New sintered material for high-speed rotary motors

A Sumitomo Electric Industries product story

Edited by the Engineeringtalk editorial team Feb 1, 2002

A new sintered material can be used as a soft magnetic material in high-performance actuators for automobile components and high-speed rotary motors used in hard disk drives

Sumitomo Electric Industries has developed a sintered material that can be used as a soft magnetic material in high-performance actuators for automobile components and high-speed rotary motors used in hard disk drives.

The material is made from fine magnetic iron powder several tens of micrometers in diameter, which is coated with an insulating layer several hundreds of nanometers thick.

An ultra-trace volume of originally-developed heat-resistant binder is then added to this powder and compressed into a solid, creating a dense sintered material with superior magnetic properties to conventional sintered materials.

The action of the insulating layer on the surface of the iron powder reduces core loss, thus achieving superior magnetic properties at higher frequencies.

The new material has a magnetic flux density of 1.6 teslas (T) at a magnetic field strength of 125 oersteds (Oe), a 20 to 30% improvement on conventional sintered soft magnetic materials.

In addition, the original heat-resistant binder added to the material provides a high degree of heat resistance.

The material has a three-point bending strength of 140 MPa at 200 degrees centigrade, about ten times that of conventional sintered soft magnetic materials.

This improved performance makes the material suitable for use in the high-speed rotary motors found in high-capacity hard disk drives, which operate at between 10,000 to 20,000 rpm.

It is also suitable for use in high-performance automobile parts that require actuators with fast response times.

To improve fuel consumption and reduce gas emissions in the latest diesel engines, actuators must open and close the fuel injection valve within 2 to 5 microseconds.

Conventional soft magnetic materials used for these applications (motor cores, etc.) were made by laminating or fitting together multiple layers of silicon steel plates or magnetic steel plates.

However, when these materials were used at high frequencies (1 to 2 kHz or higher) and required rapid response times and high-speed rotations, there was a decline in the magnetic properties caused by the core loss (generation of heat caused by eddy current.) Unlike conventional steel plates, the material is not anisotropic, which have different magnetic properties on the outside and inside of steel plates and which are in the direction of laminate, and with equal magnetic properties in three-dimensional directions, allowing dramatic improvement in the degree of freedom in parts design.

Since the material can be turned into complex parts as easily as conventional sintered parts, it enables reduction of the total cost of the parts.

Also, because the new material is made by compressing magnetic powders, it can be pulverized at low cost.

Because of this, it is simple to separate and recover the coiled wires (Cu) and motor cores (Fe), making the motors easier to recycle than those made with conventional steel plates.

SEI is already shipping samples of this new sintered soft magnetic material and is planning to begin mass production this year.