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FLEXO Magazine : June 2013
Ink should always have a slow and steady stirrer. Do not depend on the agitation of the pump or the impellers to do the stirring. Stirring the ink should be independent of pumping. Excessive pump pressure or over stirring the ink will introduce air into the ink. If pumping ink to the pressroom from another room within the building, make sure that the ink lines stay clean and free of corrosion. Stainless steel lines are recommended, so that corrosion does not become an issue over time. INK VISCOSITY Ink viscosity goes up and the ink starts to solidify. That causes more fric- tion at the surface of the anilox roller. Maintain the proper viscosity. Know what the viscosity is for every color in the press and document it. The press- room environment can cause the ink to evaporate solvents at an accelerated rate. When this happens, you will notice the viscosity goes up quickly and has to be maintained more often. This is where you need to take notice and check ink at intervals that will keep the viscosity from affecting the ink’s color and flow rate. Always add ink to the press at the running viscosity. MANUAL CHAMBERS Manual chambers for older press types will have manual inking systems. Make sure that the ink viscosity is main- tained and the ink has good flow. The ink return line should be twice the diam- eter than the in-feed line. If the chamber empties ink to fast, you will get starva- tion; not fast enough, you will create positive pressure within the chamber. If you have a dated system and cannot control the ink rate as well as needed, it can be adjusted with a hose clamp. Using more pump speed, as long as you do not whip or agitate the ink, can help as well. Do not put too much posi- tive pressure into the ink chamber, or you will get end seal leakage and poor doctoring. INK FILTRATION MAGNETS Ink filtration is mandatory. Have proper magnets needed for the ink type being used. Ink gets contaminated over time, so filters and magnets will help as- sure that the ink stays clean and flows well. Maintaining the proper pH and viscosity for the inks will also keep the ink flowing properly as well. Ink goes to a solid state if pH drops or when we get low in solvent blends the solvent inks start to solidify and get more abrasive. When this happens, the ink directly affects friction of blade to the anilox surface. Plugged anilox cells cause more friction at the surface of the anilox. Cleaner rolls wear less. SCORE LINES Many factors come into play that can create scoring. Score lines can come from ink contamination and ink abra- sion, excessive blade pressure, blade alignment and many other indirect contact points to the anilox roller. Doc- tor blade pressures and doctor blade alignment is one of the most important Corrosion can occur over time with a chamber, especially if using water-based or high pH inks. Make sure chamber materials are compatible with the ink chemistry. This corrosion will also get into the ink train and cause scoring and ink contamination. www.flexography.org June 2013 FLEXO 57 © 2013 Harper