Taming the fire-breathing dragon

Industrial ovens are a vital part of aerospace parts manufacturing and refurbishing. Whether it’s annealing metal to strengthen the part and relieve stress, drying paint and curing composites, or part de-embrittlement to soften and rehabilitate components in maintenance and repair, some basic heating facts can be the key to efficient, low cost operation of aerospace industrial ovens.
 

Convection ovens

For about 100 years, natural gas has been used to heat industrial ovens. Traditionally, air was put into a burner and blown to the other end of the oven with fans or blowers. The hot air surrounded the product and eventually heated it to the average oven temperature. In general, industrial ovens can heat products up to about 1,000°F, with typical operating temperatures of about 180°F, 450°F, and 500°F.

Convection – heat transfer via circulated air – is good for quickly heating a whole oven and for heating irregularly shaped products, particularly in batches, since the air gets into nooks and crannies. But much energy is lost by heating the entire oven, from heated air exiting the oven, and in powering fans or blowers. Even with modulating burners, heating with gas is essentially an all-on or all-off process, which is inefficient since heating the entire oven is required even for small parts.
 

Infrared technology

While people assume natural gas-powered industrial ovens cost less than electric, that is not always the case. Today, one of the most efficient ways to heat an industrial oven is with electric, infrared energy, which does not require heating the entire oven, and has no fans, blowers, or moving parts so it is silent. Infrared energy – below the visible light spectrum – imparts heat when the product absorbs its rays.

“Gas is like a fire breathing dragon; it gets hot right now but lacks the energy efficiency, finesse, and control of electric infrared,” says Jesse Stricker, president of Intek Corp., a Union, Missouri-based designer and manufacturer of industrial ovens, heaters, heating elements, process controls systems, and material handling equipment. “Electric infrared is particularly effective on exposed surfaces such as drying paint and curing composites, and for continuous, industrial inline heat process systems such as belt or monorail conveyors.”

Because of electric infrared’s energy efficiency, it has also been adopted for space-heating applications. For instance, some electric infrared space heaters can run on only 700W, but provide the same usable heat as a 1,500W conventional unit that uses a fan, blower, and heating coils. Seven hundred watts is about half the required power of a standard hair dryer. Since the low wattage draws less current, plugging in multiple heaters is less likely to trip electrical circuit breakers.

Zoned, modular electric infrared heaters can reduce industrial oven energy requirements, focus heat, and optimize performance.

Like Lego blocks, these electric infrared heater modules – typically in 12" x 24", 12" x 36", or 12" x 48" sizes – become structural members of the oven. Integrated hangers, mounting brackets, and wire connections allow modules to be designed to work individually for small areas, ganged together for larger areas, or ceiling hung or wall mounted for effective heating.

Belt conveyor ovens or monorail conveyor ovens often used in aerospace applications can also provide an element of control. Individual heat zones can be used with separate controls for more consistent, automated heating.

“If an aerospace company is heating a smaller component, it isn’t necessary to heat the entire oven,” Stricker says. “Instead, it is more efficient to heat just the necessary heat zones of the oven.”

He emphasizes, “For the greatest oven efficiency and flexibility, electric infrared heaters can provide nearly unlimited heating zones that can be turned on or off as needed. Top to bottom, front to back, every foot in a conveyor oven path can be zoned for maximum, continuous process heating efficiency, monitored by a thermocouple in each zone. To adapt to individual parts running through the oven, hour by hour, smart controllers can be used to ensure temperature tolerance and consistency.”

Electric infrared heating is also precise and adjustable, which can help ensure the tight temperature tolerances often required. Since infrared wavelength correlates with temperature, and energy absorbs into each product at certain wavelengths, manufacturers can adjust the heat to match the wavelength of a substrate in the oven for greater energy efficiency and oven performance.
 

Optimized design

Buyers often look at standard industrial ovens, but most end up with some sort of custom solution to fit their specific requirements. Fortunately, such design enhancements can be achieved affordably with electric infrared.

Custom heating elements can enhance industrial oven performance. For instance, glass or ceramic-faced heating elements can be used for high-heat applications, with flexible silicone rubber used for lower temperatures. Housing depth can be increased to allow for additional insulation, or double-wall housing insulation can be used for in-wall installation. Some custom aerospace oven designers and builders can even combine gas-convection and electric-infrared types to prevent uneven heating in the oven, top-to-bottom.

“While many aerospace companies still specify gas convection ovens, more are adding electric infrared to control their oven’s temperature zones independently,” says Stricker. “To temperature balance all areas of the oven within a degree or two, for instance, they may heat the oven’s bottom more than its top.”
 

Refurbishing ovens

Once an industrial oven goes past its useful life, it loses efficiency, which can raise costs, delay production, or compromise product quality. But before replacing the oven with a new unit, first consider whether an oven retrofit or upgrade will work.

Sometimes repairs can be as simple as installing replacement parts such as high-temperature insulation, porcelain terminal blocks, heat controls, or heating elements.

Even when the repair is more extensive, the solution can be considerably less expensive than buying a new oven.

“Updating industrial oven heaters or heating elements can often boost oven performance to its original specs or even improve them,” says Stricker. “Some oven manufacturers engineer modules that will fix a performance problem, yet are easy enough for self-installation. Upgrading from an older technology like gas convection to a modern one like electric infrared is also possible. It is time to buy a new oven when repairing, retrofitting, or updating an industrial oven is no longer cost effective to improve its performance.”

Intek Corp.
www.intekcorp.com