Paperboard warp issue Raiders three

2 Preheater removes paper moisture

The preheater is the only reliable tool for operators of corrugated board production lines to remove moisture from the tissue. It is estimated that the factors that are most likely to affect the moisture removal effect are the production speed of the corrugated cardboard production line, the degree of coating of the paper web through the preheating machine, and other factors of change, including the tension of the web when passing through the preheating machine. Whether the preheater's wrapper's wrapping direction or the preheater can rotate freely with the paper web's movement, or whether the preheater should be stationary, and the different moisture content in the paper.

The production speed of the corrugated board production line has the greatest effect on the removal of moisture content, keeping the extent of the paper web coating consistent with the brake pressure of the base paper frame, and maintaining the moisture content of the base paper at a normal level, when the corrugated board production line speed is 150 meters At 2 minutes, 2% of the moisture content in the roll was removed; when the speed of the corrugated board line was reduced to 45 m/min, the amount of water removed rose to 4%, and these data were obtained by the paper manufacturer. It can be seen that the effect of speed on the ability of the preheater to remove moisture content is inconsistent. Unsynchronized speed changes can cause board warpage.

Tension plays only a minor role in the different paper web areas in the corrugation direction, so that the web cannot be tightly attached to the surface of the preheater, and so-called "loosening" of the web occurs. The web passes "tight" on the drive side and "loose" on the operation side. Segmented web tension measuring devices can detect differences in tension on both sides of the preheater. At low speeds, the effect of tension on moisture removal is not as expected. Tension varies from 179 to 536 g/cm. When the corrugated board line speed is 60 m/min, the tension rises from 1 pound to 3 pounds, but for 26 pounds and 42 pounds of raw paper, the moisture content removed slightly increases, while for the 69 pound material the base paper does not have any effect. At speeds of 300 feet per minute or more, the amount of water removed in the base paper did not increase as tension increased from 1 pound to 3 pounds.

Moisture content measurements at normal speeds indicate that moisture removal is lower in the "loose" region of the web than in the "tight" region, because the web is in full contact with the surface of the preheater in the "tight" region. . Since the automatic tension control system is not installed in the corrugated cardboard production line, the tension will increase with the reduction of the diameter of the roller, the increased tension and the speed of the lowering (that is, the single-sided machine and the double-sided machine reduce the speed in order to match the paper-feeding). Together, these factors will greatly increase the amount of water removed. If you can't take the sync mode, it will cause serious cardboard warping changes.

The effect of the degree of paper web coating on the amount of moisture removal can be seen from the data collected. In a high-speed production state, the degree of web coating that affects the warpage of the paperboard varies considerably. It can also be understood from the point of view of the contact time of the web with the preheater. At 150 m/min, the web coating was changed from 305 mm to 1371 mm, while the contact time was only 1/3 second; at the speed of 30 m/min, the same web coating was changed and the contact time was increased to 2.1 seconds. It can be understood that when the paper web coverage is increased by 305 mm, when the existing paper web coverage is between 762 mm and 1524 mm, the moisture removal amount will be 205 g when the base paper is run at a speed of 150 m/min. From 0.75% to 1%.

Changing the wrapping direction of the web, heating from the periphery of the web to the inside, had no effect on the moisture removal or cardboard warpage of 69 lbs. One test for this change shows that there was no loss of adhesive at the highest speed. When heating the outside of the web, the speed may be 112 m/min; when it becomes heated inside the web, the speed becomes 129 m/min and there is no loss of adhesive. The coefficient of sliding friction rises to a maximum (ie, the preheat roll rotates freely at the speed of the web) to a maximum value (ie, the preheat roll rotates at rest), and the normal speed does not affect the moisture removal or the web Moisture content, however, at low speeds, moisture removal may increase with increased web tension.

It can be seen that the amount of water removed in the web under certain conditions is related to the original moisture content, and the wet paper roll will remove more moisture than the dried paper roll. Usually under a good tension condition, if the moisture content in the wet paper roll is double the moisture content of the other paper roll, the removal amount from the paper roll with the higher moisture content is 25-50%. This shows that the preheater can reduce the negative effects of wet lines, but it will not completely remove the wet lines. Wet lines often appear in areas where the web is "loose" and therefore do not adhere tightly to the preheater, causing some loss of advantage.

In the case where the paper web is almost completely covered, the preheater can eliminate 1.5 to 2.5% of the moisture content in the production of 205 g/m<2> of tissue paper at a speed of 150 m/min. A 1% change in humidity causes a change in the warpage factor of the board: for Type C, approximately 3.6 mm: approximately 4.8 mm for Type B, and 150 m/min for the entire web. The preheater can change the warpage factor of the board from 5.3 to 11.9 mm. The work of some corrugated board production lines shows that a typical corrugated board production line can, under normal conditions, overcome the difference of moisture content between 2% and 3% between single-sided paper and double-sided bottom paper. If the wet tissue paper is completely wrapped on the preheater and the coating of the dry tissue paper is minimized, most corrugated board production lines can overcome the moisture content difference between single-sided and double-sided liners. . If in a particular situation it is desired to more effectively eliminate the moisture content of the web, reducing the speed of the corrugated board line or changing the degree of coating by several feet will yield the greatest effect. At normal speeds, increasing the tension of the liner web, changing the direction of web wrapping or stopping the rotation of the tissue preheating roller will hardly contribute to the removal of moisture content.

It is also worth noting that, because the paper guide rollers on the overlay control arm of the preheater often do not work, most of the preheaters in the corrugated paperboard production line have only half of their surfaces available for contact with the paper web. The 762 mm potential coated surface is not used. The preheater is the main paper web cover control tool. The paper guide rollers for feeding and ejecting the paper should ensure the maximum coating amount. The coating amount of the single sided paper is always greater than zero, and the double sided paper is preheated. The machine should ensure that there is a so-called zero coating capability, even at the expense of the maximum coating of the web.
(to be continued)