Magnetic circuit

hugobors · 8th January 2006, 07:47 PM

Hello,

I want to experiment whith planar and ribbon and want to do this kind of magnetic circuit :
[IMG]MagneticCircuit.jpg[/IMG]

(The schematic is not in scale.)
I wanted to know which metal to use for the best field in the airgap, pure iron, stainless steel, silicium steel, and where to find it...

Thanks a lot
Hugues

poobah · 8th January 2006, 07:53 PM

Hello,

Any regular mild steel will work well... it has low cost... and is relatively easy to cut and form.

Because your magnetic field is constant (not moving), the "magnetic" properties of the steel are not important.

hugobors · 8th January 2006, 08:03 PM

Yes but isn't there some metal that can handle more or less magnetic flow?

Bazukaz · 8th January 2006, 08:08 PM

I think silicon transformer steel can.

poobah · 8th January 2006, 08:16 PM

Yes, some metals can handle more "flow" In the case of a gapped magnetic circuit, the gap will limit or control the "flow".

Magnetic circuits can be compared to resistor circuits... that is often how they are taught. Consider a 1 Ohm resistor as the IRON; and a 1000 Ohm as the AIR GAP. Place these in series... you can see that the Iron makes very little difference.

Silicon steels and other are chosen because of their properties when the magnetic field is changing... like a transformer.

SmarmyDog · 8th January 2006, 08:21 PM

Search the forum for “low carbon” for a bit of insight. I think FEMM has some of the common ones in its materials library. Be aware though that the availability and machine-ability of the metal can be a problem with the low-carbon types.

-Casey Walsh

hugobors · 8th January 2006, 08:27 PM

So pure iron is the best way? and is the thickness important?

poobah · 8th January 2006, 08:39 PM

Actually, pure iron is rather hard to find and poor to work with... What will work for you is "MILD STEEL". Steel is essentially Iron with a small amount of carbon.

And yes, the thickness will matter. The steel should be at least as thick as your gap is long (not the thickness of the gap). The shape is extremely important though. These days the shape of magnetic components is designed with software... it is rather complicated, but there are people on this site which can do magnetic modeling. It is also possible just to sketch something out and get a decent result.

Show us a sketch of your plan.

Bazukaz · 8th January 2006, 08:53 PM

There is no pure iron on the earth.In fact , the most 'pure' iron is extremely expensive and very hard to manufacture, only maybe few grams exist all over the world.
As far as i know , standard carbon steel saturates faster than special transformer steel.
I don't know about stainless steel, maybe it is better ?

hugobors · 8th January 2006, 09:46 PM

Quote:

And yes, the thickness will matter. The steel should be at least as thick as your gap is long (not the thickness of the gap). The shape is extremely important though. These days the shape of magnetic components is designed with software... it is rather complicated, but there are people on this site which can do magnetic modeling. It is also possible just to sketch something out and get a decent result.

Show us a sketch of your plan.

The problem is that I have to do something like this (picture bolow, in scale, one dot=1mm) and I have not space on both side to put so a lot of iron.... The best I can do is 1,5mm of thickness for the iron.
Do you think it wil work properly???

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8th January 2006, 07:53 PM	#2
poobah diyAudio Member Join Date: Nov 2005	Hello, Any regular mild steel will work well... it has low cost... and is relatively easy to cut and form. Because your magnetic field is constant (not moving), the "magnetic" properties of the steel are not important.

8th January 2006, 08:03 PM	#3
hugobors diyAudio Member Join Date: Feb 2002 Location: Nantes	Yes but isn't there some metal that can handle more or less magnetic flow?

8th January 2006, 08:08 PM	#4
Bazukaz diyAudio Member Join Date: Nov 2005	I think silicon transformer steel can.

8th January 2006, 08:16 PM	#5
poobah diyAudio Member Join Date: Nov 2005	Yes, some metals can handle more "flow" In the case of a gapped magnetic circuit, the gap will limit or control the "flow". Magnetic circuits can be compared to resistor circuits... that is often how they are taught. Consider a 1 Ohm resistor as the IRON; and a 1000 Ohm as the AIR GAP. Place these in series... you can see that the Iron makes very little difference. Silicon steels and other are chosen because of their properties when the magnetic field is changing... like a transformer.

8th January 2006, 08:21 PM	#6
SmarmyDog diyAudio Member Join Date: Jul 2003 Location: San Diego, CA	Search the forum for “low carbon” for a bit of insight. I think FEMM has some of the common ones in its materials library. Be aware though that the availability and machine-ability of the metal can be a problem with the low-carbon types. -Casey Walsh

8th January 2006, 08:27 PM	#7
hugobors diyAudio Member Join Date: Feb 2002 Location: Nantes	So pure iron is the best way? and is the thickness important?

8th January 2006, 08:39 PM	#8
poobah diyAudio Member Join Date: Nov 2005	Actually, pure iron is rather hard to find and poor to work with... What will work for you is "MILD STEEL". Steel is essentially Iron with a small amount of carbon. And yes, the thickness will matter. The steel should be at least as thick as your gap is long (not the thickness of the gap). The shape is extremely important though. These days the shape of magnetic components is designed with software... it is rather complicated, but there are people on this site which can do magnetic modeling. It is also possible just to sketch something out and get a decent result. Show us a sketch of your plan.

8th January 2006, 08:53 PM	#9
Bazukaz diyAudio Member Join Date: Nov 2005	There is no pure iron on the earth.In fact , the most 'pure' iron is extremely expensive and very hard to manufacture, only maybe few grams exist all over the world. As far as i know , standard carbon steel saturates faster than special transformer steel. I don't know about stainless steel, maybe it is better ?

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