Abstract:
On a two-roll rounding machine, in addition to a compressively elastic guide roll and a compressively rigid rounding roll, one or more compressively elastic rolls are provided which have both a rounding function and a supporting function for the rounding roll. These additional rolls may also be supported by a back-up roll. The result is a rounding machine that has very good rounding characteristics even at small rounding diameters.

Description:
This application is entitled to the benefit of and incorporates by reference essential subject matter disclosed in Swiss Patent Application No. 2000 2009/00 having a filing date of Oct. 12, 2000. 
     BACKGROUND OF THE INVENTION 
     1. Technical Field 
     This invention relates to an apparatus and method for forming sheet products in general and to apparatus and method for forming sheet products that utilize rolls in particular. 
     2. Background Information 
     Two-roll rounding machines are known. In these, the sheet-metal blank to be rounded is passed between a rounding roll made of metal and a guide roll with a compressively elastic coating of a plastic material (e.g. Neoprene) with the rolls pressed against each other so that an indented region is formed in the compressively elastic coating, in which deformation of the blank around the rounding roll takes place. 
     Generally speaking, rounding machines should achieve the best possible rounding of the leading and trailing edge regions of the sheet-metal blank, even in small-diameter rounded sheet-metal tubes with diameters of e.g. 30-80 mm. For this reason, on three-roll rounding machines (e.g., European Patent Applications EP-A 0368686 or EP-A 0096643) the distance between the two working rolls is kept as small as possible. On two-roll rounding machines, flat zone formation is in any event slight owing to the effect of the plastic coating of the guide roll, yet an improvement is desirable here also, particularly when the rounding roll diameter is very small, in the said range of 30 to 80 mm. 
     Therefore one fundamental problem of the invention is to provide an improved two-roll rounding machine. 
     DISCLOSURE OF THE INVENTION 
     According to the present invention, a two-roll rounding machine is provided that includes a first compressively elastic guide roll, a compressively rigid rounding roll, and a second compressively elastic roll. The second compressively elastic roll acts on the compressively rigid rounding roll. 
     By the provision of an additional roll with a compressively elastic coating (hereinafter called compressively elastic roll for simplicity), further rounding can take place, and this improves the end result. Moreover this additional roll stabilizes the rounding roll by preventing deflection, which is particularly desirable when the diameter of the rounding roll is small. 
     Preferably, two such additional compressively elastic rolls are provided, yielding, in particular, good rounding and stabilization of the rounding roll against deflection. 
     Preferably also, one or more back-up rolls are provided which in turn support the compressively elastic rolls, these back-up rolls not normally being rolls with a compressively elastic coating (they may therefore be called compressively rigid rolls). 
     Preferably also, at least one guide is provided which leads the blank emerging from the first roll pair (guide roll, rounding roll) to the second roll pair (rounding roll, additional roll). 
     A further fundamental task of the invention is to provide a rounding method which does not possess the said drawbacks. 
     According further to the present invention, a method for rounding sheet-metal blanks is provided that utilizes a two-roll rounding machine, and wherein the sheet-metal to be rounded is passed between the first compressively elastic guide roll and the compressively rigid rounding roll at least twice. It has been found that particularly good rounding is obtained if the blank makes two passes through the rounding machine according to the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Embodiments of the invention will now be described in detail by way of example and with reference to the drawings. 
     FIG. 1 shows schematically a two-roll rounding machine in a first position. 
     FIG. 2 shows the rounding machine of FIG. 1 in a second position. 
     FIG. 3 shows a further embodiment of a rounding machine according to the invention. 
     FIG. 4 shows an embodiment with a guide. 
     FIG. 5 shows a further embodiment of the present invention rounding machine. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 shows highly schematically a first embodiment of a two-roll rounding machine  1 . This machine has a machine frame, represented simply as a box  2 , in which the journals of the machine&#39;s rolls and rollers are mounted, their axes in this schematic representation being assumed perpendicular to the plane of the drawing. A drive represented simply as a box  17  for the live rolls, and an electronic control  16  which controls the drive, are also provided in or on the machine frame. In FIG. 1 the guide roll  3  of the rounding machine is shown with its coating  5  which is elastically deformable in compression. This coating is a plastic coating known in the context of such machines, and will not be described in detail here. Because of this coating, the roll  3  will hereinafter be referred to as the compressively elastic guide roll. The roll is mounted in the machine frame  2  rotatably about its axis  4 .  6  denotes the rounding roll of the rounding machine; this roll does not carry a compressively elastic coating, and will therefore be referred to as the compressively rigid rounding roll. FIG. 1 shows this roll parted from the guide roll  3  so that the sheet-metal blank  20  to be rounded can be pushed between the rolls. 
     FIG. 2, in which the same reference numbers denote the same elements as in FIG. 1, shows the actual rounding position, in which the rounding roll  6  is pressed against the guide roll  3  and makes an indentation in the compressively elastic coating  5  of the guide roll, the effect of which is that the blank is pressed on to the rounding roll. The blank is rounded in the conventional way by means of these two rolls  3  and  6 , by driving the rounding roll  6  by means of the drive  17 , which turns the rolls as shown by arrows in FIG.  2  and causes the blank  20  to be drawn between the rolls  3  and  6  and rounded around the roll  6 . 
     In the embodiment of the invention shown in FIGS. 1 and 2, two additional compressively elastic rolls, i.e. rolls which likewise have a plastic coating, are provided, which bear on the compressively rigid rounding roll  6 . In the illustrated example, these two rolls  8  and  11 , with their coatings  10  and  13  and axes  9  and  12 , which extend parallel with the axes  4  and  7  of the rolls  3  and  6 , are arranged on either side of the rounding roll  6 , in the region facing away from the guide roll  3 . The rolls  8  and  11  are symmetrically arranged with respect to the plane E passing through the axes  4  and  7 . One effect of the compressively elastic rolls  8  and  11  is to produce further rounding of the blank  20  around the compressively rigid rounding roll  6 . Another effect of these rolls is to support the rounding roll  6 , which is particularly advantageous in the case of rounding rolls  6  of small diameter, particularly in the diameter range of 30-80 mm. 
     With the configuration shown, the blank  20 , which peels away again from the rounding roll  6  after the initial rounding between it and the guide roll  3 , can impinge more or less obtusely on the roll  8 , or on the coating  10  of the roll  8 . This may result in an undesired bowing or buckling of the blank, which, however, is subsequently removed in the re-forming as the blank passes between the rolls  8  and  6  and also between the rolls  11  and  6 . Particularly good rounding results if the blank  20  makes two passes through the said rolls, that is to say, after the first rounding operation by means of the roll pairs  3  and  6 ,  8  and  6 , and  11  and  6 , it is passed one more time through the rolls  3  and  6  followed again by the rolls  8  and  6  and  11  and  6 . This reliably eliminates any unrounded, or incorrectly rounded, portions. The control  16  of the machine is suitably configured to effect a double pass of each blank. 
     In order that the rounded blank  20  can be removed, the rounding roll  6  is parted again from the guide roll  3  as shown in FIG. 1, and the rolls  8  and  11  are also parted from the rounding roll  6 , in order that the rounded blank can be withdrawn from the rounding machine in a direction perpendicular to the plane of the drawing. The rolls  8  and  11  may be moved with a translational motion downwards in the drawing, or each of their axes  9  and  12  may be swung outwards about a pivotal axis so that the rolls  8  and  11  release the rounding roll  6 . The rolls  8  and  11  are then brought back into the position shown in FIGS. 1 and 2 for the next rounding operation. 
     Instead of being continuous, the rolls  8  and  11  may be designed and constructed as a series of coaxial rolls spaced apart from one another. 
     Preferably, a back-up roll  14  is also provided to support the compressively elastic rolls  8  and  11  in their turn. In the example shown the back-up roll  14  is mounted rotatably about an axis  15  and is a compressively rigid back-up roll; i.e. it does not have an elastic coating. 
     FIG. 3 shows a further embodiment, with the same reference numbers as used hitherto designating the same elements. Here also, rounding of the blank  20  takes place between the compressively elastic guide roll  3  and the compressively rigid rounding roll  6 . Underneath the latter, only a single compressively elastic roll  21 , with coating  23 , is provided in this embodiment, and is arranged rotatably about an axis  22 . Again, the roll may be made up of a plurality of individual rollers. Underneath this roll, a compressively rigid back-up roll  24  is, again, mounted on an axis  25 , to provide support for the roll  21 . The roll  21  serves to round the blank and support the rounding roll  6  in the manner which has already been described. 
     FIG. 4 shows a further embodiment, again with the same reference numbers used to denote the same elements. Here again an embodiment with two compressively elastic rolls  8  and  11  is shown, to which is added a guide  30  which by its guide face  31  receives and guides the rounded blank emerging between the rolls  3  and  6 , so that the rounded blank is introduced between the rolls  8  and  6  in a suitable position. The guide  30  reliably prevents upsetting or buckling of the blank  20  upon initial contact with the roll  8 . In this case a single pass of the blank through the roll pairs  3  and  6 ,  8  and  6 , and  11  and  6  is usually sufficient. 
     FIG. 5 shows a further embodiment, with the same reference numbers again designating the same elements. This embodiment differs from that of FIGS. 1 and 2 (and  4 ) in that, besides the back-up roll  14  common to the rolls  8  and  11 , individual back-up rolls  32  and  33  are additionally provided for the rolls  8  and  11  respectively. The rolls  32  and  33  are rotatable about axes  34  and  35  respectively. Of course, the cycle of insertion and offloading that has been described, and the corresponding drive and control, and the building-up of individual rolls from separate coaxial rollers as already described, apply to this example also.