Electromagnetic Properties

[Michael GilliganParticipant @michaelgilligan61133]

Fellow members of the AHS ‘EHG’ will already be aware of this video, but I thought it worth sharing more widely.

https://youtu.be/0_8_sIEIhs4?feature=shared

Note: it is 42 minutes long, and a straight recording of a Zoom meeting … so is, predictably enough, not slick.

It does however contain enough useful material to inspire further investigation.

Comments from expert metallurgists, et. al. would be welcome.

MichaelG.

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P.S. __ a Google search for ‘swedish soft iron’ is a good first step.

[Anonymous]

I suppose I ought to watch the whole video, but gave up when he said B equals H. They are not the same thing. The unit H is the magnetic field strength in amps per metre, the unit B is the magnetic flux density in teslas. They are proportional in a non-magnetic medium like air. But as soon as a ferromagnetic material is introduced the relationship becomes non-linear and complex, in a mathematical sense, ie, complex numbers.

He is right that pure iron has a higher permeability than carbon steel. If I recall my lectures the problem with carbon steel is not the carbon per se, although it is diamagnetic, but when the carbon precipitates out in the form of carbides.

As hinted at by MG there are specific steels intended for magnetic applications, known as electrical steels. In simple terms the carbon is replaced by a few percent of silicon. Permeability is almost as good as pure iron, BH characteristics can be tailored and it has a much higher electrical resistance than iron. This reduces losses due to eddy currents.

Andrew

[Brian WoodParticipant @brianwood45127]

Just to add to Andrew’s notes above, transformer cores are made from these silicon steels. They do not have the magnetic retention of carbon steels, which makes them suitable for the rapidly changing magnetic fields within a transformer core.

Brian

[John HaineParticipant @johnhaine32865]

I think the motivation for this work was the poor performance of a Eureka clock reproduction using mild steel cores.  Having looked at the work and the Eureka design I actually think the problem is poor magnetic design of the Eureka which makes it susceptible to lower permeability.

[Anonymous]

I’ve just skimmed the rest of the video. Some interesting experimental results, but quite a lot of confusion about material properties and composition, as well as magnetics.

I am not familiar with the Eureka design but I assume it uses solenoids, in which case JohnH may well be right. Solenoid design is not simple and is extremely sensitive to tiny gaps (even a couple of thou) in the magnetic circuit.

Andrew

[Michael GilliganParticipant @michaelgilligan61133]

Thanks for having another look, Andrew … I value your opinion

The main reason I posted the link here is that the speaker is obviously [in the true sense of the word] an Amateur, and is conducting a reasonably well considered set of practical experiments … which some here might like to develop and pursue further.

MichaelG.

[david bennett 8Participant @davidbennett8]

Just a thought (of no use in making a pure replica Eureka clock)

If the object is just to keep a heavy balance oscillating, would a powered,  switched, un-cored coil and a neodynium magnet be enough?

dave8

[John HaineParticipant @johnhaine32865]

https://groups.io/g/Horological-Science-Newsletter/message/548 – Brian Mumford suggested something similar.

Andrew’s point on air gaps is well made, there are several joints in the magnetic circuit which could add to the reluctance.

[david bennett 8Participant @davidbennett8]

John, thanks for pointing out that discussion.

dave8

[Russell EberhardtParticipant @russelleberhardt48058]

Just a thought; why concentrate on iron?  Ferrite materials are available in both soft and hard grades, the soft grades having low remanance. Worth trying the ferrite rods used as antennas in old radios?

Russell

[david bennett 8Participant @davidbennett8]

This might be worth a try for soft iron rod

 

https://www.philipharris.co.uk/products/physics/electricity-and-electromagnetism/magnetism?p=2

[John HaineParticipant @johnhaine32865]

The Eureka magnet which forms the “spokes” of the balance wheel is actually not just a plain rod core with a coil, it’s an E-shape with a bar each side, magnetically joined at one end, and the air gap that interacts with the stator at the other.  It seems to be possible to buy soft iron rod but flat strip as would be needed for the “arms” doesn’t seem to be around.

[Anonymous]

These people offer E-I laminations in stock sizes, although of course that is not the same as actually being able to order in small quantities:

https://ascocomponents.co.uk/laminations/ei-laminations/

Andrew

[david bennett 8Participant @davidbennett8]

Try this for flat iron

dave8

 

https://www.aliexpress.com/item/1005006016395605.html?src=google&aff_fcid=5e76adcaa2234d5396979c5de72cc201-1708547603501-04540-UneMJZVf&aff_fsk=UneMJZVf&aff_platform=aaf&sk=UneMJZVf&aff_trace_key=5e76adcaa2234d5396979c5de72cc201-1708547603501-04540-UneMJZVf&terminal_id=14e706d9ab3b4488852737047f36d9ce&afSmartRedirect=y

[John HaineParticipant @johnhaine32865]

Just for context here is the rotor drawing from the 1949 ME series of constructional articles by Artificer.  The central core rod is 5/16″ dia. and the side plates 3/32 x 7/16″, length about 3.75″.  The lower end as shown in the dwg is magnetically “hot” and interacts with the stator.  Coil is on a former around the central rod. There are clamped joints in the magnetic circuit at the top between two iron clamp blocks, the central core, and the side plates.  Clearly the overall core shape is quite unlike a transformer E core.

[duncan webster 1Participant @duncanwebster1]

Rather than the design shown by JH, could the side pieces be omitted and a second fixed pole diametrically opposite the existing one be provided. These 2 poles should be magnetically connected. There would then be much less sideload on the balance wheel.

The modern way to do it would be to have the coil on the stationary bit, save having flex wires to the balance wheel.

[John HaineParticipant @johnhaine32865]

To be clear, there are no flex wires, there’s a crude commutator.  There are many ways the clock could be improved, frankly I think the original design is bonkers!  The problem seems to be that people have made new ones from designs like the ME one and find that it’s hard to make them work.

[Michael GilliganParticipant @michaelgilligan61133]

With the greatest respect to John Haine … I am a little concerned by the specific reference to the ME constructional series by ‘Artificer’

The Eureka clock was [also ?] a commercial product, and I had presumed that was the version mentioned by our antipodean friends.

MichaelG.

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Ref: __ https://www.bmumford.com/clocks/eureka/

 

… much more here: https://clockdoc.org/Default.aspx?aid=12292

 

[Michael GilliganParticipant @michaelgilligan61133]

For what it’s worth … I believe this Canadian patent to be the original 1906 version of the design by Timothy Bernard Powers

https://worldwide.espacenet.com/patent/search?q=pn%3DCA100982A

[ downloadable from that page, but it’s 11MB ]

MichaelG.

[duncan webster 1Participant @duncanwebster1]

In the first few minutes of the AHS video the presenter refers to ‘copies of the Eureka clock’, which makes JH’s supposition entirely reasonable.

[Michael GilliganParticipant @michaelgilligan61133]

I wouldn’t dispute that, Duncan

MichaelG.

[Michael GilliganParticipant @michaelgilligan61133]

It doesn’t add anything to the present discussion, but here’s a nice animation of the Eureka

http://wp.clockdoc.org/wp-content/uploads/Eureka.mp4

MichaelG.

[david bennett 8Participant @davidbennett8]

Does anyone know the approximate weight of the balance/coil assembly and the recommended oil for the bearings?

dave8

[John HaineParticipant @johnhaine32865]

The clockdoc link above has design details from which the weight could be calculated if it’s relevant.   Other docs there may give oil details.

[Michael Gilligan]

On Michael Gilligan Said:

I wouldn’t dispute that, Duncan

Just to elaborate, Duncan … the fact that a supposition is ‘entirely reasonable’ does not guarantee that it is accurate.

It is also reasonable to suppose that some copies might not be based upon the series by ‘Artificer’

It is quite clear from the text of the articles, that some aspects of the design were necessarily ‘re-imagined’ and that some of the detailing was considered optional.

The text on Page 389 is especially pertinent to the present Topic.

MichaelG.

[Author]

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