Promoting Resource Efficiency in Small & Medium size ... - UNEP

• Clean air conditioning and refrigeration condenser/evaporator
coils every three months
• Check the refrigerant charge and fix leaks if necessary
• Regularly clean or replace air filters on ventilation and heating/
air conditioning equipment; clean grease traps on ventilation
equipment
• Check freezer and walk-in seals for cracks and warping; replace if
necessary
6.4.6 Production materials
Cooling lubricants 58
The metal working process creates heat and friction during processes
such as cutting, turning and grinding, which limits the tool life.
Conventional coolants are emulsions of oil in water (approximately 5
to 7% of oil). Coolants take heat away from the tools and the material
being processed.
The useful life of coolants is limited by a variety of reasons:
• Coolants break down because the organic molecules decompose
by heat or by the activity of bacteria.
• Coolants accumulate foreign substances including tramp oil,
swarf, dissolved minerals, and/or dirt from the process
The following hints will help to increase the useful life of coolants:
• Use de-mineralized water to prepare the coolant. This prevents
the introduction of salts. The minerals present are not evaporated
and accumulate in the sump increasing the concentration of
minerals in the coolant.
• Anaerobic bacteria grow in environments lacking oxygen. They
feed upon the coolant and produce noxious byproducts such as
hydrogen sulphide. This is commonly referred to as the ‘Monday
morning’ odour. It is possible to prevent the growth of anaerobic
bacteria by agitating or aerating the sump over periods of time
when the process is not in operation, including weekends.
• A process to remove surface oil and solids is also necessary for
long coolant life.
• A variety of filter media, filtering devices and oil skimmers exist
to remove impurities including swarf and tramp oil from the
coolant.
• When coolant is changed the sumps should be cleaned
thoroughly.
• Metal swarf and tramp oil may be able to be recycled. Oil may
also be sold as a fuel.
• Separation of cooling lubricants from metal parts can be done
effectively using centrifuges and vibrating screens.
Painting
The required fluid pressure in a conventional spray gun is based on
delivering a certain amount of paint through the gun. The best way of
setting the correct pressure is the following: atomising air is shut off and
the pressure is set initially to about 0.5 pounds per square inch (psi).
The atomising air is adjusted to zero and the paint gun is triggered.
When the stream of paint leaving the gun tip is about 30 cm long, the
fluid pressure setting is adequate.
Higher pressure will result in heavy paint flow and large particle size.
In general, the fluid pressure should not be greater than 1.5 bar. If more
pressure is required, a larger paint gun tip is probably needed.
It may be necessary to reset the guns and pot pressure several times per
day if the temperature changes. The same is true when new or different
batches of paint are used.
One way to avoid changing conditions is to use heating bands on paint
pots. Not only will the guns remain set longer, fewer solvents will be
needed for thinning. Heat can be used instead of solvent to provide
paint thinning with some types of paint.
Today many paints are sold as water-based paints. Water-based paints
use water in place of some or all of the solvent used for thinning and
dispersion. Many water-based paints also contain increased content of
solids resulting in greatly increased coverage. In addition water-based
paints are comparable to solvent-based paints in performance. Some
are as good or better than solvent-based paints in adhesion, scratch
resistance, abrasion, salt spray resistance and UV resistance.
The skill of the person operatingthe spray gun has a tremendous effect
on transfer efficiency and coverage. Often painters have not been
properly trained or do not have the correct tools such as measuring
equipment or high efficiency spray equipment. Basic training for
operators can reduce problems greatly.
• Avoid clearing the gun when painting – triggering the paint gun
when the gun is pointed at the floor or ceiling or anywhere but
the part being painted wastes paint.
• Paint guns should be moved parallel to the surface and not by
moving the paint gun in an arc which will cause the ends of the
stroke to be too far away and too close in the middle.
• Avoid too much or too little overlap; a 50% overlap pattern is
usually recommended to avoid heavy and light areas.
• Avoid thick coating; the applied thickness should be
checked by measuring and comparing against the suppliers
recommendations.
• Avoid using incorrect fan pattern; a wide fan pattern is great
for wide open spaces but it is not so good for painting narrow
edges, because a narrow edge will occupy only a small portion
of the fan. The rest of the paint is overspray.
• Avoid increasing the pressure above the recommended
setting; increasing fluid and atomising pressure well above
the recommended setting is common and the result is usually
wasted paint.
• Avoid holding the gun at an angle; spray guns should be pointed
perpendicular to a surface as holding it at an angle results in some
or the entire spray pattern being too far away from the surface.
The paint booth is important from a worker exposure, quality, and paint
usage perspective. A paint booth is intended to collect overspray paint
and to remove solvent fumes from the work area. If painting is done in
an area with no ventilation, fumes will build, resulting in a fire and health
hazard. Also, overspray paint will settle on newly painted surfaces causing
quality problems. Paint booths also eliminate drafts of air that could carry
paint away from the workspace and onto neighbouring cars and buildings.
It is important to provide make-up air for the booth. If a booth exhausts
100 m³/min, then an equal amount of air must be brought into the building
to avoid negative pressure situations. Insufficient make-up air will result
in reduced flow through the booth eliminating the booth’s benefits.
Use a washing machine to clean guns.
58) http://www.p2pays.org/ref/01/00072.htm
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