Analysis of the unsteadiness of the hottest paper

Analysis of paper unsteadiness on the paper feeding board

during the printing process, accurate and stable paper feeding and accurate paper positioning are the basic requirements for the normal operation of the paper feeder and the basic conditions for obtaining qualified prints. In the process of paper feeding, there are various reasons for unstable paper feeding. To eliminate the paper feeding fault, we must understand the components that affect the stability of paper feeding and their relationships, identify the parts and grasp the key points

1. Influence of transmission parts

the printing unit and the paper conveyor are generally connected by a chain or universal coupling. During the reciprocating motion of paper feeding and taking, the paper delivery suction nozzle moves along the low point of the cam to the high point after the test piece is broken, so it is relatively stable. However, when returning to pick up the paper, it slides down along the high point of the cam to the low point. Due to the sudden reduction of the load, the chain jitters instantly, making the chain transmission speed uneven and affecting the stability of paper feeding. Therefore, when fixing the tensioner, be sure to tension the chain

the transmission of the separation head of offset press generally adopts universal coupling. After long-term use and wear, the gap between nodes will increase, and the paper delivery suction nozzle will also be unstable in the reciprocating motion, affecting the transmission of paper. At this time, a new coupling must be replaced. In addition, it is also necessary to check whether the braking device of the paper conveyor works. It is a device installed on the transmission shaft of the separation head to increase the stability of the paper conveyor, so as to prevent the phenomenon of exceeding its normal speed when the cam of the separation head slides. Of course, the compression spring of the brake band brake cannot be adjusted too tightly, otherwise it will increase the resistance of the paper conveyor

2. Influence of transfer parts

during the transmission of paper, the transfer parts that affect the smooth handover of paper are mainly the handover between the paper delivery suction nozzle and the paper receiving roller. Due to wear or improper adjustment of parts, the paper delivery suction nozzle and the paper receiving roller are prone to grab paper and pause when the paper is handed over. It is fast and slow on the paperboard, resulting in inaccurate rules and even failure to print normally in serious cases. This phenomenon is caused by the improper handover time between the paper delivery suction nozzle and the paper receiving roller. The transfer process of paper is like the baton of a relay race, which can only be controlled by two components with the same speed in the "other area of the relay". If the handover time is too short, it is easy to "drop the baton". 1. If the handover time is too long, adding appropriate cooling medium to the cooling tank of the low-temperature tank will lead to "stick grabbing" at different speeds. When the paper delivery suction nozzle sends the paper to the end, and just let go of the paper, the paper receiving roller also just presses the paper. If the paper receiving roller presses the paper before the paper delivery suction nozzle is cut off, it will cause the paper receiving roller and the paper delivery nozzle to grab paper. However, if the paper receiving roller does not press the paper when the paper delivery suction nozzle is cut off, and the paper is not controlled by the machine, the time before the paper arrives will be irregular, fast and slow. The adjustment method is: when the paper receiving roller just presses the paper, adjust the positioning screw to maintain a gap of 0.3mm with the roller, at the same time, adjust the distance between the smallest surface of the paper receiving cam and the roller on the swing rod to be about 1.5mm, and finally adjust the pressure screw of the paper receiving roller to make the pressure of the two rollers consistent

3. The influence of the transmission part

the paper conveyor belt is the transmission part of the paper. It drives the paper through friction. The stability of the paper conveyor belt movement directly affects the stability of paper transmission. The factors that affect the paper conveying belt include the roughness of the paper conveying roller, the tension of the paper conveying belt, the length of the paper conveying belt and the flexibility of the bearing. The friction between the paper conveyor belt and the paper conveyor roller depends on the tension of the paper conveyor belt and the surface roughness of the paper conveyor roller. Therefore, when checking the paper conveyor belt, it is necessary to check not only its tightness, but also the surface roughness of the paper conveyor roller. After years of use, the embossing on the surface of the paper feeding roller has been ground shallow or filled with dirt. 1. 3. The friction coefficient is reduced. At this time, the tightness of the paper belt should be greater, and the dirt in the embossing should be eliminated. In general, the paper conveyor belt should be able to lift 3-4cm on the paper conveyor. The single row centripetal ball bearings on the tensioning wheel and runner are easy to be polluted by paper wool and paper powder, and the rotation is not flexible. When doing cleaning and maintenance, the operators often ignore this place, and generally do not consider this place when the rules are unstable. Therefore, this place should not only be kept clean, but also be often filled with oil to ensure that the bearings rotate flexibly. In addition, the length of the cloth belt should be consistent and not too long, and its wrap angle with the tensioning wheel should be greater than 90 degrees. If the wrap angle with the tensioning wheel is too small, the movement resistance of the cloth belt will be increased, resulting in inconsistent speeds between the cloth belts, affecting the stability of paper feeding. As shown in Figure 1

Tianjin Nankai University printing plant Li xiulai Kong Rong

source: Printing Technology