Uneven flute height and irregular glue profile are signs of uneven corrugation. The most frequent cause of uneven flutes on the single facer is inaccurate positioning of the medium paper as it travels between rolls. The following defect analysis serves as a reference guide for corrugator line operators to troubleshoot uneven flute issues. The single facer is the primary source of this defect, and other contributing factors are covered below.

I. Medium Paper

Causes

1.Medium paper is too wet or too dry.

2.Medium paper roll is out-of-round or loose.

3.Rough medium paper or other processing quality defects related to medium paper.

Countermeasures

1.Adjust the preprocessor wrap angle or steam spray unit.

2.Replace the medium paper roll if necessary.

3.Test an alternative grade of medium paper from the same supplier, then try medium paper from another supplier. If the problem is caused by medium paper quality, seek technical consultation and support from the paper supplier.

II. Corrugating Rolls

Causes

1.Contamination on corrugating rolls.

2.Bearing wear.

3.Rough or damaged surfaces of corrugating rolls.

4.Vibration of corrugating rolls when running at critical speed.

Countermeasures

1.Clean contaminants off corrugating rolls.

2.Inspect bearing condition and replace bearings as required.

3.Grind rough surfaces of corrugating rolls or replace the corrugating rolls.

4.Check the setup of corrugating rolls and ensure the machine runs at speeds above or below the critical speed.

III. Clawless Single Facer

Causes

1.Insufficient vacuum or plenum chamber pressure.

2.Clogged vacuum holes.

3.Poor bonding between corrugated medium and linerboard.

Countermeasures

1.Refer to the manufacturer’s manual to confirm the proper vacuum or pressure setting, then adjust or repair as needed.

2.Inspect and remove contaminants.

3.Verify vacuum valve settings and vacuum levels at both ends of the lower corrugating roll; check the clearances between vacuum box baffles.

IV. Other Factors

Causes

1.Non-level or misaligned machine components, resulting in slack medium paper edges or uneven tension.

2.Preprocessor not activated or running too slowly.

3.Locked preprocessor roll that cannot rotate.

4.Dry steam status of the preprocessor steam spray unit.

5.Excessive or uneven braking tension on medium paper.

6.Improper tension from the bridge paper guide system.

7.Out-of-round glue transfer roll on the double backer.

8.Worn bearings of the glue transfer roll on the double backer.

9.Non-parallel bottom roll of the double backer glue machine or mismatched operation with the glue applicator roll.

10.Improper temperature on the single facer, usually insufficient temperature.

11.Incorrect pressure applied to corrugating rolls.

12.Inadequate and improperly operated loading mechanism for corrugating rolls.

Countermeasures

1.Check alignment and levelness of the paper stand, preprocessor and single facer.

2.Repair the drive unit or adjust operating speed.

3.Use return steam instead of high-pressure steam.

4.Adjust the brake unit.

5.Adjust the paper guide assembly.

6.Realign the glue transfer roll or roll journal to eliminate out-of-round condition.

7.Replace bearings.

8.Adjust to maintain parallelism.

9.Check steam pressure and siphons for condensate accumulation inside rolls; adjust corrugating rolls to the proper temperature.

10.Balance pressure on both sides of corrugating rolls for uniform loading.

11.Hydraulic system: Inspect for leaks and check the condition of pressure regulators.

12.Pneumatic system: Check air bags for air leakage.