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Old 17th January 2013, 07:56 PM   #111
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Quote:
Originally Posted by Hentai View Post
Time to put them in the machines.
What machines do you use?
(Just in the middle of installation of my de Valliere lathe.)

Best wishes
David
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Old 18th January 2013, 03:08 PM   #112
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Originally Posted by Frank40 View Post
Hi to all

Here is another thought, see the picture below. I have replaced the centrer pole with a magnet, this should work like stacking magnets and increase the flux and help to saturate the iron . Please comment.
Because of the magnets lower permeability than irons the flux in the gap will be less than if it was iron and maybe that will be not the the only one negative effect.
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Old 18th January 2013, 04:30 PM   #113
Baldin is offline Baldin  Denmark
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Really cool project Hentai

Here is a polish company which sells cones and other parts seperately ... might be of help

/Baldin
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Old 18th January 2013, 07:09 PM   #114
Hentai is offline Hentai  Romania
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Hi guys,

Frank my first thought was saturation of the pole pieces, stefanyovev has a point tho. If i can find the time this weekend i will run it through FEMM.

David saw your post and i took some pictures of the PUMA 400
Click the image to open in full size.
Click the image to open in full size.
Click the image to open in full size.

Also automated drilling machine and the good old lathe, working hard.
Click the image to open in full size.
Click the image to open in full size.

Would love to see a pic of your Valliere when its all setup.

Baldin Thank you for your comment. Do you have a link to that company? i cannot see it in your post.
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Old 18th January 2013, 07:34 PM   #115
Frank40 is offline Frank40  Denmark
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Stefanyovev. Are sure that magnets are less conductive than iron, this dose not sound logical to me. And it dose not correlate to my findings on the internet, see these two links.... Maybe I misunderstood some thing.

Magnetic properties of materials
Magnetic properties of materials

Hentai. Man that is one nice workshop you have, I would love to have that kind of machinery. It would be great if you can do a simulation, I am having some trouble in using the program.

Take care
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Old 18th January 2013, 08:19 PM   #116
JMFahey is offline JMFahey  Argentina
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Quote:
Are sure that magnets are less conductive than iron,
Yes, of course.
That's why magnets are used to "generate" the magnetic field, at a lower flux density, and soft iron is used to *guide and concentrate" it, in the desired gap.
By the way, a magnet used as a polepiece, besides being a *terrible* material for that, will have the added disadvantage of *opposing* the main magnet flux because it will be magnetized the wrong way, at least in any "normal" magnetizer.
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Old 20th January 2013, 01:39 AM   #117
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Originally Posted by JMFahey View Post
That's why magnets are used to "generate" the magnetic field, at a lower flux density, and soft iron is used to *guide and concentrate" it, in the desired gap.
This depends on the permanent magnet material and is partly a matter of perspective.
It helps to concentrate the flux for low flux density sources like ferrite.
For Neodymium the main reason to use soft iron is the difficulty and cost to produce a magnet with a radial field.
An axial flux magnet and steel pole piece is just cheaper.
The old Aura 18 NRT sub-woofer did use a Neo. Radial field magnet but was rather expensive and had consequently limited production.
Earlier in this thread "Linesource" showed a simulation with more than 2 tesla field where the elimination of the pole-piece was actually the key. Not a practical structure as shown but of interest. Pity he never followed up.


Best wishes
David
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Old 20th January 2013, 07:16 PM   #118
Hentai is offline Hentai  Romania
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Here are the Femm results:

For ceramic 5 PMs, 8mm gap 1010 steel:

Structure (showing polarity of PMs):
Click the image to open in full size.

Central pole made of PM, magnetic lines:
Click the image to open in full size.
Central pole made of 1010 steel, magnetic lines:
Click the image to open in full size.

Central pole made of PM, B value across gap:
Click the image to open in full size.
Central pole made of 1010 steel, B value across gap:
Click the image to open in full size.

For NdFeB40 PMs, 8mm gap 1010 steel:

Structure (showing polarity of PMs):
Click the image to open in full size.

Central pole made of PM, magnetic lines:
Click the image to open in full size.
Central pole made of 1010 steel, magnetic lines:
Click the image to open in full size.

Central pole made of PM, B value across gap:
Click the image to open in full size.
Central pole made of 1010 steel, B value across gap:
Click the image to open in full size.


Effects are less noticeable with Neo PMs but still steel wins
Attached Images
File Type: png 1010 pole piece B.png (17.3 KB, 11 views)
File Type: png 1010 pole piece lines.png (45.2 KB, 12 views)
File Type: png Ceramic 5 pole piece B.png (18.6 KB, 12 views)
File Type: png Ceramic 5 pole piece lines.png (56.6 KB, 11 views)
File Type: png Neo pole piece B.png (17.5 KB, 9 views)
File Type: png Neo pole piece lines.png (54.6 KB, 8 views)
File Type: png neo vs steel structure.png (116.3 KB, 11 views)
File Type: png Steel pole piece B.png (14.7 KB, 10 views)
File Type: png Steel pole piece lines.png (56.0 KB, 8 views)
File Type: png structure.png (49.6 KB, 12 views)
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Old 20th January 2013, 07:51 PM   #119
Frank40 is offline Frank40  Denmark
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Thanks Hentai, for the analysis. I am convinced now... steel is the way to go.
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Old 20th January 2013, 07:56 PM   #120
JMFahey is offline JMFahey  Argentina
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Thanks for simulating and posting.

And let me repeat something many don't notice:
you simulated the center piece magnetized the opposite way (geometrically) to the main external ring magnet, meaning: if, say, the outer ring has North up, you simulated the magnetic material "polepiece" North down .... which only happens in simulations
Hey!! , in Simulation World you can simulate *anything*, even if it's technically impossible
Notice I didn't say "physically" impossible.
But I stick to real world speaker production technology.

But if such speaker is magnetized in any commercially available magnetizer, *everything* within the magnetizer coil or gap will be pushed the same way, by definition.
Say, everybody "North up" , including the pole piece and any other magnetic element of that structure.
So? ........... what happens after you cut current off?
The soft iron (SAE1010) polepiece will "forget" that induced magnetization and happily take whatever the hard magnetic material tells it to (Ferrite/Alnico/Samarium/etc.).
If you use a hard magnetic material for the polepiece that will not happen and it will fight the main magnet.
In practice, it will be worse than even not using a polepiece at all

I have built my own magnetizers and use them everyday in speaker production.
Of course , I had to design them from the ground up.
No real data on Internet even today .... and we are talking mid 70's , not even Internet !!!
And one point to consider was that beyond fully magnetizing Ferrite, I had also to saturate the polepiece, or it would act as a very real magnetic short sucking lineforces from the Ferrite.
That's why magnetizers are such power guzzlers.
My "small" one at the shop, good for 105mm magnets, needs over 40A @ 220 Volts monophasic, do the Math, over 8 KW.
In fact, when magnetizing, I go "outside" and clamp it straight to the 220V Power Company line, to avoid resetting PCs , etc, at home.
The "Mid" one, good for ~150mm magnets is at a friend's factory, because it needs 3x380V full wave rectified (equivalent to around 500V DC) @ 47 Amperes= over 20 KW.
Magnetizing pulses are short, but the line must be able to deliver.
I'm building a large one, good for 190 and 220 mm magnets (so I can clone EVM, JBL, etc.) but it will be capacitive discharge because , simply, I can't afford the special reinforced Power Line it will need.
So in a wayyou took the "easy" path
You just built a "dedicated magnetizer" and made it part of the speaker.

FWIW: together with some friends, I built a 30" speaker in the early 80's .... and had to use a field coil
An incredible technical achievement, a terrible financial disgrace.
We built 4 of them but never could sell any
Oh well.

So I'm following your project with the utmost attention, brings *many* bitter sweet memories.
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