Patent Publication Number: US-6901857-B2

Title: Assembly comprising a blanket unit and a cylinder having a blanket fixing device, a corresponding cylinder, blanket unit and offset printing machine

Description:
TECHNICAL FIELD 
     The present invention relates to an assembly for an offset printing machine comprising:
         a blanket unit comprising a blanket and a blanket support plate, the front edge and rear edge of the support plate being bent over in the region of a front bend and a rear bend, respectively, the rear edge of the support plate protruding beyond the rear edge of the blanket which is located adjacent to the rear bend, and   a cylinder having an aperture for receiving the front edge and rear edge of the support plate, the cylinder comprising a device for fixing the blanket unit to the cylinder, the fixing device comprising at least one hook for tensioning the blanket unit, the hook being intended to be received in an opening of the rear edge of the support plate, which rear edge is inserted into the aperture, in order to apply to the support plate a tension load which is substantially parallel with the rear edge thereof.       

     BACKGROUND TO THE INVENTION 
     A printing machine of this type conventionally comprises, in addition to the blanket-carrying cylinder and the blanket, a plate-carrying cylinder and a plate and a pressing cylinder. 
     During operation, the plate carried by the plate-carrying cylinder is moistened then inked. The plate transfers the ink from the printing regions thereof to the blanket carried by the blanket-carrying cylinder. The blanket then transfers the ink to the paper to be printed which passes between the blanket-carrying cylinder and the pressing cylinder. 
     In order to tension the blanket on the cylinder, metal bars crimped to the ends of the blanket were traditionally used. These bars were engaged in the aperture of the cylinder, where they were pushed by a screw-type device. 
     Such arrangements lead to aperture widths which are very large, reaching 22 mm. 
     The presence of such large apertures results in shocks and vibrations when the blanket-carrying cylinder rotates against the plate-carrying cylinder and against the pressing cylinder. Such vibrations limit the rotation speeds of the various cylinders and therefore the production capacities of offset printing machines. 
     FR-2 573 347 proposed an assembly of the above-mentioned type. The front edge of the blanket covers all the front edge of the support plate and therefore extends into the cylinder aperture. The rear edge of the blanket does not extend into the aperture and is applied substantially against the region of the front bend of the blanket unit. In this manner, the gap between the start of the blanket and the end of the blanket is extremely narrow in order to limit the vibrations which result from the presence of the aperture in the cylinder. 
     However, it was found that it was extremely difficult to bend the front edge of the plate and the front edge of the blanket in order to obtain the configuration desired in this document. 
     FR-2 733 719 proposed another solution in which the device for fixing the blanket unit comprises pressing studs which apply the front and rear edges of the support plate against the front wall of the aperture. These front and rear edges of the support plate are not covered by the blanket. The forces applied by the studs are exclusively perpendicular to the front and rear edges of the support plate. 
     It was found that this arrangement did not allow the blanket unit to be tensioned satisfactorily. In addition, the fixing device described does not allow the deformations of the blanket unit resulting from the operation of the offset printing machine to be absorbed. In particular, the expansions of the support plate cannot be absorbed so that cracks in the plate adjacent to the rear bend thereof are observed. 
     FR-2 745 524 proposed that the pressing studs be replaced with one or more resilient blades. However, this arrangement does not always allow satisfactory tension of the blanket unit to be obtained. 
     An object of the invention is to provide an assembly of the above-mentioned type which allows the blanket unit to be tensioned on and fixed to the cylinder in a satisfactory manner and which is simple and economical to produce. 
     SUMMARY OF THE INVENTION 
     To this end, the invention relates to an assembly of the above-mentioned type, characterised in that the front edge of the support plate protrudes beyond the front edge of the blanket which is located adjacent to the front bend. 
     According to particular embodiments, the assembly can comprise one or more of the following features, taken in isolation or according to all technically possible combinations:
         the opening is provided in a region of the rear edge of the support plate forming an angle which is not equal to zero with the front edge of the support plate,   the hook comprises a resilient blade,   the assembly comprises means for applying the front edge of the support plate against the front wall of the aperture, these application means being separate from the hook,   the application means comprise at least one element for pressing on the front edge of the support plate, the pressing element belonging to the fixing device and being separate from the support plate,   the pressing element extends, in order to press on the front edge of the support plate, through the opening which receives the hook,   the pressing element comprises a resilient blade,   the rear edge of the support plate is itself bent in the region of an intermediate bend which delimits an end region, in which the opening for receiving the hook is provided, and an intermediate region which is intended to press against the front edge of the support plate and which thereby forms the application means,   the aperture has a width, near the peripheral surface of the cylinder, of less than 1.5 mm,   the width of the aperture is less than 1.1 mm,   the front and rear walls of the aperture form, starting from the peripheral surface of the cylinder, an angle which is less than 20°.       

     The invention also relates to a cylinder for an assembly as defined above. 
     According to one variant, the fixing device comprises at least one element for pressing on the front edge of the support plate in order to apply it against the front wall of the aperture, the pressing element being separate from the hook. 
     The invention further relates to a blanket unit for an assembly as defined above. 
     According to one variant, the rear edge of the support plate is itself bent in the region of an intermediate bend which delimits an end region, in which the opening for receiving the hook is provided, and an intermediate region which is intended to press against the front edge of the support plate in order to apply it against the front wall of the aperture. 
     The invention also relates to an offset printing machine comprising an assembly as defined above. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The invention will be better appreciated from the description below which is given purely by way of example with reference to the appended drawings, in which: 
         FIG. 1  is a schematic side view of an assembly according to a first embodiment of the invention, 
         FIG. 2  is a schematic partial cross-section, drawn to an enlarged scale, illustrating the fixing device of the blanket unit of the assembly of  FIG. 1 , 
         FIG. 3  is a schematic partial top view, illustrating part of the spindle of the fixing device of  FIG. 2 , 
         FIG. 4  is a schematic partial view illustrating the rear edge of the support plate of the blanket unit, 
         FIGS. 5 and 6  are views similar to  FIG. 2 , illustrating successive steps in the engagement of the blanket unit with the fixing device, 
         FIG. 7  is a view similar to  FIG. 1 , illustrating the position of a drive mechanism of the fixing device at the end of the fixing of the blanket unit, 
         FIG. 8  is a view similar to  FIG. 6 , illustrating a second embodiment of the invention and 
         FIG. 9  is a view similar to  FIG. 6 , further illustrating a third embodiment of the invention. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENT 
       FIG. 1  illustrates schematically an assembly  1  for an offset printing machine which comprises a cylinder  2  and a blanket unit  3  which surrounds the peripheral surface  4  of the cylinder  2  and which is carried by the cylinder  2 . 
     The cylinder  2  extends along a longitudinal axis A and the longitudinal ends  5  thereof, only one of which is visible in  FIG. 1 , are intended to be received in bearings of the support structure of an offset printing machine. In this manner, the cylinder  2  can, owing to conventional driving means which are not illustrated, rotate about the longitudinal axis A thereof in a sense illustrated by the arrow  6  in FIG.  1 . 
     Hereinafter, the terms “front” and “rear” used should be understood with reference to this sense of rotation  6 . 
     As is visible in  FIG. 2 , a longitudinal recess  8  has been provided in the cylinder  2  from the peripheral surface  4  thereof. This recess  8  is substantially in the form of a regular trapezium in cross-section with one rounded side corresponding to a portion of the peripheral surface  4  of the cylinder  2 . 
     An insert  10  is screwed into the recess  8 . 
     This insert  10  delimits inside the cylinder  2  a longitudinal cavity  12  having a substantially rectangular cross-section and a longitudinal aperture  14  having a substantially triangular cross-section. 
     The aperture  14  opens into the peripheral surface  4  of the cylinder  2  and into the cavity  12 . 
     As illustrated in greater detail by the enlarged circled portion of  FIG. 2 , the front wall  16 , which is common to the aperture  14  and the cavity  12 , is connected to the peripheral surface  4  by a chamfer  18 , for example, having a width of approximately 1 mm. 
     Similarly, the rear wall  20  of the aperture  14  is connected by a chamfer  22  to the peripheral surface  4 . This chamfer  22  has, for example, a width of approximately 1.4 mm. 
     The front wall  16  and rear wall  20  of the aperture  14  diverge as they approach the cavity  12 , that is to say, from an upstream point towards a downstream point of the aperture  14 . The walls  16  and  20  thus form between them an angle α which is typically approximately 14.8°. More generally, this angle a will be less than 20°. 
     The upstream width  1  of the aperture  14  between the walls  16  and  20 , that is to say, downstream of the chamfers  18  and  22  is approximately 1 mm. More generally, this width  1  will be less than 1.5 mm, and preferably less than 1.1 mm. 
     The cylinder  2  comprises a device  26  for fixing the blanket unit  3  to the cylinder  2 . This device  26  is arranged in the cavity  12  and comprises a spindle  28  which extends along an axis X—X which is substantially parallel with axis A of the cylinder  2 . This spindle  28  extends, for example, all the way along the cylinder  2 . 
     As illustrated by  FIGS. 2 and 3 , hooks  30  and pressing elements  32  are distributed along the spindle  28 . 
     The hooks  30  are formed by resilient blades whose free ends  34  are curved opposite the aperture  14 . 
     Similarly, the pressing elements  32  are formed by resilient blades whose free ends  36  are bent through 180°. 
     The hooks  30  and the pressing elements  32  are associated in pairs, the associated hook  30  and pressing element  32  being fixed to the spindle  28  by a common screw  38 . The pressing element  32  is arranged above the associated hook  30 . 
     The pairs comprising a hook  30  and pressing element  32  are spaced apart from each other longitudinally and distributed along the spindle  28 . 
     The spindle  28  is mounted so as to be able to rotate about longitudinal axis X—X thereof in the cavity  12  owing to, for example, bearings provided at the ends of the spindle  28  and optionally in intermediate regions thereof. 
     In this manner, the spindle  28  can move between two positions illustrated by  FIGS. 2 and 6 , respectively. 
     In the position of  FIG. 2 , or the release position of the blanket unit  3 , the hooks  30  and the pressing elements  32  are moved away from the aperture  14  and free up the access to the cavity  12 . 
     In the position of  FIG. 6  or the fixing position of the blanket unit  3 , the hooks  30  and the pressing elements  32  are moved towards the front wall  16 . 
     In order to move from the position of  FIG. 2  into the position of  FIG. 6 , the spindle  28  pivots in the counter-clockwise sense, as seen in these Figures. This pivoting can be brought about by drive mechanisms  42 , only one of which is visible in  FIG. 1 , the other having a similar structure and being arranged at the other side of the cylinder  2 . Thus, only the mechanism  42  visible in  FIG. 1  will be described below. 
     The drive mechanism  42  can comprise, for example:
         a support  44  fixed to a flank of the cylinder,   a rod  46  which is provided with a collar  48  and which is surrounded by a spring  50 ,   a block  52  which is fixed to the corresponding longitudinal end  54  of the spindle  28 , and   a moveable operating lever  56 , which is illustrated as a dot-dash line in FIG.  1 .       

     The rod  46  is articulated to the block  52  at a first end thereof. The rod  46  is mounted, at the other end thereof, in the support  44  by means of an articulation which allows it to pivot in a plane at right-angles to axis A of the cylinder  2 . The spring  50  presses, on the one hand, on the block  44  and, on the other, on the collar  48 . 
     Owing to the lever  56 , the rod  46  can move relative to the support  44  between two stable end positions. 
     The first stable end position is illustrated in  FIG. 1 , This position corresponds to the release position of the spindle  28 , illustrated in FIG.  2 . 
     The second stable end position is illustrated in FIG.  7 . In this position, the spindle  28  is in the fixing position illustrated in FIG.  6 . 
     In order to move from the position in  FIG. 1  to that in  FIG. 7 , an operator pivots the lever  56  in the counter-clockwise sense, as illustrated by the arrow  60  in FIG.  1 . 
     The rod  46  will then move through an unstable neutral position, where the axis thereof will intersect with axis X—X of the spindle  28 . The spring  50  is then compressed so that it will return the rod  46  towards the second stable position thereof, that is to say, the position of FIG.  7 . The block  52  is then pressed against an adjustable stop  58  which allows the angular position of the spindle  28  in the fixing position thereof to be adjusted. 
     In this manner, the mechanism  42  for passing through the neutral position allows the spindle  28  to be displaced manually from the release position thereof towards the fixing position thereof, and vice versa. However, it should be noted that any other type of drive mechanism  42  can be used. 
     With reference once more to  FIG. 2  it will be appreciated that the blanket unit  3  comprises a support plate  62  and a blanket  64  which is fixed to the support plate  62 . 
     The support plate  62  is produced, for example, from stainless steel. Its thickness is approximately 0.2 mm. 
     The blanket  64  conventionally comprises, for example, a plurality of layers of elastomer and fabric. The blanket  64  is fixed to the support plate  62  by adhesive bonding or vulcanisation. 
     The front edge  66  of the support plate  62  extends beyond the front edge  68  of the blanket  64 . The front edge  66  of the support plate  62  is bent in the region of a front bend  70  in order to form with the rest of the plate  62  an acute angle β. 
     The front edge  68  of the blanket  64  is arranged in a slightly withdrawn position relative to the bend  70 . In some variants, however, the front edge  68  can be in an advanced position in order to cover at least partially the bend  70 . Be that as it may, the front edge  68  will be located adjacent to the bend  70  in order not to extend into the aperture  14 . 
     The front edge  66  of the support plate  62  is not covered by the blanket  64  and is inserted into the aperture  14 . The front bend  70  extends over the chamfer  18  and the front edge  66  of the plate  62  extends along the front wall  16  of the aperture  14 . 
     The blanket unit  3  has, at the rear, a configuration similar to the rear edge  72  of the plate  62 , which edge  72  is not covered by the rear edge  74  of the blanket  64 . The rear edge  72  is bent in the region of a rear bend  76  relative to the rest of the support plate  62 , forming an obtuse angle unlike the front of the blanket unit  3 . 
     The bare rear edge  72  is inserted into the aperture  14  and extends along and against the rear wall  20  of the aperture  14 . 
     The rear edge  74  of the blanket  64  is arranged adjacent to the rear bend  22  in order not to extend into the aperture  14  and to be relatively near the front edge  68  of the blanket  64 . 
     The front edge  66  and rear edge  72  of the support plate  62  extend inside the aperture  14  as far as the cavity  12  and together form an angle which is not equal to zero. 
     As illustrated in  FIG. 4 , the rear edge  72  of the support plate  62  has, at the free end  78  thereof, a series of openings  80  distributed along the end  78 . These openings  80  are substantially of rectangular form and are each arranged facing a pair comprising a hook  30  and pressing element  32 . 
     In order to mount the blanket unit  3  on the cylinder  2 , the procedure is, for example, as follows, 
     The spindle  28  being in the release position, the front edge  66  of the support plate  62  is first inserted into the aperture  14 , then the blanket unit  3  is wrapped around the cylinder  2  until the rear edge  72  of the support plate  62  is engaged in the aperture  14 . The blanket unit  3  is then in the position of FIG.  2 . 
     The spindle  28  is then pivoted, by means of the levers  56  and mechanisms  42 , from the release position thereof in  FIG. 2 , into the fixing position thereof in FIG.  6 . 
     During this rotation, the free end  34  of each hook  30  engages in the corresponding opening  80  of the rear edge  72  of the support plate  62  and the associated pressing element  32  extends through the same opening  80 . This is illustrated in FIG.  5 . 
     As the rotation movement of the spindle  28  continues, each hook  30  which is firmly engaged against the periphery of the corresponding opening  80  progressively brings about the tensioning of the support plate  2 , whilst the associated pressing element  32  which extends through the opening  80  will press on the front edge  66  of the support plate  62  and press it against the front wall  16  of the aperture  14  and cavity  12 . 
     It should be noted that each hook  30  applies a tension load T which is substantially parallel with the rear edge  72  to the rear edge  72  of the support plate  62 . 
     Once this movement is complete, the rear edge  72  of the plate  62  is drawn by the hooks  30 , thereby ensuring satisfactory tensioning of the blanket  64 , and the front edge  66  of the support plate  2  is applied against the front wall  16 . It should be noted that the rear edge  72  again forms an angle not equal to zero with the front edge  66  of the support plate  62 . 
     In this manner, the blanket unit  3  is fixed to and tensioned on the cylinder  2  in a satisfactory manner. 
     In spite of this, the hooks  30  and the pressing elements  32  allow, owing to the construction thereof in the form of resilient elements, slight movements of the edges  66  and  72  of the support plate  2 . This allows adaptation to various operating constraints of the offset printing machine and, in particular, to the phenomenon of thermal expansion of the support plate  62  and the phenomenon known as “indention”. 
     In this manner, the rear edge  72  of the support plate  62  can, under the effect of thermal expansion or in the case of the phenomenon known as “indention” extend further into the aperture  14 , the hooks  30  allowing this movement whilst keeping the blanket unit  3  under tension. 
     The pressing elements  32  form means  82  for applying the front edge  66  of the support plate  62  against the wall  16 , which means  82  allow the blanket unit  3  to be stabilised on the cylinder  2 . 
     Since these application means  82  are separate from the hooks  30 , the stabilisation, fixing and tension of the blanket unit  3  are ensured in a relatively simple manner. 
     Furthermore, the use of the same openings  80  for receiving the hooks  30  and the pressing elements  32  allows the number of openings in the support plate  62  to be limited. 
     It should also be noted that the use of openings  80  in the support plate  62  for co-operating with the hooks  30  allows the support plate not to have a curved rear edge, and therefore to keep the width l of the aperture  14  small. The inclination of the rear edge  72  of the support plate  62  relative to the front edge  66  thereof also allows the aperture  14  to have a small upstream width  1 . 
     This width  1  is even smaller because neither the front edge  68  nor the rear edge  74  of the blanket  64  extends into the aperture  14 . 
     This allows the vibrations during the rotation of the various cylinders of the offset printing machine on each other to be greatly limited. 
     Since the blanket  64  further does not cover all the front edge  66  of the support plate  62 , as in FR-2 573 347, the construction of the blanket unit and, in particular, the bending of the support plate are simple and economical, whilst limiting vibrations during operation. 
     In another embodiment illustrated in  FIG. 8 , the application means  82  are formed, not by pressing elements  32  belonging to the fixing device  26 , but instead by a region of the rear edge  72  of the support plate  62 . 
     In this manner, the rear edge  72  has an intermediate bend  84  which delimits, in the rear edge  72 , an end region  86 , in which the openings  80  for receiving the hooks  30  are provided, and an intermediate region  88  which is bent to a lesser extent relative to the rest of the support plate  62 . This intermediate region  88  presses on the front edge  66  of the support plate  62  and applies it against the wall  16 . 
       FIG. 9  relates to a third embodiment which differs from that of  FIGS. 1  to  7  in that the means  82  for applying the front edge  66  of the support plate  62  against the wall  16  have been dispensed with. 
     In spite of the absence of the application means  82 , the fixing and tensioning of the blanket unit  3  have been found to be satisfactory. 
     It should be noted that, in the case of each of the above-described embodiments, the cylinder and the blanket unit can be sold independently of each other. 
     In general, the above principles can be used with a cylinder  2 , to which two blanket units  3  are fixed, one beside the other, along axis A of the cylinder  2 . 
     The fixing devices  42  associated with each blanket unit  3  can be offset angularly from each other relative to axis A, for example, by 180°. In this manner, the apertures  14  associated with each blanket unit  3  are diametrically opposed, which limits the vibrations caused during the rotation against the other cylinders of the printing machine, and do not extend over the entire length of the cylinder  2 .