How Does a Web Press Work?

All Webs Are Not on the Internet

When the term "web" is invariably linked to the Internet in the public mind, it is sometimes difficult to remember that it has other meanings as well. In printing, a web press is any press that uses rolls of paper instead of cut sheets. The web in this case is the continuous river of paper that runs through the press.

Printing presses may be classified in several ways. By geometry, there are flatbed presses and rotary presses. By printing technique, there are letterpresses, rotogravure presses, flexgraphic presses and offset presses. And by type of paper used, there are sheetfed and webfed presses.

The Offset Web Press

All web presses are rotary presses, meaning that the printing plate is mounted on a steel cylinder that turns. By far the most popular type of press for printing books, magazines and newspapers is the offset press. It's called "offset" because the plate itself is right-reading--it looks exactly like the printed page, instead of a mirror image, as in many other kinds of printing. Instead of transferring the ink directly to the paper, it prints onto a rubber sheet called the blanket, and is then "offset" from the blanket to the paper. This is the same technique children use when they put Silly Putty on a newspaper comic, peel it off, and then transfer the image to a plain sheet of paper.

Modern Presses

A modern web offset press can be hundreds of feet long and consist of many "units," each of which is a complete press. For a single page printed in full color, four plates are required--one each for yellow, red, blue and black ink. Each of those may have its own blanket, depending on the design of the press. While several pages can be printed side by side, if the backs of the pages are also printed, another set of plates and blankets is needed. The more pages, the more units. Finally, at the end of the printing section, a modern press has sections that can fold, cut and bind the finished product, so that a roll of paper goes in one end and a complete magazine or newspaper comes out the other.