“…and those that agreed to the theory found great success with converting the small flutes at maximum possible speeds”.
George Mills is an American engineer with 40 years of experience in the corrugated industry. 18 of them are at Langston, where, as chief designer, he led the development of a modern single facer.
For over 16 years, George served as Executive Vice President of J.S. Machine. Corrugators, inlines of J.S. are his brainchildren. He shared his thoughts on warp control with our publisher.
I apologize for being a bit late in replying to your offer but I now have the chance to sit and write out my thoughts.
You may be surprised to find that I do not have an expert thought as to warp control. I have grown up professionally from the point where there were 1000 expert views where none were absolute cures, to then seeing groups like FEFCO and TAPPI produce published treatise of common basis of root cause and correction.
Today I offer that those publications still have solid body and should be included in the base line education of operators and supervisors as the primary education.
That being said…a personal note with a few comments.
In my years of experience TWIST warp is indeed caused by two factors, tension and paper shrinkage, just like the published works say. However, should a quick fix not show to be permanent and equal next running requiring constant quick fix…it then becomes the time to consider tracing down a misalignment usually in both the vertical plane and the horizontal plane. PLUMB and LEVEL is key to a machine doing all that it can. Machines do not really know how to compensate for being out-of-plumb or being out-of-level and people are not much better.
As the publications will say, balance is the key…learn to balance moisture, learn to balance tension, and learn to balance temperature.
Most in the industry will already know that I am a strong proponent of a constant temperature approach as being primary considering the splicers will have good tension control and the user is not trying to pull the mill stand out of the floor running bad paper! There is other theory about proportional control of variables used by some companies, yet I’d wager their own customers are a bit lukewarm about real effectiveness of such proportional control. Constant temperature technology usually works the best. But then again, I’m prejudiced. The first central controlled corrugator using close-looped control was Mead Covington Georgia USA in the early 70’s. The control system on that was based on proportional control because it sounded best ‘on paper’. The results were marginal and Langston then changed to temperature control loop only and the rest on that side is history…Langston typically produced the flattest board on the market from that day until they built their last corrugator.
I’ll share a George trick on running e-flute and micro flute. Sometimes, even well trained balance variable control is not enough on these type of flutes. Metaphorically, sometimes we need to let the bear win the little fights so that we can capture him with sureness later. When E-Flute started to be common in USA production and no longer niche, normal ideas for warp never worked completely. Initially it was all blamed on inability to control heat of the process. I finally came up with an idea. Run E-flute (and later micro-flues came along) to the best of your ‘balanced variable’ abilities possible. Set the skid load aside and go monitor the developing warp at 24 hours, 48 hours and beyond. Then simply run the machine FORCING natural warp in the opposite direction to the findings of the set-asides. Sounds almost magic, but it works and those that agreed to the theory found great success with converting the small flutes at maximum possible speeds.
Best Regards and good luck with your project.