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Magnetizing

01/29/2014 11:08 PM

How can I "magnetize" a piece of sae 1018 cold rolled steel. 7/8" diam. by 1" long. I know for shure this can be done.

I have tried several diferent coils, voltages, even welder cables,etc which work well with a 12" bar, but not with the 1" piece. Any clues?. Thanks.

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#1

Re: Magnetizing

01/30/2014 12:07 AM

No clues at all.

K&J Magnetics - FAQ

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#2

Re: Magnetizing

01/30/2014 1:01 AM

You said you can magnetize a 12" piece, but not a 1 inch piece? Try this experiment: Magnetize a longer piece (your 12" piece will do) and cut a 1 inch section from it. Now you have two magnets, 1" and 11".

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#3

Re: Magnetizing

01/30/2014 1:29 AM

To magnetize a pre-cut piece, ensure that your magnetizing coil is at least 3-5 times longer than the piece, and that the piece is centered in the coil. This will ensure that the magnetic flux through the piece is parallel throughout (this is why you could magnetize a longer piece but not a shorter one - the flux lines begin to diverge slightly before the ends of the coil, with the result that much of the field in these regions exits radially leaving little net magnetization. If the piece is short, most of the field through it diverges unless you use a longer coil).

If you try the approach in my first reply, ensure the cutting does not heat the piece excessively or you'll lose some or all of your magnetization

Hope this helps.

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#18
In reply to #3

Re: Magnetizing

01/30/2014 11:29 PM

Theophilus; it also depends on how your coil is wound as well as how many joules of energy you put through the coil and the number of turns as well as the Gage of the wire. And if it is nitrogen cooled or some other cooling process through the coil to drop resistance to the energy being processed into the coil. Small steps make a big difference to the power potential of the coil and the ability to magnetize your material. And if you are using a cup type coil or a double post type of magnetizer.Duke

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#19
In reply to #18

Re: Magnetizing

01/30/2014 11:44 PM

Are you speaking of making permanent magnets or of the design of pole pieces? Insofar as pole-piece design, our EM had no trouble imaging objects at 80,000X and so I suspect we were doing something right.

Insofar as the OP's question, I answered it on his terms.

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#20
In reply to #19

Re: Magnetizing

01/30/2014 11:52 PM

Yes we were making permanent magnets. Re magnetizing magneto's for race cars and permanent magnet starters as well as a boatload of slot car motors. Oh the years of misspent youth and racing anything that rolled.Duke

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#27
In reply to #19

Re: Magnetizing

01/31/2014 10:40 AM

Sorry about leaving in the middle of the conversation but duty called and had to help granddaughter who ran out of gas on the way home. I keep telling her she can't ween the car off of gas. And now back to the subject at hand, when we did our magnetizing we were mostly using a double post set up until later we set up a capacitor bank and charged it up to 900 volts DC and discharged it into a coil with a cup inside to hold the parts to be zapped into submission. If your part is not centered in the coil it will self center as you say with a small pre-charge on the coil. If it is not exactly dead center when the main supply is energized you have the makings for a rail gun of major proportions. And parts will go anywhere they want without regard to what is in the way. It took us a little time to work out safety procedures to not get hurt at the time. There just was not anywhere to go get what we needed done locally. And had to make do with what info we could get from collage books. Before the internet was very active we actually had to read to get the info we needed. But there just wasn't that much info, so a lot of trial and error was necessary. We gained a lot of respect for the field of magnetics. My friend worked for IBM at the time that we were trying to do this and he had one of the first (PERSONAL COMPUTERS) if you could call it that, very slow and very redundant to use, not like today generally simple and almost self explaining. Duke

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#38
In reply to #3

Re: Magnetizing

02/02/2014 7:50 AM

I would like to make a small remark with respect to the usual magnetizing technology as used for instance by PM manufacturers.

The approach with a solenoid is very current consuming since the field has to be build in air and with a BIG gap. The PM for voice coil loudspeakers are magnetized with a much more smaller system using a soft iron circuit in which the PM is put between 2 pole pieces. To build up the field the capacitive discharge procedure is also used which allows a high current for only the required time to obtain the PM magnetizing and also to a cycle reduction for higher productivity. This has also the advantage to have a lighter current source only to charge the capacity not for the maximal needed current.

Of course as in the only coil based approach as soon as the PM is taken off the circuit it will loose "power" and by further installation in the working circuit it will work on its reverse line not on its B-H line.

This is the reason why as far as possible PM are magnetized assembled in the working circuit this giving a higher B for the working point and thus a smaller magnet!

If my explanation is not clear enough I can supply a picture with more detailed informations.

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#39
In reply to #38

Re: Magnetizing

02/02/2014 8:13 AM

Yes, we both realize this, but my reply is in the context of the OP's setup. Only. He is not manufacturing PMs using equipment optimized for the purpose (nor designing such, nor using suitable PM materials which 1018 is definitely *not,* by any stretch), but performing what is basically a one-off, 'homebrew' experiment and asking why he can magnetize a longer piece but not a shorter one. That was his question. He wound his own coil and I answered in that context. Only. No more, no less.

What really irks me about this forum is that people answer just about every bluddy question that WASN'T ASKED. I've stopped asking questions here as a result and resort to asking members privately, members whom I know will give me a straight answer - including "I don't know." - three words engineers in general seem utterly incapable of uttering. If I need an ANSWER, I WON'T ask it here.

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#40
In reply to #39

Re: Magnetizing

02/02/2014 1:21 PM

You noticed that and I did the same already long time ago.

I have the feeling that some participants want at any price be present in a discussion if they know or not the subject if they read or not the question.

They catch a word and make a lot of comments related to the word they caught but not to the question. A straight answer is seldom given but a lot of suggestions how to make it better without knowing the whys for the OP choice.

Funny is that those aside answers have many more times than the straight have been considered as good!

You will notice that many times the answers given above are not read so that there several repetitions on same thread.

You have not to expect more accuracy. According to studies made by scientists this is the way people behave on general sites as CR4.

But you did not answer my question (which I do not consider a side question) about the "notch" in the curve around 45°.

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#41
In reply to #40

Re: Magnetizing

02/02/2014 4:22 PM

Do I *know* why there is notch? No, I do not. Possibly a section of the piece is saturating, but the contours do not reflect this. Does the software know to handle saturation? I don't know. That is my answer.

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#42
In reply to #41

Re: Magnetizing

02/03/2014 4:24 AM

The soft can handle saturation since the curve B-H is given by points and it interpolates in between.

I think there is an explanation which considers the importance of the field in the air.

Those losses are maximal at 45° due to a combination between areas and length and thus the remaining field going through the narrow part where the B arrives at its max value is the smallest.

Before using a dedicated soft I worked with the classical method Rotters describes and this lead to a feeling for air gap resistances. It helps a lot in the case that a soft result has unusual aspect. However I did not find the explanation immediately only after a after a qualitative analysis of air gap resistance value.

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#4

Re: Magnetizing

01/30/2014 6:50 AM

Simply stroke it with a fixed magnet by hand. The motion is circular, bringing the magnet away from the bar at the end of the stroke, returning it to the start, and begin stroking again.

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#43
In reply to #4

Re: Magnetizing

02/05/2014 7:05 AM

???? Do you mean like this?

.........alright, if you insist, but get that cat out of there!!!!!!

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#5

Re: Magnetizing

01/30/2014 7:12 AM

If you can magnetize a 12 inch bar, then to magnetize a 1 inch bar, simply butt it against the end of the 12 inch bar and wrap tape around them to hold them together. Then magnetize them both at the same time.

If you wanted to magnetize a bunch of 1 inch bars, simply stack them together, wrap a piece tape around them to hold them temporarily, and then magnetize them the same way you magnetized the 12 inch bar.

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#17
In reply to #5

Re: Magnetizing

01/30/2014 11:19 PM

Usbport! Whatever you don't do that unless you want 12 projectiles going 12 different directions. Depending on how strong your field is will determine just how fast the 12 projectiles escape the coil. Ask me how I know, we were experimenting on a magnetizer at 900 volts and launched a 10" low carbon steel bar thru the ceiling and right on thru the roof it landed on the main street a hundred yards away. In your case you would have 12 smaller ones trying to go every which way, potentially lethal we were lucky no one was killed just scared and amazed that all of the 10 Gage wire vaporized at the same time and shut down the experiment.Duke

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#21
In reply to #17

Re: Magnetizing

01/31/2014 1:50 AM

Why would Usbport's pieces "fly in all directions" when the same, DC magnetic field runs through each piece making them aligned N-S-N-S...S? And why did your steel bar fly as it did, unless the field around it was asymmetric? Or did you hit it with a pulse, which would have induced sizeable eddy currents within the bar creating an opposing field? In such cases it's not magnitude only but the rate-of-change of current, essentially making the bar a single-turn, short-circuited transformer. If you apply the current more gradually in Usbport's configuration, the pieces will pull together and quite possibly center themselves in the coil's field.

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#31
In reply to #17

Re: Magnetizing

02/01/2014 11:19 AM

Is there any chance you got that on video? And how did that explanation go to the owner of that roof?

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#32
In reply to #31

Re: Magnetizing

02/01/2014 7:37 PM

It was my high-school buddy's brothers garage workshop and his brother was the one helping us with the electronics. We were all surprised when it happened and scared we had hurt someone outside. After that episode we were extremely careful to anchor all parts to the posts and later the coil cup. We had no idea how dangerous of ground we were traveling on at the time. we also had no idea how powerful of a magnetizer we had built, we had paralleled and series-ed over 200 high voltage caps through a SCR bank into a huge mercury filled #D Ignitron into the coil, we had the capabilities of reversing cobalt magnets and bring them back, we did not expect to be able to do that or be anywhere near that powerful. But it did everything we needed it to do and then some. We also did not know we were that far ahead of the military at the time in the rail gun business.

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#33
In reply to #32

Re: Magnetizing

02/01/2014 7:53 PM

I used to play with an old solenoid valve coil (ASCO RedHat ,I think) and ball bearings.

Place ball bearing in coil on table,energize coil by rubbing leads on power leads of a motor start capacitor that had been charged from a wall outlet, and watch the ball go into orbit. Most came back close by, but some I never found or heard them hit anything.Probably some space debris still up there somewhere.

If I had a capacitor bank,I probably would have used it.

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#34
In reply to #32

Re: Magnetizing

02/01/2014 8:32 PM

How much capacitance, total? If they were 'high-voltage' caps, why did you series/parallel them when you applied only 900 volts? Why not parallel all the way? What do you consider high voltage (900 volts is not typically considered high-voltage as caps go). And an SCR bank in conjunction with an ignitron? Why, when an ignitron alone would have sufficed? Especially a "huge" one.

Then there's the problem of recoil. The same force that launched your steel thru a ceiling and a roof and landed it a hundred yards away would have absolutely demolished your machine. You mentioned only melting the coil.

Please forgive me for saying so, but I am having serious doubts about your tale.

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#35
In reply to #34

Re: Magnetizing

02/02/2014 1:53 AM

(IT LOOKS LIKE ONE WHOLE POST GOT LOST THIS POST MAY NOT MAKE SENSE) Sorry I did not get this in the last post anything over 220 volts is high voltage to me, you may think that kilovolts is normal, I don't normally get anywhere near anything that high. After seeing my brother accidentally hit a 600 volt power line under a building that was not suppose to be there was enough for me to shy away from electricity. Since then I have not worked on even my own electrical at home.The later magnitizers used photo flash caps. That was the last iteration of the magnet zapper that I saw. I have not seen the original since the mid 80's. I believe that it was dismantled for the parts I believe that I have somewhere near 175 5000mf 750volt caps I traded for to rebuild the old machine a few years later. Nothing ever came of it and I lost interest I think the caps are still in my work shop still in the boxes they came in. And remember that was hillbilly engineering not done by a trained EE.

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#6

Re: Magnetizing

01/30/2014 7:51 AM

most people would just buy a magnet and avoid all the trials you've sent yourself through. I don't suppose you'd care to enlighten us why you need such an odd item?

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#12
In reply to #6

Re: Magnetizing

01/30/2014 10:32 PM

A local company needs this magnets for an European machine of the 80's

How this magnet work in the machine? I don't know (I'll find out)

I understand there was a local supplyer for this part, but a can't locate it.(I'll keep trying)

We are trying to make the part as required before we offer an alternative.

The real shape of the part is: double diameter cylinder, 19 mm and 5mm, by 22mm long each section.

Thanks to all of you that offered a solution, I'll try each one of them and keep you informed.

best regards.

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#13
In reply to #12

Re: Magnetizing

01/30/2014 10:40 PM

Sounds like you will need something more powerful than can be made in a normal shop.

Her is a link to a supplier that maybe has what you need.Plenty of other suppliers out there.Do a google search for magnets.

http://www.kjmagnetics.com/categories.asp?gclid=CPPX_bC-p7wCFW3xOgodqT8AZA

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#14
In reply to #12

Re: Magnetizing

01/30/2014 10:58 PM

A question, EGREMY: Does the customer need a magnet or a pole-piece *for* a magnet? As others here have pointed out, SAE 1018 steel makes for a lousy magnet. The remanent magnetism is weak at best and probably won't keep.

This, plus your cylinder's 'stepped' shape sort of suggests a pole piece to a magnet rather than an actual magnet, although pole pieces, if they change diameter, do so with a taper rather than a step. It all depends on the magnetic field's desired 'shape.' If your customer specified SAE 1018 cold-rolled mild steel because the part they're replacing was made from the same material, it may be for a pole-piece. Ask them.

If this part is to be used as a pole piece, lower-carbon steels are preferable, such as 1002, 1004, etc. For instance, we used 1004 for magnetic lens pole pieces in an electron microscope mainly because of its low remanence. We *didn't* want residual field (opposite of making it a magnet).

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#15
In reply to #12

Re: Magnetizing

01/30/2014 11:00 PM

What type of machine, and which particular part of the machine?

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#22
In reply to #12

Re: Magnetizing

01/31/2014 5:47 AM

The stepped design could be a reason why a weak magnet can be used. Since the flux is constant through the part the field density (B) at the 5 mm end is amplified due to the difference in sections and the high permeability of the 1018.

The factor is (19/5)^2=14.4. Even a weak flux could lead to a high (relatively) B.

The problem with magnets as AlNiCo or steel with high C content is that as soon as the magnetizing field is off they work with the air path as "resistance" and this leads to a loss of power since they position them selves on cross point between the B-H curve and the air line and after it work on the "reverse" characteristic. Only rare earth magnets have a reverse line near to their B-H curve and do not loose after the magnetizing field disappearance.

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#23
In reply to #22

Re: Magnetizing

01/31/2014 5:56 AM

Ever try to magnetize a Mobius strip at right angles to the longitudinal axis?Where would the N/S be?

Just curious

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#24
In reply to #22

Re: Magnetizing

01/31/2014 6:02 AM

Yes. Typically, though, the two diameters would be joined by a tapered section as the sudden step acts as a sort of 'air gap' for a portion of the flux between the two diameters.

Flux lines prefer not to make right angles and so some of the flux will exit the face of the larger diameter and some of these will rejoin at the sides of the smaller and some will not, looping back around instead. Ideally the flux concentrator would be tapered, consequently. This being said, the problem of remanace remains. 1018 is even worse than AlNiCo in this regard.

-T

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#28
In reply to #12

Re: Magnetizing

01/31/2014 2:24 PM

I have not in my data bank the B-H curve for 1018 magnetized. It is in fact present BUT only as low carbon non magnetized steel.To see if the concentrator effect is real I used the weakest AlNiCo5 with same dimensions as the OP gave.Here are the results. It is easy to see that the field concentration effect is present although AlNiCo5 has a lower permeability as 1018the but losses are very important and the concentration effect is reduced at the part end (5 mm diameter).The field lines show that a conical zone between the 19 and 5 mm cylinders will not reduce the loss. I will make the test to morrow if I will have time available.However the remanence of 1018 will be VERY low so that although the field is amplified the final B value will be very small. I am asking myself what is the reason for such a solution.

It would be of interest to see the complete mahnetic circuit may be then it will be clear.

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#29
In reply to #28

Re: Magnetizing

01/31/2014 5:42 PM

Hi Nick,

I'm curious to see what your software comes up with for a tapered piece. If you have time, try various tapers angles and see where there's an optimum. What software are you using?

Best,

T

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#30
In reply to #29

Re: Magnetizing

02/01/2014 10:45 AM

It is not my soft ware its femm 4.2 ( D. Meaker)free and valid only for 2D and axisymmetric problems but it covers about 95% of usual problems.

Now to your request folloowing pictures show how the field does change if the angle is modified. You will notice a trend change around 45° which I can only explain by the non lineariry of the system.

20°

30°

40°

42°

45°

50°

55°

60°

90°

The pocess was very short in time this is the reason for the quite big number and also the fact that there was a change in trends and I wanted to see if it was an error or a trend.

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#36
In reply to #30

Re: Magnetizing

02/02/2014 2:00 AM

Notice the taper angle as it appears in the '55 degree' pic and compare to those on either side. It looks out of place (more like a 40 something, perhaps? The notch in between 40 - 50 does seem a bit unusual.

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#37
In reply to #36

Re: Magnetizing

02/02/2014 4:32 AM

For the 1: it was an error of file title which I noticed too late to take it of the list.

I would like to have your explanation for the notch. I have one but I would like to have yours.

Any other comment ? Did I satisfy your curiosity ?

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#7

Re: Magnetizing

01/30/2014 9:50 AM

The steel you want to magnetize is low carbon so that the remanent field will be weak.

If you need a strong field the best is to use a bar of a low carbon steel + a high remanent PM.

The problem with your bar is that even if you magnetize it as soon as it is taken off the magnetizing field it will loose a lot of the magnetizing you "pumped" in.

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#9
In reply to #7

Re: Magnetizing

01/30/2014 12:43 PM

The Original Poster hasn't specified the strength of the magnetic field in the bar to remain at the end of the magnetising task.

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#10
In reply to #9

Re: Magnetizing

01/30/2014 1:23 PM

You are right but for once I did as many other do on CR4 I tried to give to the OP an opinion different from his request.

Many times I noticed that the answers which have been considered as good were those with no relation to the original question but suggested different solutions far away from the basic question.

In fact due to the question I assumed that the OP does not have a very thorough knowledge in the field and I wanted to warn that the result could be disappointing. If you consider this as an error I accept the critics and will try not to repeat.

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#26
In reply to #7

Re: Magnetizing

01/31/2014 9:47 AM

The steel you want to magnetize is low carbon so that the remanent field will be weak.

Its actually ferrite not carbon.

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#8

Re: Magnetizing

01/30/2014 10:02 AM

Magnaflux.

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#11

Re: Magnetizing

01/30/2014 10:32 PM

Use only Direct Current to magnetize the piece.A small piece should be no problem.

The strength of the magnetic field will depend on the current through the coil and the number of turns.More amperes,and more turns, the stronger the field.

Slowly remove the metal piece with power on, then after exiting the coil, rotate the piece 90 degrees from the coil, move the piece far away from the coil,and turn off the power.

An A/C field will demagnetize a magnet, leaving only a residual magnetic field, depending on the current at the exact moment of disconnection of the coil.

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#16

Re: Magnetizing

01/30/2014 11:04 PM

The 1018 steel you are contemplating will work okay for a DC electromagnet as long as you keep it energized. If you want a permanent magnet, you will need to use a different kind of steel like ALNICO.

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#25

Re: Magnetizing

01/31/2014 8:44 AM

Try making a complete magnetic circuit with the piece to be magnetized as part of the circuit. The magnetic flux flows through the center of the energized coil and around the outside in a continuous loop. If you give it an "iron path" which includes your piece to be magnetized, the flux will be concentrated through the piece.

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