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# Re: [femm] Material for pole pieces of Magnet

- To: <femm@yahoogroups.com>
- Subject: Re: [femm] Material for pole pieces of Magnet
- From: "C F Cheuk" <c_f_cheuk@yahoo.com>
- Date: Wed, 29 Aug 2001 18:39:03 +0100
- Disposition-notification-to: "C F Cheuk" <c_f_cheuk@yahoo.com>
- References: <122.3b5c83f.28bdce5b@aol.com>

Hi Dave, Thank you very much for your reply. Your experience give me confidence in experimenting the design. C F Cheuk ----- Original Message ----- From: dcm3c@aol.com To: femm@yahoogroups.com Sent: Wednesday, August 29, 2001 5:49 AM Subject: Re: [femm] Material for pole pieces of Magnet In a message dated 8/27/01 2:06:39 PM Eastern Daylight Time, c_f_cheuk@yahoo.com writes: Hi All, I am in the process of designing a voice coil actuator (re-inventing the wheel really). I have always been advised to use advanced magnetic material such as Vacoflux 50 for the outer pole piece . The magnet I am using is a NdFeB with Hc of 1000000 A/m. The load line is above the knee to avoid temperature de-mag effect. Theair gap need to be of the order of 3 to 4mm to accommodate the coil. [...] I think I should make a polepiece out of mild steel and test out the hypothesis. Can anyone please enlighten me. What should I watch out for if I change the expensive stuff to mild steel. Temperature effect? demagnetisation? Can't sleep at night? Am I barking up the wrong or the right tree? I've designed and built this sort of actuator before for motion control applications. For the reasons that you outlined above (i.e. core is basically carrying DC flux and there's a big, honking air gap that masks the core's properties), I have used low carbon steel before (for example 1018). It's cheap, and the actuators worked just like the were predicted to. Although materials like Vacoflux-50 (which is a Cobalt Iron--the "50" stands for 50% cobalt) have a high Curie temperature relative to other types of core iron, it's hard to imagine that this could be a factor here--the NdFeB magnet would be the limiting factor as far as the operating temperature of your machine pretty much regardless of the iron that you pick. In general, it's best to avoid Vacoflux or Hiperco if you can because ofits very high cost and poor mechanical properties. Dave. `Your use of Yahoo! Groups is subject to the Yahoo! Terms of Service.`

- References:
  - Re: [femm] Material for pole pieces of Magnet
    - From: dcm3c@aol.com

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