Printer operators are well aware that the adjustment of offsets in offset presses is one of the most frequently performed jobs in print production. However, in the adjustment process, there are some misunderstandings to varying degrees. The author will give a brief introduction to the correct adjustment of single (double) color machines and four color machines.
Single (double) color machine
Single (double) color machine (J2108 machine and J2205 machine as an example) of the decayed tooth is divided into the delivery of teeth, impression roller tusks, teeth squeezing teeth. In the printing process, thin paper (such as 52g/m2 paper) is often pleated at a certain enamel of the impression cylinder, or it is sticky when printing coated paper. At this time, the operator often shuts down, individually adjusts the small springs of the cavities, stiffens or loosens the small springs, and sometimes even removes a tooth from the socket, but these practices are not correct. Excessive stiffening can cause the small spring to lose its elasticity and cause "dead teeth". Excessive slackness can cause the small spring to fall off and press against the impression cylinder, damaging the impression cylinder. The correct adjustment method is as follows:
Step 1: Move the offset press to a place convenient for operation, find the positioning stopper and set screw of the jaw axis, and insert a piece of paper with a thickness of about 0.4 mm.
Step 2: Loosen all the fastening screws of the caries so that they do not close.
Step 3: Place the dental chip against the dental pad and apply a certain amount of pressure. Tighten the fastening screws and place a 0.1mm thick kraft strip between the dental pad and the dental pad to measure the force.
Step 4: Adjust the small springs and screws one by one so that the pulling force of all the enamel cavities is approximately the same. At the same time, adjust the gap between each cavities and the occlusal tooth so that the opening time of the cavities is the same.
Step 5: Remove the piece of paper between the set screw and the positioning block so that all cavities can increase the same force.
In this way, the overall adjustment of caries is not only faster, but also the same force of all the caries, avoiding the phenomenon of frequent downtime and repeated debugging due to the adjustment of a single caries. The adjustment of the feed teeth of the J2108 machine is basically the same as the adjustment of the impression teeth of the impression cylinder, but it should be noted that the paper between the stop stopper and the set screw should be thinner when adjusting.
In actual printing, there is often the phenomenon that a tooth on the chain does not put paper at the delivery table and takes away the paper. Some operators suddenly press the stop button during the normal printing process of the printing machine to try to find out the cavities that do not release paper. However, doing so not only damages the printing press, but it is also difficult to find the faulty tooth, work or mistake. The correct method is to stop the machine first, insert a 0.25mm shim into the contact between the stopper of the chain and the toothpaste shaft, loosen all the fastening screws of the cavities, and then put the tooth chip and the tooth base together. Fasten the screws, place a 0.1mm thick piece of paper between the dental piece and the dental pad, and adjust the screws so that all cavities have the same force and then remove the shims. If you adjust all the chains in this way and then start the printing, the phenomenon that the teeth of the chain cannot be put on paper can disappear.
Four-color machine
The four-color press cylinders and transfer cylinders are generally double-diameter cylinders, and there are two rows of teeth on it, so the adjustment is more complicated. However, it is not correct to adjust the cavities individually or to adjust the pressure of individual impression cylinders to save time. Because a four-color machine generally has four impression cylinders, and each impression cylinder has two rows of teeth. If only a certain roller or a certain row of teeth is adjusted, it is easy to cause the pressure of the impression cylinder to rake teeth. Inhomogeneity results in inaccurate four-color printing or ghost images, which seriously affects the quality of printed products. The correct method is to adjust 8 rows of teeth at the same time. Now take the 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 impression cylinder and remove the teeth.
Step 2: Use a 5mm Allen wrench to loosen the screws on the jaws to open and close the control molars, and then use a adjustable wrench to rotate the axis of the roller about 60°. At this time, all the molars leave the pad. About 0.05mm.
Step 3: Loosen all the fangs fastening screws so that the dents leave the cusp and clean the dirt on the dentition and the occlusal pad.
Step 4: Rest all the fangs on the tooth pad, tighten the fastening screws of each tooth, and then use a 0.05 mm thick piece of steel between the tooth and the pad to adjust the small spring on the base. Pull the steel sheet so that the steel sheet can be pulled and there is a certain resistance.
Step 5: After adjusting all the cavities, turn the rollers that open and close the tusks back to their original positions and tighten the fastening screws so that all cavities increase the same strength and ensure that the overprint of the print is accurate.
In general, most of the offset adjustments for offset presses follow the same pattern. That is, through a certain structure (the press is different in different structures), the dental piece leaves the dental pad for a certain distance, and then uniformly adjusts the dental caries, so that each small spring has a uniform force, and then passes through the fixed dental caries The large springs or torsion springs add the same pressure to the tusks. Remember that it is not possible to increase the pressure of the small spring on the cavities. In this way, it is possible to get out of the misunderstanding of the offset axis of the offset press and improve the quality of printed products.