GB1576864A

GB1576864A - System for vacuum mounting blanket and printing plates in offset presses

Info

Publication number: GB1576864A
Application number: GB1942177A
Authority: GB
Original assignee: Livermore and Knight Co Inc
Current assignee: Livermore and Knight Co Inc
Priority date: 1976-05-10
Filing date: 1977-05-09
Publication date: 1980-10-15
Also published as: DE2720858A1; FR2350958A1; CA1080543A; JPS52138209A

Description

(54) SYSTEM FOR VACUUM MOUNTING BLANKET AND PRINTING PLATES IN OFFSET PRESSES (71) We, LIVERMORE AND KNIGHT CO., INC., a corporation of the State of Florida, United States of America, having a place of business at 225 Seabreeze Avenue, Palm Beach, Florida 33480, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- Rotary offset printing machines typically consist of a printing cylinder, blanket cylinder and impression cylinder rotating in operable engagement. Flexible printing plates are conformed and secured to the plate cylinder. The printing plates are rotated by the plate cylinder to first pass over form rolls of a dampening inking system and then apply the desired impression to a blanket which is secured onto and rotated with the blanket cylinder. The blanket can then transfer the impression to a sheet or web passed between the blanket cylinder and the impression cylinder.

As it can be readily appreciated, it is necessary for the plate cylinder and blanket cylinder each to be provided with means to clamp and hold the printing plate and blanket respectively. Under the conditions of commercial production, these cylinders are rotated at high speeds, and it is necessary that the plates and blankets be tightly and firmly secured to the surfaces of their respective cylinders. Consequently, the prior art has heretofore proposed many and varied arrangements and devices for firmly securing plates and blankets on the periphery of a cylinder.

Typically, mechanical clamping means are utilized to engage the ends of the plate or blanket and thereby secure them firrr1, on the cylinder surfaces. The mechanical clamping means are housed in a longitudinally extending groove formed in the cylinder surface. Inasmuch as the precise requirements for clamping a printing plate differ from those of clamping a blanket, prior proposals have often been directed to either one of these clamping problems. A reason for this is that printing plates are frequently changed in the course of a production day to print different material. On the other hand, the blanket is typically thicker than the printing plate and may be used continuously a change being required less frequently, as for example, when the blanket is distorted, damaged or wears out. As a result, the printing plate cylinder will require clamping means which facilitates easy mounting, while the blanket cylinder may incorporate a construction which allows a more permanent hold. Thus the design problems encountered generally differ in each case.

Representative of a prior proposal for a blanket cylinder clamping arrangement is United States Patent No. 3,893,394. The clamping means disclosed therein provides two substantially narrow slots for blanket clamping bars arranged within a longitudinally extending groove formed in the cylinder surface. This arrangement seeks to facilitate a uniform pulling of the blanket at its edge portions thereby preventing bulging or buckling of the trailing edge of the blanket at the point of impact with the printing plate in the region of the gap defined by the longitudinally extending groove.

The objectives of this prior proposal illustrate a significant problem in the rotary offset printing art. Specifically, the adverse effects resulting from the impact of the blanket and printing plate gap in the cylinder surface, formed to house the clamping means, passes between the rotating cylinders.

The United States patent indicates one problem, namely bulging or buckling of the blanket at the gap. However, even more troublesome drawbacks are engendered by a gap or discontinuity in the cylinder surface.

Most significant is the "bounce" effect between the rotating cylinders. As we described above, the cylinders rotate in operable engagement at high speeds and under considerable pressure. The gap or discontin uity in the cylinder surfaces cause a spacing to exist between the cylinders momentarily as they rotate. Thus, they come together at the gap and are thrust apart by the impact of the edge of the gap against the opposed cylinder surface. This is a highly undesirable situation in the rotary environment of the printing machine. Moreover, the form rolls of the dampening-inking system will also bounce as they pass over the cylinder gaps causing a vibrating condition to develop in the printing machine. The bounce of the cylinders and form rolls may result in streaks, smears or double dotting on the printed page.

In addition, the jerking motion and vibrations caused by the bounce puts a strain on the entire mechanism and may eventually lead to a break down or malfunctioning.

To compensate for the bounce effect, rotary printing machines typically include mechaniisms to apply additional pressure between the cylinders to iron out the bounce. These may involve complex and expensive mechanical arrangements thereby increasing the initial cost and maintence expense of the printing machines.

As one of its basic objectives, the present invention seeks to substantially eliminate this bounce effect and thereby greatly improve the operation of rotary offset printing machines. The solution to the problem is achieved in the elimination of cylinder surface discontinuities by a highly unique application of a vacuum operated cylinder construction.

It has been proposed heretofore to utilize vacuum means to retain printing plates in position on the printing cylinders. The advantages of a vacuum printing cylinder are evident, in that it greatly facilitates plate changing operation. As was mentioned previously, easy plate mounting is of importance in a printing cylinder design.

The present invention provides for the utilization of vacuum operated cylinders for both the printing plate cylinder and the blanket cylinder. The effective use of vacuum holding power to the exclusion of mechanical clamping means necessarily eliminates the requirement of a wide groove or gap in the cylinder surface to accommodate the clamp.

Moreover, the use of a vacuum-operated blanket cylinder substantially reduces many of the problems associated with blanket mounting. For example, the elimination of the blanket clamp obviates blanket distortion caused by streching, bulging or buckling at the mechanical clamp. In addition a shorter length is required in a vacuumoperated cylinder thereby resulting in cost savings for the blanket material. The use of a vacuum mount also facilitates a speedy blanket change.

The concept of a vacuum operated cylinder permits the construction of both cylinders free of surface discontinuities and their rotation in an opposed relationship is smooth for the entire revolution. The result obviates the negative characteristics inherent in rotary printing machines with mechanical clamping means and extends the advantages of vacuum mounting to the blanket. The only "gap" remaining is the spacing between contiguous ends of the mounted plate or blanket, which is minimal in comparison to even the narrowest clamping groove.

Examples of an entirely practical means for the utilization of vacuum to hold printing plates on a rotating cylinder have been proposed in United States Patent No.

4,005,653. In the various forms disclosed, vacuum power is effectively distributed to the cylinder surface by means of independently evacuatable chambers within the cylinder which are connected to the cylinder surface by appropriately distributed flow passages.

The utilization of independently evacuatable chambers permits the application of vacuum holding power to areas of the printing cylinder actually covered by the printing plate with a minimum of leakage. The features disclosed greatly improve the efficacy of vacuum holding means and enable their advantageous use under the conditions of day-to-day commercial operation. Moreover, the effectiveness of the vacuum holding power is improved to such a degree that the plates are held on the cylinder by vacuum alone, without the aid of mechanical clamping means. The present invention can be most effectively implemented by utilizing vacuumoperated cylinders of the general type proposed in the aforementioned patent.

For a clearer understanding of the above and other advantages of the invention reference should be made to the following detailed description of a preferred embodiment thereof and to the accompanying drawings.

Fig. 1 schematically illustrates a blanket-toblanket rotary offset printing machine incorporating features of the present invention.

Fig. 2 schematically illustrates a common impression rotary offset printing machine incorporating features of the present invention.

Fig. 3 is a longitudinal cross sectional view of a vacuum-operated cylinder utilized in the offset printing machine of the present invention.

Fig. 4 is an enlarged, fragmentary cross sectional view illustrating the rotational engagement of the printing plate cylinder and blanket cylinder according to the present invention.

Referring now to the drawings, there are illustrated two conventional arrangements for rotary offset printing machines. The present invention is, however, in no way limited to these particular arrangements, which are included to demonstrate two examples of the application of the present invention. The inventive concept disclosed herein will be equally applicable to any other conventional arrangement of a rotary offset printing machine.

Attention should be initially directed to Fig. 3 which illustrates the construction of a vacuum-operated cylinder. According to the present invention, this particular form of construction is advantageously applied to both the plate cylinder and blanket cylinder of a rotary printing machine. The reference numeral 10 designates generally an elongated shaft assembly of a length suitable to extend through the entire length of a cylinder sleeve 11. The shaft assembly 10 extends sufficiently beyond the cylinder sleeve 11 to provide bearing supports (not shown) by means of which the shaft 10 is supported in a printing press in a conventional and well known manner. The shaft 10 includes a tubular central section 10a arranged to provide a pre-evacuation chamber 12. A pair of bearing shaft sections 13, 14 are securely mounted within the ends of the tubular shaft section 10a to close off the ends of the pre-evacuation chamber 12. An evacuation passage 15 runs internally of the shaft 10 from one end thereof to the bearing section 14 and communicates with the preevacuation chamber 12. The outer end of the passage 15 is arranged to be connected by an appropriate rotary coupling (not shown) to a vacuum pump.

A plurality of supporting rings 16-18 are axially applied over the shaft 10 from the ends thereof and can be secured to the shaft 10 by welding. The supporting rings 16-18 divide the annular region between the cylinder sleeve 11 and shaft 10 into separate vacuum chambers 20-23.

Extending between the cylinder sleeve 11 and the shaft 10 are a pair of end plates 24, 25 which can be welded to the sleeve and shaft 10, as reflected at 42. Each end plate 24, 25 is provided with independently valved passages to facilitate selective vacuum communication between each of the separate vacuum chambers 20-23 and the preevacuation chamber 12. The construction of each end plate 24, 25 is identical and for convenience the detailed description will be made with reference to the end plate 25.

As reflected in Fig. 3, the end plate 25 is provided with dead ended radially disposed bores 26. Blind transverse bores 27 communicate with bores 26 and open to the vacuum chamber 23 adjacent the end plate 25. The open end of each bore 27 is enlarged and threaded to receive a union fitting 28 within the vacuum chamber 23. The union fittings 28 are connected to a section of tubing 29 running internally of vacuum chamber 23 to a union fitting 30.

An elbow shaped connector 31 is connected to each union fitting 30 and is received in a bore 32 cut through shaft 10 to the preevacuation chamber 12. A plurality of transverse bores 33, 33a extend through the end plate 25 and communicate with one of the bores 26 respectively at a point spaced from blind bore 27.

To provide selective vacuum communication between the chamber 23 and the pre-evacuation chamber 12, the left hand side or internal opening of the transverse bore 33 communicates directly with the chamber 23. The right hand side or outer opening of transverse bore 33 is enlarged and threaded to receive a valve plug 34 whereby vacuum communication between the chamber 23 and the bore 26 can be established and interrupted.

Selective vacuum communication between the vacuum chamber 22 and the preevacuation chamber 12 can be achieved in a similar manner. The left-hand side or internal opening of tranverse bore 33a is enlarged and threaded to receive a union fitting 35. A section of tubing 36 is connected to the union fitting 35 and runs internally of the vacuum chamber 23 to a union fitting 37. The union fitting 37 is received in a bored passage 38 cut through the support ring 18 which separates chambers 22 from chamber 23. The right hand side or outer opening of transverse bore 33 is enlarged and threaded to receive a valve plug 34a.

As was discussed above, selective vacuum communication between the chambers 20, 21 pre-evacuation chamber 12 is achieved by an identical arrangement of valve plugs, bored passages and tubing in the end plate 24 and vacuum chamber 20. In this manner each vacuum chamber 20-23 selectively communicates with the pre-evacuation chamber via the combination of bored passages and tubing.

To provide vacuum communication between the vacuum chambers 20-23 and the exterior surface of cylinder sleeve 11, a plurality of appropriately distributed radial bores 39 are formed in the sleeve 11.

The cylinder sleeve 11 is provided with a series of continuous annular grooves 39a spaced across the entire working surface of the sleeve 11. Each of the radial bores 39 communicates with one of the continuous annular grooves 39a to provide a highly effective vacuum communication between the surface of the sleeve 11 and a mounted printing plate or blanket. At a selective point on the cylinder surface, a longitudinally extending groove 40 is formed in the cylinder sleeve 11. (Fig. 4). A soft metal strip 40a can then be tightly received in the groove 40 to form a continuation of the cylinder surface and at the same time interrupt the annular grooves 39a to form a circumferential discontinuity in each of the grooves 39a.

The longitudinally extending groove 40 can also serve as a locating line to facilitate easy mounting of a printing plate or blanket.

For example, a scribed line or the like may be formed in the metal strip 40a to serve as the locating line. Moreover, the ends of the mounted printing plate or blanket will overlay the groove 40 to prevent vacuum leakage, as illustrated in Fig. 4.

In the operation of the cylinder assembly of Fig. 3, the pre-evacuation chamber 12 is evacuated by means of a vacuum pump connected to the evacuation pipe 15. In a typical case, a flexible printing plate or blanket is cut to a suitable size to nearly cover the entire operating surface of the cylinder in the circumferential direction. The plate or blanket extends from the groove 40 around the cylinder to a point as close as possible to the groove 40. To apply the vacuum holding power of the pre-evacuation chamber 12 to the cylinder surface one or more of the valve plugs 34, 34a in the end plates 24, 25 are opened in accordance with the longitudinal dimension of the printing plate or blanket to provide selective communication between the vacuum chambers 20-23 and the pre-evacuation chamber 12. The vacuum holding power of the preevacuation chamber 12 will be immediately applied to partially evacuate the separate chambers 20-23 and provide an initial hold on a printing plate or blanket. A full vacuum hold will be developed by the vacuum pump via the pre-evacuation chamber 12.

While the present invention utilises vacuum cylinders it is not limited to this particular form of vacuum cylinder construction, the effective operation of this arrangement lends itself to achieve optimum results in the application of the inventive concept disclosed herein. Following are two examples illustrating the utilization of the abovedescribed vacuum-operated cylinder in conventional rotary printing machines according to the present invention.

Referring now to Fig. 1, there is shown a blanket-to-blanket offset printing unit. This is a well known arrangement to simultaneously print an impression on both sides of a web 56. Two ink supplies 41, 41' are each mounted in communication with a rotating roller 42, 42' which transport the ink via rollers 42-50 and 42'-50' to the ink feed rollers 51, 52 and 51', 52' respectively. The ink feed rollers 51, 52 and 51' and 52' are arranged to rotate in operational engagement with a vacuum-operated printing plate cylinder 53, 53' and thereby apply ink to a rotating printing plate secured to the cylinder 53, 53'.

A dampener form roll 64, 64' is also provided to dampen each of the printing plate cylinders 53, 53'.

In accordance with the present invention, the printing unit is provided with a pair of vacuum-operated blanket cylinders 55, 55' rotating in operational engagement with each other and with plate cylinders 53, 53' respectively. In this manner, each blanket cylinder 55, 55' can act as an impression cylinder for the other. A web 56 can then be passed between the two blanket cylinders 55, 55' to receive a printed impression on both sides thereof.

In a similar manner, the teachings of the present invention can be applied to a common impression offset printing unit, as illustrated in Fig. 2. This arrangement is used to simultaneously print two or more impressions on the same side of a sheet of paper, as for example in a two colour print.

Inking systems 57, 57' are provided to each apply ink to a pair of ink form rolls 65, 66,65', 663 which are in operational engagement with the vacuum-operated printing plate cylinders 58, 58' respectively. Moreover, dampener form rolls 67, 67' are provided to dampen each of the printing plate cylinders 58, 58'.

The plate cylinders 58, 58' rotate in operational engagement with complementary vacuum-operated blanket cylinders 59, 59' The blanket cylinders 59, 59' are arranged to rotate in operational engagement with a common impression cylinder 60. A paper web (not shown) can be passed between the impression cylinder 60 and each of the blanket cylinders 59, 59' for a double impression.

With respect to both of the presses of Figs. 1 and 2, attention should be directed to Fig. 4, which clearly illustrates advantages of the present invention. Fig. 4 demonstrates the operational engagement between any of the plate cylinders 53, 53', 58, 58' of the presses of Figs. 1 and 2 and their complementary blanket cylinders 55, 55', 59, 59'.

In accordance with the description of the operation of the vacuum cylinder assembly set forth above, a printing plate 62 and blanket 63 can be secured to their respective plate cylinders 53, 53', 58, 58', and blanket cylinders 55, 55', 59, 59'. According to the present invention, vacuum cylinders are utilized for both the plate and blanket cylinders. As reflected in Figs. 1 and 2, each cylinder may be of the type previously described. They comprise a shaft 10 provided with a pre-evacuation chamber 12 and surrounded by a cylinder sleeve 11.

Since the plate and blanket are held on respective cylinders by vacuum alone, the entire operating surface of the cylinders can be formed to a smooth finish. The only surface discontinuities will be the narrow gap between contiguous ends of the mounted printing plate 62 or blanket 63. In a typical case, the length of the plate 62 or blanket 63 can be cut so that their ends overlay the longitudinal groove 40 and define a gap which need not be more than about 30 mils wide. Moreover, the depth of the gap will be equal to the depth of the plate or blanket, which are commonly in the order of 7-15 mils for plates and 60-80 mils for the blanket.

Thus, the "gap" between the rotating cylinder will be of minimum, almost insignificant, dimensions.

Ideally, the rotation of the plate cylinder and blanket cylinder should be synchronized so that the gaps between the ends of each of the plate and blanket are aligned and synchronized. This will minimize the impact of plate or blanket ends against the opposed cylinder surface and provide smooth cylinder surfaces for substantially the entire revolution of the cylinders. In this regard synchronization of the cylinders will require that each of the plate and blanket cylinders be of the same diameter or multiples thereof.

The arrangement provided by the present invention greatly diminishes the customary bounce effect by substantially eliminating surface discontinuities and thereby improves the operation of all rotary offset printing machines.

WHAT WE CLAIM IS: 1. Rotary offset printing machine apparatus comprising a printing plate cylinder and a blanket cylinder rotating in opposed pressure-bearing relation with said printing plate cylinder, characterized by said printing plate cylinder and said blanket cylinder each comprising a shaft and a cylinder sleeve surrounding and supported on said shaft to form a cylindrical structure wherein the annular region between said shaft and said cylinder sleeve forms a vacuum chamber, first air passage means connected to each of said vacuum chambers for application of vacuum thereto, and second air passage means in each of said cylinders to provide vacuum communication between said vacuum chambers and the exterior of said cylinder sleeves to enable a printing plate to be secured to the printing plate cylinder and a blanket to be secured to the blanket cylinder by vacuum power alone, so that the surfaces of said printing plate and said blanket when secured to their respective cylinders each provide a smooth finish over substantially the entire circumference of the cylinders.

2. The apparatus of claim 1, further characterized by a printing plate being mounted on said printing plate cylinder and secured by the vacuum holding power of the second air passage means of said printing plate cylinder, a blanket being mounted on said blanket cylinder and secured by the vacuum holding power of the second air passage means of said blanket cylinder, and said printing plate and said blanket each being formed to a length suitable to extend around the cylinder surface whereby the contiguous ends of each of the mounted printing plate and blanket are closely adjacent thereby defining a narrow gap between said contiguous ends.

3. The apparatus of claim 2, further characterized by said printing plate cylinder and said blanket cylinder each having a diameter of equal length or multiples thereof, and the rotation of said printing plate cylinder being synchronized with the rotation of said blanket cylinder, whereby the gaps between the contiguous ends of said mounted printing plate and said mounted blanket are aligned.

4. The apparatus of claim 1, further characterized by printing plate means mounted on said printing plate cylinder, and secured by the vacuum thereof, and blanket means mounted on said blanket cylinder and secured by the vacuum thereof, and said printing plate means and said blanket means each being arranged and configured on their respective cylinders to minimize surface discontinuities.

5. Rotary offset printing machine apparatus substantially as herein described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. wide. Moreover, the depth of the gap will be equal to the depth of the plate or blanket, which are commonly in the order of 7-15 mils for plates and 60-80 mils for the blanket. Thus, the "gap" between the rotating cylinder will be of minimum, almost insignificant, dimensions. Ideally, the rotation of the plate cylinder and blanket cylinder should be synchronized so that the gaps between the ends of each of the plate and blanket are aligned and synchronized. This will minimize the impact of plate or blanket ends against the opposed cylinder surface and provide smooth cylinder surfaces for substantially the entire revolution of the cylinders. In this regard synchronization of the cylinders will require that each of the plate and blanket cylinders be of the same diameter or multiples thereof. The arrangement provided by the present invention greatly diminishes the customary bounce effect by substantially eliminating surface discontinuities and thereby improves the operation of all rotary offset printing machines. WHAT WE CLAIM IS:

1. Rotary offset printing machine apparatus comprising a printing plate cylinder and a blanket cylinder rotating in opposed pressure-bearing relation with said printing plate cylinder, characterized by said printing plate cylinder and said blanket cylinder each comprising a shaft and a cylinder sleeve surrounding and supported on said shaft to form a cylindrical structure wherein the annular region between said shaft and said cylinder sleeve forms a vacuum chamber, first air passage means connected to each of said vacuum chambers for application of vacuum thereto, and second air passage means in each of said cylinders to provide vacuum communication between said vacuum chambers and the exterior of said cylinder sleeves to enable a printing plate to be secured to the printing plate cylinder and a blanket to be secured to the blanket cylinder by vacuum power alone, so that the surfaces of said printing plate and said blanket when secured to their respective cylinders each provide a smooth finish over substantially the entire circumference of the cylinders.