Doctor blade angle control for wide-web cylinder metering (Part 3)
von Bill Warner, Vice President of Allison Systems,
The changing of very long and heavy steel doctor blade holders is a real challenge
(Source: GAA)
Wide-web gravure applications can have doctor blades with lengths greater than 100 in. (2540 mm). When doctor blades are that long, setting them correctly and consistently to achieve effective metering can be more difficult because slight variations will be compounded over the length of the blade. Part One of this article focused on challenges with setting the doctor blade at an appropriate position and angle; Part Two centered on applied force control. This part will cover the barriers to efficient blade changes.
The barriers to efficient blade changes
Quick and easy blade-change capability is essential when working with long doctor blades. Slow, difficult, and potentially dangerous blade changes were the norm with a very wide-web application that required a +200-in. (5080) long doctor blade. The existing bladeholder was a prime example of everything you don’t want in a very-wide-web blade holder. It needed to be removed from the press and carried to a remote location to clean the holder and install new doctor blades.
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Carrying such as long, heavy, steel doctor bladeholder with a used, sharp doctor blade installed could be challenging for the three operators typically needed to accomplish the task. To install the new blade, dozens of bolts had to be loosened and then carefully re-tightened so that the blade did not have any wrinkles. The blade holder was worn from all the years of being carried in and out of the press so that, even on a good day, it was difficult to install the doctor blade without producing wrinkles in the blade. Assuming the blade was installed without wrinkles, often the blade would have wrinkles after the bladeholder was carried back and installed on the press due to deflection of the holder while being carried. Wrinkles in the doctor blade typically lead to poor metering and printed waste. Upgrades with this project provide new components with the ability to be able to perform blade-change operations on-press, in less than 10 minutes, and without having to use tools or deal with bladeholder bolts and their associated issues.
