Combination ovens combine infrared and convection to create a unit that provides the optimal heating profile.

Combination ovens - ovens that employ two or more heating methods within a single process oven - most often connect infrared and convection heating zones together in series. This approach allows processors to enjoy the best of both heating methods: Infrared provides high heat input in a relatively short amount of time, followed by a convection zone that holds the product at temperature, eliminating the risk of temperature overshoot. While not every process is best optimized by using a combination heating approach, for those that can benefit, a combination oven provides a satisfactory heating solution.

Three case histories from Duke Power, Charlotte, NC, show how combining infrared with other heating methods can increase production output, decrease floor space consumption and improve product quality.

Mount Vernon Doubles Production With Electric Infrared Predryer

Faced with a positive challenge - growing demand for home furnishing and automotive upholstery goods - Mount Vernon Mills' La France facility near Clemson, SC, was looking for a faster way to run spun yarn through its slasher. Originally designed for drying and dyeing filament yarn, the slasher had limited drying capacity for heavier-weight yarns, making the process much slower than desired. Doubling the number of steam cans was an obvious, but expensive, option. In addition, floor space was tight, so a compact solution was desired. Wanting the best possible solution, Mount Vernon Mills decided to work with Duke Power.

After examining Mount Vernon Mills' process, Duke Power recommended adding an electric infrared predryer to its existing plant equipment. The new technology was less expensive than new steam cans and required about one-third of the floor space. The predryer offered better efficiency because it worked by heating just the yarn, not the area around it. And, because it heated the yarn without touching it, there were additional advantages. Plant manager Nick Caldwell remarked, "We saw some improvements in yarn hairiness reduction, which is tremendous - a big plus." He noted that a year of testing ended with no burning of the yarn.

After the predryer was installed, production at the La France facility doubled, from 49 yd/min of yarn to 98 yd/min or more. At the same time, total operating costs decreased by 27%.

With production up and operating costs down, Mount Vernon is considering the expansion of electric infrared technology into other areas such as dyeing and finishing. But for the present, the plant's general manager feels the electric infrared predryer alone has put the mill "on the cutting edge" by boosting drying speed, cost control and quality.

The Benefits Add Up. At Mount Vernon MIlls, electric infrared technology not only dries faster, it dries smarter. Here's how:

  • It boosts efficiency because the predryer heats just the yarn, not the surrounding areas.

  • It enhances quality because the predryer doesn't touch the yarn.

  • It cuts operating costs by 27%.

  • It doubles productivity, from 49 yd/min of yarnto 98 yd/min or more.

  • It provides an installed cost that is less than steam cans.

  • It requires one-third less floor space than steam cans.

Mount Vernon management was skeptical about the electric infrared approach at first, but plant manager Nick Caldwell noted that four tangible benefits - increased production, decreased total operation costs, reduced yarn hairiness and reduced space concerns - have convinced Mount Vernon that electric infrared was right for its process.

Table 1. Independent tests show the electric infrared predryer worked best in American Fast Print's process.

American Fast Print Improves Efficiency With Electric Infrared Predryers

American Fast Print's gas-fired predryers at their U.S. Finishing Plant in Greenville, SC, were slowing down production. A commission dyer, finisher and printer of cotton and polyester/cotton fabrics, American Fast Print was attracted to the improved production rates promised by the use of electric infrared, but the staff initially assumed that the technology would be cost-prohibitive.

"When we first compared electric and gas infrared systems, I was skeptical that electric infrared could compete -- particularly in the area of operating costs," said Martin Flynt, vice president of American Fast Print.

In textile wet processing, gas systems historically have been used to predry fabrics. Duke Power proposed a study to help evaluate the two different systems. To make a fair comparison, American Fast Print installed an electric infrared predryer and an upgraded gas infrared unit. Meters were installed, cotton and poly/cotton fabrics were tested. An independent consultant was hired to gather and analyze the data.

American Fast Print discovered the many advantages of electric infrared by testing wet pickup, drying rates and energy usage. The results pointed toward an electric system (table 1). In this application, electric infrared removed 2.5 times as much water, was more efficient than gas, and offered better quality, less maintenance and more precise temperature control.

The Bottom Line. American Fast Print found that an electric infrared predryer provides several process benefits:

  • Consistent product quality.

  • Improved heat transfer.

  • Precise temperature control that can be varied according to fabric style.

  • Zoned heating to accommodate varying fabric widths.

  • Rapid startup and cooldown cycles.

  • Significantly less maintenance and downtime.

"There are many reasons electric infrared has worked for us, but the biggest advantage is it never breaks down," said Gunther Geyer, plant engineer at American Fast Print. "We use the system 24 hours a day, six days a week, and have had virtually no downtime."

Table 2. Rim and Wheel House found that using an infrared oven allowed it to cut curing time and improve finish quality.

Rim and Wheel House Doubles Production By Installing Powder Coating

Rim & Wheel House, Spartanburg, SC, was looking for a faster method to produce its wheels. For nearly 30 years, the company used solvent-based liquid coatings to paint wheels, primarily for small-track racecars. But its sterling reputation for on-time deliveries was threatened by lengthy drying times, high employee turnover and finish quality that was less than ideal. That's when Rim & Wheel decided to work with Duke Power to find a solution.

It was decided that a powder coating system and an electric infrared oven could add speed and polish to the wheel painting process. Rim & Wheel House owner Robert Painter had considered powder coating in the past, but suppliers said his operation was too small.

Since installing the new finishing line, his operation has proven it can yield big results (table 2). Production has doubled, from 60 wheels to 120 per day. Instead of taking 8 hr to paint a day's production, the crew needs just 2.5 hr. Because leftover powder can be recycled, there's less waster and no toxic waste disposal. By radiating less ambient heat and eliminating warmup and cooldown times, the system reduces energy costs. Best of all, the quality and durability of the paint finish is much improved, leading to increased sales.

Lower operating costs, faster manufacturing speeds and better quality - an electric infrared oven gave Rim & Wheel House all these advantages and more:

  • Doubled production speed.

  • Improved quality.

  • Reduced energy costs.

  • Provided more precise temperature control.

  • Increased energy efficiency.

  • Increased employee productivity and job satisfaction.


"Overall, powder coating has been a great system for us. We're able to produce a better product in far less time, and our employee turnover is much lower," said Robert Painter, owner of Rim & Wheel House.

So, if you are struggling with a system that can't quite keep up with your production demands, consider adding an infrared predryer or oven. It may just provide the boost you need, and integrating an infrared zone usually costs less than a new system.

This article was provided by Duke Energy, Charlotte, N.C., an energy company serving Indiana, Kentucky, North Carolina, Ohio and South Carolina. For more information about Duke Power's programs for large businesses, visit