Doctor blade chamber alignment is critical for good doctor blade performance. Take a few minutes to make sure that there is proper system alignment to prevent early and excessive doctor blade and anilox wear, ink leaks, waste and downtime. Everyone knows that doctor blades are designed to remove excess ink from the surface of the anilox roll. The best way to achieve this is through light contact between the blade and the anilox along the full face of the roll. If the blade does not have even contact with the roll due to chamber misalignment, it will not shear the ink cleanly and consistently from the anilox roll surface. This results in an inconsistent lay down of ink on the substrate.
Things that cause inconsistent contact between the blade and the roll are:
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- Blade and blade holder misalignment (for example the blade is skewed, offset or not parallel to the centerline of the anilox roll)
- Poor blade seating in the blade holder
- Inconsistent pressure from one side of the chamber to the other
- Improper tightening of the blade clamp bolts securing the doctor blade
Any of these situations can cause the blade pressure to vary across the length of the anilox roll. When this happens, instead of correcting the basic cause of the problem, press operators often crank down on the pressure until the full length of the doctor blade is forced into contact with the roll. The areas of the blade that were already in contact with the face are now subject to too much pressure. While this seems to resolve the metering problem, the additional friction causes accelerated wear on the affected areas of the blade and roll. These wear patterns on the roll surface will result in reduced ink density in the corresponding areas of the roll and substrate. This excess pressure can also cause ink to be forced out of the ends of the chamber (which will be blamed on the innocent end seals!).
Steps to Ensure Proper Doctor Blade Chamber Alignment:
1. Clean the surface that the blades will rest on and insert the blades firmly against the blade stops. A buildup of hardened ink can prevent the blade from laying flat against the holder
2. Place 2 blades in the chamber without end seals
3. Tighten the blade clamps beginning in the center and work outwards. Tightening in the incorrect order or over-tightening will cause the blade to buckle or ripple
4. Slowly engage the blades against the roll
5. Make sure that both blades contact the roll at the same time
6. If both blades do not make contact with the roll at the same time evenly along the face of the roll (with the same amount of pressure), make adjustments accordingly
For printable instructions and diagrams, download our TruPoint® Doctor Blade Installation Infographic.
As a rule of thumb, blade pressure should never be increased to resolve issues relating to improper doctor blade chamber alignment or chamber leaks. If the contact area is uneven or leaks are occurring, back off the pressure and start over.
Investing a few minutes in proper doctor blade chamber set-up will be more than made up by savings in time, money and waste in the long run. Remember, keep your chamber in line or your doctor blade will act up!
