Cracked offset printing plates can occur for several reasons. So for this article, I would like to discuss several reasons why plates may crack, as well as a troubleshooting guide that a pressman can use to address the problem. Let's discuss five reasons why printing plates may crack, particularly near the gap of the press cylinder.1. Human Error
It stands to reason that this is the first place to look for the cause of cracked plates. Often when plates are hung on the press, there is room for error. If any part of the plate, including the edges, is not hugging the press cylinder then the continuous movement when the impression goes on will eventually crack it. Be sure that the pressman is hanging the plate correctly.
2. Heavy Ink and Water Forms
Especially at high speeds, the cylinder gap presents a mechanical problem for presses. With the impression on, there is a slight impact when the gap on the lead edge of the plate first impacts the blankets and the forms. This is what will ultimately cause a cracked plate if you run it long enough.
What will cause the plate to crack prematurely though is if your forms are too heavy. That impact on the lead edge is significantly increased if the forms are too heavy. Have the pressman check all the forms that touch the plate and even run them slightly on the light side to be sure this is not the case.
3. The Plate Loading System
Some presses are equipped with an automatic plate loading system while others take a more manual approach. Both systems have their weaknesses. If the lock-up system is not doing it's job, it will cause a slight bubble under the edge of the plate and ultimately cause it to crack. The pressman should ensure that his method or system of installing is not flawed or worn in any way.
4. The Plate Bender
Plate benders also need maintenance from time to time. Press manufacturers have very precise requirements for the exact angle the edges of a plate are bend as well as the size. Over time, this is something not easily noticed by a pressman. Ensure that these specifications are met by consulting the press manual or the press manufacturer.
5. Running Beyond the Plate Life
Plate suppliers give a rating to their plates which determines how long the image on the plate will last as well as how long the plate can physically last on the press. Most offset plates are made of aluminum and can last hundreds of thousands of impressions, but thickness can vary. Ensure that you are running a thick enough plate for the demand you place on it. For example, running a hundred thousand an hour web press will demand a thicker plate than a five thousand an hour Heidelberg GTO sheetfed. The pressman should consult the plate manufacturer to know what type of plate he needs.
Having said all this, there are of course other more complicated factors that can cause cracked plates. The main thing is to be systematic and try one thing at a time which are the basics of troubleshooting any offset printing press.
Related posts:
Web Press Troubleshooting Guide
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