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The maintenance for offset press


  With the computer optimization design, advanced processing technology and digital mechanic equipment, the modern offset press is with reasonable structure, super high motion and fit accuracy, thus the offset printing quality becomes more perfect.

  The modern computer technology and microelectronic technique are applied to the electrical system of the offset press, which help realized the centralization of digital control. The system is composed of control center, console and peripheral devices, which include a large amount of sensors and actuators. A device of high technology couldn’t be regularly operate without daily maintenance. Therefore, it is necessary for the manager and operator of the printing industry to learn the knowledge of the offset press, also complete the maintenance work for the offset press.

  

The maintenance of the offset press


Besides correctly operate the offset press according to the operation requirements, daily maintenance work is another important factor to keep the offset press working regularly. The main reasons cause the mechanical breakdown of the offset press are corrosion and abrasion.

Corrosion: the component surface would corrodeas the components had long time exposure to ink, water and fountain solution, thus there are many rust spots on the components, in which some might even be seriously corroded. The damage process include the roller bearing corrosion, water and ink supply system corrosion.

Abrasion: large amount of components would be abraded due to long term work of high speed and load condition. If the lubrication system breaks down or the refueling wasn’t in time, the abrasion would invalidate the components. Large amounts of dust in the printing workplace might block the oiling channel, thus the oil supply system is broke down. The main failure cause for the bearings, include the opening ball, is fatigue wear. Which means the cracks have developed in the rollers due to the long term load condition work, as the cracks spread with time goes by, the surface of the bearing will peel off. As the exfoliation area increased, the working vibration and noise of the bearings would increase, which will finally invalidate the bearings.

Daily maintenance work of the offset press include periodic cleaning the working surface of the components, filter screen cleaning and lubricating the bearings.

 

Electrical system maintenance


The electrical system is the control center of the offset press, which include main control cabinet, console, external sensors and actuator, any link problems will cause the system unable to work. Therefore, it is very important to maintain the electrical system. The following environmental factors might cause the system failure: temperature, humidity, dust and electromagnetic interference.

Temperature: The excessive temperatures will accelerate the aging of electrical components, the workshop temperature should be kept between 22-28.

Humidity: The normal humidity range should be kept between 50% and 70%, condensation might be formed on the electrical equipment due to the excessive humidity which will lead to  rust and short circuit on the components.

Dust: There are large amount of dust in the printing workshop, the cleaning devices should be installed and the component surface should be cleaned in time. The dust would accelerate the abrasion of the mechanism components, thus the lubrication system might be blocked and the circuit board might be short circuited.

Electromagnetic interference: The printing machine should be installed far away from the electromagnetic radiation equipment like high voltage transformer, for the strong electromagnetic field will interfere the normal work of the electronic control system.


The fault analysis of the offset press pulling guide control


When the books are printed, the paper is common not pulling guide in the right place of the printing machine, by increasing the pulling guidecontrol spring’s pressure, the paper pulling guide effect improves but the improvement is not enough. This phenomenon won’t occurr to all kinds of printing paper, especially to the standard paper and quarto paper the paper pulling guide are better, but for the large amplitude paper, the inaccurate paper pulling guide is more apparent. The color deviation occurred in double color printing, it wouldn’t affect the printing quality, but for four color pages printing, the pulling guide deviation would produce lots of wasted printings.

Once for four color page printing, taken the printings into consideration, the pulling guide control was dragged to the edges of the prints, thus the drawing deviation was increased, the printing work had to be stopped and examined.


Fault diagnoses


Firstly, increase the spring pressure and took down the upper part of the drawing control, clean the SKF bearing with gasoline and kerosene. The SKF bearing could flexibly rotated with a little engine oil. Then reinstalled and restart the machine, but there are no obvious improvement in the machine operation effect. Checked the paper drawing time, no fault was found. Adjusted the eccentric shaft of the drawing control’s SKF bearing, test the machine from the minimum pressure to the maximum pressure, but the test results was not good. After checked the operation process, we found the gap press plates on both sides of the bearing were too narrow, under the bearing there are drawing board, however the gap between the magnetic plates on both sides of the drawing board was too narrow. The gap size decreased from the middle to the external transfer surface. Because the gap was too narrow, when the pulling guide bearing pressed the paper and thus the pressure was produced, the pressure would restraint the paper pulling guide and the paper walking wouldn’t be in the right position. Due to the gap between the pressure board and the magnetic plate was decreased from the middle to the external transfer surface, therefore the pressure was also decreased, which would result in the pulling guide deviation for both small and big paper.

 

Troubleshooting


If replacing the old component with a new one, it was troublesome for disassemble and assemble. We solve this problem by adding pad to the machine. Specifically as following: firstly, put a thin steel plate in the gap between drawing board and baseplate, the thickness of the plate is 0.06mm and it is exactly the same as the pulling guide board. The transmission surface was seriously abraded, a steel sheet was add to it, the sheet is 15cm long, 0.15mm thick and as wide as the pulling guide board. In case the middle of the equipment was too high, the machine couldn’t be padded anymore. After the operation mentioned above, restart the machine, the pulling guide control goes back to normal condition and the problem can be solved. Keep in mind that don’t pad the machine too high, the pulling guide control would be too high to guide the paper accurately.

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