Infrared provides the heat, cure, bond and catalyst for a range of industrial processes. Its most important role, however, is the one in which it first found widespread use: the curing of liquid coatings. Whether processing solvent-based, waterborne or non-reduced coatings, infrared is the curing technology of choice among manufacturers of metal, plastic, wood and composite parts. Most ferrous and virtually all non-ferrous metal surfaces and composites that are coated with paint can be cured using electric infrared systems. The ability to precisely control and zone infrared heat provides advantages over other curing methods. Additionally, infrared penetrates the coating and heats from the substrate out, preventing blisters that can result from trapped solvents.
As the coatings industry changes from solvent-based coatings to more durable and ecologically friendly powder coatings, the role of infrared heat becomes more pronounced. Curing solutions that once were obtainable using a single curing source are no longer the best when dealing with powders. Using a convection-only curing system could have disadvantages, including:
Consuming more energy for heat up, curing and cool down.
Requiring longer curing times and slower line speeds.
Larger equipment footprint.
Inability to offer the flexibility needed to adjust heat zones for reduced energy consumption and processing of different parts.
Convection air movement and byproducts can contaminate coated parts.
By implementing an electric infrared booster oven prior to final curing, the surface can be flashed off quickly, initiating the gel (polymerization) of the powder. This will reduce contamination, color inconsistencies and keep powder from being blown off the part.
Hundreds of powder formulations are used today. Film thicknesses range from below 0.001" to more than 0.015", and the variety of colors, gloss and applications is equally vast. What these diverse powder formulations have in common is compatibility with infrared radiation as a method of curing.
New technologies are continually improving finish chemistry. Precise, reproducible oven temperature control characteristics are needed to ensure that the potential of the new powder formulas are met. This is the custom control that can be obtained with infrared curing systems.
Curing High Density Board with Infrared Heating
Infrared modular sections that incorporate custom high-density refractory board, composed of aluminum silicate and other non-organic binders, have been designed for higher watt density applications, including those for curing powder coatings. In many operations, these refractory boards are self-cleaning. High-density boards are capable of withstanding up to 100 W/in2 and act as a generator (re-radiator) of medium-wavelength infrared. This benefits the powder finishing and curing process: As the coating cures, it heats the product being coated, accelerating the curing process.
A wash cycle always precedes the application of a coating, and the removal of residual water is essential before coatings are applied. An oven that rapidly brings parts to 225°F (107°C), or higher if desired, and evaporates all moisture is helpful in these situations. Ovens that can combine drying and preheating cycles into a single process when necessary can give manufacturers the option of a complete powder cure system using only electric infrared. This reduces the system footprint and can reduce costs. Of course, practical applications for an infrared-only oven will be limited to parts that have all of the powdered surfaces directly exposed to the infrared emitters (line-of-sight). If there are line-of-sight issues, an infrared booster in conjunction with a convection final cure will still offer distinct advantages with respect to energy consumption, footprint and equipment costs.
Infrared Ovens for De-Wrinkling Vinyl and Other Unique Uses
Automotive and OEM applications often require infrared ovens that are designed for specific applications. For instance, infrared ovens are used to process seating components such as relaxing fabric, removing moisture from and de-wrinkling vinyl, and fabricating cloth and leather seats. Also, they are used to dry coatings on plastic parts and package finished parts for shipping. Infrared technologies are available for these needs in the form of shuttle ovens, storage ovens and conveyor ovens.
Shuttle Ovens. Infrared shuttle ovens condition vinyl and many other composites in less time than is required by air systems. Often purchased to improve productivity, they simplify handling by “shuttling” a warm sheet out when each cold sheet put in. The ovens have continuous feed sensors to ensure uniform temperatures and a uniform result. Some oven modules incorporate a pneumatic “trap” to clamp the vinyl on four sides, thus preventing dimensional changes prior to forming. Common applications for shuttle ovens include automotive headliners and floorliners, door panels, dashboards, steering wheel coverings and arm rests. Manufacturers of air bag components use these ovens for preheating vinyl prior to vacuum forming.
Storage Ovens. Re-engineered assembly systems for increased productivity have intensified the need for storage ovens, which heat parts such as wire harnesses to make them easier to assemble. These ovens also are used where pressure-sensitive adhesives perform more efficiently at higher temperatures and where pliability aids fit such as with rubber bushings applied to door fittings.
Conveyor Ovens. Conveyorized ovens are used for many glass performance and decorative effects. Systems are available for processes such as tempering, annealing, preheating and tacking for lamination. Specialty ovens are used to cure inks, ceramic paste and reflective coatings used on head- and taillights. Preheated vinyl sheets are used in the lamination of safety glass without heating the glass. Paint-on glass applications such as windshield “perimeter black-out” are common uses for electric infrared ovens.
Infrared and Inks. Infrared is not only suited for paint applications but can be used with many solvent-based products. For instance, infrared systems can provide effective high-speed drying of printing inks.
Electric Infrared Heat Sources
Electricity is the energy choice for many infrared applications. Reasons for its popularity include installation cost, controllability, the ability to produce high temperatures quickly and its cleanliness.
Electric infrared emitters provide flexibility in producing the desired wavelength for a particular application. A selection of electric infrared heat sources is available to meet the various requirements of industrial applications. Each of the different types of heat sources has particular characteristics that determine the suitability of the heat source for a particular application. Your infrared equipment supplier can outline the benefits and disadvantages of each type.