Abstract:
A device in an axially extending tension channel on the circumferential surface of a cylinder for fastening a flexible plate on the cylinder periphery. The leading edge of the plate is held by a leading edge fastening device in the channel, and the trailing edge is held by a trailing edge fastening device in the channel. The leading edge fastening device is a start hook-in bar which the leading edge of the plate engages. The trailing edge fastening device is formed by an end hook-in bar which is engaged by the trailing edge of the plate. The end hook-in bar projects tangentially from a tensioning shaft which is rotatable to set the tension of the plate without means to apply a clamping load. Various devices for fastening and adjusting the leading and trailing edges of the plate are disclosed.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a device, which is arranged in an axially extending tensioning channel in a cylinder, for fastening a flexible plate around the circumferential surface of the cylinder. The device is particularly for fastening a varnishing or printing plate or a rubber blanket on the periphery of a varnishing or blanket cylinder of a varnishing machine, wherein the plate has start and end edges which and point into the tensioning channel. The leading edge of the plate is held by a leading edge fastening device and the trailing edge is held by a trailing edge fastening device. 
     German Offenlegungsschrift 40 11 303 discloses a device of this type. The start and the end of a rubber blanket that is tensioned on a cylinder are clamped between a top and bottom rail. In order to tension the rubber blanket, the top and bottom rails are jointly displaced radially inward into the cylinder. The fastening device for the rubber blanket extends over a relatively long distance around the circumference of the cylinder. As a result, a corresponding section of the circumferential surface overall periphery is not available for rolling purposes. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a device of the type mentioned above which has a simple construction, and extends over only a very small distance around the circumference of the cylinder, so that the leading and trailing edges of the plate can be located very closely to each other. This enables virtually the entire circumferential surface of the varnishing cylinder to be used for varnishing purposes. The usable rolling area of the varnishing cylinder surface is thus very large, that is, optimum utilization is achieved by the invention. 
     According to the invention, this object is achieved by the leading edge fastening device being formed by a start hook-in bar. The leading edge of the plate engages behind that bar. It is further achieved by the trailing edge fastening device being formed by an end hook-in bar, which projects tangentially from a tensioning shaft extending within and parallel to the cylinder. The trailing edge of the plate engages behind that end hook-in bar. The leading and trailing edges are each held without being clamped, but merely by the edges engaging behind the start and end hook-in bars. All that is required for fastening the plate on the cylinder is for the leading and trailing edges to engage behind the start hook-in bar and the end hook-in bar, respectively. The start and end hook-in bars can thus be located opposite each other with just a very small distance between them. It is necessary for that distance to just be sufficiently large, on the one hand, for the plate to be tensioned on the circumferential surface of the cylinder by relative movement of the two bars toward each other, that is, it must be possible to realize an adequate tensioning travel, and, on the other hand, for the leading and/or trailing edge of the plate to have an adequately large entry gap available in order to permit engagement with respect to the respective fastening device during mounting and in order to loosen this engagement during dismounting. Since the plate is held at its start and end edges merely by engagement and not by means which apply a clamping load, there is no additional space requirement for such clamping means as required in the prior art, so that the start and end of the plate lie very closely opposite each other, that is, virtually without a gap. As a result, virtually the entire circumferential surface is available as a rolling area. 
     In this application, when a configuration of the plate is mentioned, then this is to be understood such that this configuration is not provided directly on the plate but on its profiled end strips. The profiled end strips are viewed virtually as a constituent part of the plate, although they constitute separate components. If, therefore, mention is made, for example, of the fact that a cutout is arranged in the region of the leading edge and/or of the trailing edge of the plate, this likewise means that the cutout can also be located in the region of the leading edge and/or trailing edge of the profiled end strip/profiled end strips. 
     It is advantageous if the end hook-in bar projects from the tensioning shaft in a tangential direction thereto. In relation to an imaginary radius of the cylinder, the end hook-in bar, viewed in cross section, diverges from this radius. Additionally, that region of the end hook-in bar which engages the trailing edge of the plate is located approximately in the region of the point of intersection of the imaginary radius with the peripheral line of the cylinder. For this purpose, the start hook-in bar, likewise viewed in cross section, which engages the leading edge, preferably diverges from the same radius with the opposite inclination as the end hook-in bar. The two bars are inclined toward each other so as to form only the narrowest possible gap between them, at approximately the level of the outer periphery of the cylinder. 
     The end hook-in bar is preferably inherently elastic, and specifically is a spring element. As a result of this elastic property, inaccuracies at the ends of the plate which may be caused, for example, by production tolerances, e.g., inaccuracies in parallelism, are compensated for. Since the end hook-in bar is arranged on the tensioning shaft, as mentioned above, that bar may be moved by rotating the tensioning shaft in the direction of the start hook-in bar. This tensions the plate on the periphery of the cylinder. The tensioning shaft has a spring element, preferably in the form of a torsion bar, by which the plate is always subjected to tensile stress, and any rolling effects, and so on, are absorbed. Additionally or alternatively to the construction of the end hook-in bar as a spring element, it is possible for the end hook-in bar to be mounted eccentrically, that is, it can be adjusted in the region of one of its ends, to compensate for any possible inaccuracies in parallelism of the plate. The eccentric bearing is located, as mentioned above, in one end region of the end hook-in bar, whereas its other end region is appropriately pivotally mounted. Since inaccuracies in parallelism and the like can also occur at the start of the plate, the start hook-in bar can also preferably be adapted to the inaccuracies in parallelism, by providing a “movable” start hook-in bar fastening. Preferably, a fastening element, for example a threaded screw, engages through one end region of the start hook-in bar providing a possibility of pivoting the start hook-in bar. In the other end region of the start hook-in bar, there is a possibility of adjustment, in particular by means of a lever mechanism, so that an appropriate oblique setting of the start hook-in bar becomes possible. 
     The engagement angle of the leading and/or trailing edge is less than 90°, and preferably about 60°, so that there is virtually a form fit in relation to the respective hook-in bar. Even a slight tensioning of the plate thus rules out the possibility of an end of the plate coming loose. On the other hand, the ends of the plate can be lifted from the cylinder without any force being expended when the peripheral tension is loosened, enabling the plate to be changed in an extremely simple and trouble-free manner. 
     In relation to the construction of the leading edge and/or trailing edge of the plate, the start hook-in bar and/or the end hook-in bar is preferably contoured in its/their respective engagement region such that the parts are caused to contact one another in a form fitting manner over a large area. This provides optimum secureness and reproducibility. 
     In a particularly simple configuration, the leading edge and/or the trailing edge is/are formed by bent start and end regions of the plate. The bent regions enable the start and end edges of the plate to engage the start hook-in bar and end hook-in bar, respectively so that there is no need for any additional parts for fastening the plate to the cylinder. Alternatively, however, it is also possible for the leading edge and/or the trailing edge to be formed by profiled end strips fastened to the start and/or end of the plate. The profiled end strips permit snug-fitting, accurate cooperation with the respective bar and have high dimensional stability. 
     In particular, the profiled end strip or the profiled end strips are held on the plate by a clamp fastening. Each profiled end strip preferably has a clamping channel, in which the plate engages for being fastened. However, it is also possible for the profiled end strip to be held on the plate by adhesive bonding. In this case, too, the profiled end strip may have a channel in which the end of the plate or the start of the plate engages, with the interposition of an adhesive. 
     According to a preferred embodiment, the plate may have a plastic substrate material, in particular polyester, or the plate may consist of this material. In such a case, the plate is technically similar to a rubber blanket. But it can be used, for example, as a varnishing plate for varnishing. The lateral position of the plate on the cylinder, that is, for example, the central position, is predefined by an alignment device so that it is an accurate fit and is reproducible. The alignment device is preferably formed by at least one pin on the start hook-in bar and/or the end hook-in bar, and a stop edge on the plate which cooperates with this pin. The stop edge can preferably be formed by means of a cutout in the plate, the cutout being located, in particular, in the region of the leading edge and/or trailing edge of the plate. 
     Finally, it is advantageous if an accurately fitted position of the plate in the rotation direction of the cylinder is achieved by hooking the leading edge on the start hook-in bar without play. This is automatically ensured when the plate is hooked over the start hook-in bar in an accurately fitting manner during mounting and is then tensioned around the cylinder periphery in this position. 
     Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a cross section through a varnishing cylinder for a varnishing machine (not illustrated) in the region of a fastening device. 
     FIG. 2 shows an illustration, corresponding to FIG. 1, in accordance with a further embodiment. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 shows a cross-section of a cylinder  1 , which is constructed as a varnishing cylinder  2  and is used in a varnishing machine (not illustrated). The cylinder  1  is penetrated, parallel to its axis of rotation, by a tensioning channel  3 , which opens into the outer surface  4  of the varnishing cylinder  2 . Viewed in cross section, the tensioning channel  3  has a wall contour  5  shaped as part of a circle, whose center  6  is located on a radius  7  of the varnishing cylinder  2 . On the printing start side DA, the part-circle-shaped wall contour  5  merges into a stepped contour  8 , which has a bottom face  9  and a side face  10 , which are preferably at right angles. With respect to an imaginary plane  11  running at right angles to the radius  7 , the bottom face  9  is tilted at an acute angle, that is to say runs at an angle in relation to the plane  11 . On the printing end side DE of the tensioning channel  3 , the part-circle-shaped wall contour  5  merges into an approximately flat wall contour  12 , which runs at an acute angle to the radius  7  in such a way that it converges toward this radius as the distance from the center of rotation of the varnishing cylinder  2  increases. The wall contour  12  and also the side face  10  open into the outer surface  4 , in each case forming a curved edge or radius. 
     A hollow tensioning shaft  13  is rotatably mounted within the tensioning channel  3 . In the region of its outer face  14 , the shaft  13  has a flat  15 , on which a trailing edge fastening device  16  is arranged. This device has an end hook-in bar  17 . The end hook-in bar  17  extends so that it projects away from the tensioning shaft  13 . The free end  18  of the end hook-in bar  17  extends within the tensioning channel  3  approximately as far as the outer surface  4 . The end hook-in bar  17  is fastened to the tensioning shaft  13  by several threaded screws  19  which are spaced apart from one another over the length of the arrangement. Each threaded screw  19  passes through a receiving hole in the end hook-in bar  17  and is screwed into a threaded hole in the hollow tensioning shaft  13 . 
     A spring element  20  is located within the tensioning shaft  13 . It is constructed as a torsion bar  21 . It is possible to pretension the rotatably mounted tensioning shaft  13  in a sprung manner in the direction of rotation. 
     A leading edge fastening device  22  is inserted into the stepped contour  8 . It has a start hook-in bar  23 . In its end region, the start hook-in bar  23  is connected to the varnishing cylinder  2  by a threaded screw  24 . For this purpose, the start hook-in bar  23  has a stepped hole  25 , through which the threaded screw  24  passes. The threaded section of the threaded screw  24  is screwed into a corresponding threaded hole  26  in the varnishing cylinder  2 . In the region of its other end, the start hook-in bar  23  has an adjusting device, in particular an adjusting device that operates in the manner of a lever, so that, as viewed in the peripheral direction of the varnishing cylinder  2 , it can be set at an angle to the axis of rotation of the varnishing cylinder, in order to be able to compensate for any inaccuracies in the parallelism of a flexible plate  28  that is to be fastened on the outer surface  4  of the varnishing cylinder  2 . A corresponding possibility is provided in the case of the end hook-in bar  17 . This is provided by one end of the end hook-in bar  17  being mounted eccentrically, so that any possible inaccuracies in the parallelism of the plate  28  can be compensated. 
     The flexible plate  28  is fastened on the outer surface  4  of the varnishing cylinder  2  by means of a device  27  that is formed by the trailing-edge fastening device  16  and the leading-edge fastening device  22 . The plate  28  is constructed as a varnishing plate  29 , so that it can be used to carry out varnishing operations. The plate  28  has an edge  31  at its start  30  and an edge  33  at its end  32 , the edge  31  forming a leading edge  34  and the edge  33  forming a trailing edge  35 . Leading edge  34  and trailing edge  35  are formed by the respective end regions of the plate  28  being bent. The bending is carried out in such a way that the leading edge  34  and the trailing edge  35  each form an acute angle with the contour of the plate  28 , which is conformably held to the outer surface  4 . These hook-like contours form engagement angles of preferably about 60°. Mating contours corresponding to the engagement angles are formed on the start hook-in bar  23  and in the region of the free end  18  of the end hook-in bar  17 . The arrangement is made in such a way that, in their respective engagement regions, the start hook-in bar  23  and the end hook-in bar  17  have such cross-sectional contours that the leading edge  34  and the trailing edge  35  of the plate  28  lie thereon in a form-fitting manner over a large area. Those regions of the plate  28  which adjoin the leading edge  34  and the trailing edge  35 , and are located substantially along the cylindrical contour of the varnishing cylinder  2  or approximately follow the outer surface contour, are also supported flat on corresponding regions of the start hook-in bar  23  and end hook-in bar  17 . 
     Correct lateral alignment of the plate  28  on the cylinder  1 , that is, for example, the central position, is ensured by the alignment device  42 . This has a pin  43  with a head  43 ′, which is held by one end in the start hook-in bar  23  and its other, free end points into the tensioning channel  3 . With the underside of its head  43 ′, the pin  43 , which passes out of the start hook-in bar  23 , projects beyond the channel-facing surface of the start hook-in bar  23  approximately by a length which corresponds to the thickness of the plate  28 . The pin  43  passes through a cutout  44 , which is made in the leading edge  34  of the plate  28  and which forms a stop edge  45 . This makes the reproducible, accurately fitting lateral positioning of the plate  28  possible. The cutout  44  becomes superfluous if the stop edge  45  is formed by a side edge of the plate  28 , which in this case is moved toward the pin  43  until that edge makes contact for the purpose of the lateral alignment of the plate. It is of course possible for the pin  43  or the alignment device  42  also to be arranged on the end hook-in bar  17 . It is also possible for a plurality of alignment devices  42  to be provided. For improved clarity, only one alignment device  42  is illustrated in FIG.  1 . 
     The following operation occurs: In order to tension a plate  28  on the varnishing cylinder  2 , the leading edge  34  of the plate is made to engage behind the start hook-in bar  23  in the region of the printing start DA. The plate is then laid around the outer surface  4  of the varnishing cylinder  2 . Then the trailing edge  35  of the plate is brought into engagement behind the end hook-in bar. The tensioning shaft  13  is located in such a rotational position that the end hook-in bar  17  exerts no tension on the trailing edge  35 . The plate  28  is then brought into the desired lateral position by means of the alignment device  42 . Then spring tension is exerted on the tensioning shaft  13  by means of the torsion bar  21  in such a way that the free end  18  of the end hook-in bar  17  approaches the start hook-in bar  23 . This engages the trailing edge  35  under spring tension and firmly tensions the plate  28  on the outer surface  4  of the varnishing cylinder  2 . For dismounting the plate, the above mentioned engagement is loosened, that is, the tensioning shaft  13  is rotated in the counterclockwise direction (FIG.  1 ), so that the trailing edge  35  is released and the plate  28  can be removed from the varnishing cylinder  2 . 
     The embodiment of FIG. 2 mainly corresponds to the embodiment of FIG. 1, and only essential changes are discussed below. The end hook-in bar  17  has a hook-shaped cross-sectional contour, with an end leg  36 , which runs approximately in the peripheral direction of cylinder  2  and has a free end  18  at which the tensioning of the plate  28  is effected. Furthermore, the plate  28  does not have bent leading and trailing edges. Instead, profiled end strips  37  are fastened to the end regions of the plate  28 . The end strips have, as viewed in cross-section, a V-shaped contour. One profiled end strip  37  has a leading edge  38  and the other profiled end strip  37  has a trailing edge  39 . The leading edge  38  and the trailing edge  39  each forms one leg of the above mentioned V-shaped contour. The other leg of the respective V-shaped contour has a channel  40  or  41  respectively, in which the respective starting/trailing region of the plate  28  engages and is held by clamping or adhesive bonding. 
     The tensioned plate  28 , which is preferably a varnishing plate  29 , is removed from the varnishing cylinder  2  in the case of the embodiment of FIG. 2 in the same way as for the embodiment of FIG.  1 . 
     Although the present invention has been described in relation to particular embodiments thereof, many other variations and modifications and other uses will become apparent to those skilled in the art. It is preferred, therefore, that the present invention be limited not by the specific disclosure herein, but only by the appended claims.