Long-Life Doctor Blades
Long-life blades typically have a single or multi-layered coating applied to the doctor blade tip, which may be radius or rounded, lamella or bevel edge. The coating helps protect the integrity of the steel for improved blade performance and extended durability when compared to traditional carbon steel materials.
The coating also increases lubrication and offers much lower friction values. The doctor blade wear particles are greatly reduced in size to help combat anilox score lines. As such, these blades require changing far less frequently than blades that are more prone to wear, uneven edges, bending or skewing, and other normal deterioration over time that can negatively impact print performance or damage other press equipment.
A long-life doctor blade results in blade and end seal costs of approximately $360 per setup, while a standard blade package is more economical at roughly $150. That said, over the course of one year, long-life blade spend is just $3,120 higher than standard—$18,720 vs. $15,600. Downtime is where the dramatic savings occurs. Downtime costs with the standard package equate to $150,000 annually; long-life options result in downtime valued at approximately $21,500. Collective savings attributed to long-life blade usage is therefore better than $125,000 annually. That’s impressive ROI!
In order to beat the average, what steps can printers take?
Preventive Maintenance
Too often, printers lose sight of the importance of deck calibrations and preventive maintenance (PM), as there is an assumption these activities cut into press productivity as non-value-added tasks. At some point, however, the question becomes whether to pay now for proper PM, or pay later, when shutting down for unexpected breakdowns and unplanned downtime. The latter typically has far worse of an impact on the bottom-line.
To ensure doctor blades perform as designed, it is essential their chambers are calibrated on a regular basis or as mechanical conditions change. For chambered doctor blade units, the alignment is very critical, so that the top and bottom blades contact the anilox roller at the same time to properly meter a consistent ink/film thickness, and to create a leak-free chamber.
A good way to check the contact is to engage an empty chamber (with no end seals) to the anilox and use a feeler gauge to make sure the amount of consistent drag is identical on both sides of the chamber, or make necessary adjustments as needed. Another important step for proper chamber alignment is to make sure the chamber is set parallel to the anilox by using a level to check its position.
“Process improvement teams’ primary focus should be to remove all non-value-added activities, so it makes sense to use long-life doctor blade and end seal products that can last the entire work week, or until the next scheduled blade change, as opposed to relying on doctor blades and end seals that require changes during each and every changeover.”
Scheduled Doctor Blade Changes
Those unpredictable doctor blade failures can be expensive in many ways—safety, quality, service and cost. Scheduled doctor blade changes optimize the performance of assets to increase the reliability and availability, while minimizing costs and reducing operational risks.
Without having some sort of cleaning checklist or CILT (clean, inspect, lube and tighten) schedule in place, those unpredictable doctor blade failures will cost precious downtime from cleaning up big messes and possibly missing critical customer deliveries.
Maintenance schedules and checklists help identify the who, what, when and where in the assignment of responsibilities—ensuring that deck chambers are being cleaned and set up to stated standards and expectations. A simple audit of the cleaning checklist will indicate whether the process is being followed, or indicate if additional training is necessary to enforce standards and maximize doctor blade life.
Pressure Control
On a central impression (CI) press, the doctor blade chambers can be controlled by either manual or pneumatic adjustments to increase or decrease blade pressure, depending on the circumstance.
Too much pressure on the doctor blade tip will cause more contact area on the anilox roll, allowing more ink to transfer onto the plate material and making it difficult to control optimal ink/film thickness. When this occurs, printers will often struggle with dirty print and dot gain issues, controlling tonal values and impacting overall print quality.
Often, when a new set of doctor blades is installed, the printer forgets or doesn’t understand the importance to back the chamber out to the home position, causing a larger contact area on a new set of blades. This can also lead to premature doctor blade wear, anilox wear, ink contamination and anilox scoring.
More and more companies are realizing the benefits of using long-life doctor blade and end seal materials. Safety, quality, service and cost are all equal in magnitude and balance the importance of using long-life doctor blade packages over time and across multiple jobs.
Where long-life blades ultimately excel is in their ability to reduce overall consumable costs, minimize the need for frequent blade/seal changes, and present favorable conditions for maintaining press uptime and profitability.