your portal to the global flexographic industry the simple
TRANSCRIPT
The Simple End Seal
By Dave Southall, Max Daetwyler Corp.
Your Portal to the Global Flexographic Industry
FlexoGlobalTM
By Dave Southall, Max Daetwyler Corp.
Features
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Technology
Ah, the End Seal. I mean how hard can it be? 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. In fact, it actually sounds rather simple.
Well if it’s that simple, why do so many presses have big issues with leaking chambers, full messy drip pans, and expensive down time to address these leaks. What about 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 $.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 change-over’s just to clean up?
Look Familiar?
Well, I would be happy to tell you that there is one end seal that will fix all of your problems! Well, to quote famed Per-sian Gulf War General Norman Swarzkopf, that statement is Bovine Scatology or plain B.S. There are so many differ-ent conditions that can affect how well an end seal performs that it’s impossible to have one type of end seal fix every-thing.
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 were 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, 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 current end seal(s) to make sure you have a proper fit. Have a chamber cleaned up and set up on a table and 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 the seal fits squarely against the chamber. Af-ter years of use and cleaning a chamber with a metal putty knife, the side of a chamber that provides the sealing surface can become less that 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 Dr. Blade. The Dr. Blade needs to have some up-ward 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 Dr. 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 Dr. 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 durometers 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 the apex of the seal. If the Dr. Blade does not come up all of the way, then the end seals
The Simple End SealBy Dave Southall, Northeast Regional Sales Manager, Max Daetwyler Corp.
7www.flexoglobal.comFebruary 2, 2010 FlexoGlobal
can actually hold the chamber off of the anilox so the Dr. Blade does not wipe correctly. If the Dr. Blade overhangs the apex of the seal, the Dr. Blade might flex enough to cre-ate a small gap between the underside 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.
After you have the chamber all set up, set it on 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. 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-dress this with your anilox supplier. If your end seal is run-ning on engraved cells, there is ink being supplied to the
radius of that end seal. This will cause an ink build up in a short amount of running time and will likely cause that seal to fail prematurely.
Check your ends seals for the proper radius.
Check your chambers to make sure the end seal slots are in good shape. As I mentioned above, after years of clean-ing with metal tools, the slots can become chipped and damaged enough that an end seal just can’t seal up as it’s intended to.
Now that you hopefully have the proper size end seal, it’s time to take a look at what the end seal is up against; the
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Technology
anilox roller. The most common harmful issue here is chips on the ends of the rollers. Rollers get dinged while chang-ing, cleaning, storing, moving, or just by sitting innocent-ly on a cart and having something else banged up against them. (I strongly recommend roll covers; they can pay for themselves so quickly). These dings not only carry ink up to the end seal causing build ups, they can physically tear up an end seal rather quickly. The good news is that most small chips, and sometimes bigger chips, can be repaired without having to have the roller recovered. Your Dr. Blade com-pany and some anilox roller suppliers should have an epoxy repair kit made for ceramic available to help you with this. There is an art to using the epoxy and certain materials are needed when smoothing it down to make sure you end up with a perfect radius. Again, check with your supplier. He or she can be a valuable resource.
Now let’s touch on the different materials used for end seals. The proper material for the specific type of inks used is a good start. Most end seal material will work enough to get by for just about all different types of inks but getting by is not what we are looking for. Foams generally are the cheap-est material and for some printers they can be a good fit. Long runs, higher press speeds and solvent inks can be bet-ter suited for felt, neoprene or rubber seals. This is an area where you need to work with your supplier. I have observed an end seal fail using one type of ink where another com-pany will have the exact same press and similar inks and the same seal works great. Another important thing to note is that different densities of the same material are often avail-able to you. Sometimes a super-firm seal does a great job. Sometimes a seal that is more collapsible and conforms to the chamber is better suited for the job. Once again, work with that valuable resource; your supplier.
Lubrication is a key area that many printers don’t pay enough attention to. The proper type and amount of a lu-bricating agent can extend the life of the seal by obviously reducing the friction between the roller and seal but also by helping to repel the ink so that harmful build-ups don’t occur. Most felt seals will come pre-soaked with petroleum jelly. It is still a good idea to keep some jars of this available in case more lubricate is needed. I have seen a food- grade lubricant used with solvent inks with good success. Since they can be water-based, the solvent does not break them down as quickly. In most cases, all seals should have a lubri-
cant applied to them before use.
It may take several attempts for you and your supplier to find the proper end seal for your application. It will take follow up and good communication and some patience and diligence on your part. There is a lot that goes on behind the scenes to modifying an end seal. Drawings have to be made. New dies might have to be fabricated. Material in the proper thickness and density has to be ordered. I can as-sure you that the effort put forth by all involved can have big payoffs. For example, I recently worked with a customer to modify their old Kidder chambers from the old plastic pieces used to seal the chambers to a proper neoprene end seal. With a few changes here and there, they were able to increase their press speeds noticeably, and just about double their Dr. Blade life while saving some money on parts. An extra bonus was much cleaner presses. All of this took some effort from both parties but it was worth it. Hang in there with your supplier.
Kidder Chamber end seal retro-fit
For something as simple as an end seal, we covered a lot of different areas in this article. Take a walk around your press-room and look at your presses. If you track downtime, take a look to see if what you just read above is an area that needs attention and can have a good payback for your company. If so, then talk with you supplier to see what can be done. You noticed that I mentioned working with your supplier several times in this article. What I said was true; he or she can be a valuable resource. By the way, in most cases, they are a valuable, free resource.
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What is print? It’s how we communicate. How enterprises are enabled and individuals influenced. Here, there, and everywhere. Kodak provides answers for a dynamic, diverse marketplace. See for yourself at Drupa. Kodak solutions are here. Print is powerful.
Visit kodak.com/go/packagingSee the power of Kodak innovation at Drupa, Hall 5.©Kodak, 2008. Kodak is a trademark.
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