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Registered Member #54278
Joined: Sat Jan 17 2015, 04:42AM
Location: Amite, La.
Posts: 367
I have several bags of iron filings from my TC'ing time. I wanted to experiment with various iron-core inductor parameters (for filters) based on hollow wire-wrapped plastic tubes filled with various iron configurations. I had Ultra-fine to coarse iron filings, iron shavings, BB's, a tube full of coat-hanger segments, and a solid iron rod. I even remember a couple of high-power toroids in the batch.
--BUT, getting to the point, -Gregary- mentioned something about araldite'ing' filings (I had to look up the word--anyone using this?) into, IIRC, coilgun projectiles that wouldn't saturate too fast and have reduced Eddy current effects.
I would like to try this. I have the aforementioned iron fillings and experience with 'resin work'. My goal would be to create an easily reproducible sturdy projectile that would not saturate too fast in a powerful B-Field produced by a high-current coilgun coil.
Registered Member #9039
Joined: Wed Dec 26 2012, 03:31PM
Location: Epping, Victoria, Australia
Posts: 117
Signification wrote ...
I have several bags of iron filings from my TC'ing time. I wanted to experiment with various iron-core inductor parameters (for filters) based on hollow wire-wrapped plastic tubes filled with various iron configurations. I had Ultra-fine to coarse iron filings, iron shavings, BB's, a tube full of coat-hanger segments, and a solid iron rod. I even remember a couple of high-power toroids in the batch.
--BUT, getting to the point, -Gregary- mentioned something about araldite'ing' filings (I had to look up the word--anyone using this?) into, IIRC, coilgun projectiles that wouldn't saturate too fast and have reduced Eddy current effects.
I would like to try this. I have the aforementioned iron fillings and experience with 'resin work'. My goal would be to create an easily reproducible sturdy projectile that would not saturate too fast in a powerful B-Field produced by a high-current coilgun coil.
Had not thought of just mixing iron filings with the liquid epoxy and molding the mixture.
It would be no doubt more convenient that frigging around with steel washers, and iron filings would be soft iron rather than inefficient steel.
Assuming one can find a convenient and cheap source of soft iron filings or course.
Registered Member #9039
Joined: Wed Dec 26 2012, 03:31PM
Location: Epping, Victoria, Australia
Posts: 117
What if you were to have a series of iron or ferrite toroids butting up against each other and get the timing of switching on one after the other just right?
The issue of constricted magnetic fields and reduced force over distance might be neutralised and the increased magnetic field strength from the core might realise an increase in energy transfer efficeincy due to the stronger magnetic fields.
Registered Member #2906
Joined: Sun Jun 06 2010, 02:20AM
Location: Dresden, Germany
Posts: 727
I have done that before. The results just suck. I tried a homemade toroid from resin and ironpowder with particle sizes of 90µm and 500µm and a mixture of both. The Attrached photo shows the quality of my achievement (90µm): no air inside, very high material content. I used acetone to make the resin thinner and a small vibrator (yes,....) to shake the mixture and make all the particles really dense.
The result is: µr = 4. I talked to a guy who actually makes ferrite/ironpowder-cores for a living (should have dione that before failure ): it seems to have something to do with the size of the particles - the smaller they get, the less effective µr they have. Additionally, since they are isolated by resin the mass is magnetically not really a whole thing but really porous... thats why ironpowder-cores are done via chemical isolation (the particles are coated with a metaloxide) and then pressed together mith multiple 10s of tons of force and heated up. My conclusion is: save your time. Yes you will make something thats really hard to saturate, but thats only because of the low µr Even professional made Ironpowder cores have only a fraction of the solid irons µr.
Maybe bigger particles will have an advantage, but they have then allready the problem of eddy-currents. Remember: transformer-sheets are 0.5mm in thickness... and thats good for 50Hz. so i dont see much point in having particles >500µm in a coulgun configuration where frequecies are in the hunrets of Hertz.
Registered Member #54278
Joined: Sat Jan 17 2015, 04:42AM
Location: Amite, La.
Posts: 367
@ Gregary, Have you seen this? Also the powered iron (last time I checked) was plentiful and cheap. I once successfully extracted the iron out of a box of 'corn flakes'! After putting them in a blender with water. I got the powered iron out with Neo magnets after the blending was done. It had the texture of baby powder! It was a very small amount--but the finest I have ever seen. So next, I tried the same thing with iron tablets (Ferrous Sulfate), a dietary supplement, with no luck. But I hardly put much effort into it. The powered iron I have out now has been sitting around for years--but I will ask my friend where he got it. What could it hurt to try??
Registered Member #2906
Joined: Sun Jun 06 2010, 02:20AM
Location: Dresden, Germany
Posts: 727
You get Iron-powder from ebay in various particle sizes. Just make sure its not iron-oxide. I am sure the supply will be even better using ebay.COM, instead of ebay.DE (in my case).. But yeah.. it doesnt hurt to try of course, but it hurts to be disapointed and waste time for something that has no chance of success. I just felt like i could share my results... success would be.. dependable on what you actually want for me µr=4 (and for coilgun applications in general) is pretty useless.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
My understanding regarding soft iron and ferrite and frequency is that the iron gets hotter than the ferrite at the same frequency, so soft iron isn't used for high frequencies BUT we are not talking about frequency in a CG, we're talking about period.
t's one shot, then a gap, then another shot. A frequency of less than one Hz, isn't it?.....you can't fire it fast enough for 'frequency' to be a problem
Registered Member #2906
Joined: Sun Jun 06 2010, 02:20AM
Location: Dresden, Germany
Posts: 727
Ash, you are wrong in your simplification. Consider a repeted shot every 10s interval. Now take the 10s current-wafevorm. Sure, it is mostly 0, but there is a peak at the beginning of the period. Now Take a fourier-transform of such a period. You will find, to represent the result you will need quite some amount of higher frequency-components. These higher freuqencies are present inside the core material. No way around it. So even a short pulse every 10s contains kHz-Frequency spectrum.
Your way of thinking implies that a solid transformer core is loss-free, if its turened on only once a year for just a minute. Thats just wrong. During this minute it will be extremely loss, even the switchign period is 1 year. You need to consider all frequencys that the core has to withstand, not just the largest fundamental period.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
I'm aware there will still be iron losses, hysteresis and eddy currents, but if the eddy currents are minimized using iron powder or whatever, you just have hysteresis losses.
Can you expand on these 'kHz frequencies'?....I was under the impression that the capacitance and inductance 'define' the 'fundamental period', especially if fast diodes are used to prevent ringing.
Registered Member #2906
Joined: Sun Jun 06 2010, 02:20AM
Location: Dresden, Germany
Posts: 727
Maybe its just a missunderstanding... i saw you aguing that the frequency is low (like i pointed out above below 1kHz) using the short frequency as reference period. What you said now, that the period is defined by RLC, is much more agreeable
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Idea for a coil gun
): it seems to have something to do with the size of the particles - the smaller they get, the less effective µr they have. Additionally, since they are isolated by resin the mass is magnetically not really a whole thing but really porous... thats why ironpowder-cores are done via chemical isolation (the particles are coated with a metaloxide) and then pressed together mith multiple 10s of tons of force and heated up. 
Even professional made Ironpowder cores have only a fraction of the solid irons µr.
I just felt like i could share my results... 
for me µr=4 (and for coilgun applications in general) is pretty useless.
