The selection, installation and adjustment of the doctor blade in gravure printing have an important influence on the quality of the printed matter. The following discusses some views on the application of squeegee blades in gravure printing and some issues involved.
Selection and installation of doctor blade
High-speed gravure printing machines generally use imported steel scrapers with high elasticity, and their thickness is 0.15mm ~ 0.2mm. When installing the squeegee, pay attention that both sides of the squeegee should be longer than the printing plate 10mm ~ 20mm to avoid the printing plate ink splashing on the rubber roller. The steps and main points are as follows:
1. The distance between the lining and the back of the knife is about 10mm. The distance between the lining and the blade is 5mm-7mm. However, according to the specific situation, the distance can also be increased appropriately (that is, installed as a soft blade), or reduced (installed as a hard blade).
2. Put the new blade behind the lining, insert it into the knife slot and tighten the back screw. The screw should be tightened from the middle of the blade first, then gradually outward, and the two sides should be tightened alternately. Here is a trick to avoid blade warpage: when tightening the screw, it should be completed two or three times, and it cannot be done in one step. While tightening the screw, hold a rag to clamp the blade and lining and pull it sideways, so the assembled knife is relatively flat. Only a flat blade can guarantee the uniform ink volume of the printing plate.
3. Select the appropriate sharpening tool and sharpening method.
When using a sharpened knife, if the whetstone is rough, it is not suitable for sharpening a new knife. According to practical experience, it is more appropriate to grind the knife with No. 1 emery paper, which can grind both new blades and old blades with large defects. It is okay to grind the new knife with No. 0 gold steel sandpaper, but it is difficult to grind well if it is used to wear the old blade with a larger notch. If sometimes it feels rougher to grind the blade with No. 1 emery paper, then use No. 0 emery paper to grind it slightly. There are generally two ways to sharpen the knife: One is to fold the sandpaper into a V shape, but pay attention to fold several layers of sandpaper to prevent the blade from cutting through the sandpaper and hurting your hands. This method is more efficient, the angle of the cutting edge is easier to control, but it is not safe; the other is to use two hands to grind the knife at both ends of the sandpaper, which is very safe, but the angle of the cutting edge is not very good control. Blades that are too blunt and too sharp have a negative impact on print quality.
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