Single-faced corrugated paperboards are glued on single-faced corrugating machines and pasting machines, with large transverse elongation, while the overprinted papers (faced papers) are over-dried due to direct contact with the preheater and the flatbed dryer of the double-sided machine. After entering the cooling unit of the double-sided machine, it is sent as corrugated cardboard.
The corrugated cardboard is exposed to the air. In order to achieve a moisture balance, moisture is discharged from the single-faced corrugated side of the large moisture, and at the same time the shrinkage occurs; while the dried noodle paper absorbs moisture and elongates, so that the warp phenomenon occurs. If the above situation is reversed (actually, the bonding speed is too high as compared with the drying capability of the flat-plate dryer), the warping occurs.
Here again, the paper moisture problem is repeated, and the warpage is caused by the moisture imbalance of the two-sided liner paper of the corrugated cardboard. Regarding the influence of the used raw paper moisture, CID conducted a large-scale experiment, ie, the raw paper of different moisture was used as the paper of single-sided corrugated cardboard and the paper of corrugated cardboard to investigate the relationship between the moisture and warpage of the raw paper.
When the liner paper using a single-faced corrugated cardboard has 3% more paper than the surface paper of the corrugated cardboard, 92% of the paper is warped.
When paper with corrugated cardboard has 3% more moisture than a single corrugated cardboard, 75% becomes warped.
Therefore, when selecting the base paper, the moisture fluctuation of the noodle paper (noodle paper of one-side machine and noodle paper of corrugated cardboard) must be kept within 3%. As a solution to warping, besides the moisture of the base paper, note also on the corrugated board machine:
(1) Increase the wrap angle between the preheater and the preprocessor at the single-faced corrugator.
(2) Minimize the amount of glue on a single-faced corrugator.
(3) Reduce the amount of single-sided corrugated cardboard stacked on the bridge and keep the speed of single-faced corrugator and double-sided machine as consistent as possible.
(4) Minimize the amount of glue on corrugated cardboard at the paper machine.
The above four items are all designed to solve the problem of cardboard upturning, so as to reduce as much as possible when the single-sided corrugated cardboard enters the double-sided machine. At the same time, in order to increase the water content of corrugated cardboard as much as possible, attention should be paid to:
(1) Reduce the wrap angle on the warm-up machine.
(2) Properly stretch the base paper.
(3) Reduce the heating temperature of the double-sided machine, or increase the speed.
In addition to this, we must also pay attention to:
(1) Single-faced corrugated cardboard without uneven corrugations.
(2) The viscosity and concentration of the gum are appropriate.
(3) The single-sided corrugated board entering the double-sided machine cannot be fanned.
(4) The pressure of the pressure roller on the double-sided machine is moderate, and the lateral pressure is even.
In the above, the cause of upward warping and downward warpage of the board and the solution to upward warpage have been introduced. The solution to the warping of the lower warp is not difficult to find from the above description, and is not listed here.
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