He's a friend of mine , and I'm going to build one soon
Few months ago I've been trying to build a mag drill (eventually someone gave me a broken one that I've managed to repair) so I've been experimenting with microwave oven transformer aka MOT magnetsThe complexities of calculating the holding force of an electromagnetic chuck is beyond me, it is a phenomenally deep subject. However, more is always better. More current flowing though larger coils over a greater area is always better. While 750Kg lifting/holding capability sounds like a lot, a fully saturated magnetic circuit in direct physical contact is phenomenally difficult to prise apart.
You may discover that "door lock" only ever gives anything like 750Kg of holding force for the precise size, shape, thickness and alloy of that specific lock mechanism. If you are only working on door locks that might be fine but for thinner, larger, irregular and nonspecific ferrous workpieces, you'd probably be better off with Blu Tack.
I bet that thicker the steel and smoother the surface , higher the force
Nothing to apologize , I've read your message with hungry of knowledge ....and you'd be dead right. The effect however is much greater than most people would imagine.
More thickness allows more of the available magnetic field to flow into, around and back to the source. It is the completion of that circuit which generates the attractive force holding the workpiece. We have all "seen" the magnetic "lines of force" in those spider-like shapes made from iron filings. Without a highly conducting solid magnetic body to flow into, those "lines of force" permeate free space. Thinner materials can only "accept" so much of the available field before the material is "saturated" and can't take any more.
Similarly, the proximity of a workpiece affects magnetic force exponentially (inverse square law). Double the distance, power falls off four times, three times the distance, one ninth of the potential force etc. For mechanical engineers working even in the generous domain of thousandths of an inch, the effect is dramatic. Say you have one ton of "holding force" in a part with a gap or gaps of up to one thousandth of an inch. If that gap increases to two thousandths, you now have 250Kg of force, not 1000Kg. At three thou, the force is a mere 110Kg, that's the difference between lifting a bathtub full of water and a large bucket - for a 2 thou difference!
You can easily test this for yourself. Take a decent size magnet or DTI magbase and test it on a thin sheet of steel, then compare that to the same magnet on a thicker section. Next try the same thing but changing only the distance with a sheet of paper. If you haven't tried that experiment it is well worth conducting, I'm willing to bet most people will sort of "know" there's a difference and even expect it but when you consider exactly what is happening and focus on the science, the first time you "test" that knowledge it can be quite surprising almost to the point of incredibility.
Sorry if I am over egging it but I genuinely find this stuff fascinating and just writing this out helps me understand the phenomena myself and yes; this is my favourite "pop-science" explanation. Just enough to make it interesting without getting bogged down in the minutia of which there are many!
I wrecked a pickup magnet the other day TIG welding next to it. It'll have been a neodymium type. I was't sure if it was the DC current next to it, or if it was just a little too hot...
Doesn't take much heat to ruin a Neodymium. Anything over 80C and it will start to degrade, after that and it gets a bit technical but 150C and I think you can kiss it goodbye. Depends on the precise grade etc. (ask @TechnicAl) but the vast majority of Chineseum "N52" magnets will be a very pale imitation of the real thing made from dust sweeps off the floor etc.
Dont ask me.....I havent a clue.........I know they are very brittle, simply from trying to screw one to a wall....had a hole but slightly too tight and they split in half.
Heat Treatments of Steels, hardening and tempering etc etc I have been involved with..........Magnets are a different science alltogther.......like you said very complex and appear to be changing (and improving) all the time.........When I was taught no-one had heard of Neodymium except that it was one of the rare earth elements and was present in mischmetal which had one use...cig lighter flintsIt was the heat sensitivity I was thinking of which I recall being something of a speciality of yours. The magnet is destroyed at its curie temperature but I hesitate to go into deep tech on subjects I have a passing interest in.
I think it's actually worse than that, the force falls away with the cube of the separation IIRC!Similarly, the proximity of a workpiece affects magnetic force exponentially (inverse square law).
I used to magnetise my screwdrivers tips using a solenoid .
If you drop the screwdriver on the floor it will loose its magnetism .
I think it's actually worse than that, the force falls away with the cube of the separation IIRC!
I must confess, the magnet in the video worked better than I expected, it's a very coarse pole spacing compared to commercially made magnetic chucks like the Eclipse ones you get on surface grinders and even with those you get special fine pitch versions for thin parts.
Here's something slightly less useful you can do with them.
LoLNonsense. I've been dropped a thousand times and I haven't lost any of my magnetism.
Of course those who approach me from the wrong direction will experience an equally strong repulsive force.
then I said i hope there isn't a powercut once its over the van dipstick didn't get it durrr