Bonded Magnet Materials

1. Is Bonded NdFeB material an alternative for ceramic magnets when greater performance is needed?

2. What is the highest bonded Sm-Co energy product? What temperature can it handle?

3. What is the maximum service temperature of Bonded NdFeB material?

4. What is the minimum thickness that a Bonded NdFeB bonded magnet can be pressed to?

5. What kind of uniformity can we expect from Bonded NdFeB material?

6. What manufacturing process variables affect Bonded NdFeB material uniformity?

7. What tolerances can be held on a pressed Bonded NdFeB part?

8. Why are injection molded magnets weaker than compression molded magnets?

9. Why should I convert to Bonded NdFeB magnet material?

    

10. Is Bonded NdFeB material an alternative for ceramic magnets when greater performance is needed?
    Bonded NdFeB material produces almost twice as much flux density as anisotropic ceramic magnets (grades 5 - 8), so substituting Bonded NdFeB material is a fairly safe way to extract greater performance from a device. Resistance to demagnetization for Bonded NdFeB material is also twice that of ceramic, so the Bonded NdFeB part can be half as thick as the ceramic magnet without a loss of performance. If possible, the steel parts onto which the Bonded NdFeB magnet is mounted should be twice as thick to carry the additional flux efficiently.

    
    

11. What is the highest bonded Sm-Co energy product? What temperature can it handle?
    New grades of bonded Sm-Co are being added periodically. One popular grade is 17, with an energy product of 16.5 MGOe, Br=8.75 kG, Hc=6.5 kOe, and Hci=11 kOe.  The functional temperature limit will be set by the thermoplastic binder used to make the magnet, around 400 °F.

    
    

12. What is the maximum service temperature of Bonded NdFeB material?
    The maximum would be 150 °C (300 °F), because the bonder holding the magnet together softens. You might be able to push slightly higher than this, but consult a Precision Magtech Applications Engineer first.

    
    

13. What is the minimum thickness that a Bonded NdFeB bonded magnet can be pressed to?
    Answer As a general rule, figure on 0.090" [approximately 2 mm].

    
    

14. What kind of uniformity can we expect from Bonded NdFeB material?
    Magnetic uniformity often exceeds the MMPA standard of +/-8% but every job is different so don't use this for every case. Within a specific lot of material, the uniformity will be very good, but lot-to-lot variations will at a minimum meet the MMPA standard.

    
    

15. What manufacturing process variables affect Bonded NdFeB material uniformity?
    Pressure & density variations and wear of the tool. The magnetizing fixture can be a factor as well.

    
    

16. What tolerances can be held on a pressed Bonded NdFeB part? For the initial run for a new tool, figure on +/-.005". We have to see how pieces will "spring-back" after ejection from the die. After the characteristics of the new tooling is figured out, the tolerances can shrink to +/-.002".

    
    

17. Why are injection molded magnets weaker than compression molded magnets?
    Compression molded magnets have much more magnet material in them than injection molded magnets, so they are inherently stronger. Compression molded magnets are made from a mixture with a high concentration of magnet powder and a small amount of epoxy as a binder. This mixture is then compressed to a high density before curing the epoxy. Injection molded magnets are made by mixing the magnet powder with a plastic that is liquid enough to inject into a mold, and pressures are lower, so injection molded parts have a much lower concentration of magnetic powders and are therefore weaker.

    
    

18. Why should I convert to Bonded NdFeB magnet material? Bonded NdFeB magnets can increase performance or reduce the size of devices made from anisotropic ceramic (grades 5 - 8) magnets. Bonded NdFeB material provides almost two times the flux and resistance to demagnetization. Substituting Bonded NdFeB magnets then gives 4 times greater energy density if substituted directly, or the Bonded NdFeB based device can be significantly smaller than its ceramic counterpart. Bonded NdFeB material is also isotropic, so it can be magnetized in any desired direction. Bonded NdFeB magnets are made from a compression molded material, so it can be molded to finished size as opposed to ceramic, which suffers shrinkage, and must be ground after pressing and firing. Some sintered Sm-Co devices are inefficient and could perform as well at a lower cost by substituting a pressed-to-size Bonded NdFeB part.