Rare-earth elements (REEs) have transformed manufacturing and product design worldwide. Minute amounts of REEs alloyed with other metals can turn even the smallest motor into a powerful tool to induce large motion.
And, when magnets are smaller, cost per piece drops as less magnet material is required to obtain the same magnetic field strength. Supporting technologies, such as coils, exchangers and cooling systems, can be reduced in size as well.
Magnetism starts with individual atoms, but only some kinds of atoms are magnetic, according to George Hadjipanayis, a professor at the University of Delaware, and one of the leading experts in nanostructural magnets. Some that are magnetic include iron, nickel and cobalt—traditional metals. But, some are more magnetic such as neodymium and samarium—rare earth metals. Many achieve better magnetism, and some have better or worse mechanical properties.
The maximum energy product of a magnet is measured in units of millions of gauss oersted (MGOe). The higher the MGOe, the more powerful the magnet. The best MGOe results include samarium-cobalt (SmCo) and neodymium-iron-boron (NdfeB). SmCo has better temperature stability, but is more expensive, and has only an MGOe of 20 to 30. NdfeB has an MGOe of 40 to 50, but is not as temperature stable and loses magnetization, which is why dysprosium (DY) is often added because of its superior thermal properties.
So, if they are so magnetic, if you will, why are many motor manufacturers throughout the motor spectrum exploring ways to eliminate rare-earth magnets (REMs) or reduce the amount of REEs used in their product?
In fact, there is a simple answer to a very complex problem. P.J. Piper, chief executive officer of QM Power, Lee’s Summit, Mo., says it comes down to supply and demand. “In general,” says Piper, “the move toward not using magnets was due to supply chain problems.”
Piper says that the process is expensive and fraught with environmental problems. Rare earth elements are captured in our earth’s crust—literally conjoined to other materials—and extracting them takes capital in terms of dollars and cents, but also energy, land and water usage.
In all, there are 17 REEs, 15 within the chemical group called lanthanides, plus yttrium and scandium. As it turns out, rare earth elements are not all that rare; some are even more abundant than copper, lead, gold and platinum.
There are 17 rare-earth elements, which include yttrium and scandium, and the 15 lanthanides: lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium.
China holds a near-monopoly on the REE market, producing about 97% of the world’s REEs. For years, China produced these materials at such a low cost that most mines folded. Over the last several years, things have changed. China has closed some mines and imposed restrictions on REE exports, citing their own needs and environmental concerns. These actions caused prices to soar, most notably in 2010 and 2011. These prices rose, in some cases, by as much as 300%, says Gary Shapiro, director of the Consumer Electronics Association, in an April 2012 editorial he wrote for Forbes.com.
While prices stabilized in mid-2012 because of faltering global demand, prices are still at elevated levels and global demand is expected to rise. Unless a company is located on China’s mainland, some manufacturers worry that REE supplies will falter.
According to a December 2011 study by PriceWaterhouseCoopers, Minerals and metals scarcity in manufacturing: The ticking time bomb, 77% of executives in seven industry sectors placed minerals and metals scarcity as their number one concern, beating out energy, water and land scarcity.
This uncertainty has led certain manufacturers to develop alternative technologies. Some of these motors are unlikely to be specified by Appliance DESIGN product designers, such as a servomotor, but with technology migration, designers should be aware of coming technology.
In the 1980s, there was a scarcity of SmCo magnet, which drove the development and introduction of neodymium magnets to the marketplace. Similarly, China’s current tightening of its grip on REM exports has caused manufacturers of low-voltage (AC induction) motors to seek alternative IE4 technologies, says Mark Meza, an analyst with IHS Research. “Manufacturers have been very creative in dealing with magnet sourcing issues by producing drive technologies that reduce the number of neodymium magnets needed in a PMSM motor, or by producing IE4 class motors that use no magnets.”
Some of the new alternatives include migrating to ferrite materials, changing magnet orientation, adjusting windings, reducing REE use through nano technology, or coating stable cores with a thinner layer of REE material.
Meza points to ABB’s Synchronous Reluctance motors and Nidec’s Switched Reluctance motors as two examples of low voltage motors that achieve IE4 levels of efficiency without the use of magnets, and that have become viable lower-cost alternatives to the traditional neo-based PM machines.
NovaTorque produces an electrically commutated PM (ECPM) IE4 motor using traditional ferrite magnets, says Scott Johnson, NovaTorque’s vice president of sales. They developed an axial motor design that focuses flux in three dimensions, rather than the two dimensions of conventional radial designs. For its Gen 2.0 PremiumPlus motors, the company uses conical magnets, as opposed to cylindrical magnets, and the conical magnets are lighter and offer more surface area. The result is a ferrite-magnet motor that delivers torque and efficiency comparable to that of rare earth versions, in a similar frame size. The motors can reach efficiencies of 93% for 3hp motors and 93% for 5hjp motors, and maintain a high efficiency throughout the load, says Johnson.
Hitachi Metals Ltd. of Japan has developed an axial flux motor technology using amorphous metal ribbons made of iron, silicon and boron (FeSiB), coupled with traditional ferrite magnet technology to achieve an IE4 level of efficiency. The axial-gap motor, in which the rotor does not sit inside the stator but lies adjacent to it, allows magnetic flux to pass across the narrow air gap that separates the stationary and moving components of the motor. Hitachi says compared to conventional motors of the same class, its new motor is smaller and delivers an energy efficiency of about 93％.
The amorphous metal is generally created by quickly cooling iron so that it forms in a non-crystalline structure, which makes it lighter and sturdy so that it can endure a large torque and centrifugal force.
A number of motor manufacturers have turned to switched reluctance motors (SRMs), a technology developed in the 1800s. SRMs do not include brushes, rotor windings, commutators or magnets. Instead, torque is produced by the magnetic attraction of rotor poles to stator electromagnets.
SR motors traditionally had noise and cogging problems, and companies are working to solve this problem via new motor designs and fast-switching semiconductor chips that allow electronic controls to operate a reluctance motor.
For instance, Hybrid Eclectic Vehicle Technologies (HEVT), a Chicago-based manufacturer of SR motors, and winner of the CleanTech Open in California, says it solved the noise and vibration problems that have plagued SR motors in the past. The company, which recently said that it wants to develop motors geared to the appliance market, has a SRM with a rotating disc inside a stationary disc. Each drive has poles that contact each other and allow the stationary disc to create a magnetic field. This moves the rotating disc and creates mechanical energy. Cogging was solved, they say, by enhanced software.
Adjusting the geometry of a motor, such as magnet orientation and windings, can also reduce magnet content while maintaining torque levels. QM Power designed a motor using a Parallel Path Magnetic Technology (PPMT) whereby the magnets’ orientation is shifted so that power from multiple magnets can be coupled to create stronger magnetic fields in the motor, says Piper. The company’s website explains that conventional motors operate with field coils or magnets arranged in “series,” meaning that there is only one flux path and a magnetic field with one unit of force.
QM’s parallel flux lines can generate four times the force for a given electrical input compared to conventional systems along that flux path.
Additionally, QM Power will soon release a line of high efficiency motors for use in appliance applications. Q-Sync uses patented electronic controls technology to achieve up to four times the efficiency of conventional motors used in household and commercial appliances.
Another company that tweaked its design was the EV motor maker Yaskawa that developed an EV motor with a ferrite-magnet core. The Japan-based company optimized torque output by changing its coil winding. Instead of using a standard round-cross section wiring, the company switched to a rectangular cross-sectioned wire, which, according to a the company, stacks better on the rotor and stator, resulting in a 30% increase in the number of windings and increasing power output.
Not all motors come from the top down. New technologies are also being developed from the ground up. At the University of Delaware, Hadjipanayis is working to develop nanostructured REMs using nanoparticles with a process called exchange coupling. These could give the magnets up to 40% lower neodymium content.
While rare earth magnets are likely to continue to dominate the market, certain at the neo-magnet level, these and other new technologies may give manufacturers stronger confidence in the future and lessen some of the concern about future REE supply and prices.