Sheet Feeding

A primary requirement for successful offset press operation is the smooth and consistent flow of paper. Sheet feeding is accomplished as either successive sheet feeding or stream feeding.

Successive sheet (or single sheet) feeders feed only a single sheet to the feedboard traveling at press speed. Because the sheet moves rapidly special attention must be paid to holding the sheet down during forwarding and keeping it moving at press speed without dragging or cocking.

Successive sheet feeders employ slowdown or preregister devices just ahead of the insertion point to prevent the sheet from buckling or bouncing.

Stream feeders feed a number of sheets traveling slower than press speeds and overlapping on the feed board. A stream feeder is better able to control the press sheet because it is traveling slower than press speeds.

Feeders may be pile feeders, continuous feeders or roll-to-sheet feeders. Pile feeders carry paper on a platform.

The pile must be straight, neat and positioned in correspondence with register settings. The main disadvantage is the press must be stopped for reloading.

Continuous feeders can be operated continuously without the press being stopped between piles of paper. The means of reloading vary.

Roll-to-sheet feeders cut individual sheets from a web of paper and the sheets are fed into the press. The feeder section of either type is divided into three distinct segments that work together. Pile table, a raisable platform where the paper to be printed is loaded.

Sheet separation unit, a device that uses both air and a vacuum to separate the top sheet from the pile. Feedboard, or feed table, a platform or ramp on which the sheet is transported to registering devices that position the sheet and time its entry into the printing unit.