There are two types of cut-off knives in a web offset press, both of which serve the same purpose: Flawless and efficient production.
Cut-off knives are responsible for:
Web severing knives reel slpicer
Have you ever been at the checkout and the paper roll at the cash register is at its end right when it's your turn?
Luckily, webfed printing presses print their paper in "endless" webs: In a lightning-fast mechanism, the beginning of the new paper roll is glued again and again to the end of the old paper roll. The splice is a waste product and has to be removed. The web severin knive at the reel splicer separates the two paper reels and the adhesive strip is removed by the waste paper ejection system.
Web severin knives web/ribbon serverin
Paper wrap ups in the printing unit or web jams in the folder can severely damage your printing machine and the removal takes a long time. It is easier to avoid these problems from the start.
If the photo cell after the printing unit doesn't "see" any more paper, although it is still running into the printing unit, an emergency mechanism is triggered: the web severing device, sitting in front of the printing machine, instantly cuts off the incoming paper web with its web severing knife.
The same principle protects the folder from damage: with the web severing knife, that cuts off the so-called ribbon under the bending rollers and leads it out of the machine until it is shut down.