Cylinder Construction

Paul D. Fleming III, Paper Engineering, Chemical Engineering and Imaging

The dominant image carrier for gravure is a thin layer of copper plated onto a metal cylinder base. There are two types of cylinder bases: sleeve cylinders and shaft cylinders.

Sleeve cylinders consist of a body with steel headers shrunk at each end. The bores of the steel headers may be double taper, continuous taper or straight bore. Double taper is the most common, with angles of 10° on each side.

Sleeve cylinders must be matched with a shaft which fits exactly into the bores of the steel headers. Shaft cylinders are equipped with permanently installed shafts.

They can be directly mounted onto the press bearings. These are generally used for higher-quality images. Most cylinder bases are made from steel.

Deflection is the downward deviation of the center of the cylinder from a straight center line under a given impression pressure.

Impression “pressure” is measured in units of force per unit length (often reported in pounds per linear inch or PLI for short).

The actual pressure obtained from the impression pressure by dividing by the contact length at the nip between the impression cylinder and the printing cylinder.

The impression force at a a given PLI increases with press width. Thus, longer cylinders have greater need for structural rigidity. For long production cylinders a deflection of less than .15 mm is desired.

Cylinder imbalance occurs when the center of mass of the cylinder does not lie on the rotational axis. This imbalance exerts a force on the bearings.

The unbalance is measured as the product of the weight and displacement from the rotational axis.

Balancing of cylinders is similar to the process of balancing automotive tires.

It eliminates the vibrations induced by the imbalance. Cylinders are balanced by drilling holes into the cylinder sides and filling them with more or less dense material.