Making Resistive Magnets

Ingredients: Only the Best

Every plate that goes into our coils starts out life as a sheet of metal no thicker than a millimeter. Depending on the specifications of the magnet, the sheet may be made of pure copper, an excellent conductor, or of a copper alloy – copper-beryllium, copper-zirconium or copper-silver.

Of course, the first thing we do with this material is test it: Quality control dictates this process right from the get-go. Engineers in our Materials Characterization Lab scrutinize each incoming batch of metal for conductivity and strength.

Raw material for a magnet.

The material has to be tough. It's going to take a licking and it needs to keep on ticking. The material will be subject to millions of pounds of pressure and power densities of 14 watts per cubic millimeter – more than in any other man-made device, according to Magnet Science & Technology Director Mark Bird.

"It is a little bit tricky because it's sheet metal, and they need to know the strength of it pretty accurately," explained MagLab engineer Bob Walsh, who developed and oversees the testing process. "The material can't have imperfections, it has to be made very well, and that way its strength is very consistent." The testing is an important first step in quality control. "We don't pay until we get this result," Walsh noted.

If the sheets pass muster, they're shipped off to an outside facility where pancake-like discs are cut out of them, each with a very particular pattern of round and elongated holes.

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