Have you ever wondered what effect your steel doctor blades are having on the lifetime of your anilox rollers?
In this article, we cover how doctor blade setup, blade materials and coatings can positively enhance the performance and lifetime of your steel doctor blades and your anilox rollers. Plastic blades do have their place in the market. However, for most high-speed, high-quality applications, a long-lasting, robust steel blade is required. In addition, there is no need to worry about the steel blade causing premature damage to your anilox rollers.
Blade Pressure
Are your doctor blades wearing unevenly? Are your chambers leaking more than they used to?
All photos courtesy of TKM United States Inc
Low, even and consistent pressure across the entire roll is preferred. Too much pressure can bend the blade tip, resulting in uneven wear, and possibly create a small metal sliver or burr. This metal sliver or burr could then break off, get trapped underneath the blade and score your anilox roller.
Your doctor blade must be installed in the chamber or holder flat (not wavy). Otherwise, damage to the anilox may occur. Furthermore, a wavy doctor blade forces the operator to use higher blade pressure to straighten out the doctor blade in order to achieve a clean wipe across the anilox roller. To avoid a wavy doctor blade, and ensure proper fit, one must make sure all mounting surfaces are smooth, cleaned and free of dried ink and debris. Furthermore, if the doctor blade is clamped with the help of screws, then overtightening them or not tightening them in the proper order can also result in a wavy doctor blade.
Another reason too much doctor blade pressure is used occurs when the chamber or blade holder is out of alignment. In this case, the operator is again forced to use more doctor blade pressure to ensure a clean wipe. Chambers and blade holders can usually be aligned by your maintenance team or the machine manufacturer. If the doctor blade is straight, and the chamber or knife holder is perfectly aligned to your anilox roller, you can use significantly less doctor blade pressure.
In order to troubleshoot uneven blade wear and leaky chambers, most doctor blade suppliers will assist you by analyzing the wear angles on the used blades.
Please keep in mind that, even with a near perfect setup, blade wear will still occur. This wear should result in the form of small, metal dust particles that you will need to capture with magnets and filter (see Figure 1). These systems have to be cleaned on a regular basis.
Are you using the right end seal and OEM-specified blade widths? If your chamber and end seals require a 25-mm. wide doctor blade and you substitute a 1-in. blade (25.4-mm.), there is the possibility you will need to over-pressure the blade for proper end seal compression against the end of the anilox roller. It is important to make sure the dimensions of the blade and end seals match with the chamber setup.
Blade Steel
Blue tempered, white carbon, bright polished, stainless—What steel material should a printer use?
Stainless steel blades should be used if blades remain in the printing unit for an extended period of time with water-based or corrosive inks. Otherwise, printers can use steel blades that are made from hardened carbon steel—similar to spring steel. Higher-quality carbon steels have some amount of chrome present, and only minuscule amounts of sulfur. Keep in mind that some carbon steel blades on the market do not have any chrome, while others benefit from having as much as 1.5 percent chrome composition (see Figure 2).
Furthermore, various small, evenly distributed chrome particles increase the wear resistance of the blade, and help the steel to break down into very small, powder-like particles. These enhanced, processed chrome particles improve blade lifetime, while further protecting your anilox roller investment. In addition, a better-quality steel can prevent issues, such as a crack-out or chip, caused by the edge of an anilox roller.
Only a few specialized steel rolling mills offer thin doctor blade material that also includes good chrome distribution, along with minimal residual amounts of sulfur or steel inclusions. Blade suppliers work very closely with these mills to ensure the material is consistent and optimized for use with ceramic anilox rollers.