4 14.1.3 Basic Gravure Concepts Methods of Cylinder Preparation-P334Diffusion etch processDirect transfer processElectromechanical processLaser cutting process
5 Fig. Cylinder engraving with stylus Fig. Cylinder engraving with stylus.a Control of the engraving head; b Electromechanical cylinder engraving (Hell Gravure Systems)
6 Electromechanical Engraving Engraving machine only consists of a lathe-like device, into which the prepared gravure cylinder is mounted.The gravure cylinder rotates during engraving at a constant surface speed (depending on the screen at approximately 1 m/s). At the same time the diamond stylus of the engraving head moves at a high frequency (4–8 kHz). The diamond penetrates the copper at different depths and produces the cell.
7 Electromechanically engraved cells on the cylinder surface Electromechanically engraved cells on the cylinder surface. The halftone values result from the varying cell volumes; variable area/ variable depth.
9 Engraving machine for electromechanical stylus engraving with up to 16 engravingheads.
10 Fig. Overview of the production of gravure cylinders
11 14.1.4 Well formation -P338 Figure14.10 Every gravure well has four variables:DepthBottomOpeningBridge
12 14.1.5 Cylinder consideration and Preparation -P340 AxisShaftDiameterCircumferenceFace length
13 14.2 Gravure Prinitng Machine Feeding unit + Printing unit + Registration unit + Delivery unitRotogravure Printing MachineEngraving Gravure Printing Machine
14 Features Direct printing Print mass-circulation products Round to Round structureFast printing speed, dry device
15 Part of a rotogravure printing press; the row of individual printing units is shown withthe ink supply tanks in the foreground.
16 Gravure Cylinder Manufacture Electroplating processGravure Cylinder Manufacture电解液直流电源整流器The cylinder receives a base copper layer on its surface, which, among other things, serves to achieve the specified diameter of the finished gravure cylinder.
17 Fig. Structure of a gravure cylinder The base copper layer is coated with an engravable copper layer (approximately 80 µm) in an electroplating电镀 process. This thin layer only allows a one-time engraving. The advantage of the thin layer technique is that all the gravure cylinders of one type have the same diameter dimensions and less mechanical surface treatment is required after the electroplating process than with thick layer processes.
18 The process sequence for preparing an engraving cylinder is generally as follows: • removing the used gravure cylinder from the gravure printing press;• washing the gravure cylinder to remove residual ink;• removing the chrome layer;• removing the copper image-carrying layer, either chemically, by means of electroplating, or mechanically;• preparing the copper plating process (degreasing and deoxidizing, applying the barrier分隔 layer if the Ballard skin method was employed);
19 • electroplating;• surface finishing with a high-speed rotary diamondmilling head and/or with a burnishing stone or apolishing band;• etching or engraving (producing the image on thegravure cylinder);• test printing (proof print);• correcting the cylinder, minus or plus (i.e., reducingor increasing the volume of cells);
20 • preparing the chrome-plating process (degreasing and deoxidizing, preheating, and – if necessary –sometimes polishing);• chrome-plating;• surface-finishing with a fine burnishing stone orabrasive paper砂纸;• storing the finished cylinder or installing it directlyin the gravure printing press.
21 A. Impression CylinderThe impression roller consists of a special rubberlayer of high shore hardness and is applied seamlessly3.5mm rubber layerB. Plate CylinderPosition Arrangement：PIuprightnessPIgradientPIhorizontal
22 The radio of cylinder diameter： Pr (P) : r (I) = 1 :2r (P) : r (I) = 1 : 1PI
24 Blade The blade is subject to a high level of wear and must be changed regularly (normally with a new print job).The blade must be aligned exactly parallel to thegravure cylinder surface, assured today by the hydraulicblade clamping with pressure selection and self-alignment.The angle of contact is also important for a goodresult and is used as a control parameter with difficultimagesPbladeØ
25 a Principal structure; b Doctor blade 支点Gravure inking unit.a Principal structure;b Doctor blade
26 D. DryingThe ink used for gravure printing has a low viscosity,so that the ink in the cells can run out properly and betransferred onto the paper.This low viscosity is principally achieved by using a high proportion of solvent with low boiling point in the ink.To dry the printed ink, the solvent must evaporate in a high velocity air dryer after leaving the printing nip.