This one showed clear signs that the hydrofoils were rubbing against a sector of the upper basket. This was odd, since they are designed for a precise clearance between hydrofoil and basket. I called the manufacturer, who blandly told me that this model had a known, underdesigned hydrofoil bearing assembly. They said they would be happy to sell me a new and improved screen for a quarter of a million dollars. And, by the way, there was a long lead time.
Rather than lose my cool -- after all, the screen had been in service for 20 years with no complaints -- I asked if they had any other ideas. It turns out they did. For $40K, they would sell us a new screen housing with beefed up hydrofoil bearings. The lead time for that solution fit nicely with our next planned shutdown.
I presented this information to the mill management, along with my belief that this rubbing issue was the origin of the hairballs. They agreed that this was a worthwhile repair, and we arranged to have the bearings temporarily shimmed before reassembly to see if that would help while we waited for the new parts.
It did help. The hairball problem completely disappeared, saving the mill about $300K/year in lost production. That also opened the door that allowed me nearly free rein to uncover and resolve a number of other operation problems at that mill.
This entry was submitted by Geoff Cram and edited by Rob Spiegel.
Geoff Cram is a mechanical engineer whose career has included work with high-voltage power cable splice and termination design, pulp and paper manufacturing, and physical test equipment development. He also spent a period as the sole member of the engineering department of a small biotech company. He is working on the development of an underwater winched profiler funded by the National Science Foundation.
Tell us your experience in solving a knotty engineering problem. Send stories to Rob Spiegel for Sherlock Ohms.
Very good engineering, and an interesting approach to implementing the solution. Being able to produce right answers consistently certainly does aid an engineers career, although some acounting types will still be upset that the direct benefits can't be shown as production.
Providing right answers is one of the things that engineers are supposed to be doing and it is what makes them both valuable and unique assets. It would be good if some management types realized that we are not all interchangeable.
I have never been in a paper mill, but I can only imagine that it is a harsh manufacturing environment. The combination of wood pulp, water, and pressure is bound to cause large "hairballs" somewhere in the facility. It was good to see that the investigation was started looking to people for their opinions on what might be causing the issue. Person to person communication is often a forgotten part of engineering.
The losses incurred were real, but it's a complicated situation. I recall that making paper was (except for some premium grades) a very low margin affair, so the mills were graded primarily on tons out the door - do anything to keep the machines running. And paper mills are marvelously complex systems, which means an enormous number of possibile root causes to investigate. Often that meant the overwhelmed operations guys would only have time to do the simplest things.
That opened up the ecosystem for people like me to come in and help out. I can't help thinking about all the other mills that must have had the same problems that I was solving, but there didn't seem to be an effective way to spread the word.
If they had fixed that 'broken window' in the first year, they would have saved about $6M. A little educated guesswork tells me that was just over 20 years ago, making your sleuthing worth more than Six Mil to them. Don't play the lottery, folks; hire an engineer! :-)
Geoff, it seems that you are good service engineer too. Basically most of the problems are occurs due to small similar negligence's. if we know the exact working principle and functionality of the machine, it's not that much complicated to rectify the problems. Like design, it's also a generic skill.
Thanks, Geoff, for this story on the headbox hairballs. The headline definitely caught my attention, and might spawn other hairball stories. It's amazing how many long terms engineering problems (this one a pest for 20 years) are ultimately solved by careful research, analysis and followthrough. Thanks again.
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