Overprint Caused by Double Diameter Roller and Troubleshooting Method

Fault one: Misalignment due to tooth row failure on double diameter roller

The company's MOV four-color offset press, when printing light coated paper, printed on the outside of each side there is a regular pattern of serious overprint is not allowed, from the point of view of the print is the first color black version and after Tricolor, magenta, and yellow are not allowed. The three colors of green, magenta, and yellow are overprinted accurately, and the rules for printing inferior products are accurate. From this it can be seen that the problem lies with a set of teeth in the double-diameter cylinders of the first and second color groups.

Shutdown inspection, the two sets of double-diameter roller cleaning teeth one by one, oil refueling, then wipe dry with a rag to reprint, the fault still exists, but not the original serious.

The paper was rubbed with a few magenta inks on the inner side of the teeth of a set of teeth of a double-diameter cylinder (3 to 4 pieces), and several more prints were made. A contrast check revealed that the deep impression of the magenta ink blot was overprinted. Quasi-proof, mouthwash position Magenta ink blotting shallow proofs are not allowed to print on the outside. Obviously, there is a problem with individual teeth on a group of teeth that have not been marked. Stop the inspection, insert 0.25+0.10mm steel sheet on the backside (outward side) of the row of teeth that has not been marked, and put a 30g/m2 copy paper strip on 11 tooth chips, and then test one by one. It was found that the opening of the 2nd and 3rd teeth on the outward side was too small (that is, we usually said too much force). First of all, to rely on this side of the tooth chip force consistent as a benchmark, the two teeth to adjust the force with the other nine teeth to achieve the same force, and then pull out 0.1mm steel in the back, and then check each The force of the tooth chip, finally, pulled out the 0.25mm thick steel sheet at the back, wiped off the magenta ink on the tooth chip, and turned on the test and printed it normally.

Fault 2 : Misalignment due to open tooth ball on double diameter roller

The open teeth are worn out or lack of oil, causing the paper transfer time to be unstable. Take the double-diameter roller between the first and second groups as an example. The phenomenon is similar to that of the fault one. The difference is that the open tooth is bad when the printed proofs are broken. The two sides are not allowed to overprint, the rules are the same, the three-color overprint line is below the black line, and the rules are disorderly. At this time, you need to change the open ball (F-74474).

(1) Replacement procedure

The first step: clean the teeth and the shafts of the double-diameter cylinders, clean the teeth, and mark the teeth on the corresponding tooth pads. Then loosen the fastening on the shaft base. Screws and fastening screws for cavities.

Step 2: Remove the fixing pin that connects the tooth shaft to the open ball, and use the crowbar to hold the cut surface (on the side of the body) of the shaft to the top in the outward direction. After the shaft is moved to a certain position, remove it. Open the ball and replace it with a new one (F-74474). Operate in the opposite direction from the operation sequence. Install the fixing pin and tighten the screw on the shaft holder.

Each tooth is fixed according to the marks that were originally made. Each grease nipple, oil eye grease, and oil change the open teeth. At this time, the double-diameter drum has changed its time and needs to be readjusted.

(2) adjustment steps

Step 1: In the first group of impression cylinders, on the side of the drive surface, the drum body has a mark near a groove on the side of the pillow. Here is the "0" point positioning line of the printing machine. Inside the hole in the plate, insert the debugging tool for positioning—the measuring tool (commonly known as the small axe). Slowly turn the car and the gauge incision is just in the groove's engraved line. The position of the measuring device is exactly the “0” position of the machine.

Step 2: Remove the first set of water roller motor, take off the sealing cover on the transfer drum after the protective cover, insert the special fixed shaft and fix it, and install the dial (only for the machine) on the shaft, take a piece The PS version is cut into triangles and the two corners are taped to the protective cover. The other corner is just at the “0” position and the dial is fixed.

Step 3: Turn the machine to the reverse corner of the PS plate and point it to the dial at 15°. At this time, the first group of transfer rollers and the double-diameter rollers are connected. The double-diameter rollers close the teeth and release the rollers. To tighten the screw, tighten the teeth in the middle of the tooth and tighten it symmetrically. Make sure that each tooth is closed and tighten the screw. After debugging, remove the measuring tool, fix the shaft, and install the water roller motor. Trial overprinting accuracy, troubleshooting.