— NdFeB magnets, mainly made from Neodymium, Iron, Boron, has earned reputation on its high qualities and competitive price, it has excellent properties of high remanence, coercivity and Max. Energy Products. It’s widely used in motors, generators, electroacoustics, hard-disc drives, magnetic separators, permanent magnet bearing, holding system, switches, NMR-analysis equipment and MRI-tomographs, relay and etc.
— Flexible & Plastic magnets, The Flexible & Plastic magnets is a kind of composite magnetic material, made by calendering, extrusion and injection, it’s like rubber, easily to be fabricated. It is widely used in industry and civil appliance, such as, motor, signposts, drawing board locking system, instruments and so on.
— Ferrite magnets, made from iron oxide, SrCO3, (or BaCO3)and other additives, having a relatively low recoil permeability, results in highly resistant to an external magnetic fields, moreover, it’s low in costs, and widely used in motors, generators, electroacoustics, separators, holding system, telecommunication system and etc.
— AlNiCo magnets, the base constituents are Nickel, Cobalt, Aluminum and iron, has excellent corrosion resistance and temperature stability. It’s hard and brittle, but can be manufactured in complex shapes which are impossible with other magnetic materials. With the characteristics of high induction remanence, specific energy and a lower variation to temperature, it can be used at quite high operating temperature. It’s widely used in motors, motors, senor, meters, magnetic separators, loudspeaker, holding system and etc.
— SmCo magnets, made from Cobalt and rare earth, is a high performance permanent magnet. It has very strong uniaxial magnetic anisotropy originating from crystalline structure which gives a high specific energy and exceptional resistance to demagnetization in the presence of opposing field, and at same time a good remanence and temperature coefficient. It’s widely used in motors, watch, transducers, instruments, positional detector, generators, radar and etc.
— Bonded NdFeB magnets, its compound of plastic, rubber and rare-earth materials, the shapes are formed by ways of compressing, injecting, extruding and etc. It has high Intrinsic Coercive force and good magnetic consistency in mass production. It’s widely used in motor, computer application and so on.
— Magnet system & assemblies, Assemblies using metal and other components, magnets can be fabricated by adhering magnets with adhesives to suit a range of environment, by mechanically fastening magnets, or by a combination of these methods.
Key feature of Neodymium magnet
High energy and high magnetic field for size
Very high resistance ability to demagnetization
Need to consider the maximum working temperature
Material is corrosive and should be coated for long-term maximum energy output.
Key feature of SmCo magnet / Samarium Cobalt magnet
High magnetic energy output
High resistance ability to demagnetization.
Good temperature stability
Not need to be coated.
Key feature of Ceramic magnet/ Ferrite magnet
High resistance ability to demagnetization.
Least expensive material compared to SmCo, Alnico and Neodymium magnet.
Not easy to form into complicated shape, due to manufacturing process
Grinding process is needed.
Stable and do not need to be coated.
Key feature for Cast alnico magnet
Will cast to varieties of shapes and sizes
Very temperature stable, great for high heat applications
Maximum working temperature 975° – 1020° F
Does not lend itself to conventional machining (hard and brittle)
High residual induction and energy product compared to ferrite magnet
Low coercive force compared to ferrite and neodymium magnet (more subject to demagnetization)
Key feature for Sintered alnico magnet
Pressed to close tolerance/minimal grinding to finish
Mechanically strongest of alnico
Very temperature stable, great for high heat applications
Maximum working temperature 975° – 1020° F
Does not lend itself to conventional machining (hard and brittle)
High residual induction and energy product compared to ferrite magnet
Low coercive force compared to ferrite and neodymium magnet (more subject to demagnetization)
|1966||18 MGOe ||Dr. Karl J. Strnat discovers the high energy product of the Samarium-Cobalt (SmCo5) compound.|
|1972||30 MGOe ||Dr. Karl J. Strnat and Dr. Alden Ray develop a higher energy product Samarium-Cobalt (Sm2Co17) compound.|
|1983||35 MGOe ||General Motors, Sumitomo Special Metals and the Chinese Academy of Sciences develop a high energy product Neodymium-Iron-Boron (Nd2Fe14B) compound.|
There many U.S. and international patents that are related to the development and manufacture of rare-earth magnetic products. Many patents related to Neodymium-Iron-Boron magnets are currently valid and enforced by their owners. Of particular importance are the patents held by Sumitomo Special Metals Co., Ltd., and Magnequench, Inc. These patents are based on the original intellectual property of General Motors, Sumitomo Special Metals and The Chinese Academy of Sciences that independently discovered the new permanent magnet material composed of neodymium, iron and boron.
Sumitomo and Magnequench have a cross-license agreement that covers the sale of Nd-Fe-B magnetic products in the United States. Only magnets produced under license to these companies are legally entitled for sale in the United States.
Many of the basic Rare-Earth-Iron-Boron patents will be expiring in the year 2003. The following table shows the expiration dates for the major composition patents:
|Company||Patent Composition|| Japan ||USA||Europe|
|SUMITOMO|| Basic RE-Fe-B Composition||2003||2003||2003|
| RE-Fe, Co-B Composition||2008||2003||2007|
| Nd, Dy-Fe, Co-B Composition ||2003||2010||2003|
| RE-Fe-B Compound||2003|| 2014 ||N/A|
| RE-Fe, Co-B Compound||2003||2014||N/A|
| MAGNEQUENCH || Basic RE-Fe-B Composition||2003||2006||2004|
| Including Co||2004||2012||N/A|
Source: Sumitomo Special Metals Co., Ltd.
There are hundreds of patents related to the development and production of rare-earth permanent magnets and related products. The following is a partial listing of some of the more notable U.S. patents. Each listing provides a link to the U.S. Patent and Trademark Office Internet Site:
Sep., 1976 Yamanaka et al. Rare earth-containing permanent magnets
Dec., 1977 Steingroever Method of making permanent magnets
Dec., 1977 Masumoto et al. Wear-resistant high-permeability alloy
Sep., 1980 Osumi et al. Alloy for occlusion of hydrogen
Sep., 1983 Koon. Hard magnetic alloys of a transition metal and lanthanide
Oct., 1983 Koon. Amorphous transition metal-lanthanide alloys
Jan., 1985 Croat High coercivity rare earth-iron magnets
Aug., 1985 Koon. Preparation of hard magnetic alloys of a transition metal and lanthanide
Jul., 1986 Matsuura et al. Process for producing permanent magnet materials
Jul., 1986 Yamamoto et al. Process for producing magnetic materials
May., 1987 Fruchart et al. Magnetic rare earth/iron/boron and rare earth/cobalt/boron hydrides, the process for their manufacture of the corresponding pulverulent dehydrogenated products
May., 1987 Mizoguchi et al. Permanent magnetic alloy and method of manufacturing the same
Aug., 1987 Matsuura et al. Permanent magnet materials
Aug., 1987 Itoh et al. Process of producing neodymium-iron alloy
Aug., 1987 Nate et al. Method for production of rare-earth element/cobalt type magnetic powder for resin magnet
Mar., 1988 Arai et al. Permanent-magnetic material
May., 1988 Ghandehari. Rare earth-iron-boron permanent magnets with enhanced coercivity
May., 1988 Itoh et al. Apparatus for producing neodymium-iron alloy
Aug., 1988 Mohri et al. Permanent magnent and method for producing same
Aug., 1988 Ishigaki et al. Process for producing the rare earth alloy powders
Aug., 1988 Jourdan Process for the preparation of pure alloys based on rare earths and transition metals by metallothermy
Sep., 1988 Ishigaki et al. Process for producing the rare earth alloy powders
Sep., 1988 Sagawa et al. Magnetic materials and permanent magnets
Dec., 1988 Lee. Iron-rare earth-boron permanent
Dec., 1988 Sagawa et al. Magnetic materials and permanent magnets
Jan., 1989 Inoue et al. Method for manufacturing permanent magnets
Feb., 1989 Croat High energy product rare earth-iron magnet alloys
Mar., 1989 Tokunaga et al. Permanent magnet having good thermal stability and method for manufacturing same
Jun., 1989 Yajima et al. Permanent magnet and method of producing same
Jun., 1989 Tokunaga et al. Method of producing neodymium-iron-boron permanent magnet
Jun., 1989 Maines et al. Anisotropic neodymium-iron-boron powder with high coercivity
Jul., 1989 Lee. Iron-rare earth-boron permanent magnets by hot working
Jul., 1989 Croat High energy product rare earth-iron magnet alloys
Aug., 1989 Mizoguchi et al. Permanent magnet
Sep., 1989 Nate et al. Rare-earth element/cobalt type magnet powder for resin magnets
Sep., 1989 Keem et al. Method of forming alloy particulates having controlled submicron crystallite size distributions
Oct., 1989 Heh et al. Process for producing rare earth-cobalt permanent magnet
Feb., 1990 Otsuka et al. Method for producing a rare earth metal-iron-boron permanent magnet by use of a rapidly-quenched alloy powder
Feb., 1990 Ma et al. Permanent magnet alloy for elevated temperature applications
May., 1990 Vernia et al. Permanent magnet manufacture from very low coercivity crystalline rare earth-transition metal-boron alloy
May., 1990 Tokunga et al. Magnetically anisotropic bond magnet, magnetic powder for the magnet and manufacturing method of the powder
Jun., 1990 DeMooij et al. Magnetic material comprising iron, boron and a rare earth metal
Jun., 1990 Mizoguchi et al. Permanent magnet
Aug., 1990 Tokunaga et al. Magnetically anisotropic bond magnet, magnetic powder for the magnet and manufacturing method of the powder
Nov., 1990 Ramesh et al. High energy product permanent magnet having improved intrinsic coercivity and method of making same
Dec., 1990 Fujimura et al. Permanent magnet
Dec., 1990 Matsuura et al. Permanent magnet materials
Dec., 1990 Sakai et al. Resin-bonded rare earth-iron-boron magnet
Jan., 1991 Takeshita et al. Rare earth-iron-boron magnet powder and process of producing same
Jan., 1991 Endoh et al. Anisotropic magnetic powder and magnet thereof and method of producing same
Feb., 1991 Willman et al. Method for producing permanent magnet alloy particles for use in producing bonded permanent magnets
Jun., 1991 Yajima et al. Permanent magnet
Jun., 1991 Young et al. Method of making self-aligning anisotropic powder for magnets
Aug., 1991 Brewer et al. Alloying low-level additives into hot-worked Nd-Fe-B magnets
Aug., 1991 Buschow et al. Hard magnetic material
Aug., 1991 Tokunaga et al. Permanent magnet having good thermal stability and method for manufacturing same
Sep., 1991 Mukai et al. Method of making rare earth magnets
Sep., 1991 Yajima et al. Permanent magnets
Oct., 1991 Croat High energy product rare earth-iron magnet alloys
Dec., 1991 Mizoguchi et al. Rare earth-iron-boron-based permanent magnet
Mar., 1992 Young et al. Hot pressed magnets in open air presses
Mar., 1992 Sagawa et al. Magnetic materials and permanent magnets
Mar., 1992 Yamashita et al. Method for manufacturing permanent magnets
May., 1992 Bogatin. Magnetic materials and process for producing the same
Aug., 1992 Fujiwara. Permanent magnet powders
Nov., 1992 Kim et al. Permanent magnet having improved corrosion resistance and method for producing the same
Nov., 1992 Tabaru et al. Rare earth permanent magnet, method of heat treatment of same, and magnet body
Dec., 1992 Yamashita et al. Process for producing a rare earth-iron-boron magnet
Dec., 1992 Croat. High energy product rare earth-iron magnet alloys
Dec., 1992 Croat. High-energy product rare earth-iron magnet alloys
Jan., 1993 Panchanathan Anisotropic neodymium-iron-boron powder with high coercivity and method for forming same
Feb., 1993 Kobayashi et al. Magnetic alloy and method of production
Mar., 1993 Sagawa et al. Magnetic materials
May., 1993 Yoneyama et al. Permanent magnet material and method for making
May., 1993 Akioka et al. Rare earth-iron system permanent magnet and process for producing the same
Jun., 1993 Endoh et al. Permanent magnet with good thermal stability
Jul., 1993 Nakayama et al. Rare earth permanent magnet power, method for producing same and bonded magnet
Jul., 1993 Endoh et al. Permanent magnet with good thermal stability
Oct., 1993 Nakayama et al. Rare earth element-Fe-B or rare earth element-Fe-Co-B permanent magnet powder excellent in magnetic and corrosion resistivity and bonded magnet manufactured therefrom
Jan., 1994 Hamamura et al. Powder material for rare earth-iron-boron based permanent magnets
May., 1994 Yoneyama et al. Permanent magnet material and method for making
Aug., 1994 Leveque et al. Recovery of neodymium/didymium values from bastnaesite ores
The discovery of the relationship between magnetism and electricity was, like so many other scientific discoveries, stumbled upon almost by accident. The Danish physicist Hans Christian Oersted was lecturing one day in 1820 on the possibility of electricity and magnetism being related to one another, and in the process demonstrated it conclusively by experiment in front of his whole class! By passing an electric current through a metal wire suspended above a magnetic compass, Oersted was able to produce a definite motion of the compass needle in response to the current. What began as conjecture at the start of the class session was confirmed as fact at the end. Needless to say, Oersted had to revise his lecture notes for future classes! His serendipitous discovery paved the way for a whole new branch of science: electromagnetics.
Detailed experiments showed that the magnetic field produced by an electric current is always oriented perpendicular to the direction of flow. A simple method of showing this relationship is called the left-hand rule. Simply stated, the left-hand rule says that the magnetic flux lines produced by a current-carrying wire will be oriented the same direction as the curled fingers of a person’s left hand (in the “hitchhiking” position), with the thumb pointing in the direction of electron flow:
The magnetic field encircles this straight piece of current-carrying wire, the magnetic flux lines having no definite “north” or “south’ poles.
While the magnetic field surrounding a current-carrying wire is indeed interesting, it is quite weak for common amounts of current, able to deflect a compass needle and not much more. To create a stronger magnetic field force (and consequently, more field flux) with the same amount of electric current, we can wrap the wire into a coil shape, where the circling magnetic fields around the wire will join to create a larger field with a definite magnetic (north and south) polarity:
The amount of magnetic field force generated by a coiled wire is proportional to the current through the wire multiplied by the number of “turns” or “wraps” of wire in the coil. This field force is called magnetomotive force (mmf), and is very much analogous to electromotive force (E) in an electric circuit.
An electromagnet is a piece of wire intended to generate a magnetic field with the passage of electric current through it. Though all current-carrying conductors produce magnetic fields, an electromagnet is usually constructed in such a way as to maximize the strength of the magnetic field it produces for a special purpose. Electromagnets find frequent application in research, industry, medical, and consumer products.
As an electrically-controllable magnet, electromagnets find application in a wide variety of “electromechanical” devices: machines that effect mechanical force or motion through electrical power. Perhaps the most obvious example of such a machine is the electric motor.
Another example is the relay, an electrically-controlled switch. If a switch contact mechanism is built so that it can be actuated (opened and closed) by the application of a magnetic field, and an electromagnet coil is placed in the near vicinity to produce that requisite field, it will be possible to open and close the switch by the application of a current through the coil. In effect, this gives us a device that enables elelctricity to control electricity:
Relays can be constructed to actuate multiple switch contacts, or operate them in “reverse” (energizing the coil will open the switch contact, and unpowering the coil will allow it to spring closed again).
When electrons flow through a conductor, a magnetic field will be produced around that conductor.
The left-hand rule states that the magnetic flux lines produced by a current-carrying wire will be oriented the same direction as the curled fingers of a person’s left hand (in the “hitchhiking” position), with the thumb pointing in the direction of electron flow.
The magnetic field force produced by a current-carrying wire can be greatly increased by shaping the wire into a coil instead of a straight line. If wound in a coil shape, the magnetic field will be oriented along the axis of the coil’s length.
The magnetic field force produced by an electromagnet (called the magnetomotive force, or mmf), is proportional to the product (multiplication) of the current through the electromagnet and the number of complete coil “turns” formed by the wire.
Permanent Magnet Magnetism is a phenomenon by which materials assert an attractive or repulsive force on other materials. Some well known materials that exhibit magnetic properties are iron, some steels, and the naturally occurring mineral lodestone. In reality all materials are influenced to one degree or another by the presence of a magnetic field, although in some cases the influence is too small to detect without special equipment.
Magnetic forces are fundamental forces that arise due to the movement of electrically charged particles. The origin and behavior of these forces are described by Maxwell’s equations.
For the case of electric current moving through a wire, the resulting force is directed according to the “right hand rule”. If the thumb of the right hand points along the wire from positive towards the negative side, the magnetic forces will wrap around the wire in the direction indicated by the fingers of the right hand. If a loop is formed, such that the charged particles are traveling in a circle then all of the forces in the center of the loop are directed in the same direction. The result is called a magnetic dipole. When placed in a magnetic field, a magnetic dipole will tend to align itself with that field. For the case of a loop, if the fingers of the right hand are directed in the direction of current flow, the thumb will point in the direction corresponding to the North pole of the dipole. In the earth’s magnetic field the North pole of the dipole will tend to point north.
Magnetic dipoles or magnetic moments can often result on the atomic scale due to the movements of electrons. Each electron has magnetic moments that originate from two sources. The first is the orbital motion of the electron around the nucleus. In a sense this motion can be considered as a current loop, resulting in a magnetic moment along its axis of rotation. The second source of electronic magnetic moment is due to a quantum mechanical property called spin.
In an atom the orbital magnetic moments of some electron pairs cancel each other. The same is true for the spin magnetic moments. The overall magnetic moment of the atom is thus the sum of all of the magnetic moments of the individual electrons, accounting for moment cancellation between properly paired electrons. For the case of a completely filled electron shell or subshell, the magnetic moments completely cancel each other out. Thus only atoms with partially filled electron shells have a magnetic moment. The magnetic properties of materials are in large part determined by the nature and magnitude of the atomic magnetic moments.
Several forms of magnetic behavior have been observed including:
Diamagnetism is a very weak form of magnetism that is only exhibited in the presence of an external magnetic field. It is the result of changes in the orbital motion of electrons due to the external magnetic field. The induced magnetic moment is very small and in a direction opposite to that of the applied field. When placed between the poles of a strong electromagnet, diamagnetic materials are attracted towards regions where the magnetic field is weak. Diamagnetism is found in all materials, however because it is so weak it can only be observed in materials that do not exhibit other forms of magnetism.
An exception to the “weak” nature of diamagnetism occurs with the rather large number of materials that become superconducting, something that usually happens at lowered temperatures. Superconductors are perfect diamagnets and when placed in an external magnetic field expel the field lines from their interiors (depending on field intensity and temperature). Superconductors also have zero electrical resistance, a consequence of their diamagnetism. Superconducting structures have been known to tear themselves apart with astonishing force in their attempt to escape an external field. Superconducting magnets are the major component of most MRI systems, perhaps the only important application of diamagnetism.
A thin slice of pyrolitic graphite, which is an unusually strongly diamagnetic material, can be stably floated on a magnetic field, such as that from rare earth permanent magnets. This can be done with all components at room temperature, making a visually effective demonstration of diamagnetism.
Paramagnetism refers to the tendency of the atomic magnetic dipoles in a material that is otherwise non-magnetic to align with an external magnetic field. The alignment of the atomic dipoles with the magnetic field tends to strengthen it, resulting in a relative magnetic permeability greater than one and a small positive magnetic susceptibility.
In paramagnetism the field acts on each atomic dipole independently and there are no interactions between individual atomic dipoles. Paramagnetic behavior can also be observed in magnetic materials that are above their Curie or Neel temperature.
Ferromagnetism is one of the strongest forms of magnetism. It is responsible for most of the magnetic behavior encountered in everyday life. Most permanent magnets are ferromagnetic, as are the metals that are attracted to them. Some examples of ferromagnetic materials include iron, cobalt, nickel, and gadolinium.
The strong magnetic forces in ferromagnetic materials arise due to a combination of the properties of the individual atoms and the properties of the crystal structure of the solid material. At the atomic level, magnetic forces arise due to the movements of electrons. Each electron has magnetic moments that originate from two sources. The first is the orbital motion of the electron around the nucleus. In a sense this motion can be considered as a current loop, which like a tiny electromagnet results in a magnetic moment along its axis of rotation. The second source of the electronic magnetic moment is due to a Quantum Mechanical property called “spin”, this property is in some ways analogous to the picture of an electron spinning about an axis and is related to the electron’s angular momentum. However, it should be remembered that the Quantum Mechanical “spin” is actually a unique phenomenon from spinning in a macroscopic sense, so the analogy doesn’t always hold. The spin magnetic moments may be in one of two directions, either the “up” direction or the “down” direction.
In an atom the orbital magnetic moments of electron pairs point in opposite directions canceling each other. The same is true for the spin magnetic moments. The overall magnetic moment of the atom is thus the sum of all of the magnetic moments of the individual electrons, accounting for moment cancellation between properly paired electrons. For the case of a completely filled electron shell or subshell, the magnetic moments completely cancel each other out. Thus only atoms with partially filled electron shells have a magnetic moment. All ferromagnetic materials have partially filled electron shells and thus posses an atomic magnetic moment.
Although atomic magnetic moments are present in both Paramagnetic and Ferromagnetic materials, magnetic forces are much stronger in ferromagnetic materials. This is not due to differences in the atomic magnetic moments, but due to the crystal structure of ferromagnetic materials. In a ferromagnet coupling interactions cause the magnetic moments of adjacent atoms to align with one another. This contrasts sharply with paramagnets, in which the magnetic moments are randomly distributed in many directions, essentially canceling each other out, except in the presence of a strong magnetic field. The alignment of the atomic magnetic moments in ferromagnetic materials results in a strong permanent internal magnetic field within the material. It is this strong internal magnetic field that causes iron or other ferromagnetic materials to be attracted by a magnet.
While coupling forces tend to cause adjacent moments to align, usually not all of the moments point in the same direction throughout the material. Instead the material consists of a number of regions called domains. Within each domain the atomic magnetic moments are aligned, however, the various domains may or may not be aligned with each other. For example, the domains in a metal paperclip are not usually aligned with each other. As a result the magnetic forces from the various domains cancel each other and two paper clips are not magnetically attracted to each other. However, if the material is placed within a magnetic field (for example if a permanent magnet is brought near a paperclip), the magnetic forces will cause some of the domains to align. This alignment will then result in a magnetic force drawing the material to the magnet and causing the material to behave as if it too were a magnet.
If the magnetic field is removed, the domains will often shift back to their original alignment and the material will no longer act as a magnet. However, if the material is subjected to a strong magnetic field for a sufficient length of time the domains will permanently align and the material will become a permanent magnet.
Superparamagnetism is a phenomena by which magnetic materials may exhibit a behavior similar to paramagnetism at temperatures below the Curie or the Neel temperature.
Normally, coupling forces in magnetic materials cause the magnetic moments of neighboring atoms to align, resulting in very large internal magnetic fields. At temperatures above the Curie temperature (or the Neel temperature for antiferromagnetic materials), the thermal energy is sufficient to overcome the coupling forces, causing the atomic magnetic moments to fluctuate randomly. Because there is no longer any magnetic order, the internal magnetic field no longer exists and the material exhibits paramagnetic behavior.
Superparamagnetism occurs when the material is composed of very small crystallites (1-10 nm). In this case even though the temperature is below the Curie or Neel temperature and the thermal energy is not sufficient to overcome the coupling forces between neighboring atoms, the thermal energy is sufficient to change the direction of magnetization of the entire crystallite. The resulting fluctuations in the direction of magnetization cause the magnetic field to average to zero. The material behaves in a manner similar to paramagnetism, except that instead of each individual atom being independently influenced by an external magnetic field, the magnetic moment of the entire crystallite tends to align with the magnetic field.
The energy required to change the direction of magnetization of a crystallite is called the Crystalline anisotropy energy and depends both on the material properties and the crystallite size. As the crystallite size decreases, so does the Crystalline anisotropy energy, resulting in a decrease in the temperature at which the material becomes superparamagnetic.
A non-magnetic discontinuity in a magnetic circuit (i.e. the distance between two magnetic poles), this gap often includes other materials such as brass, aluminium or paint.
A magnet which has a preferred direction of orientation so that the magnetic characteristics are optimum in one preferred direction.
This exists when the flux path external to the permanent magnet is confined within high permeability materials which contain the magnet circuit.
Coercive Force, Hc
The demagnetising force necessary to reduce observed induction B to zero after the magnet has been brought to saturation. Coercive force is measured in Oersteds or more recently A/m and kA/m.
Curie Temperature, Tc
The temperature at which a material loses its permanent magnetic properties completely and is no longer able to hold magnetism.
The second/left quadrant of the hysteresis loop, generally describing the behaviour of magnetic characteristics in actual use. Also known as the B-H curve.
A material whose permeability is very much larger than one, and which exhibits hysteresis magnetising and demagnetising characteristics. The greater the flux carrying potential, the bigger the value i.e. one to several thousands.
Magnetic flux is the condition existing in a medium subjected to a magnetising force. This value is quantified by E.M.F. (electromotive force). This measurement of force in cgs units is a Maxwell.
Leakage flux particularly associated with edge effects and leakage patterns in a magnetic circuit.
Lines of magnetic flux per square centimetre. Gauss is measured in cgs units, Maxwell lines and Webers per square metre or Tesla in the Si system.
A closed curve calculated by plotting corresponding values of magnetic induction: B on the abscissa against magnetising force H.
This is the magnetic flux per unit area of section in the applied magnetic direction of flux. This is measured in Gauss.
Intrinsic Coercive Force
This is a measure of the resistance of the magnet material to a demagnetising force. Permanent magnets with high intrinsic coercivity values are usually classified as ‘hard’ permanent magnets. Intrinsic coercive force indicates magnetic stability at high temperatures. Also see stabilisation.
This is the partial demagnetisation of a magnet material when introduced to external factors such as high/low temperatures and demagnetising fields. Losses can only by rectified by remagnetisation. However, magnets can be stabilised to prevent the variation of performance caused by irreversible losses.
A magnetic material which does not have a preferred direction of magnetic orientation and therefore can be magnetised in any direction without the loss of magnetic characteristics.
Knee of the Demagnetisation Curve
The point at which the B-H curve ceases to be linear. If the operating point of the magnet falls below the knee, the magnet will not be able to recover full magnetic potential without the application of a magnetising force.
This is the loss of magnetic flux which occurs through leakage caused by saturation or air gaps introduced into the magnetic circuit. This induces a loss of efficiency in the circuit which cannot be recovered.
Length of Air Gap, Lg
Indicates the length of the central flux path across an air gap.
A line drawn from the origin of the Demagnetisation Curve with a slope. The intersection of the -B/H curve and slope represents the operating point of the magnet. Also see Permeance Coefficient, Pc.
An assembly consisting of some or all of the following: permanent magnets, ferromagnetic conduction elements, air gaps, electrical currents.
The total magnetic induction over a given area.
Magnetising Force, H
The magnetomotive force per unit length at any point in a magnetic circuit. This is measured in Oersteds.
Magnetomotive Force, F
This is the potential magnetic difference between any two points.
Maximum Energy Product, BH max.
There is a point at the Hysteresis Loop at which the product of magnetising force H and induction B reaches a maximum. This maximum value is called the Maximum Energy Product and is measured in Mega Gauss Oersted, MGOe.
A unit measure of magnetising force (cgs). This is equivalent to Ampere Turns per Inch (S.I.).
Permeance Coefficient, Pc
Ratio of the magnetic induction to self demagnetising force. This is also known as the ‘load line’ or operating point of the magnet.
Usually illustrated in graph format, these curves are a representation of the relationship between the attractive force exerted by a magnet on a soft magnetic workpiece and the distance between them. Pull Gap curve diagrams are useful when selecting a magnet for a particular tractive or holding application.
Reluctance is the resistance in a magnetic circuit and is related to the magnetomotive force, F and magnetic flux (R =F/ magnetic flux) where F is the magnetomotive force.
Remenance is the magnetic induction which remains in a magnetic circuit after the removal of an applied magnetising force. If there is an air gap in the circuit, the remenance will be less than the residual induction Br.
Residual Induction Br
This represents the maximum flux output from a given magnet material measured at the point where the Hysteresis Loop crosses the B axis at zero magnetising force.
A magnetic circuit which provides a low reluctance path for the magnetic flux. Reversible Temperature Coefficient A measure of the reversible changes in flux caused by temperature variations.
This is the condition whereby a magnet or ferromagnetic material has reached a maximum value and an increase in the appliance of magnetising force produces no increase in induction i.e. saturation flux densities for steels range from 16,000 to 20,000 Gauss.
The process where a magnet is exposed to demagnetising influences expected to be encountered in operation. The exposure to these demagnetising influences such as high or low temperatures or external magnetic fields prevents irreversible losses during actual operation.
Neodymium is the strongest available rare earth magnet alloy at up to 52MGOe.
Samarium Cobalt rare earth magnets are often used in high temperature applications.
Some of the differences between neodymium rare earth magnets and samarium cobalt rare earth magnets include:
Neodymium iron boron rare earth magnets are highly reactive to environmental conditions, whereas samarium cobalt rare earth magnets are very corrosion resistant.
Samarium cobalt rare earth magnets will withstand high temperatures without demagnetizing, while care must be used when utilizing neodymium above ambient room temperatures.
Neodymium iron boron rare earth magnets are moderately priced and offer a good value when compared to performance. Samarium cobalt magnets are considerably more expensive due to their cobalt content.
Neodymium iron boron rare earth magnets are less brittle than samarium cobalt rare earth magnets and are easier to machine and integrate into magnetic assemblies. Both alloys require diamond tooling, EDM, or abrasive grinding when machining.
More information about neodymium rare earth magnets and samarium cobalt rare earth magnets can be found within each material-specific section of this website.
Matreial Content Research, Reduce the Heavy Rare Earth Material.
Magnetic steel- material, finish machining, electroplating technology
Through continuous sintering, cast strip temperature-control, grain refinement, Dy spreading and so forth, the products are improved in property.
The vacuum continuous sintering furnace, vacuum slice furnace, hydrogen crushed furnace and other advanced equipment are close to the control standard of technological parameter in Japan.
The induction eddy current heat treatment could strengthen the coercivity by 1~2kOe on the basis of tempering magnet. It has no impact to residual magnetism and square degree, and meanwhile it is applicable to the magnet with various kinds of marks.
The magnetic steel technology is standardized in requirement, and the detecting technique is breaking through.
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The magnetic moment detector researched and developed by ourselves could realize 100% automatic complete inspection, reduce personal error, and sort out the qualified and overproof products. The fluctuation of single batch could be controlled at +/-1%. Zero-defect is realized before shipment.
Suitable for precisely detecting multipole magnetization and single magnetic steel; also could realize the waveform detection of surface magnetic field to the rotor posted with magnetic steel. The accuracy doubles than that of manual gauss meter.
State of the art Matsy automatic magnetic declination detecting instrument from Germany, could realize 100% complete detection and zero defect before shipment.
Computes PC value, selects or customizes optimal mark in accordance with customers’ specification and operating temperature, assists customers in reducing cost.
Could conduct analysis to the detection data ahead of controlling molding and sintering stage. Could control the homogeneity of the magnetic steel and N/S-pole fluctuation according to customers’ assembly characteristics, such as sensor and analogue simulation.
Suitable for detecting multi-pole magnetization and single magnetic steel precisely; also could realize the waveform detection of surface magnetic field to the rotor posted with magnetic steel. The accuracy doubles than that of manual gauss meter.
The magnetic steel is well in cleanliness and fine in viscosity. The gluing and assembly process are automated.
Relevance between motor parameters and magnetic steel.
Our company LECMAG possesses professional engineer team to research the relevance between motor parameter and magnetic steel.
The basis for choosing the correct magnet
In addition to conducting measurements and tests, over the years we have invested in software for magnetic calculations based on the ‘Finite Elements Method (FEM)’. This ensures that we can develop the right magnet faster and better, for a new or existing product. This saves valuable time during the development process and ensures the proper operation of your product. These magnets are used in various devices, such as:
control units for navigation;
control buttons for household appliances, such as ovens and microwaves;
high-tech applications, such as linear drives for position determination at high speed;
magnet systems, such as magnetic grippers for handling sheet metal, magnetic filters in the food industry or metal recycling machines.
Magnetic performance can be efficiently optimized with magnet calculations. The high prices of magnetic material such as neodymium make it all the more important to optimize use of the magnets.
This allows us to accurately predict how the magnet will behave in terms of:
depth of the magnetic field;
peaks and valleys in the magnetic field over a surface;
maximum power of the magnet on another (ferromagnetic) object;
‘residual magnetism’ present when on and off (for switchable magnets);
separation of particles from a product flow (e.g. powder or chocolate flow).
With our years of experience we are able to accurately predict the effects of many previously uncertain factors in the simulations and thus optimize our products.
Knowledge is power
Once we have a clear definition of the customer’s problem, our experts can get started, on the basis of a pre-agreed step-by-step plan. They use specially developed software to determine which magnet will enable your sensor, drive or product to function as desired. Moreover, we can simulate and theoretically underpin the solution, and validate the performance, based on magnet measurements. These measurements plus the quality controls we perform provide you with the assurance that you will receive a product that meets the required specifications. In addition to ISO 9001, LECMAG is also an ISO/TS 16949- and AS9100c-certified company, so our magnets meet the strict requirements of the automotive and aerospace industries.
To ensure the magnet functions over a certain distance, just knowing the flux density is not enough. The magnetic performance depends on additional factors, such as:
how it is mounted (horizontally or vertically);
thickness of the steel present (ferromagnetic object);
presence of magnetic materials in the surrounding area that affect the magnetic field;
distance from the magnet to a ferromagnetic object;
the speed and viscosity of a product flow that contains the particles to be separated.
Magnetic calculations are a class apart in the world of finite element calculations. LECMAG has the right software, highly trained personnel and a huge wealth of experience. Therefore we can say with confidence that you can entrust us with any magnet-related engineering question.
Why magnet inspections?
Particularly in the food industry, magnet measurements and/or the validation or inspection of magnets is a requirement. Why?
To ensure the quality of the finished product.
For compliance with HACCP, the international food safety standard.
To keep up to date with ever-improving techniques for optimal separation/filtering of metal contaminants.
Does a magnet lose strength over time?
In principle, permanent magnets retain their strength for a lifetime, but there are a few things that could cause permanent degradation of the magnetic strength:
Heat: Sensitivity varies based on magnet quality; some types of neodymium magnet begin to lose strength at temperatures above 60 °C. The magnetic strength drops to zero once the Curie temperature is reached. The maximum temperature to which the magnetic strength is guaranteed is always listed in our product specifications. Ferrite is the only material that also weakens at low temperatures (below 40 °C).
Impact: An impact load can alter the structure and direction of the magnetic spins .
Contact with external magnetic fields.
Corrosion: The magnet can corrode after damage to the magnet or magnetic coating or when directly exposed to damp air. For this reason the magnets are often built-in and/or protected.
When overloaded, electromagnets can overheat, possibly resulting in corrosion of the coils. This, too, will cause degradation of the magnetic force.
What can you expect?
We check your magnets in the process line annually. In addition to measuring and inspecting the magnetic field strength, we also provide recommendations for process improvements. We document the measurements in an inspection certificate that can be used for audits.
How are the measurements performed?
Our technicians know exactly how and where they must measure, and perform the measurements on-site with a calibrated gauss meter. They take care to interrupt your processes as little as possible and carefully analyse all the installed magnet systems. For LEC magnets, we then compare the measurements with the original values. If the magnet is from another supplier, we compare the measured magnetic strength with that of a similar magnetic separator.
Be sure to also read the blog from our experts.
What does the inspection certificate show?
The inspection certificate includes the description and location of the measured magnetic separator. The flux density is shown as the measured value, the original value and a minimum value. The minimum flux density is of great importance. After all, the effectiveness of your system depends not on the highest but the lowest value. We compare the data with those from past measurements.
We also provide a report in which we include any recommendations we may have for process optimization. This report contains our evaluation of aspects such as the following:
Is the magnet placed at the correct (i.e. most effective) location in the process line?
Does the magnet meet the standard (overall minimum flux density)?
What is the physical condition of the magnet system?
Are there signs of wear?
Is there a risk of obstruction of the product flow or machine damage?
Is the magnet safely accessible for cleaning?
Is the deferrization rate (i.e. iron separation) optimal?
Is the magnet strong enough?
Is the magnet being cleaned correctly and often enough?
The answers to these practical questions provide insight into the current quality of both the product and the process and can help you improve the process.
Do you have questions or would you like to make an appointment? You can request a magnet inspection via our contact form.