COILS OF ELECTROMAGNETS
The coil is one of the main elements of the electromagnet and must meet the following basic requirements:
1) ensure reliable switching on of the electromagnet under the worst conditions, i.e. in a heated state and at reduced voltage;
2) do not overheat above the permissible temperature in all possible modes, i.e. at high voltage;
3) with minimum dimensions to be convenient for production;
4) be mechanically strong;
5) have a certain level of insulation, and in some devices be moisture, acid and oil resistant.
During operation, stresses arise in the coil: mechanical - due to electrodynamic forces in the turns and between the turns, especially when alternating current; thermal - due to uneven heating of its individual parts; electrical - due to overvoltages, in particular during shutdown.
When calculating the coil, two conditions must be met. The first is to provide the required MMF with a hot coil and low voltage. The second is that the heating temperature of the coil should not exceed the permissible one.
As a result of the calculation, the following quantities necessary for winding should be determined: d- the diameter of the wire of the selected brand; w- number of turns; R- coil resistance.
By design, coils are distinguished: frame coils - winding is carried out on a metal or plastic frame; frameless banded - winding is carried out on a removable template, after winding the coil is bandaged; frameless with winding on the core of the magnetic system.
A permanent magnet is a piece of steel or some other hard alloy, which, being magnetized, steadily stores the stored part of the magnetic energy. The purpose of a magnet is to serve as a source of a magnetic field that does not noticeably change either with time or under the influence of factors such as shaking, temperature changes, external magnetic fields. Permanent magnets are used in a variety of devices and devices: relays, electrical measuring instruments, contactors, electrical machines.
There are the following main groups of alloys for permanent magnets:
2) alloys based on steel - nickel - aluminum with the addition of cobalt, silicon in some cases: alni (Fe, Al, Ni), alnisi (Fe, Al, Ni, Si), magnico (Fe, Ni, Al, Co);
3) alloys based on silver, copper, cobalt.
The quantities characterizing a permanent magnet are the residual induction AT r and coercive force H c. To determine the magnetic characteristics of finished magnets, demagnetization curves are used (Fig. 7-14), which are the dependence AT = f(– H). The curve is taken for the ring, which is first magnetized to saturation induction, and then demagnetized to AT = 0.
flow in the air gap. To use the energy of the magnet, it is necessary to make it with an air gap. The MMF component spent by the permanent magnet to conduct the flow in the air gap is called the free MMF.
The presence of an air gap δ reduces the induction in the magnet from AT r to AT(Fig. 7-14) in the same way as if a demagnetizing current was passed through a coil put on a ring, creating tension H. This consideration is the basis of the following method for calculating the flux in the air gap of a magnet.
In the absence of a gap, the entire MMF is spent on conducting the flow through the magnet:
where lμ is the length of the magnet.
In the presence of an air gap, part of the MDS Fδ will be spent on conducting the flow through this gap:
F=F μ + Fδ(7-35)
Let us assume that we have created such a demagnetizing magnetic field strength H, what
H l μ = Fδ(7-36)
and the induction became AT.
In the absence of scattering, the flux in the magnet is equal to the flux in the air gap
Bs μ = F δ Λ δ = Λ lμ Λ δ , (7-37)
where sμ is the section of the magnet; Λ δ = μ 0 sδ/δ; μ 0 is the magnetic permeability of the air gap.
From fig. 7-14 it follows that
B/H= l μ Λ δ / s μ=tgα (7-38)
Rice. 7-14. Demagnetization curves
Thus, knowing the data on the material of the magnet (in the form of a demagnetization curve), the dimensions of the magnet l μ , sμ and gap dimensions δ, sδ , you can use equation (7-38) to calculate the flow in the gap. To do this, draw a straight line on the diagram (Fig. 7-14). Ob at an angle a. Line segment bс defines induction AT magnet. From here, the flow in the air gap will be
When determining tg α, the scales of the y-axis and abscissa are taken into account:
where p = n/m- the ratio of the scales of the axes B and H.
Taking into account scattering, the flux Ф δ is determined as follows.
Carry out a straight line Ob at an angle α, where tg α == Λ δ l μ ( psµ). Received value AT characterizes the induction in the middle section of the magnet. Flux in the middle section of the magnet
Air Gap Flow
de σ is the scattering coefficient. Induction in working gap
Straight magnets. Expression (7-42) gives a solution to the problem for magnets of a closed shape, where the conductivity of the air gaps can be calculated with sufficient accuracy for practical purposes. For straight magnets, the problem of calculating the conductivities of the stray flux is very difficult. The flux is calculated using experimental dependencies relating the strength of the magnet field to the dimensions of the magnet.
Free magnetic energy. This is the energy that the magnet gives off in the air gaps. When calculating permanent magnets, choosing a material and the required ratios of dimensions, they strive for the maximum use of the material of the magnet, which is reduced to obtaining the maximum value of the free magnetic energy.
Magnetic energy concentrated in the air gap, proportional to the product of the flux in the gap and MMF:
Given that
We get
where V is the volume of the magnet. The material of a magnet is characterized by magnetic energy per unit of its volume.
Rice. 7-15. To the definition of the magnetic energy of a magnet
Using the demagnetization curve, one can construct a curve W m = f(AT) at V= 1 (Fig. 7-15). Curve W m = f(AT) has a maximum at some values AT and H, which we denote AT 0 and H 0 . In practice, the method of finding AT 0 and H 0 without plotting W m = f(AT). Intersection point of the diagonal of a quadrilateral whose sides are equal AT r and H c , with the demagnetization curve quite closely corresponds to the values AT 0 , H 0 . The residual induction V r fluctuates within relatively small limits (1-2.5), and the coercive force H c - within large limits (1-20). Therefore, materials are distinguished: low-coercive, in which W m is small (curve 2), high-coercivity, in which W m large (curve 1 ).
return curves. During operation, the air gap may change. Let us assume that before the introduction of the anchor, the induction was B 1tg a one . When the armature is introduced, the gap δ changes, and this state of the system corresponds to the angle a 2; (Fig. 7-16) and a large induction. However, the increase in induction does not occur along the demagnetization curve, but along some other curve b 1 cd, called the return curve. With complete closure (δ = 0), we would have induction B 2. When changing the gap in reverse direction induction changes along a curve dfb one . return curves b 1 cd and dfb 1 are partial cycle curves of magnetization and demagnetization. The width of the loop is usually small, and the loop can be replaced with a straight b 1 d. Ratio Δ AT/Δ H is called the reversible permeability of the magnet.
Aging magnets. Aging is understood as the phenomenon of a decrease in the magnetic flux of a magnet over time. This phenomenon is determined by a number of reasons listed below.
structural aging. The magnet material after hardening or casting has an uneven structure. Over time, this unevenness passes into a more stable state, which leads to a change in the values AT and H.
Mechanical aging. Occurs due to shocks, shocks, vibrations and the influence of high temperatures, which weaken the flow of the magnet.
magnetic aging. Determined by the influence of external magnetic fields.
Stabilization of magnets. Any magnet before installing it in the apparatus must be subjected to an additional stabilization process, after which the resistance of the magnet to a decrease in flux increases.
structural stabilization. It consists in additional heat treatment, which is carried out before magnetization of the magnet (boiling the hardened magnet for 4 hours after hardening). Alloys based on steel, nickel and aluminum do not require structural stabilization.
mechanical stabilization. The magnetized magnet is subjected to shocks, shocks, vibrations in conditions close to the operating mode before being installed in the apparatus.
magnetic stabilization. A magnetized magnet is exposed to external fields of variable sign, after which the magnet becomes more resistant to external fields, to temperature and mechanical influences.
CHAPTER 8 ELECTROMAGNETIC MECHANISMS
To understand how to increase the strength of a magnet, you need to understand the process of magnetization. This will happen if the magnet is placed in an external magnetic field with the opposite side to the original one. An increase in the power of an electromagnet occurs when the current supply increases or the turns of the winding multiply.
You can increase the strength of the magnet using a standard set of necessary equipment: glue, a set of magnets (permanent ones are needed), a current source and an insulated wire. They will be needed to implement those methods of increasing the strength of the magnet, which are presented below.
Strengthening with a stronger magnet
This method consists in using a more powerful magnet to strengthen the original one. For implementation, it is necessary to place one magnet in an external magnetic field of another, which has more power. Electromagnets are also used for the same purpose. After holding the magnet in the field of another, amplification will occur, but the specificity lies in the unpredictability of the results, since such a procedure will work individually for each element.
Strengthening by adding other magnets
It is known that each magnet has two poles, and each attracts the opposite sign of other magnets, and the corresponding one does not attract, only repels. How to increase the power of a magnet using glue and additional magnets. Here it is supposed to add other magnets in order to increase the total power. After all, the more magnets, the correspondingly, there will be more force. The only thing to consider is the attachment of the magnets poles of the same name. In the process, they will repel, according to the laws of physics. But the challenge is to stick together despite the physical challenges. It is better to use glue that is designed for bonding metals.
Amplification method using the Curie point
In science there is the concept of the Curie point. Strengthening or weakening of the magnet can be done by heating or cooling it relative to this very point. So, heating above the Curie point or strong cooling (much below it) will lead to demagnetization.
It should be noted that the properties of a magnet during heating and cooling relative to the Curie point have a jump property, that is, having achieved the correct temperature, you can increase its power.
Method #1
If the question arose of how to make the magnet stronger, if its strength is regulated by electric current, then this can be done by increasing the current that is supplied to the winding. Here there is a proportional increase in the power of the electromagnet and the supply of current. The main thing is ⸺ gradual feed to prevent burnout.
Method #2
To implement this method, it is necessary to increase the number of turns, but the length must remain unchanged. That is, you can make one or two additional rows of wire so that the total number of turns becomes larger.
This section discusses ways to increase the strength of a magnet at home, for experiments you can order on the MirMagnit website.
Strengthening a conventional magnet
Many questions arise when ordinary magnets cease to perform their direct functions. This is often due to the fact that household magnets are not, in fact, they are magnetized metal parts that lose their properties over time. It is impossible to increase the power of such parts or return their properties that were originally.
It should be noted that attaching magnets to them, even more powerful ones, does not make sense, since, when they are connected by reverse poles, the external field becomes much weaker or even neutralized.
This can be checked with a regular household mosquito curtain, which should close in the middle with magnets. If more powerful ones are attached to the weak initial magnets from above, then as a result the curtain will generally lose the properties of the connection with the help of attraction, because the opposite poles neutralize each other's external fields on each side.
Experiments with neodymium magnets
Neomagnet is quite popular, its composition: neodymium, boron, iron. Such a magnet has a high power and is resistant to demagnetization.
How to strengthen neodymium? Neodymium is very susceptible to corrosion, that is, it rusts quickly, so neodymium magnets are plated with nickel to increase their service life. They also resemble ceramics, they are easy to break or split.
But there is no point in trying to increase its power artificially, because it is a permanent magnet, it has a certain level of strength for itself. Therefore, if you need to have a more powerful neodymium, it is better to purchase it, considering the right force new.
Conclusion: the article discusses the topic of how to increase the strength of a magnet, including how to increase the power of a neodymium magnet. It turns out that there are several ways to increase the properties of a magnet. Because there is simply a magnetized metal, the strength of which cannot be increased.
The simplest ways: using glue and other magnets (they must be glued with identical poles), as well as a more powerful one, in external field which the original magnet should be located.
Methods for increasing the strength of an electromagnet are considered, which consist in additional winding with wires or intensifying the flow of current. The only thing to consider is the strength of the current flow for the safety and security of the device.
Ordinary and neodymium magnets are not able to succumb to an increase in their own power.
Now I’ll explain: It just so happened in life that it’s impossible to be especially strong - then especially (just horror, how) you want ... And the point here is the following. Some kind of fate hung over the "regulars", an aura of mystery and reticence. All physicists (uncles and aunts are different) do not cut at all in permanent magnets (checked repeatedly, personally), and that's probably because in all physics textbooks this question is bypassed. Electromagnetism - yes, yes, please, but not a word about constants ...
Let's see what can be squeezed out of the smartest book “I.V. Savelyev. Course of general physics. Volume 2. Electricity and Magnetism," - cooler than this waste paper, you can hardly dig anything out. So, in 1820, a certain dude under the name of Oersted muddied the experiment with a conductor, and a compass needle standing next to him. Letting electricity along the conductor in different directions, he was convinced that the arrow would clearly orient itself clearly with what. From experience, the cormorant concluded that the magnetic field is directional. At a later time, it was found out (I wonder how?) that a magnetic field, unlike an electric one, does not affect a charge at rest. Force arises only when the charge moves (take note). Moving charges (currents) change the properties of the surrounding space and create a magnetic field in it. That is, it follows from here that the magnetic field is generated by moving charges.
You see, we are deviating further and further into electricity. After all, not a damn thing moves in a magnet and no current flows in it. Here is what Ampère thought about this: he suggested that circular currents (molecular currents) circulate in the molecules of a substance. Each such current has a magnetic moment and creates a magnetic field in the surrounding space. In the absence of external field molecular currents are oriented in a random way, so that the resulting field due to them is zero (fun, huh?). But this is not enough: Due to the chaotic orientation of the magnetic moments individual molecules the total magnetic moment of the body is also equal to zero. - Do you feel how the heresy is getting stronger and stronger? ? Under the action of the field, the magnetic moments of the molecules acquire a predominant orientation in one direction, as a result of which the magnet is magnetized - its total magnetic moment becomes different from zero. The magnetic fields of individual molecular currents in this case no longer compensate each other and a field arises. Hooray!
Well, what is it?! - It turns out that the material of the magnet is magnetized all the time (!), Only randomly. That is, if we start dividing a large piece into smaller ones, and reaching the very micro-with-micro chips, we will still get normally working magnets (magnetized) without any magnetization whatsoever !!! - Well, that's bullshit.
A little reference, so, for general development: The magnetization of a magnet is characterized by a magnetic moment per unit volume. This value is called magnetization and is denoted by the letter "J".
Let's continue our dive. A little from electricity: Do you know that the lines of magnetic induction of the direct current field are a system of concentric circles covering the wire? Not? Now you know, but don't believe. In a simple way, if you say, then imagine an umbrella. The handle of an umbrella is the direction of the current, but the edge of the umbrella itself (for example), i.e. a circle is, like, a line of magnetic induction. Moreover, such a line begins from the air, and ends, of course, also nowhere! - Do you physically imagine this nonsense? As many as three men were signed under this case: the Biot-Savart-Laplace law is called. The whole park comes from the fact that somewhere the very essence of the field was misrepresented - why it appears, what it is, in fact, where it begins, where and how it spreads.
Even in absolutely simple things, they (these evil physicists) fool everyone's heads: The direction of the magnetic field is characterized by a vector quantity ("B" - measured in teslas). It would be logical by analogy with tension electric field"E" call "B" the strength of the magnetic field (like, they have similar functions). However (attention!) The main power characteristic of the magnetic field was called magnetic induction ... But even this seemed to them not enough, and in order to completely confuse everything, the name “magnetic field strength” was assigned to the auxiliary value “H”, similar to the auxiliary characteristic “D” of the electric field. What is…
Further, finding out the Lorentz force, they come to the conclusion that the magnetic force is weaker than the Coulomb force by a factor equal to the square of the ratio of the charge velocity to the speed of light (i.e., the magnetic component of the force is less than the electrical component). Thus attributing magnetic interactions relativistic effect!!! For the very young, I will explain: Uncle Einstein lived at the beginning of the century and he came up with the theory of relativity, tying all processes to the speed of light (pure nonsense). That is, if you accelerate to the speed of light, then time will stop, and if you exceed it, it will go back ... It has long been clear to everyone that it was just the world tattoo of the joker Einstein, and that all this, to put it mildly, is not true. Now they also chained magnets with their properties to this labudyatin - why are they like that? ...
Another little note: Mr. Ampère deduced a wonderful formula, and it turned out that if you bring a wire to a magnet, well, or some kind of piece of iron, then the magnet will not attract the wire, but the charges that move along the conductor. They called it pathetically: "Ampère's Law"! Little did not take into account that if the conductor is not connected to the battery and the current does not flow through it, then it still sticks to the magnet. They came up with such an excuse that, they say, there are still charges, they just move randomly. Here they stick to the magnet. Interestingly, this is where it comes from, in microvolumes, the EMF is taken to make these charges chaotically sausage. It's just a perpetual motion machine! And after all, we don’t heat anything, we don’t pump it with energy ... Or here’s another joke: For example, aluminum is also a metal, but for some reason it has no chaotic charges. Well, aluminum DOES NOT STICK to a magnet !!! ...or is it made of wood...
Oh yes! I have not yet told how the magnetic induction vector is directed (you need to know this). So, remembering our umbrella, imagine that around the circumference (the edge of the umbrella) we started the current. As a result of this simple operation, the vector is directed by our thought towards the handle exactly in the center of the stick. If the conductor with current has irregular outlines, then everything is lost - simplicity evaporates. An additional vector appears called the dipole magnetic moment (in the case of an umbrella, it is also present, it is simply directed in the same direction as the magnetic induction vector). A terrible split in the formulas begins - all sorts of integrals along the contour, sines-cosines, etc. - Who needs it, can ask himself. And it is also worth mentioning that the current must be started according to the rule of the right gimlet, i.e. clockwise, then the vector will be away from us. This is related to the concept of a positive normal. Okay, let's move on...
Comrade Gauss thought a little and decided that the absence of magnetic charges in nature (in fact, Dirac suggested that they exist, but they have not yet been discovered) leads to the fact that the lines of the vector "B" have neither beginning nor end. Therefore, the number of intersections that occur when the lines "B" exit the volume bounded by some surface "S" is always equal to the number of intersections that occur when the lines enter this volume. Therefore, the flux of the magnetic induction vector through any closed surface is zero. We now interpret everything in normal Russian: Any surface, as it is easy to imagine, ends somewhere, and therefore is closed. " Zero' means that it doesn't exist. We draw a simple conclusion: “There is never a flow anywhere” !!! - Really cool! (Actually, this only means that the flow is uniform). I think that this should be stopped, because then there are SUCH rubbish and depth that ... Such things as divergence, rotor, vector potential are globally complex and even this mega-work is not fully understood.
Now a little about the shape of the magnetic field in conductors with current (as a basis for our further conversation). This topic is much more vague than we used to think. I already wrote about a straight conductor - a field in the form of a thin cylinder along the conductor. If you wind a coil on a cylindrical cardboard and turn on the current, then the field of such a design (and it is called cleverly - a solenoid) will be the same as that of a similar cylindrical magnet, i.e. the lines exit from the end of the magnet (or the proposed cylinder) and enter the other end, forming a kind of ellipse in space. The longer the coil or magnet, the more flat and elongated the ellipses are. A ring with a spring has a cool field: namely, in the form of a torus (imagine the field of a straight conductor coiled up). With a toroid, it’s generally a joke (this is now a solenoid folded into a donut) - it has no magnetic induction outside of itself (!). If we take an infinitely long solenoid, then the same garbage. Only we know that nothing is infinite, that's why the solenoid splashes from the ends, it kind of gushes;))). And yet, - inside the solenoid and the toroid, the field is uniform. How.
Well, what else is good to know? - The conditions at the boundary of two magnets look exactly like a beam of light at the boundary of two media (it refracts and changes its direction), only we don’t have a beam, but a vector of magnetic induction and different magnetic permeability (and not optical) of our magnets (media). Or one more thing: we have a core and a coil on it (an electromagnet, like), where do you think the lines of magnetic induction hang out? - They are mostly concentrated inside the core, because it has amazing magnetic permeability, and they are also tightly packed into the air gap between the core and the coil. That's just in the winding itself, there is not a fig. Therefore, you will not magnetize anything with the side surface of the coil, but only with the core.
Hey, are you asleep yet? Not? Then let's continue. It turns out that all materials in nature are not divided into two classes: magnetic and non-magnetic, but into three (depending on the sign and magnitude of the magnetic susceptibility): 1. Diamagnets, in which it is small and negative in magnitude (in short, practically zero, and you won’t be able to magnetize them for anything), 2. Paramagnets, in which it is also small but positive (also near zero; you can magnetize a little, but you still won’t feel it, so one fig), 3. Ferromagnets, in which it is positive and reaches simply gigantic values (1010 times greater than that of paramagnets!), in addition, the susceptibility of ferromagnets is a function of the magnetic field strength. In fact, there is another type of substances - these are dielectrics, they have completely opposite properties and they are not of interest to us.
Of course, we are interested in ferromagnets, which are called so because of the inclusions of iron (ferrum). Iron can be replaced by similar chemical properties. elements: nickel, cobalt, gadolinium, their alloys and compounds, as well as some alloys and compounds of manganese and chromium. This whole canoe with magnetization only works if the substance is in crystalline state. (The magnetization remains due to an effect called "Hysteresis Loop" - well, you all already know this). It is interesting to know that there is a certain "Curie temperature", and this is not a certain temperature, but for each material its own, above which all ferromagnetic properties disappear. It's absolutely awesome to know that there are substances of the fifth group - they are called antiferromagnets (erbium, disposition, alloys of manganese and COPPER !!!). These special materials have one more temperature: the “antiferromagnetic Curie point” or “Néel point”, below which the stable properties of this class also disappear. (Above the upper point, the substance behaves like a paramagnet, and at temperatures below the lower Neel point, it becomes a ferromagnet).
Why am I saying this so calmly? - I draw your attention to the fact that I never said that chemistry is an incorrect science (only physics), but this is the purest chemistry. Imagine: you take copper, cool it well, magnetize it, and you have a magnet in your hands (in mittens?) But copper is not magnetic !!!
We may also need a couple of purely electromagnetic things from this book, to create an alternator, for example. Phenomenon number 1: In 1831, Faraday discovered that in a closed conducting circuit, when the flux of magnetic induction changes through the surface bounded by this circuit, an electric current arises. This phenomenon is called electromagnetic induction, and the resulting current is inductive. And now the most important thing: The magnitude of the EMF of induction does not depend on the way in which the change in the magnetic flux is carried out, and is determined only by the rate of change of the flux! - The thought matures: The faster the rotor with shutters spins, the greater the value of the induced EMF reaches, and the greater the voltage removed from the secondary circuit of the alternator (from the coils). True, Uncle Lenz has spoiled us with his "Lenz's Rule": the induction current is always directed in such a way as to counteract the cause that causes it. Later I will explain how this matter works in the alternator (and in other models as well).
Phenomenon number 2: Induction currents can also be excited in solid massive conductors. In this case, they are called Foucault currents or eddy currents. The electrical resistance of a massive conductor is small, so Foucault currents can reach very high strengths. In accordance with Lenz's rule, the Foucault currents choose such paths and directions inside the conductor so that by their action they resist as strongly as possible the cause that causes them. Therefore, good conductors moving in a strong magnet field experience strong braking due to the interaction of Foucault currents with a magnetic field. This must be known and taken into account. For example, in an alternator, if done according to the generally accepted incorrect scheme, then Foucault currents arise in the moving shutters, and, of course, they slow down the process. As far as I know, no one thought about this at all. (Note: The only exception is unipolar induction, discovered by Faraday and improved by Tesla, which does not cause the harmful effects of self-induction).
Phenomenon number 3: An electric current flowing in any circuit creates a magnetic flux penetrating this circuit. When the current changes, the magnetic flux also changes, as a result of which an EMF is induced in the circuit. This phenomenon is called self-induction. In the article about alternators I will also talk about this phenomenon.
By the way, about Foucault currents. You can have a fun experience. Lightweight as hell. Take a large, thick (at least 2 mm thick) copper or aluminum sheet and place it at an angle to the floor. Let a “strong” permanent magnet slide freely down its inclined surface. And… Weird!!! The permanent magnet seems to be attracted to the sheet and slides noticeably slower than, for example, on a wooden surface. Why? Like, the “specialist” will immediately answer - “In the sheet conductor, when the magnet moves, eddy electric currents (Foucault currents) arise, which prevent the magnetic field from changing, and, consequently, prevent the permanent magnet from moving along the surface of the conductor.” But let's think! Eddy electric current is the vortex motion of conduction electrons. What prevents the free movement of the vortex of conduction electrons along the surface of the conductor? Inertial mass of conduction electrons? Loss of energy during the collision of electrons with the crystal lattice of a conductor? No, this is not observed, and generally cannot be. So what's stopping free movement eddy currents along the conductor? Do not know? And no one can answer, because all physics is nonsense.
Now a couple of interesting thoughts about the essence of permanent magnets. In Howard R. Johnson's machine, more precisely in the patent documentation for it, the following idea was expressed: “This invention relates to a method of using the spins of unpaired electrons in a ferromagnet and other materials that are sources of magnetic fields to produce power without an electron flow, like this occurs in conventional electrical conductors, and to permanent magnet motors for use this method when creating a power source. In the practice of this invention, the spins of the unpaired electrons inside the permanent magnets are used to create a source of motive power solely by the superconductive characteristics of the permanent magnets and the magnetic flux created by the magnets, which is controlled and concentrated in such a way as to orient the magnetic forces for constant production. useful work, such as the displacement of the rotor relative to the stator. Note that Johnson writes in his patent about a permanent magnet as a system with "superconducting characteristics"! Electron currents in a permanent magnet are a manifestation of real superconductivity, which does not require a conductor cooling system to provide zero resistance. Moreover, "resistance" must be negative in order for the magnet to maintain and resume its magnetized state.
And what, you think that you know everything about the "regulars"? Here is a simple question: - What does the picture look like? lines of force a simple ferromagnetic ring (a magnet from a conventional speaker)? For some reason, everyone exclusively believes that it is the same as with any ring conductor (and, of course, it is not drawn in any of the books). And this is where you are wrong!
In fact (see figure) in the area adjacent to the hole of the ring, something incomprehensible happens to the lines. Instead of continuously penetrating it, they diverge, outlining a figure resembling a tightly stuffed bag. It has, as it were, two strings - at the top and bottom (special points 1 and 2), - the magnetic field in them changes direction.
You can do a cool experiment (like, normally inexplicable;), - let's bring a steel ball from below to the ferrite ring, and a metal nut to its lower part. She will immediately be attracted to him (Fig. a). Everything is clear here - the ball, having got into the magnetic field of the ring, became a magnet. Next, we will begin to bring the ball from the bottom up into the ring. Here the nut will fall off and fall on the table (fig. b). Here it is, bottom singular point! The direction of the field changed in it, the ball began to remagnetize and stopped attracting the nut. By lifting the ball above the singular point, the nut can again be magnetized to it (fig. c). This joke with magnetic lines M.F. was the first to discover Ostrikov.
P.S.: And in conclusion, I will try to clearly formulate my position in relation to modern physics. I'm not against experimental data. If they brought a magnet, and he pulled a piece of iron, then he pulled it. If the magnetic flux induces an EMF, then it induces. You can't argue with that. But (!) here are the conclusions that scientists draw, ... their explanations of these and other processes are sometimes simply ridiculous (to put it mildly). And not sometimes, but often. Almost always…
There are two main types of magnets: permanent and electromagnets. It is possible to determine what a permanent magnet is based on its main property. The permanent magnet gets its name from the fact that its magnetism is always "on". It generates its own magnetic field, unlike an electromagnet, which is made from wire wrapped around an iron core and requires current to flow to create a magnetic field.
History of the study of magnetic properties
Centuries ago, people discovered that some types of rocks have original features: they are attracted to iron objects. The mention of magnetite is found in ancient historical chronicles: more than two thousand years ago in European and much earlier in East Asian. At first it was assessed as a curious object.
Later, magnetite was used for navigation, finding that it tends to take a certain position when it is given the freedom to rotate. Scientific research, carried out by P. Peregrine in the 13th century, showed that steel can acquire these features after rubbing with magnetite.
Magnetized objects had two poles: "north" and "south", relative to the Earth's magnetic field. As Peregrine discovered, it was not possible to isolate one of the poles by cutting a fragment of magnetite in two - each separate fragment had its own pair of poles as a result.
In accordance with today's ideas, the magnetic field of permanent magnets is the resulting orientation of electrons in a single direction. Only certain types of materials interact with magnetic fields, a much smaller number of them is able to maintain a constant MF.
Properties of permanent magnets
The main properties of permanent magnets and the field they create are:
- the existence of two poles;
- opposite poles attract and like poles repel (like positive and negative charges);
- magnetic force imperceptibly propagates in space and passes through objects (paper, wood);
- there is an increase in the MF intensity near the poles.
Permanent magnets support MT without external help. Materials depending on the magnetic properties are divided into the main types:
- ferromagnets - easily magnetized;
- paramagnets - magnetized with great difficulty;
- diamagnets - tend to reflect the external MF by magnetization in the opposite direction.
Important! Soft magnetic materials such as steel conduct magnetism when attached to a magnet, but this stops when it is removed. Permanent magnets are made from magnetically hard materials.
How a permanent magnet works
His work is related to atomic structure. All ferromagnets create a natural, albeit weak, magnetic field, thanks to the electrons surrounding the nuclei of atoms. These groups of atoms are able to orient in a single direction and are called magnetic domains. Each domain has two poles: north and south. When a ferromagnetic material is not magnetized, its regions are oriented in random directions, and their MFs cancel each other out.
To create permanent magnets, ferromagnets are heated at very high temperatures and subjected to a strong external magnetic field. This leads to the fact that individual magnetic domains inside the material begin to orient themselves in the direction of the external magnetic field until all the domains align, reaching the magnetic saturation point. The material is then cooled and the aligned domains are locked into position. After the removal of the external MF, magnetically hard materials will retain most of their domains, creating a permanent magnet.
Characteristics of a permanent magnet
- The magnetic force is characterized by residual magnetic induction. Designated Br. This is the force that remains after the disappearance of the external MT. Measured in tests (Tl) or gauss (Gs);
- Coercivity or resistance to demagnetization - Ns. Measured in A / m. Shows what the intensity of the external MF should be in order to demagnetize the material;
- Maximum energy - BHmax. Calculated by multiplying the residual magnetic force Br and the coercivity Hc. Measured in MGSE (megagaussersted);
- The temperature coefficient of the residual magnetic force is Тс of Br. Characterizes the dependence of Br on the temperature value;
- Tmax is the highest temperature value at which permanent magnets lose their properties with the possibility of reverse recovery;
- Tcur is the highest temperature value at which the magnetic material permanently loses its properties. This indicator is called the Curie temperature.
The individual characteristics of a magnet change with temperature. At different meanings temperature different types magnetic materials work differently.
Important! All permanent magnets lose a percentage of magnetism as the temperature rises, but at a different rate depending on their type.
Types of permanent magnets
In total there are five types of permanent magnets, each of which is made differently based on materials with different properties:
- alnico;
- ferrites;
- rare earth SmCo based on cobalt and samarium;
- neodymium;
- polymeric.
Alnico
These are permanent magnets composed primarily of a combination of aluminum, nickel, and cobalt, but may also include copper, iron, and titanium. Due to the properties of alnico magnets, they can operate at the highest temperatures while retaining their magnetism, however, they demagnetize more easily than ferrite or rare earth SmCo. They were the first mass-produced permanent magnets, replacing magnetized metals and expensive electromagnets.
Application:
- electric motors;
- heat treatment;
- bearings;
- aerospace vehicles;
- military equipment;
- high-temperature loading and unloading equipment;
- microphones.
Ferrites
For the manufacture of ferrite magnets, also known as ceramic, strontium carbonate and iron oxide are used in a ratio of 10/90. Both materials are abundant and economically available.
Due to low production costs, resistance to heat (up to 250°C) and corrosion, ferrite magnets are one of the most popular for everyday use. They have greater internal coercivity than alnico, but less magnetic force than neodymium counterparts.
Application:
- sound speakers;
- security systems;
- large plate magnets to remove iron contamination from process lines;
- electric motors and generators;
- medical instruments;
- lifting magnets;
- marine search magnets;
- devices based on the operation of eddy currents;
- switches and relays;
- brakes.
SmCo Rare Earth Magnets
Cobalt and samarium magnets operate over a wide temperature range, have high temperature coefficients and high corrosion resistance. This type retains its magnetic properties even at temperatures below absolute zero, making them popular for use in cryogenic applications.
Application:
- turbotechnics;
- pump couplings;
- wet environments;
- high temperature devices;
- miniature electric racing cars;
- electronic devices for operation in critical conditions.
Neodymium magnets
The strongest existing magnets, consisting of an alloy of neodymium, iron and boron. Due to their enormous strength, even miniature magnets are effective. This provides versatility of use. Each person is constantly next to one of the neodymium magnets. They are, for example, in a smartphone. The manufacture of electric motors, medical equipment, radio electronics rely on heavy-duty neodymium magnets. Due to their super strength, huge magnetic force and resistance to demagnetization, samples up to 1 mm can be produced.
Application:
- hard disks;
- sound-reproducing devices - microphones, acoustic sensors, headphones, loudspeakers;
- prostheses;
- magnetic coupling pumps;
- door closers;
- engines and generators;
- locks on jewelry;
- MRI scanners;
- magnetotherapy;
- ABS sensors in cars;
- lifting equipment;
- magnetic separators;
- reed switches, etc.
Flexible magnets contain magnetic particles inside a polymer binder. They are used for unique devices where it is impossible to install solid analogues.
Application:
- display advertising - quick fixation and quick removal at exhibitions and events;
- vehicle signs, educational school panels, company logos;
- toys, puzzles and games;
- masking surfaces for painting;
- calendars and magnetic bookmarks;
- window and door seals.
Most permanent magnets are brittle and should not be used as structural elements. They are made in standard forms: rings, rods, discs, and individual: trapezoids, arcs, etc. Due to the high iron content, neodymium magnets are susceptible to corrosion, therefore they are coated on top with nickel, stainless steel, teflon, titanium, rubber and other materials.
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