US3296964A

US3296964A - Dampening roller mechanism for offset printing presses

Info

Publication number: US3296964A
Application number: US358496A
Authority: US
Inventors: William J Orr
Original assignee: Roberts and Porter Inc
Current assignee: Roberts and Porter Inc
Priority date: 1964-04-09
Filing date: 1964-04-09
Publication date: 1967-01-10
Anticipated expiration: 1984-01-10
Also published as: DE1436542A1; GB1060148A

Description

w. J. OF: 3,29,,QM

EH MECHANISM FOR OFFSET PRINTING PRESSES Jam m 6? DAMPENING ROLL 2 Sheets-Sheet 1 Filed April 9, 1964 INVENTOR. w/LU/W J. 0/?/? ATTORNEYS Jam. 11% J5 05% DAMPENING ROLLER MECHANISM FOR OFFSET PRINTING PRESSES Filed April 9, 1964 2 Sheets-Sheet 2 United States Patent 3,296,964 DAMPENING ROLLER MECHANISM FOR OFFSET PRINTING PRESSES William J. Orr, Alameda, Calif., assignor to Roberts & Porter, Inc., Chicago, Ill., a corporation of Illinois Filed Apr. 9, 1964, Ser. No. 358,496 3 Claims. (Cl. 101147) This invention relates to improvements in offset printing presses and more particularly concerns new and improved dampening roller mechanisms therein. The invention is herein illustratively described by reference to the presently preferred embodiment thereof; however, it will be recognized that certain modifications and changes therein with respect to details may be made without departing from the essential features involved.

In the operation of an offset lithographic press the printing surface of the plate which enwraps the plate cylinder is dampened before inking on each cycle of rotation of the plate cylinder. The printing areas of the plate are greased so as to repel moisture and attract the greasy printing ink, whereas the nonprinting areas are either untreated or are differently treated so as to attract or hold the applied fountain etch and thereby repel the ink. The dampening function, therefore, is to insure uniformity in the dampness of the nonprinting areas. Clear and distinct prints require that this be done with great care because of the fact that the printing areas and nonprinting areas are substantially flush with each other in this type of press.

Dampening of the plate in an offset press was commonly performed heretofore by a pair of cloth-covered rubber rollers pressed against the surface of the plate cylinder. The amount of pressure was established by manually ad justable take-up mechanism which compressed the rubber body of the dampening roller to the required degree. Insufficient pressure resulted in nonuniform or insufficient dampening. Excessive pressure produced a like result because of surface slippage and wiping action on the plate cylinder caused by working of the cloth jacket and underlying rubber in the roller during its movement through the zone of contact. Slippage and wiping action also occurred as a result of imperfect coordination of surface speeds in the transmission of rotation between the plate cylinder and the dampening roller. Such surface speed variations due to defective transmission of rotation and due also to pressure variations tended to occur particularly at the ends of the plate clamped to the plate cylinder and representing discontinuities in the surface of the latter. The cloth coverings of the dampening rollers of prior offset printing presses also deposited lint on the plate surface and tended to make it difficult to obtain clean, sharp prints from fineresolution or screen effect images due'to the action of the cloth in drawing slivers of ink from defined deposit areas into intended blank areas adjacent thereto. Still another difiiculty with prior systems was the problem of printing plate Wear due to improper speed coordination and the relatively heavy pressure required of the cloth-covered dampening rolls against the plate cylinder.

A broad object of the present invention is to overcome the aforementioned difliculties. A related object is to achieve this result while simplifying the construction and reducing the cost of the dampening roller mechanism. It is also an objective to facilitate and expedite making the pressure adjustment and to do so with greater reliability than heretofore. At the same time, it is an object to avoid the problem of periodic cleaning of the cloth coverings of former dampening rollers by providing herein a dampening system in which cloth coverings are no longer necessary. In fact with this invention a single dampening roller having an exposed surface of natural or synthetic rubber or other elastomeric substance is capable of pro- 3,296,964 Patented Jan. 10, 1967 little skill or effort, and will remain constant throughout the entire cycle of rotation of the plate cylinder despite any surface discontinuities on the latter. A related object is to provide in the roller mechanism an improved rotary transmission means insuring constant coordination of surface speeds of the dampening roller and the plate cylinder. In this latter regard the present invention, directed toward the various objectives stated herein, utilizes the same means to achieve not only uniformly constant transmission of rotation between plate cylinder and dampening roller, but also convenience with reliability in the establishment of optimum pressure of contact therebetween. Moreover, the inherent action of the dampening roller in pulling some ink from the plate as it applies moisture to the plate has the effect of cleaning up the prints in terms of a greater degree of resolution and detail than was heretofore achievable.

In accordance with the invention as herein disclosed, contact pressure between dampening roller and plate cylinder is established and determined by a novel means for gauging the final position of the dampening roller axis in relation to the plate cylinder axis and at. the same time creating the desired driving connection between the roller and cylinder. In effect the novel means functions to introduce a reaction force into the take-up mechanism which is independent of roller-to-cylinder contact pressure. Such reaction force opposing increase of contact pressure is greater in magnitude and increases much more rapidly than the reaction force produced by said contact pressure when the dampening roller is being snugged against the plate cylinder. As the invention is disclosed herein, cylindrical trucks are mounted adjacent the respective ends of the dampening roller to rotate therewith on a common axis. These truc-ks engage cylindrical bearers mounted in similar relation to the plate cylinder. The two sets of cylindrical trucks and bearers constitute a rotary transmission means coordinating surface speeds of the plate cylinder and dampening roller. One cylindrical element of each set comprises an elastic material which is hard in relation to the dampening roller elastic material. Thus when the trucks are pressed against the bearers, stress in the relatively hard elastic material compressed thereby sets up a reaction force opposing increase of dampening roller pressure against the plate cylinder. By sensing this force, i.e. pressure of the trucks against the bearers, such as by means of a feeler gauge or by drawing a sheet of paper or other material through the interface between each truck and its bearer and sensing the resistance thereto the operator is able to establish bearer pressure at the optimum value. At this point the very light contact pressure necessary between the roller and cylinder for optimum dampening is established as the inherent result of the precise relative positioning of their respective axes, relative softness of the roller and the difference between the sum of plate cylinder diameter and roller diameter, and the sum of truck. diameter and bearer diameter. Accordingly, when the take-up mechanism has firmly pressed the trucks against the bearers to establish effective frictional driving contact pressure therewith the relative spacing between plate cylinder axis and dampening roller axis is reliably established such that correct design of the dampening roller for relative hardness and diameter insures optimum contact pressure thereof on the plate cylinder.

It will be noted from the foregoing that criticality in the adjustment of the dampening roller position is completely avoided by a means which, in the act of establishing firm driving contact between the coordinated members, inherently establishes optimum dampening roller position, hence its zone and pressure of contact with the plate cylinder. Moreover, because the trucks and bearers have continuous cylindrical surfaces which are in firm frictional engagement, and since the surface speed coordination between dampening roller and plate cylinder depends predominantly on the trucks and bearers, any gap in the plate cylinder surface between the ends of the plate does not cause the previous irregularity of surface speed or contact pressure of the dampening roller as it traverses the end regions of the printing plate.

One of the main benefits derived from this invention is increased plate life, as Well as clearer prints by avoiding the lint deposits and surface working attending use of the former high-pressure cloth rollers; also excess pickup of moisture and ink by the plate with conventional dampening systems. Also, the improved dampening arrangement maintains, more effectively than heretofore possible, an optimum balance between water and ink deposited on the plate so as to produce cleaner and sharper prints.

These and other features, objects and advantages of the invention will become more fully evident from the following description thereof by reference to the accompanying drawings.

FIGURE 1 is a top view with parts broken away showing the plate cylinder, the dampening roller mechanism and part of the means to moisten the dampening roller.

FIGURE 2 is an enlarged isometric view of one end portion of the plate cylinder and dampening roller mechanism assembly.

FIGURE 3 is an enlarged top view with parts shown in sections and other parts broken away illustrating details of the dampening roller mechanism.

FIGURE 4 is a simplified end view showing the driving relationship between the trucks and bearers and the related contacting relationship between the dampening roller and plate cylinder.

Referring to the drawings, plate cylinder comprises a metal (usually steel) hollow cylindrical base 12 suitably journaled in the printing press for rotation therein. None of the mounting details for the plate clylinder have been shown because they may be of any conventional nature. The printing plate 14 may be mounted in conventional manner enwrapping the plate cylinder, with the opposite ends of the plate suitably clamped or otherwise held in place, such as by the bolts 16 which are symbolic, but not necessarily representative, of a suitable retaining means. The outside surface diameter of the plate cylinder is slightly increased by the thickness of the printing plate 14 enwrapping it and as thus increased corresponds substantially to the surface diameter of the

cylindrical bearers

18 and 20 located adjacent the respective ends of the plate cylinder for rotation conjointly therewith on a common axis.

Bearers

18 and 20 are preferably formed from the base stock 12 of the plate cylinder as part of the same unitary structure. The bearers may comprise mere extensions of the plate cylinder surface or may be of a larger or smaller diameter. Preferably the peripheral surface of the bearers l8 and 20 is smooth but unpolished. Since the bearer surfaces serve as traction surfaces for the trucks to be described, they may be roughened to some degree if desired, although roughness in the sense of knurling or like surface treatment is not necessary and may be even detrimental in its effect on abrasion and wear of the trucks rolling against the surfaces to be driven rotationally thereby.

In order to dampen the plate cylinder and more specifically the printing plate, in accordance with this invention as herein disclosed a single elastic dampening roller '22 is pressed into rolling contact with the plate cylinder. The dampening roller, of any suitable elastic or elastomeric type material, receives moisture from suitable means, the details of which are not fully illustrated but which may include the fabric-covered ductor roller 24 and the elastic vibrated transfer roller 26 intermediate the

rollers

22 and 24. Dampening roller 22, whose surface should be a polished surface, is mounted for driven rotation on or as part of a core shaft 28 the axis of which, A is maintained parallel to the plate cylinder axis A The ends of shaft 28 are rotationally mounted in journal blocks 3t slidably retained in suitable guides formed in stationary mounts 32 fixed to the press frame (not shown). Take-up screws 34 threaded into the mounts to bear against the respective journal blocks 30 are shown as being illustrative of a means for advancing the journal blocks toward the plate cylinder in order to press the dampening roller 22 against the surface of the plate cylinder. Take-up screws 34 are shown to be individually adjustable and this is the preferred arrangement because there may be slight differences in relative diameters between the late cylinder and the dampening roller along the respective lengths thereof or there may be some imperfections in the mounting of these rotary elements for which compensation is necessary through independent positioning of the ends of the dampening roller shaft 28 as shown. However, this does not preclude use of a mechanism to coordinate positional adjustment of the ends of the shaft 28 toward and from the plate cylinder if desired.

Dampening roller 22 comprises essentially an elastic sleeve 36 mounted to encircle the enlarged core section 38 formed intermediate the ends of the shaft 28 preferably as an integral part of the same unitary structure. Similar core enlargements 40 formed on the same shaft stock adjacent the respective ends of the plate cylinder serve as mounts for the elastic bands or rings 42 and 44. The latter comprise the cylindrical trucks which are maintained in frictional rolling contact with the

respective bearers

18 and 20. The encircling

elastic members

22, 42 and 44 may be adhesively bonded or otherwise retained snugly in their mounted positions on the core stock.

In accordance with an important feature of this invention the elastic material of the dampening roller 22 is sufficiently softer than the elastic material of the

trucks

42 and 44, and the sum of the diameters of the dampening roller and plate cylinder is so related to the sum of the diameters of the trucks and bearers that when the take-up screws 34 have been tightened suificiently to press the trucks into firm driving contact (determined 'by a feeler gauge or otherwise as mentioned above) the zone width and pressure of contact of the dampening roller against the plate cylinder will be inherently established at the optimum values. To a certain extent the aforementioned relationship will be influenced by the relative thickness of the material in the

rings

42 and 44 and in the sleeve 36. That is, within limits the sleeve 36 will seem softer the thicker it is, while the

rings

42 and 44 will seem harder the thinner they are. All things considered, these relationships should normally be such that advancement of the truck-roller unit toward the bearer-plate cylinder unit brings the roller surface into contact with the plate surface slightly in advance of contact between the trucks and bearers. Thereupon slight additional snugging of the trucks against the bearers to the point of firmness thereon to achieve frictional driving contact, as determined by a feeler gauge or the like, produces inherently the light dampening roller contact pressure required for clear printing. In the case of bearers of lesser diameter than the plate the trucks will normally have slightly larger diameter than the dampening roller as depicted in FIG- URE 4 wherein the truck surface 42 is shown engaging the surface of bearer 18 with the dampening roller 22 hearing against the plate cylinder 10. Typically the truck material will have an elastic stiffness measured by an A Shore reading of between 60 and while that of the dampening roller will lie between 12 and 20. The relatively slight reaction force of the dampening roller 22 barely contacting or kissing the plate cylinder has much less effect on driving of the dampening roller than do the trucks. Consequently loss or reduction of contact pressure of the roller against the plate cylinder (i.e. the plate) when traversing the gap between the ends of the plate does not result in momentary stoppage or deceleration of roller rotation and consequent bounce or slippage thereof on the plate surface when contact therewith is restored. That is, because of the relatively large contact pressure between the trucks and respective bearers and the circumferential continuity of these elements, passage of the ends of the printing plate 14 across the dampening roller surface does not produce any noticeable irregularity in contact pressure or surface speed of the dampening roller in discharging its uniform dampening function with relation to the areas of the printing plate immediately adjacent its ends.

It will be noted that in the absence of the bearers and trucks performing their novel functions, the very gentle contact pressure desired between the dampening roller and the plate cylinder for most applications, and certainly continuity of surface speed coordination between roller and plate cylinder throughout the latters rotation cycle, would be very difficult or impossible to achieve. In such a case, friction in the screw threads, any roughness in the guides for the journal blocks 34 and other factors would erroneously be attributed by the operator to degree of compression of the dampening roller against the plate cylinder. The gapor recess between ends of the printing plate would preclude uniformity of driving contact and dampening pressure.

The invention also reduces the cost and simplifies the construction of such presses by reason of the simplicity of the dampening roller mechanism. By eliminating the need for cloth coverings as on previous dampening rollers, the problem of maintenance and servicing of offset presses is also simplified by this invention.

The term bearer as used herein includes not only a distinct Wheel or like element substantially the entire length of which is contacted by the associated truck, but it may also refer to and include a continuing portion of the length of a longer surface such as a projecting end portion of the plate cylinder proper, whether or not it is an integral part thereof. Similarly the term truck as used herein includes not only a distinct Wheel or like element substantially the entire length of which is contacted by the associated bearer, but it may also refer to and include a continuing portion of the length of a longer surface.

These and other aspects of the invention will be evident to those skilled in the art based on the foregoing description of the presently preferred practices and disclosed embodiment thereof.

I claim as my invention:

1. In an offset press having a plate cylinder carrying a printing surface, means for dampening the printing surface comprising a dampening roller, means for mounting said dampening roller in rolling contact with the plate cylinder on an axis parallel therewith, said dampening roller having a relatively soft elastic contact surface, a hard cylindrical bearer adjacent each end of the plate cylinder and rotative with the plate cylinder on a common axis, and a cylindrical truck adjacent each end of the dampening roller and rotative with the dampening roller on a common axis, said trucks having a relatively hard elastic contact surface in frictional rolling engagement with the respective bearers, the sum of the diameters of the plate cylinder and roller slightly exceeds the sum of the diameters of each bearer and its associated truck whereby the roller contacts the plate cylinder before the trucks contact the bearers during advancement of the roller toward the plate cylinder, said press including means to adjust contact pressure between the trucks and respective bearers, and thereby to establish the zone and pressure of contact between the printing surface and the dampening roller.

2. The press defined in claim 1, wherein the dampening roller and trucks have a common metal core of integral construction.

3. The press defined in claim 1, wherein the dampening roller comprises a core, an elastic sleeve mounted on the core, intermediate its length, the sleeve having an A Shore reading of 12 to 20, and a pair of elastic, cylindrical trucks fixedly mounted on the core adjacent opposite ends of the sleeve, the trucks each having an A Shore reading of to 85.

References Cited by the Examiner UNITED STATES PATENTS 151,688 6/1874 Ehrgott 101-148 1,543,029 6/1925 Reichart 101-348 2,014,095 9/1935 Wood 101-349 2,102,641 12/1937 Osborn 101-148 2,181,714 11/1939 Vandercook et al.

2,207,460 7/ 1940 Hotchkiss.

2,220,278 11/1940 Rapport 101-148 2,33 3,800 11/1943 Lewis et al.

2,763,207 9/1956 McWhorter 101-348 2,891,470 6/1959 Rowe et al 101-48 2,981,180 4/1961 Crissy 101-147 3,049,996 4/1962 Downie 101-349 X 3,094,065 6/1963 Roberts 101-148 ROBERT E. PULFREY, Primary Examiner.

J. R. FISHER, Assistant Examiner.