What Causes Cardboard To Warp?

  What is Warp?
A simple definition for warp is “.to become bent or twisted out of shape, typically as a result of the effects of heat or dampness”.  In the corrugated paperboard arena, this definition of warp applies to one of the most common problems that these manufacturers face – producing bent or twisted corrugated board that results in excessive scrap, waste, and reduced production rates.

What Causes Warp?
-There are several main causes of warp:
-Moisture imbalance between the top and bottom liners
-Tension imbalance between the top and bottom liners
-Corrugator component misalignment

Moisture Imbalance
In the process of applying adhesive to the liners, there should be a delicate balance of heat and bonding between the layers with the adhesive consistently applied to the flute tips. Exposure to high humidity, applying excessive adhesive, inconsistent adhesive application and improper glue roll to paper speeds will all cause moisture imbalance which in turn leads to warp in the cross-machine direction. Moisture-related warp defects will display as:
Eliminating warp continues to be a challenge faced by many corrugated board manufacturers

Up Warp – board bows up (convex)
Down Warp – board bows down (concave)
S Warp – board bows up on one corner and bows down on the opposite corner
Diagonal or Twist Warp – board curves along the diagonal of the sheet

Techniques for solving related warp are:
Install a Spray humidifier on your production process, it could solve different warp types basis on installation in different positions. 

1. Double-facer inlet part spray liner:
Complement moisture for the liner before the cardboard forming and solve the cardboard down-warp and liner bursting.

2. Before the glue machine spray the face paper inner side(adhesive side):
Complement moisture for the face paper before the cardboard forming, solve cardboard up-warp(normal warp) and face paper bursting.

3. Before slitter scorer machine Spray face paper/liner:
Complement moisture for the cardboard, solve the cardboard bursting completely, and extended cardboard storage time.

4. Single facer machine spray medium paper:
Complement moisture for the medium paper, and increase the flexibility of the fluted paper. Prevent the fluted paper broken and poor adhesion phenomenon due to a dry environment.