GB2177050A - Wed-fed printing press - Google Patents

Abstract

A printing press incorporates a unit comprising a plate cylinder 3, a blanket cylinder 6 and an impression cylinder 11 with mechanism which can move the blanket and impression cylinders relative to the plate cylinder with corresponding alteration to the web path so that the unit will print on one or the other side of the web. For example, web 37 may receive impressions from two opposed blanket cylinders 6 with impression cylinders 11 tripped out of action (Figure 9). In other embodiments, Figures 5 to 8, the units may operate in conjunction with a common impression cylinder for multi-colour printing on a single side of a web, or provide perfecting functions using the impression cylinder of the unit. The unit is preferably in the form of a cassette containing interlinked eccentrics for the cylinder trips, the cassette being independent of inking and damping mechanisms and being exchangeable for others of different print repeat length. Necessarily, the drive to the cassette should be reversible. <IMAGE>

Description

SPECIFICATION Improvements in web fed printing presses The present invention relates to web fed printing presses.

An objectofthe present invention is to provide a simple means for selectively printing multi coloured printing on one side of a web or perfect printing, that is printing on both sides oftheweb.

A particular application of the present invention is to a business forms press to give itthefacilityfor selection of multi colour or perfect printing. Such a press can have the invention incorporated into a cassette which can be readily exchanged for cassettes of a different print length. In such an arrangement when applied to a lithographic press the ink and dampening systems remain as fixtures on the printing press mainframe and cassettes of selected print repeat length are inserted into the press and use the common ink and dampening system for each cassette irrespective of its print repeat length.

In one example of printing press three such cassettes are fitted spaced around a common impression cylinder. Each cassette includes its own plate and blanket cylinder. Two of the cassettes will be similar, each applying asinglecolourtothewebpassing between its blanket cylinder and the common impression cylinder, the third cassette has a plate and blanket cylinder, but also its own impression cylinder which can selectively be brought into contact with the associated blanket cylinder, which at the same time is brought out of contact with the common impression cylinder.

This selection of impression cylinders enables a third colourto be applied to one side of the web or by selection applyacolourtothe reverse side oftheweb.

Although conventionally a three colour unit is supplied, a two orfourcoloursystem can be obtained with two cassettes with their own impression cylin dersgiving in the latter instancethefacility of printing four colours on one side of a web, three colours on one side and one on the reverse side of the web ortwo colours on one side oftheweb and two colours on the reverse side.

The actual number of units to be assembled in a complete press is immaterial to the concept of the invention.

According to the present invention a printing press unit includes a plate cylinder, a blanket cylinder and a first impression cylinderwith associated ink and dampenerfountaintrains provided with means whereby the blanket cylinder can selectively be brought on and off impression with the plate cylinder, on and off impression with the first impression cylinder and on and off impression with a second impress ioncylinderorwith averticallyorhorizontally opposed second blanketcylinderwherebytheblanket cylinderwill impartthe image on its blanket to one side of a web when the web is passed between the blanket cylinder and the first impression cylinder or on the reverse side ofthe web when the web is passed between the blanket cylinder and the second im pressioncylinderorsecond blanketcylinder.

The invention also includes a printing press unit having a plate cylinder, a blanketcylinderand an impression cylinder mounted in side frames to form a cassette capable of insertion and removal from a mainframe, the cassette supporting mechanism selectively to move the cylinders whereby the blanket cylinder can be moved on and off impression relativelyto the plate cylinder and to the impression cylinder and on and off impression to a second impression cylinder or a second blanket cylinder horizontally or vertically opposed thereto whereby the blanket on the blanket cylinder imparts its image to one side of a web when in contact with the second impression cylinder or second blanket cylinder or on the reverse side ofthe web when the blanket cylinder is in contact with the first impression cylinder.

Likewise according to the present invention a printing press unit includes a plate cylinder, a blanket cylinder and an impression cylinder mounted in side frames to form a cassette capable of insertion and removal from an associated inking and dampening train retained within a mainframe, the cassette sup- porting mechanism selectively to move the cylinders whereby the blanket cylinder can be moved on and offimpression relativelytotheplatecylinderandto the impression cylinderand on and off impression to a second impression cylinderwherebythe blanket on the blanketcylinderwould impart its image to one side of a web when in contact with the impression cylinder ortothe reverse side of the web when the blanketcylinderisincontactwiththesecond im- pression cylinder.

In the accompanying drawings; Figure lisa front elevation of a printing unit cassette Figure2isa rearelevation oftheend plateand hanger of a printing unit cassette Figure 3 is a sideviewtaken on iii-iii Figure 1 a pneumatic cylinder being omitted for clarity Figure 4 is a side viewtaken on iv-iv Figure 1 Figures 5and 6 are diagramatic views showing respectively howthree colour printing on one side of a web is obtained and how two colours on one side of a web and one colour on the reverse side of a web is obtained Figures 7and 8 are diagramatic views showing respectively how four colour printing is obtained on one side of a web and how two colours on one side of aweb and two colours on the reverse side oftheweb is obtained Figures 9 and 10 are diagramaticviews showing an application ofthe invention to a press enabling two colours to be applied to both sides of a web, Figure 9 orthree colours on one side oftheweb and one colour on the reverse side of a web, and Figure 11 shows a diagramaticgeartrain driveto a print unit.

In the drawings, Figures 1 to 4 show an application of the invention to a printing press with a common impression cylinderaroundwhich are located cassettes each containing the printing couple, that is a plate cylinder, a blanket cylinder, and an impression cylinder.

Conveniently the cassette is capable of interchange with another having a different diameter of plate cylinder enabling a printer to select repeat print lengths by the selection of a cassette with cylinders of suitable diameter.

The blanket cylinder is the same diameter as the plate cylinder or a complete multiple of it, that is, exactly twice the plate cylinder diameter and so on.

The diameterofthe impression cylinder is the same as that ofthe plate cylinder.

Inking and dampening systems, shown diagramatically in Figures 5 and 7 are common to each cassette and are mounted within the side frames of the press.

The geometry of the ink and dampening systems and ofthe cassettes is such that the plate cylinder is inked and dampened irrespective of the diameter of that cylinder.

Itwill be appreciated thatthe invention is not limited to web offset lithographic presses but is equal ly applicable to dry offset web presses orflexographic web presses and the like.

The invention can also be applied to web presses which are not of the satellite type as schematically shown in Figure 9 and 10 in which two colours may be applied to each side of a web as it passes between two opposed blanket cylinders of a conventional perfect printing unit orwhen passed through opposed units according to the invention or when passed through opposed units according to the invention can apply colour to both sides ofoneweb or can selectively apply two colours to one side of one web.

Referring to Figures 1 to 4there is shown one end of a cassette adapted to be fitted to a satellite press diagramaticallyshown in Figures5to8.

The other end of the cassette (not shown) includes drive gearing which can be selectively engaged to drive the plate, blanket and impression cylinders in the appropriate required direction as will be hereinafter described. To effect this change and electromagnetic clutch may be incorporated selectively to engage an inputdrive orspurfrom the inputgear reversing the direction of that input drive to the plate cylinder.

The cassette comprises two side frames, only one of which, 1, is shown. For the sake of clarity cross ties between the two side frames have been omitted.

The side frame 1, carries a bearing forthe journal 2 of a plate cylinder 3. The other side frame is a mirror image ofthe side frame 1 and it carries the bearing for the other end ofthe plate cylinder journal. The plate cylinder includes any form of plate lock-up mechanism, not shown.

Incorporated at the end ofthejournal 2, ofthe plate cylinder3, is an axial adjustment mechanism generally designated 8 of known kind, by which rotation of the boss 9 moves the plate cylinder axially relatively to the side frames.

A hanger4 is carried on thejournal 2 on the inside ofthesideframe 1.

The hanger4carries an eccentricbearing7sup- porting a journal 5 of a blanketcylinder6.

Journal Softhe blanketcylinder6extendsthrough a large bore lOin the side frame 1,the bore 10 being of such diameter as to allow free movement ofthe journal within the throw ofthe eccentric bearing 7.

The blanket cylinder 6 includes any conventional blanket lock-up device, not shown, or the blanket may be stuck on to the blanket cylinder. The blanketcylinder may be adapted to carry the blanket retaining meanswhich form the subject matterofthe U.K.

Application for Patent 8515159.

An impression cylinder 10 has its journal 12 carried in an eccentric bearing 13 located in the side frame 1.

Secured to the end ofthe eccentric bearing 13 is a cog wheel 14 meshing with a small cog 15 carried on a shaft 16 passing through the side frame 1 and extend ing across the cassette.

Secured to the small cog 15 is an arm 17to which is releasablycoupledtherod 18 of a doubleacting pneumatic cylinder secured to the main frame ofthe press, not shown.

The coupling ofthe rod l8tothe arm 17 is of known quick engagementi disengagement type as the rod 18 has to be uncoupled from the arm 17 whenever itis required to remove a cassette from the printing press.

The shaft 16 passes through a slot 24 in the hanger 4to allow pivotal movement of the hanger about the journal 2 ofthe plate cylinder 3.

Asecond cog wheel 20 is pinned to the shaft 16 on the inside ofthe hanger 4. This second cog wheel 20 meshes with a cog wheel 21 secured to the eccentric bearing 7 carried by the hanger 4.

A hand lever 21 is pinned to a shaft 22 which passes through the side frame 1 and has secured thereto an eccentric 23 carried in the side frame 1. The shaft 22 extends across the width ofthe cassette. The shaft 22 also passesthroughthe hanger 4.

Movementofthe handle 21 thus imparts rotational movement to the eccentric 23 and rocks the hanger4 an amount equal to the throw of the eccentric 23.

From the foregoing twill be seen thatthe impression cylinder 11 and the blanket cylinder 6 are carried in eccentrics and capable of independent within the degree of the throws oftheir eccentrics. The plate cylinder3 does not move relatively to the othertwo cylinders.

The operation of these various cylinders can be more clearly seen with reference to the diagramatic layouts shown in Figures 5 and 6.

Referring specifically to Figure 5 a three colour press is shown in which printing couples, generally designated 30,31 and 32 are spaced around a common impression cylinder 33.

Printing couples 30,31 include respectively a plate cylinder 301,311, a blanket cylinder 302,312, an ink train 303,313 and reservoir 304, 314, which may be of known type, a dampening system 305,315, including a water tray 306,316, which may also be of known type.

Wash up units, not shown, may be applied if desired.

Although printing couple 32 may be carried between the main side frames of the press it is convenientlythe unit hereinbefore described, including the side frame 1 supporting the plate cylinder3 blanket cylinder6 and impression cylinder 11.An inktrain 321 includes an ink reservoir 322 and a dampening train 323 includes a watertray324.

Waterforthe water tray 306,316, and 324 can be circulated by known means, not shown.

Web guide rollers 34,35,36, are located between the main side frames not shown, of the complete press. The printing couples 30 and 31 and the inking systems 321 and the dampening system 323 are all carried by the main side frames, not shown, ofthe complete press, these side frames also carry guide rails and supports, not shown, for the side frames 1 of the cassette, which can be slidden through a hole in one ofthe main sideframes.

If desired the plate and blanket couplets 301,302 and 311,312 can also be separately mounted in separate side frames to form interchangeable size cassettes for exchange of a cassette with cylinders of a different diameter to those just removed, the cassettes capable of being slidden into and out ofthe main side frame of the press.

Aweb37isfedfrom a reelstand, notshown,prefer- ably through an infeed system, not shown, passes round the web guide roller 34 and around a common impression cylinder 33, round the web guide roller35 and from there to the next processing unit,forexam- plea folderorsheeteror perforating unitorthe like.

In its passage round the common impression cylinder 33 the web 37 receives its first colour print from the blanket on the blanket cylinder 302; its second colourprintfromthe blanket on the blanket cylinder 312 and its third colour applied from the blanket on the blanket cylinder 6. All three colour printings will be on the same side of the web.

When it is desired to printtwo colours on oneside ofthe web and one other on the reverse side ofthe web the system shown in Figure 6 is used. In Figure 6 the inking and dampening trains have been omitted for clarity.

The same reference numberals are used in Figure 6 as in Figure Sto identify identical parts.

The web 37 receives its first colour print from the blanketoftheblanketcylinder302; its second colour print from the blanket on the blanket cylinder312 both first and second colours being on the same side ofthe web, and the web then passing between the blanket cylinder 6 and the impression cylinder 11 so thatthe blanket on the blanketcylinder6 prints the third colour on the reverse side of the web.

To obtain the various selections of which side print is applied to the web, Figure 1 shows the cassette with the impression cylinder 11 out of engagement with the blanket cylinder 6 but on impression with the plate cylinder3 and common impression cylinder 33.

In this position the position ofthe various cylinders equates to that shown in Figure 5, namely that the cassette 32 is adding the third colourto the same side of the web as the previous two printing couples 30 and 31.

The piston rod 18 ofthe cylinder 19 is in the in or retracted position and the lever 21 is parallel with the piston rod 18.

When the cylinder 19 is energised it moves the rod 18to the left, Figure 1, swinging the arm 17 to rotate the shaft 16 thereby rotating the cog wheels 15 and 20. Rotation of the cog wheel 16 drives the cog wheel 14 and with itthe eccentric 13 which in turn lifts the impression cylinder 11 to the maximum height ofthe throw of the eccentric 13. The impression cylinder is therefore right out of the way of the blanket cylinder 6.

Rotation of the cog wheel 20 causes rotation of the cogwheel 21 meshing with itandthis rotatesthe eccentric 10 carried in the hanger4causing the blanket cylinder 6 to move away and out of contactwith plate cylinder3 and also out of contact with thecommon impression cylinder 33.

Movementofthe piston rod l8ofthecylinderl9 thus brings the blanket cylinder6 offand on impression with the plate cylinder 3 and common impression cylinder 33.

In this modethe impression cylinder 11 is out of contact with the blanket cylinder 6.

When it is desired to print on the reverse side ofthe web the piston rod 18 is in the fully retracted position sothatthe blanket cylinder 6 is in engagementwith the plate cylinder3 and the lever 21 is swung through 90 degrees to rotate the shaft 22 and eccentric 23.

Rotation of the eccentric 23 causes the hanger 4to swing aboutthe plate cylinderjournal 2and liftsthe blanketcylinder6 out of contactwith thecommon impression cylinder 33 and into contact with the impression cylinder 11. In this position an inked image from the plate cylinder3istransferred tothe blanket ofthe blanketcylinder6 and on to the web 37 which passes between the blanket cylinder 6 and the impression cylinder 11.

The blanket and impression cylinders can be moved on and off impression in this mode by operation ofthe cylinder 19 which when the rod 18 isex- tended will lift the impression cylinder 11 to the maximum throw of the eccentic 13 and out of contact with the blanket cylinder 6 and the blanket cylinder 6 outof contact with the plate cylinder3 by the rotation of the cog wheels 15 and 20 as already described.

Itwill beappreciatedthatwhentheblanketcylinder 6 is on impression with the common impression cylinder 33 it will be rotating in one direction and that that direction will be reversed when the blanket cylinder is on impression with the impression cylinder 11.

Asimplegeartrain mechanism foreffecting this is shown schematically in Figure 11 in which the gears are mounted at the opposite side of the press to the control mechanism shown in Figures 1 to 4.

A main drive gear 38 meshes with an input gear39 which in turn meshes with an intermediate gear 40 and a plate cylinder drive gear 41. The cylinder drive gear 41 drives the gears 43,44 respectively ofthe blanket cylinder 6 and impression cylinder 11.

To drive gear41 is secured to the journal ofthe platecylinderand is carried in bearingsfixed in either the side frame of the cassette if the press is provisioned for exchangeable cassettes or in the main sideframe ofthe press if not. The main drive gear38 is rotatablycarried by an eccentric in the main side frame ofthe press.

The spindles of the cog wheels 39 and 40 are carried bya hanger,notshown,which is pivotally mounted at point42 to the main side frame of the press. The hanger can be pivoted about point 42 by means such as a solenoid, not shown.

When it is desired to printthree colours on one side ofthe web the gears 39,40 are engaged as shown in full lines in Figure 11.

Clockwise, Figure 11, drive of the main drive gear 38 imparts anticlockwise drive to the i m put gea r 39 and hence clockwise drive to the plate cylinder gear 41 .The intermediate gear40 is driven by the imput gear39 and takes no partintransmitting drive in this mode.

When it is desired to print on the reverse side ofthe web, the hanger is swung about its pivot point 42 bringing the gears to the position shown in dotted lines in Figure 11. The input gear 39 disengages from the plate cylinder gear 41 and intermediate gear40 engagesthe plate cylinder gear41.Asthe hanger is swung so the eccentric carrying the main drive gear 38 rotates to allow passage of the teeth of the gear 39 to pass overtheteeth of gear to this new position.

The direction of drive of the gears 38,39 and 40 remain the same but the engagement ofthe intermediate gear 40 with the plate cylinder gear 41 drives that gear41 in the opposite direction.

As shown in Figures 7 and 8the invention can also be applied to presses capable of printing morethan three colours, for example three colours on one side of one web and one colouron the reverse,fourcolours on one side of one web ortwo colours on both sides of a web.

Referring to Figure 7 the same reference numerals are used as in Figure Sto indicate identical parts. An additional printing couple 45 is located peripherally ofthecommon impression cylinder33 this couple having an inktrain 451, ink reservoir452 and adam- penertrain 453 and a water tray 454. This cou ple 45 as regards plate blanket and impression cylinders is a mirror image ofthe same couple located above it.

The web 37 passes round the web guide roller34 and around the common im pression cyiin der 33 du r- ingwhich passagethe printing couples30,31,32and 45 each print their respective colours on to the same side ofthe web. The web 37 then passes on to the next operative stage via the web guide roller 35.

Obviously one or more ofthe printing couples can be taken off impression if less than four colours are required to be printed.

In Figure 8 there is shown a diagramatiswebbing layout four printing two colours on each side of a web.

Forthe sake ofclaritythe ink and dampening trains have been omitted.

Theweb isfed on tothe common impression cylin der33 via the web guide roller34 and passes printing couples 30,31 which imparttwo colours to one side of the web.

The blanketcylinders6Ofthe printing couples32, 45 are taken off impression with the common impression cylinder 33 and into engagement with their own impression cylinders 11. The web 37 passes be tweenthe blanket cylinders 6 and impression cylinders11 and, after passagethough printingcouple32 has one colour printed on the reverse oftheweb.

The web 37 is then passed over web guide roller 36, anotherweb guide roller 50 and between the blanket cylinder 6 and impression cylinder 11 of the printing couple 45 having a second colour imparted thereto on the reverse of the web.

The web then passes overthe web guide roller35 and in to the next stage of processing.

Various combinations can be selected from this arrangement,for exampie three colours on one side of a web and one on the reverse side can be obtained by running the web through the printing couples 30, 31 and 32to impartthree colours to one side ofthe web leavingthe common impressioncylinder33to pass around the web guide roller 50 and then back between the impression cylinder 11 and blanketcylinder 6 ofthe printing couple 45, and from thence via the web guide roller 35to the next operational station.

Afurther example ofthe invention is shown in Figures 9 and 10 applied to a printing press having one or more spaced printing couples each capable of perfect printing.

Forthe sake of clarity the ink and dampening systems have been omitted.

A printing couple generally designated 51 comprises plate cylinders 52,53 and blanket cylinders 54,55.

This couple may be horizontally orvertically spaced from one or more similar or identical printing couples each capable printing a colouronthewebpassing .between their blanket cylinders.

The printing couple 51 may have interchangeable size cassettes for the plate and blanket cylinders.

A printing couple generally designated 56 has a vertically or horizontally opposed plate cylinders 3, blanket cylinders 6 and impression cylinders 11.

In the mode shown in Figure 9 the webs 37 pass between the opposed blanket cylinders 6 and is per fect printed with a colour on each side oftheweb.

The mechanism for putting the blanket cylinders 6 on and off impression is the same as that previously described with regard to a common impression cylinder,the only difference being thatthe blanket cylinders ofthe opposed unit is in place ofthe common impression cylinder.

If it is desired to print three colours on one side of a web and one colour on the reverse the arrangement shown in Figure 10 may be used.

Thetwo blanket cylinders 6 are moved off impression and to an on impression condition with their respective impression cylinders 11.

The web 37 passes between the other printing couple, Figure 10,of blanketcylinder6 and impression cylinder 11 having a colour printed on the reverse of the web, round a web guide roller, 57, a second web guide roller 58, between the blanket cylinder 6 and impression cylinder 11 of the lower printing couple, round web guide rollers 59,60 and on to the next processing station.

With the printing couple 51 and 52 in the mode shown in Figure 10 the printing couple 51 will print one colour on each side oftheweb,the other printing couple of printing couple 52 will add a colourtothe reverse oftheweb and the lower printing couplewill also add a colourto the reverse side oftheweb.

Claims (17)

1. A printing press unit including a plate cylinder, a blanket cylinder and a first impression cyinderwith associated ink and dampenerfountain trains provided with means whereby the blanket cylinder can selectively be broughton and off impression with the plate cylinder, on and off impression with thefirst impression cylinder and on and off impression with a second impression cylinderorwith averticallyor horizontally opposed second blanket cylinder whereby the blanketcylinderwill impartthe image on its blanketto one side ofawebwhen theweb is passed between the blanket cylinder and the first impression cylinder or on the reverse side ofthe web when the web is passed between the blanket cylinder and the second impression cylinder or blanket.

2. A printing press unit including a plate cylinder, a blanket cylinder, and an impression cylinder mounted in side frames to form a cassette capable of insertion and removal from a main frame, the casset tesupporting mechanism selectivelyto movethe cylinders whereby the blanket cylinder can be moved on and off impression relatively to the plate cylinder and to the impression cylinder and on and off impression to a second impression cylinder or a second blanket cylinder horizontally orverticallyopposed theretowherebytheblanketofthe blanketcylinder imparts its image to one side of a web when in contact with the second impression cylinder or second blanket cylinder or on the reverse side ofthe web when the blanket cylinder is in contact with the first impression cylinder.

3. A printing press unit including a plate cylinder, a blanket cylinder and an impression cylinder mounted in side frames to form a cassette capable of insertion and removal from an associated inking and dampening train retained within a main frame, the cassette supporting mechanism selectively to move the cylinders whereby the blanket cylinder can be moved on and off impression relatively to the plate cylinder and to the impression cylinder and on and off impression to a second impression cylinderwhereby the blanket on the blanket cylinder imparts its image to one side of a web when in contact with the impression cylinderorto the reverse side of the web when the blanket cylinder is in contact with the second impression cylinder.

4. Aprinting press unit according to Claim 1 or2 or 3wherein the blanket cylinder is mounted in eccentrics selectively moved to bring the blanket cylinder on and offimpression relativelytothe plate cylinder.

5. A printing press unit according to Claim 1 or2 or3wherein the blanket cylinder is carried in eccentrics mounted on hanger brackets rotatablysup- ported bythe plate cylinderjournalswhereby relative motion between the hanger and the frame supporting the plate cylinder moves the blanket cylinder on and offimpression relatively to the impression cylinder.

6. A printing press unit according to Claim 1 or2 or3 wherein the blanket cylinder is carried in eccentrics mounted on hanger brackets rotatablysup- ported by the plate cylinderjournals, the hangers being moved relatively to the frames carrying the plate cylinder by an eccentric selectively rotated to move the hangers to bring the blanket cylinder on and off impression relatively to the impression cylinder.

7. Aprinting press unit according to Claim 1 or2 or3 wherein the impression cylinder is carried in eccentrics and adapted to be rotated to bring the impression cylinder on and off impression relatively to the blanket cylinder.

8. A printing press unit according to Claims 4 and 7 or 5 and 7 or 6 and 7 wherein the eccentrics accuating the blanket cylinder and the impression cylinder are operated by means whereby movement of both the eccentrics is effected simultaneously.

9. A printing press unit according to Claim 8 wherein the eccentric ofthe blanket cylinder and the impression cylinder are operated by gear linkage rotatted from a common source.

10. A printing press unit according to Claim 7 wherein the eccentrics are carried in the side frames supporting the plate cylinder.

11. A printing press unit according to Claim 1 or2 or3wherein the plate cylinder is carried in side frames the blanket cylinder is carried in eccentrics carried in hangers rotatably mounted on the journals ofthe plate cylinder, the impression cylinder is carried in eccentrics mounted on side frames, the eccentrics of the blanket cylinder and impression cylinder being interlinked to provide a set of motions to bring the blanket cylinder on and off impression in relationship with the plate cylinder and the hanger eccentrics are separately operable to bring the blanket cylinder to an on and off impression relationship with the impression cylinder.

12. A printing press unit according to any ofthe preceding claims wherein the printing cylinder, blanketcylinderand impression cylinderaredriven from a driving gear imparting driveto a gearsecured to a plate cylinder in turn driving the blanket cylinder and impression cylinderthrough a geartrain,there being provided means for reversing the direction of drive applied to the plate cylinder.

13. A printing press unit according to Claim 12 wherein an idlergearcan be selectively inserted in thetrain ofgearsto reversethedirection ofdrive applied to the plate cylinder.

14. A printing press unit according to Claim 12 wherein an electromagnetic clutch is in the geartrain to selectively introduce a reversing gearto change the direction of drive to the plate cylinder.

15. A printing press unit constructed and adapted to operate substantially as hereinbefore described with reference to Figures 1 to 4 of the accompanying drawings.

16. A printing press unit incorporating the drive mechanism substantially as hereinbefore described with reference to Figure 11 of the accompanying drawings.

17. Aprinting press unit incorporating the web runs substantially as hereinbefore described with reference to Figures 5 and 6 or Figures 7 and 8 or Figures 9 and 10 ofthe accompanying drawings.