What Mill / Machine Factors Influence Paper Evenness in Final Product?

 

This past month (Aug. 2018) the paper machine manufacturer Leizhan (China) updated their website with a sub-section / list of useful tips for machine operators and mill troubleshooters titled Paper Evenness Influence Reasons And Solutions. For many TAPPI professionals this may serve as a useful review to reassure your level of troubleshooting knowledge. For other members now seeking to become more familiar and established with papermaking technology, the following list of suggestions might provide at least a few key tips to never overlook when managing quality control issues as they relate to possible malfunction or misalignment in machinery. Some of these issues, if your mill is aware of them, can be easily rectified before looking into or opening the door to more complicated issues that might also be costly and/or lead to undue downtime.

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So... the paper coming off of your rolls is being (on-the-surface) handled correctly throughout the pulping, bleaching / washing, and papermaking process so as to provide the desired product (as far as composition); but your product cannot provide a desired consistency, much less what would ever even be a tolerable level of imperfection in constant distortions that appear on the roll in an otherwise OK process?

Several problems could be at play (according to global P&P machine provider Leizhan) based on their knowledge of supplying mills with a wide range of industry-related manufacturing equipment.

1. The consistency of headbox is too high, causing fluctuation;

2. The slurry freedom may be too high (perhaps due to high temperatures) or because the slurry is in a high open state.

3. Maybe the water impact is too intense, causing the usual cloud flowers

• The slurry may be too long

4. The headbox level controller may not work properly.

5. When the speed is reduced, the headbox is flocculated and it is necessary to remove the spray water.

• There may be almost no water in the spray water.

6. The headbox or weirplate may not be adjusted (this is usually not observed on paper).

• Observe the forming fabric to see if the water is too aggressive.

7. If the paper has a high or low waveform, the case roller (if any) may be unbalanced.

8. If water is rubbed against the support roller, it will cause streaks.

• Adjust the fairing, if any, otherwise separate the support rollers.

9. Damaged paper may not be fibrillated

• This can usually be seen by the unopened paper points on the paper surface.

10. Light streaks on the paper may be attributed to the curved homogenizer (if still in use) or the lip adjustment due to the gap between the two screws. Other possible reasons are:

• The headbox used exceeds its capacity (too much water).
• The temperature difference between the spray water and the slurry is too large.
• The spray water in the headbox is too clean.

11. The reasons for the stripe shape are:

• The distance between the rectifying roller and the exit of the raft is not appropriate.
•  There is not enough cleanliness between the rectifier plate and the top and bottom of the sill plate.

12. The streaks on the wet paper are attributed to:

• Inappropriate rocker adjustments.
• The headbox concentration is too low.
• Pressing is not appropriate.
• Wrong press medium height causes wet web compensation.

13. Weak paper is due to the use of low-density wood or excessive waste paper in the raw materials. Other possible reasons are:

• Use of overcooked pulp.
• The fiber is too short.
• Excessive use of defoamers or other surfactants.