What makes a press “high speed”
For printing, speed is mostly a matter of running a continuous roll of material, called a web, through the press instead of feeding individual sheets. A web-fed press can run for long periods with no stops between sheets. The material is unwound from a large roll, printed, dried, finished inline, and then rewound or cut and folded at the exit.
Web presses are used for newspapers, magazines, catalogs, directories, packaging film, labels and many other products where volumes are large. The general ideas of presses, plates, ink and color are covered in the article on commercial printing presses. This one focuses on what changes when everything moves quickly.
Main web press types
- Web offset. The same offset principle used in sheetfed presses, applied to a roll. It is common for magazines, catalogs and newspapers.
- Flexographic web presses. These print labels, flexible packaging, paper bags and cartons from rolls, with fast-drying inks.
- Gravure web presses. These are used for long, high-volume runs where the cost of making cylinders is spread over many copies.
- High-speed inkjet web presses. These print directly with no plates, which makes it easy to vary content from one page to the next, for example in personalized mailings or transaction documents.
Web handling
Moving a thin, flexible web at speed is a mechanical challenge. If tension is too loose, the web wanders and wrinkles. If it is too tight, it stretches or breaks. A web break stops the press and can cost significant time to clear, so web handling gets a lot of attention.
The typical path has these parts:
- Unwind stand. Holds the parent roll. Many presses have two or more stands so that a new roll can be spliced to the old one without stopping the press, using a flying or automatic splice.
- Infeed and tension control. Sensors, often load cells, measure tension and adjust drive speed or brakes. Dancer rolls, which are weighted or air-loaded rollers that move up and down, absorb small variations. The concept connects to load cells, which measure force electronically.
- Web guides. Edge sensors detect sideways drift and steer the web back to the right track.
- Printing units. Each unit prints one color or coating.
- Chill rolls. After heated dryers, cooled rolls bring the web temperature down so the ink sets and the paper does not stay soft or tacky.
- Outfeed. Leads to a folder, a cutter or a rewinder.
Keeping register in a moving web is demanding, because the web can stretch slightly between units. Presses use register marks, cameras and automatic adjustments, supported by accurate position encoders, to keep each color aligned.
Drives and control
At high speed, all the units must run in precise coordination. Many presses use separate servo drives for each cylinder, synchronized electronically, in place of one long mechanical shaft. The principles are those of motion control, using servo motors and shared control networks. Large presses also use big motors and variable speed drives to ramp speed up and down smoothly.
Because everything is moving and powered, safety systems are important. Guards, light curtains, pull cords and emergency stop circuits protect staff around nip points, where rollers draw material in. Procedures for threading the web and for cleaning are written specifically to avoid hand contact with moving rollers.
Drying
Drying is often the factor that limits press speed, because ink must set before the web touches another roller or is folded.
- Heatset dryers pass the web through a long oven with hot air. The heat evaporates solvents from the ink, and the exhaust air carries vapors that must be treated or burned. This is a use of industrial dryers and burner combustion.
- UV curing uses ultraviolet lamps to harden specially formulated inks and coatings almost instantly.
- Electron beam curing is another instant method used in some packaging work.
- Infrared and hot air are used for some water-based inks and inkjet systems.
Dryers use a lot of energy, so some plants explore waste heat recovery from their exhaust. Combustion and exhaust systems need proper supervision and maintenance, a topic discussed under flame supervision.
Inline finishing
At speed, finishing is attached directly to the press. A web offset line may feed straight into a folder that cuts and folds the web into signatures, followed by stitching or gluing. Packaging lines may add varnish, die cutting, slitting, laminating or sheeting inline. This saves handling, but it also means a problem anywhere stops the whole line, so operators monitor all sections.
Paper dust and lint build up quickly on fast presses, so cleaning is built into routine care.
Keeping it running
High-speed equipment depends on proper lubrication, aligned shafts, and well-maintained bearings and rolls. Operators use vibration analysis and similar condition checks to spot developing problems before they cause a stoppage. Preventive schedules follow manufacturer manuals, and any service work follows lockout procedures by trained staff.