Lifting platelets over a distance with a large area magnet 1

[mwemag]

I need to calculate the minimum size of a magnet necessary to lift up tiny iron platelets at a large distance (40 cm) over an area of 1 square meter.

The platelets of 0.4 x 0.4 mm and 0.01 mm thickness weight 1.6 micro-grams. They lay uniformly distributed on a horizontal flat of 1m x 1m, each platelet spaced by 0.4 mm to the next one, forming a chessboard-like pattern on the flat. Now they all should be lifted up bei a large area magnet 0.4 meter above the flat. Thereby it doesn't mather whether they are not liftet uniformly or twist around etc., just the magnetic force must be strong enough to pull them all up.

So, if someone has an idea how to solve this calculation, I would be really thankful, since I am still quite inexperienced in magnetic calculations.

 

[MagMike]

Hello mwemag,

Unfortunately, what you ask is not a simple matter. There is no easy calculation that will tell one the minimum size magnet for this application. A significant amount of engineering work would be involved.

The 0.4m distance is very large for a magnet (electro or permanent). In addition, the small particle size makes it even more difficult.

 

[IRstuff]

A 1m x 1m area is absurdly large, since that's larger than most wrecking yard magnets. You'd probably magnetize everything within 10 ft of it.

TTFN

 

[nbucska]

Your Fe has a specific wt of 1. It has a volume of 1.6e-6
cm3.

If this is a schoolwork, you are on the wrong forum
else read my FAQ and give more info.





Plesae read FAQ240-1032
WEB: <

http://geocities.com/nbucska/>

 

[mwemag]

Thank you for your answers, MagMike, IRstuff and nbucska.

Actually I don't want to do a accurate calculation of the design, I just want to find out whether lifting up small particles (of the described size) over a distance of 40 cm on 1m2 could be done in principle (without to rely on superconducting-20Tesla-particle-accelerator-magnets...). If I'm lucky, combining several "standard"-coil-solenoids or big permanent magnets would work well for this application, or of course a strong wrecking yard magnet. I just assumed, that the combined magnets would have to extend over the area of 1m x 1m, since the particles are also distributed on that area, but if a smaller magnet is enough - even better. So, if one confirms me that combining several non-superconducting electro or permanent magnets over that area will do the job, then the problem is already solved.

Concerning the FAQ 240-1032, I know that my description of the magnet I need isn't accurate at all, but before a detailed model can be calculated, one has sometimes to evaluate, whether an idea in principle can be realized or whether a completely different solution must be found. That's what I want to find out. And no, this is not my schoolwork.

Anyway, there are some tools to calculate the flux density or the holding force in a magnetic field at a specified distance (air gap):

http://www.magnetsales.com/Design/Calc_filles/FluxDensityPlainRect.asp

http://www.grouparnold.com/mtc/calc_gauss_rect.htm

http://www.magnete.de/php/magnetfeldberechnung.php?rechnung=2

However, this calculations only show the flux/force on the axial centerline of the field and assume a quite large piece of steel as the holding piece compared to the thin platelets. But nevertheless the calculated values for a large size magnet at that distance are surprisingly high, for a 1m x 1m 10cm big magnet I still get flux densities over 400 Gauss at 40 cm distance (depending on the magnetic material), or holding forces over 100 kg... Can these calculations help to answer my question or am I completely on the wrong track?

 

[prex]

What you are looking for should be feasible by using a magnetic lifter of the kind that's used to grab iron debris.
You could consult a supplier of that kind of equipment.
Of course you not only can't count on any kind of uniformity in the lifted particles (powder?), but they will all pile up at the location of highest flux (presumably the center portion of a round lifter).

prex

http://www.xcalcs.com

Online tools for structural design

 

[MJR2]

You will need a magnet considerably larger than 1m but that is a not a particular problem. I just finished a design for a permanent magnet might do the job. I was an unusual request. You're not in China are you?

The magnet weighed in excess of 24000 pounds. It provided 1200 gauss at 21 inches over about a 1m square area. I don't know how they will remove material from the surface.

Your small particles might flocculate together before actually being lifted. Someone needs to test these before you get a magnet design. It's possible but difficult. However you might consider a 20 or 30 thousand pounds magnet as absurd.

Before someone wonders why I am recommending a permananet magnet that would be incredibly strong and dangerous I'm not. It's just what I was asked to design. An electro would generate the same field strength but probably be heavier.

 

[MJR2]

IRstuff,
A magnet this large is not unusual. In fact they are quite common in the mining industry for tramp iron removal. 2m widths are often used up to 3m or 4m. This is for conventional electromagnets. Field projection of 400-500 gauss at distances of 1m or more are seen. Superconducting beats that.

As far as fields to 10 feet around the magnet. Certainly the structure will see some fields but not as much as you might guess. However loose floor gratings or equipment would be really dangerous.

 

[mwemag]

MJR2: Thanks a lot. So, having a magnet (electro or PM) that is just large enough would do the job, without the need of superconducting systems, apart from the flocculation problem, right?

Did you use some kind of flux density / force calculations in relation to the magnet size in your design, like those on the links I posted above? The point is, that in these calculation tools, whilst you need a large magnet flat area like 1m2 or more, you still need much less thickness, about 4 inches, to get 500 gauss at 40 cm distance. Like this the weight of the magnet would be less than 1 ton, provided that these calculations are applicable to this task.

Would be interesting to have more data on these large mining magnets you mentioned, with 400-500 gauss at 1m distance, probably the right way to head for. If I could get more info from you on this I would be really glad. I'm not in China but Switzerland. Thanks.

 

[MJR2]

I hesitate to claim that any magnet I described will accomplish the task. What I tried to point out was the size and strength of commonly available magnets. Try a google search for 'suspended electromagnets' and you will get several very good alternative companies.

All of the magnets I commented on were designed to provide a certain field strength and force at certain working distances. If you were to take a magnet which can be well defined and pick up your part it can be scaled from there. Or one of the companies noted in the search should be able to do it for you.

I prefer anonymity here and that is expected from the commercial aspect.

As to the basic designs you have investigated. Roughly you will require a magnet that is considrably larger than 1m square to cover a 1m square bed of parts. This magnet will weigh considerably in excess of 1 ton. The PM I describe is over 12 tons. It would be very much in your favor if the working distance was smaller.

 

[MJR2]

I ran a quick FEA on four plates using the 3D PM model I have refered to. It looks like they should move. However I would do much more work before committing to that. Forces appeared to be greater than the pieces weigh. I assumed the parts to be low carbon steel.

 

[mwemag]

MJR2: I guess a FEA is a simulation program. As in the simple calculation tools i have linked, the flux density and forces are still high at 40 cm distance in the axial centerline, around 500 gauss and over 300 kg force. Since a platelet weights only 1264e-8 gram (assuming iron), the force is about 2e+10 times larger (!) than the weight of the particle.

But as MagMike mentioned, the small size is a problem, since the predicted force normally corresponds to rel. large pieces of iron or steel and might be completely unapplicable in this case.

However, with my 7cm diameter, 3 cm thick electromagnet I can lift the particles from a distance of 3.5 cm. If the force can be scaled linearly with the magnet size (can it?) then it should work with a magnet that's 12 times larger (40cm/3.5=11.4...)

After runnng a short search I found plenty of commercial magnets for mining and scrap handling, with diameters up to 90 inches and lifting capabilities of 50 tons under ideal circumstances, that is, with no air gap and compact steel blocks.

 

[MJR2]

You don't want a circular lifting magnet, such as used for scrap handling. In general they do not project the field to the distance you require. It is very unlikey that a 300kg force is acting on your parts. The forces FEA suggested were considerably less than one pound.

Most programs available 'free' make no consideration for off center field strengths. I makes a big difference for you as it is necessary to pick up plates 0.5m off centerline.

Everything must be scaled. Accurately measure the magnetic field of your electromagnet. Measurments from the surface out in small even increments is important. From this we calculate force.

 

[mwemag]

MJR2: Some manufacturers claim some of their magnets to have "deep field" or "extra deep field" capacities:

http://www.ohiomagnetics.com/sr.htm

Interesting this one:

http://www.eriez.com/Products/MagneticSeparators/MagneticDrumSeparator/PerMDS/

http://www.eriez.com/Products/FoodProcessing/PlateMagnetsFood/SuperBrutePlateMagnet/

The pdf files of the eriez-products (one must fill a registration form to access) give more details. I have it and some screenshots too. Is there a way to attach pictures here in the forum?

They claim:
"All Permanent Deep Field Magnetic Drums: This design uses Erium® permanent and bucking poles to project a deep magnetic field capable of removing ferrous from distances of up to 15 inches (380 mm)..."

"The AllElectro Agitator type utilizes a deep field rectangular-core pickup magnet to reach out and grap the ferrous..."

"All Electro/Agitator Type Scrap Drums, Drum Diameter 60 inches, Working distance: Up to 16 Inches (410 mm)"

However this details are about magnetic drums, but they also speak of rectangular deep field magnets. What do you think of that?

 

[MJR2]

The drum type separators would provide a self cleaning feature. I visualize the need to suspend a magnet over a flat area of 1m square. A square or rectangular deep field magnet could cover that area without movement. Scrap yard type magnets are generally not considered deep field.

However we are missing the process information leading up to and then after the magnet. That could change all of our recommendations.

A drum type circuit is considerably more directional or narrow than the suspended electromagnets you will find on the Eriez website. They certainly have something or can customize something that will work.

Electromagnets are generally used when the need to project the field is important. Plus as I've stated in other posts they have the safety aspect of being able to shut them off. But all I do is design magnetic devices. How people use them is their own business. I don't want to see anyone hurt however.

 

[mwemag]

MRJ2 thank you very much for your help.

Since I have found now a few suppliers that offer magnetic systems with a capacity close to the one I need, I'm pretty convinced that a customized solution would work. The following one for example claims to have rectangular plate magnets with the ability to lift a big nail from a distance of 30 cm:

http://www.greenwoodmagnetics.com/products/monster_block_magnet.htm

If I find any information about the "trick" such magnets use to generate a deep field, I will let you know. Tnx.

 

[MJR2]

Since you are looking in the UK. I've worked with these guys before. They appear to have a broader range of solutions to offer. You might ring them up.

http://www.eriez.com/AboutEriez/International/Europe/

Mike