Refrigerator Magnets

Is your frigerator real metal or the stainless steel look a like that is plastic not metal?

Replying to Comment by billyjack: Is your frigerator real metal or the stainless steel look a like that is plastic not metal?

Your pulling my leg!? About the stainless steel plastic, that is. No, plastic reefer cases would never be permitted in this house.

Check the refrigerators out at Lowe's or The Home Depot. They have metalized plastic covers on a number of there appliances. No leg pulling here.

Thanks.

This is strictly a guess so don't fault me if I am wrong but I am thinking that the magnetic material must be something that is like glue that is filled with permanent magnet dust so that the poles face in all kinds of directions and then allowed to harden. Maybe not glue but rubber cement? Also, it may have to be in very close proximity to what ever metal it is sticking to in order to actually stick, so on the other side of the card the distance would be too great? I don't know...

Regards,

Keywalker

Does sound credible, though. Thanks

All the poles are on one side. Think of the edge view of the card as a bunch of U-Magnets all tied together at their poles, North-to-North and South-to South. The width of one pole of each U-magnet is the width, or the length, of the card, and the separation between poles is generally around 1/16 of an inch.

You can verify this yourself: take two identical magnet cards and place them with the magnetic faces towards each other. Now rotate one, keeping the magnetic faces together, until you find the position where they attract most strongly; you now have their poles aligned parallel. Next slide one slowly across the other in the long direction and the short direction. If you do it slowly enough, in one direction you will find that the two alternately attract and repel as they move from NS to NN alignment.

If you move them quickly in the same direction you will see, hear, and feel them buzz across each other as they alternate between attraction and repulsion.

I indicated two identical cards, since ones from different sources may have different pole spacing, such that some poles will attract at the same time that others repel. At certain spacing ratios, the two different spacings will make the attractions and repulsions cancel, so the cards don't attract each other virtually at all.

Either this, or they're coated on one side, the one bearing the ad, with some type of MuMetal (Anti-Magnetic) coating.

(this is 75% nickel, 15% iron, with copper and molybdenum, undergone Rapid heat-treatment to increase magnetic permeability, to allow for that), or any other such treatment

Many thanks for your info on magnetic cards.

Best regards,

Arturo Perez

Replying to Comment by dkwarner:

Great! I was unable to keep the identical cards separated but close to detect magnetic force. However, rotating the cards while they were stuck together back to back demonstated that the best attraction alignment(s) occurred when the cards were perfectly aligned, length- and height-wise; they were hardest to slide or separate in this alignment.

When slid in this configuration, it was not precisely possible to detect repulsion (in the sense of how repulsion feels when manipulating ferrous bar magnets). Instead, the cards seemed to (how can I say...) flutter rapidly, as the cards were pulled across each other, lengthwise, with significant force. It was obvious, though, that the flutter was due to the opposition of poles being quickly attained and lost in succession. The fluttering was even audible as the magnetic polar alignments changed and the cards quickly slapped together repeatedly. When the cards were slid in the up and down (90 degrees from flutter) relative direction, one moved quietly and smoothly, while still attracting, across the face of its counterpart--evidently because the alignments of poles was not being disturbed. Just as you described.

Thanks very much for the new learning; and the visual aid.

BTW, This came from Sac, just down I50 from Hangtown.

Very good response!!! To the point and accurate! I acknowledge your talents!

Way to go!

Thanks Vermin. I appreciate that!

Dick

The posts above more or less covered the flexible magnets used in fridge doors.

As for your credit card. The iron based particles on the media (similar to a floppy) are magnetised (orientated) in a binary pattern. The info including an account ID is stored in a string of bits and bytes. When swiped the info is transfered to the CPU for processing.

The magnetism is minimal the only stuff the card will lift is non-magnetic money from your account.

Replying to Comment by Hendrik: Thanks but, no, I wasn't referring to recording strips on actual plastic. These are rubber-like card facsimiles which the credit issuer--AMEX in this case--sends out with invitations for signing up for a card or "improved" card. They're embossed and everything just like the real thing; but where a name would be it says, "Your Name Here"; and at the bottom it says, "This is not an actual charge card." A card is stuck to the application page that comes with the invitation and a sentence above the card advises that "This is a refrigerator magnet," so you don't just throw away or shred it with the application. I guess the point is, to have you advertise the card on your refrigerator--not so much advertise to others, but to yourself: to use the card which you already have, even if you don't "accept" the (so-called) special card invitation.

You response was appreciated, nevertheless.

Fake rubber cards will bounce when used?

Oh, and another thing...

Noticing your and DK's location given in angular coordinates reminds about another question--about GPS and surveys--I've been meaning to post. Maybe we'll be in touch again...after I figure out how to ask the question.

Thanks to all you guys.

A quick reply about Surveying - GPS

There are fixed relations between the 2 but it will depend on the projection used.

(Albers, Lambert etc)

Building plans are traditionally done in a local x-y system based on a specific plain of reference.

Maps of a rounded surface are produced on flat pieces of paper usually distorted to give a specific result or effect. (Equal area,distance, shape, direction)

Please post your question.

Yes, I thunk about mili/micro/mili-micro- and all those seconds and E-W distances (where the distance is variable: zero at two latittudes, maximal at one). And whether any stretchy formula, integration, or iteration could be found. But since I already have real things to do, and need to think on it some more--and chose my battles carefully, please be patient till I post to another forum. I'll make sure you know about it. Thanks, Hendrik.

I have no idea how it may be in South Africa, but US dollars are printed with a special ink that is very slightly magnetic. If you hold a US bill by one end and bring a good rare-earth magnet up to the other end, there will be a definite attraction. The attraction seems to be most obvious with a 1$ bill, I suspect due to the larger amount of ink used at the ends of those bills.

Dick

Ferromagnetism
Ferromagnetic materials have atomic magnetic fields that align themselves parallel to externally applied magnetic fields. This creates a total magnetic field within the material much greater than the applied field. Materials of this nature may demonstrate a relative permeability considerably greater than 1. Above a critical temperature known as the Curie temperature, the material becomes paramagnetic. Examples are iron, cobalt, nickel and most steels.

We do the printing fridge magnets here and have the ability to magnetize them the above description is from our material manufacturers website as to the type of magnetism used. Hope this is useful to you.

You can visit our website at www.cgilink.com

The refrigerator magnetic strip is a Halbach array - a very clever magnetic arrangement having a high flux on one side and almost none on the opposite side. To understand how is made and how it works, google "Halbach array" or take a look at this:

http://www.gaussboys.com/pages.php?pageid=6

The most interesting applications are in PM induction generators and magnetic levitation for trains, launchers, etc.

I'm not convinced!

The true Halbach Array is an assembly of discrete magnets with their fields arranged at 90° angles.

I haven't actually seen the refer magnets (and car door signs etc.) being made, but to be cheap they must be magnetized quickly. To my knowledge, all permanent magnets are magnetized by electromagnets. Here is a probable arrangement of electromagnet poles used to magnetize these sheets:

In practice, there is probably a single coil with an appropriate set of alternating sheets of magnetic and non-magnetic materials to produce the multiple poles, rather than the multiple coils I have shown. I wouldn't be surprised if it is arranged in a circular pattern so it would be possible to roll continuous sheets rather than magnetizing one at a time.

Knowing the shapes of magnetic fields (as shown by iron filings), I believe the arrows in the above drawing more correctly describe the magnetization of the particles within the magnetized layer than the 90° arrows of the Halbach Array

Dick

Sorry to deceive you, but the refrigerator magnetic door holder is for sure a Halbach array. The product is one thing and the technology used to make it is another. If you want to learn something, please trust those who know things.

The row material is a sheet of rubber-inserted magnetic powder (so-called rubber magnets) and the magnetizer for creating the Halbach array is a sequence of coils on both sides and around the magnetic sheet. It's a flow process, the magnetic sheet passes through and between coils which are energized with high current pulses. The length of each "individual magnet" is given by the linear velocity of the magnetic sheet and by the duration of current pulses in coils. I hope this time you can visualize it in 3D. You were right when assuming the process has to be quick.

Your description of the poles and pulses, linear motion, etc. sounds very probable. I still don't see how that will produce discrete magnets with 90° pole orientations.

I think that if you could do a microscopic examination of a slice through the card, you would find a gradually curving direction of orientation of the individual magnetic particles from one pole to the next, rather than a sudden change from vertical up to horizontal left to vertical down etc.

I was describing the magnetic door holder, not the magnetic strip in debit and credit cards. Unfortunately, I have no time to draw you the magnetizer, but using my bold words and knowing how the field generated by a DC energized coil looks like, you should visualize it.

The magnetic strip inserted in credit and debit cards is a magnetic tape and the read/write process is identical with digital tape recorders/ players. If you know those big magnetic tape memory units still in use in some computer centers, than you know what I'm talking about.

Some banknotes have inserted (as a security feature) a magnetic wire (not magnetic ink) that can be written/read in a similar manner with the magnetic tape. Historically, the very first magnetic recording and playing of sound was using a soft iron wire! Please don't ask me more because I don't want to fuel some scam or the like.

Yep! I remember wire recorders..

When I said card, I was referring to the same AmEx advertising refrigerator magnets (shaped like a credit card, but thicker, and of course magnetic) that the original poster mentioned.

OK

The thick "credit card" magnetic door holder is made of 4 or 5 parallel pieces of rubber magnet Halbach array glued together or molded in plastic. What I described to you is the raw material which is sold in bulk by feet or meter. That is a continuous sheet aprox. 10mm wide and 3mm thick magnetized the way I told you. I saw the process in a factory. Usually, this magnetic sheet is hidden in the door gasket as the attraction force is proportional to the length. The magnetic material itself is a very cheap and low-grade one. The "credit card" magnet is just a remake of the old gasket-magnet incorporating the same raw material.

No, you still haven't understood! We're not talking about the magnets that hold the door closed, but rather the ones stuck all over the outside of the refrigerator. I just counted: on our refrigerator there are 30 miscellaneous magnets. Several of them are the rotors from old floppy drives, and a few more were removed from dead hard drives; but the large majority are flexible advertising magnets. The OP and I have both received multiple mailings from American Express trying to get us to send them money (use their credit cards). Included in the mailing is a 'card' that is 54mm wide, 86mm long, and 0.7mm thick. It is imprinted on the plastic side to look like an AmEx card, but says 'your name here'; the other side is clearly a single continuous layer of brown rubbery material that obviously must contain magnetized particles.

If you take two of these cards back to back and move them around, you can feel that the poles extend the full 54mm width of the card, and as they are moved lengthwise, they attract strongly every 3.2mm, indicating a distance of 1.6mm between N & S poles. They also repel in between the strong attraction positions, but it is difficult to hold them in the repelling positions. Re-read my post #3.

There are lots of scratches, but clearly no cuts in the rubbery side (I just checked with a microscope to be sure). In the past I have cut special shapes out of this kind of magnet using scissors, and I believe I would have felt it if there were individual strips. I still believe this is a continuous (slurry before it hardened) material, not a Halbach array.

Dick

Thanks Dick.

I give up.

Regards

A couple months back, I recorded a program on the Discovery Channel that included a segment on the manufacture of these sheet magnets. As a sixties survivor I can't remember the process, but it did involve mixing rubber granules with other materials, heating it and running it through magnetised rollers that would form the sheet and align the dipoles. It was kinda neat and I am sorry I didn't recall much more. I think the whole program was on magnets so if you can search for it you might find it when it comes around again.

Thank you, Kyoto. What you say seems a little bit different from what I described as permanent magnets are used instead of electro-magnets for the magnetization process. Anyway, the making of raw material is similar as it has to be homogeneous but anisotropic in the same time and has to be cooled much under its Curie point before magnetization.

Regards

Thanks guys. All very fascinating and informative. Would you believe: that one of those wire recorders still exists, in my father's garage? Must sign off now. What a great site.

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