Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Impression cylinder having a multiple diameter
D E S C R I P T I O N
The invention relates to an impression cylinder having a mul-
tiple diameter and packings provided on the outer cylindrical
surface for carrying a sheet on the side already printed on
in a sheet-fed offset printing machine for printing and
perfecting.
Double-sized impression cylinders having a chromium-plated
and ground outer cylindrical surface are known. While the
m~ch;ne is running, the accumulating of inequalities of the
two halves of the ground cylinder may cause slurring and,
during perfecting, also a re-distribution of the ink already
printed so that the impression cylinder has to be washed more
often, thus increasing the consumption of washing solution
which is detrimental to the environment. This has
unfavourable effects on the quality.
Also known are double-sized impression cylinders which are
blasted before being chromium-plated and which, however, have
relatively rough surfaces and feature an even more inadequate
accuracy of shape due to the inequalities of the impression
cylinders each consisting of two unlike halves so that such
impression cylinders bear the risk of slurring. As soon as
the surface has worn off, the entire impression cylinder has
to be replaced, thus causing high costs for material and
assembly as well as downtimes in the printshop.
The German Patent 24 46 188 discloses an impression cylinder
of single diameter having a nickel foil with a textured
surface mounted on the outer cylindrical surface thereof,
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thus dividing said outer cylindrical surface in raised
sheet-supporting areas and in depressed non-supporting areas
for reducing the building up and accumulating of ink on the
outer cylindrical surface when coming into contact with the
freshly printed sheet side. Foils serving this purpose are
known from the DE-OS 29 16 505.
It is the object of the invention to guarantee, with
impression cylinders of multiple diameter, a high printing
quality even when perfecting, without ink depositing on the
outer cylindrical surfaces of said impressions cylinders, and
to reduce thus the washing times which, in turn, reduces the
washing-solution consumption.
This object is achieved as described by the features of Claim
1 of the invention.
A number of foils having different thicknesses and, if
required, different shapes from among which the pressman can
take his choice are assigned to the impression cylinder so
that the concentricity errors or the sum of the inequalities
of the two halves of a double-sized impression cylinder are
compensated for by selecting an appropriate foil.
If necessary, intended unparallel grinding of the foils is
possible by displacing the center of the grinding device so
that the foil surfaces run unparallel to each other in
circumferential direction, thus achieving a difference in
thickness between leading foil edge and trailing foil edge in
sheet-conveying direction. Such foils are applied onto the
impression cylinder in a stepped manner, e.g. arranged in
three steps varying by 0.01mm from each other. At any time,
the impression cylinder can be brought into a new state by
means of a fixed mark and by exchanging the foil upon
detection of inequalities of the impression cylinder halves,
or e.g. in case of wear and tear, or in the case of damages
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occurring during production. Appropriate methods of
accurately grinding the backside of the foil are already
applied by companies having specialized in this field. Also
known are appropriate measuring devices by means of which the
entire format can be detected so that the foils can be
pre-selected.
- By analogy with foils designed for impression cylinders of
single diameter, foils which are used according to the
invention can be formed of a base layer having a high modulus
of elasticity and of a chromium layer producing the textured
surface by means of which the sheet is carried.
According to the invention the drawing shows two foil
specimen embodiments distorted in scale; moreover, the
principle of a foil-processing device is illustrated.
Fig. 1 shows a section of a foil having surfaces which run
parallel to each other, the scale being distorted,
Fig. 2 shows a section of a foil having surfaces which do
not run parallel to each other, the scale being
_ distorted according to Fig. 1, and
Fig. 3 is a side view of the basic setup of a
foil-processing device according to Figs. 1 and 2.
On the basis of respective marks and measurements taken a
number of foils having stepped thicknesses, e.g. 0.3mm,
_ 0.29mm, 0.28mm according to the representation in Fig. 1, are
applied onto said impression cylinder in the region of a
sheet-carrying surface and secured in order to compensate for
the concentricity errors and/or inequalities of the two
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halves of a ground impression cylinder of double-sized
diameter.
In order to make up for the displacement of the center the
surfaces of said foils may also run unparallel to each other
according to the illustration in Fig. 2 so that e.g. the
leading edge 7 has a greater thickness than the trailing edge
8.
Accordingly, surfaces 9 and 10 running unparallel to each
other may bring about a difference in thickness between drive
side and operation side.
Fig. 3 shows the simplified setup of a device for processing
a foil serving the purpose of the invention. It consists of a
grinding cylinder 1 mounted in a frame 3 so as to pivot about
an axle 2 and features means whhich are provided on the outer
circumference for mounting and clamping a foil 4 to be
processed. A driven grinding disk 5 the axle 6 of which runs
parallel to the axle 2 acts on said foil 4. In order to
obtain an unparallel foil 4 surface extending in
circumferential direction the axle 2 of the bearing of the
grinding cylinder 1 is displaced, with respect to the axle 6
of the grinding disk 5, in the common plane of the two axles
2 and 6 in direction 2a.
Furthermore, if required, it is possible to modify the angle
of the parallel position of the two axles 2 and 6 in order to
obtain varying foil thicknesses on the drive side as well as
on the operation side, e.g. with respect to cone-ground
cylinders.
In a known manner the foil itself may consist of a base layer
and a top layer having said textured surface which prevents
ink from accumulating and building up when perfecting.
