Creating ZonesWe apply powder coating to a very large assembly that includes some heavy steel (a 2" thick steel plate) and some light gauge metal (16 gauge steel braces). We have to keep the part in the oven for more than 60 minutes to achieve full cure on the heavy area, but we have color and gloss problems on the lighter gauge steel. We have been told that an IR oven will help solve this problem. What type of IR should we look at and how can we set that up for curing these assemblies?
Infrared heating is an excellent way to address this problem. You should be able to improve the finish quality and shorten dwell time as well. Unlike convection heating, it is very easy to zone the infrared heat to put more heat where it's needed and less where it's not. This can be done by positioning more emitters near the dense portion and/or by increasing the intensity of the emitters near the dense portion.
Using infrared to cure powder coatings on light/heavy gauge metal assemblies can be done with short, medium, or long wavelength infrared emitters. The members of the Infrared Equipment Division of IHEA, are equipped to evaluate your specific process and provide proposals for custom built ovens to efficiently cure your parts.
Heating the SurfaceI have a part that is made of metal but has a gasket inside that cannot take temperatures above 250°F. The low temperature limits my options for thermally cured coatings. If I use an infrared oven, will I be able to use a coating that requires a higher temperature and then heat the surface without overheating the gasket?
This is a tough question to answer because we do not have all the variables that an IR oven provider would need to know. However, with many of these applications, IR may be the only method of heating the surface coating without damaging a gasket or other materials that have a lower tolerance of heat.
If you allow us to make a few assumptions, and possibly take a few liberties with your exact application, we can provide information that can be helpful in making your decision. First, we are going to assume the gasket is inside the product being heated and will not see any direct infrared energy. Second, we will assume the coating can be cured quickly. One of the major advantages of IR is the ability to heat objects very fast. By getting the surface of the product to the desired temperature and quickly curing the coating, heat will not have as much of a chance to conduct into the product and damage the temperature-sensitive material, such as the gasket.
We noted in previous Q & A articles the important characteristics of IR. Because we do not know all the variables involved in this specific question, we need to again point out that infrared is generated through an emitter, and these emitters vary with respect to wavelengths, and coatings will vary in response to these wavelengths (absorptivity, reflectivity and transmissivity of infrared waves). These variables will have a direct affect on the speed in which the coating can be properly cured, and how well heat is kept from penetrating the coating and product, and affecting the more heat-sensitive gasket. With the broad range of emitters available today, chances are very good that one or more IR emitters offer solutions for your application.
IR energy is also "line-of-sight" heat. If there are areas on the product that are not coated, the IR oven could be configured to heat only the coated areas of the product. By limiting the heat being applied to the product, the likelihood of over-heating the gasket will be reduced.
All IRED manufacturers offer free testing, and you are encouraged to bring your product to them to determine if the application is safe for the temperature-sensitive materials, and to determine the most effective and expedient IR heat source(s) for the application. You also might consider bringing in the coating supplier, as they may offer a suitable coating that can be cured at lower temperatures than the coating you currently use.
Answers provided by members of the Infrared Equipment Division (IRED) of the Industrial Heating Equipment Association (IHEA). Visit www.ihea.org.