Corrugated board flatness analysis and improvement method

The flatness of corrugated board is one of the important indicators in the production technology of carton. It is directly related to the quality of product printing, die cutting or slotting. Corrugated cardboard has poor flatness, which will produce a variety of arch shapes of corrugated cardboard, easy to jam when mechanically adsorbed and printed, and forced to stop the cleaning after the cardboard is scrapped; uneven printing and uneven coloring are easy to occur in two-color printing or multi-color printing. There are gaps in the color overlap, etc.; the slot size displacement on the printing start, the upper and lower flaps of the carton overlap or not; the die-cut feeding also causes jamming and dimensional displacement, etc., which may cause the secondary cardboard to be scrapped, or equipment. Damage was forced to stop finishing. In short, the poor flatness of the cardboard will make the feeding inconvenience and increase the number of secondary waste in the production process.

In order to improve the smoothness of the corrugated class and ensure the product quality pass rate and normal production efficiency, we continuously test and analyze in the carton production practice, and explore some improvement methods. It is summarized as follows and is for reference only.

The shape of the corrugated cardboard with poor flatness

Corrugated cardboard has a flat shape that is roughly classified into three types: a lateral arch, a longitudinal arch, and an arbitrary arch.

Transverse arching refers to an arch formed along the corrugated direction. Longitudinal arching refers to the arch shape of the cardboard produced along the direction of the line speed. Any arch shape refers to an arch shape that produces undulations in any direction. The surface of the paper is arched as a positive arch, and the surface of the paper is called a negative arch. The surface of the paper is undulating and is called a positive and negative arch.

The main reason that affects the flatness of cardboard

1. The type and grade of paper in the face are different. There are imported, domestic kraft paper, imitation kraft paper, corrugated paper, tea board paper, high-strength corrugated paper, etc., and divided into A, B, C, D, E, grade. According to the paper quality difference, the general paper is better than the paper.

2. The main technical parameters of the paper are different. From the carton performance requirements or the user's cost reduction, the paper in the carton is required to be different, usually:

(1) The amount of paper in the face is different. There are large amounts of facial paper than paper, and there are also small ones.
(2) The paper has different moisture content in the paper. Due to the different environmental humidity of the supplier, transportation inventory, etc., the paper has a larger moisture content than the paper, and it is also small.
(3) The amount of paper in the noodles is different from the water content. First, the paper is more quantitative than the inner paper, and the water content is larger than the inner paper or less than the inner paper. Second, the amount of paper is less than the inner paper, and the moisture content is greater than the inner paper or less than the inner paper.
3. The moisture content of the same batch of paper is different. The moisture content of a part of the paper is greater than the moisture content of the other part of the paper or the ends of the paper, the outer edge side and the inner core side.
4. The length of the heated surface of the paper through the heat exchanger (including the corner) is improperly selected or adjusted or the length of the heated surface cannot be adjusted arbitrarily. The former is affected by improper operation, and the latter affects the preheating drying effect due to equipment limitations.
5. The steam spray device or the spray device on the equipment cannot be used correctly, so the humidity of the paper cannot be arbitrarily increased.
6. After the paper is preheated, the water is not enough time or the environment is humid, the ventilation is poor, and the production line speed is improper.
7. The amount of glue applied to the single-faced corrugating machine and the gluing machine is improper and uneven.
8. The steam pressure is insufficient, unstable, the traps and other accessories are damaged or the pipeline water is not drained, resulting in the preheater not working properly.

Related factors, parameter testing and qualitative analysis

In view of how to improve the flatness of cardboard, we have tested and analyzed the physical properties, process equipment and other related factors and parameters of several commonly used papers.

(1) The same type of paper is quantitatively increased, and the shrinkage rate is slightly reduced. The relationship between the quantitative, water content and shrinkage rate of some imported kraft paper, domestic cattle (imitation) paper, tea board paper, high-strength corrugated paper.
(2) The steam pressure supplied by the corrugated board production line is proportional to the surface temperature of the preheater. The higher the pressure. The higher the surface temperature of the preheater.
(3) Quantify paper with high water content, preheating and drying slowly, and vice versa. The paper with different quantitative and moisture content is preheated and dried on a preheater with a pressure of 1.0 Mpa/cm2 (172 °C).
(4) The larger the length of the heated surface (wrapped angle) of the paper on the preheater, the lower the water content. The relationship between the length of the heated surface and the moisture content after baking at a preheater temperature of 172 ° C and a production line speed of 0.83 m / s at a preheater temperature of 10%.
(5) After preheating, the single-faced corrugated paper naturally emits water slowly, and the fan ventilates and returns to the powder quickly. Quantitative 220g/m2 and 150g/m2 single-faced corrugated paper after preheating at 172 °C, moisture content of 13%, in the greenhouse 20 ° C, humidity 65% ​​of the environment, the natural emission of water and the fan fan ventilation speed comparison.

Qualitative analysis

The above test results show that the paper, the quantitative, the water content are different, and its shrinkage rate is also different, which is an important physical property of the paper. The paper used in the same paper is the same, and the cardboard is easy to achieve a good flatness. The opposite is hard. It is necessary to comprehensively consider the changes of the above five main factors and make appropriate adjustments. The difference in flatness depends on the shrinkage rate of each layer of paper. To make the paperboard have a good flatness, the shrinkage of each layer of paper must be basically the same, and the main part of the paper is the lining paper. The shrinkage rate of the facial tissue is smaller than that of the inner paper, and the negative arch is reversed. The unevenness of the shrinkage of the paper in the front is positive and negative arch. From the analysis of the process of forming the production line of cardboard, the control of the shrinkage rate can be divided into two stages.

(1) The stage of corrugation formation. That is, each process before the base paper is fed to the secondary coating is a key stage for controlling the shrinkage rate. According to the actual situation of the paper, steam pressure, ambient temperature and humidity of each layer of the tile in the face, the preheating temperature, the length of the heating surface (wrap angle), the way of venting moisture, steam spray, and the amount of glue are separately selected. , the production line speed lamp technical parameters, so that each layer of paper through a suitable and effective process control, each freely shrinking, Zui final shrinkage rate is basically the same.

(2) Cardboard forming stage. That is, the bonding, drying and ironing of the secondary coating to the subsequent process. At this time, each layer of paper can not be freely contracted by each other, and the shrinkage of each layer of paper after being bonded into the paperboard is mutually restricted, and the bonding point can be said to be the starting point of the arching of the cardboard. It is necessary to select and adjust the technical parameters such as the amount of glue, the temperature of the baking sheet, the speed of the production line, and the difference of the shrinkage rate to the small limit of the Zui, and to flatten the arch shape produced by the cardboard as much as possible.

Cardboard flatness improvement method

Improvement ideas for the flatness of corrugated board:

First, the base paper provided by the supplier is required to have a qualified and stable quantitative and moisture content, avoid rainwater in transportation and handling, and maintain a substantially constant environmental humidity during storage in the factory.

The second is to use paper of the same kind or paper with the same kind of paper or quantitative, moisture content and grade as much as possible.

Third, the paper with a large water content increases the length of the heating surface (wrapped corner) of the preheater, ventilates with the electric fan, increases the time of water emission, and slows the speed of the production line; the paper with a small moisture content passes through the preheater (the wrap angle) Reduce the length of the heated surface, natural ventilation, steam spray, and speed up the production line.

Fourth, the amount of glue applied to each layer of paper is consistent, and the amount of glue on the full width along the corrugated direction is even and moderate.
Fifth, the pipeline fittings such as air pressure stability and traps maintain normal functions.

There are many factors affecting the flatness of corrugated board, and the changes in the flatness of various factors change. The improvement must be tailored to local conditions, targeted, and grasp the main contradictions to solve. The following are examples of common problems in the production of single and double corrugated cardboard in our factory.

Cardboard is arched horizontally

It is known that the facial tissue is 250g/m2A kraft paper with a moisture content of 7.7%; the (clip) paper is 150g/m2 domestic high-strength corrugated paper with a moisture content of 10%; the inner paper is 250g/m2B kraft paper with a moisture content of 14%; The production line speed of 1.1Mpa/cm2 is 60m/min. ways to improve:

(1) The length of the heating surface of the inner (clip) tile paper is increased by 1 to 1.6 times and 0.5 to 1.1 times by the preheater (wrap angle).
(2) The inner (clip) tile line is moved at a speed of 0.9KW electric fan on the moving line of the production line, and the window of the workshop is naturally ventilated.
(3) A small amount of steam spray on the face paper.
(4) The production line speed is reduced to about 50m/min.
According to the above selection parameters, the original lateral arch can disappear.

Cardboard is arched from the longitudinal direction

ways to improve:
(1) The facial paper increases the movement resistance before the three-layer preheater, and increases the rotational braking force of the paper.
(2) Riva paper reduces the movement resistance by the guide wheel and tensioner before the three-layer preheater.
After proper adjustment, the original longitudinal arch can disappear.

Cardboard is negatively arched in the horizontal direction

It is known that the facial tissue is 200g/m2B grade kraft paper, the moisture content is 8%; the air pressure is 1.0Mpa/cm2; the production line speed is 50m/min. ways to improve:
(1) The length of the heating surface of the surface (clip) of the preheater is increased by 0.9 to 1.4, 0.6 to 1.12 times, respectively.
(2) The inner paper reduces the length of the heating surface of the preheater or sprays it with a small amount of steam.
(3) The production line speed is increased to about 60m/min.

Cardboard longitudinally arched

ways to improve:

(1) The facial paper reduces the movement resistance before the three-layer preheater and reduces the rotational braking force of the paper.
(2) Riva paper increases the resistance to movement in the guide wheel and tensioner before the three-layer preheater. After proper adjustment, the original longitudinal arch can disappear.

Cardboard is negatively arched in the horizontal direction

It is known that the facial tissue is 200g/m2B kraft paper with a moisture content of 13%; the (clip) paper is 150g/m2 high-strength corrugated paper with a moisture content of 10%; the inner paper is made of 200g/m2 B-grade imitation kraft paper with a moisture content of 8%; The air pressure is 1.0 Mpa/cm2; the production line speed is 50 m/min. ways to improve:
(1) The length of the heating surface of the surface (clip) of the preheater is increased by 0.9 to 1.4, 0.6 to 1.1 times, respectively.
(2) The inner paper reduces the length of the heating surface of the preheater or sprays it with a small amount of steam.
(3) The production line speed is increased to about 60m/min.
The paperboard is negatively arched in the longitudinal direction:
(1) The facial paper reduces the movement resistance before the three-layer preheater and reduces the rotational braking force of the paper.
(2) The tension of the Riva line in front of the three-layer preheater increases the resistance to motion.

Cardboard is arched

There are two types of positive and negative arches, and the improvement methods are different. Only the common lateral positive and negative arches are illustrated here.
It is known that the facial tissue is 180 g/m2 kraft paper, the moisture content is 8% 14%; the air pressure is 1.1 Mpa/cm2; and the production line speed is 70 m/min.

ways to improve:

(1) The surface paper is partially sprayed with steam in the laterally arched region.
(2) A partial steam spray of paper in the transverse negative arched area.
(2) The production line speed is reduced to about 60m/min.
(4) Adjust the 180° direction of the inner tube.
In addition, there is a way to make up the difference. For the partially arched cardboard that has just been made from the production line, the stacking of the upper and lower pressure plates is carried out in a stack of about 10 pieces, so that the cardboard is subjected to positive and negative during the semi-finished product storage process. The external force of the flattening can achieve a good flatness after a few hours (according to the ventilation and heat dissipation conditions of the plant).

Ideas and recommendations

In the technical requirements of corrugated cardboard, it is proposed to have a flatness regulation.

The national standard GB6544-86 "corrugated cardboard" 2.3 made a qualitative requirement: "the surface of the corrugated board is flat..." At present, with the improvement of the automation level of the packaging industry, the board printing, cutting, slotting, and bonding Multi-functional machine operations such as binding, strapping, etc. and the packaging production line for carton users are widely used, and the requirements for flatness are getting higher and higher. The cardboard that does not meet the requirements will be automatically shut down or withdrawn by the machine packaging production line. We believe that it is necessary to have provisions for the flatness of corrugated board, which is convenient for operators and quality inspectors to follow the operation test, which is beneficial to control the quality of the process.

The flatness of the corrugated board shall be measured after being placed horizontally without any external force, and the chord height shall be measured. The flatness is divided into 3 levels:

The first-level precision is suitable for the production of multi-function machines such as printing, cutting, slotting and chamfering, and is used for high-precision machine packaging cartons;
The second-level precision is suitable for printing and cutting machine production, and is used for packaging cartons with high precision;
The three-stage precision is suitable for single-machine production such as printing, wire indentation and slotting machine, and is used for explosive carton with high precision.

Improve and improve corrugated board production line equipment

(1) The preheater required for each layer of paper, especially the preheater required for the paper, should be able to adjust the length of the heated surface of the paper (wrapped angle);
(2) There must be sufficient space for each paper to emit moisture after passing through the preheater, especially to ensure the space for the facial paper to emit moisture;
(3) An electric fan ventilation device shall be added to the area where the water is released after preheating;
(4) Each paper must be equipped with a steam spray device, and the amount of steam can be arbitrarily adjusted in the direction of corrugation.

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