Abstract:
A method and apparatus for manufacturing a duct bank comprising the steps of loading a frame with a series of templates, positioning the frame adjacent a pipe extruder, aligning a set of a plurality of holes with a die of the pipe extruder, extruding a pipe of a first length into the set of holes, repeating the steps of aligning and extruding for each set of holes, thereby forming the duct bank, banding the duct bank, and removing the duct bank from the frame.

Description:
FIELD OF THE INVENTION 
       [0001]    The field of the invention relates to the manufacture of plastic pipe. In particular, the field of the invention relates to a method and apparatus for the prefabrication of plastic duct bank. 
       BACKGROUND OF THE INVENTION 
       [0002]    The transmission of electrical power, data, and telephone communications beneath buildings is carried out through wires and cables installed inside conduit pipes. The pipes are often assembled into bundles known as “duct banks.” Duct banks consist of multiple sections of ducting arranged in a rectangular pattern and held in position by “templates.” The templates are generally flat rectangular spacers each having a pattern of holes through which the pipes are inserted. 
         [0003]    Duct banks are typically assembled on site or transported to a construction site where they are installed. During installation each duct bank is loaded into a trench along a predetermined route. Each duct bank is then joined with other similar duct banks with couplings, sealed and encased in concrete. 
         [0004]    In the prior art, duct banks are assembled on the job site either in the trench or above ground near the trench. Typically, a first set of workers holds a set of templates at a predetermined angle and at the correct spacing to position and hold the ducts in place. A second set of workers positions each pipe in a set of corresponding holes in the templates by sliding it through the holes. The process is labor-intensive, dangerous, and subject to frequent interruption during assembly in order to provide realignment of the templates and undo jamming of the pipes. 
         [0005]    The prior art has attempted to solve some of these problems. For example, U.S. Pat. No. 3,606,395 to Salerno, et al. discloses a method and apparatus of laying underground cables using preformed conduit sections. The preformed conduit sections are rectangular blocks having four longitudinal holes forming conduit pipes. The preformed conduit sections are aligned end to end to form four continuous ducts. However, the block conduit sections in Salerno require excess material to surround each conduit in order to form the conduit section. This excess material requires additional raw materials, which increases manufacturing costs. 
         [0006]    U.S. Pat. No. 3,711,127 to Raffa discloses a closure to arrange conduit members into a duct bank. The closure includes a horizontal base, upright side walls formed integrally with the base, longitudinal side walls, and upright members attached to the base having a generally rectangular shape adapted to align and support conduit members. The upright side walls have tapered sleeves sized to align and support the conduit members. The closure is sealed and filled with an inert gas to improve insulation and heat dissipation. However, Raffa requires the use of a housing to encase the duct bank and inert gas to fill the housing, thereby making the arrangement expensive to manufacture and assemble. 
         [0007]    U.S. Pat. No. 5,605,419 to Reinert discloses a method for assembling and installing duct banks. The duct banks are assembled with upright plastic grids having apertures sized to axially receive conduits. The grids are spaced apart along the length of the conduits. Spacers are installed in groups of four, onto conduit members, one on each corner of the cross section of the duct bank. Wooden supports are placed across the conduits to support the duct bank. However, the method requires the duct bank to be assembled at the jobsite, which requires additional workers and exposes the workers to unnecessary dangers, thereby increasing installation costs. 
         [0008]    The prior art fails to disclose or suggest a method and apparatus for prefabricating duct banks at the point of pipe extrusion. The prior art also fails to disclose an automated method of assembly of duct banks. Therefore, there is a need in the prior art for a method and apparatus for manufacturing and preassembling a duct bank that reduces time and labor costs and increases worker safety. 
       SUMMARY 
       [0009]    In a preferred embodiment, a method for manufacturing a duct bank comprising the steps of providing a set of rigid templates, each of the templates comprising a set of patterned holes; providing a frame having a set of supports for the templates loading the set of supports with the set of templates; positioning the templates to align a set of holes; positioning the frame adjacent an extrusion machine, the extrusion machine having a coaxial extrusion die, a cooling section, and a cutter; aligning the set of holes with the extrusion die; extruding a pipe of a first predetermined length into the set of holes; repeating the steps of aligning and extruding until a pipe is extruded into each set of holes, thereby forming the duct bank; banding the duct bank; and removing the duct bank from the frame. 
         [0010]    In a preferred embodiment, the step of extruding a pipe of a first predetermined length into the set of holes includes the steps of cooling the pipe and cutting the pipe at the first predetermined length. 
         [0011]    In a preferred embodiment, the step of extruding at least one pipe of the second predetermined length includes the steps of cooling the at least one pipe and cutting the at least one pipe at the second predetermined length. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The disclosed embodiments will described with reference to the accompanying drawings. Like pieces in different drawings carry the same number. 
           [0013]      FIG. 1  is a flow chart of a preferred embodiment. 
           [0014]      FIG. 2A  is a side view of a template of a preferred embodiment. 
           [0015]      FIG. 2B  is a side view of a template of a preferred embodiment. 
           [0016]      FIG. 2C  is a side view of a template of a preferred embodiment. 
           [0017]      FIG. 3A  is a top view of a frame of a preferred embodiment. 
           [0018]      FIG. 3B  is a side view of a frame of a preferred embodiment. 
           [0019]      FIG. 4  is a side view of a preferred embodiment. 
           [0020]      FIG. 5A  is a side view of a preferred embodiment. 
           [0021]      FIG. 5B  is an end view of a preferred embodiment. 
           [0022]      FIG. 5C  is a plan view of a preferred embodiment. 
           [0023]      FIG. 6A  is a side view of a preferred embodiment. 
           [0024]      FIG. 6B  is an end view of a preferred embodiment. 
           [0025]      FIG. 6C  is a plan view of a preferred embodiment. 
           [0026]      FIG. 7A  is an isometric view of a duct bank of a preferred embodiment. 
           [0027]      FIG. 7B  is a partial section view taken along line I-I of  FIG. 7A  of a duct bank of a preferred embodiment. 
           [0028]      FIG. 8A  is a computer architecture schematic of a controller system of a preferred embodiment. 
           [0029]      FIG. 8B  is a flowchart of a method executed by the controller system. 
       
    
    
     DETAILED DESCRIPTION 
       [0030]    Referring to  FIG. 1 , a method for manufacturing a duct bank is described. In a preferred embodiment, in step  1 , a movable frame is provided having a set of regularly spaced template supports. In step  2 , a set of templates is provided, each including a set of holes in a pattern. In step  3 , the set of templates are loaded into the template supports. In step  4 , the set of templates are positioned so that each of the sets of holes is aligned to form a set of coaxially aligned holes or “receivers” for the duct pipes. In step  5 , the frame and the set of adjusted templates is positioned adjacent a pipe extrusion machine, the pipe extrusion machine having an extrusion die, a cooling section, and a cutter. In an optional step  6 , a chosen receiver is positioned relative to an x-y plane to be coaxial with the extrusion die. In step  7 , a pipe of a first predetermined length is extruded into the receiver. Step  7  includes the optional step of cooling the pipe. In step  8 , the pipe is cut to a first predetermined length. In step  9 , steps  6 ,  7  and  8  are repeated until all receivers are full, thereby forming a duct bank. The duct bank is banded in step  10  and removed from the frame in step  11 . 
         [0031]    Referring to  FIGS. 2A ,  2 B, and  2 C, examples of preferred embodiments of the templates are shown. Templates  101 ,  102 , and  103  each have generally rectangular hole pattern  104 ,  105 , and  106 , arranged in x-y plane  99 . Each hole has a larger diameter than the diameter of the pipe to be received. In a preferred embodiment, the holes have a diameter about 15-20% larger than that of the pipe. The diameter of the pipe and the number of holes, including the number of rows and columns, vary according to the desired duct bank to be assembled. Other geometrical patterns, besides rectangular, may be employed. 
         [0032]    In a preferred embodiment, the templates are generally flat having a thickness of approximately ¾ inch. Other shapes and thicknesses may be employed. In a preferred embodiment, templates  101 ,  102 , and  103  are made of plastic, such as HDPE, Delrin, or Teflon. Other durable materials known in the art may be employed. 
         [0033]    Referring to  FIG. 3A , frame  200  includes rails  201  and  202 . Angled member  203  has first end  234  and second end  235 . Angled member  204  has first end  232  and second end  233 . First end  234  of angled member  203  attaches to rail  201 . First end  232  of angled member  204  attaches to rail  202 . Second end  233  of angled member  204  attaches to second end  235  of angled member  203 . Cross members  205 ,  206 ,  207 ,  208 , and  209  connect to rails  201  and  202 . Hitch  231  attaches to angled members  203  and  204  at second ends  233  and  235 . Wheels  227  and  228  attach to rail  202 . Wheels  229  and  230  attach to rail  201 . Post  225  attaches to rail  202  and angled member  204  adjacent first end  232  of angled member  204  and rail  202 . Post  226  attaches to rail  201  and angled member  203  adjacent first end  234  of angled member  203  and rail  201 . 
         [0034]    Referring to  FIG. 3B , supports  210  and  211  attach to cross member  205 . Supports  210  and  211  form slot  212 . Slot  212  receives, supports, and orients template  130  generally perpendicularly with respect to rails  201  and  202 . Supports  213  and  214  attach to cross member  206 . Supports  213  and  214  form slot  215 . Slot  215  receives, supports, and orients template  131  generally perpendicularly with respect to rails  201  and  202 . Supports  216  and  217  attach to cross member  207 . Supports  216  and  217  form slot  218 . Slot  218  receives, supports, and orients template  132  generally perpendicularly with respect to rails  201  and  202 . Supports  219  and  220  attach to cross member  208 . Supports  219  and  220  form slot  221 . Slot  221  receives, supports, and orients template  133  generally perpendicularly with respect to rails  201  and  202 . Supports  222  and  223  attach to cross member  209 . Supports  222  and  223  form slot  224 . Slot  224  receives, supports, and orients template  134  generally perpendicularly with respect to rails  201  and  202 . 
         [0035]    The distance between cross members  205 ,  206 ,  207 ,  208 , and  209 , and thereby the distance between loaded templates  130 ,  131 ,  132 ,  133 , and  134 , is dependent upon the strength, the length, and the diameter of the desired pipe to be used in the duct bank. In one preferred embodiment, the cross members are spaced evenly to support 40′ sections of pipe. In another embodiment, the cross members are spaced evenly to support 20′ sections of pipe. 
         [0036]    In a preferred embodiment, rails  201  and  202 , angled members  203  and  204 , cross members  205 ,  206 ,  207 ,  208 , and  209 , and supports  225  and  226  are made of steel. Other rigid and durable materials known in the art may be employed. 
         [0037]    In a preferred embodiment, supports  210 ,  211 ,  213 ,  214 ,  216 ,  217 ,  219 ,  220 ,  222 , and  223  are made of steel angle iron. Other rigid and durable materials known in the art may be employed. In other embodiments the cross members can have different cross sections, such as box channel and/or triangular supports. 
         [0038]    In a preferred embodiment, wheels  227 ,  228 ,  229 , and  230  are castor wheels. Other wheel types known in the art may be employed. 
         [0039]    Referring to  FIG. 4 , in one embodiment, proximal end  251  of frame  200  is positioned adjacent extrusion system  300 . Extrusion system  300  includes extruder  304 , extrusion die  301  attached to extruder  304 , cooling section  302 , aligned with extrusion die  301 , and cutter  303 , aligned with cooling section  302 . Each of templates  130 ,  131 ,  132 ,  133 , and  134  is identical, and includes a set of holes arranged in the same pattern. The sets of holes are aligned by adjusting the templates, one to another, until the holes match the sets of aligned holes for receivers for the pipes. 
         [0040]    Pipes  450  and  451  are shown positioned in the set of holes of templates  130 ,  131 ,  132 ,  133 , and  134 . Each pipe is cut to a predetermined length. The pipes can have different predetermined lengths. In one preferred embodiment, workers  801  and  811  manually transport pipe  452  from cutter  303  and insert it into one of the set of coaxially aligned holes of the templates. Workers  801  and  811  repeatedly transport and insert each pipe into the set of holes until each of the set of coaxially aligned holes contains a pipe. 
         [0041]    The duct bank is then banded for transport. Banding includes the steps of inserting blocks at chosen intervals between the pipes and between the templates. Steel straps, as known in the art, are then positioned around the duct bank and secured in other to prevent the templates and pipes from changing position during transport. The duct bank is then lifted from the frame and transported to the jobsite for installation. 
         [0042]    Referring to  FIGS. 5A-5C , in another embodiment, proximal end  251  of frame  200  is positioned adjacent extrusion system  300 . Extrusion system  300  includes extruder  304 , extrusion die  301  attached to extruder  304 , cooling section  302  collinearly aligned with extrusion die  301 , and cutter  303  collinearly aligned with cooling section  302 . The holes of templates  130 ,  131 ,  132 ,  133 , and  134 . The position of the frame in the x-y plane is adjusted so as to coaxially align with extrusion die  301 , cooling section  302 , and cutter  303  with a set of collinear holes in the templates. 
         [0043]    In this embodiment, frame  200  is horizontally and vertically positioned with respect to extrusion system  300  by position system  700 . Position system  700  includes indexing tracks  701  and  702 , winches  703 ,  704 ,  715  and  750  connected to the frame by cables. The winches are typically supported overhead by attachment to beams  752  and  754 . In a preferred embodiment, winches  703 ,  704 ,  715 , and  750  are electric winches capable of lifting about 2,000 pounds. In one preferred embodiment, each winch is locally controlled with a drop switch (not shown). In another preferred embodiment each winch is connected to a programmable controller. 
         [0044]    Winches  703 ,  704 ,  715  and  750  are attached to the frame by a series of cables or wire ropes. Winches  703 ,  704 ,  715  and  750  are movably attached to track  701  and  702  through a rolling suspension system including a set of carriages  797 ,  799 ,  795 , and  793  operatively attached to wheels  740 ,  741 ,  762 ,  764 ,  738 ,  739 ,  766  and  768 , respectively. 
         [0045]    Winch  703  is attached to indexing track  701 . Winch  703  is also attached to main cable  705 . Secondary cables  707  and  708  attach to main cable  705 . Hook  711  attaches to secondary cable  707 . Hook  711  connects to eye hook  253 . Eye hook  253  attaches to rail  202  of frame  200 . Hook  712  attaches to secondary cable  708 . Hook  712  connects to eye hook  254 . Eye hook  254  attaches to rail  202  of frame  200 . 
         [0046]    Winch  704  is attached to indexing track  702 . Winch  704  is also attached to main cable  706 . Secondary cables  709  and  710  attach to main cable  706 . Hook  713  attaches to secondary cable  709 . Hook  713  connects to eye hook  255 . Eye hook  255  attaches to rail  202  of frame  200 . Hook  714  attaches to secondary cable  710 . Hook  714  connects to eye hook  256 . Eye hook  256  attaches to rail  202  of frame  200 . 
         [0047]    Winch  715  is attached to indexing track  701 . Winch  715  is also attached to main  768 . Secondary cables  716  and  756  attach to main cable  759 . Hook  770  attaches to secondary cable  716 . Hook  770  connects to eye hook  774  attached to the frame. Hook  772  attaches to secondary cable  756 . Hook  772  connects to eye hook  776  connected to the frame. 
         [0048]    Winch  750  is attached to indexing track  702 . Winch  750  is also attached to main cable  778 . Secondary cables  758  and  760  attach to main cable  778 . Hook  780  attaches to secondary cable  758 . Hook  780  connects to eye hook  784 . Eye hook  784  is attached to the frame. Hook  782  attaches to secondary cable  760 . Hook  782  connects to eye hook  786 . Eye hook  786  is connected to the frame. 
         [0049]    Winches  703 ,  704 ,  715  and  750  enable movement of frame  200  along y-axis  743 , thereby enabling positioning system  700  to position each hole of geometrical  106  at a set of predetermined positions along y-axis  743 . 
         [0050]    Linear motivators  790  and  794  are positioned at the respective ends of indexing track  701 . Linear motivator  790  is connected to a threaded receiver incorporated into carriage  797  by threaded rod  798 . Linear motivator  794  is connected to a threaded receiver incorporated into carriage  799  by threaded rod  796 . A similar set of motivators  788  and  792 , threaded rods  789  and  791 , and carriages are included in indexing track  702  which is connected to winches  704  and  750 . Wheels  738 ,  739 ,  740 , and  741  roll within indexing track  701 , and wheels  762 ,  764 ,  766  and  768  roll within indexing track  702 , thereby enabling movement of frame  200  along x-axis  742  and enabling position system  700  to position each hole of geometrical pattern  106  at a set of predetermined positions along x-axis  742 . When activated, the linear motivators rotate the threaded rods to move the carriages and the winches along an x-axis. In a preferred embodiment, linear motivators  790  and  794  are electric motors with the appropriate transmissions to rotate the threaded rods at a desirable slow speed. In one preferred embodiment, the motivators are controlled locally by a drop switch. In another preferred embodiment, the motivators are connected to and controlled by a programmable controller which positions the frame. 
         [0051]    Referring to  FIGS. 6A-6C , in another embodiment, proximal end  251  of frame  200  is positioned collinearly adjacent extrusion system  300 . Extrusion system  300  includes extruder  304 , extrusion die  301  attached to extruder  304 , cooling section  302  collinearly aligned with extrusion die  301 , and cutter  303  collinearly aligned with cooling section  302 . The holes of templates  130 ,  131 ,  132 ,  133 , and  134  coaxially align with extrusion die  301 , cooling section  302 , and cutter  303 . 
         [0052]    In this embodiment, frame  200  is horizontally and vertically positioned with respect to extrusion machine  300  by position system  950 . Position system  950  includes indexing tracks  923  and  925  connected to a series of hydraulic lifting pistons. Indexing tracks  923  and  925  support frame  200 . Indexing track  923  slidably engages with inside track  922 . Inside track  922  attaches to piston rods  920  and  936 . Piston rod  920  attaches to piston  951 . Piston  951  slidably engages with cylinder  918 . Piston rod  936  attaches to piston  957 . Piston  957  slidingly engages cylinder  935 . 
         [0053]    Indexing track  925  slidably engages with inside track  924 . Inside track  924  attaches to piston rods  921  and  812 . Piston rod  921  attaches to piston  952 . Piston  952  slidably engages with cylinder  919 . Piston rod  812  attaches to piston  808 . Piston  808  slidingly engages with cylinder  809 . Position system  950  further includes piston rod  936  connected to inside track  922 . Piston rod  936  further connects to piston  957 . Piston  957  slidably engages with cylinder  935 . 
         [0054]    Each of the cylinders is connected to hydraulic fluid line  930 . Hydraulic fluid line  930  connects to pump  931 . In one embodiment, pump  931  is manually controlled by a foot switch. In another embodiment, pump  931  connects to controller  933  with communication line  932 . Controller  933  connects to monitor  934  and keyboard  735  for data management and entry by an operator. 
         [0055]    Linear motivator  802  is attached to outside track  923 . Linear motivator  802  includes pinion  806 . Pinion  806  engages rack  1000  attached to inside track  922 . Linear motivator  800  is attached to indexing track  925 . Linear motivator  800  includes pinion  804  which engages rack  1002  of inside track  924 . In a preferred embodiment, the linear motivators include electric motors which rotate the pinions which thereby move the racks along the x-axis. In one preferred embodiment, the motivators are controlled locally using a drop switch. In another preferred embodiment, the motivators are connected to and controlled by a programmable controller which positions the frame. 
         [0056]    The sliding engagement between inside track  922  and indexing track  923  enables movement of frame  200  along the x-axis and moves the frame to position the templates to predetermined positions along the x-axis. 
         [0057]    Pressure from the hydraulic fluid against the pistons enables movement of frame  200  along y-axis  954  and moves the frame to position the templates to predetermined positions along the y-axis. 
         [0058]    Referring to  FIG. 8A , control system  1150  is described. Controller  1152 , in a preferred embodiment, includes a programmable microcontroller or a computer work station programmed with suitable programming to carry out method steps necessary to move the x motivators and the y motivators to predetermined positions in order to move the frame to a predetermined location in the x-y plane. Controller  1152  is connected to x position motivators  1154 , y position motivators  1156  and stop sensor  1158 . 
         [0059]    In a preferred embodiment, stop sensor  1158  is a simple mechanical limit switch, fixed in a position of axial alignment with the extruder and in a position to sense contact with the end of the pipe as it is completely inserted in the axially aligned holes or receivers. In another embodiment, the limit switch can be an optical sensor and transmitter pair connected to the controller. 
         [0060]    Referring to  FIG. 8B , the method  850  is described that is executed by the program resident on controller  1152 . 
         [0061]    At step  852 , the program starts. At step  854 , input is received from the operator regarding a maximum number columns in the template (“MAXX”) and the maximum number of rows in the template (“MAXY”). At step  855 , input is received which identifies each unique location in the x-y plane of an axis corresponding to the center of a particular receiver. The locators are numbered in a sequence of rows and columns each having an x-y address. 
         [0062]    At step  856 , the program then initiates and sets a variable x to 1, and initiates and sets a variable y to 1. 
         [0063]    At step  857 , the controller sends signals to the x position motivators  1154  and y position motivators  1156  sufficient to locate the frame and associated templates to the x=1, y=1 position corresponding to the first axis physical location. 
         [0064]    At step  858 , the controller waits for a signal from stop sensor  1158  indicating that a pipe has been inserted. At step  860 , the controller compares the x location to the variable MAXX. If the variables are not equal, the program moves to step  862  and increments the x value by  1  and then proceeds to step  863 . At step  863  the controller sends signals to the x and y motivators sufficient to physically move the frame to its x position. The new position coaxially locates the next receiver in order with the extruder and extrusion die. The program then returns to step  858 . If the variables are equal, then the program proceeds to step  864  and resets the value of x to 1. At step  865 , the controller send signals to the x motivators sufficient to return them to their original x position thereby aligning the original receiver with the extruder. 
         [0065]    At step  866 , the value of y is incremented by 1. At step  868 , the program compares the value of y to MAXY. If the position of y is not greater than MAXY, then the program returns to step  869  where the controller send signals to the y position motivators sufficient to advance the frame to the next y position. The next y position corresponds to the row of empty receivers above the first row. The program then returns to step  858 . If the value of y is greater than MAXY, then the program proceeds to step  870  and ends. 
         [0066]    In a preferred embodiment the receivers are filled in order from left to right and bottom to top in order to increase duct bank stability. However, other orders of x-y positions can be used with success. 
         [0067]    The program in a preferred embodiment is written in a basic interpretive language such as Basic or FORTRAN. However, other languages may be employed. In a preferred embodiment, the program is stored in physical memory at the controller. However, in other embodiments the program may be stored on a computer network connected to the controller on a removable permanent memory accessed by the controller. 
         [0068]    Referring to  FIG. 7A , by way of example, after assembly, duct bank  400  comprises pipes  401 ,  402 ,  403 ,  404 ,  405 ,  406 ,  407 ,  408 , and  409  inserted through templates  130 ,  131 ,  132 ,  133 , and  134 . 
         [0069]    In a preferred embodiment, pipes  401 ,  402 ,  403 ,  404 ,  405 ,  406 ,  407 ,  408 , and  409  are made of polyvinyl chloride (PVC). Other materials known in the art may be employed. 
         [0070]    Band  475  surrounds pipes  402 ,  405 , and  408 . Blocks  417  and  418  position within duct bank  400  and held in position with band  475 . Block  417  is held adjacent pipes  402 ,  405 , and  408  by band  475 . Block  418  is held adjacent pipes  402 ,  405 , and  408 , opposite block  417  by band  475 . Band  410  surrounds pipes  401 ,  402 ,  403 ,  404 ,  406 ,  407 ,  408 , and  409 . Blocks  415  and  416  position on the outer sides of duet bank  400  and maintained in position by band  410 . Block  415  is held adjacent pipes  403 ,  406 , and  409  by band  410 . Block  416  is held adjacent pipes  401 ,  404 , and  407  by band  410 . 
         [0071]    Referring to  FIGS. 7A and 7B , by way of example, band  412  surrounds pipes  402 ,  405 , and  408 . Blocks  419  and  420  position within duct bank  400  and held in position with band  412 . Block  419  is held adjacent pipes  402 ,  405 , and  408  by band  412 . Block  420  is held adjacent pipes  402 ,  405 , and  408 , opposite block  419  by band  412 . Band  411  surrounds pipes  401 ,  402 ,  403 ,  404 ,  406 ,  407 ,  408 , and  409 . Blocks  413  and  414  position on the outer sides of duct bank  400  and maintained in position by band  411 . Block  413  is held adjacent pipes  403 ,  406 , and  409 . Block  414  is held adjacent pipes  401 ,  404 , and  407  by band  411 . 
         [0072]    The position of bands  410 ,  411 ,  412  and  475  and the distance between each band is dependent upon the length, the strength, and the diameter of pipe to be used in duct bank  400 , and the height and the width of duct bank  400 . Further, the number of bands and blocks employed varies and is dependent upon the length, the strength, and the diameter of pipe to be used in duct bank  400 , and the height and the width of duct bank  400 . 
         [0073]    In a preferred embodiment, bands  410 ,  411 ,  412  and  475  are made of polyester. Other materials known in the art may be employed. 
         [0074]    In a preferred embodiment, blocks  413 ,  414 ,  415 ,  416 ,  417 ,  418 ,  419 , and  420  are made of wood. Other durable materials known in the art may be employed. 
         [0075]    It will be appreciated by those skilled in the art that modifications can be made to the embodiments disclosed and remain within the inventive concept. Therefore, this invention is not limited to the specific embodiments disclosed, but is intended to cover changes within the scope and spirit of the claims.