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Development of "High Performance Magnetic Core" for Induction Hardening Equipment

8/29/2014

Composite material with proprietary mix, and special compression molding technology for the industry highest performance

NTN Corporation (hereafter, NTN) has developed a "High Performance Magnetic Core" with the industry's highest level of magnetic properties and strength by coating the surface of iron power with thermosetting resin*1 and applying compression molding.

Machine parts such as bearings and gears are heat treated to increase strength and to improve reliability. In particular are parts related to drive equipment commonly found in automobiles, which have a complex shape and require strength in certain areas, thus calling for heat treatment for high-frequency induction heating (induction hardening)*2 to harden required areas. The heating coil section of induction hardening equipment features magnetic material attached called a "core" that contributes to reducing heat treatment time and improving hardening precision, however suffered from issues related to low material strength, and excessive processing man-hours and material loss.

The newly developed "High Performance Magnetic Core" uses iron powder for powdered metallurgy as the magnetic powder, with a proprietary mix of thermosetting resin added for granulation processing to apply an insulating coating over the surface of the iron. A special type of compression molding and thermal hardening help to limit damage to the coating.

These features reduce contact between powders, and the saturated magnetic flux density*3, the market index for magnetic properties, is improved by 10%, the relative permeability*4 is increased by 30%, and the iron loss*5 is reduced by 15% to achieve the industry's highest level of magnetic properties. The radial crushing strength is also 5-times that of commercially available products, which drastically improves core cutting work and handling. Utilization of the developed product brings improvements to induction hardening efficiency for more accurate hardening, which helps to reduce the time required for heat treatment, and increase both strength and hardness of machined parts.

The "High Performance Magnetic Core" is already in use with equipment at NTN, however the product is being marketed to new manufacturers of induction hardening equipment and high-frequency heat treatment machining companies. Induction heat treatment is gaining attention as a form of heat treatment that does not require fossil fuels or detergents. NTN will make efforts to increase sales activities of the developed product as its utilization contributes to performance improvements of induction hardening equipment.

*1) Resin that becomes harder with heating due to polymerization.
*2) A heat treatment method that generates electromagnetic induction with electromagnetic waves to heat the surface of metals and harden them.
*3) Limit value of the magnetic flux achieved per unit area in a vertical direction from the magnetic field.
*4) Ratio of magnetic permeability in a vacuum, and is used as a scale to compare the ratio of the degree of magnetic flux density and magnetic field strength.
*5) Loss within a coil that has a core exhibiting magnetic properties, where electrical power is consumed as heat due to magnetic hysteresis and eddy currents, causing energy loss.

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