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Jan 1, 2002 12:00 AM
This article is an online sidebar to "A new breed of floor-model folders," January 2001.
There are two basic types of folds and folders. Buckle folders make parallel folds. Often used for leaflets and brochures, a parallel fold involves making two or more folds in a sheet where the folds are oriented in the same direction.
Knife folders make right-angle folds. A right-angle fold involves making a fold in a sheet, rotating the sheet 90 degrees and making a second fold. One fold makes four pages, two right-angle folds makes eight pages, etc. A combination folder, which combines buckle and knife folding, is typically used for book work.
A buckle folder uses diagonal rollers to position a sheet against side guides. Feed rollers push the sheet between two metal plates--collectively known as a fold plate. This preset stop causes the sheet to buckle. An additional set of rollers then grasps the sheet and forms the first fold. Additional sets of rollers and fold plates make additional folds.
A knife folder is used for heavier stocks. It operates by means of a thin knife blade that forces a sheet of paper between two rotating rollers. First the sheet is carried to the knife folder and comes to rest at a fold gauge. The knife blade is then lowered between the two rotating rollers until the rollers' ridged surfaces catch the sheet, crease it and pass it out of the way so the next sheet can be moved into register.
High-end folders can reach a maximum workflow speed of 9,000 inches per minute--the equivalent to 60,000 sph. Automating a folder's delivery with a bander or bundler keeps the machine moving at top speed, since there's no need to wait for a pokey human being to collect the output.
Issues to consider when buying a folder include folding imposition, sheet size, paper thickness and stock. Most commercial printers need to fold a 28 x 40-inch sheet; trade binderies have broader requirements. Rickard Bindery (Chicago) for example, has more than 60 folders ranging from miniature to map-sized.
Source: "The GATF Encyclopedia of Graphic Communication;" "Printing Technology 5E;" MBO America; Heidelberg USA.