One of the hidden problems in corrugators are uneven glue application along the width and even sometimes in machine direction. Let’s concentrate here on the doublebacker glue machines.
Luckily there is such thing as a wet film glue metering gauge that helps you checking the evenness of the glue application. The instrument is simple and actually brilliant.
The glue metering gauge is a high precision tool. Protect it well so it doesn’t get damaged. The two side metal circles are perfect circles. In the middle there is an oval where the height difference corresponds with the markings on the wheel. There where we have 100 microns, this means at that particular place there is a 100 microns difference between the two side circles and the oval. If you put the gauge on the glue roll one will be able to read the exact glue amount you have on the glue roll. This does not tell you anything about the amount of glue that is transferred to the flute tip. Other factors that influence the amount of glue are the glue roll engraving and the amount of pressure applied with the small shoes or rider roll on the singlefaced material pushing it to the glue roll. The rheology of the glue is also a factor and for sure the capability of the flute tip to absorb the glue or at least the water.
So if you run a non-absorbing liner with a very absorbing flute, playing around with the borax can help…
At least the metering gauge learns you how much glue you have on the glue roller and you can then calibrate your digital settings. It also allows you to measure the parallelism of your glue machine. If you have more glue OS then DS then you need to do something about it. It is normal that there will be more glue in the middle of the web then at the two sides.
When running C flute – and even B flute – with for instance 10 microns difference between OS and DS will not be catastrophic but you will end pushing more starch then needed. To have enough glue on one side you will need to open the glue machine with an extra 10 microns…..so that is a waste of money and also a risk to have warped board or excessive washboarding.
The measuring with the glue metering gauge should happen at a speed above 150 meters per minute. If you need to open the glue pan leave it a bit running before you measure so that dried starch is dissolved again.
Unfortunately more and more safety instructions and also the construction of glue machines make it more difficult to access the glue machine for measuring. So hopefully someone invents quickly a device that can measure accurately without any impact. Maybe it exists already in other industries? If you know of it, please don’t hesitate to comment on this post.
I also sometimes have the tendency to measure the upper glue machine by accident, hitting the emergency red mushroom with my fat ass 🙂 If this happens twice in 20 minutes then the operators have the tendency not to smile at me anymore and are starting to say dirty words in their communication headsets…
The doctor roll needs to stay intact and smooth as glass, otherwise uneven glue application will be a fact. Again it maybe not be a big thing on big flutes but on N or G flute, where we are maybe talking about 80 microns of glue, then 10 microns more or less is a big difference. This is sometimes one of the reasons why people have problems running E flute or lower.
You can also understand that the scale of the metering device is important. In some places I see people use one from 0 to 500 microns or even from 0 to 1000 microns. You can give it to your kids and let them play with it; the scale is just too big to read small differences. Use one from 0 to 200 or 250, that’s definitely working out the best.
This type of parallelism I described you can have as well in doublebacker glue machines as in the SF glue units.
Glue splashing in glue machines is another issue where one is adding unneeded glue in the valleys of the flutes that is absolutely of no use what so ever.
Please have a look at the picture, this is what happens if maintenance did not do a good job… you can see a glue machine running without paper, it helped to see clearly where the problem was. Guess where the board constantly opened up?
Last but not least and sometimes forgotten, the best way to check your glue application is still to make a iodine image. The iodine reacts with the starch and gives you a pretty nice image of how the glue is applied on the flute tips and on the liners.
Please feel free to put comments or add if I forgot some things.