The Impression Cylinder

The impression unit carries the substrate into the printing unit. Contact with the blanket transfers the image. The impression cylinder also has gears and a gap.

The impression cylinder may or may not be undercut. It is approximately the diameter of the bearers of the other two cylinders.

The distance between blanket and impression cylinders must be adjustable to control the transfer squeeze.

Squeeze is a measure of impression pressure. However, it is not measured in pressure units, instead it is measured in units of length.

Plate to blanket squeeze is the combined height of the plate and blanket over their respective bearers. Blanket to impression squeeze is the blanket height over its bearer.

Squeeze pressure transfers ink from plate to blanket and from blanket to substrate. Squeeze pressure is controlled by plate and blanket packing.

A packing gauge is used to measure the height difference between cylinder and bearer. Therefore it can be used to measure squeeze.

Excessive squeeze causes friction that wears plate images. Insufficient squeeze can cause rough edges, snowflaking or low ink density.