Packing an offset blanket is one of the most critical adjustments a press operator can make. Due to the complex interaction of cylinder diameters, blanket properties and variations in paper, this adjustment, although simple in nature can be very intimidating to many press operators.
Once thought of as a tool only for large offset presses, today the packing gauge is available for all presses, both large and small. The use of a quality gauge can improve overall print quality and speed up the troubleshooting of printing related problems. Used on a regular basis a packing gauge will become a primary Total Quality Management Tool.
Older packing gauges were bulky and cumbersome to use. This made checking blanket and plate packing difficult. As a result of this, these gauges were used primarily to troubleshoot problems after they showed up on the sheet. Today's gauges are smaller, lighter and easier to use. This means that checking packing can be done on every make-ready, allowing the press operator to correct potential problems before the first sheet is printed.
Why check packing at all? A question that is often asked. Even though packing sheets and blankets are clearly marked to indicate their thickness, many factors can influence how thick a particular blanket and packing set will be when mounted on the press.
Specifications. A common misconception is that a blanket marked .075" is actually .075" thick. Blanket and packing manufacturers, like all manufacturers, have a range of tolerances that they try to hold their product to. Because of this range, some blankets and packing sheets might be a few thousandths thicker or thinner than others. This does not indicate a problem or any kind of manufacturing defect, but can affect your overall packing thickness and print quality. Once this difference is know, you can then compensate for it when making ready.
Mounting. Another factor that affects blanket thickness is mounting. A properly mounted blanket is thinner than the same blanket off of the press. Measuring the blanket off of the press with a micrometer will not give you an accurate indication of its thickness when properly tensioned on the press. This factor makes it very important to check blanket and packing on a properly mounted blanket.
Beating down. As a new blanket is exposed to the constant pressure applied during the printing process, a beating down effect occurs. The majority of this occurs within the first few 1000 sheets, and the effect continues after that at a reduce rate. Although the amount that a blanket beats down will vary from one manufacturer to the next and from one type of blanket to the next, some reduction in overall thickness can be expected. Again, checking on the press is the only way to accurately measure this effect.
Printing Problems. After you have done everything right and you still have problems with print length or image quality, it's time to get out the packing gauge and do some troubleshooting. Most service technicians can relate many stories about "perfectly packed presses that won't print". A large number of these service calls are resolved within just five minutes and a packing gauge. Two sheets of packing material stuck together, a four ply instead of a three ply blanket, a .012" plate instead of an .008" plate, etc. are just a few common reasons to measure packing on the press.
Plates. Although plates are more stable than blankets as a general rule, a quick check when troubleshooting will eliminate any discrepancies with the plate or it's packing sheets.
Knowing that plate and blanket packing should be measured directly on the press, we are offering to you use the Digi Blankets Thickness Guage.