Dryer Surface Care   |  Conditioning Calender Rolls  |  Couch Roll Twin Doctoring

DOCTORING TIPS:

TITLE: DRYER SURFACE CARE

Cast Iron surface hardness is usually in the 40-50 shore "C" range, consequently if a harder blade than this, such as Carbon Steel is used, wearing of dryer surface must occur.

This is also a very real fire hazard due to friction of carbon steel blade against cast iron can causing sparking, which ignites dust.

Metal blades are also prone to rusting particularly if dryer felt cleaning equipment uses water and if mill standard is Dryers doctors and are left loaded when wash downs take place, rust build up at blade tip on dryer will occur. K-4000 Hi temperature FiberGlass blades will eliminate fire hazard and rusting problems.

Should dryer surface be extremely dirty with a build up of pitch and rust etc. to clean this requires a "K" Abrasive blade. This blade is a cotton laminate blade with highly abrasive Carborundum center filler.

This blade should be installed for only 3 or 4 days. After surface is clean you can then use "K" 4000 blade. This blade is a fiberglass epoxy resin bonded blade, which is specially designed for high temperature dryer applications. This blade will not damage dryer surface and will also continue to keep dryer surface polished.

On new dryer and newly ground dryers, it is advisable to install a soft bronze blade. During this short time bronze blade will pick up the grind stone residue from regrinding of roll. Discard the bronze blade after running a maximum of 8 hours and install your usual blades.

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TITLE: CONDITIONING CALENDER ROLLS

Good care of calendar rolls will prolong the time between roll grinds eliminating costly down time, hence increasing efficiency.

Note: Calendar Roll will case harden white on machine. You must remove at least .008 to .012 per side per grind to remove this case hardened material and reach chilled iron.

Upon installation of new calendar roll or after a calendar roll has been reground:

When roll is installed it is very important, to help prolong roll life, that a soft bronze doctor blade be installed, This soft bronze will accomplish two things.

• Pick up any residual grinding dust left on rolls from grinding stones.
• Burnish roll and fill in any small fissures or surface cracks.

After 8 hours’ use, remove blade and scrap. Replace with high quality fiberglass blades.

RECOMMENDATIONS

Up to 2000 FRM : K2000

2000 to 3500 FRM : K4000

3500 to 5000 FRM : K5000

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TITLE: COUCH ROLL TWIN DOCTORING

Most couch rolls on Fourdriniers cause many problems such as:

• Debris like fines, filler, etc.
• Excess water
• Random Streaking
• Plugged up holes
• Edge defects

Couch rolls usually have no effective doctoring.

Normally a couch has a save all pan to prevent white water falling on return side of wire and blinding the wire. Typically the only form of doctoring is a rubber wipe on edge of save all.

In 95% of cases the rubber wipes cause many of the problems because it removes only part of the water and leaves a streaked moisture profile on the roll.

Typically the centrifugal action of the water on the couch produces a capillary action which tends to hold water, fines and fillers in the holes which then can produce many of the problems in the first paragraph above.

From our experience on twin doctors for press section we learned that if you load a doctor blade against a roll the sealing action of the blade against that roll produces a partial vacuum behind the blade. The build-up of debris behind the blade was what gives us the clue to the existence of this vacuum. This partial vacuum, we were able to measure in lab to be about 4" – 6" H20 water pressure.

Of course this vacuum on a press roll doctor is detrimental to its runnability in presses due to the accumulation of debris behind the blade. When one of our clients, Kruger Pulp & Paper at Trois Riviers, Quebec, #5 P.M. suggested he was getting poor performance of de-watering from his suction couch we suggested that by putting two blades against a couch roll we could use this partial vacuum to help pull water, fines and fillers from suction roll holes. Of course the actual doctor blade would effectively remove surface moisture very effectively.

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