The invention relates to a sheet transport drum in a sheet printing machine, the transport drum including a first comb segment and a second comb segment, of which the latter is mounted so as to be rotatable relative to the first comb segment for adjusting to a format length corresponding with a printing-material sheet.
Heretofore known sheet transport drums of the foregoing general type are subject to the following problem: depending upon how far the second comb segment is rotated relative to the first comb segment, interspaces of greater or lesser size gape open between prongs of the comb segments, and air flows outwardly through the interspaces from the interior of the sheet transport drum under the action of centrifugal force. The air flowing out of the sheet transport drum in an undesired manner causes the printing-material sheet overlapping the interspaces to be lifted off in an uncontrolled manner as the sheet is transferred from the sheet transport drum to a further sheet transport drum. Until the present, this unavoidable disruption of the sheet transport resulting from the construction of the heretofore known sheet transport drums has stood as an obstacle to a further increase in the rotational speed of the sheet transport drum, i.e., the speed of the sheet-fed printing machine.
It is accordingly an object of the invention to provide a sheet transport drum with comb segments which prevent the printing-material sheet from being lifted off the drum in an uncontrolled manner even at very high machine speeds.
With the foregoing and other objects in view, there is provided, in accordance with one aspect of the invention, in a sheet-fed printing machine, a sheet transport drum, comprising a first comb segment and a second comb segment, the second comb segment being mounted so as to be rotatable relative to the first comb segment for providing an adjustment to a format length corresponding with that of a printing-material sheet, the comb segments being formed of prongs having interspaces therebetween, and at least one covering provided for covering the interspaces between the prongs.
In accordance with another feature of the invention, the at least one covering engages, at the inside thereof, at least one of the comb segments.
In accordance with a further feature of the invention, the at least one covering is constructed so as to be actuatable pneumatically.
In accordance with an added feature of the invention, the at least one covering is inflatable.
In accordance with an additional feature of the invention, the at least one covering is selected from the group consisting of a flexible tube, a bellows and a balloon.
In accordance with yet another feature of the invention, the at least one covering engages at the outside thereof with at least one of the comb segments.
In accordance with yet a further feature of the invention, the at least one covering is a foil.
In accordance with yet an added feature of the invention, the at least one covering is partially wound up.
In accordance with another aspect of the invention, there is provided a sheet-fed printing machine including at least one sheet transport drum, comprising a first comb segment and a second comb segment, the second comb segment being mounted so as to be rotatable relative to the first comb segment for providing an adjustment to a format length corresponding to that of a printing-material sheet, the comb segments being formed of prongs having interspaces therebetween, and at least one covering provided for covering the interspaces between the prongs.
In accordance with a further feature of the invention, the sheet-fed printing machine includes a reversing device of which the sheet transport drum is a constituent part.
In accordance with a concomitant feature of the invention, the sheet transport drum is constructed as a storage drum, and the reversing device includes a further sheet transport drum constructed as a reversing drum.
Thus, the invention calls for interspaces between prongs of the comb segments to be covered by at least one covering.
Of course, this covering is not identical with the printing-material sheet.
The printing-material sheet is guided on the sheet transport drum according to the invention just as reliably as on a sheet transport drum having a continuous circumferential surface or as on an impression cylinder, even at very high machine speeds of, for example, 15,000 or more printed sheets per hour.
It is possible, for example, to provide a first covering for covering interspaces between the prongs of the first comb segment, and a second covering for covering interspaces between the prongs of the second comb segment. The at least one covering may be constructed so that it can be pneumatically actuated and/or wound up and unwound. It is also possible for the covering, at the outside or the inside thereof, to engage with at least one of the comb segments.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a sheet transport drum, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, wherein: