“Daring to take the plunge and test the new Valmet Doctor Blade Dual* wasn’t exactly a difficult choice,” comments Lennart Johansson, Assistant Superintendent for Stora Enso Kvarnsveden’s PM 12. “We weren’t happy with our old air doctors. They wore out rapidly and were very costly to replace. They ran for a maximum of two months and ‘consumed’ large quantities of air, which made them real energy thieves. In addition, the noise level around the air doctoring is a big problem, as we all know.
“Two of our air doctors had previously been replaced by blades, and it was time to do something about the third and final doctor position at a press suction roll with a soft cover. After seeing a presentation on the new blade, we decided to act immediately – and the equipment was in place by December 2010,” says Lennart Johansson. Kvarnsveden thus became the first mill in Sweden to install Valmet Doctor Blade Dual.
“We’re really pleased that Kvarnsveden, despite having a relatively new paper machine, still decided to go one more step and invest in further development,” says Dennis Dahlman, Valmet’s** Product Sales Manager. “I’m not thinking specifically of the doctor blade, but rather the interest in taking on board new products and ideas. That is a major factor at Kvarnsveden.”
“The installation was done during an ordinary service shutdown, with the work being completed in just under two hours,” continues Johansson. “Everything fitted perfectly – all that was needed was a slight adjustment, and then everything was fine.
“We perform regular checks on the equipment and can confirm that doctor blade dual practically looks after itself. After it had been running for almost a year, our blade assessments found no wear. That bodes well, considering how long it runs for,” says Johansson. “The doctoring from the roll has definitely improved – in fact it’s almost too good! You only need to see doctor blade dual in action to realize that it doctors more water than the air doctor. The tray sometimes gets full when we run higher basis weights.”
So far, about 100 Valmet Doctor Blade Dual installations have been completed around the world. “There was a lot of interest in the blade right from the start – which is hardly surprising considering the substantial savings mills can make, above all by doing away with the need for expensive air doctors,” notes Dahlman.
And the figures speak for themselves. There are mills that, after replacing their air doctors with this Valmet doctor blade, have reduced their doctoring costs by around EUR 60,000 a year – not to mention the big savings made by not having to regrind roll covers after damage by air doctors – as happens occasionally.
“Once the last of the three original air doctors had been replaced, we could dismantle one of our compressors that supplied the air doctors with energy,” says Johansson. "We have made big savings by not needing to run the compressor and the three air doctors."
The aim of developing the Valmet Doctor Blade Dual blade was to produce an effective, low-cost solution for dewatering suction rolls and grooved rolls. Previous doctoring solutions always involved a choice – either efficient dewatering at a higher operating cost (with compressed air) or more inefficient dewatering at a low operating cost (plastic doctor blades or traditional foil doctoring). With doctor blade dual, you no longer need to make this choice. The blade can be used as an ordinary doctor that rests against the roll, but it can also be turned, giving it a foil function. The design and specific angle of the blade cause water and dirt to be sucked from the drill holes on the roll, which means that the effect of the dewatering process can be further strengthened.
“We’ve used doctor blade dual as an ordinary doctor blade, but it would be interesting to make a comparison with a turned blade with foil doctoring. That may be relevant when we decide about replacing a blade next time,” concludes Lennart Johansson.
*earlier known as ValDual
**(Metso (Paper) until Dec. 31, 2013)