There is no set time period to use in determining when to replace a bar. The way the bar is used and the materials that the bar is used with will determine the frequency of replacement. The specific requirements of the final drawdown are also key in determining the useful life of the bar.
If the bar is showing any gouges or chips in either the edge of the blade that passes over the paint or on the flat part of the blade that makes contact with the drawdown chart the bar should be replaced. Both of these conditions will result in a non-uniform drawdown from edge to edge or at a set point along the length of the drawdown. Even a slight variation in low mil thickness draw-downs used to determine contrast ratio could result in unnecessary batch adjustments.
Wire Wound Rods
Keeping wire wound rods clean is very important. The rods are difficult to clean, and the more that they are used the more that the spacing between wires is filled with dried material. Vigorous scrubbing with a brass brush and the appropriate solvent may remove the dried paint but may also cause burs on the wire that interfere with a smooth pull of the rod on the drawdown card. Soaking them between uses in an appropriate solvent may help prevent some of the buildup of dried material.
Jim Roberts is a Technical Support Manager at BYK-Gardner USA, Columbia, MD.
More Information on Film Application
For more information on Film Applicators, visit this website.
For more information on Automatic Film Applicators, visit this website.
For more information on Drawdown Charts, visit this website. Or visit our June 2014 and July 2014 blogs on Drawdown charts.
Video: How to do a drawdown