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When you mention infrared process heating, most people visualize the orange-red light and intense energy of a short-wave infrared heater. Although these images are synonymous with infrared process heating, they represent only a small portion of usable infrared energy available within the electromagnetic spectrum. Medium- and long-wave infrared heaters provide unique process benefits of their own.

Intense short-wavelength energy is widely used in manufacturing for such industries as foundry and heat treating. These processes require large amounts of energy to directly heat large mass materials efficiently. Process temperatures in these industries can exceed 1500 to 2000°F (815 to 1093°C). This causes many to wonder if infrared energy can be used on materials requiring lower temperatures or sensitive processes such as polymer annealing, precision drying and coatings. Fortunately, many lower temperature applications can be accomplished with long- or medium-wavelength infrared emitters and proper controls.

The priority when applying an infrared heating system in any process is to understand the basics. Infrared energy (also called radiant energy) travels in wavelengths within the electromagnetic spectrum in the same manner as sound and light. An easily relatable source of infrared is the sun. Infrared can be used for heating your process much like you can be warmed by standing in direct sunlight even on the coldest day of the year. Likewise, shielding areas of a product will reduce infrared heating much like you can be cooled by standing in the shade on the warmest day.

2 PH 0422 Intek Taming Infrared Energy Electromagnetic Spectrum

The type of infrared energy is defined by its wavelength on the electromagnetic spectrum. Infrared energy can be and classified as short (near), medium (mid) and long (far) wavelengths. Photo credit: Intek Corp.

The type of infrared energy is defined by its wavelength on the electromagnetic spectrum; typically, infrared energy is classified as short (or near), medium (or mid) and long (or far) wavelengths. Wavelength directly relates to temperature as per Wein’s Displacement Law. Radiant energy is either absorbed or reflected by a given substrate. The rate of absorption is different for all materials. This variance is the greatest reason for partnering with a reputable process heating vendor that will guide you through the process of determining the most appropriate heating tool to match a given material or substrate.

The following case studies focus on solutions made possible by utilizing medium- or long-wavelength electric flat-panel emitters. This style of infrared heater offers a homogeneous, controllable heat source and has been applied to many heat-sensitive materials such as plastics, films and coatings. The real-world scenarios are intended to show how infrared can be used to deliver precise, even heating while lowering a manufacturer's carbon footprint and reducing or eliminating the need for fossil fuels.

3 PH 0422 Intek Taming Infrared Energy intek Temp-to-Wavelength Meter

Wavelength directly relates to temperature as per Wein’s Displacement Law. Radiant energy is either absorbed or reflected by a given substrate. The rate of absorption is different for all materials. Photo credit: Intek Corp.

Polymer Annealing

The use of polymers is widely seen in manufactured goods and processes. One of the most prominent consumers of polymer materials is the automotive industry. At the same time, automobile efficiency and carbon footprint are at a high level of scrutiny, especially when discussing global climate issues and initiatives. Every ounce of weight that can be removed from an automobile design directly impacts its efficiency.

Polymers play a key role in the latest generation of all-electric (EV) vehicles. An average of 30,000 parts are used in an electric vehicle — one-third of which are made of plastic. More than 70 percent of the plastics used in automobiles are one of four polymers: polypropylene, polyurethane, polyamides or polyvinyl chloride. Many of these parts are injection molded and need to be annealed — heated and cooled slowly — to remove the internal stresses created during the molding process and to strengthen the finished part.

Many manufacturers use a standard method for annealing polycarbonate material that involves the use of a batch process with a gas-fired convection oven. Process times average two hours per batch and require excessive material handling, as many batch processes do.

A Tier 2 automotive supplier wanted a more efficient process and sought a new system from a process heating and infrared heater manufacturer. The main requirements for the annealing process were to have tight control on the material ramp temperature and, more importantly, tight control during the soak (hold) temperature interval.

4 PH 0422 Intek Taming Infrared Energy heater controls package

In many instances, low temperature or sensitive processes can be successful with electrically powered long or medium wavelength flat-panel infrared emitters and proper controls. Photo credit: Intek Corp.

Annealing occurs as the material enters glass transition temperature between 250 and 275°F (121 and 135°C). Annealing will not occur below 250°F (121°C), and material deformations occur at temperatures beyond 275°F (135°C). To be successful, a controllable, homogeneous heating solution would need to be employed.

After extensive testing, a six-zone, long-wave, flat-panel electric infrared continuous oven was designed that provides an efficient, controllable solution. The Tier 2 parts manufacturer achieved savings in process time, energy and labor. “Today, we use infrared heating after our injection-molding press that makes appliqués for automobile exteriors,” said Jim Anderson, engineering manager. “We used to do our batch annealing in a gas oven, but that was a two-hour process. We worked with [the heater manufacturer] to design an oven to meet our product needs, bringing that particular step from hours [using batch ovens] down to minutes.”

At the Tier 2 parts manufacturer’s facility, the revised annealing process was incorporated into 15 assembly lines. It has been in production for seven years with only single-digit heater replacement necessary during that time.

Curing Powder Coating

The powder coating industry has blossomed over the past decade due to innovations in application equipment, powder chemistry, surface-preparation processes and equipment, and process heating equipment.

Most of the energy required for the powder coating process is consumed within the heating stage, whether it be drying, preheating or final powder cure. Solutions for energy savings are becoming more necessary as energy becomes more costly. As the saying goes, “Necessity breeds invention.” This has led powder coaters to look at new methods for their heating process.

One of these methods is to add infrared heating technology into the process, especially at the beginning when the most energy is required. Applying this principle allows cure times to be shortened by reducing oven length, thus saving energy. Secondary benefits include faster gel times, which helps reduce the disruption of loose powder, as well as providing more efficient color changes.

Varying wavelength infrared technologies can be utilized within the process. Flat-panel infrared modular heaters are useful in drying, preheating, curing and even burn-off on many industrial paint and powder coating lines. Powder and wet paint finishes experience numerous benefits from infrared heat such as improved finish quality and reduced drying times. It also is possible to reclaim floor space because infrared ovens typically are smaller than convection ovens. In large conveyorized systems or small batch processes, flat-panel infrared heaters are effective and energy efficient.

One such application involved a customer with an existing gas-fired convection oven that, although it had served the company well in the past, was not able to handle increased production demands. In addition, residual moisture was causing problems in the paint application. Larger parts and a need for faster line speed had management discussing expensive options like the replacement of an aging but still operational oven.

As an alternative solution to buying a new oven, electric, long-wave, flat-panel infrared modular heaters were added to one end of the existing oven tunnel. The results were significant: Minimal downtime, improved performance, and a retrofit cost that came in well under the budget for a new system.

5 PH 0422 Intek Taming Infrared Energy Hybrid-style continous oven

In many cases, a new approach to the process may provide energy, time or space savings. A hybrid-style continuous oven such as this one may allow a manufacturer to gain more throughput from an existing system. Photo credit: Intek Corp.

Precision Drying

One of the largest segments of process heating is drying. Drying is a general term defined as “a mass transfer process consisting of the removal of water or another solvent by evaporation from a solid, semi-solid or liquid.”

Process drying can be split into two groups: large and small scale. Large-scale dryers such as those used in organic processes require mass amounts of energy to remove moisture by such means as evaporation, centrifugal force, contact or pulverization. By contrast, small-scale or precision drying is accomplished by evaporation in many cases.

The pharmaceutical industry is one of the major industries utilizing precision drying technologies. New technologies for this industry are constantly being developed, creating a demand for process heating. One such example involved a medical testing development company with a specific process that required the removal of microliters of water from a reagent. The product tray was lightweight, which created a challenge for a standard convection dryer due to the airflow necessary to both heat the product and remove the moisture. Temperature tolerances were tight at ±35°F (±19.4°C) at a maximum process temperature of 194°F (90°C).

6 PH 0422 Intek Taming Infrared Energy six zone IR oven

It was determined after extensive testing that a six-zone, long-wave, flat-panel electric infrared continuous oven provided the most efficient, controllable solution for a manufacturer of automotive parts. The manufacturer achieved savings in process time, energy and labor. Photo credit: Intek Corp.

The final solution was found by combining low air-velocity convection and flat-panel electric infrared heater technology. Precision controls allowed the source temperatures to be held to the necessary tolerances. This is one of many examples where the taming of infrared energy created a simple, effective, environmentally friendly solution.

In conclusion, as energy and environmental demands continue to expand, manufacturers will seek innovative solutions for even basic process heating applications. Processes that once consumed large amounts of fossil fuels may need to be re-evaluated to minimize energy consumption using new applications and technologies. This demand is why partnerships between process heating solutions suppliers and equipment manufacturers have and will continue to become key components in the success of such change. Strong partnerships and open communication — along with practical actions such as product testing — help ensure that a final solution is successful.