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Obtaining good fit on a sheet

Sep 1, 2007 12:00 AM


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Most medium to large plants have employed computer-to-plate (CTP) as their primary platemaking method, the promise being improved fit. In many cases, however, improved fit was not noted because of other factors.

Items that can have a dramatic influence on fit include:

  • Corrosion of the plate cylinder, especially on the outer edges. This is why plastic packing is important. The preferred plastic packing is one that has pressure-sensitive adhesive.
  • Corrosion of the blanket cylinder on the outer edges. This usually is caused by sloppy application of water-miscible solvents to the blanket.
  • Worn plate clamps and/or clamps that are loose.
  • Damaged pins in the press.
  • Inaccurate plate punching.
  • Improper packing of the blanket cylinder.
  • Inaccurate setting of the blanket to impression pressure.

Of the above listed items, inaccurate plate punching and improper packing of the blanket cylinder are the two I find the most often.

A good idea is to observe five makereadies and count the number of plate/plate cylinder moves. During a recent audit, I counted six to 10 moves per job. The time spent was 12 minutes to get fit. The normal number of moves with CTP is two. If you are using CTP and many moves are required, look at the press.

I use a digital PIA/GATF register grid with the same image on each plate to test a press for fit. Strike in the lead edge and then strike in lead to tail at the center of the edge. Once that is done, analyze the sheet.

Editor's note: Ray Prince's “Tech Thought” series appears each month in AP's New Products section. See www.americanprinter.com. And, don't miss his new podcasts at www.napl.org.

Raymond J. Prince is a leading expert in pressroom technical and operational issues. He recently joined NAPL (Paramus, NJ) as vice president and senior consultant, operations management. Contact him at (605) 941-1492 or e-mail RaymondJ.Prince@aol.com.