August 2019 55
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Powder Coating
and similar symbol is used in electronic
circuits. The other common use is when
referring to “earth grounding” that
we find in domestic or infrastructure
electrical distribution systems. Electronic
ground and earth ground have become
interchangeable in a confusing manner.
It would be incorrect to think of earth
ground as an electrically negative point.
It is simply a void, which will soak up
either a negative or positive charge in
order to create a neutral state. In tribo
spray coating we are dealing with static
charges. In the tribo system the powder
is stripped of its electrons, leaving it
positively charged. These positive ions
are attracted to the grounded target
object. Grounding in this instance means
earth grounding. Earth ground can be
considered an electrical void of charge,
and this is why both Positive powder ions
from a tribo gun or Negative powder ions
from a corona gun are both attracted to
earth ground. The charge rules do still
apply: Positive is attracted to negative,
and negative to positive. Like charges
repel each other, but both positive
and negative charged particles will be
attracted to the void of earth ground as
the electrical potential attempts to equal
out to zero.
Masking
There are some places you do not want
powder, such as threaded holes or precision
bores. These areas can be masked off with
a high temperature Kapton masking tape,
photo 11.
Silicone tapered plugs can be inserted
in holes too. Plug sets are available online
but are pricey. Good tapered plugs can
be made by letting silicone sealant cure
inside the cartridge nozzle. A plug is
visible in photo 12.
Kapton tape is not all that flexible and
can end up where it is not wanted during
curing. Some users suggest that it be
removed at first fusion, but before full
curing takes place. A scalpel works best
for trimming.Rack and Oven
There are two remaining components
required for a powder coating system. They
are the rack and oven which enable you to
effi ciently carry out the process, photo 13.
Looking on the web, a search for “Mini
oven” or “Compact Oven” shows a variety
on off er from about £20. They have only a
9 or 10 Litre volume, so coating and curing
large parts is diffi cult. But they do a good
job for small parts.
The circular element of our budget line
domestic fan oven burned out a couple
of years ago. With powder coating on the
“future projects for the workshop” list, I
kept it. YouTube showed that the element
replacement could be done in under 5
minutes. A new element was only £8 on
Amazon. This oven has a volume of 20010 11
Earth grounding rod and cable connection.
Kapton tape is used to mask threads.12
Internal bores are covered with Kapton tape
trimmed fl ush.