Magnet Thermal Aging, Thermal Degradation of Magnetics, Effect of thermal aging on magnet, magnet aging fixture, Thermal aging of melt-spun NdFeB magnetic powder
What is magnet thermal aging?
Even though we usually say “permanent magnet”, but magnets do not remain magnetism permanently. In general, permanent magnets are gradually demagnetized by the impact of heat variations. This behavior of magnet can be determined by total flux change over time for a given temperature, also known as “flux loss”.
Thermal aging of melt-spun NdFeB magnetic powder in hydrogen
•Injection molded NdFeB magnets age rapidly in automatic transmission fluid (ATF).
•Coercivity loss is not due to direct chemical reaction between ATF and the powder.
•Chemical reaction with the binder does not play a major role in aging.
•Hydrogen dissociates from ATF and diffuses into Nd2Fe14B, reducing coercivity.
High energy product neodymium-iron-boron (NdFeB) magnets are the premier candidate for demanding electrified vehicle traction motor applications. Injection molded (IM) or compression molded (CM) magnets made using NdFeB powders are promising routes to improve motor efficiency, cost, and manufacturability. However, IM and CM NdFeB magnets are susceptible to substantial thermal aging losses at motor operating temperatures when exposed to the automatic transmission fluid (ATF) used as a lubricant and cooling medium. The intrinsic coercivity Hci of NdFeB IM and CM magnets degrades by as much as 18% when aged for 1000 h in ATF at 150 °C, compared to a 3% loss when aged in air. Here we report aging studies of rapidly quenched NdFeB powder in air, ATF, and H2 gas. Expansion of the NdFeB crystal lattice in both ATF and H2 identified hydrogen dissociated from the ATF during aging and diffused into the primary NdFeB phase as the probable cause of the coercivity loss of IM and CM magnets.
Which factors have impact on magnet thermal aging?
Shape of magnet.
Operating condition and time.
Magnetic properties of magnet.
Composition of magnet.
Microstructure of magnet.
Surface state of magnet.
Coating property of magnet
Permanent magnets,Neodymium-iron-boron,Thermal aging,Melt-spun,Injection molding
What are characteristics of recoverable irreversible loss?
This part of flux loss usually lost after temperature recovery. These losses are only recoverable by re-magnetization.
Thermal aging is used to test the ability of a product to withstand elevated temperatures for an extended period of time. This test measures the change in LLCR and mating / unmating force both before and after the parts have been thermally exposed in a thermal chamber.
The normal program used to test Samtec’s products is at 105°C for 250 hours, and is based on the standard EIA-34-17 “Temperature Life With or Without Electrical Load Test Procedure for Electrical Connectors and Sockets.”
What are characteristics of unrecoverable irreversible loss?
This kind of loss is also called structural loss. The structural loss can’t recoverable even if re-magnetization.
AGING METHODS – There are various standards and frameworks published by ASTM, NEMA, UL and IEEE for aging methods, measurement techniques and statistical analysis. These standards were established for assessing an EIS quality for industrial use in electric machines. Accordingly, different classes of wire as defined in Table 1 have different aging temperature limits. As when the different stresses are combined in the AA, this does not allow for the impact of each individual stress to ascertained. In addition, the aging process within an EIS cannot be accurately represented by a simple equation due to the large of amount of variables contained in a process of the degradation. However, simplified equations, statistics and rules of thumb are often used in industry despite their inaccuracy as it is typically not feasible to factor in the specific aspects of the end application. It is clear that this is a highly complex and multifaceted area and one that is not well understood. Hence, more experimental studies and multi-physics modeling should be investigated to factor in the various aspects of electric machine design, coil and wire geometries, drive cycles and the various environmental conditions present.
Why consider the total flux loss during engineering design?
In some application of magnet, the magnets are usually exposed at an elevated temperature which causes flux reduction. Designer need to fully consider the factors of flux loss can improve the service life of magnets.
How to implement aging treatment of magnets?
The magnet should be stabilized by exposing is to elevated temperature for specify time, and the magnets will more stable during its use.
Effect of thermal aging on stability of transformer oil based temperature sensitive magnetic fluids
Synthesizing stable temperature sensitive magnetic fluids with tunable magnetic properties that can be used as coolant in transformers is of great interest, however not exploited commercially due to the lack of its stability at elevated temperatures in bulk quantities. The task is quite challenging as the performance parameters of magnetic fluids are strongly influenced by thermal aging. In this article, we report the effect of thermal aging on colloidal stability and magnetic properties of Mn1-xZnxFe2O4 magnetic fluids prepared in industrial grade transformer oil. As-synthesized magnetic fluids possess good dispersion stability and tunable magnetic properties. Effect of accelerated thermal aging on the dispersion stability and magnetic properties have been evaluated by photon correlation spectroscopy and vibration sample magnetometry, respectively. Magnetic fluids are stable under accelerated aging at elevated temperatures (from 50 °C to 125 °C), which is critical for their efficient performance in high power transformers.
Magnetic fluids,Thermal aging,Co-precipitation,Hydrodynamic size,Magnetic properties
The test sequence is as follows:
Measure contact gaps
Test force to mate / unmate
Test initial LLCR
Thermal Aging (Sit in the thermal chamber for 250 hours undisturbed)
Retest the force to Mate / Unmate
Remeasure contact gaps
Thermal Degradation of Magnetics
Magnetics, such as transformers and chokes, are often not considered when temperature concerns arise during design reviews. Since transformers are typically custom made, many do not come with a temperature rating.
So, how do you determine when it is too hot for magnetics? There are three key issues of concern which can all be solved using simulation software.
The first is that the current saturation curves for ferrite materials tend to obscure when these materials starts to saturate. Saturating the magnetic material will not damage a magnetic, but it will appear to be shorted — causing the circuitry to fail.
The second issue is that designers sometimes mistake a magnetic’s maximum temperature rating as being equal to the Curie temperature (when a magnet’s properties change considerably at around 100 C – 300 C or 212 F – 527 F). However, core loss (magnetic alterations) usually begins at temperatures between 50 C – 100 C (122 F – 212 F). Depending on the ferrite design, structure and cooling, the magnetic can go into a thermal runaway if the core temperature gets into the core loss range.
Finally, thermal aging is a primary concern for powder iron cores — which are lower cost and sometimes more appropriate than ferrite cores. Long-term exposure to elevated temperatures can induce thermal aging of the binding agents. As thermal aging progresses, the eddy current loss becomes significantly higher. Increasing core loss results in higher core temperatures and failure of the magnetic component.
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