Industrial-size furnaces may have to move over andd make room for microwave ovens for heat treating metal.

Engineers at Dana Corp. have developed a way to use microwave ovens to braze, harden, and carburize metals, replacing the out-sized industrial furnaces that have been used for years.

Dana's technology heats the metal indirectly, avoiding the electrical arcing and magnetron destruction you would expect heating metal in a microwave oven. The system encloses the metal component within a ceramic insulating cavity containing microwave-absorbing plasma created from inert gas. The plasma heats the metal.

The technology works quickly, Dana engineers say, because of the low thermal mass of the plasma and the efficiency of the microwave system. How fast? Dana says it can reduce cycle time by two-thirds compared to the conventional heating process.

Besides heat treating, the Dana system reportedly can deposit a variety of hard coatings normally applied under pressure with chemical vapor deposition.

Among successes Dana reports with the process are the following, all involving parts weighing hundreds of grams:

* Carburization of 8620H steel alloy gears (60-80 minutes at 1,000C).
* Sintering of a powdered-steel gear (20-40 minutes at 1,200C).
* And brazing of low-carbon steel (90 seconds at 1,100C).

Though the company has set no date when commercial systems would be available, it predicts that it could be as soon as early 2005. For now, the company will use the technology for its own internal needs.