How to select, install, and adjust the scraper, which is better for the printing process?

In intaglio printing, the selection, installation and adjustment of the doctor blade have an important impact on the quality of printed matter. How to select, install, and adjust the scraper, which is good for the printing process?
1、 Selection and installation techniques of ink scraper
High speed gravure printing machines generally use imported elastic steel ink scraper blades with a thickness of 150-180 μ m。
When installing the ink scraper, make sure that both sides of the scraper are 10-20mm longer than the printing plate to prevent ink from splashing onto the rubber roller. The steps and key points are as follows:
1. The distance between the lining and the blade back is approximately 10mm. The distance between the lining and the blade is 5-7mm. However, depending on the specific situation, the distance can also be appropriately increased (i.e. installed as a soft blade) or reduced (installed as a hard blade).
2. Place the new blade behind the lining, insert it into the slot, and tighten the screw on the back of the blade. It should be tightened from the middle of the blade first, then gradually outward, and both sides should be tightened alternately.
Here is a tip to avoid blade warping:
When tightening the screw, it should be completed twice or three times and cannot be completed in one step. You should tighten the screws while holding a piece of rag to clamp the blade and lining and pull it forcefully to one side, so that the assembled knife is smoother. A flat blade is necessary to ensure even ink volume on the printing plate.
3. Choose suitable sharpening tools and methods. When grinding a knife with a rough stone, it is not suitable for grinding a new knife. Based on practical experience, it is more suitable to use No.1 emery paper to grind the blade, which can be used to grind both new blades and old blades with significant defects. If you use No. 0 steel sandpaper to grind a new blade, it is still possible, but if you use it to wear old blades with slightly larger notches, it is difficult to grind them well. If you sometimes feel that using No. 1 emery paper to grind the blade is still rough, you can use No. 0 emery paper to slightly fine grind it.
There are generally two ways to grind a knife: first, fold the sandpaper into a V-shape, but pay attention to folding several layers of sandpaper to avoid cutting through the sandpaper and injuring your hands. This method has high efficiency and is easy to control the angle of the blade, but it is not very safe; Another method is to use both hands to pull the ends of the sandpaper to grind the knife, which is very safe, but the angle of the blade is not easy to control. Too dull and sharp blades have a negative impact on printing quality.
2、 Reasonably adjust the doctor blade
The pressure, sharpness, and contact position of the scraper have an impact on printing quality. Adjusting these factors reasonably according to actual needs can solve many printing problems.
1. Pressure
The factors that affect the pressure of the ink scraper are the size of the cylinder pressure, the difference in hard and soft blades, and the angle of intersection between the ink scraper and the printing plate. The larger the slope, the greater the pressure. Excessive pressure will reduce the ink transfer rate and cause significant wear on the printing plate and blades; Excessive pressure can easily lead to dirty plates or scraper lines.
2. Sharpness of the knife
The sharpness of the knife depends on whether it is new, the angle of the blade when grinding, and the type of sandpaper (oilstone) used. The suitable sharpness of the knife should be to effectively scrape off the ink without generating any knife threads. Scrapers that are too sharp are often prone to generating blade marks and also wear out the printing plate.
3. The distance between the ink scraper and the printing plate
Reducing the distance between the scraper and the printing plate is beneficial for improving the ink transfer rate, but it is also prone to generating dirty plates; On the contrary, it can effectively solve the dirty version and avoid some small line marks, but it will reduce the ink transfer rate.
4. Flatness of the knife
The flatness and warping of the knife mainly depend on the installation method, and of course, it may also be related to foreign objects sticking to the slot of the knife holder or the blade or lining. When the flatness of the knife is poor, it can cause some water droplets like marks on the edge of the printing surface, or intermittent line marks from time to time. Some people believe that rough ink and poor ink fluidity can lead to the above phenomenon, but in fact, uneven knives can also cause this situation.
5. The movement of the doctor blade
The left and right movement of the ink scraper plays an important role in reducing the scraper line, improving the utilization rate of the scraper, and reducing wear and tear on the plate. If the ink scraper does not move properly, ways should be found to improve it.
3、 Scraper related faults in printing
When there are line marks in printing, one is causing plate damage, and the other is that the scraper is not sharp. However, another reason is that there are foreign objects sticking to the back of the blade. The solution is to move the ink scraper back and forth, up and down, in order to remove the adhesive. If it cannot be removed, the only option is to stop the machine and wipe the ink scraper.
Another challenge is related to the scraper, and many people misunderstand it as caused by ink. This refers to the occasional occurrence of dozens of irregular lines of varying lengths, which look like ink piles. Unlike scraper lines, they are not continuous, but sometimes absent, or only appear in 1/2 or 1/3 of the printed area. This is actually caused by the pressure of the scraper being too small or the scraper being not sharp enough.