Tension control of the most popular shaftless rota

Tension control of shaftless rotary offset press (Part 1)

tension control of shaftless universal 70 rotary offset press is very important, because the tension control mode of printing press has changed greatly under the condition of shaftless transmission, which is very different from that under the condition of shaft transmission. The tension control of shaftless drive is mainly affected by the tension of the paper feeding part, the speed ratio of the paper feeding roller, and the speed ratio of RTF (the paper pulling roller in front of the triangle plate of the newspaper folding machine). Compared with shaft drive, the tension control of shaftless drive is more flexible, but the increase of variable factors also increases the difficulty of tension control, which requires us to constantly explore the laws of the three in practice to achieve the best cooperation mode. Here the author calculates the shore a hardness value This hardness tester uses a sensor to measure the displacement of the pressure needle, and then talks about some experiences of tension control on the shaftless universal 70 rotary offset press through the CPU calculation

composition of the tension control part of the paper feeding part

the tension control part of the paper feeding part is composed of brake pads, brakes, floating rollers, etc. in order to keep the tension of the paper tape constant, the paper roll brake must be able to automatically adjust according to the fluctuation of the tension of the paper tape to ensure that the paper tape enters the printing device at a uniform speed and smoothly. During the smooth operation of the machine, ensure that the tension of the paper tape is stable at the given value, and prevent the paper tape from overloading and loosening at will during startup and braking. In the printing process, with the continuous reduction of the diameter of the paper roll, in order to maintain the constant tension of the paper tape, the braking torque needs to be adjusted accordingly

meg dlp1000 paper feeding machine adopts the shaft braking mode for the braking of the paper roll. The brake pad and brake disc are set at the shaft end of the paper roll core, and the braking force is loaded by air pressure, that is, the pneumatic tension control system. During the printing process, the linear speed of the paper tape remains unchanged, while the angular speed of the paper roll increases with the decrease of the diameter of the paper roll. Without considering the inertia moment and resistance moment generated by angular acceleration, in order to ensure the stable operation of paper tape, the following conditions should be met:

f × R＝T × R

f is the tension of the paper tape, R is the radius of the paper roll, t is the braking force of the paper roll core, and R is the braking force radius of the paper roll core

it can be seen that as the radius of the paper roll decreases, if the braking force is not changed, the tension on the paper tape will become larger and larger, and eventually the paper tape will be pulled apart. Therefore, on the premise of keeping the tension of the paper tape stable, with the reduction of the radius of the paper roll, the braking force must be reduced according to a certain law

in short, a certain amount of friction is generated after the brake pad contacts the brake disc, so that the paper tape has a certain tension. The floating roller swings under the action of tension and drives the potentiometer on it to change to a certain extent. The change of tension is converted into an electrical signal to control the air pressure of the brake cylinder, so as to achieve the purpose of controlling the amount of friction and realize the automatic control of paper tape tension

the distance between the brake pad and the brake disc should be between 1 ~ 2mm. If the gap is too large, the brake pad cannot be clamped effectively when the air pressure of the cylinder changes, resulting in too small tension, causing the floating roller to be pulled down suddenly when starting up and the paper tape to be stretched and broken; If the gap is too small, the cylinder will always clamp the brake pads, and the change of air pressure in the cylinder cannot adjust the clamping degree of the brake pads and brake discs, which will eventually pull the paper tape apart. Especially when the tension display value changes from 4 digits to 3 digits when the machine is turned on, the paper will break due to the excessive tension of the paper tape

the wear of the brake pads should be checked regularly according to the different materials, and the clearance should be adjusted appropriately, otherwise the tension control will be affected by the driving distance of more than 600 kilometers from Binzhou to Linyi. The failure of the brake pad will cause extremely unstable tension control, especially when the floating roller swings greatly during the paper receiving, and the paper belt floats before entering the RTF. Adjusting the tension of the paper feeding roller and the RTF and the paper feeding department cannot solve the problem. After the paper receiving, the tension disappears instantly (the floating roller adjusts greatly after the paper receiving), resulting in paper breaking. The reason for the reduction of the braking effect of the brake pad is that the material of the wear-resistant layer of the brake pad is relatively soft and its debris cannot be discharged in time. After friction, it accumulates on the brake pad to form a glaze like material, which reduces the friction coefficient. At this time, the brake pads can be polished, the glaze like substances can be removed, the number of chip removal grooves can be increased or the brake pads can be replaced

control of the inlet tension of the printing department

the inlet tension of the printing department and the tension of the paper feeding department are bounded by the paper feeding roller, which is installed on the paper path between the printing device and the paper feeding machine to force the paper belt to run, so as to avoid the fluctuation of the paper belt tension before the paper feeding roller directly affecting the paper belt tension after the paper feeding roller, and ensure that the paper belt entering the printing device is more stable after two tension controls. The control principle of the secondary tension system is realized by friction based on the difference between the speed of the paper belt and the linear speed of the paper feeding roller. Generally, the linear speed of the paper feeding roller is less than the speed of the paper tape. When the paper feeding roller is used, the tension of the paper feeding Department has a certain impact on the inlet tension of the printing department. Reasonably setting the speed ratio of the paper feeding roller motor and the drum motor through the main console of the printing machine is the key to accurately control the inlet paper tape tension of the printing department, which is generally set at -0.15% left and right (according to the number of Liu Qiang, chief engineer of Jixiang Automobile Research Institute of the printing department, the value is slightly different, but the difference is not too great)

the shaftless transmission mode has completely changed the previous mode of controlling tension by mechanical devices. The tension is controlled by the relative speed difference formed by the speed change between digital motors, that is, a small speed difference is formed between the linear speeds of the paper feeding roller, the printing drum and the folding machine RTF to control the tension. A decrease in the speed of the feed roller motor will increase the inlet tension of the printing section, and vice versa. In addition to the speed ratio, another factor affecting the tension control of the paper feeding roller motor is the pressure of the paper feeding roller and the press roller. The pressure is reflected by the indentation during press, which is generally 5 ~ 6mm. If the indentation is too small, the contact pressure of the two rollers is small, the friction between the paper feeding roller and the paper is also small, and the tension decreases under the same speed ratio of the paper feeding roller motor; If the indentation is too large, the rubber closing roller and the paper feeding roller will generate too much heat due to the large contact pressure during the counter pressing operation, which will accelerate the rubber deletion record: the aging of the roller and reduce its service life. The paper feeding roller is very important to ensure the printing quality. It can effectively prevent the problem of running out of order in the printing process

(to be continued)