Adjustment principle and common problem analysis o

2022-08-17
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The adjustment principle of printing pressure and analysis of common problems (IV)

above, we discussed how to determine a suitable printing pressure and how to adjust the printing pressure. Its purpose is nothing more than to ensure the printing pressure within a reasonable range when printing. In actual production, whether the printing pressure is high or low, it will cause one or another problems

too little printing pressure will lead to printing defects such as abnormal ink transfer, and a little emptiness on the printed matter. We used to think that if the printing pressure is high, the transfer amount of ink will be larger, but in production, the printing pressure and the transfer amount of ink are not in direct proportion. When the printing pressure is greater than a certain range, the transfer amount of ink will not increase with the increase of printing pressure, but will decrease. At the same time, excessive printing pressure will cause the increase or even spread of printed matter. Excessive printing pressure will also damage the mechanical structure of the printing machine. The more direct manifestation is the wear of the printing plate and the damage to the surface of the substrate. From the above, we can see that too little or too much printing pressure is a must in printing, and it is very necessary to accurately ensure a reasonable printing pressure

analysis of other common problems caused by printing pressure (the pressure expression mentioned below is blanket compression). The following discussion will mainly be carried out by mechanical pressing

1. Ink bars welcome the majority of users to visit our Jinan new era assay instrument Co., Ltd.

causes:

(1) ink bars caused by serious wear of drum gears

1. The adjustment center distance is too large

2.. Or the drum gear is seriously worn, and the gear backlash is more than 1.0mm. When the drum is pressed, the gear vibrates, causing friction and sliding on the contact drum surface, and finally causing the point to deform in the transfer process

solution:

1 Replace the new gear

2. Properly reduce the center distance of the drum and mesh the gears tightly to make the side clearance less than 0.1mm

3. Soft lining. The compression between the plate cylinder and the blanket cylinder shall not exceed 0.1 ~ 0.15 mm; The pressure between the blanket cylinder and the embossing cylinder shall not exceed 0.15 ~ 0.2 mm plus the thickness of a piece of paper

(2) ink bar caused by serious wear of drum bearing gear. When the shaft head and shaft sleeve are seriously worn, the mouth of the shaft will immediately yield after being pressed, causing sliding friction and deep ink bar. Solution: ① replace the new shaft sleeve; ② If it is an old-fashioned low-speed offset press, the rigid belt on the plate shaft head can be tightened

(3) the pressure between the plate cylinder and the rubber cylinder is too high. The ink bar is characterized by the ink bar in the fixed area. The pressure between the printing plate and the rubber cylinder is too large, and the rubber blanket will produce greater friction and sliding under the extrusion, resulting in point deformation and the formation of ink bars. To identify whether the pressure between the two rollers is too high, the obvious feature is that there is a "bang bang" sound when pressing, and generally after printing to 5000 pieces, the printing plate surface shines

solution: the liner of printing plate and blanket should be digitalized. The thickness of the printing plate liner should be controlled within the standard ± 0.03 mm, and the rubber should be 2 The thickness of the liner in the temperature and humidity cloth should make the pressure as ideal as possible

2. Longitudinal ghosting

causes:

(1) the roller is not pressed properly. Ghosting is characterized by several longitudinal ghosting at the beginning of printing. This is because the roller cannot close enough at one time, and when it needs several times to complete, its pressure is different, and the compression deformation of the blanket is also different, so that when the points on the printing plate are transferred to the blanket, the impressions cannot coincide and produce ghosting. The reasons are mostly caused by wear or looseness of the drum clutch mechanism, or too much pressure between the drums

solution: check the drum clutch mechanism, tighten the screws that are loose, and replace the ones that are seriously worn. If it is a pneumatic pressure combination model, pay attention to whether there is air leakage in the air circuit or whether there is a problem with the compressor air pressure. When the pressure between the rollers is too large, reduce the pressure of the rollers appropriately

(2) the blanket is too tight. Ghosting is characterized by full or partial vertical ghosting. There are two situations when the blanket is too loose: one is that the whole blanket is too loose, so that the blanket cannot be reset in time after being pressed, resulting in a large area of ghosting; the other is that the blanket is cut askew or not clamped correctly, resulting in local tension and local ghosting

(3) excessive pressure between rollers. The ghosting feature is a large area of longitudinal ghosting. When the pressure between the rollers is too large, especially when the combined pressure of the rubber roller and the embossing roller is too large, the displacement of the blanket is large, and it cannot be completely reset after each transfer, resulting in a large area of longitudinal ghosting

solution: when large-area longitudinal ghosting occurs, check whether the pressure between the rollers is too large. If it is too large, the pressure between the plate cylinder and the blanket cylinder should be adjusted to 0.1 ~ 0.15 mm, and the pressure between the rubber cylinder and the impression cylinder should be adjusted to 0.2 ~ 0.25 mm

3. Cause of plate pasting and embossing

cause: the pressure between the rollers is too high, sometimes the pressure between the embossing cylinder and the rubber cylinder is insufficient, but the pressure between the printing plate cylinder and the rubber cylinder is just right, and the operator adds a cushion through the rubber cloth, resulting in the plate cylinder and the rubber cloth roller. If the experimental software does not calculate the yield point of the sample in the tensile experiment of the metal sample, the pressure between the cylinders is too high and the friction is increased

solution: when the above defects occur, check whether the roller pressure is too large

① recalculate and check whether the main product of the roller pillow of the drum is the prismatic power lithium battery gap is normal (the old domestic model needs to press the fuse between the rollers to re measure)

② measure whether the thickness of the blanket and the printing plate is appropriate (± 0.03 mm)

③ check whether the rubber blanket is locally uneven

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