Board warps in autumn and winter
Board warps most in winter. Recently, many carton insiders response that the board is warping due to the dry weather. Where is the cause lying and how to deal with it? Here we are going to teach you how to deal with the warping easily.
How to judge the board warps?
There is a general definition among the industry that the warp ratio is the proportion of the chord height and board width. It is generally considered as straight board if the warp ratio is under 1%. A board is 24 inch and its warp height is no more than 0.24 inch, then the board is considered as straight board. Or if the 600mm board has chord height no more than 6mm, then it is basically considered as straight board as well. At present, this is an international standard for warp ratio judgment.
How to prevent the warping in the board production link?
- Base paper
The moisture content is suggested to be 8% ±1 best and the moisture deviation should be controlled within 1%, or there will be S-Shape warp.
- Gram deviation of liner and inner liner
The gram deviation is not suggested to be over 50g, or it will cause the shrink ratio difference between the inner liner and liner. Too different moisture content is not suitable for production, unless there is process adjustment.
How to prevent the warps in the link of board piling?
There is a situation that the board is very smooth once it is produced, but becomes warped after a period of storing. So we need to take some measures to prevent it in the link of board piling.
- First, pile boards both positively and negatively and pressed with wood in the place of ventilating and heat dissipation for 4~8 hours to make the moisture content balanced. Many boards are suggested to print after 4 four hours.
- In the storage, the tray cannot be smaller than the boards on it, or it will induce the warp as well.
- The storage place cannot be too ventilated. Wrap the boards if necessary to prevent the moisture loss and warp.
How to make it up if there is warp?
- water on the board surface;
- turn over the board with 2~5 boards each positively and negatively; Pay attention that the boards should be squaring from left to right and from front to back, and the pile cannot be too high and is suggested under 1.5 m;
- press the board after turning over; Press a pad or a wood on the board and press a heavy substance on the wood, increase the weight on the pressing wood and maintain for some time, the warp can be improved.
- humidify the warped board and sprinkle steam and back press Turn over the boards every five sheets and press heavy substance on them before sprinkling steam after which put the base paper on the warped board.
Summary: the board warp will be improved a lot with the improvements of the above steps.