PD IEC TR 62518 pdf download – Rare earth sintered magnets — Stability of the magnetic properties at elevated temperatures

PD IEC TR 62518 pdf download – Rare earth sintered magnets — Stability of the magnetic properties at elevated temperatures

PD IEC TR 62518 pdf download – Rare earth sintered magnets — Stability of the magnetic properties at elevated temperatures
1 Scope
The scope of this technical report is to describe the temperature behaviour of rare earthsintered magnets in detail for use in designing magnetic circuits exposed to elevatedtemperatures. The temperature behaviour of SmCog,Sm,Co47 and Nd-Fe-B sintered magnetsis described.
The various changes of open circuit flux which can occur due to temperature are discussed inClause 4.The long term stability of the magnets is discussed in Clause 5. The experimentalprocedures are described in Clause 6.Results of the measurements of the flux loss occurringat the ambient temperature after heating isothermally at 50 °C,75 °C,100 °C,125 °C,150 °℃and 200 °C for up to 1000 h are given in Clause 7.The effect of length to diameter ratio(L/D)of the magnet samples and the influence of Hj on the flux loss were also studied.The resultsare discussed in clause 8.
The data in this technical report was provided by the Institute of Electrical Engineers of Japan(IEEJ) and its subcommittees.This data has been gathered from the members of these sub-committees.
The temperature stability correlated with the complex corrosion behaviour and the spin re-orientation phenomena at cryogenic temperatures will not be given in this technical report.
2Normative references
IEC 60050-121,International Electrotechnical Vocabulary – Part 121:Electromagnetism
IEC 60050-151,International Electrotechnical Vocabulary – Part 151:Electrical and magneticdevices
IEC 60050-221:1990,International Electrotechnical Vocabulary – Chapter 221: Magneticmaterials and components
Amendment 1 (1993)
IEC 60404-8-1,Magnetic materials – Part 8-1: Specifications for individual materials -Magnetically hard materials
3Terms and definitions
For the purpose of this document, the following terms and definitions apply. In addition,mostof the technical terms used in this document are defined in IEC 60050-121,IEC 60050-151,and lEC 60404-8-1(the product standard).
magnetic flux loss
the reduction due to an external influence,primarily temperature,in the flux of permanentmagnets in a magnetized state,unit of Wb.Three kinds of flux loss,reversible flux loss,irreversible flux loss and permanent flux loss, are used to discuss the temperature stability ofrare earth sintered magnets.
reversible flux loss
a magnetization change which is recovered by the removal of a disturbing influence such astemperature. lrreversible flux loss is the partial demagnetization change caused by thetemperature changes. The irreversible flux loss is fully recovered by remagnetization.Permanent flux loss is caused by permanent change in the metallurgical state and is generallytime and temperature dependent. The permanent loss cannot be recovered to the initialmagnetization value by remagnetization.
uniformity field strengthHk
the uniformity field strength (of a magnetically hard material) as defined in IEC 60050-221-02-62(Amendment 1 (1993)) was originally called“knee field” [6]. H is the negative value of themagnetic field strength when the magnetic polarization of a magnetically hard material isbrought from saturation to 90 % of the value of the remanent magnetic polarization by amonotonically changing magnetic field.
reversible temperature coefficient
the reversible temperature coefficient of magnetic flux is the percentage changes in fluxper degrees Celsius by the change in temperature,which is reversible. The temperaturecoefficient is expressed as %/RC. The temperature range must be stated to make themquantify.The reversible temperature coefficient of magnetic flux (denoted as a )) is thequotient of the percentage change of magnetic flux by that change in temperature:
where oand grer are the flux at temperature 0 and 0,er respectively.
Generally rare earth sintered magnets exhibit a non-linear change of flux with temperature.
“Temperature coefficient of B, (denoted as cxB,)” can be defined from the temperaturedependence of B, in the temperature range to have the quantitative values.The temperaturecoefficient of B,is the quotient of the relative change of B, due to a change in temperature bythat change in femperature:
(B,)=(Br- Brret)/Bpret Bra-1/(0- eet)
where B, and B7ref are the B,at temperature of 0 and respectively.“Temperaturecoefficient of Hoj (denoted as x(H.j))” can be also defined as mentioned above.
The revised evaluation method for temperature coefficients of B, and Hj are given in lEC/TR61807(1999) in which the temperature dependence of B, and Hj is expressed by a quadraticfunction of temperature, see Annex B.To define the “temperature coefficient” the temperaturerange must be stated because of the non-linearity of the temperature dependence.
anisotropy fieldHA
the anisotropy field(denoted as H,) is the field required to rotate into the hard direction or thefield to saturate the material in the hard direction, and it is a measure of the anisotropy.Therelationship between HA,K (crystalline anisotropy constant) and M (saturationmagnetization) is as follows: