Finishing Wood Window Blinds

curing a wavy finish in a flat line finishing system - March 17, 2000

by WOODWEB's Finishing Team:
John Buries and Bob Niemeyer

Q. I run a flat line finishing system for wooden blinds, and I'm ending up with a wavy finish......any ideas?.

A. John Buries responds: When you are flat-line flow coating or "curtain coating," there are a number of variables that can contribute to a flawed or wavy finish. First of all, creating a wall or curtain of paint that can be up to 52 inches in length and holds together in a continuous film means precision equipment and properly formulated paint. When you pass the piece to be coated through this wall at a high rate of speed any air or break in the curtain will show up as a flaw.

Usually waves or tiger stripes mean there is a variation of gloss caused by inconsistent film thickness.

Check the doctor blades for any nicks, scratches, or a build up of dried coating. Even a small flaw in the blades can create problems. You may not see a break in the film, but the application of inconsistent film thicknesses can create gloss variation across the panel. Here are a couple of things to watch for that will help keep your finish smooth and consistent:

  • Lacquer or paint being used for curtain coating is specially formulated. There is a delicate balance between viscosity, solids and evaporation rate of these coatings. These factors start to change almost immediately when the paint is run through the coater. You will have to continuously monitor and adjust the viscosity. Your coating supplier can give you the specifications and proper solvents to maintain proper viscosity.

  • Make sure the panels running through the curtain are not bouncing or vibrating from a faulty transfer belt or non-level surface. This can cause uneven application of wet film, creating gloss variations that appear as waves in the film.

  • A curtain or wall of paint can be very sensitive to outside air movement. Try directing a fan or create air movement around the curtain and see how much it distorts. Check for an unwanted breeze in the vicinity of your curtain coater and shield it from hitting the curtain.
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