US2856848A - Means for dampening the surface of a rotating cylinder - Google Patents

Description

Oct. 21, 1958 H. A. PRITCHARD 2,856,848

MEANSFOR DAMPENING THE SURFACE OF A ROTATING CYLINDER Filed May 5, 1955 [28 HIGH [3 l2 VOLTA 6E SOL/R05 INVEN TOR. HOWd/PO A. W 7' 67% BY I $41M United States Patent Ofitice 2,855,848 Patented Oct. 21, 1958 MEANS FOR DAMPENING THE SURFACE OF A ROTATING CYLINDER Howard A. Pritchard, Hiram, Ohio, assignor to Harris- Intertype Corporation, Cleveland, Ohio, a corporation of Delaware Application May 5, 1955, Serial No. 506,188

7 Claims. (Cl. 101-147) This invention relates to means for dampening the surface of a rotating cylinder, particularly to electrostatic means for dampening the lithographic plate cylinder of a printing press, and to means for collecting and reclaiming moisture particlesnot adhering to the plate.

Most ink repellent solutions used for dampening the plates of lithographic presses are toxic and corrosive. This presents a serious problem when the solution is applied to the plate or other rollers of the dampening system as a fog, spray or mist. Being of a toxic nature, ink repellent moisture particles suspended in air can be injurious to the lungs of a press operator, and also can corrode printing press parts to which the moisture particles cling.

One of the objects of this invention therefore is to collect moisture particles not adhering to the surface of a rotating cylinder to which moisture is being applied.

Another object is to provide electrical precipitating means for collecting excess particles of ink repellent moisture.

Still another object of the invention is to provide an enclosed recirculating dampening system in which air pressure is utilized to create fine moisture particles and assist in directing them into a field of force by means of which they are impelled toward and onto a rotating member, and in which vacuum is utilized to exhaust those moisture particles not adhering to the member.

A further object is to provide means for electrostatical- 1y precipitating moisture along an exhaust line from a dampening area, whereby exhausted moisture particles are prevented from getting into the vacuum pump.

A further object is to reclaim moisture particles which do not adhere to the lithographic plate of the press.

Another object is to collect stray moisture particles of ink-repellent solution, which particles have escaped from their normally confined area by being ejected due to air pressure which is utilized to create the moisture particles.

Still another object is to provide means for returning reclaimed moisture to its source whereby it may again be used.

According to the invention, an electrical field of force is provided adjacent the surface of a rapidly rotating cylinder. Means including an air pressure line is provided for creating a fine fog of air and moisture particles and directing it into the field of force. The electrical field serves to charge and impel the particles toward and onto the surface of the cylinder. Vacuum exhaust means is provided, eifective in the area of the field of force, to prevent undue building up of air pressure in that area and to collect the fog containing those moisture particles which do not adhere to the cylinder. Some air pressure is needed to carry the fog to the field of force, but after the fog reaches the field of force the pressure should be dissipated, as otherwise it will carry the fog outward laterally and into the atmosphere surrounding the machine. Both air pressure for creating and directing the fog into the field of force and vacuum for exhausting air and fog are preferably provided by the same pump. Means is provided along the vacuum line for collecting the excess moisture particles, preferably by electrical precipitation, so that they are removed from the exhausting air, thus preventing them from contaminating the air around the press and, where a single pump is used, preventing them from getting into the pump. The collecting means may be so arranged that the moisture may be reclaimed.

In the drawing, the figure illustrates a generally schematic elevational and partially sectional view of a portion of a plate cylinder of a lithographic printing press and the preferred means for dampening the plate.

As shown in the figure, a plate cylinder 10 has mounted thereon a lithographic plate 11, the ends of which extend into a gap 12. In the embodiment shown, the plate cylinder is electrically grounded as at 13 and rotates in a counterclockwise direction. A housing 14 and a pan 15 confine a fog created within the housing 14 and containing moisture particles 16 of ink repellent material. The housing 14 comprises top, rear and end walls. The forward portion of housing 14 comprises a semicylindrical shell 40, the purposes of which will presently appear.

The fog of air and moisture particles 16 is created by a motor-driven pump 17 which provides air pressure in lines 18 and 19 that extend into the housing 14. The housing 14 extends the full length of the plate cylinder but may be divided into a series of smaller sections if desired. In such cases there may be one line 13 and one line 19 provided for each section. The forward end of line 18 inside the housing 14 is in the form of a jet or nozzle 9. A tube 20 is connected to line 18 and has its other end inserted below the level of liquid 21 contained in the pan 15, by means of which liquid is drawn into line 18 ahead of the nozzle. Line 19 has an opening 22 directly opposite the jet or nozzle 9 and has a plug 23 to enclose air within the line 19 except for the opening 22. The fog containing moisture particles 16 is created by the opening 22 and nozzle 9 being directed toward each other, line 18 sucking up liquid 21 through the tube 20. The blast of air from line 19 and the blast of air and liquid from line 18 create the fog containing moisture particles 16 in the housing 14. Pressure with in the housing 14 causes the fog containing moisture particles 16 to flow down and over the liquid in pan 15 and to pass through an opening 24 between a forward portion of the housing 14 and a rebent portion of the pan 15.

Moisture is thus directed into a field of force created by an electrode 25 connected by means of wires 26 and 27 to a high voltage source 28 grounded at 29. The electrode 25 is shown as being a small diameter wire but any suitable kind of electrode may be used. The field of force exists between the electrode 25 and the grounded plate cylinder 10 and serves to electrically charge and impel moisture particles 16 toward and onto the plate 11 of the grounded cylinder 10. It will be noted that the semicylindrical shell portion 40 of housing 14 is substantially concentric with the electrode 25, and on its forward side constitutes a chamber 41 which serves as a charging zone for the moisture particles and also as a fogconfining area around the electrical field of force. The chamber 41 is provided with end walls, one of which is shown in the drawing at 42.

Rotary switching means 30 is provided in conductor 26 and is timed with the rotation of cylinder 10 to turn off voltage to electrode 25 each time the gap 12 of cylinder 10 comes opposite the electrode. This switching means may comprise a pair of contact brushes 44 and 45, between which turns a circular wiper 46 with an interrupted segment, that maintains the circuit through conductor 26 during .the major part of each revolution. This serves to minimize the deposition of moisture particles in the gap where they may accumulate on the mechanism or form droplets which may be thrown out of the gap by centrifugal force. The opening and closing of switch means 30 should be so timed that a sufiicient amount of dampening solution gets to the edges of the plate while getting as little as possible into the gap.

A portion 31 of the housing 14 and a portion 32 of the pan 15 lie as close to the surface of the cylinder as is practical to confine the fog around the field of force. The housing 1.4 and pan may be of insulating or conducting material as desired. If made of conducting material, the housing 14 may be electrically grounded to assist in the collection of charged stray moisture particles.

Since there is some space between the portion 31 of housing 14 and the cylinder it), and since cut-off of voltage to the electrode occurs each time the gap 12 comes around, and since lines 18 and 19 provide a slight pressure of air within the housing 14, it can be seen that some or" the moisture particles may escape into the atmosphere surrounding the press. By the present invention means is provided 'to collect those moisture particles. This collection is accomplished by the pump 17 which creates a vacuum through a line 33 communicating with an exhaust chamber 34. The vacuum through line 33 and the air pressure through lines 18 and 19 are pref erably continuous and as shown are all created by the same pump 17. When the gap 12 is in the position shown in dotted lines, the space between portion 31lof housing 14 and the cylinder iii will be enlarged and will augment the action of the vacuum in relieving air pressure and in drawing away excess fog accumulating around the electrode 25.

To prevent the moisture particles 16 from getting into the pump 17, means is provided along line 33 to electrically collect the moisture particles. This means is shown on a reduced scale relative to the other parts of the mechanism. It comprises a second electrode 35 connected to wire 27 and a sleeve 36 grounded at 38, the bottom of the sleeve having a drain tube 3'7 connected thereto and preferably arranged to return moisture to pan 15. It can be seen that fog containing moisture particles evacuated from the chamber will pass through line 33 and that the moisture particles will be again electrically charged by the electrode 35, and be impelled onto the sleeve 36 by a field of force created between the electrode 35 and the grounded sleeve. There they accumulate and are conveyed by tube 37 back into the pan 15. As shown, voltage is continually applied to electrode 35 so that the moisture-laden air is cleansed of moisture and may be re irculated through lines 18 and 19.

It should be understood that this invention is equally adaptable to applying ink repellent moisture particles to a vibrating roller which in turn passes the moisture to a pair of molleton rollers which then pass and lay down moisture upon the plate, or to applying moisture to inking rollers by which the moisture is conveyed to the plate. Also, while the electrode 25 as shown serves both to charge the particles and to create the field impelling them toward the plate, the particles may be previously charged by separate means and then brought into the electrical field.

Having thus described my invention, I claim:

1. In a lithographic printing press, an electrically grounded rotating member, an electrode parallel to but spaced from said member, a high potential source of electricity to which said electrode is electrically connected, there being an electrical field of force between the electrode and the grounded member, means for creating a fog containing finely divided ink repellent moisture particles, said fog being directed into said field of force and said field of force impelling the particles toward and onto said grounded member, vacuum creating means, exhaust means connected with said vacuum creating means for collecting those moisture particles not adhering to the grounded rotating member, and electrical precipitating means intermediate the point of collection of moisture particles and said vacuum creating means for reclaiming the moisture and preventing it from entering said Vacuum creating means.

2. The invention set forth in claim 1 in which the means for creating the vacuum also creates air pressure which is utilized in creating the fog.

3. In apparatus for dampening the surface of an electrically grounded rotating cylinder, a wire electrode parallel to but spaced from said cylinder, at high potential source of electricity, an electrical connection between said source and said electrode, a shell partially enclosing said electrode and open toward said cylinder, means including an air pump for creating a fog of air and finely divided moisture particles, means for directing the fog into the field of force between the electrode and the grounded cylinder whereby the moisture particles in said fog are impelled by said field toward and onto the grounded cylinder, exhaust means for collecting fog including moisture particles not adhering to said cylinder, said exhaust means comprising a vacuum line to said air pump, and means for clearing the exhausted fog of moisture particles, said last named means comprising electrical precipitating means.

4. The invention set forth in claim 3 in which the air cleared of moisture particles by said electrical precipitating means is recirculated for creating additional fog.

5. The invention set forth in claim 4 including means for returning moisture precipitated by said electrical precipitating means to its source.

6. In a lithographic printing press, an electrically grounded plate cylinder having a gap, a lithographic plate mounted on said cylinder with its ends extending into said gap, an electrode parallel to and adjacent said cylinder, a high potential source of electricity to which said electrode is electrically connected to provide an electrical field of force between the electrode and grounded cylinder, means comprising a combination air pressure and vacuum pump for creating a fog of air and finely divided moisture particles and presenting said fog into said field of force whereby said particles are charged and impelled toward and onto said plate, exhaust means connected to the vacuum side of said pump for collecting fog containing moisture particles not adhering to said plate, a second electrode intermediate the point of collection of said fog and said pump for again charging the moisture particles in said exhausted fog, grounded means on which said recharged particles are precipitated, and switching means timed with the rotation of said cylinder to turn ofi electricity to said first electrode each time the gap in said. cylinder comes opposite said field of force between the.

first electrode and the cylinder.

7. In apparatus for dampening the surface of an electrically grounded rotating cylinder, an electrode parallel to but spaced from said cylinder, a source of high potential electricity, an electrical connection between said source and said electrode, a shell partially enclosing said electrode and open toward said cylinder, means including an air pump for creating a fog of air and finely divided moisture particles and for moving said fog under pressure into the shell around said electrode and into the field of force between the electrode and the grounded cylinder, whereby the moisture particles in the fog are impelled by said field toward and onto the grounded cylinder, exhaust means efiective in the area of said field of force for lower-' ing the air pressure in said area and for collecting fog including moisture particles not adhering to said cylinder,

5 and electrical precipitating means for clearing the eX- hausted fog of moisture particles, said exhaust means comprising a vacuum line to said air pump in which said precipitating means is located, whereby the air entering the intake side of said pump is free of moisture.

References Cited in the file of this patent UNITED STATES PATENTS 2,551,582 Carlson May 8, 1951 Pethick Apr. 7, 1953 Martin Aug. 30, 1955 FOREIGN PATENTS Great Britain Dec. 1, 1954

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