Doctor Blade Selection
Many chamber manufacturers specify—and pressmen will use—the same blade on both sides of the chamber, without regard to whether using steel, composite or plastic blades. When this is done, the potential for installing the blades in the wrong location is obviously eliminated, as well as the need to inventory multiple blade types. However, since the containment blade does not need to meter the ink—and you really do not want it to—using a different blade for the containment position can increase overall chamber performance, reduce anilox roll wear, minimize back doctoring and reduce the cost of consumables.
For many applications, a thin plastic blade in the containment position will perform well. Depending on the chamber design, a plastic containment blade that is 0.0625-in. to 0.125-in. wider than the doctor blade will force the contact angle to be flatter and increase potential for anilox surface ink to pass by the containment blade to minimize back doctoring. Some chambers are designed to provide a flatter containment blade angle, so the plastic containment blade does not need to be wider than the doctor blade.
Plastic blades do not work for some containment blade applications, due to either aggressive solvent contamination, heat or pressurized auto-wash systems. If this is the case, using a steel blade thinner than the doctor blade with a rounded edge shape is a viable alternative to plastic.
Choosing the correct doctor blade for the application is crucial for achieving optimum print results as well as controlling blade costs. There are numerous options for doctor blades, and I would suggest working with your blade supplier to determine the best for you. Most chambers are designed to accommodate blade thicknesses of 0.030-in. or less, with the exception being corrugated presses that can often use plastic blade thicknesses between 0.060-in. and 0.090-in.
You will need to determine your chamber blade thickness limitations before investigating alternative blade materials or thicknesses. Keep in mind that the same blade does not have to be used on each print station of the press.
Just about any blade can be used in a single-blade system limited only by the blade thickness the holder will accommodate. Some holder designs are based on using steel blades, so this will restrict some plastic or composite blade options. Conversely, corrugated press holders are often designed for thick plastic blades, so that using a thin plastic or steel blade may not be an option. Blade choice will depend on the application. Hence, it is suggested to work with your blade supplier to determine the best blade options for your application.
“A reverse angle blade is commonly compared to an ice or paint scraper, where the blade scrapes the ink from the surface of the anilox.”
Doctor Blade System Maintenance
Maintenance for any type of blade system is essentially the same, even though the chambered systems have many more components to consider. All components need to be in good mechanical condition, which means they need to be checked for damage and deformation while paying attention to the straightness of the blade clamping components.
Chamber bodies can bend or twist over time, which will make blade-to-anilox alignment very difficult at best. Check moving parts and bearings for wear and smooth motion. Cleanliness is very important, as any accumulated ink in the blade clamping areas will tend to alter the position of the doctor blade, or cause blade wrinkles, when they are installed. Clean, repair or replace any components found to be compromised.
Alignment of the system—specifically the doctor blade to the anilox roll—needs to be checked and adjusted when warranted. Some blade systems have controls that allow the operator to adjust basic alignment whenever a new setup is made; others have adjustment mechanisms intended to be used only for maintenance-type operations.
All blade systems should have regularly scheduled preventative maintenance alignment checks included with other press maintenance tasks.
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