Custom Designed Convection & Infrared Ovens
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Ovens play a key role in the paint finishing process and serve pre-heat, dry-off and/or cure functions. Each oven is specifically designed taking into consideration the product and process requirements, energy efficiency and proper NFPA, NFGA, NEC and OSHA code requirements. Testing is recommended to evaluate the part heating characteristics and prove the process. HERR Industrial, Inc. designs and builds two types of ovens, convection and infrared (IR) each of which has wide variety of types and features to accommodate your specific need.
Convection ovens use fan pressure, as well as natural convective force, to circulate heated air within an insulated enclosure. Typically gas fired, convection ovens can be direct-fired or indirect-fired. Direct-fired ovens circulate air directly through a flame; indirect-fired ovens circulate the air through a heat exchanger in contact with a flame. An indirect-fired oven is usually recommended in instances where the products of combustion may interfere with the process, for example, bright white coatings. In these instances, electric resistance ovens can also be used but are typically limited to small batch ovens due to energy cost.
The amount of air circulated in the oven relative to the oven volume and the supply and return duct design rate are the primary determiners of the temperature regime in the oven. The time-temperature curve or "oven profile" is matched to the process. For example, liquid coatings should heat up slowly to allow solvents to escape before the coating "skins" over. However, powder suppliers generally ask for a temperature profile that abruptly rises then levels off at the maximum temperature before falling abruptly at the exit. The amounts of air and duct design also determine the temperature variation within the product envelope, how easy it is to change the profile and how energy-efficient the oven operates.
The oven exhaust rate and air seal are also key elements of the oven's energy efficiency. HERR employs VFD control of the exhaust in order to adjust the rate to minimize heat loss yet meet process requirements. Our air seals feature adjustable air knife slots on horseshoe duct coupled with a heat trap fan intake that effectively segregate the oven from the outside atmosphere. Bottom-entry ovens are used where practical for the greatest energy efficiency by trapping heat in the oven and eliminating air seal fans.
HERR's convection ovens are designed to meet your specific part and process requirements but flexible enough to meet your future demands. The following convection oven features are available:
- Dry-Off, Pre-Heat, and Cure
- Natural Gas, Propane, Electric
- Direct or Indirect Fired
- Energy Efficient VFD on Exhaust
- Heat Recovery and Reuse
- Heavy-Duty Construction
- Fine Tuned, Adjustable Even Air Distribution
- Internal Structural Frame with High Temp Paint
- T&G Panels, Mineral Wool w/ Aluminized Skins
- Clean ability features for Class A Finish
- Circulation Air Filtration
- Ovens Constructed Inside or Outside Plant
Infrared (IR) is a type of radiant heat that uses energy waves in the infrared portion (1 µm 1000 µm) of the electromagnetic spectrum to heat a part surface that is in the "line-of-sight" to the emitter. Conduction then transfers the heat throughout the part. Other types of radiant heat used to a lesser degree in paint systems include the shorter wavelength ultraviolet (UV) as well as magnetic induction.
Depending upon your specific process, product and production rate, IR may be used to dry-off, pre-heat (gel) and / or cure the parts. The advantage of IR in a paint system is the transfer of heat energy directly to the part rather than air. In general, this allows IR to heat parts 3-4 times quicker than convection allowing a smaller physical footprint; an advantage with high a line speed or heavy mass parts. However, IR is not without constraints. The "line-of-sight" issue may be inflexible to a complex or changing part geometry and the high emitter face temperature (800°F to 1800°F) can pose a risk of overheating parts if they stop in front of the emitter.
IR is available in electric or gas-fired types and each type has a variety of emitters that vary in terms of efficiency, cost and process applicability. HERR works with a variety of IR types designed to fit your needs and confirms performance with testing prior to proposing a concept. The most common application includes its use in combination with convection, especially as a retrofit to achieve a higher production rate. When incorporated at the convection zone entrance, IR can shorten the overall cure time and / or provide a "gel" zone to fuse powder before it passes through a high velocity air seal knife.