Technical Field

The present invention relates to a spray tube for a blanket washing device at a printing press, the tube being provided with holes or nozzles for spraying a washing liquid.

Background of the Invention

A blanket washing device or blanket washer is used in a printing press for cleaning a certain cylinder therein, preferably provided with a blanket. A washing liquid, for example a mixture of a mineral oil fraction and water, is sprayed on a cleaning web, consisting of paper, non-woven fabric, felt or some other absorbent material. The web is intermittently advanced to a pad of the blanket washer and is brought in contact with the rotating cylinder. When this web portion cannot perform its cleaning function properly any more, the web is advanced, so that a new web portion with new washing liquid gets in contact with the cylinder. The function of the spray tube in the blanket washer is accordingly to intermittently spray the washing liquid on the cleaning web. For different reasons it has become normal practice in the art to fill the tube with washing liquid to a level under the holes or nozzles and then to press the liquid out through the holes or nozzles by suit¬ able means. This may according to EP-B-0 025 806, which is regar¬ ded as the closest prior art, be obtained in that pressurized air is supplied to the tube. The principal drawbacks with this procedure are that it is virtually impossible to obtain a uniform pressure for all the nozz- les, that liquid drops will leave the nozzles after the proper spraying, and that towards the end of the spraying there is a tendency for aerosol formation (the pipe

"steams") .

The Invention

These and other drawbacks are according to the inven¬ tion obviated in that the tube is provided with an inter- nal, elastic partition wall, dividing the tube into separate compartments for the washing liquid and for a fluid under pressure, which at a spraying action is intended to expand the wall towards the washing liquid compartment for pushing the liquid out through the holes or nozzles.

This partition wall may have different configurations. It may for example extend diametrically in a tube with circular or rectangular cross section.

In a preferred embodiment, however, the tube is provided with an internal, elastic sleeve, expandable by means of the fluid under pressure, the washing liquid being contained between the tube and the expandable sleeve.

Hereby the pressure on the washing liquid may be com¬ pletely uniform, and the spraying action may be more precisely governed, especially towards the end, when no tendency for dripping or aerosol formation will occur.

It is preferred that the expandable sleeve is arranged on an axial support rod centrally arranged within the tube. This support rod is hollow and provided with openings for supplying fluid under pressure to the sleeve. The fluid is preferably pressurized air. As an alternative to arranging the expandable sleeve on a support rod for its proper central positioning in the unexpanded condition, the sleeve may be provided with external spacer means, such as knobs or the like. The Drawing

The invention will be described in further detail be¬ low reference being made to the accompanying drawing, in which Fig 1 is a schematic side view of a blanket washing device incorporating a spray tube according to the inven-

tion. Fig 2 is a partly sectional view of the spray tube, and Figs 3a and 3b are cross sectional views along the line III-III in Fig 2 through the spray tube in two operational conditions. Detailed Description of a Preferred Embodiment

A blanket washing device 1 consists in principle of a frame 2, in which a supply roller 3 and a receiving roller 4 for a cleaning web 5 is rotatably mounted. On its way between the two rollers 3 and 4 the cleaning web 5 passes over a spray tube 6 and a pad 7 connected to the frame 2.

The spray tube 6 is mounted to the frame 2, and the cleaning web 5 glides on its surface. The spray tube 6 is intended to spray a washing liquid on the cleaning web 5, before the latter reaches the pad 7. When a printing press cylinder 8, normally provided with a blanket, is to be cleaned, the blanket washing device 1 is advanced by suit¬ able means (not shown), so that the pad 7 is slightly pressed against the cylinder 8.

An end portion of the spray tube 6 is shown in Fig 2. Means for attaching the tube to the frame 2 are not shown, neither are means for supplying washing liquid to the interior of the tube from a supply thereof.

The tube 6 is provided with a fixed end piece 9, sealed in relation thereto by means of an O-ring 10. A support rod 11 is centrally arranged in the tube 6 with its end 11' received by the end piece 9 and sealed in relation thereto by means of an O-ring 12.

A sleeve 13 is arranged over the support rod 11 and is attached to the end thereof by means of a strap 14. In order to ensure tightness in the region of the strap 14 an O-ring 15 is arranged thereunder. The sleeve 13 is made of a fluid-tight, elastic material so as to be expandable to such an ext nt that it can get into contact with the inner surface of the tube 6. Such expansion can be accomplished by means of a fluid under pressure, preferably pressurized

air, introduced in the area between the support rod 11 and the sleeve 13. This introduction is performed in that the support rod 11 is hollow and has a certain number of through openings 16 and in that the end piece 9 has a bore 17 for the supply of fluid under pressure to the hollow support rod 11 and the sleeve 13.

As already stated, means (not shown) are provided on the tube 6 for admitting washing liquid 18 (Figs 3a and 3b) to the concentric space between the sleeve 13 and the tube 6, which is provided with holes or nozzles 19 for spraying this liquid. The number of holes or nozzles 19 on the spray tube 6 is selected so as to evenly wet the cleaning web 5 over its entire width.

The operation of the blanket washing device with the spray tube according to the invention as shown and described is as follows:

The spraying action is to be performed intermittently in order to provide the cleaning web 5 with washing liquid, before the wetted area is advanced to the pad 7 by drive means (not shown) for one of or both rollers 3 and 4.

In the period between two spraying actions the volume in the tube 6 outside the sleeve 13 may be filled with washing liquid up to the level of the holes or nozzles 19 as shown in Fig 3a; the sleeve 13 is unexpanded. The spraying action is performed in that pressurized air (or any other suitable fluid under pressure) is intro¬ duced through the bore 17, into the hollow support rod 11 and the sleeve 13 through the rod openings 16, so that the sleeve 13 is forcefully expanded to the condition shown in Fig 3b and the washing liquid 18 is sprayed out through the holes or nozzles 19.