Abstract:
A concrete form having a tubular body formed from a flexile strip wound helically in successive passes to define a wall of the form. The adjacent edges of the strip being releasably engaged with one another to inhibit axial separation of the strip.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation application of U.S. patent application Ser. No. 11/779,143 filed Jul. 17, 2007 which claims priority from U.S. Provisional Patent Application No. 60/831,226 filed on Jul. 17, 2006, the contents of which are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to forms for moulding material and to methods and apparatus of creating such forms. 
       SUMMARY OF THE INVENTION 
       [0003]    Forms are used in a variety of applications to provide temporary containment for mouldable materials. A typical application of such form is in the pouring of concrete where it is necessary to hold the concrete in the desired shape until it has set. A commonly used form is a cylindrical tube that is used to establish pillars or piers to support additional structure. Typically, these tubes, commonly known by the trademark “Sonotube” are formed from layers of paper material that are helically wound and glued to one another during forming to produce a rigid structure. The tubes have sufficient strength to support concrete and, upon setting, the layers of the tube can be removed to expose the concrete. 
         [0004]    Such tubes are widely used and are available from building supply stores in a variety of sizes. The sizes may range from 6 inches to 12 inches and the tubes are stored in a length that permits transportation, typically 20 feet. However, the storage of such tubes is difficult since they cannot be easily stacked one on top of the other due to their circular nature and is also in efficient as one tube occupies a large volume. Although some efficiency can be realized by nesting a smaller diameter tube within a larger one for transportation, this is impractical in the environment of a building supply store and also time consuming to pack the nested tubes. 
         [0005]    There is therefore the need for a form that can offer efficiencies for storage and transportation without impairing the utility of the tube. 
         [0006]    In general terms, the present invention provides a form that is helically wound from a flexible strip. The strip has a groove formed adjacent one edge and a complementary tongue formed on the opposite edge. The tongue and groove are dimensioned so as to be a snap fit to retain successive passes of the strip in forming a helical tube. 
         [0007]    Preferably, the groove is undercut and the tongue has an enlarged head to enhance the retention within the groove. As a further preference, a locking key may be provided to expand the tongue after insertion and thereby enhance the retention of the tongue within the groove. 
         [0008]    By providing a form of the structure described above, it is simply necessary to store rolls of strip that can then be deployed to form a cylinder of the required dimension and length. 
         [0009]    In a further aspect of the invention, a forming machine is provided with an expandable mandrel to guide a strip in a helical path. A pinch roller is provided to force a tongue into an adjacent groove and as a further preference, a key strip may be pressed into the tongue subsequent to the pinch roller. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    An embodiment of the invention will now be described by way of example only with reference to the accompanying drawings in which: 
           [0011]      FIG. 1  is a perspective view of a cylindrical form. 
           [0012]      FIG. 2  is a view on the line II of  FIG. 1 . 
           [0013]      FIG. 3  is an enlarged view of a section of a strip used to form the tube shown in  FIGS. 1 and 2 . 
           [0014]      FIG. 4  is a schematic representation of a machine to form the tube of  FIG. 1 . 
           [0015]      FIG. 5  is a view similar to  FIG. 2  of an alternative embodiment. 
           [0016]      FIG. 6  is a view similar to  FIG. 2  of two further embodiments. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0017]    Referring therefore to  FIG. 1 , a form indicated by reference numeral  10  has a cylindrical wall  12  formed from a helically wound strip  14 . Abutting edges of the strip  14  are interconnected by a tongue and groove joint generally indicated at  13  and seen in greater detail in  FIGS. 2 and 3 . The tube  10  is formed to a nominal diameter D which typically will range between 6 and 12 inches. The wall  14  has a nominal thickness indicated at b that is chosen so as to be sufficiently flexible to accommodate the radius of curvature required whilst withstanding the pressure that may be exerted when used as a form. A nominal thickness of ⅛″ is believed to be appropriate. 
         [0018]    Referring therefore to  FIG. 2 , the strip  14  has a body  15  with lateral edges  17  and oppositely directed faces  19 . Complementary formations in the form of a groove  16  and a tongue  18  are formed on opposite lateral edges  17 . The strip  14  is preferably made from a plastics material which is flexible so as to be able to be formed into the smallest required diameter but also has sufficient strength to withstand the hydrostatic pressure of concrete placed within the tube. 
         [0019]    As can be seen from  FIG. 2 , adjacent edges of the strip  14  are inter-engaged by the tongue  18  being inserted into the groove  16 . As will be described in more detail below, the cross section of groove  16  has a re-entrant formation and the tongue  18  is of complementary cross section with an enlarged end such that a snap fit is obtained between the two to securely retain the tongue within the groove but allowing it to be removed subsequently. A locking key in the form of a strip  20  is inserted into a slot  22  formed in the tongue  18  to further secure the tongue within the groove. 
         [0020]    Referring therefore to  FIG. 3 , the groove  16  has a part cylindrical base  24  that terminates at shoulders  26 . The shoulders  26  extend in opposite directions from a channel  28  extending to an outer surface  30  of the strip  14 . A rabbet is formed at the outer edge of the strip  14  so as to intersect the channel  28  and form a step  32  of a height less than the thickness of the strip  14 . 
         [0021]    The opposite edge of the strip  14  is undercut as indicated at  34  to provide a flange  36  that is complimentary to the step  32 . The tongue  18  projects from the flange  36  and has a profile complementary to that of the groove  16 . The tongue  18  has a part cylindrical head  40  terminating in abutment faces  42 . A neck  44  of the tongue  18  connects the tongue to the flange  36  and has a pair of opposed walls  46  that define a slot  22 . 
         [0022]    To define a cylindrical tube  10  as shown in  FIG. 1 , the strip  14  is wound in a helical form so that the tongue  18  is aligned with the groove  16 . The cylindrical head of the tongue permits it to be inserted into the channel  28  such that the abutment faces  42  engage the underside of the shoulders  26  and securely hold the tongue within the groove. In this position, by virtue of the provision of the step  32  and the flange  36 , adjacent passes of the strip are aligned presenting a continuous smooth surface. The key  20  may then be inserted into the slot  22  to expand the neck  44  within the channel  28  and further secure the tongue  18  within the groove  16 . 
         [0023]    With a cylindrical tube defined, it may be used as a form with, for example, concrete, to hold the concrete until it is solidified. Upon setting of the concrete, the key  20  is removed and strip  14  may then be unwound by pulling the tongue  18  out of the groove  16 . This will proceed in a smooth progressive manner along the length of the strip to release the tube from the outer surface of the cured concrete. 
         [0024]    It will be apparent from the above description that the strip  14  may be stored in rolls of sufficient length provided to permit a tube of the required diameter and length to be formed. The diameter through which the strip is wound may be varied to provide tubes of different length. 
         [0025]    To facilitate the formation of the tube  10 , a winding apparatus as shown schematically in  FIG. 4  may be used. 
         [0026]    Referring therefore to  FIG. 4 , a forming machine  50  has an unexpandable mandrill  52  about which the strip  14  may be rolled. The mandrill  52  is mounted upon a shaft  54  which in turn is rotatably mounted upon a support  56 . A spider assembly  58  is fixed to the shaft  54  adjacent the support  56  and carries four arms  60  that are pivotally connected to the spider  58 . A slidable spider  62  is mounted on the opposite end of the shaft  54  and similarly carries arm  64 . Support bars  66  extend between the outer ends of the arms  64  to define the mandrill  52 . The spiders  58 ,  62  are mounted on splines provided on the shaft  54  so that they may rotate their width. However, the slide at the spider  62  is axially displaceable along the shaft to define the outer diameter of the mandrill  52 . 
         [0027]    The shaft  54  is driven through a belt drive  66  from an electric motor  68  that is mounted on the support  56 . The support  56  also carries a nip roller  70  that is mounted upon a shaft  72 . The shaft  72  is rotatably mounted on the support  56  and driven through a belt drive  74  from the motor  68 . The nip roller is adjustable relative to the shaft  54  so that it may be positioned adjacent to but spaced from the bars  66 . 
         [0028]    To form a tube  10 , strip  4  shown in ghosted outline of  FIG. 4  is fed at an angle onto the mandrill  52  between the nip roller and the outer surface of the bars  66 . The nip roller  70  progressively forces the tongue  18  into the groove  16  as the mandrill is rotated to provide a continuous forming of the tube  10  that projects axially from the mandrill. After the desired length of tube has been formed, the strip may be cut and the ends of tube trimmed square for subsequent use. 
         [0029]    Where a key is inserted into the slot  22 , an additional roller  76  is spaced from the nip roller  70  and the key fed into the slot  60  and forced into the slot  22  by the action of the roller  76 . 
         [0030]    It will be appreciated that the formation of the tube  12  may be conducted at a building supply outlet or can be delivered as a strip on site where the tube can then be formed of the required diameter. 
         [0031]    Reinforcement of the tube  10  may be provided by forming multiple layers on the tube. Such an arrangement is shown in  FIG. 5  where a first layer of the wall  12  is formed as described above. In this arrangement, the strip  14   a  is formed with a groove  16   a  intermediate the lateral edges of the strip  14   a.  The groove receives a tongue  18   a  projecting from the underside of a further strip  14   b.  The strip  14   b  is formed with the inter-engaging formation at opposite lateral edges but has the additional tongue  18   a  for engagement with a radially inner wall. 
         [0032]    A further embodiment is shown in  FIG. 6  in which like reference numerals will be denoted by like components with a prefix 1 for clarity. Referring therefore to  FIG. 6 , the strip  114  is formed with a grove  116   a  intermediate the lateral edges of the strip  114 . The groove  116   a  is arranged to receive a tongue carried on the underside of an additional strip arranged radially as shown with respect to  FIG. 5 . The laterally outer edges of the strip  114  are formed with a groove  116  and tongue  118  that are simple hook members and do not provide a re-entrant formation. The groove  116  and tongue  118  inhibits axial separation of adjacent passes at the strip but radial locking of the strip is provided by the inter-engagement of the re-entrant intermediate groove  116   a  and the corresponding tongue carried by the adjacent layer. 
         [0033]    It will also be observed in  FIG. 6  that the strip  114  is formed with hollow cells  180  defined between a pair of webs  182 ,  184 . The cells  180  may be formed during extrusion of the strip in a conventional manner. The provision of the cells  180  decreases the weight of the strip whilst maintaining the structural integrity. 
         [0034]    As a further alternative as shown on the right hand side of  FIG. 6 , the strip may be formed with a single web  182  with the groove  116   a  upstanding from the web  182 . Flanges  186  are provided intermediate grooves  116   a  so as to provide a re-entrant channel on one side of the web  182 . The flanges provide the necessary radial stiffness but also facilitate the attachment of support brackets  190  that may be snapped into the re-entrant channel at discrete locations. In the embodiment shown in  FIG. 6 , the bracket  190  is arranged to receive a standard dimensional lumber brace, typically a two by four, so that the brace may be secured to the tube to assist in maintaining it in its desired location during pouring of the concrete. The brackets  190  may be attached at a number of different locations about the circumference of the tube and at different axial positions along the tube. 
         [0035]    It will be seen therefore that a simple yet effective tube is provided which may be assembled from strip to facilitate storage of the material. Assembly of the tube from the strip is relatively straightforward and permits the tube to be made to the desired length and diameter to suit particular circumstances. The tube may be formed with multiple layers and the strip may have different configurations to facilitate manufacturer.