US3587460A

US3587460A - Dampening system for rotary offset press

Info

Publication number: US3587460A
Application number: US729118A
Authority: US
Inventors: Louis Jean Chambon
Original assignee: Societe dEtudes de Machines Speciales SA
Current assignee: Societe dEtudes de Machines Speciales SA
Priority date: 1967-05-22
Filing date: 1968-05-14
Publication date: 1971-06-28
Anticipated expiration: 1988-06-28
Also published as: NO126558B; IE31915L; CH517592A; ES354441A1; AT303082B; DE1761404A1; LU56084A1; DK135157B; FR93677E; DE1761404B2; IE31915B1; SE338574B; DE1761404C3; DK135157C; BE715185A; IL29986A0; IL29986A; NL146094B; GB1219828A; NL6807253A

Abstract

A DAMPENING DEVICE FOR AN OFFSET-TYPE ROTARY PRINTING PRESS IN WHICH A DRIVEN TRANSFER ROLLER, PARTIALLY IMMERSED IN A DAMPENING FLUID, APPLIES A FILM OF DAMPENING FLUID TO A DRIVEN DAMPENED ROLLER WITH WHICH IT COACTS. A METERING ROLLER HAVING A RESILIENT AND DEFORMABLE SURFACE COACTS WITH THE TRANSFER ROLLER WITH SUFFICIENT PRESSURE BETWEEN THEM TO DEFORM THE METERING ROLLER INWARDLY SO THAT THE THICKNESS OF THE FILM OF DAMPENING FLUID IS MAINTAINED UNIFORM PERIPHERALLY AND AXIALLY OF THE TRANSFER ROLLER REGARDLESS OF OUT-OF-ROUNDNESS OF THE TRANSFER ROLLER AND FLEXURE OF THE TRANSFER AND METERING ROLLERS. THE DEVICE IS PROVIDED WITH A DRIVE THAT ALLOWS THE DRIVEN DAMPENED ROLLER TO DRIVE THE TRANSFER ROLLER VARIABLY IN DEPENDENCE UPON CHANGES OF THE THICKNESS OF THE FILM OF DAMPENING FLUID BETWEEN THE DAMPENED ROLLER AND THE TRANSFER ROLLER. THE DAMPENED ROLLER WILL VARY THE SPEED OF THE TRANSFER ROLLER SO THAT IT INCREASES OR DECREASES THE THICKNESS OF THE FILM OF DAMPENING FLUID

THEREON AS A FUNCTION OF ITS SPEED CHANGES SO THAT THE FILM THICKNESS IS MAINTAINED CONSTANT AUTOMATICALLY.

Description

United States Patent [54] DAMPENING SYSTEM FOR ROTARY OFFSET PRESS 7 Claims, 8 Drawing Figs.

[52] US. Cl 101/148, 101/350, 64/30 [51] Int. Cl 84" 23/04, B411 25/02 [50] Field ofSearch 101/350,

363, 207,208, 351, 148;64/30; l18/(Doctors and Scrapers Digest) [56] References Cited UNITED STATES PATENTS 176,193 4/1876 Rhell 101/148 1,302,352 4/1919 French 118/126 1,575,637 3/1926 Neth 64/30 1,993,055 3/1935 Gerstenberg 165/90 2,066,782 1/1937 King 118/119 2,337,386 12/1943 Grupe 1 101/350X 2,406,928 9/1946 Taylor et al 101/350 2,659,220 1 1/1953 Cherry 64/30X 2,695,004 1 H1954 Montgomery et a1 1 18/262 3,038,405 6/1962 Wojciechowski et al. 101/148 3,062,138 1 1/1962 Worthington 101/350 3,098,437 7/1963 Tyma, Jr. etal. 101/350 3,106,154 10/1963 Saul 101/148 3,170,397 2/1965 Dutro et 3.1.... 101/350 3,343,484 9/1967 Dahlgren 101/148 Primary Examiner-Edgar S. Burr Assistant Examiner-Clifford D. Crowder Attorneys-Robert E. Burns and Emmanuel J. Lobato ABSTRACT: A dampening device for an offset-type rotary printing press in which a driven transfer roller, partially immersed in a dampening fluid, applies a film of dampening fluid to a driven dampened roller with which it coacts. A metering roller having a resilient and deformable surface coacts with the transfer roller with sufficient pressure between them to deform the metering roller inwardly so that the thickness of the film of dampening fluid is maintained uniform peripherally and axially of the transfer roller regardless of out-of-roundness of the transfer roller and flexure of the transfer and metering rollers. The device is provided with a drive that allows the driven dampened roller to drive the transfer roller variably in dependence upon changes of the thickness of the film of dampening fluid between the dampened roller and the transfer roller. The dampened roller will vary the speed of the transfer roller so that it increases or decreases the thickness of the film of dampening fluid thereon as a function of its speed changes so that the film thickness is maintained constant automatically.

DAMPENING SYSTEM FOR ROTARY OFFSET PRESS BACKGROUND OF THE INVENTION The present invention relates to dampening systems, notably for rotary offset printing presses.

A device designed. for dampening the etched plate or cylinder of an offset printing machine is already known, wherein this dampening step is performed prior to the inking proper, by means of rubber form rollers covered with a fabric lining soaked with a dampening fluid, as a rule water. These rollers roll on the press plate. Due to the unequal transfer of water to the plate between the etched'and unetched portions thereof, a transverse adjustment of the water feed must be made as a function ofiwater consumption. Now this adjustment is generally difficult and sometimes impossible in the case of a sudden variation. Moreover, this known device requires an adjustment of the position of the form rollers in case of a change in the paper or web size.

Another dampening device is also known which comprises two tangent rollers rolling on each other without slipping and without exerting a mutual pressure. To obtain an approximately uniform waterfilm at the outlet of the contact zone of these two rollers and at the periphery of the dampening roller, the effect of flextures or bending must be corrected either by resorting to elaborate adjustments or by using special constructional or mechanical arrangements taking due account of this bending, these solutions obviously making this mechanism particularly costly.

SUMMARY OF THE INVENTION It is the object of the present invention to avoid the inconveniences of known dampening devices by providing a much simpler and therefore economical device capable of forming an extremely thin and uniform film of dampening fluid.

To this end, this dampening device, notably for an offset rotary printing machine, comprises a hard transfer roller having an hydrophilic surface from which a film of a dampening fluid is transferred to another surface in contact with the transfer roller such as an etched plate or cylinder of the printing machine. A soft wiping or metering roller having a resilient peripheral surface contacting the transfer roller, is provided. The hard transfer roller is constantly partially'immersed in a trough containing the dampening fluid means are provided by which the soft metering roller is held against rotation, and other means are provided for urging the soft metering roller against the hard transfer roller with a force sufficient to cause the thickness of the film of dampening-fluid adhering to the peripheral surface of the transfer roller to be practically independent of pressure variations likely to be caused by mechanical defects, flections and out-of-roundness.

According to a complementary feature characterizing this invention, means are also provided for varying the peripheral velocity of the transfer roller in relation to the plate speed, so as to permit the proper adjustment of the thickness of thelfllm of dampening fluid, on said plate.

The dampening device according to this invention is also advantageous in that it makes it possible to'form on the surface of the transfer roller a film having a constant or uniform thickness throughout the cylinder length by using particularly I simple means. The arrangement according to the. present invention permits dispensing with the hitherto customary means for effecting the transverse adjustment of the water pick up, and the water consumption corresponds exactly to the amount necessary for properly dampening the plate.

Moreover, the device according to this invention permits forming an extremely thin film of water for dampening'the plate.

In a specific application of this invention to an offset-type rotary press the hard transfer roller, of the variable rotational speed type, is tangent to. a resilient applicator or form roller.

The quantity of water delivered to the press plate is adjusted by the velocity or speed of rotation of the transfer roller. Of course, this adjustment'is subordinate to the linear printing speed of the machine: the higher the transfer roller speed, the thicker the waterfilm delivered to the plate.

Now, due to the pressure produced between the applicator roller and the transfer roller, the latter is more or less rotatably driven from the former. When the water film thickness decreases, the friction between the two rollers increases. Consequently, if the thickness of the film of water delivered by the transfer roller tends to decrease, this friction effect increases, thus tending to rotate the transfer roller from the applicator roller at a higher speed and therefore to increase the film thickness; under these conditions, an automatic correction is obtained.

It is another object of this invention to free the operator of the printing machine from the necessity of modifying the dampening adjustment each time the velocity of the machine has to be changed.

To this end, according to an additional feature characterizing this invention, the hard transfer roller is rotatably driven from a DC motor of the constant but adjustable speed type, the drive being transmitted from the motor to the roller through the medium ofa freewheel device.

According to a specific form of embodiment, the transfer roller driving system comprises a shunt motor controlled through a bridge rectifier; in this case the freewheel action is obtained when the motor operates as a no-load generato due to the provision of the rectifier.

According to another form of embodiment, the transfer roller driving system comprises a series motor, i.e. a motor of which the velocity of rotation is inversely proportional to the reaction torque.

With this device, it is only necessary to adjust the velocity of rotation of the electric motor for properly dampening the plate at low press speeds, and to subsequently adjust the pressure exerted by the transfer roller against the soft applicator roller of the inking system for obtaining a satisfactory dampening at high printing speeds. Thus,'the dampening effect obtained with the arrangement of this invention will be satisfactory throughout the speed range of the printing machine, i.e. between its maximum and minimum speed values.

Practical tests carried out on offset rotary presses proved that the speed could vary in a broad range without producing any appreciable change in the quality of the dampening action thus obtained, and without any necessity of readjusting the dampening process.

BRIEF DESCRIPTION OF THE DRAWINGS Typical forms of embodiment of this invention will'now be described by way of example with reference to the accompanying drawing in which:

.FIG. 1 is a diagrammatic vertical section view showing a dampening device according to this invention, associated with an offset rotary press;

FIG. 2 is a fragmentary view partly in section showing the same device;

FIG. 3 is a diagram of an elevation view illustrating the inking and dampening systems embodying the invention incorporated in a rotary offset press;

FIG. 4 is a diagram of a fragmentary elevation view illustrating a modified form of embodiment of the dampening device according to this invention, and

FIGS. 5, 6, 7 and 8 are diagrams of graphs illustrating plots of the variation in the thickness of the film of water deposited on the peripheral surfaceof a soft applicator roller as a function of various parameters.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The dampening device illustrated in FIG. 1 comprises a sump or trough I containing a certain amount of a dampening fluid, for example water, of which the level can be kept at a constant value by means of a suitable pumping system (not shown). A transfer roller 2 rotatably mounted on a horizontal shaft 3 has its lower portion constantly immersed or dipped in the dampening fluid contained in the trough 1 This transfer roller 2, is rotatably driven in a counterclockwise direction as viewed in the drawing and at an adjustable speed, either through gears 4, from a variable-speed motor or, as illustrated more particularly in the drawing, through a variable speed transmission 5 interposed between the transfer roller 2 and a main power shaft 6 of the machine.

The peripheral surface of the transfer roller 2 consists of a relatively hard, substantially nonresilient lining material, preferably chromium, having an affinity for water that is hydrophilic.

A fixed wiping or metering roller 7 is mounted parallel to the transfer roller for engagement with the transfer roller 2 in a contact region or zone 8 overlying the horizontal plane containing the axis of the transfer roller shaft 3. The fixed metering roller 7 comprises a central core 70 of relatively hard material such as steel, and a surface layer or lining 7b of soft material such as rubber.

On the other hand, means are provided for pressing the soft metering roller 7 against the movable transfer roller 2 with a relatively high pressure, at least sufficient to cause the soft surface layer 7b of metering roller 7 to be deformed inwardly or compressed with force in said contact zone 8 against the hard transfer roller 2. Various conventional means may be used for adjustably pressing the fixed metering roller 7 against the movable transfer roller 2.

D Byway ofillustration, there is shown in the drawing a device wherein the shaft 9 of the fixed metering roller 7 is eccentrically mounted in trunnions 11 carried in turn by bearings of the machine frame structure 10. These trunnions 11 are angularly adjustable in said bearings and the angular adjustment of each trunnion may be obtained by means of a pair of

screws

12 and 13 carried by bracket 14 rigid with said frame structure and engaging shoulders fonried on a plate 15 rigid with the relevant trunnion 11. It is clear that by rotating more or less the trunnions 11 about their axes 16 the longitudinal axis of metering roller 7 can be moved towards or away from the longitudinal axis of the transfer roller 2 to vary the pressure produced between these two rollers. It was observed from practical experiments that when a sufficient pressure is exerted by the metering roller 7 (lined with soft material) against the hard transfer roller 2, the surface layer 7b is deformed in the contact zone 8 inwardly and at the outlet end of this zone, the transfer roller 2 carries on its peripheral surface a film of water 17 having a constant thickness throughout the length of the transfer cylinder 2. This constant thickness is independent of possible pressure variations caused by mechanical defects, flections or bending and out-of-rounds.

The transfer roller 2 will thus entrain at the outlet end of said contact zone 8 a film of water 17 of reduced and constant thickness, which is deposited at a variable speed on a roller 18 also lined with soft material which is tangent to the aforesaid transfer roller 2 and revolves at a constant speed. In a rotary offset press, this roller 18 may be either the applicator or form roller engaging the etched plate or cylinder of the printing machine, or alternately an immediate distributor roller. The peripheral surface of roller 18 will thus receive a film of water of variable thickness, this thickness being proportional to the velocity of rotation of the transfer roller 2. Thus, the quantity of water delivered to the plate of the offset press is on the one hand dependent on the thickness of the film of water 17 formed on the transfer roller 2 and on the other hand directly proportional to the velocity of rotation of the transfer roller 2.

Considering the elastic distortion of the rubber material constituting the flexible or resilient surface lining 7b of the soft metering roller 7, the throttled water stream produced betweenthe

rollers

7 and 2, and the reduced thickness of the film of ester 17 in relation to the dimension of the "crushing effect applied to the soft layer 7b in the contact zone 8, the thickness ho/2 of the water film 17 formed on the peripheral surface of transfer roller 2 may be expressed by the following equality:

wherein it designates a constant inherent to the machine, which takes due account of the physical constants of the rubber material, of the dimensions of the rollers and of the V being the linear speed ofthe plate.

Therefore, the quantity of water delivered to roller 18 can be adjusted very easily bevarying the velocity of rotation v of the transfer roller 2, this variation being obtained by properly controlling the variable speed transmission 5 or the variablespeed motor.

in the form of embodiment illustrated in FIG. 2 the shaft 9 of wiping or metering roller 7 is locked against rotation by means of a friction device. This device, illustrated diagrammatically in the HQ, comprises a disc 19 rigid with a shaft 20 held against rotation. This disc 19 is urged by a spring 21 against an antagonistic disc 22 rigid with the end of shaft 9 of cylinder 7. The tension of spring 21 may be adjusted by means of a screw-threaded adjustment member 23 engaged by said spring 21 and screwed in a yoke 24 rigid with the frame structure 10 of the machine.

This friction locking device operates as follows: when the machine is started, the peripheral surface of transfer roller 2 is dry as well as that of metering roller 7. As a result, the coefficient of friction between the contacting surfaces is relatively high. The tension of spring 21 is so adjusted that under these conditions the driving torque exerted by the transfer roller 2 on the metering roller 7 exceeds the reaction torque exerted by the friction disc 19 on the antagonistic disc 22.

Therefore, just after the machine has been started, the transfer roller 2 will drive the metering roller 7 in a clockwise direction.

However, immediately after a film of water entrained by the transfer roller 2 has penetrated into the contact zone 8, this water acts as a lubricant and the coefficient of friction drops considerably in this zone. As a result, the reaction torque exerted by the friction disc 19 on the shaft disc 22 becomes greater than the driving torque exerted by transfer roller 2 on metering roller 7, so that the metering roller 7 is held against motion due to the friction coupling constituted by the

discs

19 and 22.

The above-described arrangement is advantageous in that each time the machine is started the peripheral surface portion of the soft or flexible layer 7b which contacts the rotary transfer roller 2 is changed, so that any premature wear of the surface layer 7b is safely avoided, as contrasted with arrangements wherein the transfer roller 2 is in constant engagement with the same portion of said soft layer.

Now, a typical example of the application of the dampening device according to this invention to an offset rotary press will be briefly described with reference to FIG. 3 of the drawing. in this FIG. the same elements as those illustrated in FIGS. 1 and 2 are designated by the same reference numerals. The offset rotary press comprises an inktrough 25, a hard inking roller 26, a flexible pickup roller 27 brought in contact by turns with said inking roller 26 and another hard roller 28 constituting the inking plate. This roller 28 is tangential to a soft distributor roller 29 tangential in turn to a hard loading roller 31 tangentiallto the distibutor or applicator roller 18 of FIG. 1. The loading roller 31 is also tangential to a soft transmitter roller 32'tangent in turn to a pair of

hard rollers

33 and 34 to which a lateral reciprocating motion is imparted. The laterally reciprocating roller 33 is also tangential to the distributor roller 18 and to a pair of

soft inking rollers

35 and 36 contacting the etched plate or roller 37 The reciprocating roller 34 is on the other hand to a soft transmitter roller 38 tangent in turn tangential to a pair of

hard rollers

39 and 41 tangential to a common soft roller 42. Roller 39 is also reciprocated axially and contacts two

soft inking rollers

43 and 44 also rolling on the etched plate or roller 37. The two pairs of inking

rollers

35, 36 and 43, 44 are disposed symmetrically in relation to a vertical plane containing the axis of rotation of the etched plate or roller 37, on the one hand, and the axes of

rollers

26 and 34, on the other hand.

In this specific form of embodiment of the offset rotary press the transfer roller 2 is tangential to the applicator roller I8 having a fixed position irrespective of the paper size. FIG. 3 shows in dash and dot lines the variations in the positions of the inking

rollers

36 and 44 when the etched plate or roller has the minimum size, and thick lines corresponding to the use of the largest size.

Of course, according to a modified form of embodiment, the transfer roller 2 may be brought in direct contact with an inking roller such as roller 36. However, due to the fact that, in case of a change in the paper size, the position of the inking roller 36 will change, it would then be necessary to modify the position of the complete dampening device, which would be rather complicated. Therefore, the first solution is preferred.

Now reference will be made to FIG. 4 illustrating a modified form of embodiment of this invention. The soft applicator roller 18 is rotatably driven through suitable means (not shown) from the offset rotary press. Its velocity of rotation is therefore variable as a function of the machine speed.

On the other hand, the hard transfer roller 2 is rotatably driven from an electric motor 50 through a freewheel device 51 and a train of gears 4.

To describe the mode of operation of the dampening device illustrated in FIG. 4, it will firstly be assumed that the transfer roller 2 is not driven by any mechanism or, in other words,

i that the driving motor 50 is suppressed. Under these conditions, the transfer roller 2 is driven only as a consequence of its peripheral contact with the soft applicator roller 18, at a tangential speed V lying in the range from (since the metering roller 7, held against rotation, acts as a brake) to V which is the tangential velocity of applicator roller 18v driving the transfer roller 2 by frictional contact.

Be h the thickness of the film of water formed between the metering roller 7 and the hard transfer roller 2, and e the thickness of the film of water formed on the soft roller 18 of the inking system, the following output equality may be noted:

The pressure exerted between the soft metering roller 7 and the hard transfer roller 2 is adjusted at a sufficient value to which corresponds a constant crushing d, of the flexible surface 7b of roller 7, so that a constant thickness ha/2 of the film of water on the peripheral surface of transfer roller 2 is obtained throughout the roller length, irrespective of the cylinder flexure. On the other hand, it will be assumed that at the point of contact between

rollers

2 and 18, the pressure and therefore the "crushing d of the surface layer of roller I8 are adjustable.

Calculation will prove that the thickness e of the filmof water formed on the soft roller 18 of the inking system is given by the formula:

This formula (2) shows that the thickness e of the film of water distributed over the inking system will vary as the square root of theytinear printing speed V This law governing the variation is therefore parabolic when graphed and FIG. illustrates a series of parabolic curves corresponding to different values d (1,, d of parameter d, i.e. of the degree of crushing of roller 18.

If we plot in abscissa the value e, denoting the thickness of the film of water necessary for obtaining a satisfactory dampening (which remains the same irrespective of the speed of the printing machine, and if on the other hand we draw the parabolic curve corresponding to the value d, of parameter d and intersecting the straight line Fe at D, we note that the,

dampening effect thus obtained will be satisfactory for a printing machine speed V but if the machine is operated at a lower speed the dampening will not be sufficient and if the machine is operated at a higher speed the dampening will be in excess of the normal desired value. These theoretical remarks are on the other hand confirmed by practical tests.

Now let us consider the behavior of the same film of water on the periphery of the applicator roller 18 when the transfer roller 2 is rotatably driven from a constant-speed motor 50 (which may be adjusted at the proper speed when assembling the device), the motor speed remaining constant in spite of speed variations of the printing machine.

From the above formula (I) we have:

wherein V is a constant. The curve corresponding to the variation of e as a function of V is then a hyperbola for a given value of V As the rotary press speed whereat the dampening device is adjusted is the minimum speed V' by properly adjusting or controlling the motor 50 driving the transfer roller 2, and therefore by causing the variation of V it will thus be possible to obtain a series of hyperbolic curves corresponding to various values V V V etc. of V as clearly illustrated in FIG. 6.

If the value 2,, of the thickness of the water film which is necessary for producing a satisfactory dampening effect is plotted in abscissa, and if we draw the hyperbolic curve corresponding to the value V of parameter V (this curve intersecting the straight line e=e at point M), it will be seen that a satisfactory dampening action will be obtained at printing speeds V but on the other hand at lower speeds it will be seen that the dampening is not sufficient and that at higher speeds an excess of water will result.

These theoretical remarks are also confirmed by practical experience.

Under these conditions, a value V,, is selected among the values V V VM etc. such that the point of intersection of the corresponding curve I (FIG. 7) with the straight line V =V lies within a zone extending on either side of e in which the dampening is considered as adequate. Be A the point of intersection thus determined.

Now, let us consider the fact that the motor 50 drives the transfer roller 2 through the medium of the freewheel device 51. In other words, if the roller 2 is driven from the applicator roller 18 at a speed higher than that imparted thereto by the motor 50, the transfer roller can rotate at said speed without any stress. This freewheer effect can also be obtained electrically if the transfer roller 2 is driven from a shunt motor 50 energized through a bridge rectifier 52, when this shunt motor operates as a no-load generator due to the presence of said bridge rectifier.

FIG. 7 illustrates in dash lines the curve II corresponding to a curve of FIG. 5 i.e. the curve corresponding to the value 11 of parameter d) and showing the variation in the thickness e as g a function of the speed V,- of roller 18, as already explained hereinabove.

Let B be the point of intersection of curves I and II. The are AB of curve I denotes the variation in the thickness e of the film of water as a function of the speed V of operation of the printing machine when the speed at which roller 2 is driven from motor 50 is greater than the speed of the same roller 2 which is due to the driving thereof by the applicator roller 18. On the other hand, the are B-C of curve II shows the variation in this thickness e when the velocity of rotation of the transfer roller 2 driven from the machine becomes higher than that of motor 50.

The are A-B is essentially dependent on the adjustment of V that is, on the driving speed of motor 50, and arc B-C is essentially dependent on the crushing effect d, therefore on the pressure existing between the transfer roller 2 and the soft applicator roller 18 of the inking system.

It is therefore easy to devise an adjustment giving a set of arcs AB and BC lying within two limits as close as possible to each other and to the ideal dampening constant e In this case, the points A and C should have the same abscissa.

The adjustment of point A is obtained by adjusting the speed V of motor 50 as required for a low-pressspeed, and the adjustment of point C is obtained by adjusting the crushing d of the soft roller 18 of the inking system, for a high press speed.

From FIG. 7 it will be readily understood that to obtain closer dampening tolerances it is advantageous to attenuate the peak B of the are assembly ABC. ln this respect, according to an improvement provided by the present invention, the constant-speed motor-50 is replaced by a series-wound motor, that is, a motor of which the speed is a reverse function of the reaction torque (reversible control).

This motor adjusted at a low speed V, of the printing machine, permits of determining the point A; then, when the speed V of the press increases, the torque necessary for driving the transfer roller 2 from the electric motor 10 decreases, due to the fact that the transfer roller 2 is driven from the soft applicator roller 18 of the inking system.

Therefore, the speed at which the transfer roller 2 is driven may increase, this increment is attended by a corresponding increment in the thickness of the film of water in relation to that corresponding arc A-B.

When the speed of the'printing machine attains a very high value V the driving torque of the series-wound motor 50 is practically zero since the transfer roller 2 is then driven only and completely by the printing machine itself.

The curve lll (FIG. 8) denoting the variation in the thickness of the film of water obtained from the dampening device driven from a series-wound motor will thus start at point A and end asymptotically on are BC.

It will be readily seen from this FIG. 8 that the dampening tolerances, are very considerably narrowed in relation to the preceding case illustrated by the arcs A--B and BC of curves 1 and II. The thus defined arc AC of curve Ill may easily be assimilated to a vertical having an abcissa equal to said value e corresponding to the ideal dampening adjustment.

Besides, it will be readily understood by anybody conversant with the art that the various forms of embodiment of the invention which have been described and illustrated in the accompanying drawing should not be construed as limiting the present invention since many modifications may be brought thereto without departing from the spirit and scope of the invention as set forth in the appended claims.

Thus, although the above description refers to a device for delivering a relatively thin film of water, it is clear that this invention is also applicable to the formation and delivery of a film of uniform thickness of any other liquid.

Iclaim:

l. A dampening device for an offset-type rotary printing press comprising, means defining a trough for containing therein in operation a dampening fluid, a rotatably driven first roller to which a film of said dampening fluid is to be transferred and automatically maintained peripherally and axially thereon at a substantially uniform and constant thickness irrespective of peripheral speed of rotation variations thereof, a rotatably driven transfer roller having a hard, hydrophilic peripheral surface circumferentially and axially thereof, first mounting means mounting said transfer roller in position with a portion axially thereon in said trough immersed in said dampening fluid for adhering a film of said dampening fluid disposed peripherally on and circumferentially of said transfer roller and variable in thickness in dependence upon varying of ,8 the peripheral speed of rotation of said transfer roller, said first mountin means being dis ose d mounting said transfer roller paralle to said first rol er, in contact therewith for transfer of said film of dampening fluid to said first roller, said first-mounting means including means rotatably mounting said first roller in position effecting contact with said transfer roller at a selected pressure for rotatably driving the transfer roller from said first roller at a peripheral speed of rotation varying in dependence upon the variations of thickness of said film on said transfer roller for automatically correcting the thickness of the film on said transfer roller as a function of the speed of rotation of said transfer roller thereby to maintain the thickness of said film thereon constant, means to maintain said film on the transfer roller substantially uniform in thickness axially and circumferentially thereon comprising a rotatably mounted metering roller having a resilient peripheral surface circumferentially thereof, second mounting means rotatably mounting the metering roller with its axis parallel to the axis of said transfer roller in position for said transfer roller and said metering roller to contact each other along a contact region extending axially along both the transfer and metering rollers and a limited distance in a circumferential direction of both said transfer and metering rollers with a contact pressure effective to deform said resilient surface of said transfer roller inwardly along said contact region to maintain said film of dampening fluid on said transfer roller, during relative peripheral movement of said transfer and metering rollers, at a uniform thickness independently of contact pressure variations in said contact region caused by flexure of the transfer roller and the metering roller and caused by out-of-roundness of said transfer roller, drive means driving said transfer roller including means allowing varying the peripheral speed of said transfer roller under control of said first roller to adjust the thickness of said film of said dampening fluid thereon, and holding means rendered effective automatically to hold said metering roller from rotating relative to said transfer roller only when said film of dampening fluid on said transfer roller is disposed in said contact region.

2. A dampening device for an offset-type rotary printing press according to claim I, in which said second mounting means includes means for variably shifting the axis of said metering roller relative to the axis of said transfer roller in a parallel relationship to change said contact pressure in said contact region.

3. A dampening device for an offset-type rotary printing press according to claim 1, in which said means allowing varying the peripheral speed of said transfer roller under control of said first roller comprises a freewheel device.

4. A dampening device for an offset-type rotary press according to claim, 3 in which said drive means comprises a DC electric motor having a constant but adjustable speed for rotatably driving said transfer roller.

5. A dampening device for an offset-type rotary printing press according to claim 4, in which said freewheel device is disposed intermediate said motor and said transfer roller.

6. A dampening device for an offset-type rotary printing press according to claim 4, in which said electric motor comprises a series wound DC motor having a speed of rotation inversely proportional to reaction torque.

7. A dampening device for an offset-type rotary printing press according to claim 1, in which said holding means comprises, a first friction disc mounted to rotate in conjunction with said metering roller and connected thereto, a second friction disc movably mounted for variable frictional engagement under pressure with the first friction disc and means to adjust pressure applied by the second friction disc to the first friction disc to thereby adjust frictional engagement between the frictional discs, whereby the metering roller is rotated by the transfer roller in the absence of a film of dampening fluid therebetween in said contact region and said metering roller is held from rotating only when said film of dampening fluid is disposed in said contact region.