Magnetics exert a growing power

DN Staff

January 8, 2001

4 Min Read
Magnetics exert a growing power

What makes magnets so attractive? Thanks to advances in magnetic materials, design engineers involved with automotive, appliance, and electronics projects will increasingly find themselves answering in just three words: power, packaging, and pricing.

Consider permanent magnets, the kind that keep a pit bull-like hold on their magnetizing force. With applications in a variety of electronic components and just about any field that uses electric motors, permanent magnetic materials have been growing at a fast clip. Global sales of all the material types increased about 12% last year to $2 billion, according to a study conducted by Wheeler Associates (Elizabethtown, KY). But not all magnetic materials have equal prospects. High-energy magnets, particularly those made from alloys of neodymium iron boron (NdFeB) have started to outpace classic magnetic materials, such as ferrite.

The reason why is simple. High-energy magnets can pack more power into smaller spaces than lower-energy magnets. "The high energy materials can give you a better end product, a smaller end product, or a combination of the two," notes Port Wheeler, president of Wheeler Associates.

This shift to high-energy magnets ties into a motor design trend already sweeping through the automotive and appliance industries. "Everyone wants higher power densities, so they can pack more output power in an existing frame size or pack the same power in smaller frame," says Jake Ring, vice president of Magnequench (Anderson, IN), a supplier of NdFeB powders and magnets. Over the past couple of years neodymium magnets have appeared in applications that would have in the past gone to ferrite or wound magnets. As examples, Ring cites a recent Porter Cable cordless drill and a column-mounted power steering motor on the Opal Astra. And he argues that the switch to high energy magnetics stands to accelerate over the next few years as appliance makers put out smaller, lighter cordless products and as auto makers adopt 42 volt electrical systems to power vehicle functions.

High-energy magnets do have to overcome a couple of hurdles if they are to become more widespread. For one, NdFeB magnets have a temperature limitation of 200C, which rules out some high-temperature applications. And then there's price. "On a kilogram to kilogram basis, neodymium magnets can cost an order of magnitude more than ferrite," Ring says. To offset that disadvantage, Magnequench, one of the largest suppliers, has committed to price cuts of more than 7% per year through 2005.

But designers shouldn't focus on price alone, because neodymium magnets don't typically make sense as a one-to-one replacement for ferrite. "Most applications can use a smaller neodymium magnet than ferrite," Ring says. In fact, simply dropping a high-energy magnet into the place of a low-energy one would waste money at best and lead to an oversaturated magnetic circuit at worst. For this reason, the best applications for high-energy magnets may be new design projects in which engineers have the freedom to balance power, sizing, temperature, and cost constraints. "Working with high-energy magnets poses a classic engineering problem," Ring says. For more and more engineers, it may be a problem worth solving.

Pumping magnets

Santa Ana, CA -Permanent magnet motor technology and unique soft magnetic materials recently enabled ShurFlo Inc. to create an axial pump that has only one moving part and no dynamic seals.

Best thought of as a dc brushless motor with an impeller instead of a conventional rotor, ShurFlo's pump runs on the magnetic attraction between electromagnetic windings on its stator and a disk-shaped permanent magnet embedded in its impeller. "If you replaced the impeller with a rotor, you'd have an axial flux motor," says John Loarie, the company's vice president of advanced motor technology.

For the stator, a ring-shaped part crowned by nine poles that support the copper windings, a ceramic-coated iron powder and proprietary manufacturing process from Mii (West Lebanon, NH) beat out conventional laminated steel, a tooled magnetic core material, and a hybrid of injection molded plastic and cold-rolled steel. According to Loarie, only the Mii powder had the right balance of magnetic and manufacturing properties. The Mii material features a low eddy-current loss required for efficient motor operation at high frequencies. And Mii's net-shape manufacturing offset the stator's budget-busting combination of high production volumes and a complex geometry.

The choice of permanent magnet lends some design flexibility to ShurFlo's axial flux concept. The first version of the axial pump, a fractional-horsepower model for marine applications, boasted a ceramic magnet. But ShurFlo can create more powerful pumps by switching to high-energy magnets. For example, Loarie has a new version under development in which a NdFeB magnet produces a five-hp unit capable of pumping five gallons per minute at 150 psi. For all that extra capacity, "it uses the same stator as our original pump," he adds.

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