Japan's Mitsubishi's multi-color printing presses have been printing 780mm x 540mm paper for many years. With the development of books and books tending to be international, they have changed to 880mm x 540mm paper. When the operator was using the machine to complete the superimposition of the magenta and yellow plates, it was found that there was an ink bar about 80 mm from the paper drag. At first it was thought that there was a problem with the magenta group. Check the pressure between the ink roller and the ink roller, the ink roller and the printing plate, check whether the ink roller seat is loose, and replace the new blanket and pad according to the technical parameters, and adjust the equipment to the best condition. After retrying the test, the ink stick still exists. The operator changed the magenta version to another color group, and the ink sticks also existed. Due to tight delivery schedules, the operator had to switch to another four-color printing machine to print on the folio. Unexpectedly, the ink sticks still appeared in the same position on the paper. Therefore, the operator suspects that there is a problem with the film, and then re-prints the film in one direction. As a result, the ink stick is still in the same position, so that the ink stick is not related to the ink roller and the film.
Next, proceeding to check the mechanical aspects, when putting a sheet of paper with printed ink sticks on the front gauge to move into the process cartridge inspection, it was accidentally found that the surface of the impression cylinder had a relatively bright trace. The ink bars on the paper are in the same position, and the operator goes to inspect the other color groups and finds a bright spot in the same position in each color group. In the past, these two Mitsubishi presses mostly printed 780mm×540mm papers, and the embossing drum had a certain amount of abrasion at a distance of 540mm.
Case 2
The 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 caused severe equipment wear. If the ink bar is caused by the impression cylinder, it means that the two devices can only print 780mm × 540mm specifications of the print, so the operator decided to confirm whether it was caused by the impression cylinder.
When the surface of the impression cylinder was visually and manually measured, the operator found that there were bright marks on the circumferential edges of the 780 mm and 540 mm specifications around the 780 mm position. However, when printing 880 mm×540 mm size prints, there was no visible period on the paper. Traces. Therefore, the operator first pressed the equipment and used a fuse to inspect the rollers. As a result, no abnormalities were found in the three rollers, and all of them met the technical requirements. The gap was between 0.05 and 0.06 mm.
The operating personnel who have experienced using this equipment know that the pressurizing mechanism adopts a three-point suspension type. The center distance between the three rollers has been adjusted before leaving the factory, and they cannot be easily moved, and the plate is also attached with a fixed The liner does not need to be replaced like a domestic offset press at each loading. But this time, the operator decided to break the technical parameters specified in the specification, peeled off the liner immediately on the printing plate, washed off the glue on the surface of the printing cylinder, and placed the pressure gauge in the “0†position. Compress the roller body for a 4mm fuse. The results show that the gap between the impression roller and the blanket roller is 3.2mm, and the gap between the blanket roller and the plate roller is 3.65mm. From the above data analysis, usually blankets with pad thickness of 3.25mm, plus the thickness of printing paper, printing pressure is about 0.13mm is more ideal, and the thickness of the plate plus pad is 0.6mm, then the rubber roller The printing pressure of the plate cylinder is 0.2 mm, which indicates that the printing pressure between the blanket cylinder and the plate cylinder is too large. Therefore, the operator reduced the thickness of the printing plate plus a pad to 0.5 mm, so that the printing pressure between the blanket cylinder and the plate cylinder was about 0.1 mm, and the failure disappeared. The printing plate liners and rubber liners of these two printing presses are used according to the above data, and the above-mentioned failure is completely eliminated.
Case 3
When the four-color printing press was used, there was a phenomenon that one end of the printing product was imaginary. At the same time, the machine suddenly stopped automatically and then turned on. The machine could not operate, but the front and rear cars could move.
First check the pressure of the water and ink rollers. No abnormalities were found. Look at the water roller brackets carefully. No damage was found. Later, it was considered that the motor or the electrical system had a problem that caused the machine not to operate, but the electrician did not find any problems with the equipment. Shake the machine manually with a shake and feel that the machine is extremely heavy. Open the right side cover inspection and found that the fixing screws of one connecting block of the rubber roller are loose, causing the pressure not to be in place. The roller pressure is light and heavy, causing the end of the printed product to become false. Retighten the screws and try to turn on the machine. Unexpectedly, the machine can run, and the prints no longer appear to be empty. It seems that the same cause has caused this double failure. After analysis, it was found that the failure occurred at the pressure-compressing part, which resulted in a lighter pressure on the drum. Therefore, the printed product naturally becomes imaginary, and the drum loses its balance when it is not parallel, and the resistance is naturally increased during operation. Therefore, the operation is difficult.
Case 4
An offset press often has skewed paper feeds. The amount of slanting starts is small and 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 feed skew error reappeared, and the skewness was larger than the previous time. Adjusting the transfer belt to the tightest and the amount of suction to the maximum did not work. Adjust the unilateral pressure roller, with the help of the front suction and the rear suction, still no effect. Due to business constraints, ramps have little impact on printing, so they have been dragged and not resolved. After a period of time, the slanting amplitude is larger, and the machine is often stopped due to oblique slumping, which seriously affects normal production and print quality.
Since adjusting all the operative parts of Feida does not work, it is considered that the fault is caused by mechanical reasons. After resetting the above adjustment, the operator measured the conveyer belt on the feeder part of the machine. As a result, he found that the two transfer belts had a difference of 6 mm between the positions of the two conveyers at the same time. Therefore, it was suspected that the conveyer belt was aging. The slower transfer tape was replaced, and the printer was restarted. The transfer sheet was still not removed, and the position of the two transfer belts was still 5 mm apart. Therefore, the problem was not identified in the transfer tape.
For this thorny problem, the operator had to follow the steps and check all the mechanical parts related to the transfer belt. It was found that the transfer belt under the transfer paperboard had a tight adjustment lever, but it could not be adjusted to such a large extent; the bearings on both sides of the front gauge were basically similar; looking up again, it was found that the top side of the transfer belt was a rubber sleeve and that it could be The diameter is adjusted by the universal shaft. After adjusting the boot test, troubleshooting.
Case 5
There is a Mitsubishi off-press, which is mainly used for color newspaper printing all the year round. However, the phenomenon of unstable tension often occurs during the printing process, resulting in inaccurate overprinting.
First, the tension in the printing process was increased, but the number of breaks quickly increased. After analyzing the paper break process, it was found that the breaks in paper breakage or the large fluctuations in tension were mainly concentrated on acceleration or deceleration. At this time, the change in tension was large and sometimes resulted in web breaks. By analyzing the phenomenon of failure, combined with the control theory, the ultimate understanding of the nature of this failure. The tension system of the printing press is a closed-loop control system in which the magnetic powder 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. As there are many links, the factors that affect system stability are complex. Control theory evaluation The indicators of the general system are mainly stability and rapidity. Specific to this failure, there is more rapidity and less stability. Therefore, this failure is not a problem with one part, but the parameter adjustment of the entire tension control system is not accurate and reasonable. At constant speed, the problem does not show up. However, due to the impact of speed on the system in the variable speed state, the system will become unstable, and even under certain conditions, it will enter the self-excited state and the amplitude will become larger and larger, eventually leading to paper breakage. Even if the paper is constantly printed, this dramatic change in tension is extremely detrimental to the printing press registration.
From the control theory, it can be seen that increasing the system integral coefficient can improve the system stability, so a 1μF capacitor is added to the integral part 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 shuts down automatically.
When the fault occurs, press the "Bell" and "Run" buttons immediately, the indicator light of the slip clutch will light normally, but the machine will not start running. This shows that the control circuit of the main thermal relay FR1 in the main circuit is powered off, and the main AC contactor KM1 is simultaneously de-energized. Taking into account the flexible rotation of the mechanical part, the three-phase current value of the main motor is also determined to be normal, so it is determined that the fault may occur in the fuel supply circuit. Because there is a problem in one of the two oil pump motors in the oil supply circuit, the corresponding thermal relay FR7 or FR8 may be caused to jump off, so that the main thermal relay FR1 connected in series with FR7, FR8 and the neutral wire also breaks, making the machine Loss of power shutdown.
According to the above analysis, overhaul the oil supply circuit. After starting operation, use the electric pen to measure the 62 lines of the FR8 thermal relay. After a while, the machine trips and shuts down by itself. The electric pen is also red, indicating that the problem is indeed in the circuit of the FR8 thermal relay. But what's wrong with the M8 pump motor? We started up again and used the multimeter's AC voltage profile to measure the voltages of the three lower contact points of the FR8's M8 three-phase windings, which were all 380V. Shutdown, remove the three leads of the M8 lower contact point, to avoid the loop effect caused by the M7 and M8 pump motor sharing a single AC contactor power supply, and use a resistance profile to measure the resistance between the three-phase windings of the M8 three-phase winding. Are normal. Measure the resistance between the three leads M7 and the three-phase winding of the lower contact of FR7, exactly the same as the case of M8.
Then, is the trip caused by the obstruction of the oil circuit of the M8 pump motor and the increase of the load? We opened the fan cover of the M8 oil pump motor and moved it by hand to make the fan blade rotate lightly. This shows that the mechanical drive and the oil path of the M8 oil pump motor are smooth and there are no problems. What about the three-phase currents? Mount the fan blade cover and measure the three-phase current value of the FR8 lower contact point with a clamp ammeter in the power distribution cabinet, which is 2.0A, OA and 1.2A, and the three-phase unbalanced. At the same time, the three-phase current value of the next FR7 contact point is measured, and the three-phase current value is balanced, which is basically zero.
The same supply voltage, the same three-phase winding resistance and the same oil circuit load, why the three-phase current value of the two pump motors will be so far apart, whether there are other circuit currents 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 fuse blown, and this phenomenon does not occur. In the final analysis, it was thought that the FR8 may be affected by the magnetic field of a large power transformer in the vicinity, making the reading of the clamp ammeter uncorrect.
In order to verify this idea, we shut down again and removed all the FR8's lower contacts from the corresponding three leads on the M8 pump motor, and connected them directly with three new leads to test the machine. As a result, the current value distribution is still as good as Previously measured, the three-phase current value was unbalanced, but the current values ​​of the three lead wires outside the power distribution cabinet were balanced and, like the M7, were essentially zero. The previous analysis and judgment are correct. The root cause of the problem is indeed FR8 is damaged or too sensitive. We decided to switch to a new thermal relay, but there are no ready-made spare parts. In order to respond to the emergency, we had to align the two pump motor leads with each other and received the other's thermal relays. Test machine, troubleshooting.
Next, proceeding to check the mechanical aspects, when putting a sheet of paper with printed ink sticks on the front gauge to move into the process cartridge inspection, it was accidentally found that the surface of the impression cylinder had a relatively bright trace. The ink bars on the paper are in the same position, and the operator goes to inspect the other color groups and finds a bright spot in the same position in each color group. In the past, these two Mitsubishi presses mostly printed 780mm×540mm papers, and the embossing drum had a certain amount of abrasion at a distance of 540mm.
Case 2
The 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 caused severe equipment wear. If the ink bar is caused by the impression cylinder, it means that the two devices can only print 780mm × 540mm specifications of the print, so the operator decided to confirm whether it was caused by the impression cylinder.
When the surface of the impression cylinder was visually and manually measured, the operator found that there were bright marks on the circumferential edges of the 780 mm and 540 mm specifications around the 780 mm position. However, when printing 880 mm×540 mm size prints, there was no visible period on the paper. Traces. Therefore, the operator first pressed the equipment and used a fuse to inspect the rollers. As a result, no abnormalities were found in the three rollers, and all of them met the technical requirements. The gap was between 0.05 and 0.06 mm.
The operating personnel who have experienced using this equipment know that the pressurizing mechanism adopts a three-point suspension type. The center distance between the three rollers has been adjusted before leaving the factory, and they cannot be easily moved, and the plate is also attached with a fixed The liner does not need to be replaced like a domestic offset press at each loading. But this time, the operator decided to break the technical parameters specified in the specification, peeled off the liner immediately on the printing plate, washed off the glue on the surface of the printing cylinder, and placed the pressure gauge in the “0†position. Compress the roller body for a 4mm fuse. The results show that the gap between the impression roller and the blanket roller is 3.2mm, and the gap between the blanket roller and the plate roller is 3.65mm. From the above data analysis, usually blankets with pad thickness of 3.25mm, plus the thickness of printing paper, printing pressure is about 0.13mm is more ideal, and the thickness of the plate plus pad is 0.6mm, then the rubber roller The printing pressure of the plate cylinder is 0.2 mm, which indicates that the printing pressure between the blanket cylinder and the plate cylinder is too large. Therefore, the operator reduced the thickness of the printing plate plus a pad to 0.5 mm, so that the printing pressure between the blanket cylinder and the plate cylinder was about 0.1 mm, and the failure disappeared. The printing plate liners and rubber liners of these two printing presses are used according to the above data, and the above-mentioned failure is completely eliminated.
Case 3
When the four-color printing press was used, there was a phenomenon that one end of the printing product was imaginary. At the same time, the machine suddenly stopped automatically and then turned on. The machine could not operate, but the front and rear cars could move.
First check the pressure of the water and ink rollers. No abnormalities were found. Look at the water roller brackets carefully. No damage was found. Later, it was considered that the motor or the electrical system had a problem that caused the machine not to operate, but the electrician did not find any problems with the equipment. Shake the machine manually with a shake and feel that the machine is extremely heavy. Open the right side cover inspection and found that the fixing screws of one connecting block of the rubber roller are loose, causing the pressure not to be in place. The roller pressure is light and heavy, causing the end of the printed product to become false. Retighten the screws and try to turn on the machine. Unexpectedly, the machine can run, and the prints no longer appear to be empty. It seems that the same cause has caused this double failure. After analysis, it was found that the failure occurred at the pressure-compressing part, which resulted in a lighter pressure on the drum. Therefore, the printed product naturally becomes imaginary, and the drum loses its balance when it is not parallel, and the resistance is naturally increased during operation. Therefore, the operation is difficult.
Case 4
An offset press often has skewed paper feeds. The amount of slanting starts is small and 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 feed skew error reappeared, and the skewness was larger than the previous time. Adjusting the transfer belt to the tightest and the amount of suction to the maximum did not work. Adjust the unilateral pressure roller, with the help of the front suction and the rear suction, still no effect. Due to business constraints, ramps have little impact on printing, so they have been dragged and not resolved. After a period of time, the slanting amplitude is larger, and the machine is often stopped due to oblique slumping, which seriously affects normal production and print quality.
Since adjusting all the operative parts of Feida does not work, it is considered that the fault is caused by mechanical reasons. After resetting the above adjustment, the operator measured the conveyer belt on the feeder part of the machine. As a result, he found that the two transfer belts had a difference of 6 mm between the positions of the two conveyers at the same time. Therefore, it was suspected that the conveyer belt was aging. The slower transfer tape was replaced, and the printer was restarted. The transfer sheet was still not removed, and the position of the two transfer belts was still 5 mm apart. Therefore, the problem was not identified in the transfer tape.
For this thorny problem, the operator had to follow the steps and check all the mechanical parts related to the transfer belt. It was found that the transfer belt under the transfer paperboard had a tight adjustment lever, but it could not be adjusted to such a large extent; the bearings on both sides of the front gauge were basically similar; looking up again, it was found that the top side of the transfer belt was a rubber sleeve and that it could be The diameter is adjusted by the universal shaft. After adjusting the boot test, troubleshooting.
Case 5
There is a Mitsubishi off-press, which is mainly used for color newspaper printing all the year round. However, the phenomenon of unstable tension often occurs during the printing process, resulting in inaccurate overprinting.
First, the tension in the printing process was increased, but the number of breaks quickly increased. After analyzing the paper break process, it was found that the breaks in paper breakage or the large fluctuations in tension were mainly concentrated on acceleration or deceleration. At this time, the change in tension was large and sometimes resulted in web breaks. By analyzing the phenomenon of failure, combined with the control theory, the ultimate understanding of the nature of this failure. The tension system of the printing press is a closed-loop control system in which the magnetic powder 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. As there are many links, the factors that affect system stability are complex. Control theory evaluation The indicators of the general system are mainly stability and rapidity. Specific to this failure, there is more rapidity and less stability. Therefore, this failure is not a problem with one part, but the parameter adjustment of the entire tension control system is not accurate and reasonable. At constant speed, the problem does not show up. However, due to the impact of speed on the system in the variable speed state, the system will become unstable, and even under certain conditions, it will enter the self-excited state and the amplitude will become larger and larger, eventually leading to paper breakage. Even if the paper is constantly printed, this dramatic change in tension is extremely detrimental to the printing press registration.
From the control theory, it can be seen that increasing the system integral coefficient can improve the system stability, so a 1μF capacitor is added to the integral part 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 shuts down automatically.
When the fault occurs, press the "Bell" and "Run" buttons immediately, the indicator light of the slip clutch will light normally, but the machine will not start running. This shows that the control circuit of the main thermal relay FR1 in the main circuit is powered off, and the main AC contactor KM1 is simultaneously de-energized. Taking into account the flexible rotation of the mechanical part, the three-phase current value of the main motor is also determined to be normal, so it is determined that the fault may occur in the fuel supply circuit. Because there is a problem in one of the two oil pump motors in the oil supply circuit, the corresponding thermal relay FR7 or FR8 may be caused to jump off, so that the main thermal relay FR1 connected in series with FR7, FR8 and the neutral wire also breaks, making the machine Loss of power shutdown.
According to the above analysis, overhaul the oil supply circuit. After starting operation, use the electric pen to measure the 62 lines of the FR8 thermal relay. After a while, the machine trips and shuts down by itself. The electric pen is also red, indicating that the problem is indeed in the circuit of the FR8 thermal relay. But what's wrong with the M8 pump motor? We started up again and used the multimeter's AC voltage profile to measure the voltages of the three lower contact points of the FR8's M8 three-phase windings, which were all 380V. Shutdown, remove the three leads of the M8 lower contact point, to avoid the loop effect caused by the M7 and M8 pump motor sharing a single AC contactor power supply, and use a resistance profile to measure the resistance between the three-phase windings of the M8 three-phase winding. Are normal. Measure the resistance between the three leads M7 and the three-phase winding of the lower contact of FR7, exactly the same as the case of M8.
Then, is the trip caused by the obstruction of the oil circuit of the M8 pump motor and the increase of the load? We opened the fan cover of the M8 oil pump motor and moved it by hand to make the fan blade rotate lightly. This shows that the mechanical drive and the oil path of the M8 oil pump motor are smooth and there are no problems. What about the three-phase currents? Mount the fan blade cover and measure the three-phase current value of the FR8 lower contact point with a clamp ammeter in the power distribution cabinet, which is 2.0A, OA and 1.2A, and the three-phase unbalanced. At the same time, the three-phase current value of the next FR7 contact point is measured, and the three-phase current value is balanced, which is basically zero.
The same supply voltage, the same three-phase winding resistance and the same oil circuit load, why the three-phase current value of the two pump motors will be so far apart, whether there are other circuit currents 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 fuse blown, and this phenomenon does not occur. In the final analysis, it was thought that the FR8 may be affected by the magnetic field of a large power transformer in the vicinity, making the reading of the clamp ammeter uncorrect.
In order to verify this idea, we shut down again and removed all the FR8's lower contacts from the corresponding three leads on the M8 pump motor, and connected them directly with three new leads to test the machine. As a result, the current value distribution is still as good as Previously measured, the three-phase current value was unbalanced, but the current values ​​of the three lead wires outside the power distribution cabinet were balanced and, like the M7, were essentially zero. The previous analysis and judgment are correct. The root cause of the problem is indeed FR8 is damaged or too sensitive. We decided to switch to a new thermal relay, but there are no ready-made spare parts. In order to respond to the emergency, we had to align the two pump motor leads with each other and received the other's thermal relays. Test machine, troubleshooting.
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