Doctoring system

In paper making, a doctoring system is an arrangement of doctor blades and holders used to clean, control, or remove material from the surface of rolls and cylinders throughout the paper machine. Doctors are essential to keep rolls clean, prevent sheet defects, and control sheet release.  

Key Functions of a Doctoring System in a Paper Machine:

1. Cleaning – Removes water, fiber, pitch, resin, fillers, coatings, or stickies from roll surfaces.
2. Sheet Control – Helps in sheet separation from rolls, guiding the sheet along the correct path.
3. Maintenance of Roll Condition – Prevents buildup and wear by continuous cleaning.
4. Improved Runability – Ensures smooth operation, reducing breaks and downtime.

Main Components:

1. Doctor Blade Holder – Holds and positions the blade against the roll surface.
2. Doctor Blade – A thin strip (metal, composite, or plastic) that scrapes contaminants.
3. Oscillating Mechanism – Moves the blade sideways to avoid wear grooves.
4. Loading System – Pneumatic, hydraulic, or mechanical system to apply controlled pressure.
5. Lubrication / Showering System – Uses water, steam, or chemical sprays to assist cleaning and reduce blade wear.

Types of Doctors in Paper Machines:

1. Primary/Secondary Doctors – For cleaning press rolls and preventing rewetting.
2. Saveall Doctors – For removing water and contaminants.
3. Coater/Calender Doctors – For uniform coating and surface finish.
4. Creping Doctors (in tissue machines) – To create softness and bulk.

The correct design, material selection, angle, and loading pressure are critical, since poor doctoring can cause sheet breaks, increased energy use, or roll damage.