Method for adjusting ink scraper of gravure printing machine

With the continuous progress of social development, people's requirements for external packaging are becoming higher and higher. The main advantages of gravure printing are rich colors and thick colors. The main advantages of gravure printing determine that exquisite outer packaging generally requires gravure printing. However, there are many factors that affect the quality of gravure printing, such as: environmental impact, operator's technical level, ink quality, equipment quality and so on. The effect of the ink blade on the quality of gravure printing is particularly important. The adjustment of the ink blade not only directly affects the quality of the printing, but also has a great impact on the life of the ink blade.

In order to facilitate the adjustment of the doctor blade and to ensure the quality of the printed product, the ink on the plate roller can be wiped clean without the defect of the wire or the plate fog, so the doctor blade mechanism is divided into several functional devices. Its functional parts mainly include a driving device for the left and right movement of the doctor blade, a doctor blade clutch pressure device, a doctor blade lifting device, a doctor blade angle adjustment device, and a doctor blade clamp device. The squeegee moves left and right, some are driven by a separate motor, and some are driven by the main drive through worm gear deceleration and then driven; the clutch pressure of the squeegee is realized by the air cylinder through the manual reversing valve to cut off the air. Disengaged from the plate roller; the doctor blade lifting device is realized by the rack and pinion, which can realize the pressure adjustment; the doctor blade angle adjustment is realized by the worm gear, the appropriate angle is crucial; the doctor blade clamping device is formed by the upper clamping plate , Lower splint, scraper pad and scraper blade, you can easily adjust the extension of the scraper.

Fig.1 The doctor blade mechanism of gravure printing machine
Figure 1 The squeegee mechanism of gravure printing machine Click here to see all news pictures

1 doctor blade clamping device 2 doctor blade lifting device 3 doctor blade clutch pressure device 4 doctor blade angle adjustment device 5 doctor blade drive device

The functional parts of the squeegee mechanism affect the quality of printed products from different aspects. Therefore, it is very important to adjust the squeegee. In long-term production practice, it is found that as long as the functional devices of the squeegee mechanism are properly adjusted before printing, defects that affect the quality of the printing can be avoided. The following are some experiences of doctor blade adjustment:

1. The doctor blade moves left and right through the rotation of the eccentric shaft. There is a sudden change in speed from the left limit to the right limit, so the ratio of the number of reciprocating movements of the doctor blade per minute to the speed of the plate roller per minute is infinite decimal. Generally, 1/7 or 1/9 is used, which can change the trajectory of the doctor blade on the plate roller, and can carry the impurities on the doctor blade through the left and right movement, reduce the knife line, and make the ink scraper effect better. Rotate the eccentric shaft to the left limit and adjust the thread of the joint bearing so that the compression spring inside the left bracket receives the maximum compression.

2. The overall rigidity of the squeegee mechanism is also a major factor affecting print quality, especially high-speed gravure printing machines. When the plate roller rotates, the plate roller brings the ink under the doctor blade, and the ink has a force on the doctor blade, which causes the blade to turn outward, the cylinder overcomes this trend, and there is a pressure on the plate roller to force the plate roller The ink outside the mesh pit is scraped off. If the rigidity of the squeegee is too bad, in order to scrape the ink out of the mesh pit, the air pressure of the cylinder will be increased, thereby increasing the pressure of the squeegee against the plate roller. In this way, the blade and the plate roller It is easy to wear and causes relatively large waste. Of course, the best working condition is to scrape the ink outside the mesh of the plate roller with the minimum blade pressure, which saves the blade and the plate roller is not easy to wear. The adjustment of the doctor blade pressure is generally 0.2 ~ 0.3Mpa. [next]

3. The installation accuracy of the squeegee mechanism is also a major factor that affects the printing quality. When installing the squeegee mechanism, the level of the squeegee bottom plate must be ensured. If the horizontal accuracy of the squeegee bottom plate is too poor, the left and right height of the squeegee bottom plate will be increased. The inconsistency causes the left and right heights of the doctor blade to be inconsistent, which causes the pressure of the left and right doctor blades to be inconsistent, which affects the quality of the print. During the printing process, if you find that the left and right coloring is different, you need to find whether the horizontal accuracy of the squeegee bottom plate meets the requirements.

4. The machining accuracy of the upper and lower splints in the doctor blade also affects the print quality. If the flatness of the upper and lower splints of the doctor blade is very poor, then when the upper and lower splints will scrape the blade and the blade pad When installed together, the flatness of the doctor blade will be affected, becoming a micro wave shape. In order to eliminate this micro wave shape, the ink outside the plate roller pit will be scraped off, which will increase the pressure of the doctor blade. As a result, the doctor blade and plate roller are worn. Squeegee blade installation and squeegee angle adjustment are also important factors affecting print quality. When installing the squeegee blade, the squeegee blade and the squeegee pad are installed between the upper and lower cleats of the squeegee. After adjusting the installation length , Tighten the upper and lower clamping plates with screws, so that the scraper pad and the scraper blade are clamped. The installation of the scraper is very careful. The scraper is installed too prominently. The scraper is easily deformed and wavy. In printing, some places can be scraped. Clean, some places are not clean, which affects the print quality; the blade extends too short and lacks elasticity, so the pressure of the blade must be increased to scrape the ink outside the net pit, so it is easy to wear the plate roller. In general, the scraper pad extends 20-30 mm from the splint, and the scraper blade extends 5-7 mm from the scraper pad. As shown in Figure 2, the scraper blade splint device. The thickness of the squeegee pad is generally 0.3-0.5mm, and the purpose of adding the squeegee pad is to strengthen the rigidity of the squeegee. The squeegee blade generally uses high-quality steel sheets with a thickness of 0.1-0.15mm.

Figure 2 Squeegee clamping device
Figure 2 Squeegee Clamp Device Click here to view all news pictures

1 Upper splint 2 Lower splint 3 Squeegee pad 4 Scraper blade

6. The adjustment of the doctor blade angle is also very important. The angle refers to the size of the contact angle α (the angle between the tangent line at the contact point of the blade and the plate roller) of the doctor blade and the plate roller (see Figure 3). The larger the contact angle α, the better the scraping effect, but the blade is easy to wear. The contact angle α is too small, so that the contact area between the scraper and the plate roller is increased, the scraping effect is poor, the plate fog is easy to produce, and it is easy to wear. In general, the contact angle α is preferably 45 ° -65 °, and the angle is determined according to the material to be printed, the ink used and the printing speed.

Figure 3 Contact angle of doctor blade
Figure 3 Contact angle of squeegee blade Click here to view all news pictures [next]

7. The adjustment of the doctor blade pressure is also one of the key factors for the quality of the print. The doctor blade pressure refers to the pressure that the doctor blade applies to the platen roller. The doctor blade has two main functions: the first is to scrape off the ink outside the mesh pit in the non-graphic area; the second is to resist the ink The impact force prevents ink from flowing out of the knife edge. Squeegee pressure is too low, it is easy to cause plate fog or knife line in the non-graphic area. When the printing speed increases, the plate roller speed increases, the line speed of the ink carried by the plate roller increases, and the impact of ink on the doctor Increased force makes it easy to lift the doctor blade, which seriously affects the quality of the print. If the pressure of the doctor blade is too high, the transfer rate of ink will be reduced, and the plate roller and the doctor blade will be greatly worn. The pressure of the doctor blade is determined by its function, namely:

P = P1 + P2

P is the pressure required by the squeegee blade P1 is the pressure required to wipe off the ink outside the network pit in the non-graphic area P2 is the pressure required to resist the impact force of the ink

The pressure P2 required to resist the impact force of the ink is related to the pressure angle of the blade and the linear velocity V of the ink. That is: P2∝COSαV2

Therefore, the larger the blade pressure angle, the smaller P2, the smaller the pressure P required by the squeegee. Also, the smaller the pressure angle of the doctor blade, the greater the P2, the greater the pressure P required by the doctor blade; the greater the printing speed, the greater the linear velocity V of the ink, the greater the P2, the doctor blade The required pressure P is also greater.

In actual work, according to the above method to adjust the doctor blade, you can ensure the corresponding print quality. After using the printing machine for a period of time, due to various reasons such as wear and tear, the accuracy of related important parts may be reduced, and the same print quality problems may also occur. This requires further analysis and judgment. So as to eliminate the impact of the doctor blade on the printing quality in time, reduce the scrap rate, improve the yield rate and improve the production efficiency.

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