In flexography, print defects can stem from a multitude of moving parts, making troubleshooting feel like a constant game of chase. Much like the human body, with proper care and maintenance, all parts of this highly complex system can work together in harmony.
While the anilox roll is the heart of the printing press, the doctor blades are the workhorses that let the anilox do its job properly. Without even, consistent ink metering, the anilox is unable to deliver a uniform, measured ink film to the printing plate surface– its primary (and only) function. Ensuring your doctor blades are set properly in the press can make or break your printed result.
By inspecting the contact patch surface, information can be gathered to determine if the blade pressure across the chamber is set evenly. Uneven blade pressure can be due to misaligned chambers or incorrect installation of the doctor blade into the blade holder. Also, contaminants in the ink can leave behind score lines in the blade, or worse, the anilox roll. Looking for these clues and correcting the issue with proper ink filtration can prevent anilox refinishing and costly press downtime.
Installation of the doctor blade into the holder is easily one of the most commonly overlooked factors in the process. If the blade is installed incorrectly, it is nearly impossible to achieve proper ink metering. Doctor blades should always be installed into a clean holder, completely free of ink residue or other debris. When placing the new blade into the holder, ensure the blade is fully seated, then secure the blade from the center, working your way out to the ends. Following this simple procedure will ensure you’re starting a straight and true blade with each changeover.
This photo shows the precise measurement of a used doctor blade’s wear angle. (Click image to enlarge.)
If the press uses a chambered system, you’ll need to ensure the end seals fit properly and the blades are in the proper position in relation to the end seal. Check the fit of the seal in the chamber by looking for any gaps or excess compression around the seal. Also be sure that the anilox radius is an exact match to the anilox used on press. The fit should always be snug and accurate. To further prevent leaks, ensure the doctor blade overlaps the end seal halfway.
Once the blades are properly installed, the correct blade pressure is set, and the press is up and running, how can we know everything is performing as expected? This is where doctor blade analysis comes in. By carefully analyzing the used blades (both metering and containment, where applicable), APR’s Technical Solutions Group can pinpoint issues such as improper blade angles, poor blade mounting, or uneven chambers. This can be quite helpful when troubleshooting an existing problem, setting up a new press, or testing doctor blades.
To schedule a doctor blade trial or find out more about our analysis services, contact Catherine Green at [email protected].
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5 thoughts on “Are Your Doctor Blades Due for a Checkup?”
Very good Article ! Doctor Blade is very important!
This is a great question. The answer is, it depends on your anilox configuration. Rounded tip blades are common in wide web and where courser LPI anilox rolls are in use. Anilox rolls with higher line screens (such as 800-1200 LPI) require a thinner tip to achieve a clean wipe. This is where a lamella tip blade comes in handy. Lamella tip blades have a thinner wiping edge, with a thicker edge on the blade holder side to maintain stability. A bevel tip would also be suitable for a higher LPI anilox, but the wiping edge will get thicker as it wears, unlike the lamella which will maintain the same wiping edge thickness throughout it’s useful life. Please let us know if you have any additional questions. We have a wide array of doctor blades to fit just about any need.
Hello again, Catherine.
For now i am still student. I am just curious about this stuffs because generally we do not study flexography … I understood what you saying, except this “courser LPI anilox rolls”. Can you please explain for me this types of anilox ?
P.S. You said that commonly rounded tip blades are used in wide web, can we get good wiping in narrow web or it will not be enough for good print results ? If the machine is with one blade does it matter what type of blade will be used ?
Thanks for your response.
Sorry for my bad english i hope you understand what i am saying.
Have a nice day!
Very good Article ! Doctor Blade is very important!
Best Regards,
Marli Moncon
Thank you Marli! If you would like more information about doctor blades, please feel free to email me – [email protected].
Hello Catherine!
Nice article ! Can you tell me please what is the main + and – between lamella and rounded tip blades ? Wich is better for flexo printing and why ?
This is a great question. The answer is, it depends on your anilox configuration. Rounded tip blades are common in wide web and where courser LPI anilox rolls are in use. Anilox rolls with higher line screens (such as 800-1200 LPI) require a thinner tip to achieve a clean wipe. This is where a lamella tip blade comes in handy. Lamella tip blades have a thinner wiping edge, with a thicker edge on the blade holder side to maintain stability. A bevel tip would also be suitable for a higher LPI anilox, but the wiping edge will get thicker as it wears, unlike the lamella which will maintain the same wiping edge thickness throughout it’s useful life. Please let us know if you have any additional questions. We have a wide array of doctor blades to fit just about any need.
Hello again, Catherine.
For now i am still student. I am just curious about this stuffs because generally we do not study flexography … I understood what you saying, except this “courser LPI anilox rolls”. Can you please explain for me this types of anilox ?
P.S. You said that commonly rounded tip blades are used in wide web, can we get good wiping in narrow web or it will not be enough for good print results ? If the machine is with one blade does it matter what type of blade will be used ?
Thanks for your response.
Sorry for my bad english i hope you understand what i am saying.
Have a nice day!
Best regards,
Denislav