Discussion on the maintenance experience of the ho

2022-10-16
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Mitsubishi equipment maintenance experience

Mitsubishi folio multi-color printing machine in Japan has been printing 780mm 540mm paper for many years. With the internationalization of books and periodicals, it has changed to print 880mm 540mm paper. When the operator used the machine to complete the overprint of magenta and yellow, he found an ink bar about 80mm away from the paper trailing tip. At first, I thought there was something wrong with the magenta group. Then check the pressure between the inking roller and the inking roller, between the inking roller and the printing plate, check whether the inking roller seat is worn and loose, and replace it with a new blanket and liner according to the requirements of technical parameters. After the equipment is adjusted to the best state, try printing again, and the ink bar still exists. The operator changed the magenta version to another color group for printing, and the ink bar also existed. Due to the tight delivery time, the operator had to change to another folio four-color printing machine to print. Unexpectedly, the ink bar still appeared on the same position of the paper. Therefore, the operator suspected that there was a problem with the film, so he changed the film to another direction and re print the machine. As a result, the ink bar still appeared in the same position, so it was determined that the ink bar had nothing to do with the ink roller and the film

next, start to check the machinery. When a printed paper with ink bars is placed on the front gauge and jogged into the printing color group for inspection, it is accidentally found that there is a relatively bright mark on the surface of the embossing cylinder, which is exactly in the same position with the ink bars on the paper. The operator checks other color groups and finds that there is such a bright mark in the same position of each color group. In the past, these two Mitsubishi printing machines mostly printed 780mm 540mm paper, and the embossing cylinder was worn 540mm away from its mouth

case 2

these two Mitsubishi multicolor offset presses have been used for more than 10 years, and the long-term three shift operation and offset paper printing have made the equipment seriously worn. If the ink bar is caused by the embossing cylinder, it means that these two devices can only print prints with specifications below 780mm and 540mm, so the operator decided to confirm whether it is caused by the embossing cylinder

when visually and manually measuring the surface of the embossing cylinder, the operator found that there were bright marks on the circumferential edges of the left and right sides of 780mm 540mm, but there were no circumferential marks on the paper when printing 880mm 540mm. Therefore, the operator first pressed the equipment and checked the roller pillow with a fuse. The results showed that no abnormality was found in the three rollers, and they all met the requirements of technical parameters, with a gap of 0.05 ~ 0.06mm

operators who have used the equipment know that the pressing mechanism adopts the three-point suspension type. The center distance between the three rollers has been adjusted before leaving the factory, and it can't be moved casually. In addition, the printing plate is also pasted with a fixed pad. It doesn't need to replace the pad like domestic offset printing machines every time. But this time, the operator decided to break the technical parameters specified in the manual, peel off the gasket clinging to the printing plate, wash the glue off the surface of the printing plate cylinder, place the pressure gauge at position 0, and use a fuse with a diameter of 4mm to counter press the cylinder body. The results show that the gap between the impression cylinder and the rubber cylinder is 3.2mm, and the gap between the rubber cylinder and the plate cylinder is 3.65mm. From the above data analysis, usually the thickness of rubber cloth plus pad is 3.25mm, plus the thickness of printing paper, the printing pressure is about 0.13MM, which is ideal, while the thickness of printing plate plus pad is 0.6mm, so the printing pressure of rubber cylinder and printing plate cylinder is 0.2mm, indicating that the printing pressure between rubber cylinder and printing plate cylinder is too large. Therefore, the operator reduced the thickness of the printing plate and pad to 0.5mm for trial printing, so that the printing pressure between the rubber cylinder and the printing plate cylinder was about 0.1mm, and the fault disappeared. Now the plate liners and rubber liners of these two printing machines are used according to the above data, and the above-mentioned faults are completely eliminated

case 3

when using the split four-color printing machine, there was a phenomenon that one end of the printed matter was false. At the same time, the machine suddenly stopped automatically and started again. The machine could not run, but the positive and negative cars could jog

first check the pressure of the water and ink roller, and no abnormality is found. Then carefully check the water roller support, and no damage is found. Later, it was thought that the machine did not work because of the failure of the motor or electrical system, but the electrician did not find any problems in the comprehensive inspection of the equipment. Shake the machine by hand with the handle, and feel that the machine is extremely heavy. Open the right shield and check it. It is found that the fixing screw of a connecting block of the rubber drum is loose, resulting in inadequate pressure. The pressure of the drum is light at one end and heavy at the other, resulting in one end of the printed product being empty. Retighten the screw and try to start the machine. What is unexpected is that the machine can run and the printed matter is no longer false. It seems that the same reason caused this double fault. After analysis, it is known that the failure of the pressure closing part causes the pressure at one end of the drum to become light, so the printed matter will naturally become weak, while the drum will lose balance if it is not parallel, and the resistance will naturally increase during operation, so it is difficult to operate

Case 4

an offset press often has paper feeding skew for a period of time. The range of oblique tension at the beginning is small, which can be solved by adjusting the tightness of the paper belt and the air suction volume. But after a period of time, the paper feeding skew fault reappears, and the skew amplitude is larger than the last time. Adjusting the paper conveyor belt to the tightest and the suction air volume to the maximum did not work. Adjusting the single side paper pressing wheel with the help of front suction and rear suction still has no effect. Due to business tension, skew has little impact on printing, so it has been delayed. After a period of time, the skew tension range is larger, and the machine is often shut down due to poor paper feeding caused by skew tension, which seriously affects the normal production and print quality

because all operable parts of the regulator Feida are inoperative, it is considered that the fault is caused by mechanical reasons. After the above adjustment and reset, the operator measured the paper transfer belt at the flying part of the machine, and found that the difference between the two paper transfer belts is 6mm when they rotate one time at the same time, so it is suspected that the paper transfer belt is aging. The paper transfer belt with slow speed was replaced, and the machine was restarted for trial printing. The oblique paper feeding was still not ruled out, and the position difference of the two paper transfer belts for one turn was 5mm, so it was determined that the problem was not the paper transfer belt

for this thorny problem, the operator had to follow suit and check all the mechanical parts related to the paper tape. It was found that the tension adjusting rod of the paper tape under the paper conveyor was normal, but it could not adjust such a large range; The bearings on both sides of the front gauge are basically similar; Looking up again, I found that the operating side shaft at the top of the paper tape is a rubber shaft sleeve, and the diameter can be adjusted through the universal shaft rod. After adjustment, start the machine for trial printing, and troubleshoot

case 5

there is a Mitsubishi folio printing machine, which is mainly used for color newspaper printing all the year round, but in the printing process to ensure that the tension experiment can be used normally, the tension is often unstable, resulting in inaccurate overprint

first, increase the tension in the printing process, but soon found that the number of paper breaks increased linearly. After analyzing the paper breaking process, it is found that the phenomenon of paper breaking or the fluctuation of large tension is mainly concentrated in the acceleration or deceleration, when the tension changes greatly, sometimes leading to paper breaking. By analyzing the fault phenomenon and combining the control theory, we finally realize the essence of this fault. The tension system of the printing press is a closed-loop control system, in which the magnetic particle brake is the actuator, the tension control board is the control element, the tension sensor is the feedback element, and the paper path from the paper roll to the tension sensor is the delay link. Because there are many links, the factors affecting the stability of the system are complex. The indicators of control theory evaluation of general systems are mainly stability and rapidity. Specifically, in this fault, there is more rapidity and less stability. Therefore, this fault is not the problem of a certain part, but the parameter adjustment of the whole tension control system is not accurate and reasonable. The problem still doesn't show up in the constant speed state, but in the variable speed state, due to the impact of speed on the system, the system will be unstable, and even enter the self-excited state under specific circumstances. The more the amplitude is displayed according to the market monitoring data, the greater the amplitude, and finally lead to paper breakage. Even if there is no paper, this large tension change is extremely detrimental to the registration of color newspaper printing

according to the control theory, increasing the system integration coefficient can improve the stability of the system, so a 1F capacitor is added to the integration link of the system control board, which can improve the stability of the system and inhibit the rapidity. Through practical use, the effect is satisfactory

case 6

during normal operation, the machine sometimes stops automatically

when this fault occurs, immediately press the bell and the operation button, and the indicator light of the slip clutch will normally light up, but the machine cannot be started and operated. This indicates that the main thermal relay FR1 control line in the main circuit is powered off, resulting in the simultaneous power loss and release of its main AC contactor KM1. Considering the flexible rotation of the mechanical part and the normal three-phase current value of the main motor, it is determined that the fault may occur in the oil supply circuit. Because one of the two oil pump motors in the oil supply circuit has a problem, it can cause the corresponding thermal relay FR7 or fr8 to trip, causing the main thermal relay FR1 connected in series to FR7, fr8 and the zero line to trip, so that the machine loses power and stops

repair the oil supply circuit according to the above analysis. After starting up and running, use the electric pen to measure the 62 wire of fr8 thermal relay, and then the machine trips and stops automatically. The electric pen is also red, indicating that the problem really lies in the circuit of 3 mechanical connectors of fr8 thermal relay. But what will happen to the M8 oil pump motor? We started the machine again and measured the voltage of the three lower contacts M8 three-phase windings of fr8 with the AC voltage gear of the multimeter, all of which were 380V. Shut down the machine, remove the three leads of M8 lower contact, so as to avoid the circuit influence caused by M7 and M8 oil pump motor sharing an AC contactor for power supply, understand the contribution of advanced material technology to sustainable development, and use a resistance gear to measure the electrical resistance between the three lead M8 three-phase windings, which are all normal. Then measure the resistance value between the three-phase windings of M7 of the three leads at the lower contact of FR7, which is exactly the same as that of M8

then, did the M8 oil pump motor trip due to oil circuit blockage and heavy load? We open the fan blade cover of M8 oil pump motor and move it by hand. The fan blade rotates quickly, which shows that the mechanical transmission and oil circuit of M8 oil pump motor are smooth and there is no problem. Then what about the three-phase current? Install the fan shroud, and use the clamp ammeter to measure the three-phase current value of the lower contact of fr8 in the distribution cabinet, which are 2.0A, OA and 1.2A respectively, and the three-phase is unbalanced. At the same time, measure the three-phase current value of the next FR7 lower contact, and the three-phase current value is balanced, basically 0

with the same supply voltage, the same three-phase winding resistance and the same oil circuit load, why the three-phase current values of the two oil pump motors are so far different? Is there any other circuit current in series into the M8 circuit, but careful analysis seems unlikely. Because if so, other circuits must not work normally, and there should be corresponding fuse burnout, which did not happen. Finally, it is considered that fr8 may be affected by the magnetic field of the nearby large power transformer, which makes the reading of the clamp on ammeter incorrect

in order to verify this idea, we shut down again and connect the lower contact of fr8 with the corresponding three on the M8 oil pump motor

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