Two-color machines fail to correct each other and eliminate

Overprint accuracy is one of the main technical indicators of offset printing quality. Once printing is inaccurate, it will affect the quality and even cause a lot of waste products.
The main factors of inaccurate offset printing are: improper adjustment of the machine, poor mastery of the plate layout, high humidity in the workshop, poor quality of the paper, low accuracy of the plate making, and abrasion of the machine parts. In particular, the two-color machine is worn due to mechanical parts. It is difficult to solve faults that are incompatible with each other. How to analyze and eliminate faults in your work is now introduced to your peers as follows:
I have a factory in Taipei with a J2205 dual-color machine that has been in use for more than a decade. In the past two years, there have been failures of small color prints and large under color prints, and the two colors are inaccurate. At that time, we thought that it was caused by the loss of elasticity of the lining and required the staff of the machine to change the cloth frequently. At the beginning, it was still effective, but as time went on, changing the cloth and changing the rubber market would not help. Later, we also considered that the pad of the plate liner and blanket was not properly formed and the line speed was inconsistent. I started measuring the pads myself, added them in accordance with the design requirements of the machine, and checked them after printing. The fault persists. We consider again and again that it is caused by the loosening of the pressure regulating mechanism and the shifting of the center distance of the roller, so the center distance of the roller is measured by means of a pressure fuse. As a result of the measurement, the center distance of several rollers has not changed, and the clearance of each roller is within the tolerance. Why does this happen?
In order to solve this problem, I have repeatedly pondered and analyzed: I believe that one of the reasons for this is that the machine has been used for a long time and the parts have been worn badly and misaligned. The second reason is that due to the low level of prints in the past, the number of double-sided monochrome prints is higher, and the number of two-color machines is higher. Can only play the role of a monochrome machine. The color roller is a load operation, and the color roller is an idling operation, causing the upper and lower rollers to have different loads. Especially when the plate cylinder is working, it is necessary not only to overcome the friction of the blanket cylinder, but also to overcome the friction between the ink roller and the water roller. All in all, the greater the friction, the greater the wear and tear; the different loads on the machine, the longer the running time, the greater the degree of wear of the various parts. Obviously, color plate cylinder gear wear is more severe than other roller gears. The gears are worn badly, the teeth of the gears are sharpened, and the gap of the gears is expanded, which will affect the smooth running of the plate cylinder. When the pressure is combined, the splaying of the upper printing platen roller produces a jump, and the phenomenon of stagnation occurs instantaneously. At this time, the color-sweeping mark is smaller than the color-seal mark. Due to the engagement of the rubber roller gears and the reaction force, the roller accelerates to complete the imprinting area in advance, and the colored trailing edge print is smaller than the lower color trailing edge. In the 360° rotation cycle, color plate cylinders exhibit stagnation and acceleration. Because these two phenomena will cause the front and back (also called the size) of the printing plate to be compressed, the gear wear is the main reason for the inaccurate setting of the two colors.
For the above failure analysis, the author compared the upper and lower two-color imprinting. After measurement, the color imprinting is less than the lower color imprinting with 1.2mm. In order to be foolproof and to avoid detours, it is necessary to calculate the padding data of the 1.2mm print. The calculation steps are as follows:
Plate diameter D=299.65mm (including plate and liner)
The arc length of one revolution of the drum is:
D printed p = 299.65 '3.1415926 = 941.378 22 (mm)
The arc length for each degree of operation is:
941.378 22?360°=2.6149 39(mm)
The multi-pad printing plate 0.1mm, the cylinder diameter increased by 0.2mm, the diameter of the plate cylinder reached 299.85mm, the arc length of the cylinder increased to 942.0065mm, and the arc length per degree increased to 2.616684mm.
If the printing plate is 530mm in width, ie, the arc length is 530mm, the printing plate prints this picture with a standard pad. The degree of rotation of the printing plate is:
530 ? 2.614 939=202.68°
When the printing plate is more than 0.1mm, the printing plate is printed after...
530?2.616684=202.53°
The multi-cushion liner is 0.15° less than the standard liner, and the arc length of the multi-cushion is:
2.616684 ′′ 0.15°=0.39 (mm)
If the plate imprinting is expanded by 1.2mm, the little pad data is:
1.2'0.1?0.39=0.3(mm)
In order to enlarge the printing plate imprint by 1.2mm, the spacer should be reduced by 0.3mm compared to the standard gasket, which means that there is no pressure and meaningless.
To solve this problem, I think that according to the current conditions we are in, we can only solve this problem by appropriately retracting the center distance of the printing plate cylinder. For prudent reasons, I use the method of pressure fuse, first small 0.1mm, artificial pressure method, manual operation of the machine, after careful observation of the center distance adjustment, the roller gear meshing with top tooth phenomenon. The results show that there is a certain gap when the gear meshes. Therefore, I again take a small 0.05mm. After the adjustment, the gear meshed well and the machine was moved easily. Then the plate liner was also subtracted by 0.15 mm. After the printing inspection, the print was expanded by 0.6 mm, and the expected effect was achieved. Based on the principle of thick pad and small print, I added 0.15mm to the under color plate. Re-check the print, the problem is solved. The two colors overlap. After more than one year of production inspection, the machine is now operating normally, overprinting is accurate, and the printing plate is resistant to printing forces, which are generally over 100,000 impressions.