GB2294662A

GB2294662A - A damping system for a printing press

Info

Publication number: GB2294662A
Application number: GB9522275A
Authority: GB
Inventors: Robert Ranft
Original assignee: Individual
Current assignee: Individual
Priority date: 1994-11-02
Filing date: 1995-10-31
Publication date: 1996-05-08
Anticipated expiration: 2015-10-31
Also published as: GB9522275D0; GB2294662B

Abstract

To control the actual coverage of damping fluid in a lithographic press more effectively, a linear motion slide 14, 16 carrying a jet nozzle 18 is traversed backwards and forwards on a guide rail 12 across the width of the press, and lengthwise of a roller 38, by a servo-motor. The jet nozzle 18 receives damping medium from a pump by way of a ring main 36 and a solenoid-operated on/off valve 32, and supplies it at a constant flow rate to the feed roller 38 in permanent peripheral contact with a distribution roller which transfers it to an associated plate. The jet nozzle 18 is operative in one direction of traverse, during which the speed of traverse of the slide 14, 16 can be programmed so as to differ selectively over different notional sections of the effective width of the press. In the other direction of traverse, the jet nozzle 18 is inoperative and the speed of traverse of the slide 14, 16 is fixed. <IMAGE>

Description

"A Damping System for a Printing Press" This invention relates to a damping system for a printing press of the lithographic type which requires two liquids, namely ink and a water-based damping medium.

In a conventional lithographic printing press, the damping medium is supplied to the surface of a printing plate by a damping system comprising a series of rollers.

More specifically, said system comprises a cloth-covered feed roller which is moveable cyclically by a cam mechanism between one position in which it mazes peripheral contact with a fountain roller and another position in which it makes peripheral contact with a distribution roller. The fountain roller rotates in a trough containing the damping medium, which is thus transferred from said roller to the feed roller, from the feed roller to the distribution roller, and from the distribution roller to the printing plate.

The conventional damping system outlined above has the serious disadvantage that it tends not to supply the damping medium in the required amounts across the width of the printing plate. This can occur due to many individual factors or combinations thereof, said factors p rticul including draught~, which can dry out the supply of ain medium to any section across the width of a printing press affected thereby; special demands of high aural it work where various forms are combined on one printing plate, for example large solid areas of ink combined with fine type or half tone; special demands associated with low quality inks or ultra-violet curing inks, which are more sensitive to the supply of damping medium than normal high quality lithographic inks and need fine tuning of the damping system across the width of a printing press; and wear in the cam mechanism and/or elsewhere in the damping system.

The object of the present invention is to provide a damping system which reduces or overcomes the aforesaid disadvantage.

According to one aspect of the invention, a method of supplying damping medium to a lithographic printing press comprises traversing a jet backwards and forwards across the width of the press.

The method preferably further comprises directing the jet onto a feed roller and maintaining said roller i.n permanent peripheral contact with a distribution roller.

Preferably, the method further comprises varying the speed of traverse of the jet.

Preferably, also, the method further comprises selectively changing the speed of traverse of the jet as it moves from one to another of notional sections into which the press is divided across its effective width.

According to another aspect of the invention, a damping system for a lithographic printing press comprises means for traversing a jet backwards and forwards across the width of the press.

The jet preferably supplies damping medium to a feed roller which is in permanent peripheral contact with a distribution roller.

Preferably, the speed of traverse of the jet is variable.

Preferably, also, the press is divided into notional sections across its effective width and the speed of traverse of the jet can differ selectively from section te section.

Preferably, the means comprise a programmable closed-loop-controlled linear motion slide unit.

Preferably, also, the slide unit is driven by a servc--motor.

Preferably, the jet is operative and its speed is variable in one direction of traverse, the jet being inoperative and its speed fixed in the other direct ion of traverse.

Preferably, also, the jet it supplied ty a pump circulating damping medium around a ring main containing a variable pressure regulator, the jet communicating with the ri main by way of a tube in which there is nt erposed a so 1 eno id-operated valve.

According to a further aspect of the invent ion, a lithcgrayhic printing press is provided as original equipment with a damping system according to any one of the preceding eight paragraphs.

Alternatively, a lithographic printing press is provided as a retro-fit with a damping system according to one of said eight paragraphs.

A preferred embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings of which: Figure 1 is a plan view of part of a damping system employing a traversing jet for a lithographic printing press; Figure 2 is a side elevation of said part on a larger scale showing one additional component; Figure 3 is an enlargement of a portion of Figure 2; and Figures 4, 5 and 6 are respective cross-sections on the lines 4-4, 5-5 and 6-6 in Figure 3.

Referring now to the drawings, a damping system for a lithographic printing press includes a base plate 10 formed of nylatron which is fixed to the press so as to etend over the full effective width thereof and has secured to it a linear motion slide unit comprising a guide rail 12 of square cross-section along which a slide 14 is arranged to be traversed backwards and forwards by a servo-motor (not shown). The slide 14 carries an elongated dy IC. formed of nylatron onto which there is screwed a stainless steel jet nozzle 18 with an outlet orifice having a diameter of, say, approximately 0.5 to 1 millimetre.The jet nozzle 18 is locked in place by a stainless steel assembly comprising a latch 20 on a pin which can be withdrawn manually by means of a ring 24 against the action of a spring 26 to enable said nozzle to be changed. Tie ;et nozzle 18 is connected by a bore 28 formed in the body 16 and a flexible tube 30 to an on/off valve 32 operated by a built-in solenoid and secured to the base plate 10. The bore 28 and the tube 30 each have an internal diameter of, say, 4 millimetres. The valve 32 iz connected by a T-piece 34 to ring main 36 formed of fleible tubing with an internal diameter of, say, 15 to 20 millimetres. A water-based damping medium is circulated around the ring main 36 by a pump (not shown), and a variable pressure regulator (not shown) interposed in the in main 36 enables the pressure in the system to be set at any value between, say, 2 and 10 pounds per square inch. The jet nozzle 18 and the valve 32 are arranged to direct the damping medium onto a feed roller 38 (see Figure 2! as said nozzle traverses in one direction across the width of the press. The feed roller 38 is in permanent pr:5heral contact with a conventional distribution roller (not shown), whereby the dampinG medium is transferred fr the feed roller 38 to the distribution roller and thence to the printing plate.The usual fountain roller, the trough in which it rotates, and the cam mechanism associated with the feed roller are thus no longer required.

A press having a width of, say, 1180 millimetres across the feed roller 38 is divided into, say, twenty equal notional sections of, say, 59 millimetres across its width, and the speed of traverse of the slide 14 across said width in said one direction can be caused to differ selectively from section to section by programmable closed-loop control means (not shown) for the servo-motor of the linear motion slide unit. Said control means can be programmed to increase or decrease a standard set speed of traverse by any selected amount up to, say, 50 per cent across any individual section. Thus, as the flow through the jet nozzle 18 is set at a constant rate, more of the damping medium will be supplied to sections in which the speed of traverse is slow than to sections in which the speed of traverse is fast.This makes it possible to vary the supply of the damping medium in such a way as substantially to obviate the effect of factors which would hitherto have resulted in said medium not being supplied in the required aunts across the width of the press and ic would have produced lithographic printing of poor quality. If the speed of traverse in said one direction iz set at the standard value for every section, the damping medium will of course be supplied to the feed roller 38 at a uniform rate, the time then taken to make a full traverse in said one direction being, say, 3 seconds. The same time is always taken to make a full traverse in the other direction, as the speed of traverse is then not variable but is fixed at the standard value. During traverse in said other direction, the flow of the damping medium to the jet nozzle 18 is cut off by the valve 32.

Typical but non-limiting litographic printing press widths are between, say, 508 and 1778 millimetres. Such a press can be provided with a damping system according to the invention either as original equipment or as a retro-fit.

In a modification, the programmable closed-loop control can be variable continuously instead of sect ion by section.

Claims

Claims:

1. A method of supplying damping medium to a lithographic printing press comprising traversing a jet backwards and forwards across the width of the press.

2. A method according to claim 1, further comprising directing the jet onto a feed roller and maintaining said roller in permanent peripheral contact with a distribution roller.

3. A method according to either of the preceding claims, further comprising varying the speed of traverse of the jet.

4. A method according to claim 3, further comprising selectively changing the speed of traverse of the jet as it moves from one to another of notional sect ions into which the press is divided across its effective width.

5. A damping system for a lithographic printing press comprising means for traversing a jet backwards and forwards across the width of the press.

6. A damping system according to claim 5, wherein the jet supplies damping medium to a feed roller which is in permanent peripheral contact with a distribution roller.

7. A damping system according to claim 5 or claim 6, wherein the speed of traverse of the jet is variable.

B. A damping system according to claim 7, wherein the press is divided into notional sections across its effective width and the speed of traverse of the jet can differ selectively from section to section.

9. A damping system according to claim 7 or claim 8, wherein the means comprise a programmable closed-loopcontrolled linear motion slide unit.

10. A damping system according to claim 9, wherein the slide unit is driven by a servo-motor.

11. A damping system according to any one of claims 7 to 10, wherein the jet is operative and its speed is variable in one direction of traverse, the jet being inoperative and its speed fixed in the other direction of traverse.

12. A damping system according to any one of claims 5 to 11, wherein the jet is supplied by a pump circulating damping medium around a ring main containing a variable pressure regulator, the jet communicating with the ring main by way of a tube in which there is interposed a solenoid-operated valve.

13. A lithographic printing press provided as original equipment with a damping system according to any one of claims 5 to 12.

14. A lithographic printing press provided as a retro-fit with a damping system according to any one of claims 5 to 12.

15. A method of supplying damping medium to a lithographic printing press substantially as hereinbefore described with reference to the accompanying drawings.

16. A damping system for a lithographic printing press constructed, arranged and adapted to operate substantially as hereinbefore described with reference to, and as illustrated by, the accompanying drawings.

17. A lithographic printing press provided with a damping system constructed, arranged and adapted to operate substantially as hereinbefore described with reference to, and as illustrated by, the accompanying drawings.