R & D
The lamp is the heart of a UV curing system. Important not to
forget, as the complete performance of your application depends on
this. On this page short about; UV Output,
Lamp-types, Lifetime and Choice of lamp type.
The output from a mercury lamp is divided into Heat and UV. The
amount of heat is app. 70% and UV the rest - 30%. The useful UV is
again divided into three areas - UV-A 315-380Nm, UV-B 280-315 Nm and
UV-C 200-280 Nm. Normally UV is the "curing power", but on
some older colours and special applications, heat or higher
wavelength (moving up from UV-C>B>A) is required. But just like the design of the mechanical system is determined
by your application, so is the choice of lamp-type.
types are merely Mercury lamps doped with different materials,
giving very different UV output. In Europe the most common used lamp
type is a standard Mercury. If you go to the far east it is an Iron
doped Mercury lamp. They both have the same amount in UV output, but the
Mercury has more energy in the low UV range (UV-C). Other types can
be used, normally for more specific applications and often as advice
from the ink/lamp manufacturer.
The lifetime of a lamp is determined by use. A standard Mercury
lamp loses 30% of UV energy after 2000 hours, an Iron doped last
only 8-900 hours, because of decomposition of the Iron. Lamp
lifetime is also determined by how many times it is ignited, as the
small particles from electrodes will contaminate the inside of the
lamp, which eventually will fail to ignite. Use of high frequency
power supply will extend the lifetime, as the particles tend to stay
(on the inside of the quartz) near the electrodes.
||It is seen that the difference in UV output is
in the UV-C region. The energy from the UV-C region has moved
up in UV-B and UV-A, on the Iron doped lamp.
As the UV-C is difficult to handle, easy to loose energy in
reflection and in air, the choice of an Iron doped lamp can be
For further information:
further information on lamp types: http://www.alpha-cure.com/metal-halide-lamps.htm
The reason of choice:
Choice of lamp depend also on your UV system. On poor UV systems the
most common reason for lamp exchange are two things. To narrow curing width,
caused by "black ends" - particles from ignition, and
secondly the cooling-air in non-water system will contaminate the surface of the lamp, blocking
out the UV light. In some cases the loss of UV can be 20-30%, after
300 hours of use. The typical colour thickness will also effect your
choice - as UV-C cures in the toplayer, the longer wave lengths UV-B/A, penetrates down into thick layers.
So the choice can be made from your UV system and your colour. An older
Transformer system, using unfiltered air, would probably gain from
using for example an Iron Doped Lamp as the lifetime will be short
in any case. A new closed system with clean filters, or water cooled,
will have a much longer lifetime, using a standard Mercury Lamp. But
again your Ink/varnish and thickness might require a special lamp