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FLEXO Magazine : March 2010
24 FLEXO MARCH 2010 www.flexography.org TECHNOLOGIES & TECHNIQUES Let's face it---end seals are no big deal, right? I mean, it's a piece of foam, felt, neoprene or rubber designed to seal up the ends of a doctor blade chamber. There really can't be that much to it. Sounds pretty simple if you ask me. If so, why do so many presses have big issues with leaking chambers and full messy drip pans? A lot of expensive down- time goes into addressing these leaks. And then there's the not-so-obvious issues, such as scored rollers due to the extra loads press operators put on chambers just to stop leaks. Why are there printers who would rather save $0.25 on a seal but end up throwing away many dollars in ink that has leaked from the end of a chamber? (How much is that opaque white ink per pound these days?) What about the cost of extra time spent on changeover's just to clean up? I would be happy to tell you that there is one end seal that will fix all of your problems! Sadly, to quote famed Persian Gulf War General Norman Swarzkopf, that statement is Bovine Scatology---or plain B.S. There are so many different conditions that can affect how well an end seal performs that it's impossible to have one type of end seal fix everything. SIZE (AND SHAPE) MATTERS For starters, a common issue some printers have is that the end seals that are being used are often not even the correct size and shape for the chamber. When the press was new, the OEM sent a couple of week's supply of end seals with the press. A sample of the end seal was given to a supplier who had the end seal drawn up and some samples made. Maybe the drawing was off just a bit, maybe the radius changed ever so slightly, or the shoulders were made a tiny bit longer. After a few years, you gave a different supplier an end seal to match up. However, the same minute changes were made by mistake and so on and so on. If your seals have bolt clearance holes, it is possible the hole centers have changed over time. Take a few minutes with your current supplier to look at your end seal(s) to make sure you have a proper fit. Have a chamber cleaned up and set up on a table. Then install new end seals. Check to make sure it is a snug fit on both sides and on the bottom. You shouldn't have the seal so tight that it distorts when it is put in. Check to make sure the face of the seal fits squarely against the chamber. After years of use and cleaning a chamber with a metal putty knife, the side of a chamber that provides the sealing edge can become less than a 90° surface for the seal to butt up against. If you have a side plate that you bolt up to keep the seal in, that plate should not distort the shape of the seal when tightened down. A firm hold is all that is needed. Install your doctor blade. The doctor blade needs to have some upward pressure from the seal against it to ensure an adequate seal is made between the shoulder of the end seal and the underside of the blade. A very slight rise in the doctor blade is OK. The firmer the end seal, the more prominent the rise will be. It should not rise so much that it will take extra loading pressure to get the doctor blades to wipe the center of the anilox clean when loading the chamber. Work with your supplier on this. End seals are available with different durom- eters or compression ratios to help with this. Make sure the doctor blade comes up to the apex of the seal but does not extend beyond it. If the doctor blade does not come up all of the way, then the end seals can actually hold the chamber off of the anilox so the doctor blade does not wipe correctly. If the doctor blade overhangs the apex, it might flex enough to create a small gap between the un- derside of the blade and the shoulder of the end seal when loading the chamber. Both of these scenarios are generally remedied by the operator by using extra loading pressure to help seal the chamber. ROLL WITH IT After you have the chamber all set up, set it squarely on top of an anilox roller. Take a flashlight and closely inspect the end seal to make sure the radius of the end seal and the radius of the roller match up perfectly. If they don't, there is a good chance that your press operators have had to add extra loading pressure to the chamber just to close that gap. If your current seals do not have a radius cut in them, you really need to address this. Not having relief cut in the end seal so it forms to the anilox is just adding to the load your operator will have to add to get the ends to seal up. Check to make sure the dead bands on the roller line up with the end seals. If they don't line up, you will need to ad- • Make sure the end seal properly fits. • Make sure the doctor blade comes up to the apex of the seal but does not extend beyond it. • Chips in the anilox roll can damage end seals. • Work with your suppliers to ensure the seal material is compatible with the ink system. An end seal without a radius. All art courtesy Max Daetwyler Corp. It's Just an End Seal With Some Effort, Leaks Can be Prevented
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