Analysis and Countermeasures of Cracking in Die-cut Lines

In the carton industry, the proportion of the box-forming process using die-cutting has grown rapidly in recent years. This is mainly due to the fact that the automatic packing lines introduced in a large number of product packaging industries have put forward new requirements for the carton structure; various specially designed special-shaped packing boxes ( Boxes) have also been used in large quantities; at the same time various high-end products (such as notebook computers, liquid crystal displays, etc.) have imposed stringent requirements on packaging; there are also some large carton factories to meet the demand for large-scale product delivery to increase production efficiency. The use of die-cutting into the box method, so die-cutting into a box popular, especially round-bore circular die-cutting because of its unique advantages of high production efficiency, one-time completion of the printing die-cutting and relatively simple equipment manufacturing, is increasingly more for each Carton factory used.

No matter which method is used for die-cutting, no matter whether it is flat or flat or round, and no matter how complicated the product is, the whole process of die-cutting is to complete two kinds of actions, one is to cut off excess material, and the other is The creases (pressure lines) are pre-pressed for forming. The action process of these two kinds of actions is not the same, and their stress conditions are also very different. By analyzing their stress process, we can see that the removal of scrap is to complete the cutting of the board by the cutter, and the contact between the cutter and the board is line contact; and the pressure line is the tool to deform the board by local force to cause deformation, the cutter and the board The contact is surface contact. Whether or not the shape of the board can be changed (cutting, squeezing) will ultimately depend on the pressure on the unit area, that is, the pressure. In the die-cutting process, the force exerted by the die cutter and indentation knife on the cardboard is certain, but due to the different contact surfaces between the cutter and the cardboard, the pressure on the cardboard is different, and the pressure of the indentation line is less than the cutting pressure. The process of simultaneous cutting is actually the process of breaking the paper after it is stretched by external force, and the process of pressing the wire is actually the process in which the paper is compressed by the stretched corrugation. In general, the compressive properties of solid materials are far greater than the tensile properties.

From the above simple analysis of force, we can see that to complete the cutting process of the cardboard, the force required by the pressure line is much greater than the force required for cutting. One is that cutting one is crushing different physical changes. This also determines why the problem of pressure lines in die cutting production is much greater than that of cutting. Understanding the mechanics in the process of touching can help us solve many problems in die cutting production. Pressure cracking is a quality problem often encountered in die-cutting production, and the difficulty of solving is relatively large. While under normal circumstances we are more concerned about the results of cutting, although the shape is quite important, but the pressure line can not be ignored, it relates to whether the product can be formed smoothly, the precision after shaping can meet the requirements, and the pressure line will also affect the product The strength thus weakens the protective function of the package. In fact, the reason why many products are returned to customers after they are mainly returned to the pressure line.

To solve the problem that the depth of the pressure line is appropriate but not to rupture is the key to improve the quality of the touch. It can be analyzed from three aspects of equipment, board, and operation. What is the reason why the cardboard is subjected to force exceeding its breaking strength, so as to find a solution to the problem? Method. Whether the mold design of the equipment is reasonable, especially the height of the knife and the choice of the height of the knife are reasonable. When the board passes through the touch-cutting part during the production process, the main pressure to advance the paperboard is the pressure line. If the pressure knife is too low, it will not only make the pressure line very shallow, but also cause the die-cut to flee due to insufficient transmission force. However, if the pressure knife is too high, the cardboard will be cracked due to excessive force. Therefore, the choice of tool height is very important and should be determined according to single and double wattage, pressure line depth requirements, and paper quality. In addition, installing pressure line protection strips on both sides of the pressure knife can effectively reduce the pressure line cracking phenomenon. After the pressure line guard is installed, the pressure line guard at the time of die cutting can press and softly deform the paper, corrugated, and core paper on both sides of the paperboard pressure line, thereby effectively deforming the pressure line guard. Reduce stress concentration to reduce or eliminate pressure line rupture.

Under normal circumstances, the height of the pressure line protection bar is about 0.9 mm lower than the pressure knife, and the shape of the pressure line protection bar can be selected according to the use effect. Now circular die cutting adopts soft die cutting. The cutters on the die will continuously cut on the polyurethane anvil to form many grooves to make the surface uneven, and the cardboard will occupy various points in the die cutting process. The reaction force will also be different, so it is necessary to check the surface condition of the felt surface frequently. If there is a deep groove or notch, it should be repaired in time. In addition, when the die-cutting part is working, the force is large. In operation, a large transmission gap and a large radial runout of the die-cutting wheel and the anvil wheel will adversely affect the die-cutting quality, and in particular, the phenomenon of cracking of the pressure line will occur. The poor quality of the cardboard itself is also one of the causes of the cracked lines.

When the warped cardboard passes through the contact part, not only is it easy to cause die-cut fleeing, but the stress at certain points is too concentrated to break through the tensile strength of the cardboard due to the inability of the pressure to be transferred in a balanced manner; some cardboards are in the process of pulling Due to the excessive tension in the paper or the excessive pressure on the pressure wheel, the paperboard itself has a defect that the indentation line is too deep or the paper has great stress on the paper. Such a paperboard is slightly damaged by the external force, not to mention the pressure. When the line is under a lot of pressure, it is often broken during cutting.

Of course, this type of paperboard will improve its cracking phenomenon when the humidity is increased, but it will also increase the difficulty of cutting and waste. With the rise of paper prices, the competition in the profit margin of the carton has become fiercer. Therefore, the carton factory will have a lot of brains and especially paper in the selection of paper, and more and more papers will be used. Worse paper, and these papers have low rupture strength. It is difficult to resist the pressure when the die-cutting is done. It is inevitable that such paperboards will die if the die quality is poor.

Of course, to reduce or avoid the phenomenon of pressure line rupture operators operating technology is also a very important part, pressure adjustment and speed control is one of the key. The pressure adjustment during touching is obtained by adjusting the gap between the cutter wheel and the anvil wheel. Under normal circumstances, when a good crimp quality is obtained, the larger the gap between the two wheels, the better. If other quality problems occur, such as stealing does not occur. Good, fleeing, and so on, operators often solve the problem by increasing the pressure is not appropriate, sometimes the problem is solved, it is also accidental or call it right, most of the time it will generate new problems. It is a cracked line. In addition, the speed of touching and cutting must also be controlled so as to achieve perfection. Too fast speed means that the time for each piece of cardboard to pass through the cutting part will be shortened, while the cutting force and pressure line force will not change when touching, that is to say force. The acceleration will increase greatly, and the chance of cracking the pressure lines will naturally increase.

Source: Corrugated Boxes - Issue 4, 2005

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