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Internationally, the degree of board warping is usually measured on the basis of US or Japanese standards.
The American standards are as follows: (The string height of a one-meter long corrugated cardboard warping
Very slight - less than 5mm;
Slightly -10mm;
Moderate --15mm;
Severe -20mm;
Very serious - 30mm.
Japanese standards are as follows (same as above):
They are required for cardboard partitions. Generally, a maximum allowable warpage of 20 mm above the board of 1.2 m width is allowed; for the 600 mm or less, the maximum allowable limit is 6 mm; for the width of 1000 mm, the allowable limit is 10-15 mm.
China's national standard stipulates that the warp of a one-meter-long corrugated cardboard should not exceed 20mm. In contrast, the Japanese standard should be the most reasonable.
The warpage of the corrugated board can be measured by a special warping gauge, or the cardboard can be placed on a platform to measure the chord height of the side arc of the cardboard warped surface.
In general, when the board has just exited the double-sided machine, the pressure and moisture are not yet in balance, and the board is generally flat. With the extension of the storage time, the board warpage will appear. To determine whether or not the corrugated board is warped, place the newly produced single sheet of paper in the air for three minutes to see if it warps. Then check the moisture and temperature of the finished board products and the various semi-finished products of the production line according to the specific conditions. Analyze the causes and find out the correctness. Warping method.
Second, the main cause of warpage and corrugated board warpage caused by corrugated board warp is the most fundamental reason is due to the corrugated board surface, the paper size changes caused by the difference, this size change is due to the paper inside the cardboard Different moisture content, corrugated board to reach the moisture balance after the double-sided machine, high water content paper release moisture caused by this side of the paper shrink, low water content paper absorbs moisture caused by this side of the paper elongation causes the size difference caused by cardboard warping .
The factors that cause the above changes in water content can be analyzed from the following factors:
(1) The nature, type, and moisture content of the paper in the dough. In general, if the water content of the paper is higher than 3% in the paper, 92% of the board is warped;
If the facial tissue is 3% more moisture than the liner, 75% of the cardboard is warped.
If the moisture distribution in the full width of the base paper is not uniform, S-curvature tends to occur.
In addition, due to the different types of base paper, such as the degree of stretching of kraft liner board and tea board paper, due to the difference in fiber composition. Different manufacturing methods vary, and warping tends to occur when combining two grades of corrugated paperboards having a large correlation between A and C grades.
If the quantitative weight difference between the paper surface is also very different, it is easy to cause warping.
(2) Ambient temperature, tension The ambient temperature of the workshop also has an effect on the warpage of the cardboard. For example, in summer, moisture in the air is higher than in winter. In such an environment, the cardboard easily absorbs moisture in the air to achieve a moisture balance. Causes warpage due to differences in the size of the paper.
In addition, the tension of the paper base paper tray brake, the preheater tension, etc., also cause the paperboard to shrink laterally.
(3) Mechanical equipment and operation Due to the difference in operation, the warp is caused by the difference in water content of the paper in the cardboard surface.
(4) Characteristics of the glue and the amount of glue attached. The manufacturing process of the glue is different, and the difference in the amount of glue attached can cause the board to have a difference in water content and warp.
Third, the types of corrugated board warping Corrugated board warping types are the following:
(1) Longitudinal Warpage (A) Longitudinal Warpage (B) Longitudinal Warpage (2) Lateral Warpage (A) Lateral Warpage (B) Lateral Warpage (3) S-Warpage ( A) Two-way warpage 4. Correcting methods for different types of warping Although warpage of corrugated cardboard is unavoidable due to various reasons, we can control the board warpage phenomenon within the scope of standard requirements through the adjustment of the operating method. These adjustments are carried out under certain conditions, that is, the glue production process is stable and the base paper has been put into use.
(A) Lateral Warpage Control Lateral Warpage:
1. Increase the preheating angle of the paper;
2. Reduce the preheating angle of the paper;
3. Increase the production speed under the premise of guaranteeing the quality of the board;
4. Reduce the amount of glue on the single-sided machine;
5. Increase the amount of single-sided cardboard on the flyover (if possible, increase the number of blowers to reduce the moisture content);
6. Increase the degree of single-sided cardboard in the triple preheater winding, heating paper to reduce warpage, heating and corrugated adhesion;
7. On the premise of no effect on the quality of the paperboard, increase the amount of glue on the double coater;
8. Under the premise of not affecting the adhesion, the temperature of the hot plate of the double-sided machine is appropriately reduced;
9. If the core paper is sprayed with steam before adjustment, it should be appropriate or stop spraying;
10. If the paper in the same surface can also be exchanged paper;
11. Spray water mist on the paper out of the machine.
Control the warping operation downwards:
1. Increase the preheating angle of the paper;
2. Reduce the preheating angle of the paper;
3. Reduce the speed of production on the premise of guaranteeing the quality of the board;
4. To reduce the amount of single-sided cardboard pile on the flyover;
5. Reduce the degree of winding of the single-sided cardboard in the triple preheater;
6. On the premise of not affecting the quality of the cardboard, reduce the amount of glue on the double coater;
7. Increase the tension in the forward direction of single-sided corrugated board machines;
8. Surface paper exchange;
9. Spray paper on the inside;
10. Increase the amount of glue on the single-sided machine;
11. Properly reduce the speed of the vehicle;
12. Slowly increase the hot plate temperature of the double sided machine (by increasing steam pressure or increasing the number of hot plates that pass steam);
(b) Longitudinal Warpage Control Vertical Warpage:
1. Reduce the drag force of the friction plate at the exit of the flyover;
2. Check the overpass pipe guide plate of the control paper gap;
3. If the overpass piles up, the amount of accumulation on the overpass should be reduced;
4. Reduce the brake friction on the preheater;
5. Correct the preheater and idler to allow it to rotate freely;
6. Use base paper with high tension.
Control vertical warpage:
1.Under the influence of paperboard quality, use the base paper with low tension;
2. Increase the pressure of the cotton web on the cardboard to increase the paperboard's force on the hot plate;
3. Reduce preheater brake drag force;
4. Increase the drag force of single-sided corrugated board on the overpass;
(C) S-type warpage 1. The moisture distribution of the base paper is not uniform, and the moisture content of each segment of the paper web can be measured and adjusted by a single-side sprayer;
2. Occasionally, due to uneven wear of corrugated rollers due to the use of different widths of base paper for a long period of time.
(4) Bi-directional warping 1. The unevenness of the moisture in the base paper, the adjustment method is the same as in three (1);
2. The transverse tension of the belt is uneven, resulting in uneven tension;
3. The original paper holder is not horizontal, the center line of the guide roller, paper holder or preheater is not aligned;
4. The paper guides on the overpass are uneven, unfair or biased;
5. The gluing machine or its rubber roller is not horizontal;
6. The paper roll is too loose or too tight;
7. There is uneven or diagonal stress in the original roll.
Two-way warpage adjustment is relatively complex, and generally it is first adjusted to one-way (horizontal or longitudinal) warpage and adjusted accordingly.
Fifth, warpage cardboard remedies 1. Will warp cardboard positive and negative pressure;
2. Wet the warpage cardboard storage environment;
3. Apply mechanical force.
In short, the warpage of corrugated paperboard is caused by many reasons. To reduce the warpage phenomenon, it is only necessary to analyze the reasons in detail according to specific conditions and make careful adjustments to find out the correct remedy.
(Hefei Meiling Packing Products Co., Ltd. Xu Weiqing)
1. With regard to the warping of corrugated board, the social division of labor has become increasingly finer. Today, corrugated board has become a cartons factory where products are sold to downstream processing. Their demands for warpage of corrugated paperboard are getting stronger and stronger; in addition, due to social development, cartons After the mechanization of the road is becoming more and more high, in order to facilitate the mechanical feeding, to ensure the printing quality, but also require corrugated cardboard flat. Therefore, the flatness of corrugated board has become an important indicator to measure the quality of corrugated board.