In the packaging and printing industry, various production line maintenance problems are often encountered. Today, the editor of the paper industry network has inquired about the relevant information to show you the relevant maintenance methods from the production line.
5 Main causes and countermeasures of various warpage
5.1 Warping up
The single-sided corrugated cardboard needs to be glued at the single facer and the pasting machine, and the horizontal extension is long, and the liner (surface paper) is in an over-dried state due to direct contact with the preheater and the flat dryer of the double-sided machine. After entering the cooling section of the duplexer, it is sent out as corrugated cardboard. When corrugated cardboard is exposed to the air, in order to achieve moisture balance, the single-sided corrugated side with large moisture releases moisture and shrinks at the same time; while dry linerboard absorbs moisture and elongates, resulting in upward warpage. When the above situation is reversed (actually the bonding speed is too fast compared to the drying capacity of the flat dryer), the undercut occurs.
When the liner paper of single-sided corrugated cardboard is used with 3% more moisture than the liner of corrugated cardboard, 92% of the rolls will be warped. When the moisture content of corrugated cardboard liner is 3% higher than that of single corrugated cardboard liner, 75% becomes lower warpage. Therefore, when choosing base paper, the moisture fluctuation of liner paper (liner paper of single-sided machine and liner paper of corrugated cardboard) must be kept within 3%.
In order to solve the upper warpage, in addition to the moisture of the base paper, we should also pay attention to the following on the corrugated board machine:
5.1.1 Increase the wrapping angle of the preheater and the pretreatment machine at the single facer.
5.1.2 Minimize the amount of glue applied to the single facer.
5.1.3 Reduce the accumulation of single-sided corrugated cardboard on the bridge, and keep the speed of the single facer and the double-sided machine as consistent as possible.
5.1.4 Minimize the amount of glue applied to the corrugated cardboard at the pasting machine.
The above 4 items are all set to solve the upturning of the cardboard and minimize the excessive moisture when the single-sided corrugated cardboard enters the double-sided machine.
5.2 S-type warpage
Both the upper warping and the lower warping are simple warping, and the S-shaped warping and the diagonal warping described later are very troublesome warping. When this kind of warping occurs, 10-20 sheets of cardboard should be turned over 180 degrees at the delivery point of the production line before they can be stacked. At the same time, when the warpage is serious, in addition to the above method of stacking, a heavy object should be added to flatten the warpage, otherwise it will cause obstacles in the subsequent box making process.
S-shaped warping occurs because:
5.2.1 Wet streaks in the transverse direction of the hanging paper roll.
5.2.2 There is a lot of moisture on the side of the liner roll.
5.2.3 The heating temperature of the double-sided machine is uneven.
From the above 3 items, it can be concluded that the main key to overcome the S-shaped warpage is that the moisture content of the base paper should be uniform, followed by the uniform temperature control of the double-sided machine.
5.3 Warpage in the longitudinal direction
The warpage in the length direction of corrugated board has nothing to do with the base paper, which is caused by the tension adjustment in the production process of corrugated board. That is because the tension of the corrugated cardboard surface paper on the paper rack and the three-layer preheating machine is too tight, and the tension difference between the single-sided corrugated cardboard is too large. At the same time, the tension of the face paper of the corrugated cardboard is too tight, which is also one of the reasons for the length error on the paper cutter. The solution is to reduce the difference in tension between the single-sided corrugated board and the corrugated board in operation.
5.4 Diagonal Warping
Diagonal warpage is the warpage produced by the combination of longitudinal and transverse warping. The main reasons are that the single-sided corrugated cardboard is piled up too much on the bridge to become overload, the tension on the single-sided corrugated cardboard is too large (the tension is the cause of the longitudinal warpage), and the upwarping, downwarping or S-shaped warping is as mentioned above. It is caused by the moisture difference of corrugated cardboard destroying the balance of expansion and contraction. Therefore, to solve the diagonal warpage, it is necessary to comprehensively consider the above-mentioned various situations, and eliminate the above-mentioned bad situations one by one in the operation, and observe while operating. For example, the water content of the cardboard can be balanced by spraying water on the single-sided corrugated cardboard or the surface paper; the paper tension can be adjusted by adjusting the brake tension of the paper rack, the wrapping angle of the preheater can be adjusted, and the wrapping angle of the pretreatment machine can be adjusted. Control the tension of the cardboard; can control the speed of the corrugated cardboard production line to run in a stable condition, and reasonably reduce the amount of accumulation on the bridge without overloading it.
6. The produced cardboard is soft
The soft cardboard is a common problem with paper cotton threads, mainly due to factors such as material, starch paste, temperature, and environmental humidity.
6.1 The quality of materials is the main reason. With the increasingly fierce market competition, various manufacturers lower their prices to seize the market. Some factories use inferior raw materials to reduce production costs. These low-gram base papers are characterized by uneven thickness, very little sizing, high sand content, and very little tough fibers. This material not only cannot make high-quality cardboard, but also accelerates the wear of corrugating rollers.
6.2 Many people think that starch paste is too thick to be very sticky, which is wrong. On the contrary, the pulp is too thick or the amount of single and double-sided machine pulp is too large, which is the reason for the softness of the cardboard.
6.3 The production temperature of paperboard includes steam temperature and ambient temperature. The temperature of the steaming soup of the cardboard line is usually between 165 °C and 185 °C. The temperature should be increased when the speed is high, and the temperature should be lowered when the speed is low to avoid high temperature and low speed production. If the temperature difference between the cardboard and the environment is too large, the cardboard will easily absorb moisture and become soft, especially if the base paper without sizing is used.
6.4 Improper adjustment of the pressure will also cause the cardboard to be soft. Pay attention to the adjustment of the gap between the rubber roller and the pressure roller on the double-sided machine and the height control of the hot bed pressure roller. When the pressure roller is adjusted too low, it will cause the deformation of the corrugated peak and cause the cardboard to be weak against insufficient pressure.
Contact Person: Ms. Christina
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