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December 3, 2012

How many types of print cylinders are there, and which is the most accurate?

Probably the best know print cylinder is the integral shafted cylinder.    

While the most rigid and most accurate over the years has the journal shaft, running completely through the tubular core, it is also much heavier as a result when compared to the stub shafted design. The stub shafted integral roll journals are heat shrunk and often welded for added strength but are more susceptble to deflection, which in turn can lead to a lot more plate bounce. Its major benefit however is that the roll is much lighter and cheaper to build, which makes it more popular.

The next type of plate cylinder is a tubular core with a shaft that it can be mounted on and off. Original designs used tapered cones and lock nuts but have been largely replaced with more modern expandable shafts that use hydraulic or pneumatic expansion of the shaft to lock it to the inner bore of the core.

Finally there is probably the most popular which is the air cylinder. In most cases it looks just like a normal plate cylinder but has a hole drilled usually in the header on one side of the cylinder and 3-4 smaller holes drilled through the outer shell of the core with perhaps one other in the center. Plates are mounted on a sleeve consisting of polyester, fiberglass, carbon fiber or a combination of these materials and is slid onto the outside of the cylinder after air has been pumped into the cylinder from the header air valve. The air escaping from the smaller surface holes on the cylinder creates a cushion of air that the sleeve can slide over and locks into place once the air supply is stopped. Due to the action of sliding the sleeves on and off the cylinder, and the likelihood that dirty, moist air very often is put through unfiltered air lines, these cylinders are prone to scratching and corrosion and as a result will usually need refurishment and even replacement after several years of regular use.

The tubular demountable cylinders can be very accurate but great care needs to be taken to ensure that the shafts are not bent or scratched during installation and removal. Of the two shafted integral designs, the straight through shafted is the most durable and accurate but this often gets overlooked in today’s rush to reduce weight and cost but if you are willing to make the initial investment as well as the right lifting equipment, they will last you a lifetime if properly maintained and looked after.

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