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Aluminum

A new, improved induction heater

By Liz Sommerville

December 2008 - Although induction heating has been used in the metals industry for decades, the energy inefficiency of the system left some companies wanting a new option that provided both economic and environmental efficiencies. After five years of research and development, Zenergy Power Inc., South San Francisco, Calif., has found the answer that will change induction heating.

New technology
A conventional induction heater uses a water-cooled copper coil to create a magnetic field and an alternating current to create a changing magnetic field. When the changing magnetic field is introduced to a conductive material like metal, it creates eddy currents, which heat the metal. The drawback with conventional induction heating for nonferrous metals, like aluminum and copper, is that it's only about 50 percent energy-efficient.

Zenergy Power GmbH, Rheinbach, Germany, the company's German operation, spent five years creating environmentally friendly technology for induction heating that centered on using superconductors for energy efficiency. The result was the world's first commercial high-temperature superconductive induction heater, featuring a superconductor coil.

"Instead of using alternating current and a changing magnetic field, we're using direct current and creating a large but energy-efficient magnetic field--a DC, constant magnetic field," says Dr. Larry Masur, vice president of business development for Zenergy Power.

Because there needs to be some changing of magnetic state to induce eddy currents, the company discovered rotating the metal billet in the presence of the magnetic field would create the eddy currents to heat the billet. "We've turned conventional induction heating on its head," says Masur. "Instead of having a stationary billet and an alternating magnetic field, we're having a stationary magnetic field and a rotating billet. The result is more than 80 percent energy efficiency. We save energy by using the superconductors, as well as by using efficient electric motors that rotate the billet and efficient motor drives that run the motors."

As Zenergy Power developed the HTS induction heater, it found that, in addition to the increased energy efficiency, the machine would also provide more uniform heating. By rotating the billet, the eddy currents are able to penetrate deeper into the billet and create better temperature homogeneity. "Those were the two principal benefits that we knew about: significant energy efficiency and more uniform heating for better product quality," says Masur. "But we weren't sure how the end customer would experience the benefits of the more uniform heating."

Reaping the benefits
That question was answered when Zenergy Power successfully installed and implemented the first commercial, full-scale HTS induction heater for Weseralu GmbH & Co. KG, Minden, Germany, an aluminum profile extrusion company. It's designed specifically for heating large aluminum billets that can be manipulated when softened and shaped for various products in the automotive, aerospace and machine-building industries.

As a result of the homogeneous billet temperature, Weseralu found it could improve the productivity of its extrusion process by about 25 percent. "Now, for almost the same amount of labor costs and the same machine time, [the company] is getting 25 percent more output, and its operating costs have gone down," says Masur. By having a more accurate knowledge of what the billet temperature will be, Weseralu could more accurately tune its extrusion process to take full advantage of the temperature homogeneity.

The HTS induction heater also requires less maintenance than traditional induction heaters because it doesn't use copper coils, which require multiple replacements during the machine's lifetime because they sit so close to the hot billet. With Zenergy Power's technology, the superconductive coil is separated from the billet by 10 inches to 12 inches and sits at a constant temperature. These coils can last 20 to 30 years without needing to be repaired or replaced.

Since the HTS induction heater was implemented in July, Weseralu has seen a 50 percent decrease in energy costs and a 25 percent increase in productivity. Masur says the technology has the potential to save even more.

"The energy savings can be anywhere between $50,000 to $300,000 a year," he says. "But that gets dwarfed by the increased productivity numbers, which can be $300,000 to $2 million a year. That's what companies really care about." MM

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