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FLEXO Magazine : June 2013
face. Newer chambers have self-clamping systems that avoid using any small screws or bolts. END SEAL ALIGNMENT This is an area that everyone has struggled with at some time. Proper end sealing is critical to blade pressure settings and relates directly to the life of the anilox. If seals are leak- ing, the first response from an operator is usually to increase blade pressure. If the blades are set properly for doctoring, you may want to look at the end seal design to make sure that a modification is needed or not in that area. The blade needs to rest on the end seal and stop where the land flat ends. That is where the curvature of the end seal starts for the circumference of the roller. If the blade over- hangs the land flat in that area, you may have issues with ink drying under the blade and causing build up of ink there, until it finally will blow out an end seal. Try various types of materials that the end seals are made of. Different inks require different types of materials to create a proper seal. Polyurethane rubber, felts, and soft foams all react differently, based on chamber type and ink chemistry. Based on wear and age of the chamber, this can change over time and by making a material adjustment, you just may get a better seal. Water-base and solvent inks have different abrasive proper- ties and this affects the end seals and how they seal. Also consider the compression of the seal material, harder, softer. Some presses use a dead band area in the seal location and some do not. Having an engraved seal area does keep the end seal lubricated, however, if the engraving is a low line screen, it could add more friction to the seal surface and wear prema- turely. Keep this in mind when running coatings and heavier volume ink applications. The same can go for dead band identification when running sleeves. If the anilox is an 180ls cell, the anilox supplier will engrave the dead band identification with the same line screen. The 180ls is a coarse engraving and may wear the end seal prematurely. The circumference of the end seal should match up per- fectly with the circumference of the anilox roller. This is an area you do not want to force the fit. The blade should never overhang the end seal, but should stop in the middle of the end seal. Whatever type or material is used for the end seal it needs to fit well all on its own. Once the fit of the end seal is verified, if there are still sealing issues, move to trying different end seal materials. Suggested Improvements: Try different seal materials and compression - Check for proper fit end seal land, height as well as circumference - Is the end seal material compatible with the ink chemistry? - Customize the seal from what it is, to what you perceive is needed to correct the leakage. WASH-UP CYCLE For presses with auto wash systems, there are many critical settings that affect the ink or solvent flow during a wash-up cycle. These settings need to be verified at startup on these presses, but should also be checked occasionally to insure that they have not changed from the start date. These settings control the unloading of ink and solvent from the chamber during the wash cycle. If not synchronized properly, they can allow the anilox to starve or not get enough solvent during a wash cycle. This allows the blades to run dry against the anilox roller. Always verify that the wash-up system is timed correctly. BACK DOCTORING Choosing the correct blade thickness and edge type is important when it comes to blade wear and chamber contain- ment. Back doctoring is an issue where ink gets doctored on the containment side, rather than going back into the cham- ber. Many containment blades have lower contact angles, or can be increased in length slightly to insure that the blade does not doctor sharply against the bottom side of the anilox, but acts as a flap to let ink go back into the chamber and seal the ink as well. Back doctoring is noticed when you get ink in the form of stalactites dripping off the bottom clamp of the chamber. As they build up on the blade, these stalactites can cause light polish lines to appear on the anilox roller. These are not score lines but they are lightly polished lines that will create a light print in that area as they polish the roller surface. NO SHORTCUTS! We are all guilty of taking short cuts, forgetting to follow stan- dard operating procedures and not keeping to the specifica- tions that we ourselves set at times. Spell out to the letter what is expected in the pressroom. Hold yourself and your people to these standards and the efficiencies expected will show benefit. If modifications need to be made, make them! Soft to hard foam, polyurethane, felt, rubber--these are just a few of the materials that end seals are constituted from. If the seal needs more pressure from the chamber to seal properly, add 1/8-in. or so to the seal height, so that it makes contact with anilox sooner and creates a better seal. 60 FLEXO June 2013 www.flexography.org