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Encyclopedia Britannica - Main :: EMS-EUD |
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ENGRAVING OF COPPER ROLLERS The engraving of copper rollers is one of the most important branches of textile-printing and on its perfection of execution depends, in great
(I) Engraving by hand is the oldest and most obvious method of engraving, but is the least used at the present time on account of its slowness. The design is transferred to the roller from an oil-colour tracing and then merely cut out with a steel graver, prismatic in section, and sharpened to a bevelled point. It requires great
special
work
(2) In the etching process an enlarged image of the design is cast upon a zinc plate
plate
original
original
print
of its size, and is so arranged that when its pointer or " stylus " is moved along the engraved lines of the plate a series of diamond points cut a reduced facsimile of them through the varnish with which the roller is covered. These diamond points vary in number according to the number of times the pattern is required to repeat along the length of the roller. Each colour of a design is transferred in this way to a separate
(3) In machine engraving the pattern is impressed in the roller by a small cylindrical " mill " on which the pattern is in relief. It is an indirect process and requires the utmost care at every stage. The pattern or design is first altered in size to repeat evenly round the roller. One repeat of this pattern is then engraved by hand on a small highly polished soft steel roller, usually about 3 in. long and 4 in. to 3 in. in diameter ; the size varies according to the size of the " repeat " with which it must be identical. It is then re-polished, painted with a chalky mixture to prevent its surface oxidizing and exposed to a red-heat in a box filled with chalk and charcoal; then it is plunged in cold water to harden it and finally tempered to the proper degree of toughness. In this state it forms the " die " from which the " mill " is made. To produce the actual " mill " with the design in relief a softened steel cylinder is screwed tightly against the hardened die and the two are rotated under constantly increasing pressure until the softened cylinder or " mill " has received an exact replica in relief of the engraved pattern. The " mill " in turn is then hardened and tempered, when it is ready for use. In size it may be either exactly like the " die " or its circumferential measurement may be any multiple of that of the latter according to circumstances.The copper roller must in like manner have a circumference equal to an exact multiple of that of the " mill," so that the pattern will join up perfectly without the slightest break in line. The modus operandi of engraving is as follows:The " mill " is placed in contact with one end of the copper roller, and being mounted on a lever support as much pressure as required can be put upon it by adding weights. Roller and " mill " are now revolved together, during which operation the projection parts of the latter are forced into the softer substance of the roller, thus engraving it, in intaglio, with several replicas of what was cut on the original " die." When the full circumference of the roller is engraved, the " mill " is moved sideways along the length of the roller to its next position, and the process is repeated until the whole roller is fully engraved. End of Article: ENGRAVING OF COPPER If you wish, you can link directly to this article.
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