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Old 12th February 2011, 10:53 AM   #11
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What kind of steel rod is needed? 4140?
Anyone have a US source for this?

Last edited by SpinMonster; 12th February 2011 at 10:56 AM.
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Old 13th February 2011, 08:22 AM   #12
brunob is offline brunob  Germany
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Quote:
Originally Posted by ABJensen View Post
Thanks for the measurements. I reproduced the FEMM simulation.

See attached file.

The picture below shows the predicted magnetic field strength in the gap (range is -0.27 to 0.19).

There might be some differences with the simulation shown on the website since I don't have all the details (e.g magnet strength).

Something to keep in mind: the FEMM simulation is only 2D. In the third dimension, we have a long magnetic system. When the magnetic system gets longer, then the field strength decreases. In my ribbon system, with only one magnet pair (Length = 4 cm), the measured B in the middle of the gap is 0.51, with 3 magnets (3x4cm = 12 cm), the measured B is 0.48 and with 5 magnets (5 x 4cm = 20 cm), the measured B is 0.42. Note that I wrote "measured" not "computed".
Attached Images
File Type: gif B_t.GIF (20.7 KB, 321 views)
Attached Files
File Type: zip tall_neo_ribbon.zip (960 Bytes, 34 views)
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Old 13th February 2011, 08:49 AM   #13
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Quote:
Originally Posted by brunob View Post
When the magnetic system gets longer, then the field strength decreases.
Hi, brunob, do you know why that is?

Does FEMM calculate the field strength for infinite length in the 3rd dimension?

Thanks,
Kenneth
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Old 13th February 2011, 11:21 AM   #14
brunob is offline brunob  Germany
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Quote:
Originally Posted by kavermei View Post
Hi, brunob, do you know why that is?
I don't have a an explanation but I have an observation. When assembling one side of a long magnetic system, placing the first magnet is easy. The second one has be pushed against the first because there is a strong repulsion. I think that this repulsion could be connected to the magnetic field decrease in the ribbon gap for longer ribbon systems.

For a small 20 cm ribbon system, I measured already a 21% decrease of the magnetic field when compared to 4 cm long one. I wonder what the decrease would be for a 1 meter tall ribbon?

Quote:
Originally Posted by kavermei View Post
Does FEMM calculate the field strength for infinite length in the 3rd dimension?
I don't know.


Bruno

Last edited by brunob; 13th February 2011 at 11:30 AM. Reason: more precise
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Old 13th February 2011, 11:30 AM   #15
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Spinmaster,
Check this thread out on this forum. It tells you everything you need to know in great detail with lots of pictures. Valvetude has done a fabulous job.
A 60" Ribbon w/TL Loaded Extremis Hybrid .
So far the magnets4less folks have the best price. If you find a better price please post it on your site. Remember when you glue several dozen strong magnets with opposite polarity and are going to join them with a small gap the combined pull is TREMENDOUS. Be very careful.

Good Luck Tad
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Old 11th April 2011, 08:27 PM   #16
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Hello Bruno,

maybe the reason for the decrease is that the steel comes to saturation?

Mario
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