Extreme Magnets

hi in our first video on magnetohydrodynamics I had promised that we were building a much larger more powerful magnet assembly to improve the performance of our MHD pumps to allow us to construct a system to generate electricity from seawater as well as be the first stage in our railgun project [Music] so it occurred to me that the building of this large magnetic assembly is interesting in itself and what I'd like to do is go through some of the principles the design and then the very interesting process of inserting these enormous ly powerful magnets into the assembly if you'll remember from the first video I have this little channel built to allow us to pump liquid and generate a little electricity that was based on an N 40 neodymium magnet that's identical to the one that I have here outside of the Assembly if you take a look at this Gauss meter that I have up here turned on here and I take the probe and I hold it next to the surface of the magnet for an N 40 magnet this is a typical field strength outside of its coating and a half a millimeter or so away and you'll notice that the 254 Militello decreases very quickly as I begin to move away from the surface as I pull the probe up you'll see how it goes down goes up goes down and if I move it laterally away from the center position you'll notice it also very quickly drops off now what's happening here I'll show you on this drawing is that the magnet field lines are strongest as they leave the poles simply because the billions and billions of tiny little magnetic domains that exist within the magnet want to form closed loops from their north to their South Pole and because they're packed together in the magnet here the intensity of the magnetic field is represented by the density of these field lines at the poles they are strongest at the center it's the strongest as you begin to move away from the surface these field lines tend to pull away from each other as they're trying to make their way down to the southern end of this magnet two axioms that we will just assume for this point we can look up the details or you can if you would like to are that magnetic field lines do not cross they can be compressed together and they can spread out but they do not cross and the second one is they generally don't like each other they tend to pull apart from each other so as soon as the field lines move away from an area with constrained to try to get to the north pole of these little micro domains they begin to spread out and move apart and that as we see the field decreases as we move laterally and it decreases as we move vertically now that's a problem because in this channel what we were seeing is that all the pumping action was probably occurring within a fraction of a millimeter of the surface of that magnet the upper area centimeter or so above there the weakness of the field meant we're probably getting a lot of vortices a lot of inefficiency not such a good way to produce a magnetic ID row dynamic pump if you want to produce a much stronger field a more homogeneous field and relatively inexpensive to do is simply to build a two magnet gap although this looks like a magnetic yoke it is not this is aluminium it's not ferromagnetic stainless steel fasteners there's nothing in this structure other than as a support for two of the exact same type of magnets that we demonstrated here before but the difference if you see with a Gauss meter is that if we place the meter in between these this gap and we put it down on the surface you can see that instead of the 250 odd that we had in the previous example we're up to almost twice the field strength in between the gap and if you look as I raise this up between the two poles I'll try to line this up with a camera a little better and you look at the meter at the same time you'll notice there's almost no decrease in the field either and it's a little bit there very little and if I move laterally out here it's almost as strong so almost no decrease in strength if anything a slight increase as you move laterally and almost no decrease through the entire volume so just for the price of an additional magnet you can double the field strength and probably increase the volume of the field strength of that field by as much as eight fold what's happening here and you can see this on the diagram is effectively the field lines that are coming from the North Pole here want to try to find a South Pole but they are promiscuous they don't care who's a South Pole and because the magnet above it is so close these field lines can make a nearly direct connection here and don't tend to spread out as much nevertheless there is this drawing isn't perfect and there is a bulging and a distortion because as you get near the edges of the magnets this field line sees the upper pole here but it also isn't that far from its its southern end down here and so the bulging of the field here decreases the potential strength of the magnet so if we want to increase the magnetic strength even more what we have to try to do is hide these poles from the gap and the way we do that is we will essentially conduct the field lines that would be going around here and trying to pull this field out to do that we build a yoke now as I said this is not a magnetic yoke but we can build a poor-man's version of this by simply taking some Plains steel and constructing a little magnetic yoke right in front of your eyes this is plain steel nothing magnetic or fancy about it but if we put these pieces of steel here and we take our probe as we did before and we put it in between remember we had almost 500 not quite like 480 and you can see that the field strength is not only extremely homogeneous across the gap it's very homogeneous as you move laterally as well and it's stronger now the increase here doesn't seem all that tremendous but that has to do with the fact that this is not an optimized yoke and what do I mean by optimized joke what's happening when we are trying to guide the magnetic field away from here we're taking advantage of the fact that ferromagnetic materials just like the magnets are made up of billions of small little tiny magnetic domains and if placed in a magnetic field they will line up north to south north to south and can guide the field lines through them so if we do this example here where we take this magnet and we place it near these ball bearings these are actually a fairly low magnetic stainless steel but nevertheless they will be affected by the magnet you can see that they're pulled in toward the magnet but notice how close we have to get probably two centimetres or so before they start to really react however if I take this piece of steel and attach it here now place this steel close to the balls I can affect the balls at a much greater distance not with the same strength as putting the magnet next to there but much farther away then I would be able to do if I take the rod off like that so what's happening here if we look at the diagram is with this rod attached what's happening with the field lines is that the magnetic field lines are still traveling out of the sides of the magnet up here but they're being guided to the end of the tip there where the balls are and effectively it's distorting the magnetic field in such a way that it's going here and it's going here and that's how we affect the balls in a much greater distance when we place this magnetic rod here now one of the properties of any kind of a yoke material is called saturation this can only handle so many magnetic field lines different metals have different saturation levels but dollar-for-dollar plain steel is probably one of the best choices for a yoke because its saturation level is fairly close at about one Tesla to the magnetic strength or the magnetic field density for the pole pieces of n42 and 52 magnets so you want to essentially produce a yoke that has a cross-sectional area of steel guiding the field lines that's proportional or equal or slightly greater than the surface area of the poles that it's guiding the magnetic field lines from now in the large row that we're building over here we're following pretty much that same guideline this large magnetic yoke is sort of what's called an H design or a box design is we have heavy steel plates for them bolted together we have a small groove milled in the center of each of these plates the same thing at the bottom to this guides the magnets which fit into this little groove here the magnets we are using our n 52 1 by 2 by 3 inch same as these 1 2 3 blocks and the magnets effectively will sit in this groove and slide all the way along here until you get all the way to the other end at the other end there's a small keeper that is bolted into the end of the block screwed down there to keep the magnets from just squirting out at the end when we push them all the way in there'll be three magnets 1 2 3 and there'll be three magnets on the bottom 1 2 3 each one kept in by this little keeper here the aluminum blocks here are simply fixtures that are going to be used to hold the apparatus that we intend to place in between the magnet magnets that we're putting in there and this will just keep the load of all the forces that are going to be present inside the magnetic yoke from pushing on the actual magnets themselves so these things have nothing to do with the magnetic properties of yolk these are just structural in addition to that this is just a temporary loading block with a slight step down so that when we push the magnets in there they don't catch on the front end the forces involved with 600-pound magnets being pushed into this yoke and mean that we're going to grease the trough to make it easy to insert the magnets finally once we've put three magnets in one side then we will flip the entire assembly over and we will repeat the process this piece of acrylic will be sitting between the magnet layers just in case things go a little sideways they're not able to go really sideways because the forces here can break fingers and explode magnets and we want to be very careful this is simply acrylic so we can kind of see what's going on inside there that's pretty much the layout of the block if you go over to applied science where Ben has done a very good video his most recent video he shows an example of what's called a c yoke mat netic block there's no reason why this has to be a symmetrical flow of magnetic field lines just sufficient metal to guide the field lines around and a si yoke is more common because it gives more access to the inside of the magnetic field for experimentation purposes for our purposes were perfectly happy with a long structurally sound trough for what we're going to be using for this force so this H type of block is a less common so I'm going to get everything set up and we're gonna try to see if we can load this in without getting hurt see in a sec alright now we get to the scary part of this whole process first thing I'm going to do is I'm going to grease the channel to minimize any friction from the high loading of these magnets so we're gonna put some lithium grease in here I'm going to drag it around into the channel where the magnet is going to go all the way to the end there make it nice and slimy doesn't hurt to do the walls a little bit alright now we'll get the grease out of here and I'm going to take one of my first magnets and we're going to push it in between there we're going to take this acrylic plate and put it in the gap simply to keep things from going sideways if they want to go sideways this is the magnet that we're going to be putting in here 600-pound pull neodymium in 52 so when I put this I can already start to feel it pulling to the block here so I have to make sure that I get it into the guide and well positioned before it has a chance to free up and then they're gonna pull itself in there very powerfully now if I look carefully I still see the esses up so it didn't flip that was important and now what we're gonna do is I'm gonna push it all the way to the other end using my non-magnetic wooden bar what they I greased it notice how I had to clamp the entire assembly down and then clamp the assembly to the table and then lock that everything down to a three-quarter ton table just to get this to work that was number one next magnet same polarity s up now we're gonna guide this in between the sideways and expect it to do it's kind of wild let go here and that's scary those are forces and I think we still have the same polarity I don't see how it could have possibly flipped so now I'm going to push this fellow in now normally be almost impossible to put these two magnets close to each other so what the point is the yoke guides the field lines that would normally oppose them and so it's much easier to move them close to each other who Easy's a relative word though all right let's get another magnet same thing got to be very careful as we get close to the metal don't let it take off till last minute and then it takes over now we'll take my little pusher good okay now we have to secure these magnets so that they're not going to be popping out of here so what we're going to do is I'm going to release these clamps so I can move this base plate a little off the end of the table another interesting thing too is that the yolk contains the magnetic field pretty effectively doesn't stick nice huh makes it safer to work with we're gonna do pull this off the edge of the table sufficiently so that I can get to this little hole here where I'm going to secure the stop in the end of the magnet and pull out my little plate put my screw on the end of this so if you see what I'm gonna do here if you look in the end of the magnet yoke would insert the screw up through there and the idea is I'm going to put this little diskeeper on the end it's sort of a space or nut and screw this in place I'm holding my hand as soon as I can and what that's going to do is support that so that the magnets can't come out later on we'll be inserting a smaller magnet in there just to fill up the remainder of the gap now the trick is we have to flip everything around so that we can repeat this for the other side all right now the other side let's do our greasing thing you have the trough nice and slimy go ahead and start here I guess I'll just start grazing it up all the way to the end saves muscle power I'm going to take my acrylic safety guard put it in between the guides here slide it in and now I'm going to grab magnet number four in this case we're going to make sure that we have the self poles down so here goes little boy I can already feel it pulling yeah man that goes in there now if you look you can see that it pulled itself a little further in because of the other magnet but it likes the steel better than it likes the magnet that's about a centimeter and a half away and that's what we're depending on to keep the magnets in place nevertheless I need to get this Merrigan farther down so then I have to push it I think I need more grease more muscles I think I got this to the other end yep and now we're going to be more liberal on this Gries all right let's go ahead and slime this up each magnet probably cleans out the grease and makes it less slippery for the following magnet so we're gonna help it now magnet number two self pull down I don't like this part frightening let's go ahead and get our pusher you shove it on a little further too it's buddy all right one last magnet self pull down all right the part I hate it's just scary boom all right looks like it lined up pretty well I don't think I'm gonna be able to push it in any further and like I said before in this remaining gap between this magnet and that keeper we've got a couple of shorter magnets on order that are gonna fill up that final gap and that'll be loaded in just like you saw those but that will then complete the entire 14 inch or what would that be 35 centimeter channel between the two blocks but as I said before one of the neat things about this is it contains the magnetic field very effectively you can barely get that buddy to stick so the saturation of this metal has not been overtaken by the the strength of the magnets and that's kind of a nice thing because then this is a lot safer to keep inside of a laboratory or shop even though it's got a tremendous magnetic field in between so you know little while would be producing the videos that are gonna be utilizing this magnet for all those purposes that I described early on in this in this video so I want to thank you very much for watching and please subscribe it helps us a lot and you have a wonderful afternoon [Music]

Channel: Tech Ingredients

Views: 855,315

Rating: 4.8815165 out of 5

Keywords: Magnets, Neodymium Magnets, Magnetic Field, Magnetic Yoke, Gauss Meter, Magnetic Field Lines, Magnetic Saturation, Magnetohydrodynamics, Railgun

Id: B015P0XFl9g

Length: 21min 25sec (1285 seconds)

Published: Tue Sep 04 2018

Reddit Comments

[u/TeleFruity]

I didn't blink the whole time while he was introducing the magnets, thinking it would shoot out and hit him.

[u/MrMentat]

I understood some of those things.

[u/[deleted]]

When's the next video of it in use?