Research & Innovation
Taking the risk out of Extreme;
It is stating the obvious to say that the mill environment is a harsh one that often makes doing any sort of work, even the most routine maintenance, difficult and often dangerous. What then is the ke...
July 1, 1999 By Pulp & Paper Canada
It is stating the obvious to say that the mill environment is a harsh one that often makes doing any sort of work, even the most routine maintenance, difficult and often dangerous. What then is the key to extreme environment maintenance? In any dangerous environment, safety is of paramount importance. But new technology is decreasing the risks involved by removing the human element from the mix. Ed Slachta, supervisor, maintenance services, Donohue, Thorold, ON, discussed some of the areas that used to pose particular problems. The dryer section is hot and can be greasy but mills have to check for vibration. Felt roll bearings can be high and virtually inaccessible. “Anything in the dryers is tough. It’s a very unpleasant environment. It’s not a place you want to send people.” Online vibration sensors gather information and send it back to a central monitoring system where operators can check the information in comfort and safety.
Air flow and pocket humidity measurements are often done by clothing company personnel using spacemen-like suits to protect them from the extreme heat in the dryer section.
Sewers can be another nasty place to work, checking for plugs and leaks. Robotics and fibre optics have come into play here. The Thorold mill hires a company to come in to inspect sewer lines using a remote camera hooked onto a robot.
High dust levels can make chip handling and paper machine rooms an unpleasant place to work. In the machine room, the dust is often packed onto the rafters, another virtually inaccessible area. Again, the mill hires outside contractors, specialists in this area, to travel along the tresses vacuuming away the dust. It is done on the fly and the company must take care to avoid letting the dust fall onto the web when it is working over the wet end.
More and more, mills are taking hazardous maintenance out of hands of their employees, using remote controlled equipment or, as Slachta said, they are using the services provided by experts in these fields.
One company specializing in this area is Denross Contracting, which entered the maintenance business by accident. Denross was a construction contractor specializing in hospital, automotive and steel industry projects. About five years ago, the company was doing work for the Domtar (now Norampac) mill in Mississauga, ON. When Denross president Dennis Barrett saw the dryer cans with the build-up of contaminants, he told the mill manager that he could clean them. The mill manager was skeptical because it was a longstanding problem that seemingly had no easy solution.
Denross was doing cleaning (blasting with sodium bicarbonate) work in the mill to prepare surfaces for coating. Barrett took a hand held wand and starting on a dryer can, within minutes, reaching as far as he could go with the wand, the dryer can surface was clean.
Back at the shop, Barrett developed an aluminum alloy/titanium bar that holds a wand that travels across the dryer can. One man can set it up and operate it. Since that day in Mississauga, Denross has evolved so that it is no longer a construction contractor and 100% of its business is pulp and paper related.
Proper preparation is the key to successful maintenance and preparation begins with safety. Barrett said Denross stresses safety with all its employees because of the risks inherent in working in a mill and the lack of familiarity his employees may have with pulp/paper mills. As a result, the company’s WCB claims are far below industry averages.
Barrett said there were three main obstacles to maintenance in extreme environments. “The first problem is always moisture.” Secondly, there are other contaminants such as hydraulic oils. And, finally, in a mill there are a lot of clamped-in-place pipes and equipment, often in almost inaccessible locations. “You can’t walk around with needle guns or grinders. Accessibility is a big problem.”
High-pressure cleaning with water and chemical cleaning agents will remove oils and paper residues but may leave contaminants in the form of the chemicals used in the cleaning process.
Sand blasting in a mill can be risky as gauges and bearings can be destroyed by it. Barrett said he happened upon bicarbonate of soda after he saw the Statue of Liberty in New York being cleaned with it. Baking soda will clean all around pipes and miscellaneous equipment. Seals, bearings, gauges, rubber hose are not affected. Potential damage to bearings was the Mississauga’s mill biggest concern but it was soon obvious that they suffered no ill effects from the soda blasting. On dryer cans, soda blasting will remove hot melts and other contaminants that adhere to dryer cans and negatively affect paper profile.
Depending on the amount of dirt on the dryer can, it takes four to six hours to clean one. Barrett said that if a mill uses recycled pulp, the more recycled pulp it uses, the dirtier the can tends to be. About 0.10 lb/min of sodium bicarbonate is needed at 60 to 80 psi. Food grade #5 soda is used. It is most commonly found in bakeries. Barrett estimates that Denross uses about 300 tonnes per year, mostly for cleaning dryer cans. Clean-up is done with a straight water wash and takes about 10 minutes.
The same process can also be used to clean machine rooms and equipment frames, using hand held wands. Barrett said many mills experience problems with coatings because the equipment is not prepared properly. Therefore, the coatings chip or peel soon after application. Often, mills tend to blame the coating but, usually, the problems are a result of poor surface preparation.
Soda blasting gives surfaces a profile, Barrett explained, and this helps provide a mechanical lock, rather than chemical lock, between the surface and the coating to be applied. This is the key to a long-term solution, Barrett added. The whole key to successful maintenance is preparation — cleaning the area properly and getting rid of all the contaminants.
Denross uses Devoe offshore (marine) coatings by ICI. There are three basic coatings: a primer (Cath-coat), a rust inhibitor (Bar Rust) and the final coat (224 HS high build epoxy). They are low in volatile organic content, low-odor, quick drying and have high resistance to most chemicals.
Barrett noted that Denross is doing a job in one mill coating the ceiling rafters over the wet end and is doing it on the fly. The cost is a fraction of replacing the rafters, which can cost upwards of $1 million each.
The system can also be used to clean felt rolls. Barrett said he saw one mill where the contaminants were up to 0.75 in. thick on the roll. “You may as well have used a log, knots and all, as a roll, it would have done a better job.”
Clean felt rolls will prevent felts losing their seams and will keep the felts straighter.
Denross has also developed a method to clean board and corrugating medium dryer felts on the fly. A 45-micron soda is used. Norampac will be the first to try it.
Clean machines mean fewer breaks, better profiles, increased productivity, increased profitability and longer equipment life. Perhaps more importantly, a clean environment leads to a better and safer work atmosphere. Barrett said mills need to be open to new ideas and processes. He noted that it took the company four years to reach $1 million in sales in Canada. It achieved the same thing in six months in the US. Now, about 75% of the company’s business is American-based. Having just opened an office in Michigan, Barrett hopes to open one in the southeast US soon.
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