Tests carried out by Heraeus Noblelight have demonstrated the effectiveness of combining infra red heaters with air knives in reducing the drying time of water-based coatings.
With the changeover from solvent-based to water-based coatings, in accordance with the VOC Directive, drying times in hot air circulation ovens have increased, resulting in reduced throughput. One way to ameliorate this situation, according to tests performed by Heraeus Noblelight (www.heraeus-noblelight.com/en/infrared-heat), 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, infrared 'boosters' 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 infra red source is significant. In particular, the tests showed that carbon medium-wave infrared emitters out-performed conventional short-wave ones and consumed up to 30 per cent less energy.
This drying performance can be improved still further by the addition of an air knife. Using an air knife supplied by ACI, it was demonstrated that exhausting the water-saturated air efficiently from the drying zone reduced drying times significantly. This is because there is not a build-up of moisture-laden air for the drying system to overcome. Consequently, energy is used more efficiently, again helping to reduce costs.
Air knives are particularly suitable for this drying application due to their ability to deliver accurately controlled air flows in terms of volume and velocity; air is delivered as a continuous, even curtain across the full width of product, and air knives can be produced in lengths to match the application.
These features are said to complement infrared's ability to dry coatings from the inside out, which eliminates skinning and blistering and ensures excellent surface qualities are achieved.