While the reduction of solvent emissions within VOC guidelines is an important goal throughout industry, it has been challenging for drying oven suppliers. Competitive pressures in the coating sector demand that energy costs are reduced and finishing times are shortened. A conversion from solvent-based lacquers to powder coatings requires a completely new plant. Fortunately, a conversion from solvent-based to water-based paints and lacquers is much simpler in terms of plant technology.
Conventionally, lacquers and paints have been dried and cured using hot-air ovens. Because water takes much longer to evaporate than solvents, however, the conventional hot-air ovens may not be suitable. For example, if the drying length must remain the same because of space limitations, then to dry water-based coatings using the same hot-air oven, the flow speed through the oven must be reduced to increase dwell time. This can lead to production bottlenecks, which no coater wants.
A practical solution to this problem is offered by infrared technology. Infrared emitters and systems, because of their compact design, easily can be retrofitted within existing hot-air drying systems.
Carbon Infrared Emitters Reduce Energy Consumption
The wavelength of the infrared radiation has a significant effect on drying water-based coatings. Water evaporates quickly when irradiated with medium-wave infrared. This is because, in contrast to very short-wave near infrared, the medium-wave radiation is absorbed efficiently by water and then directly converted into heat. Because of this characteristic, carbon emitters have been developed specifically for medium wave.
Infrared emitters incorporating carbon technology are capable of providing power densities up to 150 kW/m² and short response times. Carbon infrared emitters combine medium-wave radiation with high power densities to accelerate the drying of water-based paints and lacquers.
In company testing, carbon emitters have been shown to dry water-based lacquers more efficiently than short-wave infrared emitters. Also, the carbon infrared emitter requires less energy than a conventional short-wave emitter to carry out the same drying process.
Two application examples show how carbon infrared emitters were used to improve industrial processing.
Carbon infrared emitters provide effective drying of a nonslip coating on disposable tray mats.
Infrared Lamps Help Light Cluster Production
Infrared cassettes incorporating fast-response carbon emitters are helping in the production of rear-light clusters for cars.
The manufacturing process for the rear-light clusters required spraying a water-based, aluminum reflective paint onto the surface of the cluster. It was necessary to dry this paint quickly in order to be compatible with production-line speeds. To help solve this problem, the manufacturer contacted an infrared heating system provider.
Following trials at the system provider’s test-and-evaluation center as well as on-site engineering to determine power ratings using portable infrared equipment, it was decided to install an infrared drying system that used fast-response, medium-wave carbon emitters.
The process development testing predicted that carbon emitters would be well suited for this application. Once installed, the carbon infrared system has proved to perform better than the drying systems previously used that relied on a combination of short-wave infrared and hot-air drying.
Drying Nonslip Coating on Paper Mats
A carbon infrared system is helping to achieve the quality of nonslip coating required on disposable tray mats to meet the stringent demands of major passenger airlines. Disposable tray mats can be manufactured from coated or uncoated paper or crepe, and they are printed to a very high standard.
When a British company developed a new line of nonslip tray mats to meet the specifications of a major airline, a new manufacturing line was set up. The manufacturing technology was adapted to allow a high quality nonslip coating to be applied. The manufacturers of the new water-based coating advised that it should be dried quickly after application, and they suggested that the most effective method of achieving the required drying rates would be infrared radiation.
Proving trials established that a carbon infrared system could achieve the required drying at web speeds of up to ~230 ft/min (70 m/min). As a result, a full-size system was installed.
Since installation, the infrared system has proven to be energy efficient. Its high power density coupled with the suitability of medium-wave infrared for water removal has ensured that the applied coating is dried effectively to provide a high quality finish. The fast response of carbon infrared also is important in this application. The heating can be switched off rapidly if needed, preventing any damage to the web in the event of production-line breakdown.
Fast-response carbon emitters are helping in the production of rear-light clusters for cars.
Infrared Boosters for Large Components
Another use for infrared within drying systems is as a booster zone. By retrofitting an infrared heating zone before the existing dryer when converting to water-based lacquers, it is possible to maintain product throughput and, often, even to increase it. Often called an infrared booster, such an approach solves many system conversion problems because infrared radiation heat provides the required energy to evaporate the water in the lacquer. By using infrared, especially for large products, time savings of up to 50 percent can be achieved in reaching the stoving temperature compared with conventional hot-air ovens.
By using an infrared module fitted before the existing dryer, the product is brought to the correct temperature, and the existing dryer can then hold this temperature for as long as possible.
It has also been shown in practice that, by retrofitting an infrared booster, the existing hot-air plant can be used as a cool-off zone. Very large components such as gearbox housings, which have to be coated with water-based lacquers, are not only dry at the end of the conveyor section but are also cooled off to the extent that they can be immediately packed.
This drying test unit has carbon infrared emitters. Carbon infrared emitters combine medium-wave radiation with high power densities to accelerate the drying of water-based paints and lacquers.
Energy Efficiency through Emitter Selection
Infrared heating technology offers several possibilities of optimizing energy consumption in industrial heating processes, including:
- High heat transfer capacity.
- Contact-free heat transfer.
- Efficient energy transfer through the use of optimum wavelengths.
- Use of energy only when required due to fast response times.
In conclusion, modern infrared emitters can be selected to match product and process in terms of wavelength, power and emitter shape. In every case, it is worthwhile to select the heating source based on the characteristics of the process and material. This ensures that not only is the production speed increased but that quality also is improved while reject rates are cut and costs are saved.