What do they look like?
Calender cuts are relatively small wrinkles, usually 5 to 8 centimeters long that run at a slight angle to the grain direction of the paper. These wrinkles are compressed to the point that they make an actual cut in the paper. However not all calender cuts actually cut the paper.
How do they happen?
As the paper is being made, it passes through the paper making machine and loses moisture. Near the end of the machine, when it is almost complete, it passes through what is called a super calendering process.
Calendering means that the paper is squeezed through a series of steel rollers to make it the proper caliper and basis weight. The pressure is so great that any imperfections can cause cuts in the paper. If the paper has a poor profile before entering this squeeze, excess paper will crease when it passes the nip point.
Foreign objects like fibers or hairs can cause hair cuts. But a calender cut is not a foreign object. It is a wrinkle. The pressure is so great over the wrinkle that is causes a cut.
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| Calendering nip. |
Calender cuts usually cause paper jams and web breaks in offset printing presses. Press operators should try to find evidence of this defect after a paper jam or web break to communicate it to the paper company. Additionally, a claim can sometimes be made for waste and downtime.
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