Analysis of cutting quality
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Causes and solutions for curling after printing on tissue paper
In the process of cutting thin paper sheets (such as dictionary sheets), curling and warping of the sheets often occur, which affects the progress and quality of the cutting process. The reason for the analysis is mainly caused by the imbalance between the water content of the printed sheet and the ambient temperature and humidity, which can be solved by the following methods.
1. Dehumidification method
Since the inside of the printed sheet is lower than the water content in the air, the cut radial section will quickly absorb moisture to achieve a corresponding balance. Therefore, the moisture in the indoor air should be appropriately reduced to avoid curling of the radial section after cutting. Solution: Using the dehumidification function of the air conditioner to remove excess water in the indoor air, the purpose of dehumidification can be effectively achieved. The relative humidity is 50% RH, the temperature is 20 ~ 29 ° C, the temperature and humidity meet the standard requirements, and the printed sheet is not easily curled and deformed.
2. Page method
If the paper is curled after printing, it can be solved by the sheet method. First, the cut sheet is turned over, and the curled sheet is tapped on a plurality of fold lines by a manual "pick-up" method, and the bent sheet is forcibly changed to make it relatively flat by the supporting force generated between the fold line and the fold line.
3. Paper drying method
The paper-drying method uses a paper machine to ventilate the cut or uncut white paper, so that the internal humidity and air humidity of the paper are relatively balanced, and it is not easily deformed during printing and post-pressing, which can improve the printing quality. It also reduces the trouble of the binding process.
In addition, in order to ensure the reasonable moisture inside the paper (about 5%), you should also pay attention to the stacking position of the paper, not against the wall, by the window, by the heating (winter), not to be placed in the open air, so as not to be too dry, damage the paper to reasonable moisture. , causing paper warpage inequality.
Dot-line cutting method
In the traditional paper-feeding table, the tail of the printed sheet is usually a vertical line, but sometimes the printed sheet is irregularly jagged, and it is very accurate to observe the front and back of the printed sheet. How can we cut the prescribed line? Through careful observation and research on the cutting process and the equipment used, as well as on the printing press, we have found a rule: any print that deviates from the vertical line (a vertical line formed by the combination of the tail lines after the collision) is skewed. Uneven sheets, specifically, those that are not right angles are offset from the vertical line. So how to solve and deal with it? We have drawn the following conclusions from various aspects of discussion and analysis:
(1) If you want to solve the problem fundamentally, you need to make the cut paper 90°.
(2) The solution to the cutting method of the finished printed sheet, that is, the "dotted line cutting method".
To explore this method, we must first understand the paper feeding mechanism of the printing press. The paper feeding mechanism of the printing machine is to feed the paper to the paper feeding table by Feida, then send the paper to the front stop by the belt drive, and then pull the paper to the specified position through the side gauge (as shown in Figure 1). . The paper sent to the cardboard has to go through two actions before it can be given to the tooth decay: the first motion is the longitudinal motion, which is the motion that moves forward when coming; the second motion is the lateral motion, which is the motion of the pull gauge. Observed that if the paper sent to the front gauge is less than 90° near the pull gauge, the corner tip will be out of the pull gauge (as shown in Figure 1); any paper larger than 90° (by the pull gauge side) ), the side of the tail will also exceed the pull gauge. Once the crux is found, there is a solution. The position of the printed paper is composed of dots and lines. The point is the point determined by the pull gauge bearing, and the line is the line formed by the front gauge. Through the understanding of the printing press, in order to cut out more accurate finished products, we decided to transform the collision table. Transform the paper table into a dotted structure. To do this, add a plate with a width of about 100mm and a thickness of about 20mm to the original paperboard, which is about the height of the side plate of the original paper table, and put it in the position of the pull gauge. With this type of page hitting method, the printed sheet is very in place, and the printed sheet is also particularly suitable for the cutting requirements. However, the method of cutting does not change, or the ideal requirements are not met, so a cutting device is added. Specific practice: Fix it on the paper feeder with the same size plate. Through measurement and practice, use the double-strand 8 wire wire to form the horseshoe at the side of the paper feeder from 110 to 120mm (the position of the printing machine). Shape, one end is stuck on the board, one end is stuck behind the paper feeder, and the thickness of each stack should be 70mm. This method is convenient and flexible to handle, and does not affect the structure of the cutter. As long as the overprinting is accurate, it can be beautifully cut, improve the reliability of quality products, reduce the loss rate of “bleeding” caused by cutting, and the cost loss caused by the replacement printing, and improve the work efficiency. After more than 10 years of application, the effect is very good.
The effect of the structure and style of the blade on the cutting quality
The style of the blade depends primarily on the edge angle. There are usually two types of bevel angles: the arc-shaped bevel angles milled with a vertical knife sharpener, as shown in Figure 2(a); the edge angles ground with a horizontal grinder are straight, as shown in Figure 2 ( b) shown. There is also a special type of corner angle as shown in Fig. 2(c), which can be adapted to change the cut objects of various soft and hard materials at any time. The method of processing such a blade: the blade is further ground at an angle of 26° at its edge at 24°. It is more suitable for a knife with an initial slower speed. Because this edge angle is initially undercut, the resistance is small, which is mainly due to the angular shape of the corner. It is worth noting that the cutting speed of the knife is slow and the smaller corner angle should be selected within the allowable range. If the cutting speed of the knife is faster, a larger cutting angle should be selected within the range. The relationship between the cutting speed of the cutting knife and the cutting angle is also inseparable, and should be properly adjusted and flexibly mastered. Refer to Table 1 for the selection of the blade angle.
In addition, the effect of the blunt knife on the cutting quality is also very large. Since the blade forms a round head, when the blade is cut down, the blade cannot cut the paper at a time, but is pressed down until the paper is grooved (as shown in Fig. 3). At this time, the paper basket is almost a whole, and the blade cuts through the paper to complete the cutting. However, the cut paper has formed a corner on the paper, which is not a right angle at all, but an arc that protrudes from the paperboard at around 60°. Corner. Therefore, the probing part must be larger than the paper below the paper basket, forming a so-called upper and lower knife edge. Therefore, it should be changed in time after the paper is found to be stuck after cutting, so as not to affect the cutting quality. Under normal circumstances, the blade can be changed by cutting 1000 to 1500 times.