In a basic system (without a reflector), only 45 % of the UV radiation reachethe substrate.
The presence of efficient reflectors in a UV dryer enables the remaining 55 % of the UV energy emitted by the lamp to be recovered. This explains the reason why manufacturers of UV equipment have to select materials and design equipment with very high reflective power. Aluminium, one of the most accessible and reflective materials, allows around 90 % of UV radiation to be reflected. Very sensitive to high temperatures, the aluminium surface must be specially treated to ensure it remains efficient over long periods.
Influence of the geometry of the reflectors and the surface
Depending on the manufacturer and the application area, UV dryers are generally equipped with parabolic, elliptical or specific geometry reflectors. Reflectors also differ by the type of cooling system employed (air or water). The base of the reflector is an extruded section with good heat resistance properties. After polishing the reflectors, which allows a degree of surface roughness adapted to the reflection of UV energy, a layer of pure aluminium is deposited under vacuum, then covered by a protective quartz layer. The purity of the aluminium used is vital for optimal reflection of the UV energy.
Different geometries of UV reflectors – Source IST®
Over the last few years, reflectors with a specific coating have been developed, including dichroic reflectors, the reflective layer of which is composed of around 60 different metal oxide layers. Dichroic reflectors, or cold mirror reflectors, reflect UV radiation in the range from 200 to 450 nm with around 98 % efficiency, while enabling infrared energy to be transmitted (via the dichroic coating) towards the base section, which is itself water cooled. Although air cooling is still the most widely used process in UV systems, it can also be combined with water cooling.
The temperature needs to be controlled to maintain the lamp at a stable temperature so that it operates at maximum efficiency. Temperature sensors are installed in the dryer and communicate with the control system to ensure that the correct volume of air is being drawn through the system at all times. Very often, the system is designed as a closed circuit so that the volume of circulating air is continually adjusted as a function of the temperature measured in the UV system.
Reflectors are key elements of the UV dryer. Correctly maintaining the reflectors and regularly changing the lamps are therefore vital to ensure optimum efficiency of the dryers.
It often happens that the lamps of dryers are changed whereas the lack of efficiency in fact stems from an incorrectly maintained reflector.
TURS® cold mirror reflector technology®
A new generation of cold mirrorreflectors has been designed toincrease the efficiency of dryer systemsin a significant manner. Thesereflectors enable an increase of around
20 % in the quantity of UV energy reachingthe substrate for the same power consumption compared to conventional reflectors. The result is increased production output and savings in energy consumption.
How they work
IST’s new URS® reflectors combine the advantages of aluminium and CM (cold mirror) reflectors. Only UV energy is reflected, while infrared energy (i.e. heat) is transmitted via the dichroic coating to the extruded section, which is efficiently water cooled.
Thanks to this new reflector technology, it is now possible to attain production rates with 140 W/cm lamps equivalent to those obtained previously with 200 W/cm lamps.
URS® reflector – Source IST®
These new URS® reflectors can be adapted to the desired geometry.
This technology offers advantages notjust in terms of energy savings, but also in reducing infrared radiation (which heats the substrate) and therefore helps to reduce substrate deformation.
Individual adaptation of reflectors
The advantage of this new technology is that it can be adapted to meet the specific needs of clients (modification of the geometry, coatings, etc.), thereby considerably simplifying handling and cleaning.