Printing – Inkers – Roller
Reexamination Certificate
2002-03-06
2003-10-28
Eickholt, Eugene H. (Department: 2854)
Printing
Inkers
Roller
C101S169000, C101S363000
Reexamination Certificate
active
06637330
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention concerns a doctor blade system for printing units as described in the preamble of claim
1
. Also, the invention concerns a clamping device for a doctor blade.
In the present application, the invention will be explained specifically in connection with doctor blade chambers but may also be utilised in other doctor blade systems where a doctor blade is secured between a beam and a doctor rail.
In rotating printing units for offset printing, flexo printing etc. there is advantageously used systems including so-called doctor blade chambers. A doctor blade chamber is an ink container which by means of so-called doctor blades fits tightly to an ink transfer roller, and from which container ink is transferred to this roller, often a raster roller transferring the ink to further rollers forming a part of the printing process.
The doctor blade chamber, which may be several meters long, consists mainly of a doctor beam constituting the wall of an ink chamber, in the front side of which, facing the roller, there is an open channel and two or more doctor blades clamped onto the doctor beam. These doctor blades are thin, elongate blades having one longitudinal side firmly connected to the doctor beam and with their opposite sides resting under a certain spring force against the roller.
Often two doctor blades are used in the doctor blade chamber system, where one doctor blade serves for sealing for the ink chamber against the roller, and the other serves for sealing the ink chamber against the roller as well as supplying the roller with an even layer of ink; these functions are advantageous as compared with system where the roller collects ink from an open ink container as in that case it is difficult to achieve an even and precise ink transfer. Besides, an open ink container has the disadvantage that a part of the ink is sprayed around the roller at the collection due to the great speed of the roller, thereby contaminating the printing unit.
The doctor blades, which, in spite of this common name, may also be made of synthetic material, are wear parts in a printing unit. A doctor blade is a thin blade resting on the ink transfer roller, for example the raster roller.
Depending on the quality of the roller and on the ink, a doctor blade lasts between one day and several weeks after which it has to be replaced. For replacing the doctor blade, according, to prior art the doctor blade chamber usually has to be taken out of the printing unit which is a disadvantage. After demounting a clamping rail disposed on the beam of the doctor blade chamber and keeping the doctor blade clamped between the rail and the bean, the doctor blade may be replaced after which the clamping rail may be mounted again.
According to prior art, this clamping rail is screwed onto the doctor blade chamber beam with a number of screws, implying some disadvantages. First, quite a number of screws (10 screws per meter of doctor blade chamber) have to be loosened and tightened, making the replacing process slow. Second, it is a well-known problem that the clamping rail does not clamp quite evenly on the doctor blade as the screw system implies a raised pressure right around the screws. The consequence is that the doctor blade does not lie evenly to the roller but “flickers”, i.e. has shape like a wave. These variations in distance between the doctor blade and the roller, even though they are very small—in the magnitude of few micron—, result in the application of ink on the roller not being quite even, thereby depreciating the printing quality. Furthermore, at the areas between the screws ink may penetrate between the doctor blade and the clamping rail and between the doctor blade and the doctor beam, further enhancing the “flickering” effect and requiring frequent cleaning. Third, tools are required for loosening and tightening the screws. During work it may be a great source of irritation for the workers if this tool is not available for the replacement, for example because a colleague has mislaid it.
A quick replacement of the doctor blade is achieved with a mechanism as described in American patent U.S. Pat. No. 5,517,918 where the doctor blade is secured by means of a couple of leaf springs. The leaf springs overlap some of the doctor blade and is prestressed so that the doctor blade is pressed against the beam. By replacing the doctor blade there is used a displacing mechanism in the form of a resilient tube, which may be expanded automatically whereby the springs are pushed away from the doctor blade which is thereby loosened.
This mechanism has the disadvantage that the springs are fastened by a row of screws in analogy to the holding of the clamping rail in traditional doctor blade chambers. As the springs are a lot thinner that traditional clamping rails, the above flicker-effect is still more pronounced than in traditional printing units, making this system unsuitable for print where high quality is demanded.
Another system has been described in American patent U.S. Pat. No. 3,085,275 where the doctor blade is secured between the clamping rail and the beam by the force from a pneumatic expanding tube is transferred to the clamping rail by means of a tip mechanism. In this system it is not the holding mechanism itself which causes flickering in the doctor blade but a guide rail provided on the doctor blade, the guide rail being fastened with screws to the doctor beam. Furthermore, in this system it is disadvantageous that the doctor blade is fastened to a rail which together with the doctor blade has to be pushed laterally out of the chamber when changing doctor blade. As printing units may be very long, much space beside the printing unit is required. A further drawback is that the printing unit only functions satisfactorily if there is sufficient pneumatic pressure. By pressure failure the printing unit will not be able to work satisfactorily any more.
Different pressure systems exist where the doctor blade is clamped between the clamping rail and the beam without flicker appearing. Such a system is described in American patent publication U.S. Pat. No. 4,938,131. By pneumatic expansion of a flexible tube, the clamping rail is pressed against the doctor beam whereby the doctor blade is secured therebetween. This system has, however, the great disadvantage that the doctor blade is no longer secured if failure of the pneumatic supply occurs. This implies a great risk of danger as the doctor blade, due to the rotating printing roller, may be flung out of the doctor with great speed with risk of damage to equipment and people around the printing unit.
SUMMARY OF THE INVENTION
The purpose of the invention is to provide a doctor blade chamber with a clamping device for doctor blades which does not have the above drawbacks.
This purpose is achieved with the present invention by a doctor blade system of the kind mentioned in the introduction, and which is peculiar as described in the characterising part of claim
1
.
Such a clamping device may be used in doctor chambers with a doctor blade, e.g. single doctor blades for use in intaglio or screen process printing, or in doctor devices with two or more doctor blades, e.g. doctor blade chambers for rotary printing.
By designing the beam of the doctor blade chamber and the clamping rail with a groove, preferably T-shaped, in which there is mounted a suitable, for example T-shaped, sectional rail, there is achieved a continuous connection between the clamping rail and the beam not having the drawbacks of the previously described pointed connection where screws are used.
To achieve clamping of the doctor blade, the beam is designed with a groove in which the sectional rail may be displaced in direction against the bottom of this groove so that by this displacement a clamping of the doctor blade between the clamping rail and the doctor blade chamber is effected. The trouble implied in loosening and tightening the row of screws is avoided by this device.
In practice, the displacement of the sectional rail is effected in the way
Bastrup Uffe
Gydesen Erik
Larsen Jan Kjaer
Nordby Klaus
Creighton Wray James
Eickholt Eugene H.
Narasimhan Meera P.
Tresu Production A/S
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