Powder Application

The most common way to apply powder coating materials requires a spray device with a powder delivery system and electrostatic spray gun. A spray booth with a powder recovery system is used to enclose the application process and collect any over-sprayed powder.

Powder delivery systems consist of a powder storage container or feed hopper and a pumping device that transports a mixture of powder and air into hoses or feed tubes. Some feed hoppers vibrate to help prevent clogging or clumping of powders prior to entry into the transport lines.

Electrostatic powder spray guns direct the flow of powder. They use nozzles that control the pattern size, shape and density of the spray as it is released from the gun. They also charge the powder being sprayed and control the deposition rate and location of powder on the target. Spray guns can be either manual (hand-held) or automatic (mounted to a fixed stand or a reciprocator or other device to provide gun movement). The charge applied to the powder particles encourages them to wrap around the part and deposit on surfaces of the product that are not directly in the path of the gun.

Corona charging guns, the most commonly used, generate a high-voltage, low-amperage electrostatic field between the electrode and the product being coated. Powder particles that pass through the ionized electrostatic field at the tip of the electrode become charged and are deposited on the electrically grounded surface of the part.

An alternative charging mechanism is a tribo charging spray gun. In such a gun the powder particles receive their electrostatic charge from friction which occurs when the particles rub a solid insulator or conductor inside the gun. The insulator strips electrons from the powder, producing positively charged powder particles.

Powder can also be applied by a spray device called a bell or rotary atomizer. Powder bells use a turbine that rotates in an enclosed powder bell head. Powder is delivered to the bell head and spread into a circular pattern by centrifugal force. The powder passes through an electric field between the bell head or an externally mounted electrode and either the grounded object to be coated or a counter-electrode positioned behind the bell head.

Use of oscillators, reciprocators and robots to control spray equipment reduces labor costs and provides more consistent coverage in many applications. Gun triggering—turning the gun on and off using a device that can sense when parts are properly positioned—can reduce over-spray, which results in lower material and maintenance costs.