Patent Publication Number: US-6655182-B2

Title: Apparatus and method for reshaping tubes

Description:
TECHNICAL FIELD 
     The present invention relates to an apparatus and a method for reshaping tubes, in particular helically-wound lock-seam tubes for ventilation ductwork. 
     BACKGROUND ART 
     WO-A-99/51371 discloses an apparatus, referred to as ovalizer, for forming round ductwork to oval, that is an apparatus for altering the cross-section of a tube from round to oval. In particular, the tube is a spiral duct, also referred to as helically-wound tubing by the skilled person. 
     To achieve this reshaping of the tube, the apparatus has an elongate, horizontal duct forming assembly with two duct forming members vertically spaced from each other. The two duct forming members are connected to each other by power means configured to move the duct forming members to and from each other vertically. 
     A round tube to be reshaped is placed on the duct forming assembly and the power means (several hydraulic cylinders) is activated. As the distance between the duct forming members is increased, they press against the inner surface of the tube in two opposite locations and the tube is reshaped to an oval cross-section. Each duct forming member has a semi-circular head which presses against the inner surface of the tube. 
     This known technique has, however, some drawbacks which will be discussed below. 
     First, due to the pressing action against the inside of the tube, the tube wall is deformed and the material is stretched. This stretching may lead to ruptures and other defects in the tube wall. 
     Second, when the tube is a helically-wound lock-seam tube (normal case), the pressing action may lead to slippage or sliding in the lock seam, which in turn may produce tubes with different dimensions at each end. This makes it difficult to connect the tubes in a ventilation duct system. 
     Third, the semi-circular heads of the duct forming members have to be replaced for each diameter of the tube. The replacement operation is time-consuming, and several duct forming heads have to be kept in stock. This adds costs. 
     Fourth, the known apparatus has low flexibility since it can only be used for reshaping from round to oval. 
     Fifth, the deformed or reshaped tube (oval) tends to return to its original shape (round) due to stresses in the tube wall induced by the deformation. 
     Thus, there is a demand for an improved technique for reshaping of tubes. 
     As to background art, the so-called bending machines should be mentioned as well. A bending machine has a roller assembly to which a plate or sheet of metal is fed and formed to the desired shape, for instance to round cross-section. In a final step, the tube is closed by a longitudinal weld along the tube wall. However, these bending machines cannot be used for reshaping of a tube from, for instance, round to oval since the starting material always is a flat plate or sheet. 
     SUMMERY OF THE INVENTION 
     An object of the present invention is to provide a new and improved technique for reshaping of tubes, in particular helically-wound lock-seam tubes for ventilation ductwork, thereby avoiding or at least making the disadvantages discussed above less severe. 
     This object is now achieved by an apparatus for reshaping a tube, the tube having a wall with a periphery, an inner surface, an outer surface, a longitudinal axis and a cross-section having at least one radius of curvature, comprising: 
     means configured to rotate the tube about the longitudinal axis in the apparatus; 
     a first shaping roller parallel with the longitudinal axis of the tube and configured to engage the outer surface of the tube; 
     a second shaping roller parallel with the longitudinal axis of the tube and configured to engage the inner surface of the tube; and 
     means configured to move the first and second shaping rollers in relation to each other and in relation to the rotation means, in order to apply bending forces to the tube wall for altering said at least one radius of curvature and thereby reshaping the cross-section of the tube. 
     By this apparatus, the problems of the prior art technique are solved. Thanks to the ingenious arrangement of the shaping rollers and the means for moving these, it is very easy to reshape the tube. The material of the tube is not stretched since the circumference of the tube is not changed by the reshaping operation. Hence, no defects occur in the tube wall. 
     Furthermore, the apparatus can be used for reshaping a great number of tubes, from round to oval, from oval to round, etc. In principle, any cross-sectional shape of the tube is possible to achieve, as long as it has rounded corners, for instance triangular, rectangular, etc. Thus, the operation of the inventive apparatus is very flexible. 
     Another very important advantage is that the same apparatus can be used for all dimensions. No tube forming members have to be replaced when tubes of various dimensions are to be reshaped. The same roller arrangement can be used for all dimensions. Indeed, this is advantageous in comparison with the apparatus known from WO-A-99/51371 discussed by way of introduction. 
     In a preferred embodiment, the shaping rollers are configured to apply the bending forces in points of action which are spaced with respect to the periphery of the wall. As a result, a very smooth reshaping operation can be achieved. Preferably, the shaping rollers are configured to apply the bending forces along generatrices of the tube, which further enhances the reshaping operation. 
     It is preferred that the rotation means comprises a roller nip which has two opposite rollers configured to engage the tube wall in a nip and drivingly rotate the tube along its longitudinal axis. Such a roller nip provides for a secure and smooth rotational operation. Most preferably, the shaping rollers and the nip rollers are parallel in order to provide for simple control of the reshaping operation. Furthermore, the structure of the apparatus is very compact by this arrangement. 
     In a preferred embodiment, the apparatus comprises a frame with two opposite, spaced frame members between which the tube is disposed in operation. Each frame member has guiding means to which end portions of the shaping rollers are connected and which are configured to provide said movement of the shaping rollers. These guiding means in the frame members provide for a very distinct control of the reshaping movement of the shaping rollers. No disadvantageous inertia is involved. 
     Preferably, the guiding means are grooves provided in the respective frame members. Furthermore, it is preferred that actuator means, such as hydraulic cylinders, are mounted between the end portions of the shaping rollers and the frame members. Consequently, a distinct movement of the shaping rollers is achieved. 
     In one aspect of the invention, there is provided a roller unit for reshaping a tube having a cross-section and a longitudinal axis, comprising: 
     a first roller assembly configured to rotate the tube about the longitudinal axis, 
     a second roller assembly configured to apply bending forces to the tube directed towards or away from the tube, thereby altering the cross-section of the tube. 
     The object is also achieved by a method of reshaping a tube, the tube having an inner surface, an outer surface, a longitudinal axis and a cross-section having at least one radius of curvature, comprising the steps of: 
     rotating the tube about the longitudinal axis; and 
     applying bending forces on the inner and outer surfaces of the tube; 
     hereby altering said at least one radius of curvature for reshaping the cross-section of the tube. 
     The advantages of the method of the invention, and its preferred variants, are basically the same as discussed above in relation to the apparatus. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention and its advantages will be further described in the following, reference being had to the accompanying schematic drawings which illustrate presently preferred embodiments by way of example. 
     FIG. 1 is a perspective view of an apparatus according to a first embodiment of the invention. 
     FIGS. 2-4 are side views of a reshaping mechanism of the apparatus shown in FIG.  1 . 
     FIG. 5 shows various positions of rollers included in the reshaping mechanism. 
     FIGS. 6-8 are side views of an alternative reshaping mechanism with an additional roller. 
     FIG. 9 is a perspective view of an apparatus according to a second embodiment of the invention. 
     FIG. 10 is a side view of a reshaping mechanism of the apparatus shown in FIG.  9 . 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     With reference to FIGS. 1-5, an apparatus according to a first embodiment of the invention comprises a frame  1  with two opposite, spaced frame members  2  and  3 . A tube  4  having a wall  5 , a periphery  6 , an inner surface  7 , an outer surface  8  and a longitudinal axis C is disposed between the frame members  2  and  3 . A roller arrangement comprises two rotatable nip rollers  10 ,  11  and two rotatable shaping rollers  12 ,  13 . The nip rollers  10 ,  11  provide means for drivingly rotating the tube  4  about its longitudinal axis C, and the shaping rollers  12 ,  13  provide for reshaping of the tube  4 . This will be further described below. 
     The tube  4  shown in this example is a helically-wound lock-seam tube of sheet metal, suitable for ventilation ductwork. 
     All rollers  10 - 13  are parallel with each other and with the longitudinal axis C of the tube  4 . 
     The nip rollers  10 ,  11  are rotated by a motor M mounted in the frame  1  (schematically shown in FIG.  1 ). 
     At each frame member  2 ,  3 , there is a mounting assembly connecting the ends of the rollers  10 - 13  to the respective frame members. Only one mounting assembly is shown in FIG.  1 . This assembly comprises two arms  14 ,  15  which are pivotally mounted on the frame member  3  (at  14   a ,  15   a , respectively, see FIGS.  2 - 4 ). The arm  14  is connected to an end shaft portion  12   a  of the shaping roller  12  inside the tube  4 , and the arm  15  is connected to an end shaft portion  13   a  of the shaping roller  13  outside the tube  4 . The pivotal movements of the arms  14 ,  15  (see double arrows) are operated by actuator means, here shown as hydraulic cylinders  16 ,  17  mounted on the frame member  3 . 
     The upper nip roller  10  inside the tube  4  is rotatably connected to the frame members  2 ,  3  at its two end shaft portions  10   a . However, this nip roller  10  is “stationary” in the sense that it cannot be moved from its position in the frame  1 . The lower nip roller  11 , however, is vertically moveable with the aid of actuator means, here a hydraulic cylinder  18 , mounted on the frame member  3 . 
     The principles of the operation of the tube reshaping apparatus are illustrated in FIGS. 2-5. A tube  4  of circular cross-section is arranged in the apparatus and rotated clockwise by the nip rollers  10 ,  11  clamping the tube wall  5  in the nip. The inner or upper shaping roller  12  engages the inner surface  8  of the tube  4 , whereas the outer or lower shaping roller  13  engages the outer surface of the tube  4 . The shaping rollers  12 ,  13  are applied to the tube wall  5  along generatrices G of the tube  4 . 
     By pivotal rotation of the arms  14  and  15 , the shaping rollers  12 ,  13  apply bending forces to the tube wall  5  in points of action  19 ,  21  which are spaced with respect to the periphery  6  of the tube  4 . Thus, the shaping rollers  12 ,  13  are moved in relation to each other and in relation to the nip rollers  10 ,  11 . By this feature, the tube  4  can be formed to the intermediate cross-sectional shape shown in FIG.  3  and finally to the aimed-at oval cross-sectional shape shown in FIG.  4 . In operation, the movements of the shaping rollers  12 ,  13  are precisely controlled by a computer (not shown). The mutual cooperative action between the two shaping rollers  12 ,  13  applying said bending forces to the tube wall  5  provides for smooth reshaping of the tube  4 . 
     The first shaping roller  13  serves to decrease the radius R of curvature of the tube  4  whereas the second shaping roller  12  serves to increase the radius of curvature of the tube  4 . The outer shaping roller  13  applies bending forces substantially directed to the center of the tube  4  whereas the inner shaping roller  12  applies bending forces directed away from the center of the tube  4 . In operation, the two shaping rollers  12 ,  13  cooperate for providing the appropriate bending action. 
     Preferably, the arms  14 ,  15  are pivotable in a plane P which is perpendicular to the longitudinal axis C of the tube  4 . 
     The end positions of the shaping rollers  12  and  13 , respectively, are shown by dotted lines in FIG.  5 . Indeed, the end positions may vary depending on the aimed-at final shape of the tube  4 . 
     In this example, it is shown how a round tube  4  is reshaped to an oval tube, that is altering the radius R of curvature of the tube. However, the apparatus can also be used for reshaping an oval tube to a round, etc. There are no specific limitations on the reshaping as to the initial or final cross-section of the tube. 
     As seen in FIG. 1, the frame member  3  is pivotably mounted at  21  so that this part of the frame  1  can be “opened” for feeding tubes into the apparatus, and removing reshaped tubes from the same. Of course, the inner rollers  10 ,  12  have to be disconnected from their mountings when a tube is to be fed into or removed from the apparatus. 
     The number of rollers are not crucial to the reshaping. As an example, an alternative embodiment is shown in FIGS. 6-8. The rollers  10 - 13  are the same as in the embodiment described above, but an additional outer shaping roller  22  has been added. Since this additional shaping roller  22  and the outer shaping roller  13  are disposed on either side of the outer nip roller  10 , a very smooth and effective reshaping operation is achieved. By raising and lowering these two shaping rollers  13  and  21  in a well defined sequence (controlled by a computer), a very favorable reshaping is accomplished. 
     A second embodiment of the apparatus is shown in FIGS. 9-10. The main difference between this embodiment and the first embodiment concerns the means for mounting and moving the rollers  10 - 13 . The apparatus of FIGS. 9-10 has two sets of mounting means, one at each end. In the following, only one set will be described. 
     The end shaft portion  11   a  of the outer nip roller  11  is received in an elongate recess or groove  23  in the frame member  3 , and the end shaft portion  13   a  of the outer shaping roller  13  is received in an elongate recess or groove  24  in the frame member  3 . These grooves  23 ,  24  constitute means for guiding the movement of the associated rollers  11  and  13  by actuator means, here (as in the first embodiment) hydraulic cylinders  18  and  17 . The design of the grooves  23 ,  24  has to be calculated with respect to the desired movement and reshaping operation. Normally, the grooves  23 ,  24  are linear, but they could have a slight curvature as well (not shown). 
     As in the first embodiment, the outer or lower nip roller  11  is vertically moveable, whereas the inner or upper nip roller  10  is “stationary” (but of course rotatable). The inner and outer shaping rollers  12  and  13 , respectively, are moveable in directions which form an angle with the vertical movement of the lower nip roller  11 . It is seen in FIG. 9 that the two grooves  23  and  24  form an angle. 
     A slightly modified hydraulic cylinder  16 ′ is connected to the end shaft portion  12   a  of the inner shaping roller  12 . The difference with respect to the cylinder  16  shown in FIG. 1 is that the modified cylinder  16 ′ is detachably connected to the end shaft portion  12   a  by means of a gripping member or claw  25 . Thus, the cylinder  16 ′ can be detached from the shaping roller  12  and swung to a vertical position about a pivot  26 , allowing a change of tube. When a tube is to be fed into or removed from the roller nip  10 ,  11 , the nip roller  11  is lowered by means of the cylinder  18 , the gripping member  25  is detached from the end shaft portion  12   a  and the cylinder  16 ′ is swung to its vertical position. 
     As in FIG. 1, the frame member  3  is pivotable at  21  so that this part of the frame can be “opened”. 
     Preferably, the cylinders  16 ′,  17  and  18  are disposed substantially in a common plane which is perpendicular to the longitudinal axis C of the tube  4 . This results in a very compact and reliable structure. 
     For achieving a smooth movement of the inner shaping roller  12 , its end shaft portion  12   a  is connected to the end shaft portion  10   a  by means of a link member  27 . This link member  27  also serves to hold the upper nip roller  10  when a tube is replaced from the nip  10 ,  11 . 
     As in the first embodiment, the first shaping roller  13  decreases the radius of curvature whereas the second shaping roller  12  increases the same. In FIG. 10, the inner shaping roller  12  is shown in its highest position above the nip rollers  10 ,  11 , but the shaping roller  12  can be lowered in the direction of the cylinder  16 ′ to a position in which it applies bending forces to the tube wall  5  in cooperation with the outer shaping roller  13 . Then the cylinder  16 ′ is pivoted about the pivot  26 . 
     Very good practical results have been achieved by means of this apparatus. Helically-wound lock-seam tubes, to be used in ventilation duct systems, have been reshaped from round to oval without any experience of the drawbacks of the prior art technique discussed by way of introduction. A simple and improved method of reshaping tubes has been developed by the invention. In particular, it is favorable that the circumference of the tube remain unchanged during reshaping. 
     Finally, it should be emphasized that the invention is by no means restricted to the embodiments described herein, and several modifications are feasible within the spirit of the invention as it is defined in the appended claims. For instance, it should be mentioned that another number of rollers can be used than described here, and the invention is not limited to any particular type of tubes. Furthermore, other actuator means than hydraulic cylinders can be used, for instance pneumatic cylinders and the like. Alternative means for rotation, mounting and movement of the rollers can also be used.