Replies

1. 
   Kevin | Jan 03, 2004 09:13am | #1

   Allison,

   It sounds like dry spray to me. It could be caused by either using too much atomizing air or not enough thinner, or a combination of the two. Or you could be spraying too far from the surface of the box. That would yield the same end result as using too much atomizing air - partially flashing the lacquer before it hits the box.

   Spraying inside corners is always dicey with equipment that uses air to atomize. I've heard it referred to as the "Caged Faraday Effect." What happens is the air movement causes turbulence when it enters an enclosed area such as a three-sided inside corner or even some two-sided corner (such as the inside corner of a right angle, like on your box lid). The atomized lacquer swirls around instead of laying down on the wood like it's supposed to.

   I would suggest doing what I like to call a two-step lacquer finish. I spray on a medium wet coat of lacquer, give it anywhere from a one to five minutes to flash (depending on how much retarding solvent is being used). Then I spray the entire thing again with a slightly wetter coat. The first coat won't have completely flashed off and this will allow the second coat to flow right into it. It's a good way to get enough lacquer to flow out in problem areas without risking runs or sags because the partially flashed first coat holds the second coat on without sagging. This is particularly effective with a more heavily reduced lacquer. I would also reduce the lacquer more.

   Which Sherwin-Williams lacquer are you using? I use SW clears almost exclusively and really like them a lot. I've found that reducing with MEK works very well because the MEK changes the surface tension of the lacquer particles - causing them to flatten out much better when they hit the surface. Just that one change alone might go a long ways toward mitigating the dry spray problem. In my experience the combination of reducing with MEK and a retarder along with the two-step process virtually eliminates dry spray and over spray... even in situations where one would expect to have left at least some overspray.

   That's a very attractive box, BTW. The gloss with that rich color is spectacular.

   Regards,

   Kevin

   The Independent Voter.com

   "Rather fail with honor than succeed by fraud" - Sophocles.

2. 
   Tao | Jan 03, 2004 08:41pm | #2

   Check your fluid pressure.  With the atomizing air cut off and the fluid knob open about three turns, the coating should go out about 12 to 18 inches before it starts to curve down.  Also check your film thickness with a thickness gauge you should be able to get fo free from your coatings supplier.  Coating thickness immediately after spraying should be a minimum of .003 inches in order to flow out properly, and you can go up to .005 on larger surfaces.

   Check your atomizing air pressure with the trigger pulled against that recommended by the gun manufacturer.

   Too much air, or too little fluid is the usual cause of what you describe, but from your description is could also be clumps of flattener that havent been broken up enough in mixing. Always strain your lacquer through a fine mesh cone strainer or equivalent before spraying.

   You are correct not to overthin.  Most modern coatings work best when sprayed at or close to package consisntency.  Overthinning leads to sags and runs and other problems.

   Michael R