In order to produce bonded metallic powder coatings, a process is required that will heat
the powder to its softening point, usually 45-550C. The heat input will be achieved by a
combination of mechanical energy from high speed mixing tools, from a hot water jacketed
mixer, or a combination of the two. The mixing speed will be variable, as generally high
speed is required to heat up the powder within a reasonable time scale, but low speed is
preferable for mixing in the pigment and achieving the adhesion. Low speed minimises
damage to the pigment structure. When bonding is achieved, it is important to cool the mix
as quickly as possible to avoid excessive agglomeration and lump formation. In the
extreme, bonded batches can completely solidify in the bonding mixer if overheated or not
cooled fast enough. Cooling will be achieved either by introducing chilled water into the
bonding mixer jacket, or cooling in a separate cooler mixer
The amount of time required to clean the mixer/cooler combination shouldn’t be
underestimated and it may be necessary to remove the mixing tools to clean properly.
Solvent may be needed to remove ‘stubborn’ stains. Use of polished stainless internals
can help reduce build up and cleaning time, although care must be taken not to scratch the
polished surface as this will promote adhesion and extend cleaning time.
Use of internal cooled mixing tools can help prevent adhesion to the tools. However, experience has
shown that use of cooled tools extends the heat up time and introduces the risk of water
ingress, which is not recommended with aluminium present. Also, cooled tools are more
complex to remove for cleaning. 'Use of cooled tools therefore is not a good option for
the Bonding process'.