Abstract:
A tube forming machine for making a tube from a sheet is disclosed. The forming rolls of this invention include various V-shaped rolls at least some of which are used as part of a three-point bending technique. The three-point bending technique entails the use of a V-shaped bottom roll and a narrow top roll. The sheet is shaped running the sheet through a gap between the narrow top roll and the V-shaped bottom roll. The technique allows a wide variety of tubing to be made from the same set of forming rolls, because the curvature obtained in a sheet can be varied by opening or closing the gap. A V-shaped forming roll disclosed herein is also used at a pinch roll stand with a second complementary V-shaped roll. The pinch roll stand of this invention creates an initial V-shaped sheet which facilitates the threading of the sheet at the start of a forming operation. Brimmed rolls are also disclosed. Brimmed rolls have a relatively sharp included angle, and are used to engage the edges of a sheet and to press the sheet against a single bottom roll in brimmed roll stand.

Description:
BACKGROUND AND SUMMARY OF THE INVENTION 
     The present invention relates to an apparatus for manufacturing tubing from sheet stock using a series of rolls. In particular, the invention relates to an improved tube forming machine and method which utilizes new roll shapes and bending techniques which provide a number of advantages over prior art machines and methods. 
     Steel tubes have for many years been produced by forming an initially flat sheet or strip into a round shape using cage rolls, cluster rolls and fin-pass rolls, and eventually welding the edges of the sheet together to form a seam. Conventional equipment utilizing such rolls for the formation of steel tubing from strips can be seen in U.S. Pat. Nos. 5,673,579 and 5,784,911. 
     Because a large component in the cost of producing steel tubing from sheet material is the cost of the sheet material itself, producers of steel tubing are often forced by competition to use the least expensive sheet steel available. However, inexpensive sheet stock often has more variability in the hardness, thickness and other important properties of the sheet as compared to more expensive sheet stock. When inexpensive steel sheet is used with traditional tube forming machines and techniques, a number of problems arise. Those problems include twisting of the sheet as it passes through the various rolling stands, difficulty in controlling the position of the sheet, and difficulty in feeding the sheet at the start of a continuous tube forming operation. Conventional tube forming machines require rolls to be changed frequently in order to form tubing having different sizes and wall thicknesses. It is therefore desirable to provide a tube forming machine which has improved ability to handle inexpensive sheet steel and which has increased capacity to make tubing from different forming rolls. 
     Important objectives in the design of tube forming equipment include ease of initial threading of the strip into and through the machine, consistent positioning of the sheet both at the forming stands and at the point in the process where the edges of the sheet are welded to form a seam, efficient handling of the strip without damaging either the edges or the surfaces of the sheet, and ability for the machine to handle a wide range of tubing sizes and wall thicknesses without changing the forming rolls. 
     The present invention utilizes three point bending techniques at various stages in the tube forming operation. One of the three point bending techniques of the present invention involves the use of a V-shaped roll and an opposing narrow roll, with the extent of curvature obtained depending on the relative position, i.e., the proximity, of the two roll. If the narrow roll is brought closer to the V-shaped roll with which it cooperates, a smaller diameter is obtained. Conversely, if the gap between the narrow roll and the V-shaped roll is increased, a larger diameter results. The present invention also utilizes a V-shaped bottom and top roll at an initial or pinch roll stand. The flat surfaces of opposing V-shaped rolls at the first stand in the machine results in improved gripping of the sheet for purposes of driving the sheet through subsequent stands. The resulting V-shaped profile of the sheet after it leaves the initial pinch roll stand is a strong shape for purposes of driving the sheet as it is threaded through the remaining non-driven stands. The initial forming stand is equipped with a duplex regulating system in which hydraulic pressure is used to pinch the sheet between the two V-shaped rolls. Each side of the top roll of the initial station may be independently controlled for purposes of adjusting pressures applied to each side of a sheet being processed to compensate for variability of thickness of the sheet material. 
     The tube forming machine described below also includes the use of a brimmed roll in which a circumferential slot is formed between two angled surfaces. A pair of brimmed rolls are used to engage the edges of a sheet, and the two brimmed rolls cooperate with a concave bottom roll to form the sheet into a smoothly rounded cross-section. 
     More detailed descriptions of the inventions disclosed herein are set forth below and will be better understood upon a reading of the following specification read in conjunction with the accompanying drawings wherein: 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an overall side elevational view of a machine arranged in accordance with the present invention; 
     FIG. 2 is a top plan view of the machine shown in FIG. 1; 
     FIG. 3 is a diagram showing the various stages of the tube forming process for large diameter tubing (right side) and small diameter tubing (left side) which can be produced with the machine of the present invention; 
     FIG. 4 is an elevational view in partial section of driving stands of the machine of the present invention, the right cross-sectional portion corresponding to the first driving stand and the left cross-sectional portion corresponding to the second driving sheet; 
     FIG. 5 is a top plan view of the stands shown in FIG. 4 with the rolls not shown; 
     FIG. 6 is a side elevational view of the station shown in FIGS. 4 and 5; 
     FIG. 7 is a schematic diagram of the hydraulic circuit used to apply clamping pressure at an initial driving stand of the machine of the present invention; 
     FIG. 8 is a partial side elevational view of a driving stand of the present invention showing the vertical adjustability of the rolls; 
     FIG. 9 is an elevational view in partial section of the adjustment mechanism for a bottom roll; 
     FIG. 10 is an elevational view in partial section of a forming roll stand of the present invention; 
     FIG. 11 is a top plan view of the stand shown in FIG. 10; 
     FIG. 12 is a side elevational view of the stand shown in FIGS. 10 and 11; 
     FIG. 13 is an enlarged elevational view in partial section of the mechanism used to vertically adjust the rolls shown in FIG. 10; 
     FIG. 14 is an enlarged elevational view in partial section of a three point bending stand of the present invention; 
     FIG. 15 is an enlarged elevational view in partial section of a second three point bending stand of the present invention; 
     FIG. 16 is an enlarged elevational view in partial section of a third three point bending stand of the present invention; 
     FIG. 17 is an enlarged elevational view in partial section of a fourth three-point bending stand of the present invention; 
     FIG. 18 is an enlarged elevational view in partial section of a top and bottom roll at a three point bending stand of the present invention; 
     FIGS. 19 and 20 are elevational views of a top and bottom roll showing alternative ways in which the rolls may be adjusted to obtain different curvature in a workpiece; 
     FIG. 21 is an elevational view in partial section of a forming stand of the present invention in which brimmed rolls are utilized; 
     FIG. 22 is a side elevational view of one side of the stand shown in FIG. 21; 
     FIG. 23 is a top plan view of the stand shown in FIG. 21; 
     FIG. 24 is a elevational view in partial section of a brimmed roll and its mounting; 
     FIG. 25 is a top plan view of the roll and mounting shown in FIG. 24; 
     FIG. 26 is a side elevational view of the roll and mounting shown in FIG. 24; 
     FIG. 27 is an elevational view showing two brimmed rolls and a bottom roll at a forming stand of the present invention; 
     FIG. 28 is a top plan view in partial section of a brimmed roll and its mounting mechanism made in accordance with the present invention; 
     FIG. 29 is an end elevational view of a cage roll stand for use in a machine of the present invention; 
     FIG. 30 is a side elevational view of the cage roll stand shown in FIG. 29; 
     FIG. 31 is a diagram of the rolls in a cage roll stand; and 
     FIGS. 32 and 33 are examples in plan view of conventional tube forming machines. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 is a side elevational view showing the various forming stations used in accordance with the present invention. The tube forming machine of the present invention includes pinch roll stands  11  at the first and fourth stations shown in FIG.  1 . The second, third, fifth and sixth stations are three point bending stands  21 . The seventh through twelfth stations are alternating brim roll stands  31  and cage roll stands  41 . After the alternating brimmed and cage roll stands, a series of three fin-pass stations  51  operate on the sheet which is to be formed into tubing. The final rolling station is a squeeze roll station  61 , after which the sheet is welded along a longitudinal seam. As can be seen in the top plan view of FIG. 2, the pinch roll stands and the fin-pass stands  51  are used to drive and pull, respectively, the sheet through the tube forming machine. 
     FIG. 3 shows the profile of the sheet as it progresses from the initial pinch roll stand through the fin-pass stands. The profile designated  211   a  corresponds to the initial pinch roll stand at the left end of FIGS. 1 and 2. The profiles marked  221   a  through  221   d  correspond to the profile at the four three point bending stands  21 . The profiles designated  231   a  through  241   c  correspond to the shape of the sheet at the series of six alternating brimmed rolls and cage roll stands shown in the center portion of FIGS. 1 and 2. Finally, the profile designated  251   a  corresponds to the shape of the sheet at the fin-pass stands  51 . 
     The angle “α” (alpha) shown in the lower portion of FIG. 3 is the angle with respect to the horizontal of each side of the initial V-shape of the sheet as it is formed by the top and bottom roll of the pinch roll stands shown in FIGS. 1 and 2. The V-shaped transverse cross-section of a sheet formed by the combination of the first and second pinch roll stands  11  will have good resistance to buckling as it is passed through non-driven roll stands. This resistance to buckling is particularly important with respect to initial threading of a strip at the time when the machine is first started into operation. 
     FIGS. 4,  5  and  6  are elevational views of a pinch roll stand  11  with its top and bottom rolls driven by drive equipment  12 . The drive equipment  12  includes a gear box  12   b  driven by an electric motor  12   a.  The upper drive spindle  14   a  and lower drive spindle  14   b  are connected to the gear box  12   b  and are also connected to the top roll shaft  16   a  and bottom roll shaft  17   a,  respectively. It should be noted that the right hand portion of the top roll corresponds to the first pinch roll stand in FIGS. 1 and 2, while the left portion of the top roll shown in FIG. 4 corresponds to the second pinch roll stand in FIGS. 1 and 2, which is the fourth in the series of stations shown therein. Because the top and bottom rolls shown in FIG. 4 provide the driving force for the sheet as it is threaded through the tube forming machine of the present invention, it is important that good gripping contact exists between the sheet and the top and bottom rolls. To achieve this, hydraulic cylinder/piston assemblies  15  apply downward force to the shaft  16   a  which supports the top rolls  16 . A keyway  16   b  formed in the shaft  16   a  receives a corresponding projection which allows the transfer of driving force to the shaft  16   a  and to the top roll  16 . 
     A roll stand frame  13   b  supports the roll shafts  16   a  and  17   a.  An electric motor  13   e  operates the height adjustment  13   d  for the lower roll  17 . As in the case of the upper roll  16 , the lower roll  17  has a key which fits into a keyway  17   b  to allow driving forces to be transferred from the lower drive spindle  14   b  to the lower roll  17 . The ends of the shafts  16   a  and  17   a  are each supported in a bearing box such as  13   f.  The bearing boxes  13   f  are supported by a frame  13   b.    
     FIG. 7 is a diagram of the hydraulic circuit used to operate the assemblies  15  which apply clamping pressure to the sheet as it passes through the pinch roll stands  11 . A hydraulic pump  110  supplies hydraulic fluid from oil reservoirs  120 . A solenoid operated directional valve  111  is used to control the flow of hydraulic fluid from the pump to the driving side of the piston within the assemblies  15 . The pilot operated check valve  112  prevents backflow of hydraulic fluid in the direction of the solenoid operated directional valve  111 . A speed control valve  113  is used as a main control of large flows of hydraulic fluid to the pressing cylinder/piston assemblies  15 , whereby hydraulic fluid is used to apply and release clamping pressure to the top roll of a pinch roll stand  11 . More precise (i.e., fine) control of clamping pressure is achieved by an operator who may send a signal to the electrical signal converter  115  to apply more or less clamping pressure to one or both cylinders  15 . The circuit uses the pressure regulators  114  and  116  to increase or decrease the pressure applied by the pistons within the cylinder/piston assemblies  115 . Indeed, the operator in some instances may want to apply more pressure upon one side of a roll than upon another the opposite side of the same roll to compensate for uneveness in the thickness, hardness, friction or other property of a strip being processed. 
     Pressure relief valves  119  are in the circuit to protect against machine breakage in the event that the rolls encounter an obstacle. The main hydraulic pressure sensors  117  provide a reading of the pressure within the pressing assemblies  15  at the main control panel of the machine. Auxiliary pressure gauges  118  allow visual inspection of the pressure being applied to the clamping rolls at the pinch roll stands  11 . 
     As can be seen in FIG. 8, the pressing assemblies  15  are used to raise and lower the top roll of the pinch roll stands  11 . The driving equipment  12  is linked by the drive shafts  14   a  and  14   b  through universal joints at each end to the shafts upon which are carried the top and bottom rolls of the pinch roll stands  11 . 
     FIG. 9 shows the basic elements of the mechanism used to raise and lower the bottom roll of a pinch roll stand  11 . The bottom roll shaft  17   a,  upon which is mounted the bottom roll  17 , extends into a bearing box  124 . The bearing box  124  is mounted to a lifting screw  123  which is raised and lowered by rotation of the worm wheel  121 . Rotation of the worm wheel  121  is achieved by rotation of the worm  120 . 
     FIGS. 10,  11 ,  12  and  13  are end elevational, top plan and side elevational views, respectively, of a three point bending roll stand  21 . A three point bending roll stand  21  of the present invention includes a pair of opposing rolls, a top roll  91  and a bottom roll  94 . Each pair is mounted to a main vertical frame  21   b  which carries a forming roll mechanism  21   a,  described in more detail below. The forming roll mechanism  21   a  is carried by a vertical slide frame  77  which slides along a vertical slide rail  78 . Rotation of the screw rod  75   a  causes the raising and lowering of the slide frame  77  and the forming roll mechanism  21   a.  The screw rod  75   a  is rotated by operation of the forming roll height adjust drive motor  72  through drive worm shaft  72   a  and worm wheel  75 . 
     Horizontal adjustment of the main vertical frames  21   b  is achieved by operation of the forming roll with adjust drive motor  71 . Operation of the motor  71  causes rotation of the driving worm shaft  71   a  which causes horizontal movement of the main vertical frames  21   b,  toward and away from each other depending on the direction of the rotation of the shaft  71   a.    
     FIGS. 14 through 18 are more detailed depictions of the forming roll mechanisms of a three point bending stand  21 . Each forming roll mechanism includes a roll gap adjusting motor  82  which drives a pinion  82   a.  The pinion  82   a  engages a gear fixed to the end of a screw rod  83 . The screw rod  83  is axially fixed but rotatable within an internally threaded member  84  such that rotation of the screw rod  83  results in movement of the threaded member  84  along the screw rod  83 . The top roll holder  85  is connected to the threaded member  84  and slides along a top roll slide roll  86  when the screw rod  83  is rotated within the threaded member  84 . Motion of the top roll holder  85  along the slide rail  86  causes movement of the top roll  91  towards or away from the bottom roll  94 . As can be seen in FIGS. 14 through 18, the main adjustment of the position of the top roll  91  is at an angle of about 45° relative to horizontal. A fine adjustment mechanism  89  may be used to further adjust the position of the top roll  91  with respect to its associated bottom roll  94 . The bottom roll  94  is mounted to a bottom roll support shaft  93  which is in turn carried by a bottom roll holder  95 . The bottom roll holder  95  is attached to and carried by a vertical base plate  81 . Depending upon the gap between the top roll  91  and the bottom roll  94 , the curvature of the sheet passing through the rolls  91  and  94  can be increased or decreased by the use of the three point bending technique which will be described in more detail below. 
     Each of the bottom rolls  94  shown in FIGS. 14 through 18 has a V-shaped configuration which supplies two of the three points in a three point bending technique. The top roll  91  is a generally narrow roll which provides the third and middle point of a three point bending operation. As can be seen in FIGS. 19 and 20, bringing the top roll  91  close to the bottom roll  94  results in a relatively sharp, or small radius, curvature in the sheet between the rolls for use in making smaller diameter tubing. In contrast, the provision of a larger gap between the top roll  91  and the bottom roll  94  results in a less curved sheet as shown in FIG. 19, which results in larger diameter tubing. The same top and bottom rolls are used in each case, thus reducing costs associated with the manufacture (or acquisition) or rolls and the labor and down-time associated with changing rolls. 
     The shape and orientation of the top rolls  91  and bottom rolls  94  in a three-point bending stand  21  are important. The bottom rolls  94  have an overall V-shaped configuration, with each bottom roll  94  having two frustoconical (i.e. partially conical) sections which meet at a circumferential crease. The crease defines a plate in which the bottom rolls  94  are disposed. The planes defined by the two bottom rolls of a three-point bending stand are generally parallel to the longitudinal axis (or Z-axis ) of the machine, i.e. they are generally parallel to the direction of the flow of workpiece material through the machine. The three points (or workpiece engagement locations) referred to as part of a three-point bending technique are the two points of contact on the V-shaped bottom rolls  94 , and the single point of contact provided by the narrow top roll  91 . The degree of curvature obtained by this combination of rolls can be varied greatly simply by adjusting the gap between the rolls. Depending upon the thickness of the sheet material and the distance between the top and bottom rolls, a small or large diameter bend will be imparted to the sheet. One distinct advantage of using a three-point bending technique of the present invention is the reduced amount of friction as compared with tube forming methods in which there is broad lengths of contact between a forming roll and a workpiece. The broad lengths of contact not only create added friction which is not the case with the present invention, but more contact can, in some instances, result in a greater chance for marring of the surface of tube, which can result in tubing products which are not acceptable to customers. It should be noted that planes as they are referred to herein, and in the tube forming field generally, are defined with reference to axes, i.e. the X-axis being the transverse horizontal axis (with respect to work flow), the Y-axis being a vertical transverse axis, and the Z-axis being the longitudinal axis or the direction of work flow. A plane is sometimes identified by reference to the axes which lie in or are parallel to the plane. 
     FIGS. 21,  22  and  23  are end elevational, side elevational and top plan views, respectively, of a brimmed roll stand  31  of the present invention. The brimmed roll  133   a  are carried by brimmed roll holders  133 , each of which includes an adjusting mechanism. The brimmed roll holders  133  are mounted to main vertical frames  132 . The lateral positions of which are controlled in a manner similar to the lateral position adjustment mechanism of previously described three-point roll stands  21  shown in FIG. 10, i.e., the lateral position is adjusted by operation of the width adjust drive motor  137 , and the vertical position of the brimmed roll holders  133  is adjusted by operation of the height adjust drive motor  136 . 
     The brimmed roll stand  31  includes a pair of brimmed rolls  133   a,  each of which engages an edge of a sheet. The shape of a brimmed roll, as shown in FIGS. 24 and 25, includes a cicumferential slot with frustoconica sections forming an angle of somewhat less than about 90 degrees. A third or bottom roll  139  in a brimmed roll stand  31  engages the underside of the sheet to support and provide upward bending force to the sheet which is resisted by the two brimmed rolls  133   a.  The vertical position of the bottom roll  139  is adjusted by operation of the bottom roll height adjust drive motor  136 . The motor  135  drives the drive shaft  135   b  which is connected to a worm and worm wheel gearbox  135   a.    
     Adjustment of the brimmed roll body  144 , as shown in FIGS. 24,  25 ,  26  and  28 , is in the X-Y plane. Vertical adjustment in the X-Y plane of the position of the brimmed roll body  144  is achieved by use of adjustment mechanism  142 . Rotation of the shaft  142   a  results in rotattion of the worm  142   c  carried thereby. The worm  142   c  engages the teeth  145   a  in the top roll holder  145 , and rotational movement of the worm  142   c  results in rotation upward and downward of the brimmed roll holder  145  and brimmed roll body  144 . Dotted lines in FIG. 28 show various positions of the brimmed roll assembly by  133   a  which achievable by rotation of the worm  142   c.  It should be noted that the worm and associated teeth are shown schematically without reference numerals in FIGS. 21 and 24. 
     FIG. 29 shows a cage roll stand  41  of the kind used in combination with other roll stands, as shown in FIGS. 1 and 2, to achieve a tube in accordance with the present invention. Opposing forming roll assemblies  153  include cage rolls  161  acting upon a sheet in combination with a single bottom roll  159 . Each cage roll  161  is held by a cage roll holder  163 , and each cage roll  161  pivots on a cage roll shaft  162 . The cage roll holders are mounted to main vertical frames  152 , which include vertical slide rails  153   b.  The cage roll holders  163  are raised and lowered by rotation of the screw rod  153   c  within a threaded bore in the cage roll holders  163 . The lateral position of the cage rolls  161  is adjusted by operation of the cage roll width adjusting motor  157  which moves the vertical frames  152  on slide rails  152   b.  The cage roll height adjusting motor  156  is used to raise and lower the cage roll holders  163  (and the cage rolls  161 ). The drive motor  155  drives the shaft  155   b,  which connects to the gear box  155   a,  to raise and lower the bottom roll  159 . 
     FIG. 31 shows the rolls  161  and  159  which are typical of the cage roll stands  41  used as part of the present invention. 
     While specific embodiments of the inventions disclosed herein have been shown and described in detail, those embodiments are only examples, and it will be apparent to those skilled in the art that numerous other alternatives, modifications, and variations of the inventions may be made without departing from the spirit and scope of the appended claims.