With the change-over from solvent to water based coatings, in accordance with the VOC Directive, drying times in hot air circulation ovens have increased, reducing throughput. One way to ameliorate this situation, according to tests performed by Heraeus Noblelight, is the introduction of infra red dryers just before the main drying oven. By raising the temperature sufficiently to achieve water evaporation before entry to the drying oven, IR ‘boosters’ are said to make it possible to attain time savings of up to 50 per cent compared with conventional drying ovens.
The tests carried out by Heraeus Noblelight also demonstrated that the choice of IR source is significant. The tests showed in particular that carbon medium wave IR emitters out-performed conventional shortwave ones and consumed up to 30 per cent less energy.
This drying performance can be improved still further, it is claimed, by the addition of an AirKnife. Using an AirKnife supplied by Air Control Industries, it was demonstrated that by exhausting the water saturated air efficiently from the drying zone drying times are reduced significantly. This is because there is no build-up of moisture laden air for the drying system to overcome. Consequently, energy is used more efficiently, again helping to reduce costs, says Air Control.
AirKnives are particularly suitable for this drying application due to their ability to deliver accurately controlled air flows in volume and velocity; air is delivered as a continuous even curtain across the full width of product; and they can be produced in lengths to match the application. These features are said to complement infra red’s ability to dry coatings from the inside out. This eliminates skinning and blistering to ensure excellent surface qualities are achieved.
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