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Japan's Mitsubishi folio multicolor printing presses have been printing paper of 780mm × 540mm size for many years. With the publication of books and periodicals becoming more and more international, they have changed to printing 880mm × 540mm size paper. When the operator used the machine to complete the overprinting of the magenta and yellow editions, he found an ink bar about 80 mm from the trailing edge of the paper. At first I thought it was a problem with the magenta group. Check the pressure between the inking roller and the inking roller, the inking roller and the printing plate, check whether the ink roller seat is worn and loose, and replace with a new blanket and liner according to the technical parameters to adjust the equipment to the best state After retrying printing, the ink stick still exists. The operator changed the magenta version to another color set for printing, and the ink bar also exists. Due to the tight delivery time, the operator had to change to another two-color printing machine to print. The unexpected thing was whether the ink bar appeared at the same position on the paper. Therefore, the operator suspected that there was a problem with the film, so he re-printed the film in another direction and tested the machine. As a result, the ink stick still appeared in the same position, so the ink stick was not related to the ink roller and the film.
Next, I started to check the mechanical aspects. When I put a printed paper with an ink bar on the front gauge and moved it into the printing color group for inspection, I accidentally found a relatively bright mark on the surface of the impression cylinder. The ink bars on the paper are in the same position, and the operator goes to check 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 impression cylinder had some wear at 540mm from the grip.
Case 2
The two Mitsubishi multicolor offset presses have been in use for more than 10 years, and the long-term three-shift operation and offset paper printing have caused serious equipment wear. If the ink stick is caused by the impression cylinder, it means that the two devices can only print the prints of 780mm × 540mm or less. Therefore, the operator decided to confirm whether it is caused by the impression cylinder.
When visually and manually measuring the surface of the impression cylinder, the operator found that there were also bright marks on the circumferential edges on the left and right sides of the 780mm position of 780mm × 540mm, but when printing 880mm × 540mm, there was no visible on the paper. To traces. Therefore, the operator first pressed the equipment and checked the roller pillow with a fuse. As a result, no abnormalities were found in the three rollers, and they all met the technical parameter requirements, and their gaps were between 0.05 and 0.06 mm.
Operators who have experience in using this equipment know that the pressure-combining mechanism adopts a three-point suspension type, the center distance between the three rollers has been adjusted before leaving the factory, and it can not be moved casually, and the printing plate is also fixed The liner is not changed every time the plate is installed like the domestic offset printing machine. But this time, the operator decided to break the technical parameters specified in the manual, peel off the liner closely attached to the printing plate, wash off the glue on the surface of the printing plate cylinder, set the pressure gauge to the "0" position, and use the diameter For the 4mm fuse, perform counter pressure on the roller body. The results show that the gap between the impression cylinder and the rubber cylinder is 3.2 mm, and the gap between the rubber cylinder and the plate cylinder is 3.65 mm. From the above data analysis, the thickness of the blanket and the pad is usually 3.25mm, and the thickness of the printing paper is added, the printing pressure is about 0.13mm, and the thickness of the plate and the pad is 0.6mm, then the rubber cylinder The printing pressure with the plate cylinder is 0.2mm, indicating that the printing pressure between the rubber cylinder and the plate cylinder is too large. Therefore, the operator reduced the thickness of the printing plate plus liner to 0.5mm for trial printing, so that the printing pressure between the rubber cylinder and the plate cylinder was about 0.1mm, and the failure disappeared. Both the printing plate pads and rubber pads of the two printing presses are used according to the above data, and the above-mentioned faults are completely eliminated.
Case 3
When the four-color folio printing machine was in use, the phenomenon that the printed product was frayed at one end occurred at the same time. At the same time, the machine suddenly stopped automatically and restarted. The machine could not run, but the front and back cars could jog.
First check the pressure of the water and ink rollers, no abnormalities are found, and then carefully check the water roller bracket, no damage is found. Later, it was thought that the failure of the motor or electrical system caused the machine not to run, but the electrician did not find any problems in the comprehensive inspection of the equipment. Shake the machine by hand with a handle, feeling the machine is extremely heavy. Open the right side shield to check, and found that the fixing screw of a connecting block of the rubber roller is loose, resulting in the incomplete pressure, and the pressure of the roller is lighter and heavier, resulting in a virtual end of the printed product. Re-tighten the screw and try to turn on the machine. It is unexpected that the machine can run and the printed product is no longer false. It seems that the same cause of this double failure. After analysis, it is found that the failure of the pressure-bonding part causes the pressure at the end of the cylinder to become lighter, so the printed products naturally become imaginary, and the cylinder is not parallel to lose balance, and the resistance naturally increases during operation, so the operation is difficult.
Case 4
An offset press often has skewed paper feeding for a period of time. The initial slanting range is small, which can be solved by adjusting the tightness of the transfer belt and the amount of air suction. However, after a period of time, the paper skew failure reappeared, and the slanting amplitude was larger than last time. Adjusting the transfer belt to the tightest position and the maximum suction volume have not worked. Adjust the unilateral pressure roller, with the help of front suction and rear suction, it still has no effect. Due to business tension, the effect of diagonal sheets on printing is not large, so it has been dragging and not solving. After a period of time, the slanted sheet has a larger amplitude, and often stops due to poor paper feed caused by the slanted sheet, which seriously affects normal production and print quality.
Since all operable parts of the adjustment feeder do not work, it is believed that the failure is caused by mechanical reasons. After resetting the above adjustments, the operator measured the transfer belt at the feeder part of the machine, and found that the difference between the two transfer belts when rotating one back and forth at the same time was 6mm, so it is suspected that the transfer belt is aging. The slower transfer belt was replaced, and the trial printing was restarted. The skewed paper sheet was not ruled out, and the position of the two transfer belts in one revolution was still 5mm different, so the problem was not the transfer belt.
For this thorny problem, the operator had to follow the vines and check all the mechanical parts related to the paper belt. It was found that the tension adjustment lever of the paper belt under the paperboard was normal, but it could not be adjusted by such a large range; the bearings on both sides of the front gauge were basically similar; looking up again, it was found that the operating side shaft at the top of the paper belt was a rubber bush, and it could Adjust the diameter through the universal shaft. After adjustment, start trial printing and troubleshoot.
Case 5
There is a Mitsubishi folio printing machine, which is mainly used for color newspaper printing all year round, but tension instability often occurs in the printing process, resulting in inaccurate overprinting.
First, increase the tension in the printing process, but soon found that the number of paper breaks increased linearly. After analyzing the paper break process, it is found that the paper break phenomenon or large fluctuations in tension are mainly concentrated during acceleration or deceleration. At this time, the change range of the tension is large, sometimes causing paper break. By analyzing the fault phenomenon and combining with the control theory, we finally realized the essence of this fault. The tension system of the printing press is a closed-loop control system. In this system, the magnetic powder brake is the actuator, the tension control board is the control element, and the tension sensor is the feedback element. The paper path from the paper roll to the tension sensor is a delay link. As there are many links, the factors that affect the stability of the system are complex. The control system evaluates the indexes of general systems mainly as stability and rapidity. Specifically, in this failure, the rapidity is sufficient but the stability is insufficient. Therefore, this failure is not a problem with a part, but the parameter adjustment of the entire tension control system is not accurate and reasonable. The problem can not be shown under the constant speed state, but under the speed change state, the impact of the speed on the system will cause the system to become unstable, and even enter the self-excited state under certain circumstances, the amplitude will become larger and larger, and eventually cause the paper break. Even with continuous paper, this large tension change is extremely detrimental to the registration of color newspaper printing.
It is known from the control theory that increasing the system integration coefficient can improve the system stability, so a 1μF capacitor is added to the integration link of the system control board, which can improve the stability of the system and suppress the rapidity. Through actual use, the effect is satisfactory.
Case 6
During normal operation, the machine will sometimes stop automatically.
When the fault occurs, immediately press the "bell" and "running" buttons, the indicator light of the slip clutch is normally lit, but the machine cannot start running. This shows that the control line of the main thermal relay FR1 in the main circuit is de-energized, which causes the main AC contactor KM1 to lose power and be released at the same time. Considering that the mechanical part rotates flexibly, the three-phase current value of the main motor is also normal after measurement, so it is determined that the fault may appear in the oil supply circuit. Because one of the two oil pump motors in the oil supply circuit fails, 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 neutral line to also trip, causing the machine Power failure and shutdown.
Repair the oil supply circuit according to the above analysis. After starting up, use the electric pen to measure the 62 line of the FR8 thermal relay. After a while, the machine trips and stops automatically. The electric pen also turns red, indicating that the problem is indeed in the circuit of the FR8 thermal relay. But what will happen to the M8 oil pump motor? We started the operation again, and measured the voltage of the three lower contact M8 three-phase windings of FR8 with a multimeter AC voltage file, all of which were 380V. Shut down, remove the three leads of the M8 lower contact to avoid the loop influence caused by the M7 and M8 oil pump motor sharing an AC contactor power supply, and use a resistance file to measure the resistance between the three leads M8 three-phase winding , Are normal. Then measure the resistance between the three leads M7 three-phase winding of the FR7 contact, and the situation is exactly the same as M8.
So, did it trip due to the blockage of the oil circuit of the M8 oil pump motor and the increased load? We open the fan blade cover of the M8 oil pump motor and turn it by hand. The fan blades rotate quickly, indicating that the mechanical transmission and oil path of the M8 oil pump motor are smooth and without problems. So how about its three-phase current? Install the fan blade cover, and use the clamp-type ammeter to measure the three-phase current value of the FR8 lower contact in the power distribution cabinet, which are 2.0A, OA and 1.2A respectively, and the three-phase unbalance. Simultaneously measure the three-phase current value of the next FR7 contact, the three-phase current value is balanced, basically 0.
The same power supply voltage, the same three-phase winding resistance and the same oil circuit load, why the three-phase current value of the two oil pump motors will be so different, whether there are other circuit currents stringed into the M8 circuit but careful analysis, it seems Not too possible. Because if this is the case, other circuits must work abnormally, and there should be a corresponding blowout of the fuse, which does not happen. In the final analysis, it is considered that it may be that the FR8 is affected by the magnetic field of the nearby large power transformer, which makes the reading of the clamp ammeter incorrect.
In order to verify this idea, we shut down again, and removed the FR8 lower contact and the corresponding three leads on the M8 oil pump motor, and used three new leads to connect them directly to the test machine. As a result, the current value distribution is still the same As measured before, the three-phase current value is unbalanced, but the current value of the three leads outside the power distribution cabinet is balanced, and is the same as M7, which is basically 0. Explain that the previous analysis and judgment are correct. The source of the problem is indeed FR8 damaged or too sensitive. We decided to change to a new thermal relay, but no spare parts were available. For emergency, we had to adjust the lead wires of the two oil pump motors to each other and connect them to each other's thermal relays. Test machine, troubleshooting.
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