The weather is dry in autumn and winter, and corrugated cardboard loses water often has bad phenomena such as line breaks, corrugated broken, and difficult to form. In the spring and summer, it will rain again and excessive corrugated cardboard will absorb moisture in the air, causing softening, compressive strength and other disadvantages. . As the seasons change, corrugated cardboard also changes. Because we ignored these changes, or did not attract our attention at all, let it happen, resulting in quality accidents such as softening of corrugated cardboard in spring and summer, and corrugated cardboard in autumn and winter. Occurs frequently. The lighter ones are complained by customers, and the more important ones are returned.
According to the author's investigation, the occurrence probability of this phenomenon is more than 90%, most of which is reflected in the season of seasonal change, and it occurs every year. Therefore, the loss caused to the producer accounts for 30-50% of the total quality loss. According to common sense, this year happened, and preventive measures will be taken next year, but otherwise! The purpose of the author's writing this article is to remind friends in the same industry that they should often use "anti-epidemic needles" for corrugated cardboard to prevent similar repetitive mistakes from happening again. The author will introduce the factors that caused the corrugated cardboard "outbreak":
1. Influencing factors of warehousing environment
The storage environment is mainly reflected in the temperature and humidity, corrugated cardboard is more sensitive to the temperature and humidity environment. Everyone knows that the delivery moisture of corrugated cardboard according to the GB / T6544-2008 standard should not be greater than 14%. In fact, the moisture content of corrugated cardboard produced is mostly between 8-10%, because the moisture content of the cardboard paper currently used At about 8%, the moisture content of corrugated paper is about 11%. When heated by preheater, corrugator, dryer, etc. for many times, a large amount of water is evaporated. Although a certain amount of water is added during the glue application process, it is When the dryer is finalized, it consumes more than half. When the humidity of the storage environment air is greater than the moisture content of the cardboard, the corrugated cardboard absorbs the moisture in the air until it is balanced with the humidity and moisture in the air, so that the corrugated cardboard softens; otherwise, the dry air absorbs the moisture of the corrugated cardboard, so the corrugated cardboard The cardboard is severely dehydrated and loses its toughness, and it will break, break, and warp during the later carton forming construction. High temperature and high humidity, high temperature drying (low temperature drying) have a greater impact.
Let's look at the following experiment:
The materials used are: facial paper 150g domestic B-grade kraft paper, internal paper 120g domestic B-grade boxboard paper, corrugated paper and sandwich paper are 110g high-strength tile paper, specifications 1000 Ã— 600 AB corrugated five-layer corrugated cardboard 3000 sheets, according to Sampling in "GB / T2828-2003 Counting Sampling Inspection Procedure", and then sampling according to "GB / T450-2002 Paper and Paperboard Samples", using "GB / T462-2003 Paper and Paperboard Moisture Determination", "GB / T6545 -1998 Determination of the bursting strength of corrugated cardboard "," GB / T6546 Corrugated cardboard edge compression strength measurement method "respectively measured moisture 12%, bursting resistance 1350kPa, edge compression strength 7.20kN / m. After recording the inspection data, the 3000 pieces are divided into three groups, and each group of 1000 pieces is placed in the room temperature, low temperature and high temperature laboratory stacking, and then sampling, sampling and testing are performed.
1. Store at low temperature from 0-30 Â° C for 6 hours from low to high, still sampling according to "GB / T2828-2003 Counting Sampling Inspection Procedure", adopt "GB / T450-2002 Paper and Cardboard Sample Selection" for sampling, Use "GB / T462-2003 Determination of Moisture in Paper and Paperboard", "GB / T6545-1998 Corrugated Cardboard Bursting Strength Measurement Method", "GB / T6546 Corrugated Cardboard Edge Pressure Strength Measurement Method" to determine. When the humidity of the laboratory is between 55-65%, the moisture of the corrugated cardboard is 11.65%, the burst resistance is 1345kPa, and the edge pressure strength is 7.00kN / m; when the humidity of the laboratory is between 70-80%, the moisture of the corrugated cardboard is tested 13.65%, burst resistance 1325kPa, edge compression strength 6.5kN / m.
2. Store at low temperature -10-1 â„ƒ for 6 hours from low to high, still sampling according to "GB / T2828-2003 Counting Sampling Inspection Procedure", and adopt "GB / T450-2002 Paper and Cardboard Sample Selection" Sampling, using "GB / T462-2003 paper and cardboard moisture determination", "GB / T6545-1998 corrugated cardboard bursting strength measurement method", "GB / T6546 corrugated cardboard edge compression strength measurement method" to determine. When the laboratory humidity is between 55-65%, the experimental corrugated board moisture is 9.65%, the burst resistance is 1140kPa, and the edge pressure strength is 6.00kN / m; when the laboratory humidity is between 70-80%, the experimental corrugated board moisture 11.0%, bursting strength 985kPa, edge compression strength 5.5kN / m.
3. Store at a high temperature of 31-45 Â° C for 6 hours from low to high, still sampling according to "GB / T2828-2003 Counting Sampling Inspection Procedure", adopt "GB / T450-2002 Paper and Cardboard Sample Selection" for sampling, Use "GB / T462-2003 Determination of Moisture in Paper and Paperboard", "GB / T6545-1998 Corrugated Cardboard Bursting Strength Measurement Method", "GB / T6546 Corrugated Cardboard Edge Pressure Strength Measurement Method" to determine. When the humidity of the laboratory is between 55-65%, the moisture of the corrugated cardboard is 8.0%, the burst resistance is 1135kPa, and the edge pressure strength is 6.3kN / m; when the humidity of the laboratory is between 70-80%, the moisture of the corrugated cardboard is 18 %, Bursting strength 960 kPa, edge compression strength 3.0 kN / m.
According to the experimental results, it is not difficult to see that the storage environment of corrugated cardboard is preferably between 55-65% air humidity, and the temperature is preferably 0-28 â„ƒ. The temperature has little effect on the edge compression strength of corrugated cardboard, and it has an impact on the burst resistance. The burst resistance below -1 â„ƒ has dropped by about 25%, and the effect of humidity on corrugated cardboard is very obvious. With the increase of temperature and humidity, the edge compressive strength of corrugated cardboard showed a significant downward trend, and began to decrease sharply at a temperature of 30 Â° C and a humidity of 80%, and the decrease range was more than 50%. [next]
2. Influencing factors of transportation
When centralized board making and decentralized box making, the transportation means of corrugated cardboard is mostly automobile transportation, and automobile transportation is divided into open transportation (open truck) and closed transportation (van truck). Open car transportation is easy to soften when the air temperature is high and the air humidity is high; when the air temperature is low and the air humidity is small, the cardboard is easy to lose water, causing warping and breaking, especially when entering the next process. Now most corrugated cardboard processing enterprises have adopted van truck transportation, which will not be repeated here.
3. Influencing factors of storage time
Corrugated cardboard is most suitable for entering the next process 4-6 hours after the cardboard assembly line is off the line, because the cardboard has been completely shaped at this time, and the physical properties will not change during the printing, stamping and other forming processes. In other words, the quality of the corrugated cardboard at this time is the most stable. After several hours of "internal adjustment", its adhesive strength, burst strength, edge pressure strength, thickness and other indicators have returned to the extreme, and the moisture is also balanced with the optimal storage environment. Too. Of course, the storage time also depends on the material used for corrugated cardboard. If the paper fiber inside is short and the toughness is poor, it is necessary to enter the next process as soon as possible in the shortest time off the line, otherwise quality problems such as crimping, folding and breaking will occur. . In the dry climate in spring, autumn and winter, pay special attention to the storage time of more than 6 hours, the cardboard will be seriously dehydrated, causing quality accidents when entering the molding process; summer high temperature and rainy cardboard absorbs moisture in the air to achieve moisture balance with the environment, The cardboard becomes soft and the compressive strength drops sharply.
We did an experiment in September, the temperature was 23-28 â„ƒ, the humidity was between 60-65%, 1500 pieces of corrugated cardboard were sampled, the material, corrugated type, specifications, process, equipment, and off-line time were the same, and the moisture was measured by sampling 12%, bursting strength 1386kPa, edge compression strength 6.6kN / m. It is divided into 3 groups according to 500 tablets, and stored for 6 hours, 24 hours and 240 hours respectively. The test data obtained from the experiment are as follows:
Results at 6 hours: moisture 11.5%; bursting strength 1450 kPa; edge compression strength 6.8kN / m
Results for 24 hours: moisture 10.5%; bursting strength 1290 kPa; edge compression strength 6.3kN / m
Results after 240 hours: moisture 7.5%; bursting strength 950 kPa; edge compression strength 5.1kN / m
Corrugated cardboard storage time 6 hours of bursting strength and edge compression strength not only did not decrease, but increased somewhat. With the extension of storage time, moisture, bursting strength, and edge pressure strength have decreased to varying degrees, but the largest decrease is the bursting strength. This shows that the storage time is closely related to the quality of corrugated cardboard. [next]
4. Influencing factors of stacking method
The stacking of corrugated cardboard is the process of dissipating heat, removing moisture, increasing the adhesive strength, restoring the corrugated height and preventing the warpage and deformation of the corrugated cardboard production line. Therefore, the shape, height, environment, time and number of turns of the cardboard stacking, and even the pallet used directly affect the quality of the finished box. The storage environment and storage time of corrugated cardboard have been described above. The following is a brief analysis of the stacking tray, stacking shape, stacking height, and the number of turns of the stacking:
1. The impact of stacking trays. The carton industry generally uses wooden or rigid plastic pallets, the general specifications are 1100 Ã— 1200mm or 1200 Ã— 1500, and the height is 150 ï½ž 200mm. According to production practice, wooden pallets are better. The reason is that during the stacking process of the cardboard, the wooden tray can absorb the moisture of the cardboard in contact with it, but the plastic tray does not absorb moisture, and eventually it will be absorbed by the cardboard in contact with it, causing the tissue at the contact site to be wet, wrinkled or glued. In addition, the height of the pallet and the gap between the slats on the pallet are important ways for air convection after stacking the cardboard. The higher the height and the larger the gap, the more favorable the moisture distribution of the cardboard is. However, considering the handling of the cardboard and the flatness of the cardboard under the stack, the height of the pallet should be 150-200mm, and the spacing between the slats should be 100-150mm.
2. The shape effect of stacking. There are only four types of cardboard stacking: single-row parallel stacking; double-row parallel stacking; Tic-Tac-shaped layered stacking stacking; multi-layer layered cross stacking. The advantages and disadvantages are as follows:
â‘ Single line parallel stacking
Advantages: The board can get sufficient heat dissipation from top to bottom and all around; the positive and negative turns are uniform, which is conducive to the smoothness of the board; the later bonding is sufficient.
Disadvantages: The heat in the center of the cardboard is not dissipated in time, and the surroundings of the soft people are hard; the corrugated cardboard in the lower part of the stack is also soft, and the thickness becomes thinner after compression;
â‘¡Double-row parallel stacking
In addition to the advantages and disadvantages of single-row parallel stacking, the stacking has the following advantages and disadvantages: less trays and saving storage space; the heat between the two stacks of cardboard is difficult to dissipate, causing the cardboard to be hard and soft on one side.
â‘¢Tic-tac-toe stacking stacking code
Advantages: The cardboard has good flatness and no warpage. Due to the special stacking method, there is a gap between the layers, and the tray is directly connected to the tray. The air circulation is smooth, and the heat is evenly and quickly distributed, compared with the above two stacking. Take up fewer pallets and save space.
Disadvantages: At the overlapping part of the board area of â€‹â€‹2/5, the moisture can not be radiated endlessly; if the quality of the adhesive is slightly poor, the composite layers of paper are easy to crack; the amount of cardboard between different layers will be deformed by compression.
â‘£Multi-layer hierarchical cross stacking
Advantages: Compared with the above three types of stacking, the pallet utilization rate is the highest, the floor space is the smallest, the cardboard flatness is the best, the adhesive is slightly poor, and the glue is not opened.
Disadvantages: The heat of the cardboard is not easy to dissipate, making it soft; the corrugated height is difficult to recover, and the cardboard becomes thinner; the required strength is also discounted. In severe cases, the thickness of the five-layer cardboard falls below 4mm, and the three-layer cardboard falls below 2.5mm Other factors affecting the thickness of the cardboard are under normal circumstances).
Based on the above analysis, it is clear that the tic-tac-to-stack stacking code is the best choice.
3. The effect of the number of turns per stack. Due to the different materials of the corrugated paperboard and face paper, the tension is also different. Even if the paperboard produced is flat, it will naturally warp during the cooling and cooling process. Insiders know that no matter which stacking method is used, positive and negative stacking is most beneficial to the flatness of the cardboard. However, in actual production, the number of positive and negative boards per turn will not be the same, some of them are ten pieces, and some are dozens of pieces. The more the number of each turn is, the more it is not conducive to the flattening and later bonding of the cardboard. Practical experience tells us that it is more appropriate to choose 5 sheets of five-layer cardboard and 10 sheets of three-layer cardboard as one turn. Verify the quantity.
4. The effect of stacking height. The higher the stacking capacity, the more the space can be fully utilized and the space can be saved, but the higher the pressure on the lower and middle cardboards is, which is not conducive to the recovery of the corrugated height. Especially when the stacking is not neat, it is also easy to cause unevenness of the cardboard. The printing of this kind of cardboard is not clear when it is formed, and the groove is neither shallow nor deep. After many verifications, the stacking height is preferably 1.2 ~ 1.5m.
The above factors are the "epidemics" that occur under the conditions of equipment, raw and auxiliary materials, process technology, personnel operation skills, teamwork, temperature, pressure, and even adhesives that fully meet the production of qualified products. When we fully understand the cause of the "incidence" that affects the corrugated cardboard after it goes down the production line, and its "pulse" is called, we then make appropriate adjustments and prevention according to the storage environment, transportation means, storage time, stacking method, etc., Will a similar problem occur?
Remember: Corrugated cardboard also needs to be "vaccinated" frequently!
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