Hedson IRT PowerCassette EMBA 245 Mode D'emploi page 4

5. General information
5.1 Generals
How is heat transferred?
There are three ways to transfer heat:
1. Conduction
2. Convection
3. Radiation
Conduction means heat is transferred through the
contact of two solid bodies, from the one with the higher
temperature to the one with the lower - e.g. from a dry-
ing cylinder to a paper web.
Convection means that heat is transferred from one body
to another by means of an energy storage transport
medium such as hot air or hot gas. This method is used,
for example, in air dryers.
The third form of heat transfer, IR heating, means that
radiation emitted by a body is converted to heat when it
hits another body. This is the case when the sun transfers
its heat to the earth.
What is IR heating?
All bodies emit energy in the form of electromagnetic
radiation. There is a direct connection between the
temperature of a body and its ability to emit IR radiation.
When the body has a high temperature it emits short
wave, high intensity IR radiation.
Transfer requires no other energy storage transport me-
dium and takes place at a speed of over approx. 300,000
km/s.
The level of the product temperature depends on the
characteristics of the heat source (e.g. temperature, wave
length distribution and intensity) in combination with the
products characteristics (e.g. absorption, wave length
distribution and heat capacity).
IR radiation is the most efficient of all radiation forms in
the electromagnetic spectrum with regard to the transfer
of heat.
5.2 Drying of flexographic print
Previously there was not a great demand of extra drying
capacity within the flexographic print industry. The high-
water absorbency of uncoated liner was usually sufficient
to dry the print. Coated liner provides significantly higher
quality printing, but also has significantly inferior water
absorbency. It's normally necessary to drastically reduce
the speed of the printing press or to print in several
stages to prevent the print from setting off onto the next
printing station or stencil.
The short-wave IR energy effectively penetrates into a
print surface. The surface dries quickly "inside to out".
This gives a gentle drying process. As the IR energy is
distributed into the print and paper and not just on the
surface, as with conventional drying methods, drying is
rapid and intensive.
Using IR technology, you can effectively "freeze" the print
on the surface and in so doing, prevent the print from
bleeding out or reduce the degree of expensive pig-
ments that are absorbed into the sheet/web.
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5.3 Process ventilation
Air supplied to IRT PowerCassette cools the IRT-lamps.
The heated air is released in the front of the IRT Power-
Cassette through the gaps between the reflector cover
glasses with high speed and thereby functioning as an
air knife. This process allows you to break up the mois-
ture saturated air layer that forms closest to the printed
surface and thus making the drying process quicker and
more efficient.
It is important to clean the protective glass in IRT Power-
Cassette regularly. Heavy staining impairs IR-transmission
giving rise to increased energy consumption at the same
time as the risk of internal overheating of the IR lamps
and heat modules is increased.
5.4 IRT Heating module
The IRT heater consists of a closed, gas-filled IR-lamp and
an aluminum reflector body fitted with a fixed, replace-
able pure gold coated reflector foil. The IRT-lamp is
screwed into a special lamp fitting using two screws. The
IRT-lamp as well as the reflector foil is easily replaced.
The IRT-lamp's maximum filament temperature is approx.
2,200°C. The low mass of the filament means that it takes
about 1 second from the start time to full output and
that it cools, after being switched off, to approx. 10% of
the original output in the same time. The outer tempera-
ture of the IRT-lamp is normally lower than 600°C. The
temperature of the lamp and thus the heat emission can
be continuously changed from room temperature to
maximum temperature in seconds.
The IRT-lamps are protected against mechanical effects
by being enclosed in the reflector body. This means that
the IRT-lamps do not heat each other, which results in a
significant increase in the lamp's service life.
The IRT-lamp has a guaranteed service life of at least
5,000 hours at nominal voltage. The normal service life is
around 10,000 - 15,000 hours.
The reflector foil has practically an unlimited service life,
assuming that it is not damaged or exposed to heavy
soiling. The gold foil has an extremely high reflection
capacity for heat radiation (98%) and does not oxidize.
The IRT-lamp is easily changed from the front by loosening
two screws. Thereafter a new lamp can be fitted in seconds.
5.5 IRT PowerCassette
The IRT PowerCassette consists of an IR-section with the
IRT-heaters, and a cooling air section with duct. The IRT
PowerCassette is equipped with external cooling fan,
and air will come from outside.
The IRT PowerCassette is easily dismounted for service.
The IRT PowerCassette is supplied with a protective front
of quartz glasses.
IRT PowerCassette can also be supplied with a built-in ex-
haust air unit, which removes the heated cooling air after
being directed towards the web.
The IR-section consists of heaters with exchangeable gold
reflector foils and equipped with IRT-lamps. The heaters are
electrically connected with heat-resistant cable. The cassettes
temperature is monitored by temperature switches, which will
prevent overheating if, for example, fans should stop.
The cooling air cools the lamps and heaters and prevents
gas and dirt to reach the heaters.
EN
196397 rev 3