Printing – Antismut device – Cleaners
Reexamination Certificate
2001-05-23
2003-08-19
Hirshfeld, Andrew H. (Department: 2854)
Printing
Antismut device
Cleaners
C101S424100, C271S195000, C271S204000, C271S211000, C118S312000, C118S326000
Reexamination Certificate
active
06606946
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The invention lies in the field of printing. The invention relates to a sheet-fed offset printing process, in which flow relationships in the interior of a housing of a sheet delivery of a sheet-fed offset printing machine are altered to prevent the uncontrolled spread of powder in the housing. Powder-laden air is extracted from the housing on at least one point along an empty run of a sheet conveying device and/or air is fed into the housing from outside. The invention relates further to a sheet-fed offset printing machine having a sheet delivery and a powdering device disposed in a housing of the sheet delivery to powder the printed sheets. The machine has air feed devices to feed air into the housing from outside and/or air extraction devices to extract powder-laden air from the housing. The devices are disposed on at least one point along an empty run of a sheet conveying device to prevent the uncontrolled spread of powder in the housing by altering the flow relationships inside the housing.
Printing processes and printing machines are described, for example, in my German patent application DE 198 01 949.1, from which priority is claimed in my U.S. patent application Ser. No. 09/619,975 through PCT/EP99/00271. U.S. patent application Ser. No. 09/619,975 is hereby incorporated herein by reference. The application proposes to feed air deliberately into the interior of the housing of a sheet delivery of a sheet-fed offset printing machine to prevent the uncontrolled spread of powder in the interior of the delivery or into the surroundings by altering the flow relationships. With a view to limiting the spread of powder and reducing the necessary amounts of powder, particularly good results are achieved if the air was fed into the housing from above through the empty run in a region located downstream of a powdering device in the direction of motion of a conveying run of the sheet delivery, and/or at the same time powder-laden air was extracted from such region.
In the sheet deliveries of conventional offset printing machines, air turbulence occurs to a great extent. Various effects cause the air turbulence. For example, underneath and above the conveying run and the empty run of the sheet delivery, the suction action of the moving sheet grippers and chains entrains air in the direction of motion of the respective run. Also, printed sheets carried along by the conveying run flutter or, when being deflected from an oblique angle into the horizontal, flip up at their rear edge (also known as the lashing or flag effect). Further, air is blown from below against the sheet from the sheet guide plate to guide the sheet over the guide plate without contact, but some of the air flows upward between the adjacent sheets and laterally past the sheets.
As a result of the air turbulence, a large part of the powder emerging from the powdering device is swirled and entrained by the air. Thus, it does not pass as desired onto the printed surface of the sheets directly underneath the powdering device. Instead, the powder is distributed over the entire interior of the sheet delivery by the air flows, in particular, those along the two runs of the sheet delivery. The distribution not only leads to increased wear of moving parts and relatively long down times for cleaning the sheet delivery, it also aggravates operating personnel because the swirled powder emerges into the surroundings through all the openings in the sheet delivery, in particular, through the sheet outlet opening and air outlet grating on the top of the housing.
In addition, as a result of the powder being transported back as far as the impression cylinder of the last printing unit or as far as the delivery drum of the printing machine, powder gets onto the still moist surface of the printing material or the printing ink directly after the printing material has emerged from the printing machine. The powder, which usually includes starch, picks up part of the liquid present there, for example, surface water originating from the feed of damping solution, and possibly also relatively highly volatile or low-viscosity constituents of the printing ink. Because the liquid picked up by the powder is not absorbed into the printing material, or is absorbed considerably more slowly, and does not participate in the chemical crosslinking process of the printing ink either, the moisture content of the sheets is higher when they are deposited on the sheet stack. Such moisture delays the drying, and there is an increase in the time intervals needed before the further processing of the printed products. Next, in the event shear is exerted on the moist printing ink, the liquid picked up by the powder can also have a decreasing effect on the shear strength of the printing ink if deposited powder particles are detached. Such detachment can result in the exposure of incompletely dried point-like surface areas of the printing ink located underneath the detached particles.
The adverse affect is counteracted, according to my co-pending U.S. patent application Ser. No. 09/619,975, by feeding air into the housing of the sheet delivery from above through the empty run. The air feed firstly prevents powder from being transported in the direction of the printing machine by the empty run and by air flows along the empty run and, secondly, in conjunction with one or more brush strips, the empty run being freed from adhering powder. If some of the air fed in, after passing through the empty run, is deflected in the direction of the printing machine, the deflected air also prevents powder in the region of the powdering device from getting as far as the empty run of the sheet delivery and from being transported by the empty run in the direction of the printing machine. As a result, at least in the case of sheet-fed offset printing machines with short sheet deliveries, the region of the sheet delivery located directly downstream of the delivery drum could be kept virtually powder-free, a status that not only reduces wear and powder emissions into the surroundings but, surprisingly, could also accelerate the drying of the printing material and the printing ink, probably because of the action mechanism described in the preceding paragraph.
The amount of excess powder emerging into the surroundings of the sheet delivery could be reduced once more by extracting part of the air fed in and of further powder-laden air from the interior of the housing of the sheet delivery in the direction of movement of the conveying run downstream of the powdering device, as proposed by my co-pending U.S. patent application Ser. No. 09/619,975.
Trials and experience with processes and devices for keeping clean or cleaning a sheet delivery of a sheet-fed offset printing machine of excess powder according to my U.S. patent application Ser. No. 09/619,975 have shown, however, that further improvements are possible with regard to reducing the powder emissions inside and outside the sheet delivery.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a sheet-fed offset printing process and a sheet-fed offset printing machine that overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices and methods of this general type and that reduces the spread of powder.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a sheet-fed offset printing process, including the steps of altering flow relationships in an interior of a housing of a sheet delivery of a sheet-fed printing machine to prevent uncontrolled spread of powder in the housing by at least one of extracting powder-laden air from the housing on at least one point along an empty run of a sheet conveying device; and feeding air into the housing from outside the housing on at least one point along the empty run, channeling air flows inside the housing by feeding air not laden with powder into the housing and leading the air not laden with powder into an air flow path along the empty run downstream
Ghatt Dave A.
Greenberg Laurence A.
Heidelberger Druckmaschinen AG
Hirshfeld Andrew H.
Locher Ralph E.
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