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FLEXO Magazine : June 2012
excessive pressure will increase the wear on the blade and anilox roll---both of which are undesirable. So, how do you know what the wiping pressure should be? The blade wiping pressure should be low enough to obtain a clean wipe and maintain minimum blade deflection thru the printrun. Remember, the ink pressure on a reverse angle blade increases as the press speed increases. If the doctor blade is setup with deflection at idle, it may over deflect at high production speeds. Using a stiffer blade or thicker doctor blade is not the answer to solving this phenomenon; correct application pressure is the way to control blade deflection. If your chamber system is air loaded, set the application pressure by adjusting the air pressure after initial forward movement of the chamber system. It may require a larger pressure to move your chamber forward, but after the cham- ber has moved into position, lower the pressure to zero and use a plastic feeler gauge to set the blade pressure. Gradu- ally increase the air pressure until the feeler gauge fits snugly between the blade tip and anilox. Use the same procedure to adjust mechanically loaded chamber systems by using the adjustment mechanisms provided. The message is the same for either system of applying pressure, when a new blade is installed, adjust the chamber so that the minimum amount of pressure is being applied to the blades as described above. Any additional pressure will have a negative effect on doctoring uniformity. If you must add more air pressure to prevent end seal leakage, or achieve proper metering, you may be using the wrong end seal for your application, or you may have damaged or misaligned chambers. CONCLUSION The doctor blade is a critical part of the precision process that is flexographic printing. When treated as such, it will per- form well and deliver the consistent metering that is required. John Wooden, the hall of fame basketball player and coach, is quoted as having once said, "If you don't have time to do it right, when will you have time to do it over?" These words cer- tainly apply to doctor blade selection and application. Take the time that is necessary to choose the correct doctor blade for your job and set it up correctly. If you believe you have taken the necessary steps and still have blade related issues, work with your blade supplier to resolve the situation. About the Author: Bill Warner is vice president of Allison Systems Corp. He has 24 years of experience working with doctor blades and developing custom retrofit doctor blade systems for flexographic, gravure, and other printing pro- cesses. He can be reached at 856-461-9111 or wjwarner@ allisonblades.com www.flexography.org JUNE 2012 FLEXO 81