Method for mounting a blanket for a rotary press

Abstract: An object of the present invention is to provide an economical and highly operable blanket mounting apparatus in which the width of a cylinder gap on a blanket cylinder is further decreased to eliminate a printing trouble such as shock-streak and to shorten the non printing length. To achieve this object, a flat bar 15a, 15b is installed at each end of a blanket 2, a notch 16 with the same size as that of the leading edge flat bar 15a is formed in a cylinder gap 3, the leading edge flat bar 15a of the blanket 2 is inserted along a leading edge opening 3a of the notch 16, and a tail edge 2b of the blanket 2 to which a flat bar 15b is fixed is reeled by a reel bar 14, by which the cylinder gap opening is blocked by the leading edge flat bar 15a.

Description: FIELD OF THE INVENTION AND RELATED ART STATEMENT The present invention relates to a method for mounting a blanket for a rotary press on a blanket cylinder of a printing machine and more particularly a method for mounting a blanket, which can reduce the vibration caused by a cylinder gap on a blanket cylinder and the length of an unprinted portion (hereinafter referred to as a non printing length). A blanket cylinder of a printing machine comes in contact with a plate cylinder, a blanket cylinder or an impression cylinder, and rotates on the mating cylinder while cooperating with each other. FIG. 6 shows a most basic cylinder arrangement for a printing unit on an offset printing machine. With this system, paper is made to pass between an outer blanket cylinder 61 and an inner blanket cylinder 62 to make printing on both faces of the paper at the same time. In FIG. 6, reference numerals 64 and 65 denote an outer plate cylinder and an inner plate cylinder, respectively. On the blanket cylinder 61 (62) of such a printing machine, a blanket-mounting cylinder gap 3 for stretching a blanket 2 around the blanket cylinder is formed in parallel with the cylinder axis. The lower part of this cylinder gap 3 communicates with a through hole 67 for providing a blanket reel bar 54. FIG. 7 shows a blanket mounting apparatus 50 which has so far been used generally. For this apparatus, a blanket having aluminum pieces 59, 59 pressed onto both ends thereof is used. The pieces 59, 59 at both ends of the blanket are inserted in a gap in two reel bars 54, 54 provided in the blanket cylinders respectively, and the blanket 2 is stretched around the blanket cylinder 1 by the double reel method by turning the reel bars 54, 54. The cylinder gap 3 on the blanket cylinder 61 (62) of the printing machine meets the cylinder gap 3 of the rotating mating blanket cylinder 61 (62) every one rotation, and also meets a plate mounting gap 66 on the plate cylinder 64 (65). Therefore, when these cylinder gaps 3, 3 meet each other during rotation, a printing pressure is released in a moment, which creates a large disturbing force acting on the printing machine, resulting in a printing trouble such as a lateral stripe called shock-streak on the print surface. Also, since ink does not stick to the portion of this cylinder gap 3, a greater gap width increases the non printing length. Therefore, various improvements have been made conventionally on the blanket mounting apparatus to prevent the shock-streaks and to shorten the non printing length. FIG. 8 shows a publicly known double reel type blanket mounting apparatus 4 which has been developed to prevent the shock-streaks. On this apparatus, an elastic filler 48 is installed at the opening between a leading edge 2a and a tail edge 2b of the blanket 2 at the cylinder gap 3. FIG. 9 shows a publicly known blanket mounting apparatus which has recently been developed to prevent the shock-streaks and to shorten the non printing length. On this apparatus, a blanket 2 is affixed to the surface of a base plate 32 using a form plate material, and a mechanism 34 of a plate lock up device for plate cylinder, which can decrease the cylinder gap width, is applied. FIG. 10 shows a single reel type blanket mounting apparatus 20 (see e.g. WO-A-89/01866) which has recently been developed and widely used now to prevent the shock-streaks and to shorten the non printing length. On this apparatus, a blanket 2 having thin flat bars 25a, 25b affixed on one side at both ends thereof is used so as to decrease the width of a cylinder gap 3 on a blanket cylinder 1 to the limit point such that there is no difficulty in mounting the blanket 2. As described above, various improvements have been made on the blanket mounting apparatus for the rotary press, but there still remain the following problems. (1) The width of the cylinder gap on the blanket cylinder practically used at present has already been decreased to the utmost, reaching the limit point such that there is no difficulty in mounting the blanket. Accordingly, with the present method, the cylinder gap width cannot be decreased to shorten the non printing length and to prevent a printing trouble such as shock-streak. (2) There is a method in which an elastic filler is installed at the opening of cylinder gap to prevent a printing trouble such as shock-streak caused by vibration. With this method, however, the non printing length cannot be shortened. Also, it is difficult to control the height of the filler so as to be flush with the outer surface of the blanket cylinder. (3) There is a method in which a blanket is affixed onto the surface of base plate using a form plate material to shorten the non printing length by making use of the fact that the width of the press plate mounting cylinder gap on the plate cylinder can be made smaller than the width of the cylinder gap on the blanket cylinder. With this method, however, the running cost is high, and when the blanket becomes thin during use, it is difficult to solve the problem by using an under packing. A rotary web printing press is taught in US Patent 2,986,085 utilizing a blanket mounting apparatus of a type having a blanket with a flat bar and a tail edge. In accordance with the teaching of DE-A- 2,163,417 the flat bar of a blanket is shown inserted into the leading end of a gap when mounting the blanket around a blanket cylinder. OBJECT AND SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above remaining problems and to provide an economical and highly operable blanket mounting method in which the width of a cylinder gap on a blanket cylinder is further decreased to eliminate a printing trouble such as shock-streak and to shorten the non printing length. To achieve the above object, the present invention provides a method for mounting a blanket for a rotary press on a blanket cylinder of a printing machine having blanket mounting apparatus of a type in which the blanket has a flat bar fixed at each end thereof and a tail edge with the tail edge reeled by a blanket reel bar provided at the lower part of a cylinder gap of the blanket cylinder, a notch along the leading edge opening of said cylinder gap and inserting the leading edge flat bar of said blanket into the notch to mount said blanket around the blanket cylinder characterized in that the flat bar is attached to only a single side of the blanket at the leading edge thereof and the notch is formed on the surface of the blanket cylinder extending from its circumference in a direction parallel with the radius passing the center of the blanket cylinder gap and having a depth and width equal to the width and thickness of the flat bar at the leading edge such that upon inserting the leading edge flat bar into the notch contact is made with the tail edge of the blanket and while in this state fixing the leading edge and the tail edge to one another by reeling the tail edge by the blanket reel bar. In the method in accordance with the present invention, the gap width including the notch formed at the leading edge opening of the cylinder gap on the blanket cylinder is preferably equal to the dimension of the maximum thickness of two blankets plus the thickness of the leading edge flat bar of the blanket. For the blanket mounting method in accordance with the present invention, since the above measures are taken, when the blanket is mounted around the blanket cylinder, the tail edge of the blanket is first inserted in the gap of the reel bar in the blanket cylinder. Then, the leading edge is inserted in the notch formed at the opening of the cylinder gap on the blanket cylinder. At this time, the leading edge is pushed into the notch until the tip end of the leading edge flat bar of the blanket comes in contact with the lower face of the notch. Finally, the blanket reel bar is turned to stretch the blanket around the blanket cylinder. Thereby, the notch formed at the opening of the cylinder gap on the blanket cylinder is blocked by the leading edge flat bar of the blanket, so that the width of the gap on the blanket cylinder is decreased by the thickness of the flat bar as if a filler with a thickness of flat bar is inserted. Also, since the gap width of the blanket cylinder excluding the width of the notch at the opening of the cylinder gap is formed into a dimension equivalent to the maximum thickness of two blankets, the leading edge and the tail edge of the blanket come in contact with each other at the entrance of the gap on the blanket cylinder, so that the non printing length caused by the gap width of the blanket cylinder can be decreased to a dimension equivalent to the maximum thickness of two blankets. Therefore, the disturbing force during operation and the non printing length can be reduced significantly by the decrease in gap width. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of the principal portion of a blanket mounting apparatus in accordance with one embodiment of the present invention, showing a state of a blanket cylinder before a blanket is mounted; FIG. 2 is a sectional view of the principal portion similar to FIG. 1, showing a state when the blanket is being mounted; FIG. 3 is a sectional view of the principal portion similar to FIG. 1, showing a state when the blanket has been mounted; FIG. 4 is a side view of a blanket used on the apparatus of the embodiment shown in FIG. 3; FIG. 5 is a graph showing an effect of the apparatus of the embodiment shown in FIG. 3; FIG. 6 is a view for illustrating the cylinder arrangement for a basic offset printing unit; FIG. 7 is a sectional view of the principal portion of a conventional double reel type blanket mounting apparatus; FIG. 8 is a sectional view of the principal portion of a conventional blanket mounting apparatus with a filler; FIG. 9 is a sectional view of the principal portion of a conventional plate lock up type blanket mounting apparatus; and FIG. 10 is a sectional view of the principal portion of a conventional single reel type blanket mounting apparatus. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS One embodiment of a method and an apparatus for mounting a blanket in accordance with the present invention will be described in detail with reference to FIGS. 1 to 4. FIGS. 1 to 3 are sectional views of the principal portion of a blanket mounting apparatus in accordance with one embodiment of the present invention. FIG. 1 shows a state of a blanket cylinder before a blanket is mounted, FIG. 2 shows a state when the blanket is being mounted, and FIG. 3 shows a state when the blanket has been mounted. FIG. 4 is a side view of a blanket used in this embodiment, and FIG. 5 is a graph showing an effect achieved by this embodiment. Next, the configuration of an apparatus of this embodiment will be described. In FIGS. 1 to 4, reference numeral 10 denotes a blanket mounting apparatus in accordance with this embodiment, 1 denotes a blanket cylinder thereof, 2 denotes a blanket stretched around the blanket cylinder 1, 3 denotes a blanket mounting cylinder gap formed in parallel with the axis of the blanket cylinder 1, and 14 denotes a blanket reel bar provided at the bottom part of the cylinder gap 3. On the blanket 2 for the apparatus of this embodiment, as shown in FIG. 4, steel flat bars 15a on the leading edge side and 15b on the tail edge side are affixed to the leading edge 2a and the tail edge 2b at both ends, respectively. In the blanket mounting cylinder gap 3 on the blanket cylinder 1, as shown in FIG. 1, a notch 16, whose depth and width are equal to the width w and thickness t of the flat bar on the leading edge side of the blanket, respectively, is formed on the surface parallel with the radius r passing the center of the cylinder gap 3 along a leading edge opening 3a of the cylinder gap 3. The cylinder gap 3 is so formed that the apparent width B thereof on the blanket cylinder 1 including the width of the notch 16 at the leading edge opening 3a is equal to the maximum thickness of two blankets plus the thickness t of the flat bar 15a on the leading edge side. On one blanket reel bar 14 provided at the lower part of the cylinder gap 3, as shown in FIG. 1, a gap 17 is formed to insert the tail edge 2b of the blanket, and this reel bar is configured so as to be turned via a worm gear mechanism, not shown. For the blanket mounting apparatus 10 in accordance with this embodiment, since the above-described measures are taken, when the blanket 2 is mounted on the blanket cylinder 1, as shown in FIG. 2, the tail edge 2b of the blanket 2 is first inserted in the gap 17 of the blanket reel bar 14. Then, the leading edge 2a of the blanket 2 is inserted in the notch 16 formed at the leading edge opening 3a of the cylinder gap 3 on the blanket cylinder. At this time, the leading edge 2a is pushed into the notch 16 until the tip end of the leading edge flat bar 15a of the blanket 2 comes in contact with the lower face of the notch 16. Finally, the blanket reel bar 14 is turned in the arrow-marked direction via a worm gear, not shown, for tightening, so that the blanket 2 is stretched around the blanket cylinder 1. Thus, the notch 16 formed at the leading edge opening 3a of the cylinder gap 3 on the blanket cylinder 1 is blocked by the leading edge flat bar 15a of the blanket 2, so that as shown in FIG. 3, the leading edge 2a and the tail edge 2b of the blanket 2 come in contact with each other at the portion where the blanket 2 enters the cylinder gap 3. Therefore, the substantial width of gap on the blanket cylinder 1 is decreased by the thickness t of the leading edge flat bar 15a, becoming a dimension equivalent to the maximum thickness of two blankets, so that a state as if a filler with the thickness t of the flat bar 15a is inserted is established. As a result, the non printing length L produced by the gap width of the blanket cylinder can be decreased to a dimension equivalent to the maximum thickness of two blankets. By this decrease in gap width, a disturbing force generated when the cylinder. gap 3 on the blanket cylinder 1 meets the cylinder gap 3 of the mating cylinder cooperating with each other can be reduced significantly. FIG. 5 shows the relationship between the rotational speed of the blanket cylinder 1 and the response amplitude ratio. In this figure, × mark indicates the case of the above-described advanced type conventional blanket mounting apparatus 20, and O mark indicates the case of the blanket mounting apparatus 10 of the present invention. As is evident from FIG. 5, when the apparatus 10 of the present invention is used, the response amplitude ratio can be reduced by about 20% over the whole range of normal speed as compared with the conventional apparatus 20. Therefore, as the operating speed increases, the effect of decreased vibration increases. Thus, for the blanket mounting apparatus 10 in accordance with the present invention, the substantial gap width of the blanket cylinder 1 is decreased to shorten the non printing length L, and the vibration during operation is reduced significantly, by which high-quality printed matters without a printing trouble such as shock-streak can be obtained over the whole range of the used rotational speed of rotary press. The present invention achieves the following effects because the leading edge flat bar is inserted in the notch formed at the leading edge opening of the cylinder gap on the blanket cylinder. (1) The cylinder gap opening on the blanket cylinder is blocked by the leading edge flat bar of the blanket as if a filler is installed in the cylinder gap, so that the disturbing force caused by the meeting with the mating cylinder gap is reduced. Therefore, high-quality printing without a printing trouble such as shock-streak caused by vibration can be performed. (2) The non printing length caused by the cylinder gap on the blanket cylinder is shortened to a dimension equivalent to the maximum thickness of two blankets, approaching the width of the cylinder gap on the plate cylinder. Therefore, the printable area is increased, so that printed matters can be obtained efficiently. (3) When the tail edge of the blanket is inserted in the cylinder gap, the insertion work in the blanket reel bar is easy because the opening width of the cylinder gap is widened by the width of the notch. Also, the leading edge of the blanket is simply inserted in the notch. Therefore, the work for mounting the blanket is made easy. Therefore, the present invention provides a blanket mounting apparatus in which the non printing length is shortened by further decreasing the width of the cylinder gap on the blanket cylinder, and high-grade printing without a printing trouble such as shock-streak can be performed by decreasing the change in printing pressure, and moreover the operability is excellent.

Claims: A method for mounting a blanket (2) for a rotary press on a blanket cylinder (1) of a printing machine having blanket mounting apparatus of a type in which the blanket (2) has a flat bar (15a) fixed at each end thereof and a tail edge (2b) with the tail edge (2b) reeled by a blanket reel bar (14) provided at the lower part of a cylinder gap (3) of the blanket cylinder (1), a notch (16) along the leading edge opening of said cylinder gap (3) and inserting the leading edge flat bar (15) of said blanket into the notch (16) to mount said blanket around the blanket cylinder characterized in that the flat bar is attached to only a single side of the blanket at the leading edge thereof and the notch is formed on the surface of the blanket cylinder extending from its circumference in a direction parallel with the radius passing the center of the blanket cylinder gap and having a depth and width equal to the width and thickness of the flat bar at the leading edge such that upon inserting the leading edge flat bar (15a) into the notch (16) contact is made with the tail edge (2b) of the blanket and while in this state fixing the leading edge (2a) and the tail edge (2b) to one another by reeling the tail edge (2b) by the blanket reel bar (14). A method for mounting a blanket for a rotary press according to claim 1, wherein the gap width (B) including said notch formed at the leading edge opening of the cylinder gap on the blanket cylinder is equal to a dimension of the maximum thickness of two blankets plus the thickness (t) of the leading edge flat bar of the blanket.

Inventors: SHOJI YUKIKAZU, SHOJI, YUKIKAZU, Shoji, Yukikazu, Mihara Machinery Works
Applicants: MITSUBISHI HEAVY IND LTD, MITSUBISHI JUKOGYO KABUSHIKI KAISHA
Application year: 1997
Main classification: B41F30
IPC codes: B41F30, B41F13