Electrostatic Powder Coating

andrewfei

Electrostatic Powder Coating
Monitoring Moisture in a Coating System’s Compressed Air Supply

For decades, the electrostatic powder application process
has been used to finish metal parts. Major appliances such
as washers, dryers, and refrigerators have been powder
coated for more than 25 years. The cost savings from
reduced waste (high transfer efficiency) and the durability of
the finish make powder coating the finish of choice. This
finishing system is also popular for automotive components
and furniture.
One of the benefits of powder coating systems is the ability
to reclaim nearly all of the oversprayed powder. The ratio of
coating material applied to an object divided by the amount
of coating used is called transfer efficiency. Through a
reclamation system, the electrostatic powder application
process achieves transfer efficiencies near 99 percent. A
conventional “spray gun” using liquid paint can have
transfer efficiencies as low as 30 percent. Another
advantage of the electrostatic powder coating process is the
durability of the finish. Although the texture is not as
smooth as many liquid paints, powder coatings provide an
extremely durable, scratch-resistant finish.
The coating applied during the electrostatic process is
typically an organic powder. As the powder is sprayed out
of the applicator, it travels through an electrostatic field.
Parts targeted for coating are typically grounded by hanging
them from an overhead conveyor. The static charge in the
airborne powder is attracted to the part. Enough residual
charge remains on the powder to prevent the powder from
falling off. The part continues along the conveyor line into
an oven. The powder coating melts, flowing into a resilient,
color-fast coating. A large volume of parts can be coated if
the conditions within the system are properly monitored and
controlled. In any continuous coating application, large
quantities of powder must course through the entire system
process achieves transfer efficiencies near 99 percent. A
conventional “spray gun” using liquid paint can have
transfer efficiencies as low as 30 percent. Another
advantage of the electrostatic powder coating process is the
durability of the finish. Although the texture is not as
smooth as many liquid paints, powder coatings provide an
extremely durable, scratch-resistant finish.
The coating applied during the electrostatic process is
typically an organic powder. As the powder is sprayed out
of the applicator, it travels through an electrostatic field.
Parts targeted for coating are typically grounded by hanging
them from an overhead conveyor. The static charge in the
airborne powder is attracted to the part. Enough residual
charge remains on the powder to prevent the powder from
falling off. The part continues along the conveyor line into
an oven. The powder coating melts, flowing into a resilient,
color-fast coating. A large volume of parts can be coated if
the conditions within the system are properly monitored and
controlled. In any continuous coating application, large
quantities of powder must course through the entire system
smoothly and without interruption. Large hoppers store bulk
quantities of the powder for transfer into the system. They
typically use compressed air to fluidize the powder,
simplifying its transfer. A venturi pump, also powered by
compressed air, usually transfers the fluidized powder into
the system.
Fluidized bed hoppers, venturi pumps, and other pneumatic
components of a powder coating system must have a dry
compressed air supply to function properly. If the
compressed air were to become saturated with water, wet
powder would clog the entire system in minutes, forcing the
entire coating system to grind to a halt.
It's very expensive to shut down an entire system to find one
faulty compressed air dryer. Many powder coating systems
use refrigerated air dryers, making them perfect candidates
for an rh-plus analyzer, or MMR 30 DewPro transmitter. It
would monitor the moisture content of the air at the outlet.
Systems using a desiccant air dryer would benefit from a
HygroGuard, or MMY 30 DewPro transmitter to monitor the
trace moisture content of the compressed air lines. Installing
either of these General Eastern systems to monitor air quality
in an electrostatic powder coating system provides an early
early warning system at a small price.