Printing – Antismut device
Reexamination Certificate
2000-07-20
2004-10-12
Walsh, Donald P. (Department: 3653)
Printing
Antismut device
C101S424000, C101S424100, C347S102000, C118S312000, C118S326000, C271S207000
Reexamination Certificate
active
06802256
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a method and a device for preventing uncontrolled spread of powder in a printing machine. The invention relates in particular to a method in which sheets printed in a sheet-fed printing machine are conveyed through a sheet delivery system above a sheet deposit pile by a sheet conveying device and, in the process, are dusted with a powder, and wherein uncontrolled spreading of excess powder is prevented, and to a device for preventing uncontrolled spreading of powder in a housing of a sheet delivery system of a sheet-fed printing machine, the housing surrounding a sheet conveying device for transporting printed sheets over a sheet deposit pile, and a dusting device for dusting the printed sheets with a powder. Furthermore, the invention relates to a sheet delivery system for a sheet-fed printing machine and to a sheet-fed printing machine having such a device for preventing the uncontrolled spreading of powder.
During sheet-fed offset printing in larger sheet-fed offset printing machines, the paper sheets printed on one or both sides, after passing through the printing units of the printing machine, are usually picked up by a chain conveyer of the paper or sheet delivery system, i.e., a chain conveyer having two parallel chains connected by delivery gripper systems or sheet grippers and, within a housing that encloses the sheet delivery system and the printing units of the printing machine, are transported to a location over a sheet pile, whereon they are subsequently deposited above one another. Because the printing ink has not yet completely dried when the sheets are piled above one another, in most of the sheet-fed offset printing machines on the market, at least one surface of each sheet, before the sheet is deposited on the pile, is dusted with a powder which sticks to the printed parts of the paper sheets and prevents set-off, i.e., a sticking together of the paper sheets in the sheet pile. The powder that is used is usually finely powdered potato starch or other powdery starch products. In order to apply the powder, use is made of a so-called spray powder device or any other dusting device which, as a rule, is arranged in an intermediate space between the forward-running conveyor strand transporting the sheets and the returning empty strand of the chain conveyer, and dusts, with powder from above, the sheets which are carried by the lower conveyor strand of the chain conveyer and transported past the powder device.
High-speed sheet-fed offset printing machines for printing large editions, such as the sheet-fed offset printing machines sold by Heidelberger Druckmaschinen AG under the designation Heidelberg Speedmaster, are usually provided with a high-pile sheet delivery system, in order to be able to stack or pile up more sheets. In such sheet delivery systems, the conveying strand of the chain conveyer initially extends obliquely upwardly and is then deflected into the horizontal, in order to align the printed sheets horizontally before releasing them over the sheet deposit pile. The dusting device is disposed thereat usually just before the upper end of the oblique portion of the conveying strand, in the interspace between the latter and the empty strand of the chain conveyor.
During the operation of sheet-fed offset printing machines of this type, it has been determined that considerably more powder is consumed than is actually necessary for dusting the paper sheets. At the same time, the ambient air around the sheet delivery system has a considerably increased dust content, caused by powder particles, while deposits of powder form to an increased extent on movable and immovable parts in the interior of the housing of the sheet delivery system. The high dust content in the ambient air which, to some extent, can be referred to as a virtual powder mist, is found to be extremely unpleasant by the operating personnel, while deposits of powder in the interior of the housing, in particular on movable parts, lead to increased wear and relatively long downtimes of the machine, due to a requirement for more frequent cleaning and maintenance work.
During investigations and testing by the applicant to clarify the causes of the dust loading caused by powder in the ambient air, as well as the powder deposits in the housing of the sheet delivery system, it has been established that air turbulence occurs to a great extent in the sheet delivery systems of conventional offset printing machines. This air turbulence is caused, inter alia, by the fact that, in each case, underneath and above the conveying strand and the empty strand of the sheet delivery, air is entrained in the direction of motion of the respective strand as a result of the suction action of the moving sheet grippers and chains, by the fact that printed sheets entrained by the conveying strand flutter or, when being deflected from the oblique into the horizontal position, flip upwardly at the rear or trailing edge thereof (a so-called whipping or flapping effect), and by the fact that air is blown from below towards the sheet from the so-called sheet guiding plate, in order to guide the sheet over the guide plate without contact, but some of this air flows upwardly between the adjacent sheets and laterally past the respective sheet.
Due to this air turbulence, a great part of the powder emerging from the powder dusting device is swirled about and entrained by the air so that it does not pass onto the surface of the printed material directly underneath the powder dusting device, as desired. Instead, the powder is distributed over the entire interior of the sheet delivery system by the airflows, in particular those along the two strands of the sheet delivery. This results not only in increased wear of moving parts and longer downtimes for cleaning the sheet delivery system, but also to irritation or disturbance of the operating personnel, because the swirled powder also escapes into the environment through all the openings in the sheet delivery system, in particular through the sheet outlet opening and air outlet gratings on the top of the housing.
In order to reduce the high dust loading of the ambient air and to eliminate further problems caused by excessive powder, in U.S. Pat. No. 5,265,536, a suction hood arranged above the sheet pile and a sheet outlet opening is proposed, which serves for extracting or sucking powder-laden air upwardly through the empty strand, in order then to clean the air. Some of the powder-laden air, however, is entrained by the suction of the empty strand as it passes therethrough and flows along the empty strand in the direction of the printing machine.
In addition, the published German Patent Document DE 42 07 118 A1 discloses a sheet delivery system in a sheet-fed printing machine, having a housing wherein, in the vicinity of the powder dusting device above the delivery strand, devices are provided for extracting or sucking excessive powder and, therefore, for preventing the uncontrolled spreading thereof. Devices of this type immediately extract or suck up a large portion of the applied powder again, but this often has the result that the operating personnel increase the supply of powder, and in this way even more powder is consumed. On the other hand, the problem of powder spread due to air suction in the interior of the housing is not solved.
In addition, the German Published Prosecuted Patent Application (DE-AS) 2 148 757 discloses a sheet delivery system in a printing machine wherein, along an upper horizontal portion of the empty strand of a sheet conveyer, a cleaning device is provided, which includes a housing, a number of brushes arranged in the housing and an extraction or sucking device for extracting or sucking away the powder cleaned off the chains and gripper systems by the brushes. However, in this published German patent application, neither the problem of the spread of powder due to the powder-laden air entrained by the suction of the empty strand was detected, nor is the described cleaning device
Heidelberger Druckmaschinen AG
Shapiro Jeffrey A.
Walsh Donald P.
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