Introduction: A Way to Cover Powerful Neodymium Magnets
Neodymium iron boron (NIB) magnets are extremely powerful. Even moderate-sized ones can be amazingly dangerous to handle at first.
In this project I demonstrate a simple, cheap, relatively effective way to cover 2-inch (5cm x 2.5cm x 1cm) NIB magnets. This size is commonly used in home wind-generator projects.
Materials: aluminum foil, duct tape, masking tape, double-sided tape.
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Step 1: Safety Precautions
Part of the reason I came up with this covering system was because these magnets are so powerful that they can easily injure you. The covering as shown makes them much safer and easier to handle (though caution is still required).
If you've had experience with NIB magnets you've already learned this, and probably the hard way: these things are very dangerous if not handled properly!
Be careful with NIB magnets of any mass...any magnet larger than a penny is definitely dangerous (and even smaller ones can be if they slam together and shatter). These magnets are sintered, which means that they are not a solid mass of metal or ceramic, but are rather compressed powder. Thus they splinter or shatter very easily.
Additionally, they are so strong that two (or more) of them can react while several inches apart, and these two-inchers could easily rip one's flesh off if they pinch together right. They will also attract iron-based metal objects from a distance: scissors, knives, or other objects will unexpectedly be attracted.
So when working with these, before you begin make sure you clear your work area of any metal objects. Work with one magnet at a time until you become very certain of your procedures. If two of the magnets used in this project slam together, there is essentially no way to get them apart without damaging them (actually I'm sure a way could be found to separate them, but it's certainly best to not let them join).
When cutting the tape off the ends there is a special technique I use to prevent letting my scissors attach to the magnet, which I will explain directly
Step 2: Gather Materials
- Standard duct tape (I used black)
- 1/4" masking tape.
- Double-sided tape (I used 3M brand)
- Aluminum foil (4" square)
- Small scissors (larger ones will be more strongly attracted to the magnet)
- Magnet (keep far away from scissors or any other metal objects, except intentional attachment)
Step 3: Wrap Magnet in Foil
The foil is simply used to prevent the tape from sticking to the magnet. The cover can then be changed or removed as desired in the future.
Wrap tightly, then pinch the ends closed. Don't pinch tightly or the foil will tear at the corners as they are sharp. The excess at the ends can be torn off carefully, or cut with scissors, leaving 1mm or so overhang that is then folded down and compressed.
To cut with scissors: grip magnet tightly in a fist so that the edge of the magnet is 2 or 3mm below the thumb-side of your closed fist. Rest the scissors against your hand...you will feel the magnet pull the scissors tightly against your hand. Keeping a firm grip on the magnet, angle the scissors slightly up so as not to cut any of your skin; cut the aluminum.
(Use this same technique for cutting the excess duct-tape in Step 6.)
*In this picture I'm a little too close to my clipboard...moving that magnet 1cm to the right would cause an unwanted attraction.
Step 4: Add Double-Sided Tape
The double-sided tape is around a millimeter thick. The small amount of distance diminishes the at-surface strength by a surprising amount (since the intensity of the magnetic field diminishes with distance according to an inverse square law i believe).
This tape will make it easier to remove the magnet from a flat surface or dense ferric object, and will protect the surface from rapidly accelerating objects.
For some applications you may want to leave the double-sided tape off of one or both polar surfaces to maximize the magnetic field; the other layers will provide some surface protection.
Step 5: Cover One Side With Duct Tape
Cut a 12 inch or so piece of duct tape in half so that you have two pieces of equal length. Turn one piece over so the sticky side is up. Center the magnet over the duct tape and set magnet down; press for full adhesion. Leave duct tape flat.
*I wrapped the outer edge of this magnet with masking tape because the foil was a bit torn. Normally this isn't necessary. I tried tearing the foil rather than cutting it as I usually would; tearing didn't work too well.
Step 6: Place 2nd Piece of Duct Tape; Join Both Pieces. Cut Ends
While looking straight down over the magnet and duct tape, align the other piece of duct tape from above and place it on the magnet. Try not to let the ends of the two pieces of tape make contact yet - just let the tape touch the magnet. Once they have adhered well, fold up the sides of the bottom piece of tape along the long edge of the magnet; if the magnet is centered properly the tape should reach nearly to the top surface.
Fold down the long edge of the top piece of tape, and allow the ends of the top & bottom tape-pieces to meet. They may meet in a very sloppy fashion but this won't matter. Sometimes I strive to make them line up or fold over very carefully but the end result isn't much different.
Finally, cut the ends of the tape with scissors. Grip magnet tightly in a fist with your non-dominant hand so that the edge of the magnet is 2 or 3mm below the thumb-side of your closed fist. Rest the scissors against your hand...you will feel the magnet pull the scissors tightly against the circle of your thumb and forefinger. Keeping a firm grip on the magnet, angle the scissors slightly up so as not to cut any of your skin; cut the tape.
(This technique is also used for cutting the excess aluminum foil in Step 3.)
Step 7: Wrap Edge With Masking Tape
This step is mostly cosmetic. However the duct-tape join is sticky and thus the edge-wrap prevents unwanted duct-tape adhesive from getting on your hands or any objects the magnet is attached to. Definitely provides a neater and more finished appearance.
This is 1/4-inch tape and is approximately the same width as the magnet and works perfectly; I think it's from an art-supply store but it may be sold at hardware stores as well.
Step 8: Finished!
I bought these magnets for a generator project I re-considered and wondered what to do with them...they were so strong that attaching them to a flat metal surface was very problematic (if I ever wanted to get them off). They were also very prone to cracks and surface damage from attraction-impacts.
With this 5-minute covering job these are now serving as holders for things like knives and towels in my kitchen, a crowbar, various small tools, and my retractable dog leash. It's surprising how quickly they disappear as I find previously-unconsidered uses for them.
*The paper in the picture is much larger than 8.5 x 12 so the scale seems off.