How is it done — electrostatic spray?
The powder is applied with an electrostatic spray gun to a part that is at earth (or ground) potential.
Before the powder is sent to the gun it is fluidised:
to separate the individual grains of powder and so improve the electrostatic charge that can be applied to the powder and
so that the powder flows more easily to the gun.
Because the powder particles are electrostatically charged, the powder wraps around to the back of the part as it passes by towards the air offtake system. By collecting the powder, which passes by the job, and filtering it, the efficiency of the process can be increased to 95% material usage.
The powder will remain attached to the part as long as some of the electrostatic charge remains on the powder. To obtain the final solid, tough, abrasion resistant coating the powder coated items are placed in an oven and heated to temperatures that range from 160 to 210 degrees C (depending on the powder).
Under the influence of heat a thermosetting powder goes through 4 stages to full cure.
MELT, FLOW, GEL, CURE
The final coating is continuous and will vary from high gloss to flat matt depending on the design of the powder by the supplier.
Powder coating guns
There are at east three types of electrostatic guns in use:
Corona charging guns where electric power is used to generate the electrostatic charge. Corona guns are either internal or external charging.
Tribo charging guns where the electrostatic charge is generated by friction between the powder and the gun barrel.
“Bell” charging guns where the powder is charged by being “flung” from the perimeter of the “bell”
Not all powder is applied using guns. One system makes use of electrostatic tunnels.
How is color introduced?
Colour is added to powder coatings during the manufacturing process, ie before the powder reaches the powder coater. There is little that can be done to change the colour consistently, once the powder leaves the manufacturing plant.
Post time: Jul-28-2020