The good news is that are several ways to build an ink chamber that will deliver exactly the results you need every time you fire up the press. The bad news is that you have to do it over and over again. Learning to do it right helps ensure consistent performance from every chamber you build. It’s easier if you have a narrow- or mid-web press because all the parts are visible and (usually) easily accessible. It’s more difficult with a big CI press but once you’re familiar with the process it becomes much easier. Either way it all comes down to the parts you use.
The most common issue is doctor blades. We’ve talked about these in different ways on this blog but they are so important that it’s worth revisiting. The thing is, doctor blades seem deceptively simple. They are basically strips of steel that look more or less the same except for different tips. But there can be remarkable differences in their performance, all of which can and do show up on press.
When things go sideways
Doctor blades, aka metering blades, have but one job to do: They control the amount of ink that is spread across your anilox roll. So you put a blade in place, fire up the press and the job runs. All is well for a few jobs and you are getting the most out of the low-cost blade you’re running. Then you load up the last job of the day, 29,000 feet of 20-inch wide labels, figuring it will wrap up on second shift and there’ll be plenty of time for your crew to clean up before they go home. But no. About 7:45 PM your pressman notices a problem, a streak running an inch or so in from left edge. It looks like there’s a problem on the deck being used to put a clear coating on the label and that it has been going on for about 20 minutes. So the press is stopped.
The pressman is checking to see if something is caught under the blade when he notices the tip of the doctor blade is breaking up. Not only that, he spots an eighth-inch shard of the containment blade lying loose on the end seal. Then he remembers not bothering to replace the magnets in the chamber during the full clean up earlier in the shift.
So he puts on new blades, gets the press up to speed and color again, burns through a few hundred feet more of substrate and all is well on the shop floor. Except that that failed blades just cost you $1700 in substrate, consumables, ink and downtime. Plus the extra hour the pressman spent on clean up after the shift ended. Probably more if the job was on a big CI press.
With a long enough press run this scenario can happen no matter which blades you choose but is less likely to raise your blood pressure when you use higher quality blades because they can be run longer before replacement is required. Blades that only work well for a shift or two are more likely to shed bits of blades when the press is running. High-quality Swedish steel, like that used on most blades from Provident, breaks into smaller pieces that are less likely to damage an anilox roll. And you do have magnets in your chambers, right?
All doctor blades are consumables, and while Provident’s doctor blades also break down, they last, on average, three or four times longer than less expensive blades. When you run the numbers—including the all-to-real cost of press downtime—it’s your call as to whether paying a little less per blade is worth the risk of added downtime, lost substrate and anilox wear.
Using better blades is especially important when running abrasive fluids, like white ink—which contains titanium dioxide—or certain coatings. With those substances using a harder, more durable blade is essential to keeping a press running and delivering the quality you need.
The other item to consider is your end seals, and that’s a story for another day. Suffice it to say, end seals—especially as your press ages— are a vital part of building a better chamber and making sure you don’t have to stop in the middle of a run.
For a free evaluation of the ink systems on your flexo presses contact Provident and ask about sample blades to test on your own presses.