How We Set Tension On Our Web Press
I've written before about controlling web tension on an offset press, but wanted to share exactly what the tension settings are on our press. Above is a screen shot of the tension settings on our 4 unit heat-set press. To give you a better idea of what our web press looks like, I include here a picture below to imagine what it looks like.
We've recently done much tweaking to get just the right tension between all nip points on our press and I just wanted to share our conclusions. Likely it will resemble what you may already have. If not, it may give you an idea where to start. First of all, I realize the screenshot above does not have enough detail to reveal the tension settings, so I will spell them out here:
Our tension settings:
After infeed nip: 70 daN
Between last print unit and chill nip: 73 daN
Right after chill nip: 67 daN (+1%)
After first nip on superstructure: (+1%)
The ribbons split the web and after each ribbon nip: 20-24 daN (+.8%)
RTF above the former: (+1%)
Nip point below the former board: (+.7%)
Last nip before entering cutting cylinder: (+.7%)
Each number in brackets is the theoretical number. The number in decanewtons shows the actual result. Sorry for the metric, it's just the way the press came.
Now here are just a few of the variables that helped us to come to those settings:
- compensation stability
- oven air bars
- slur unit 1
- slur unit 4
- turner bars
Let me explain. We have a number of other presses that have played with these numbers for years. By comparing, we got a starting point. We also found stability with the automatic compensation changed with the tension settings. It took some time to find a sweet spot where it was stable. Additionally, the web had a tendency to rub against the air bars in the oven if the tension was too low. We also tried to minimize slur in unit 4 this way. Slur in unit 1 could also be minimized with the right setting.
We also found that we had to reduce tension going around the turner bars in the superstructure. It took much troubleshooting to discover this. It also helped to reduce setoff.
As a general rule, we found that once we changed a tension setting somewhere in the process, we had to almost start at the beginning (infeed nip) and work our way forward since all adjustments had a domino effect on the rest of the press.
All that being said, we still have differences in philosophy between the pressmen as to what is the "proper" way to set the tension. Even from shift to shift some of the pressmen will tweak the tension depending on paper and running conditions. This is normal in my opinion, but should be monitored closely and controlled.
How To Control Web Tension on Your Web Press
The Web Press Troubleshooting Guide