Thanks, Mike
Wisconsin

Hi Mike,
IR for a clear coat is tricky business. IR works best and most completely when the coating contains a pigment. With clear coats, here’s what happens: the dry powder absorbs heat from the IR until it melts. It then becomes transparent and essentially stops absorbing much more radiant energy. I suspect that the IR-cured sample is partially cured and hence the cracking.

If the substrate was a dark color, it would absorb more IR and affect further energy absorption, and hence, cure. However, clear coats are typically applied to bright metallic surfaces, which reflect rather than absorb IR energy. A good way to check is testing solvent resistance. Rub each sample with a rag soaked with acetone, MEK, or lacquer thinner. This will give you an idea of degree of cure. Let me know what you find.

Kind regards,
Joe

John
Iowa

Hello John,                                                                                                                                                                                                                                              Particle size is critical for your end use. In fact, everything associated with your powder application system is critical. Let’s tackle the particle size issue first. You should specify a particle size distribution that is somewhat narrow, avoiding a high concentration of fines and coarse particles. On the low end, you want to have no more than 7% of your particles less than 10 microns. On the coarse side, you want nothing over 100 microns. This will give you a median particle size of roughly 35-40 microns.

Keep in mind that specifying particle size is tricky. Powder coating particle size fluctuates within a range during its production. Singular data points for a large batch of powder coating can be misleading. It is best to require statistical information for the batch, not just an average on these three critical parameters.

Other application parameters are equally important. Next on the list is ensuring that you have an adequate ground. You should have no more than 500 megohms resistance from the part to the ground – less is even better. This means you need to keep all connections (hooks, swivels, etc.) and contact points clean. Build-up not only hurts powder penetration, but it also can create a dangerous build-up of current that will eventually arc. Arcing can ignite a powder coating cloud with dire consequences.

Powder conveyance parts need to be clean and dry. This includes hoses, internal gun parts, powder venturies, and pick-up tubes. Regular cleaning will ensure consistent flow of powder from the fluidizing hopper to the gun tip. Speaking of gun tips, these need to be cleaned regularly to avoid excessive build-up and subsequent impairment of corona ionization.

Fluidizing hoppers need to be kept clean, dry, and properly maintained. The porous plate on the bottom of the hopper should be cleaned regularly with dry, oil-free compressed air. A combination of a refrigerated air dryer and air/oil separation filters must be in place and be regularly maintained. It's also very wise to keep meticulous logs of data for the powder you use and the application system performance. This helps you keep track of what works and provides useful data when troubleshooting. I hope that this helps.

Best regards,
Joe

Best regards,
Joe