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Dailymag
Magnetics offer a full
line of Permanent Magnets,
Magnetic Assemblies (Magnetic
Tools) and Magnetic
equipments in China.
Dailymag
International (Ningbo) Limited manufactures ndfeb
magnet, strong
magnets, permanent
magnets (Sintered NdFeB magnet, SmCo magnet, Ferrite
Magnet, AlNiCo Magnet, Flexible Rubber Magnet) and all
these magnets can be used in industry field. In the area of Permanent
Magnets, neodymium
magnet belong to rare earth magnet. It is
the third
generation of rare-earth permanent magnet, is the most powerful and
advanced commercialized permanent
magnet today. The less strength
magnet is ceramic magnet and low cost but be widely
use, so it is one of our important magnets to export. Please
contact us for further
cooperation.
Glossary of
Magnetic Terms
Air Gap:
A low permeability gap in the flux path of a
magnetic circuit. Often air, but inclusive of other
materials such as paint, aluminum, etc.
Anisotropic Magnet:
A magnet having a preferred direction of magnetic
orientation, so that the magnetic characteristics
are optimum in one preferred direction.
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Closed Circuit:
This exists when the flux path external to a
permanent magnet is confined within high
permeability materials that compose the magnet
circuit.
Coercive
Force, Hc:
The demagnetizing force, measured in Oersteds,
necessary to reduce observed induction, B, to zero
after the magnet has previously been brought to
saturation.
Curie Temperature, Tc:
The temperature at which the parallel alignment
of elementary magnetic moments completely
disappears, and the material is no longer able to
hold magnetization.
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Demagnetization Curve:
The second quadrant of the hysteresis loop,
generally describing the behavior of magnetic
characteristics in actual use. Also known as the B-H
Curve.
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Eddy Currents:
Circulating electrical currents that are induced
in electrically conductive elements when exposed to
changing magnetic fields, creating an opposing force
to the magnetic flux. Eddy currents can be harnessed
to perform useful work (such as damping of
movement), or may be unwanted consequences of
certain designs, which should be accounted for or
minimized.
Electromagnet:
A magnet, consisting of a solenoid with an iron
core, which has a magnetic field existing only
during the time of current flow through the coil.
Energy
Product: Indicates the energy that a magnetic material
can supply to an external magnetic circuit when
operating at any point on its demagnetization curve.
Calculated as Bd x Hd, and
measured in Mega Gauss Oersteds, MGOe.
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Ferromagnetic Material:
A material whose permeability is very much
larger than 1 (from 60 to several thousand times 1),
and which exhibits hysteresis phenomena.
Flux:
The condition existing in a medium subjected to
a magnetizing force. This quantity is characterized
by the fact that an electromotive force is induced
in a conductor surrounding the flux at any time the
flux changes in magnitude. The cgs unit of flux is
the Maxwell.
Fluxmeter:
An instrument that measures the change of flux
linkage with a search coil.
Fringing
Fields: Leakage
flux particularly associated with edge effects in a
magnetic circuit.
Gauss:
Lines of magnetic flux per square centimeter,
cgs unit of flux density, equivalent to lines per
square inch in the English system, and Webers per
square meter or Tesla in the SI system.
Gaussmeter:
An instrument that measures the instantaneous value
of magnetic induction, B. Its principle of operation
is usually based on one of the following: the Hall
effect, nuclear magnetic resonance (NMR), or the
rotating coil principle.
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Hysteresis Loop:
A closed curve obtained for a material by plotting
corresponding values of magnetic induction, B, (on
the abscissa) against magnetizing force, H, (on the
ordinate).
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Induction, B:
The magnetic flux per unit area of a section
normal to the direction of flux. Measured in Gauss,
in the cgs system of units.
Intrinsic
Coercive Force, Hci:
Measured in Oersteds in the cgs system, this is a
measure of the material's inherent ability to resist
demagnetization. It is the demagnetization force
corresponding to zero intrinsic induction in the
magnetic material after saturation. Practical
consequences of high Hci values are seen in greater
temperature stability for a given class of material,
and greater stability in dynamic operating
conditions.
Intrinsic
Induction, Bi:
The contribution of the magnetic material to the
total magnetic induction, B. It is the vector
difference between the magnetic induction in the
material and the magnetic induction that would exist
in a vacuum under the same field strength, H. This
relationship is expressed as: BI = B-H.
Irreversible Loss:
Defined as the partial demagnetization of a magnet
caused by external fields or other factors. These
losses are only recoverable by re-magnetization.
Magnets can be stabilized to prevent the variation
of performance caused by irreversible losses.
Isotropic
Magnet:
A magnet material whose magnetic properties are
the same in any direction, and which can therefore
be magnetized in any direction without loss of
magnetic characteristics.
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Keeper:
A piece of soft iron that is placed on or
between the poles of a magnet, decreasing the
reluctance of the air gap and thereby reducing the
flux leakage from the magnet.
Knee of
the Demagnetization Curve:
The point at which the B-H curve ceases to be
linear. All magnet materials, even if their second
quadrant curves are straight line at room
temperature, develop a knee at some temperature.
Alnico 5 exhibits a knee at room temperature. If the
operating point of a magnet falls below the knee,
small changes in H produce large changes in B, and
the magnet will not be able to recover its original
flux output without re-magnetization.
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Leakage Flux:
That portion of the magnetic flux that is lost
through leakage in the magnetic circuit due to
saturation or air-gaps, and is therefore unable to
be used.
Length of
air-gap, Lg:
The length of the path of the central flux line
in the air-gap.
Load Line:
A line drawn from the origin of the
Demagnetization Curve with a slope of -B/H, the
intersection of which with the B-H curve represents
the operating point of the magnet. Also see
Permeance Coefficient.
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Magnetic Circuit:
An assembly consisting of some or all of the
following: permanent magnets, ferromagnetic
conduction elements, air gaps, electrical currents.
Magnetic
Flux: The total
magnetic induction over a given area. When the
magnetic induction, B, is uniformly distributed over
an area A, Magnetic Flux = BA.
Magnetizing Force, H:
The magnetomotive force per unit length at any
point in a magnetic circuit. Measured in Oersteds in
the cgs system.
Magnetomotive Force, F:
Analogous to voltage in electrical circuits, this is
the magnetic potential difference between any two
points.
Maximum
Energy Product, BHmax:
The point on the Demagnetization Curve where the
product of B and H is a maximum and the required
volume of magnet material required to project a
given energy into its surroundings is a minimum.
Measured in Mega Gauss Oersteds, MGOe.
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North Pole:
That pole of a magnet which, when freely
suspended, would point to the north magnetic pole of
the earth. The definition of polarity can be a
confusing issue, and it is often best to clarify by
using "north seeking pole" instead of "north pole"
in specifications.
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Oersted, Oe:
A cgs unit of measure used to describe magnetizing
force. The English system equivalent is Ampere Turns
per Inch, and the SI system's is Ampere Turns per
Meter.
Orientation Direction:
The direction in which an anisotropic magnet
should be magnetized in order to achieve optimum
magnetic properties. Also known as the "axis", "easy
axis", or "angle of inclination".
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Paramagnetic Material:
A material having a permeability slightly
greater than 1.
Permeance:
The inverse of reluctance, analogous to
conductance in electrical circuits.
Permeance
Coefficient,Pc:
Ratio of the magnetic induction, BD, to its self
demagnetizing force, HD PC = BD / HD This is also
known as the "load line", "slope of the operating
line", or operating point of the magnet, and is
useful in estimating the flux output of the magnet
in various conditions. As a first order
approximation, BD / HD = Lm/Lg, where Lm is the
length of the magnet, and Lg is the length of an air
gap that the magnet is subjected to. PC is therefore
a function of the geometry of the magnetic
circuit.
Pole
Pieces:
Ferromagnetic materials placed on magnetic poles
used to shape and alter the effect of lines of flux.
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Relative Permeability:
The ratio of permeability of a medium to that of a
vacuum. In the cgs system, the
permeability is equal to 1 in a vacuum by
definition. The permeability of air is also for all
practical purposes equal to 1 in the cgs system.
Reluctance, R:
Analogous to resistance in an electrical circuit,
reluctance is related to the magnetomotive force, F,
and the magnetic flux by the equation R =
F/(Magnetic Flux), paralleling Ohm's Law where F is
the magnetomotive force (in cgs units).
Remanence,
BD: The
magnetic induction that remains in a magnetic
circuit after the removal of an applied magnetizing
force. If there is an air gap in the circuit, the
remanence will be less than the residual induction,
Br.
Residual
Induction, Br:
This is the point at which the hysteresis loop
crosses the B axis at zero magnetizing force, and
represents the maximum flux output from the given
magnet material. By definition, this point occurs at
zero air gap, and therefore cannot be seen in
practical use of magnet materials.
Return
Path:
Conduction elements in a magnetic circuit which
provide a low reluctance path for the magnetic flux.
Reversible
Temperature Coefficient:
A measure of the reversible changes in flux caused
by temperature variations.
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Saturation:
The condition under which all elementary
magnetic moments have become oriented in one
direction. A ferromagnetic material is saturated
when an increase in the applied magnetizing force
produces no increase in induction. Saturation flux
densities for steels are in the range of 16,000 to
20,000 Gauss.
Search
Coil: A coil
conductor, usually of known area and number of turns
that is used with a fluxmeter to measure the change
of flux linkage with the coil.
Stabilization:
Exposure of a magnet to demagnetizing influences
expected to be encountered in use in order to
prevent irreversible losses during actual operation.
Demagnetizing influences can be caused by high or
low temperatures, or by external magnetic fields.
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Temperature Coefficient:
A factor, which describes the change in a
magnetic property with change in temperature.
Expressed as percent change per unit of temperature.
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Weber:
The practical unit of magnetic flux. It is the
amount of magnetic flux which, when linked at a
uniform rate with a single-turn electric circuit
during an interval of 1 second, will induce in this
circuit an electromotive force of 1 volt.
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