How to Make Magnets Magnetic Again

April 05, 2022 Kommentar veröffentlichen

Remagnetizing Refrigerator Magnets

A flexible magnet and a neodymium magnet

Tin a flexible refrigerator magnet exist re-magnetized using neodymium magnets? Yes! Read on to learn how.

We've been asked this question a number of times, so it seems like a good idea to demonstrate the process. We'll use a handful of neodymium magnets to re-magnetize a flexible magnet. While at that place's a slicker, faster setup used in the manufacturing of flexible magnets, our demo shows the bones thought. When companies manufacture large sheets of this stuff, they use a very similar process to magnetize larger sheets.

What is a flexible magnet?

A flexible magnet with printed graphics

Unlike the neodymium magnets we provide, flexible magnets are not fabricated with rare earth elements. They are a mix of ferrite powder (think ferrite or ceramic magnets) mixed into a safety or polymer resin. It'due south magnet textile dust mixed into a flexible plastic canvas.

They're often sold in rolls, like tape, or in sheets. Many are sold with ane side that can exist printed on, which is why yous run across then many graphics on them. Most magnets you see on the backs of cars are fabricated with this kind of flexible magnet material.

Are they strong?

No. They are non nearly every bit potent as a neodymium magnet in several important ways. Beginning, allow's consider pull strength. The pull force is much, much weaker than a neodymium magnet. Depending on how you measure out it, a neodymium magnet is going to be roughly seven-twenty times stronger than a flexible magnet of the same size. In some cases, this number tin exist fifty-fifty college.

Of course, flexible magnets don't have to be very strong to only hold themselves on the back of your car. They're non lifting very much. They don't stick out into the air current. They are actually great for funny bumper "stickers." Just don't expect to lift heavy weights with i.

Longtime readers of our blog know that pull force isn't the only important measure of a magnet'southward strength. Coercivity is too key. Coercivity is a magnet's resistance to getting demagnetized by a magnetic field. The greater the coercivity, the stronger magnetic field you need to magnetize (or de-magnetize) it.

For example, rubbing a strong magnet across a credit carte's magnetic strip can erase the information on it. That'southward because the strip'southward coercivity is depression. It is unable to resist the magnetizing field from the magnet.

Flexible magnets are the same way. Considering their coercivity is depression, they're easily influenced by a powerful neodymium magnet.

What practice Halbach arrays have to do with it?

Earlier nosotros prove how to remagnetize a flexible magnet, let's take a expect at how they should be magnetized in the first place. Back in our article about Halbach Arrays, we showed how flexible magnets are magnetized in multiple directions. They're non magnetized in one management throughout, like a simple neodymium disc magnet.

Flexible magnets are magnetized in alternating patterns, where the polarity changes as you move to different positions along the surface. If yous could make yourself really small and walk effectually the surface with a tiny compass or pole identifier, you would run into alternating north and south poles.

That sounds too complicated. Can't I but magnetize it in one management and be done already?

No, not if you want the flexible magnet to piece of work. Remember, these things aren't very powerful. If y'all magnetize information technology all in one management, it'due south not able to provide much magnetic forcefulness at all. It won't stick to the refrigerator door.

By magnetizing flexible magnets in alternating directions like this, y'all can go a practiced amount of forcefulness from what would otherwise be much too weak. Information technology's actually quite ingenious. The alternating fields both give it more strength and help information technology to resist demagnetization.

How tin I magnetize the flexible magnet in all those crazy directions?

Back in our article nigh horseshoe-shaped magnets, we used a neodymium magnet to re-magnetize an Alnico horseshoe magnet. It was pretty uncomplicated to selection which pole to touch the horseshoe magnet. When we stick one pole of the strong neo magnet confronting the weaker horseshoe magnet, it is magnetized in the management of the field it sees.

Magnets are stacked with like poles facing 1 another, repelling each other.

For the flexible magnets, we need a fashion to brand the strip "run into" that alternating pattern. How can nosotros practice that? By stacking a agglomeration of sparse disc or band magnets together, bundled so that they are repelling 1 another. This makes a strong magnetic field along the edge of the stack, shaped in exactly that alternating pattern nosotros desire.

This is a chip challenging to get together, since the magnets act to repel each other apart. We use a long spiral and nut to hold the stack together.

How does that piece of work?

Stack of R821 band magnets on a screw, repelling with like poles facing one another.

Now that the stack is assembled, let'southward visualize what the field looks like right near the curved surface of the cylindrical stack of magnets. The black lines of flux bespeak the field direction at a given point. The field management is parallel to those black lines.

If you lot move from left to right along the surface, y'all encounter the field direction changing. In the lower picture, the dark-green arrows evidence the field direction. Say, that looks a lot like a Halbach assortment!

If we roll or slide a flexible magnet right up against this stack of neodymium magnets, the flexible magnet will "run across" that strong magnetic field in the directions shown. After the stack of neodymium magnets are slid away, the flexible magnet retains magnetization in those directions.

In the video beneath, we:

take a new flexible magnet and show its alternating fields using a slice of MV43 green viewing film,
wipe a relatively large neodymium magnet beyond the face up of it, changing the magnetization direction and eliminating the pattern, and
whorl a stack of R821 ring magnets across it to make new patterns.

That video used R821 ring magnets and the MV43 viewing film.

Allow's go creative with odd patterns.

Flexible magnet manufacturers tend to favor that pattern of long stripes, mainly because it's easy to magnetize big sheets quickly. Just roll the sheet beyond the array of neodymium magnets, and viola! You're washed.

To make things a niggling more interesting, we tin can besides make other patterns. If they're alternating patterns, they can likewise provide good strength. In the video below, we magnetize it with a checkerboard pattern of north and south, plus a few other silly patterns.