Throughout my printing career, I’ve met lots of people who have given me great ideas. Most, I’d never heard before and haven’t heard since, even though I’ve been printing for quite a while. Some of the ideas have been shared here on FlexoExchange; many have not. There are plenty of useful ideas and techniques in practice within the flexo industry that I have never seen addressed in any of the available literature. In many cases they are viral in nature, spread through the process of employees changing companies and sharing ideas with new co-workers. With the advent of the Internet, we have yet another method for getting our ideas out there.
One such idea or technique that I’d like to share is the marking of printed rolls with flags or indicators to signal to others, further along the workflow, where the defects are within a printed roll. More specifically, it’s a way to indicate where defects begin and where they end throughout a roll’s length. Of course, the printer must be aware of the defects as they are happening.
Here’s the problem:
Printing defects occur while the machine is printing, of course. Armed with video cameras, web scanners, and bare-naked eyeballs, press operators must keep a continuous eye on the quality of the print while the press is running. Defects may include printed artifacts caused by lint on a plate, colors that are out of registration, impression adjustments made during a roll run, moments where ink metering problems occur, or any of a variety of other situations resulting in waste within a printed roll.
Here’s an example:
Let’s say a press is running well after the operator has just set up and started the first roll. He decides he has time to make some improvements after everything has settled. His paperwork is caught up, and he wants to adjust the impression to minimize some halos in one or more of the colors. The impression is not terrible, as he just got it signed off by the supervisor, but he knows it can be improved.
The roll will run for a long time, and the operator doesn’t want the whole thing to run with excess impression. He is familiar with policy, and the Work Oder does not indicate that there may be no splices in the rewound product, opening up the option to make adjustments. Knowing that there will be sections of bad print generated in the process, the least the operator can do (and probably is required to do) is to try to point out to the person converting the roll in the next process where these bad areas are. This way, the next person to work with the roll can either cut out the bad section, splice, and keep rewinding, stop packing bags, turn off the wicketter, or otherwise take the appropriate action with the waste, based on what the process is. Helping the next person down the line to find that waste more easily can increase production, decrease waste, and foster peace on the floor.
Any of a variety of situations may arise that result in sections of waste being sent to downstream processes. If you’re reading this, you probably know exactly what I mean. New technologies that help to automate the process of identifying and even removing printed waste sections in rolls are available for some applications and are used by some lucky few for whom the planets line up. However, if you’re like most of the folks I know in the business, you probably have a more manual approach to the problem.
The most common ways to address this, that I have seen, have been to either mark the web with a permanent marker on the surface, make a mark or marks on the side of the roll, or stick scraps of paper or tape into the side of the roll as the roll winds up to indicate a bad section. These methods can work fairly well, have been in practice for many years, and seem to be used just about everywhere.
However, there is a method I came across just a few years ago that I found handled this problem in a simple but very effective way. It’s a slight variation of the practice of “flagging” defective sections in rolls with tape or paper scraps as the rolls are wound. The improvement to this practice that I found particularly helpful is to use specific colors to identify defective sections, effectively “bracketing” the defects in such a way that the next operator can tell, at a glance, where they begin and end.
Revisiting the scenario I described, let’s add a few details, and incorporate the color coding idea to see what it might look like:
The problem in the above example is impression. While the print passed the quality check and was signed by the supervisor, the operator decided it was worth fixing during the run. In fact, so did the supervisor.
In this case, the operator obviously knows when he starts adjusting and when he is done. At all times, there are strips of 1” green and red tape conveniently affixed at the press frame at the rewind section.
Just before the operator begins to make his adjustments, he carefully sticks a piece of green tape onto the roll, such that approximately a one-inch green square is jutting out of the side of the roll. As always, please use caution around equipment.
The operator then walks over to the print station and makes the adjustments. Once he is satisfied with the results, he walks back to the roll that is being wound, waits until all of the bad print passes by and gets wound up, and inserts a red flag in the same manner as he did the green flag. The rest of the roll runs without a problem.
Also in this particular example, the roll is going to be slit and rewound on a slitter-rewinder. The end product will go to the customer in the form of smaller, one-image-across rolls. Therefore, whether the customer will accept splices or not, it is more economical to remove the badly printed sections at the rewinder, rather than at the press, which as you know, results in much more scrap.
Here’s where the colors, and the relative sequence in which they are affixed to the roll, add a nice benefit:
The press operator first applied a green flag to the roll, and then finished with a red flag. However, the rewinder or inspector will first see the red flag, and then the green flag. As you probably know, the sequence will reverse each time the roll is rewound onto another core, in a way similar to the wind direction reversing with each rewinding.
The practice of affixing the green flag to the roll before making adjustments and then waiting until the print that is winding onto the roll is good before affixing the red flag assures the rewinder that everything up until the red flag is good, and that everything beyond the green flag is good. The rewinder operator stops the machine and begins to remove the bad material by whatever means is appropriate and normal. Once the operator reaches the green flag, it is safe to splice the web and keep rewinding, as usual.
Operators can be creative and improve on the concept. For example, flags can be preprinted with the type of the defect, further aiding downstream operations. You may think of other ways to improve on the scheme.
The size of the flag and the material used may vary from place to place, or situation to situation. However, I have seen more situations where the practice of making adjustments to print quality during a roll run is the rule rather than the exception. Introducing a little color can go a long way toward improving interdepartmental communication and, consequently, efficiency.