How to Identify Dryer Cylinder and Doctor Blade Problems Behind Repeated Paper Breaks

While the paper machine is running, have you ever encountered a situation where the paper breaks repeatedly near the same dryer cylinder? After cleaning the cylinder surface, the paper machine resumed normal operation for a time. After replacing the doctor blade, the buildup of material on the dryer cylinder also decreased.

However, after running for some time, abnormalities such as paper nicking and tearing reappeared at the same location, and the paper breakage issue still had not been completely resolved.

At this point, two conclusions are likely to arise on-site: “There’s a problem with the dryer cylinder surface” or “The doctor blade isn’t cleaning properly.”

Repeated paper breaks in a stationary dryer cylinder do indeed indicate a localized problem. Still, it is necessary to correlate the location of the paper damage, the abnormal area on the dryer cylinder surface, and the point of contact with the doctor blade to determine the origin of the problem.

Check for Recurring Defects on the Dryer Cylinder Surface

Focus on inspecting three conditions on the surface of the dryer cylinder.

Check for Repeated Deposit Buildup

First, check whether material buildup is repeatedly forming in the same area on the dryer cylinder surface. Record the location of the paper buildup across the width of the paper machine and compare it with the area where the paper sheet begins to tear.

At the same time, observe whether the buildup is distributed continuously around the circumference of the dryer cylinder or is concentrated only in a specific section of the circumference.

Check for Localized Deposits and Recurring Fiber Adhesion

Next, check the dryer cylinder surface for any localized sticky spots or deposits, and determine whether fibers are likely to adhere to these areas.

If material buildup recurs in the same location shortly after cleanup, you’ll need to investigate further to determine the cause of the recurring buildup.

You cannot determine the origin of the accumulated material based solely on its color or appearance.

Check for Dryer Cylinder Surface Damage

At the same time, the surface of the dryer cylinder should be inspected for scratches, localized roughness, corrosion, or damage to the coating.

These surface irregularities may affect the contact between the dryer cylinder surface and the paper sheet, and may also affect the performance of the doctor blade.

If paper defects recur at approximately fixed intervals, you can compare the defect spacing to the circumference of the dryer cylinder. If the two values are close, this may provide a clue as to the source of the problem.

However, it is also necessary to inspect other rotating components and consider the effects of factors such as paper elongation or slippage on defect spacing.

Inspect the Doctor Blade Beyond Its Condition

New doctor blades may also fail to make uniform contact due to improper clamping, blade holder, or dryer cylinder surface conditions.

Therefore, before removing the doctor blade for replacement, mark the operating side, the drive side, and the installation direction. Check the doctor blade for chips, curled edges, uneven wear, or material buildup, then compare these findings with the residue patterns on the dryer cylinder and the locations where the paper sheet begins to tear.

If a doctor blade notch and material buildup appear in the same area across the dryer cylinder, the blade may not be removing deposits effectively in that area.

However, the dryer cylinder surface needs to be inspected further, as surface damage or hard deposits may also cause notches in the doctor blade and affect the blade's normal operation.

Therefore, it is not enough to simply replace the doctor blades. You should also inspect the condition of the dryer cylinder surface at the corresponding location.

You Should Assess the Dryer Cylinder and Doctor Blade Together