Comparison of Convection and IR Drying and Curing Systems

Introduction

Manufacturers across the globe utilize a number of different types of heating to accomplish drying and curing tasks, but the two most common types are convection and infrared. This post seeks to explain the advantages of each of these two forms of heating while also identifying when it is better to use one over the other. In some applications it may also be best to use a combination of the two heating types to take advantage of both of their strengths.

Convection Drying and Curing

Convection heating ovens heat and circulate the air in the oven and then use that air to heat up the product. It is characterized by the following features and advantages:

• All air inside a convection oven chamber is heated and circulated. This means that any surface that is exposed to air will absorb the heat, leading to uniform heating even on complex geometries.
• As the entire chamber is at a set temperature, convection systems are ideal for bulk material heating/drying/curing/annealing that takes place over a long period of time as it will ensure that all material reaches the set temperature during the cycle without overheating the surface.
• Air circulation can be useful in carrying away solvents and VOCs.

Some disadvantages/challenges:

• Drying/curing parts of various sizes/densities can be challenging since convection ovens are difficult to accurately zone.
• Longer heat up time as entire chamber’s volume must be heated
• Energy wasted on heating air volume rather than product

Infrared Drying and Curing

Infrared heat is delivered to the product in the form of electromagnetic radiation measured in wavelengths ranging from about 1 to 12 microns typically. The following features/advantages of infrared heating have made it popular among manufacturers:

• IR energy is transferred to a product via radiative heat transfer, so it is directly absorbed by the paint, ink, or coating without heating the air. This can lead to significant energy savings, since energy is not wasted on heating air.
• IR drying and curing delivers more energy to the coatings or substrates than convection systems in smaller areas, leading to more compact systems and less floor space utilization.
• Rapid heat-up and cool down allows these systems to be easily switched off or reduced whenever not required, further increasing energy savings.
• Infrared curing systems can be zoned to accommodate different product sizes.
• IR heating is particularly effective when used on water-based coatings, which has helped manufacturers move away from solvent-based coatings; reducing VOC emissions.
• Lack of required air movement is useful when coating is easily disturbed, such as a powder coat.

Some disadvantages/challenges:

• Penetration into a product’s thickness is limited so it is not as effective at heating thick or bulky materials.
• It is a line of sight technology, which means energy is delivered only to surfaces with a direct line of sight to the heating source.  This can make heating complex geometries difficult.
• Some materials and coatings are IR-reflective and will reflect a large portion of the IR energy directed at them.

Combination Convection and Infrared Systems

Some applications will be best suited to a system using a combination of both forms of heating to take advantage of the strengths of convection and infrared heating.

For example, in the glass industry it is becoming increasingly common for manufacturers to have one surface of the glass coated with an IR-reflective coating making it difficult to heat that surface using infrared.  In these types of applications, manufacturers find it useful to heat the coated side with convection heat while heating the opposite side of the glass with infrared to maintain processing speed while not having energy waste due to reflection.

Other applications will benefit from using the two forms of heating at different stages in the process, rather than simultaneously.  In many powder coating applications it can be useful to first use IR heat to “gel” the coating and then use convection heat to finish the drying/curing process.  This prevents the coating from being disturbed in the first stage where IR is used and thus air movement is not required, and then allows the convection heat to finish the process to ensure the full thickness and geometry of the parts are heated.

Casso-Solar Technologies is extremely knowledgeable and experienced with both forms of heating.  Contact us today and we will craft a solution that is suited to work with your unique application while maximizing efficiency and processing speed while minimizing energy usage.

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