This is a frequent question. In upcoming newsletters we will be examining the different aspects of the coating and gun set-up which affect having or not having orange peel.
First, you should not expect a smooth finish when spraying industrial coatings or latex house paint with HVLP guns. Why? Answer: High solids or emulsions formulas are very difficult to atomize with just 10 psi of air pressure from an HVLP gun. These coatings were designed for spraying with airless equipment or conventional air spray guns (coating reduced) for small jobs.
Assuming you are using a coating that is designed for a smooth finish and designed to be atomized with HVLP spray technology, we will discuss how the coating flow rate will affect the orange-peel. Just as industrial coatings are difficult to atomize with HVLP, so is excessive coating flow rate--both in volume and FPM exiting a HVLP gun with 10 psi of air pressure. Ideally, the flow rate on a pressure feed gun should be set without air to the gun and with full trigger travel resulting in 8” to 10” in length of fluid stream. This fluid stream is set shorter or longer by adjusting the air pressure in the pressure pot. The flow rate can be fine tuned by sizing the fluid nozzle orifice size for more or less coating. Secondly, a coating exiting the HVLP gun at 60 FPM versus 1200 FPM is easier for the 10 psi to keep up with and properly atomize the coating.
Finally, turn off the incoming air and pull the trigger of your pressure feed gun. If the stream is measured in yards not inches you should see an improvement in your finish by reducing your coatings’ flow rate and FPM of volume.