advances gradually in an upward direction. The top edge  230  and the bottom edge  240  of the tank  10  in  FIG. 14   a  are cut to form circumferential edges each lying in a plane parallel to the ground as shown in  FIG. 14   b  (obviously, whether the circumferential edges are parallel to the ground or some other point of reference is a matter of design choice). After completion of the welding and cutting of the bottom edge  240 , the tank can be lowered to the ground by reversing the rotation along the single and double rollers (see  FIGS. 1 and 2 ). Any number of prior art techniques can be used to finish or cut the top edge  230  and the bottom edge  240  of the circular tank  10  and to weld and seal them to, for example, a concrete base. 
     SUMMARY 
     The invention disclosed herein may be conveniently summarized, at least in part, with reference to the following enumerated statements: 
     Statement 1. The invention includes a method for manufacturing a circular metal tank, comprising the steps of: providing an elongated sheet of metal; bending said sheet of metal along an upper longitudinal edge thereof to produce a first bend; bending said sheet of metal along a lower longitudinal edge thereof to produce a second bend; moving said sheet of metal in a helical trajectory such that said second bend comes into proximity above said first bend; welding said second bend to said first bend to form a wall of said tank, said wall having a continuous, helical weld; wherein said first and second bends cooperate to form a helical roller track on an outside of said tank; and wherein said tank is supported on a plurality of rollers that engage said roller track; and wherein said tank is rotated about its longitudinal axis on said rollers such that said tank moves upwards as said sheet of metal, is welded to a bottom thereof. 
     Statement 2. The invention includes the method of Statement 1 wherein said elongated sheet of metal is a coiled sheet of metal which is decoiled prior to said bending steps. 
     Statement 3. The invention includes the method of Statement 1 wherein said first bend is an “L”-bend and said second bend is a chair-bend. 
     Statement 4. The invention includes the method of Statement 1 wherein said metal sheet is corrugated before said welding step. 
     Statement 5. The invention includes the method of Statement 1 wherein prior to said welding step adjacent portions of said first and second bends are gross positioned and then fine positioned. 
     Statement 6. The invention includes the method of Statement 1 wherein at least one of said rollers is motorized and said tank and said metal sheet are moved by means of said motorized roller. 
     Statement 7. The invention includes the method of Statement 1 wherein said metal sheet is made of one of aluminum, galvanized steel, stainless steel, carbon steel. 
     Statement 8. The invention includes the method of Statement 1 wherein said first bend forms an angle of between 45 and 135 degrees with a body of said metal sheet. 
     Statement 9. The invention includes the method of Statement 1 wherein said first bend has a width of 5 mm to 100 mm. 
     Statement 10. The invention includes the method of Statement 1 wherein a width of a horizontal portion of said second bend is between 5 mm to 100 mm. 
     Statement 11. The invention includes the method of Statement 1 wherein a width of a vertical portion of said second bend is between 5 mm to 150 mm. 
     Statement 12. The invention includes the method of Statement 1 wherein a top of said tank is cut so as to create an upper circumferential edge which is parallel to the ground. 
     Statement 13. The invention includes the method of Statement 1 wherein a bottom of the tank is cut during operation to create a lower circumferential edge which is parallel to the ground. 
     Statement 14. The invention includes a system for manufacturing a circular metal tank, wherein the system comprises a decoiler for decoiling a coiled sheet of metal; a bender/corrugator for introducing a first bend along an upper longitudinal edge of said metal sheet and a second bend along a second longitudinal edge of said metal sheet; a support system having rollers for moving said metal sheet along a helical trajectory, supporting said tank and for rotating said tank about its longitudinal axis as said metal sheet is added to a bottom edge of said tank; a welding positioner for positioning said second bend proximate and above said first bend; a welder for welding said first and second bends together to form a circular wall of said tank; wherein said first and second bends cooperate to form a helical roller track on an outside of said tank; and wherein said tank is supported on said rollers that engage said roller track. 
     Statement 15. The invention includes the system of Statement 14 further comprising a vertical coil seam welder for butt-welding an end of a first coiled metal sheet to an end of a second coiled metal sheet before said metal sheet pass through said bender/corrugator. 
     Statement 16. The invention includes the system of Statement 14 further comprising a welding pre-aligner for gross positioning said first and second bends before said first and second bends are positioned by said welding positioner. 
     Statement 17. The invention includes the system of Statement 14 wherein said first bend is an “L”-bend and said second bend is a chair-bend. 
     Statement 18. The invention includes the system of Statement 14 wherein said bender/corrugator additionally corrugates said metal sheet. 
     Statement 19. The invention includes the system of Statement 14 wherein at least one of said rollers is motorized and said tank and said metal sheet are moved by means of said motorized roller. 
     Statement 20. The invention includes the system of Statement 14 wherein said metal sheet is made of one of aluminum, galvanized steel, stainless steel, carbon steel. 
     Statement 21. The invention includes the system of Statement 14 wherein said first bend forms an angle of between 45 and 135 degrees with a body of said metal sheet. 
     Statement 22. The invention includes the system of Statement 14 wherein said first bend has a width of 5 mm to 100 mm. 
     Statement 23. The invention includes the system of Statement 14 wherein a width of a horizontal portion of said second bend is between 5 mm to 100 mm. 
     Statement 24. The invention includes the system of Statement 14 wherein a width of a vertical portion of said second bend is between 5 mm to 150 mm. 
     Statement 25. The invention includes the system of Statement 14 further comprising means for cutting a top of said tank so as to create an upper circumferential edge which is parallel to the ground. 
     Statement 26. The invention includes the system of Statement 14 further comprising means for cutting a bottom of the tank to create a lower circumferential edge which is parallel to the ground. 
     While this invention has been described with reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications of the illustrative embodiments, as well as other embodiments of the invention, will be apparent to persons skilled in the art upon reference to this description. It is therefore contemplated that the appended claims will cover any such modifications or embodiments as fall within the true scope of the invention.