Get out of the misunderstanding of gripper adjustment of offset press
Operators of printing presses all know that the adjustment of the gripper of offset presses is one of the tasks often performed in printing production. But in the adjustment process, there are some misunderstandings to varying degrees. The following is a brief introduction to the correct adjustment of single (double) color machine and four color machine gripper.
Single (dual) color machine
Single (double) color machine (take J2108 machine and J2205 machine as an example) gripper is divided into transfer gripper, impression roller gripper, conveying chain row gripper. In the printing process, thin paper (such as 52g / m2 paper) is often pleated at a gripper of the impression cylinder, or the blanket is stuck when printing coated paper. At this time, the operator often stops, debugs the small spring holding the teeth separately, stiffens or loosens the small spring, and sometimes even removes a certain tooth slice from the tooth holder, but these practices are not correct. Excessive stiffening will make the small spring lose its elasticity, causing "dead teeth"; excessively loosening will make the small spring fall off and press on the impression cylinder, damaging the impression cylinder. The correct adjustment method is as follows:
Step 1: Jog the offset press to a place where it is convenient to operate, find the positioning stopper and positioning screw of the gripper shaft, and insert a piece of paper with a thickness of about 0.4mm.
Step 2: Loosen all the clamping screws of the gripper so that they are not closed.
Step 3: Put the dental tablet against the dental pad and make it have a certain pressure, then tighten the fastening screw, and place a 0.1mm thick kraft paper strip between the dental pad and the dental pad to measure its gripping force.
Step 4: Adjust the small springs and screws one by one so that the tensile force of the kraft paper strips held by all grippers is about the same, and at the same time, adjust each gripper to have the same gap with the tooth holder to make the gripper opening time consistent.
Step 5: Remove the piece of paper between the positioning screw and the positioning block, so that all grippers can increase the same gripping force.
In this way, the overall adjustment of the gripper not only is faster, but also the gripping force of all grippers is the same, which avoids the phenomenon of frequent shutdown and repeated debugging caused by the adjustment of a gripper alone. The adjustment of the delivery teeth of the J2108 machine is basically the same as the adjustment of the gripping teeth of the impression cylinder, but it should be noted that the paper between the positioning stop and the positioning screw should be thinner during the adjustment.
In the actual printing, there is often a phenomenon that a gripper on the chain row does not put the paper at the receiving table and takes the paper away. Some operators suddenly press the stop button during the normal printing process of the printing press, trying to find out the gripper without paper. But doing so not only damages the printing press, but also makes it difficult to find the faulty gripper, which is laborious and time-consuming. The correct way is to stop the machine first, insert a 0.25mm gasket at the contact between the chain block gripper block and the dental pad shaft, loosen all gripper fastening screws to bring the dental disc and the dental seat together, and then Tighten the screw, place a 0.1mm thick piece of paper between the dental pad and the pad, adjust the screw so that all grippers have the same gripping force, and then remove the gasket. After adjusting all the chains like this and restarting the printing, the phenomenon that the chains grip the teeth without paper can disappear.
Four-color machine
The impression cylinder and paper transfer cylinder of the four-color machine are generally double-diameter cylinders, which have two rows of grippers, so the adjustment is more complicated. However, it is not correct to adjust the gripper springs individually or to adjust the gripper of a certain impression cylinder to save time. Because the four-color machine generally has 4 impression cylinders, each impression cylinder has 2 rows of gripping teeth. If only a certain cylinder or a certain row of gripping teeth is adjusted, it is easy to cause the gripping force of the gripping row of the impression cylinder Unevenness, resulting in inaccurate four-color overprinting or image ghosting, seriously affecting the quality of printing. The correct method is to adjust 8 rows of grippers at the same time. Now take Shanghai Gaussian four-color machine as an example.
Step 1: Open the protective cover of the impression cylinder and jog the machine to expose the gripper row of the impression cylinder.
Step 2: Use a 5mm Allen wrench to loosen the screw on the gripper shaft that controls the gripper opening and closing rollers, and then use a spanner wrench to rotate the roller shaft about 60 °. At this time, all gripper pieces leave the pad About 0.05mm.
Step 3: Loosen all gripping screws to remove the dental pads from the dental pad, and clean the dental pads and the dirt on the dental pad.
Step 4: Place all grippers against the dental pad, tighten the tightening screws of each gripper, and then use a 0.05mm thick steel sheet between the dental pad and the dental pad to adjust the small spring on the dental seat To pull the steel sheet, the steel sheet can be pulled with a certain resistance.
Step 5: After adjusting all grippers, turn the rollers that open and close grippers back to the original position and tighten the tightening screws. In this way, all grippers increase the same gripping force, ensuring accurate overprinting of printed products.
In general, the adjustment of the grippers of offset presses generally follows the same rules. That is, a certain structure (different structures of the printing machine) is used to move the dental disc away from the dental pad a certain distance, and then the gripper is uniformly adjusted to make the force of each gripper small spring uniform, and then fixed by the gripper The big spring or torsion spring puts the same pressure on the gripper. Remember not to monotonically increase the pressure on the small spring on the gripper. In this way, we can get rid of the misunderstanding of the offset axis adjustment of the offset press and improve the printing quality.
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