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Forum: Reliability & Maintainability Questions and Answers

Topic: Reliability & Maintainability Questions and Answers

Topic Posted by: Reliability & Maintainability Forum ( )
Organization: System Reliability Center
Date Posted: Mon Aug 31 12:47:36 US/Eastern 1998

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Posted by: Peter Kirchhofer ( )
Organization:JAQUET Ltd
Date posted: Thu Nov 25 5:09:20 US/Eastern 1999
Subject: Rear Earth Magnets
Datasheets specify the Curie temperature and the much lower maximum allowable ambient temperature for the different magnet materials. Q1: What happens to the magnet during prolonged temperature cycling between normal and above maximum allowable temperature? Q2: Has vibrational stress any influence on the magnetic properties?


Subject: Magnetic Properties
Reply Posted by: Bruce Dudley ( )
Organization: Reliability Analysis Center
Date Posted: Mon Nov 29 15:37:29 US/Eastern 1999
In an old paper by D.I. Gorden of the U.S. Naval Ordnance Laboratory, Silver Spring MD, called "Magnetic Cores and Permanent Magnets in Hyper-Environments" 1960 Institute of Environmental Sciences Proceedings, I found information related to the temperature question that you proposed. For soft magnetic material the greatest influence on magnetic properties occurs just below the Curie point or near the temperature of a phase transformation. Most soft materials showed significant irreversible changes as a result of exposure to 500 degrees centigrade and cooling to room temperature. These irreversible changes included: increase in coercive force, decrease in maximum permeability, decrease in high field and residual inductions and (for rectangular loop materials) decrease in squareness ratio. For permanent magnets of the Alnico type, most can be used up to 500 degrees centigrade with small changes in remanence being reported. Alnico 1 through 7 as well as remalloy, indalloy, vicalloy and carbon steel all show small changes with varying degrees of reduced performance. Alnico 12, tungsten, chrome and colbalt steels, barium ferrite, Cunico and Cunife 1 are not usable at this temperature. No information on the effect of vibration on magnetic materials was discovered in our library.

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