At its Indiana Transmission Plant, DaimlerChrysler installed Kanthal Advanced Powder Metallurgy (APM) alloy heating elements and radiant tubes in 19 heat treating furnaces. Productivity improvements provide additional capacity equivalent to 22 furnaces. Twenty-two “free” furnaces if you will.

Fig.1. Converting eight carburizing furnaces to APM alloy bayonet heating elements and radiant tubes reduced heat cycles by 50%, providing capacity equivalent to four additional furnaces

As Reported to Industrial Heating Magazine

Kokomo, Ind., may well be the transmission capital of the world. DaimlerChrysler Corp. has three transmission plants with 10 million sq. ft. of floor space in this rural community 60 miles north of Indianapolis. Six-thousand people produce front and rear-wheel-drive transmissions for Chrysler, Dodge and Jeep vehicles. Supporting transmission-manufacturing operations is the Kokomo Casting Plant, the world’s largest die casting facility.

Chris Aviah-Gyebi is area manager for heat-treating operations at Indiana Transmission Plant I. One of his job responsibilities is identifying new technology to improve the efficiency of heat-treating furnaces. Working in conjunction with Jason Williams, president of Williams Industrial Services Inc., Bowling Green, Ohio, he looked at high-temperature heating-element alloy developed in Sweden. His idea was to replace corrugated stainless-steel heating elements in austempering furnaces with bayonet heating elements and radiant tubes fabricated from an iron/chrome/aluminum APM material developed by Kanthal Corp. Aviah-Gyebi proposed an eight-week, in-plant evaluation of the APM products.

Austempering Program

In 2004, the transmission plant ordered a dozen APM heating elements and radiant tubes from Custom Electric Manufacturing Co., Wixom, Mich. Custom Electric distributes Kanthal APM heating elements, tubes and bulk wire.

Refractory Engineering of Indiana and plant maintenance personnel installed the APM tubes and bayonet elements in an AFC-Holcroft austempering furnace. Start-up and furnace monitoring was handled by Williams Industrial Services. For two months, the test furnace worked side-by-side with the plant’s other AFC-Holcroft furnaces.

“We processed transmission gears and shafts six days a week, three shifts a day, 52 weeks a year under production conditions,” says Aviah-Gyebi. “We expected some improvement in performance, but nothing like what we achieved. Comparing the output of the test furnace to our other austempering furnaces was like comparing night to day.”

Fig. 2.  APM alloy heating elements and tubes operate at temperatures up to 2280°F

Test Results

With the test furnace online, Daimler-Chrysler noted a significant reduction in austempering cycle times. For example, it took 4.75 hours to process transmission shafts in furnaces heated by the corrugated stainless-steel heating elements. In the test furnace equipped with APM elements and tubes, the transmission shaft was heated in 2.37 hours. This is a 50% reduction in cycle time.

A number of different components were processed during the eight-week test. The heat cycle to process a different shaft was reduced from 2.02 hours to 1.03 hour. This represented a 49% reduction in cycle time. The time to process a transmission gear dropped from 5.53 hours to 3.7 hours, a 33% reduction in cycle time. Based on results of the eight-week test, the Indiana Transmission Plant decided to convert a total of eight austempering furnaces. It placed another order for approximately 100 APM radiant tubes and bayonet elements.

“For every two austempering furnaces converted to APM tubes and elements, DaimlerChrysler gains heat-treating capacity equivalent to a third furnace,” says Aviah-Gyebi, “a free furnace if you will. This is based on an average reduction in cycle times of 50% for the variety of components processed.”

With eight furnaces converted to APM tubes and elements, Transmission Plant I gains capacity equivalent to four additional austempering furnaces. “This saves DaimlerChrysler spending approximately $2 million on new equipment,” says Aviah-Gyebi, “and provides an immediate payback of the cost to upgrade the eight furnaces.”

Savings related to shorter cycle times is only a fraction of the total savings DaimlerChrysler attributes to APM technology. Longer heating-element life and reduced downtime to replace heating elements had an even greater impact on operating costs.

Longer Element Life

The original heating elements installed in the eight austempering furnaces at the Indiana Transmission Plant were fabricated from corrugated 330 stainless steel. These elements are approximately 10 in. wide x 8 ft. long. Because they weigh more than 300 lbs., they are fabricated in two sections.

According to plant maintenance records, the corrugated-steel heating elements had a service life of six to nine months, the average being 30 weeks. APM heating elements have a projected service life of four years depending on the application and furnace operating parameters.

Over the same four years, corrugated stainless-steel heating elements typically had to be replaced six times in each of the eight austempering furnaces.

“APM elements do not cost seven times more than stainless-steel elements, so we are saving a lot of money,” says Aviah-Gyebi. “We save even more when time lost to replace heating elements is factored into the equation.”

Fig. 3.  APM alloy heating elements are expected to last seven times longer than corrugated stainless-steel heating elements

Reduced Downtime

According to Aviah-Gyebi, it takes six weeks to replace corrugated heating elements in an austempering furnace. Over four years, this represents 288 weeks of downtime to replace elements six times in eight furnaces.

APM heating elements can be replaced in one day from the top of a furnace. Over four years, this is eight days of downtime to service eight furnaces, compared to 1,728 days of downtime to replace corrugated elements in eight furnaces. The transmission plant gains austempering capacity equivalent to five additional furnaces based on a 144 hour-per-week production schedule. It also avoided spending $2.5 million on new equipment. Add to this the equivalent capacity of four furnaces gained through shorter cycle times and DaimlerChrysler has gained the output of nine austempering furnaces and avoided spending about $4.5 million on new equipment.

Carburizing Program

Before it had even completed the conversion of its eight austempering furnaces, DaimlerChrysler decided to expand the APM program. It placed another order for more than 130 APM heating elements and radiant tubes to upgrade 11 Lindberg carburizing furnaces.

The Lindberg furnaces were equipped with the same style of corrugated heating elements used in the austempering furnaces. In this application, the primary benefit of the APM products was longer heating-element life and reduced downtime to replace heating elements.

Fig. 4.  APM alloy radiant tubes work equally well in electric and gas thermal-processing equipment

Element Performance

Corrugated heating elements have the same service life in carburizing furnaces as they do in austempering furnaces, about 30 weeks. The APM heating elements also had the same projected service life of about four years.

“Just on the basis of seven times longer heating element life, we are able to recover the cost for converting the 11 carburizing furnaces,” says Aviah-Gyebi. “The reduction in downtime to replace corrugated heating elements simply made the decision easier.”

Reduced Downtime

It takes twice as long to replace corrugated heating elements in a carburizing furnace as it does to replace them in an austempering furnace.

“For the 11 Lindberg furnaces,” says Aviah-Gyebi, “we would average 660 weeks (3,960 days) of downtime over a four-year period to replace corrugated heating elements five times in each of the 11 furnaces. This compares to 11 days downtime over four years to replace APM elements. The added capacity we gain by reducing heating element downtime is equivalent to gaining 12 additional carburizing furnaces.” This will save DaimlerChrysler approximately $6 million.

Fig. 5.  APM tube performance chart

Bonus Benefits

The carburizing process differs from austempering in that you cannot significantly reduce cycle times. However, the APM elements heat up faster, reducing recovery time between loads. They also operate at higher temperatures. With APM elements, furnaces can run at temperatures up to 1922°F (1050°C), compared to the normal carburizing temperature of 1760°F (930°C).

“The carburizing and austempering furnaces equipped with APM tubes and elements also are tighter than our old furnaces,” says Aviah-Gyebi. “This has improved the plant environment. We also see an improvement in part quality and wash-cycle efficiency.”

APM Technology

Kanthal Corp. was a pioneer in the development of high-temperature powder-metal (PM) alloys for heat-treat furnaces. The iron/chrome/aluminum alloys it introduced 70 years ago remain the standard for high-temperature applications in the heat treating, steel and aluminum industries. APM (advanced powder metallurgy) products are produced from the same iron/chrome/aluminum alloy using a more sophisticated powder metal process. Current APM products include high-temperature wire for electric heating elements and extruded radiant/protective tubes for gas and electric furnaces.

Custom Electric introduced Kanthal APM tubes to the North America market about 10 years ago. Since then, the market has grown twenty-fold. Initially, APM tubes were used as an alternative to nickel/chrome, graphite and ceramic tubes. Most were installed in seal quench furnaces. Today the high-temperature tubes and heating elements are used in gas and electric heat-treating furnaces, aluminum dosing furnaces, aluminum melting and holding furnaces, hardening and tempering furnaces, wire annealing furnaces and sintering furnaces.

“We have gained a tremendous amount of application experience with this technology over the past 10 years,” says Bob Edwards, president of Custom Electric. “We have customers using a broad range of equipment in a variety of industries. Seldom have we encountered an application where the use of APM products does not have a dramatic impact on total operating costs.”

For More Information:

Contact Chris Aviah-Gyebi, Area Manager, DaimlerChrysler Corp., Indiana Transmission Plant, 3660 North US Hwy 31, Kokomo, IN 46904; tel.: (765) 854-4280; fax: (765) 854-4280; e-mail:cya@daimlerchrysler.comor Bob Edwards, President, Custom Electric Manufacturing Co., 48941 West Rd., Wixom, MI 48393; tel.: (248) 305-7700; fax: (248) 305-7705;

Additional related information may be found by searching for these (and other) key words/terms via BNP Media LINX austempering, APM, corrugated heating element, bayonet heating element, carburizing

APM Properties

The APM material is an iron/chrome/aluminum powder metal alloy that can be extruded into seamless tubing. When heated to 2280°F (1250°C), an aluminum oxide layer is formed on the inside and outside surfaces of the tube. This protective layer provides four times the carburization resistance of conventional nickel/chrome tubes and is equally resistant to sulfurous atmospheres. Because the oxide layer does not spall, problems associated with loose oxides contaminating the tube interior and reducing heat-transfer efficiency are eliminated.

APM wire is available in diameters from 0.039 in. to 0.32 in. (1.0 mm to 8.25 mm). Extruded APM tubes are available with an OD/ID from 8.7/8.0 in. to 0.23/0.2 in. (220/203 mm to 6.0/5.2 mm).

A modified version of the APM alloy, designated APMT, was recently introduced. APMT tubes offer improved form stability to minimize sagging when long tubes have to be mounted in a horizontal plane. In most applications, APM and APMT alloy radiant tubes offer from two to four times longer service life than conventional radiant tubes.


When you review the math, there is little doubt Kanthal APM tubes and heating elements had a dramatic impact on austempering operations at the Indiana Transmission Plant. Austempering cycle times were cut 50%, downtime to replace heating elements was reduced from 17% to 1% and austempering capacity was increased by the equivalent of nine furnaces.

The carburizing program was equally successful. Downtime to replace heating elements dropped from 28% to 1%, and production capacity increased by the equivalent of 13 furnaces.

By switching to APM radiant tubes and elements, DaimlerChrysler’s Indiana Transmission Plant gained additional heat-treating capacity equivalent to 22 furnaces and avoided having to spend more than $10 million on new equipment.

“The program has been successful,” says Aviah-Gyebi. “So successful, in fact, we now are converting two Lindberg endo-gas generator heating systems to APM tubes and elements just as we did on the batch furnaces.”