UV Safety:
The spectra available for ultraviolet curing and
drying is quite varied. Coatings, inks, and adhesives
may
be composed of formulations that require strong
UV intensity of various wavelengths. Longwave ultraviolet
radiation (320-420 nanometers) is considered most
practical. Shielding is absolutely mandatory. Medium
pressure UV lamps radiate harmful UV radiation
that
can cause serious burns to skin and eyes. While
thermal burns are felt immediately, UV burns are not
felt
for several hours. Short exposure to lamp radiations
can cause severe burning of skin and eyes. UV burn
of the eyes affects the cornea that takes several
days to heal. UV burn is identical to 'Welder's
Burn' and will feel like sand in the eyes that cannot
be
washed out. The discomfort is transitory. Extreme
caution must be taken - high power UV radiation
can cause blindness. Exposure to UV radiations, of
only
limited time, will evoke erythema on normal skin.
Such erythema is transitory and will not produce
blistering, nor tanning, as only a small amount
of radiation penetrates the Malpighian layer. Extreme
caution must be taken - high power UV radiation
can
cause severe burns to the skin. Shielding material
can be of cloth, glass, plastic, wood, or metal.
As infrared energy is generated along with intense
visible light, fireproof as well as opaque material
that does not degenerate under UV radiation must
be utilized. Direct light from the UV processor
should not be visible to the operator nor other personnel.
Bounce (reflected) light should be minimized and
avoided. Total shielding with openings minimized
for product entrance and egress from the UV processor
should be incorporated into processor design. Reflective
surfaces coated with black UV absorbing paint reduce
reflected UV radiations. Protective clothing and
safety spectacles should be worn if optimum shielding
cannot be attained.
Thermal Safety:
Infrared energy, an inherent product of the arc utilized
to create UV energy in UV processors, can cause
overheating of processor components when adequate safeguards
are not incorporated into the UV processor design
and application.
Cooled heat sinks should provide protection to
the press, conveyor, and other process components
in or
near the UV processor. The cooling system should
be carefully designed and properly maintained.
In air-cooled
systems, filters must be properly cleaned or replaced
on a maintenance schedule related to powder, dust,
and dirt conditions where the UV processor is operating.
Halon #1211 fire extinguishers are to be used in
the event of fire. CO2 fire extinguishers with
dry chemical
or water are NOT recommended. If a fire occurs, all
residue of damaged substrate should be removed from
curing area. Soot and ash must be cleaned from lamps
and reflectors before re-start. Investigation to
determine the malfunction causing the fire is most
important.
Correction must be made to eliminate re-occurrence.
UV processor electrical systems should be serviced
only by qualified electricians.
Ozone Safety:
Triatomic oxygen or ozone (O3) is the only by-product
of the UV lamp. It is formed by oxygen being exposed
to 254nm wavelengths of UV energy. Ozone can be
effectively eliminated in the processing area by exhausting
air
of the cooling system of the UV processor to outside
the building. Such exhausting has no danger as the
hot gas is very unstable and breaks down to oxygen
rapidly in ducting.
UV Lamp Handling:
Fused quartz (Silicon di-oxide, SiO2) with a high
melting point and excellent UV transmissivity is used
in
fabrication of UV processor lamps. A 22 x 25 mm diameter
tube with wall thickness of 1.0 to 1.5 mm used with
tungsten electrodes sealed into each end is typical.
Lamps are manufactured from 1" to 180: arc length.
Quartz is very fragile and special cushioned packaging
is utilized for safe transportation. Upon receiving
new lamps the carton should be opened fully so the
lamp can be lifted out of the packaging with no twisting
or pulling. Unpacking should take place in an area
large enough to eliminate the possibility of inadvertently
striking lamp against walls, pillars, pipes, beams,
or machinery. Lamp must be wiped with alcohol before
placing in service. Bare skin contact with the quartz
envelope must be avoided. Compounds from the skin
when heated on lamps operating at 600o to 850oC will
form permanent etching (devitrification) on the quartz
surface, decreasing UV energy transmission. A contaminated
lamp eventually will overheat causing premature failure.
UV Processor Maintenance:
Lamps and reflectors must be clean at the time of
installation and maintained so the UV energy generated
can reach
the ink or coating. Since the UV processor is an
optical system, all types of dust, powder, grease,
smoke, and coatings must be cleaned from the lamp
and reflectors. Electrical fittings must also be
kept clean to prevent arcing between fitting and
lamp ends. Dirty reflectors will reduce cure rates
and increase temperature. The reflectors return approximately
50-60% of lamp energy. Overheating from a dirty condition
can cause warping, possibly reducing electrical spacing,
and cause a short of the arc to ground. A mild detergent
and distilled water mixed at a ratio of 1¼ ounces
to 1 gallon makes a good cleaning solution. After
cleaning, rinse with clear distilled water and wipe
or polish with a clean cloth. Grease or ink on the
lamp or reflectors will require washing with a solvent
rather than cleaning with a detergent solution. Clean
alcohol or ammonia and distilled water can also be
used for cleaning. The use of steel wool, emery paper,
or abrasive powders is not recommended for cleaning
lamps or reflectors.
CAUTION: Ultraviolet lamps emit radiation, which is
harmful to eyes and skin. Great care should be taken
to insure that personnel are not exposed to direct
or reflected light.
PDF version to be attached (Client will
provide using DB’s template
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