Analysis of longitudinal overprint inaccuracy of t

Analysis of longitudinal overprint inaccuracy of beiren sheet fed offset press (I)

overprint inaccuracy is a relatively complex technical problem in printing, which has four phenomena and three factors. There are four phenomena, namely, the overall overprint of the printing sheet is not correct, the partial overprint of the printing sheet is not correct, the repeated overprint is not correct, and the front back overprint is not correct; There are three factors, namely, the original version inaccuracy caused by plate making, sheet production and plate making, the overprint inaccuracy caused by paper expansion, and the overprint inaccuracy caused by the failure of offset press or improper operation and debugging. Overprint inaccuracy can be divided into two types: longitudinal overprint inaccuracy and horizontal overprint inaccuracy. Next, combined with production practice, dozens of overprint failures are summarized and analyzed, and solutions are put forward

longitudinal overprint is not allowed

1 One side of the paper cannot go in place. Refer to gb/t 2828.1 (2) 012 sampling inspection procedures by attributes Part 1: inaccurate overprint from the batch by batch inspection sampling plan retrieved according to the acceptance quality (AQL)

one side cannot go in place. Inaccurate overprint refers to the cross line overprint on one side in the longitudinal direction, and the cross lines that are inaccurate overprint are all in the mouth direction of the standard line. There are 7 common fault analysis and solutions

(1) the falling time of the side gauge is too early

refers to that when the normally transported paper has not reached the front gauge, the side gauge pulls the paper pressing ball to fall too early to press the paper, so that the paper is not in place, resulting in inaccurate overprint

solution: the normal falling time of the side gauge should be after the paper is normally transported to the front gauge; The time of picking up should be at the same time when the paper teeth swing to hold the paper tightly, that is, when the swing opening and closing teeth roller leaves the cam. Loosen the two set screws on the side gauge cam and reverse the cam until the above falling and lifting time is met

(2) the front gauge stop tongue is too low

when the current gauge stop tongue is less than 3 times the thickness of the printed paper, the paper will be blocked and cannot go in place when entering the front gauge

solution: loosen the adjusting screw of the front gauge, lift the front gauge, pad three printing sheets under the paper stop tongue, and tighten the adjusting screw. Idle the machine for several weeks, stop at the position where the front gauge falls, and then insert three printing sheets under the paper stop tongue for retest, so that three sheets of paper can enter and exit freely, and four sheets of paper can not be inserted

(3) the paper feeding positioning time is too late

sometimes the paper arrives at the front gauge too slowly, especially when the side gauge considers that the paper is pressed by the side gauge and cannot move forward, and the other side continues to move forward to reach the front gauge, which will also cause the fault that one side cannot move in place

solution: loosen the fine-tuning screw to adjust the speed of paper feeding time, turn the hand wheel of the paper feeder in the direction of fast paper feeding, and then tighten the screw for retest. After the front gauge falls into place, the distance between the front edge of the paper and the paper stop tongue should be 6 8mm

(4) the side gauge pulls the paper pressure ball up too slowly

the reason is: when the swinging paper teeth hold the paper and start moving forward, the paper pressure ball still presses the paper, and pulls the paper out of the swinging paper teeth. The printing is the same as the misregister that cannot go in place on one side

si solution: the side gauge pulls the paper pressure ball up too slowly, indicating that the working point of the cam is not adjusted well. At this time, loosen the two set screws of the side gauge cam, then turn the cam forward, tighten the screws, and then retest until it meets the requirements

(5) the paper gripper is too light

the paper gripper of the imprint cylinder and the paper gripper of the swing are too light, too little or uneven, which is also easy to cause inaccurate overprinting, which is reflected in the same phenomenon as inaccurate overprinting when it is not in place

solution: if it belongs to the fatigue problem of the support spring or tension spring, it should be replaced; If the tooth pad of the swinging paper gripper is too low and uneven, the whole set should be replaced. After installation, you can use the method of general adjustment to jog the printing machine to the junction of the embossing cylinder and the oscillating gripper, and the distance between the oscillating tooth pad and the plane of the embossing cylinder is 0.3mm. During the overall adjustment, loosen the overall iron plate of the tooth pad, adjust the nut on the swing shaft, turn the tooth pad clockwise to raise, and turn the tooth pad counterclockwise to lower until it reaches 0. 3mm distance. As for too little paper, you must ensure that the paper teeth are swung and embossed, and the paper teeth are between 5mm and 6mm. Generally, do not change the front rules when changing the version and adjusting the rules

(6) the positioning brush with trailing tip loses its function

the positioning brush with trailing tip mainly prevents the paper from ejecting after entering the front gauge. It may lose its function for the following reasons: ① when the paper feeding stops due to the skew of the paper feeding, in order to take out the paper on the paper feeding board, the action of turning the frame up and down is too heavy, causing the brush to tilt up or turn over, etc. ② The brush is fixed in one position for a long time. If it is used for too long, the part where the brush rubs against the edge of the paper will be damaged and lose its function. ③ The position of the brush pressing the paper is incorrect, and the paper is on the tip or root of the brush

solution: ① and ③ problems need to readjust the brush; The second problem is to remove the gross refresh energy vehicle production and sales growth rate of more than 50% and scald it on the fire. The method is: first burn a flat small iron plate in the fire, pick it up and lay it flat on the ground, then gently stroke the brush on the red iron plate according to the original slope, and the high place will be ironed. If the wear is large, you can iron it several times until it is ironed (please note that this brush should not be cut)

(7) the brush wheel is too light or the two paper pressing wheels at the trailing tip are not against the paper at the rear edge of the paper. 2. Torque measuring precision: 2 paper pressing wheels at 1% tip can ensure the stability and accuracy of the paper when entering the front gauge. Their pressure on the paper should not be too heavy or too light, too heavy is easy to cause the back to rub dirty; Too light will lose its due function on the paper, and it is easy to make the paper go out of place. Sometimes, one of the two brush wheels or two paper pressing wheels has appropriate pressure, and the other has light pressure. The light end will cause one side not to walk in place

solution: the pressure of the two brush wheels and the two paper pressing balls at the trailing tip, which play an important role in overprint, should be consistent and in place, that is, the brush wheels must be pressed on the paper surface on the paper conveyor belt; The two paper pressing balls at the trailing tip should firmly press against the rear edge of the paper