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Welcome to our series on the fundamentals of process heating dryers. Choosing-the-Right-Fuel-Source-for-Your-Process-Heating-EqptThis week we focus on infrared (IR) dryers.

If you missed our previous installments and want to learn about impingement, through-air and flotation dryers, see:

What is an infrared (IR) dryer?

Unlike convection dryers that transfer heat using streams of heated air, infrared dryers transfer heat by sending waves of electromagnetic energy to the object to be heated. IR provides a source of high heat with an intense burst of energy.

Designed properly, IR dryers are very efficient and energy intense. Because of higher rate of heat transfer, IR dryers are often less than half the size of an equivalent hot air dryer.

The infrared wavelengths used for industrial heating applications range from 1.17 micron (4000ºF) to 5.4 micron (500ºF), and the wavelength is inversely proportional to the temperature of the emitter.

Short wave emitters have the highest unit area power output and temperatures that range from 2150ºF to 4000ºF. They are often used for heating metal and for applications where space is restricted, since the high heat often means the product can be dried faster with a shorter length dryer.

Medium wave emitters are the workhorse dryers for a wide variety of industrial applications requiring temperatures between 900ºF and 2150ºF.

Long wave emitters produce a lower power intensity for longer dwell time applications and those requiring temperatures between 500ºF and 900ºF.

Blackbody Radiation by Micron Bandwidths
Infrared Spectrum

Common applications for IR dryers

IR is usually the best choice where the process requires a high temperature. Some applications can require oven temperatures to reach as high as 800°C. To build a hot air oven capable of handling this type of application, the components required (such as heavy-duty blowers and 8 inch thick oven walls) would be extremely expensive. Infrared technology can handle these temperatures easily and with lower capital expense.

IR dryers are commonly used for heat setting as well as drying and curing thinner coatings, such as pressure-sensitive adhesives on masking films for appliances and electronics, which can be as thin as .5 mil. IR provides an energy-efficient method for quickly drying these thin coatings when you don’t have a concern about skinning.

If you’re working with a powder-based coating application, such as laminating foam to fabric for automotive materials, IR is the best choice because of the absence of moving air. The blowing air in a hot air dryer would blow much of the powder off the product. IR heaters for such applications do not use blowers, so it’s ideal for these types of coatings.

Gas IR is often the best choice for preheating or partial drying because it packs a very high energy density, so a lot of heating can be achieved with a small heater bank. Also, gas is much less expensive than electric power.

7 reasons to choose an IR dryer

1. Higher unit area heat transfer than convection dryers. Unit area heat transfer is the amount of energy a dryer is able to deliver per unit area of the heater surface, typically measured in watts/sq. in. (WSI) for electric IR and Btu/sq. ft. for gas IR.
2. Shorter dryer sizes that take up less manufacturing floor space, due to higher density heat output.
3. More energy efficient than convection dryers.
4. Easy to zone in machine direction and across machine direction for uniform heating and width variations. For example, hot air convection ovens can be zoned primarily in the machine direction because the nozzles are full width. With IR heaters, especially electric IR heaters, you can run the elements in the machine direction and shut down the elements on the edges. This can save energy as well as allow for a narrower product width. Or, you can adjust the edge zones to run at a higher temperature in order to get better product uniformity.
5. Quick start up and shut down. IR dryers get up to temperature very quickly, and cool down immediately upon shutdown, unlike other types of ovens that have large thermal inertia. IR’s quick response can often result in faster response to changing process conditions, depending on your application.
6. Very precise temperature control and infinite adjustability are possible with electric IR heat source.
7. Lower capital and installation cost than comparable convection dryers.

BONUS: You can easily add banks of IR heats to existing convection dryers to increase line speed.

IR dryer limitations

1. Not suitable for thicker coatings. IR’s high heat may cause some thicker coatings to skin and blister because the surface becomes overheated before the entire thickness of the coating is dry.
2. Not usually suitable for solvent-based coatings due to high temperature.
3. Slower speeds and temperature-sensitive substrates may not be good candidates for IR drying.
4. Energy costs for electric IR are generally higher than equivalent gas IR.
5. Gas IR has limited turn down and hence limited temperature range, typically between 1600ºF and 1300ºF. Electric IR heaters can operate easily between 600ºF to 1700ºF.
6. IR dryer sizing is job-specific so the dryer may not be as adaptable to multiple products with different drying requirements. The IR dryer size is determined by the task the dryer is expected to perform. You can run a variety of products in an IR dryer as long as the drying requirements are similar. If you deviate too far away from the dryer specs, the performance may suffer.

Design considerations

If your product seems suitable for an IR dryer, there are a number of important design decisions to be made so that the dryer is optimized for your product and process requirements. When you work with an experienced dryer manufacturer, these design options can be precisely configured according to your needs:

  • Choice of gas-fired or electric
  • Correct choice of wavelength and dryer size
  • Styles such as open resistor or quartz tube
  • Access for cleaning and maintenance

Confirm your IR dryer design with pilot testing

Since IR dryer designs are so application-specific, it’s essential to confirm your IR dryer size and process details by performing trials in a lab or pilot line.

This is especially valuable if you’re using IR for the first time and need to find new equipment vendors that you can trust. Purchasing expensive capital equipment from an unfamiliar source can be risky, and doing pilot testing with a vendor under consideration can be a valuable way to get to know their capabilities.

Like many, you may be concerned about the risks of buying equipment from a new vendor. Take a look at our free guide that can help you properly vet the company and avoid making the wrong choice: CHANGE WITH CONFIDENCE: Mitigating the Risk of Choosing a New Equipment Vendor.

Get Your Free Guide to Mitigating the Risks of Choosing a New Equipment Vendor