Squeegee adjustment tips

The adjustment of the squeegee angle is also important. The angle refers to the size of the contact angle α between the squeegee and the platen roller (angle between the blade and the tangent at the contact point of the platen roller).

Therefore, the larger the blade pressure angle, the smaller the P2, the smaller the pressure P required for the squeegee; the lower the printing speed, the smaller the linear velocity V of the ink, and the smaller the P2, the required pressure of the squeegee P. The smaller the value is, the smaller the value is; the smaller the blade pressure angle is, the larger the P2 is, the larger the pressure P required by the squeegee is. The higher the printing speed is, the larger the linear velocity V of the ink is. The larger P2 is, the larger the squeegee blade is. The greater the pressure P required. The thickness of the squeegee pad is generally 0.3-0.5 mm, and the purpose of adding the blade is to enhance the rigidity of the blade. Generally, a high-quality steel sheet having a thickness of 0.1-0.15 mm is used for the scraping blade.

The precision of the upper and lower splints in the squeegee splint also affects the quality of the prints. If the flatness of the squeegee upper and lower splice plates is poor, then the upper and lower splints will scrape the blade and scraper plate. When installed together, the flatness of the doctor blade will be affected and become a microscopic wave type. In order to eliminate this microscopic wavy form, the pressure of the squeegee is increased by scraping off the ink outside the plate roller net. As a result, the blade and the plate roller wear. The functional components mainly include a drive device for squeezing the blade left and right, a squeegee blade clutch pressure device, a squeegee blade lifting device, a squeegee blade angle modulating device, and a blade clamp device.

In the printing process, if it is found that there are different shades of color, it is necessary to find out if the horizontal accuracy of the squeegee base plate meets the requirements.

The overall rigidity of the squeegee mechanism is also a major factor affecting the print quality, especially high-speed gravure printing presses. Therefore, the adjustment of the squeegee is very important. In the long-term production practice, it has been discovered that as long as the functional devices of the squeegee mechanism are properly adjusted before printing, the defects that affect the quality of the printed product can be avoided. Squeegee pressure is too small, easy to produce non-graphic area fog or knife line, when the printing speed increases, the plate roller speed increases, the roller line with the ink line speed increases, the impact of the ink on the squeegee The increase in force will easily lift the squeegee and severely affect the quality of the printed product. When the platen roller rotates, the platen roller brings the ink under the doctor blade, the ink has a force effect on the doctor blade, so that the doctor blade from the tendency of turning outwards, the cylinder overcomes this tendency, and there is a pressure on the platen roller, forcing the platen roller The ink outside the pit is scraped off. If the rigidity of the scraper is too bad, in order to scrape the ink outside the net pit, the air pressure of the cylinder will inevitably increase, thereby increasing the pressure of the blade against the plate roller. Thus, the blade and the plate roller Easy to wear, resulting in a larger extravagance.

The functional components of each department of the squeegee mechanism affect the quality of printed products from different aspects. Squeegee pressure is too high, will reduce the transfer rate of the ink, the wear of the plate roller and the blade is very large. In general, the contact angle α is preferably 45°-65°, and the angle is determined according to the materials to be printed, the ink used, and the printing speed. The greater the contact angle α, the better the squeegee effect, but the blade is easily worn and the contact angle α is too small, which makes the contact area of ​​the squeegee and the platen roller larger, and the squeegee effect is poor, and it is easy to generate fog and wear. Squeegee blade installation and angle adjustment of the squeegee blade are also important factors affecting the quality of printed products. When squeegee blades are installed, the squeegee blade and blade plate are installed between the squeegee and the lower plate, and the length of the installation is adjusted. , Screw the upper and lower clamps tightly, so that the scraper plate and the scraper blade are clamped, the scraper installation is very particular, the scraper installation is too convex, and the scraper is easily deformed and wavy. When printing, some places can Scraping is clean, and some areas are not cleanly scratched, which affects the quality of the printed product; the blade is too short, and it lacks elasticity. Therefore, it is necessary to increase the pressure of the blade to scrape the ink outside the mesh pit. This makes it easy to wear the plate roller. The following are some lessons from squeegee adjustment:

In order to facilitate the adjustment of the squeegee and to ensure the quality of the printed product, the ink on the plate roller can be scraped cleanly without the occurrence of knife wire or fog defects. Therefore, the squeegee mechanism is divided into several functional devices. That is: P2∝COSαV2

P2 is the pressure required to resist the impact of ink

P1 is the pressure required to clean the ink outside the pits in the non-graphic area

P is the pressure required by the doctor

The adjustment of the squeegee pressure is also one of the key elements of the quality of the printed product.

The installation accuracy of the squeegee mechanism is also a major factor affecting the printing quality. When installing the squeegee mechanism, it is necessary to ensure the level of the squeegee base plate. If the horizontal accuracy of the squeegee blade base plate is too poor, the left and right height of the squeegee base plate will be achieved. Inconsistent, resulting in inconsistent blade height, resulting in inconsistent pressure around the squeegee, thus affecting the quality of printed products. Of course, the best working condition is to scrape the ink outside the roller roll with a minimal squeegee pressure, which saves scraping and the roll is less prone to wear. Some of the left and right squeegee blades are driven by a separate motor, and some are driven by the main drive and then decelerated by the worm gear. The clutch pressure of the squeegee is achieved through the air-to-air shutoff of the squeegee. Its function is mainly to make the squeegee contact or Off-print roller; squeegee blade lifting device is realized by rack and pinion, which can realize pressure adjustment; squeegee blade angle adjustment is realized by worm gear and worm, suitable angle is crucial; scraper plate clamp device consists of upper clamp plate , Lower splint, scraper pad and scraper blade make it easy to adjust the extension of the scraper. Squeegee pressure adjustment is generally 0.2 ~ 0.3Mpa.

The left and right squeegee of the squeegee is realized by the rotation of the eccentric shaft. There is a sudden change of the speed from the left limit to the right limit, so the ratio of the number of reciprocating movements per minute from the squeegee to the rpm of the platen roller is infinitesimal. , generally choose 17 or 19, this can change the track of the squeegee on the plate roller, and it can bring the impurities on the squeegee down through the left and right squeezing to reduce the knife line and make the squeegee effect better. The squeegee pressure refers to the pressure applied by the squeegee blade to the platen roller. There are two main functions of the squeegee pressure: the first is to scrape the ink outside the image area and not only the outside of the pit; the second is to resist the ink. The impact force prevents the ink from flowing out of the knife edge.

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

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