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Trouble-shooting

The following problems are typically caused by excessive amounts of coating being applied.

  1. Board is warped
  2. Board is sticking in stacks
  3. Board appears streaky
  4. Board has build-up of sandy, rough foreign looking material

Warped board is almost always due to too much coating being applied. Excessive moisture on one side of the board causes the warp. Reduce the amount of coating by increasing the pressure on the blade. Some types of paper, especially lightweight liners, are more prone to warp and moisture may need to be applied to the opposite side of the board to compensate for the moisture in the coating. If coating is being applied to the single face, allow more time for the single face to dry before feeding through the double backer by running extra single face on the bridge. If the problem is chronic, fans installed on the bridge will accelerate the drying.

Items 2 – 4 are usually due to a combination of too much coating and insufficient drying. Check blade for wear and damage on the coater. Make sure that preheat drums are at their maximum temperature and that wrap arms are set for a full wrap to maintain maximum contact time. Adjusting the speed of the corrugator may help or solve this problem. Each corrugator will have an optimum speed for running coating. Only trial and error method will determine this. Highly sized paper can cause drying problems as the coating cannot penetrate the liner and tends to “ride” on the surface. This is more typical of recycled liners and some may not be appropriate for coating.

Paper Breaks

Weak splices being fed through the coater most often cause paper breaks. The simplest solution is to avoid splices whenever possible or reinforce splices when running coating. Other paper breaks are caused by worn blades or blades that have been allowed to build up layers of dried coating. Blades should only be used once and then replaced.

Coater Problems

  1. Excessive foam
  2. No or little coating coming through pumps

The above two problems often occur simultaneously and are caused by a dirty or damaged pump. A diaphragm air operated pump works much like a human heart.

Over time the chambers of the pump accumulate a build-up of dried coating making the pumping chambers smaller than their original design. The pump must be run at a higher speed to compensate for the smaller chambers and introduce air to the coating causing it to foam. The wall of the chamber is a polymer-based material that wears and is subject to cracking and tearing. The valves of the pump are ball valves and are also subject to build-up of coating and can therefore stick or do not seat properly. Regular maintenance (once a month) and thorough flushing with water are extremely important.