Powder coatings are usually supplied to the bonding facility in pre-weighed bags directly
from the mills or storage area. Therefore further pre-weigh shouldn’t be required provided
bonding is carried out in multiples of the base bag weights. Aluminium pigment will be
normally supplied in metal drums.
Explosion prevention during pre-weigh is achieved primarily by control of dust
concentration and ignition sources. Therefore reliance is placed on careful handling and
use of efficient dust extraction to prevent dust emissions.
Good housekeeping in the pre-weigh area is necessary to prevent accumulation of dust
layers and risk of secondary explosion. A 1mm thick dust layer can be raised to a
flammable cloud if disturbed. Operators should wear anti-static footwear, the floor should
be suitably conductive, or a stainless steel earthed plate should be provided for the
operator to stand on during powder handling operations. The weigh scales themselves
should be protected to IP65 as a minimum, and the use of any non-enclosed electrical
equipment such as 240/120 V sockets, light fittings etc., should be avoided near to any
area where aluminium or powder coating is being handled.
In terms of pre-weigh container specification for aluminium powders, an earthed metal
container should ideally be used and the aluminium should be weighed from its original
metal container into it. The original metal container would also need to be earthed during
weighing. If only small quantities of aluminium are involved <5kg, it would be acceptable to
weigh into a plastic bag, provided that the operator carefully places the aluminium pigment
into the mixer and that he didn’t shake the plastic bag afterwards. The plastic bag should
be as small as possible and of a heavy-duty type. Bags made from anti-static polythene
Weigh scoops should be made from stainless steel and should also be earthed. A way of
achieving this would be to attach the scoop to a flexible wire, connected to earth. This way
the portability of the scoop is maintained. With weights greater than 5kg an earthed metal
container should be used to load the mixer or screw feeder.