Dropping permeability of (1018?) fillister head 'bucker type pole screws

[Helmholtz]

So sonic differences from pole piece material (if they really stand up to double blind listening tests) would be expected to be from the conductivity.

Yes, that's the other approach I am taking.

[Helmholtz]

Stainless steel type 400? (410,416,430) have relative permeabilities about 20% lower than 1018 steel.

Based on what data?

[Helmholtz]

No, those measurements are for 1.5 Tesla / 60Hz.

Initial permeability which roughly corresponds to small signal AC µ should be considerably lower. For ARMCO steel I found a µi of 200.

[Helmholtz]

There won’t be a lot of difference in plain carbon steels used for magnetic applications.

From a table I found on Wikipedia, conductivity of pure iron is about 40% higher than that of 1010 steel.

https://en.wikipedia.org/wiki/Electr...d_conductivity

[Diablo]

From a table I found on Wikipedia, conductivity of pure iron is about 40% higher than that of 1010 steel.

https://en.wikipedia.org/wiki/Electr...d_conductivity

I don’t believe the value given in that table for pure iron. The value given for 1010 steel is correct and should be the same for pure iron.

In my past life, I had an equation for calculating the electrical resistance of iron as a function of the alloy content for low alloy electrical steel. P, Si, Al have strong effects, and Mn is weaker. All of these steels are decarburized.

[Helmholtz]

I don’t believe the value given in that table for pure iron. The value given for 1010 steel is correct and should be the same for pure iron.

I found several sources that confirm the value for pure iron.

E.g.: https://www.thoughtco.com/table-of-e...ctivity-608499
https://www.researchgate.net/figure/...fig3_228407964
https://www.thebalance.com/electrica...metals-2340117

[Diablo]

Maybe this helps.
https://www.nde-ed.org/GeneralResour...ivity_Iron.pdf

https://books.google.com/books?id=Fe...20iron&f=false

[Helmholtz]

Maybe this helps.
https://www.nde-ed.org/GeneralResour...ivity_Iron.pdf

Thanks, this table I also found. It confirms the pure iron conductivity value given by wikipedia.

The google books link doesn't show text.

[Diablo]

Thanks, this table I also found. It confirms the pure iron conductivity value given by wikipedia.

The google books link doesn't show text.

That’s strange, the google book opens when I click on it.

[David King]

Is the effect of conductivity strictly limited to eddy currents or are we talking about something else entirely?

[Helmholtz]

That’s strange, the google book opens when I click on it.

Book doesn't open here. Maybe due to European copyright regulation.

[LtKojak]

Italy here, the Google book link opens just fine.

[Helmholtz]

Is the effect of conductivity strictly limited to eddy currents or are we talking about something else entirely?

Yes, it's all related to Eddy currents. But conductive ferromagnetic cores show an additional phenomenon that tends to increase the typical Eddy current effects caused by conductive but non-magnetic parts (like reduced inductance and increased damping/losses).
This is the magnetic Skin effect (see Zollner, "Physics of the Electric Guitar", https://www.sciencedirect.com/scienc...04885300004145, https://www.researchgate.net/publica...ower_frequency )

The Eddy current rotating around the magnetic axis of the core produces a counter H field inside the core which reduces total flux. As a result the effective permeability of the core drops with increasing frequency.
Eddy currents increase with conductivity and so does the magnetic skin effect.