Causes and Solutions of Broken Wall Faults

Newsprint, letterpress, and offset book and paper, which are used in large amounts, are mostly loaded on the press with the start of a web. Therefore, we attach particular importance to web breaks in job suitability. In particular, newsprint is one of the items that have the greatest impact on the quality of identification paper in all printability projects. This is the rate of web breaks (the number of web breaks that occur during the printing process for 100 webs). The reason why paper breakage is so valued is that the print job is stopped for a few minutes each time the paper breaks, and sometimes the paper and blanket are damaged at the time of paper break, so that the non-adjusted version cannot be printed. When this happens, it will affect the delivery time. If the printing speed is reduced to prevent paper breaks, the efficiency of the printing job must be reduced. Therefore, regardless of the occurrence of paper break or to prevent breaks and reduce the printing speed, the printing efficiency is reduced.

The longitudinal tensile strength of newsprint, offset book, etc. is generally 2.0kg/1.5cm or more. According to the weight of the reel and the size of the friction force, it can be calculated that the average tension applied to the paper during printing is about 400 g/1.5 cm. According to this corollary, no paper breaks will occur. So, what are the reasons for the occurrence of paper breaks in printing, and how can we prevent and reduce web breaks?

The main reason for paper breaks is as follows.

The tension that paper is subjected to during printing is unstable, and it is likely to increase more than three times beyond the normal tension. In particular, when the printing speed increases rapidly, the impact tension often breaks the paper.

The elasticity of the two ends of the paper roll is inconsistent. When the tension is too high at the time of printing, the tension is small, and the tension is likely to be reduced at the small tension side, and the tension is likely to occur at the high tension side.

The paper roll is deformed or the core is not round, and the roll rotates like a cam or an eccentric during printing, so that the paper breaks easily.

The humidity of the web is relatively large. After being stored in a relatively dry environment, due to the volatilization of the end surface, the paper on both sides of the web shrinks and a tight edge occurs. During the printing, the tension is concentrated on the edge of the paper and the paper is broken.

The end surface of the roll paper is bruised or bruised by sand during transportation, and the tearing at the place at the time of printing can also cause web breaks. Even if the paper is cut cleanly on both sides, the edge of the paper is not straight enough, and the paper will break due to stress concentration.

The problem of web joints is a major cause of web breaks. When paper breaks occur on the paper machine or when the paper roll must be exchanged in the middle of rewinding, both ends of the paper need to be glued together. This part is generally called a joint. Webs should have obvious defects at the joints. If the joint is properly bonded, it will not generally break at this point. However, the joints often have the following three improper adhesion conditions.

Bonding is not strong. The tension that the joint can withstand cannot reach the tension required for normal printing.

Stick up and down. When joining the two ends of the paper together, the joints bond the joints with the inner layer or the inner layer or even the inner and outer layers thereof, so that when the printing is in this position, the reels cannot be reversed rather than broken. No.

The connector is not correct. After the joint can not keep the two sides of the paper still form a straight line, but on both sides at the same time folded in one direction. When printing reaches this position, the paper does not resist tension along the full width, but resists tearing on one side. This can easily lead to a broken end. And before and after this position there will be a margin.

Some of the broken ends of webs are determined by the production of paper, which is unavoidable in use, while others can be avoided or reduced by certain measures. From the user's point of view, the following measures can be taken to reduce web breaks.

Do not speed boot, do not suddenly increase the speed.

Be careful not to injure the side of the web when carrying it, and do not stand it on sand or dusty ground.

Pay attention to the various marks of the reel during printing, and reduce the speed of the joints when the joint is approaching. Wait for the joint to increase the speed.

An arcuate roller with an appropriate curvature can be provided at the paper feed portion of the printing machine so that the tension on the paper web is appropriately distributed in the middle of the paper, and the tension on both sides of the paper is reduced.

Reprinted from: Fuzhou Printing Network