While under pressure against the cylinder, the doctor blade encounters deflection. Deflection is a slight bowing of the blade caused by the cylinder motion, pressure, and blade thickness. This deflection must be accounted for when setting the blade angle. This movement provides even wear and helps remove any loose debris that may have collected under the blade which may cause streaks. The maximum movement should be about 1 inch and can be adjusted.
Doctor blades are extremely sharp and require care in handling.
Any nicks or chips in the blade edge will result in streaking or hazing. Additionally, the extremely sharp blade edge needs to be handled carefully to avoid cuts to hands or other parts of the body. Mechanical problems include uneven blade wear and excessive cylinder wear. In order for the ink to be transferred from the printing cylinder to the substrate, there must be a great amount of pressure applied between the substrate and cylinder. This pressure is supplied by the impression roll.