Ask the Expert Question-and-Answer Archive

by Ron Joseph

January, 2005

Solvent Popping in MDF Wood Finishing

Q. My company paints MDF kitchen panels in two pack polyurethane and this process is performed in a full downdraft spray booth providing 0.4m of air flow per second. The panels are painted with enough flash time between coats then placed in a drying rack with 14 shelves a side and gap of 100mm between each shelf. 1/3 of the upper rack is fine and clean where as any thing below ends up with solvent pop. I am thinking that air flowing across the panels horizontally would be better than direct vertical air flow. What do you think?

It seems that you have confirmed that air flow will solve the problem. After all, the panels near the top perform well but those lower down don't. Your next step should be to try to replicate the air flow on the lower racks. You might need to install a floor fan that forces air over the racks, and it might also be a good idea to insure that the air is warm. You don't want to blow cold air over the coating, especially if you operate under humid conditions. Condensation of moisture on the coating can cause blushing and then you will be trading one problem for another.

Finally, be aware that the fan or blower must be explosion proof to prevent a spark, fire or explosion if the concentration of the solvent vapors is near the LEL (Lower Flammable Limits).

Please get back to me and tell me of the additional air resolves the problem.

Best wishes,

Ron Joseph