- Background and History
- Design
- Magnet Selection
- Surface Treatment
- Magnetizing
- Dimension Range, Size and tolerance
- Safety principle for manual operation
1. Background and History
Permanent magnets are a vital part of modern life. They are found
in or used to produce almost every modern convenience today. The
first permanent magnets were produced from naturally occurring rocks
called lodestones. These stones were first studied over 2500 years
ago by the Chinese and subsequently by the Greeks, who obtained
the stone from the province of Magnetes, from which the material
got its name. Since then, the properties of magnetic materials have
been profoundly improved and today?s permanent magnet materials
are many hundreds of times stronger than the magnets of antiquity.
The term permanent magnet comes from the ability of the magnet to
hold an induced magnetic charge after it is removed from the magnetizing
device. Such devices may be other strongly magnetized permanent
magnets, electro-magnets or coils of wire that are briefly charged
with electricity. Their ability to hold a magnetic charge makes
them useful for holding objects in place, converting electricity
to motive power and vice versa (motors and generators), or affecting
other objects brought near them.
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2. Design
Superior magnetic performance is a function of better magnetic
engineering. For customers who require design assistance or complex
circuit designs, AMOEBA's team of experienced application
engineers and knowledgeable field sales engineers is at your service.
AMOEBA engineers work with customers to improve or
validate existing designs as well as develop novel designs that
produce special magnetic effects. AMOEBA has developed
patented magnetic designs that deliver extremely strong, uniform
or specially shaped magnetic fields that often replace bulky and
inefficient electro-magnet and permanent magnet designs. Customers
are confident when hey bring a complex concept or new idea that
AMOEBA will meet that challenge by drawing from 10
years of proven magnetic expertise. AMOEBA has the
people, products and technology that put magnets to work.
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3. Magnet Selection
Magnet selection for all applications must consider the entire
magnetic circuit and the environment. Where Alnico is appropriate,
magnet size can be minimized if it can be magnetizing after assembly
into the magnetic circuit. If used independent of other circuit
components, as in security applications, the effective length to
diameter ratio (related to the permeance coefficient) must be great
enough to cause the magnet to work above the knee in its second
quadrant demagnetization curve. For critical applications, Alnico
magnets may be calibrated to an established reference flux density
value.
A by-product of low coercivity is sensitivity to demagnetizing effects
due to external magnetic fields, shock, and application temperatures.
For critical applications, Alnico magnets can be temperature stabilized
to minimize these effects
There are four classes of modern commercialized magnets, each based
on their material composition. Within each class is a family of
grades with their own magnetic properties. These general classes
are:
Neodymium Iron Boron
Samarium Cobalt
Ceramic
Alnico
NdFeB and SmCo are collectively known as Rare Earth magnets because
they are both composed of materials from the Rare Earth group of
elements. Neodymium Iron Boron (general composition Nd2Fe14B, often
abbreviated to NdFeB) is the most recent commercial addition to
the family of modern magnet materials. At room temperatures, NdFeB
magnets exhibit the highest properties of all magnet materials.
Samarium Cobalt is manufactured in two compositions: Sm1Co5 and
Sm2Co17 - often referred to as the SmCo 1:5 or SmCo 2:17 types.
2:17 types, with higher Hci values, offer greater inherent stability
than the 1:5 types. Ceramic, also known as Ferrite, magnets (general
composition BaFe2O3 or SrFe2O3) have been commercialized since the
1950s and continue to be extensively used today due to their low
cost. A special form of Ceramic magnet is "Flexible" material,
made by bonding Ceramic powder in a flexible binder. Alnico magnets
(general composition Al-Ni-Co) were commercialized in the 1930s
and are still extensively used today.
These materials span a range of properties that accommodate a wide
variety of application requirements. The following is intended to
give a broad but practical overview of factors that must be considered
in selecting the proper material, grade, shape, and size of magnet
for a specific application. The chart below shows typical values
of the key characteristics for selected grades of various materials
for comparison. These values will be discussed in detail in the
following sections.
| Magnet Material Comparisons |
| Material
|
Grade |
Br |
Hc |
Hci |
BH max |
T max (Deg C)*
|
| NdFeB |
39H |
12,800 |
12,300 |
21,000 |
40 |
150 |
| SmCo |
26 |
10,500 |
9,200 |
10,000 |
26 |
300 |
| NdFeB |
B10N |
6,800 |
5,780 |
10,300 |
10 |
150 |
| Alnico |
5 |
12,500 |
640 |
640 |
5.5 |
540 |
| Ceramic
|
8 |
3,900 |
3,200 |
3,250 |
3.5 |
300 |
| Flexible
|
1 |
1,600 |
1,370 |
1,380 |
0.6 |
100 |
| * T max (maximum
practical operating temperature) is for reference
only. The maximum practical operating temperature of any magnet
is dependent on the circuit the magnet is operating in. |
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4. Surface Treatment
Magnets may need to be coated depending on the application for
which they are intended. Coating magnets improves appearance, corrosion
resistance, protection from wear and may be appropriate for applications
in clean room conditions.
Samarium Cobalt, Alnico materials are corrosion resistant, and
do not require to be coated against corrosion. Alnico is easily
plated for cosmetic qualities.
NdFeB magnets are particularly susceptible to corrosion and are
often protected in this way. There are a variety of coatings suitable
for permanent magnets, Not all types of coating will be suitable
for every material or magnet geometry, and the final choice will
depend on the application and environment. An additional option
is to house the magnet in an external casing to prevent corrosion
and damage.
| Available
Coatings:
|
| Su rface
|
Coating |
Thickness (Microns)
|
Color |
Resistance |
| Passivation
|
|
1 |
Silver Grey |
Temporary Protection
|
| Nickel |
Ni+Ni
|
10-20 |
Bright Silver |
Excellent
against Humidity
|
| Ni+Cu+Ni
|
| Zinc |
Zn |
8-20 |
Bright Blue |
Good Against
Salt Spray
|
| C-Zn |
Shinny Color |
Excellent
Against Salt Spray
|
| Tin |
Ni+Cu+Sn |
15-20 |
Silver |
Superior Against
Humidity
|
| Gold |
Ni+Cu+Au |
10-20 |
Gold |
Superior Against
Humidity
|
| Copper |
Ni+Cu |
10-20 |
Gold |
Temporary Protection
|
| Epoxy |
Epoxy |
15-25 |
Black, Red,
Grey |
Excellent
Against Humidity
& Salt Spray |
| Ni+Cu+Epoxy
|
| Zn+Epoxy
|
| Chemical |
Ni |
10-20 |
Silver Grey |
Excellent Against
Humidity
|
| Parylene |
Parylene |
5-20 |
Grey |
Excellent Against
Humidity, Salt Spray. Superior Against Solvents, Gases, Fungi and Bacteria.
FDA Approved. |
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5. Magnetizing
Permanent magnet supplied under two conditions, Magnetized or no
magnetized, is usually not marked its polarity. If the user require,
we could mark the polarity by the means agreed on. When placing
the order, the user should inform the supply condition and if the mark
of the polarity is necessary.
The magnetization field of permanent magnet is related to the permanent
magnetic material type and its intrinsic coercive force. If the
magnet need magnetization and demagnetization, please contact with
us and ask for technique support.
There are two methods to magnetize the magnet: DC field and pulse
magnetic field.
There are three methods to demagnetize the magnet: demagnetization
by heat is a special process technique. demagnetization in AC field.
Demagnetization in DC field. This asks for very strong magnetic
field and high demagnetization skill.
Geometry shape and magnetization direction of permanent magnet:
in principle, we produce permanent magnet in various shapes. Usually,
it includes block, disc, ring, segment etc. The detailed illustration
of the magnetization direction is below:
| Directions of Magnetization
(Diagrams Indicating Typical Directions Of Manetization) |
|
| |
| oriented through thickness |
axially oriented |
axially oriented in segments |
| oriented laterally
multipole on one face |
multipole oriented in segments
on outside diameter* |
multipole oriented in segments
on one face |
| radially oriented * |
oriented through
diameter * |
multipole oriented in segments on inside diameter* |
|  |
 |
all available as isotropic or anisotropic material |
| * only available in isotropic and certain anisotropic materials
only |
| radially oriented |
diametrical oriented |
|
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6.
Dimension Range, Size and tolerance
Except for the dimension in the direction of magnetization, the
maximum dimension of the permanent magnet is not exceed 50mm, which
is limited by the orientation field and sintering equipment. The
dimension in the unmagnetization direction is up to 100mm.
The tolerance is usually +/-0.02 --+/-0.05 -- +/-0.10mm.
| Ring |
Outer Diameter |
Inner Diameter |
Thickness |
| Maximum |
250.00mm |
150.00mm |
100.00mm |
| Minimum |
0.5mm |
0.2mm |
0.2mm |
| |
|
|
|
| Disc |
Diameter |
Thickness |
|
| Maximum |
250.00mm |
100.00mm |
|
| Minimum |
0.5mm |
0.2mm |
|
| |
|
|
|
| Block |
Length |
Width |
Thickness |
| Maximum |
250.00mm |
200.00mm |
100.00mm |
| Minimum |
0.5mm |
0.2mm |
0.2mm |
| |
|
|
|
| Arc-segment |
Outer Radius |
Inner Radius |
Thickness |
Degree |
| Maximum |
250mm |
200mm |
100mm |
179 |
| Minimum |
0.5mm |
0.5mm |
0.2mm |
1 |
Remark: Other shapes can be manufactured according
to customer's sample or blue print
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7. Safety principle for manual
operation
1. The magnetized permanent magnets with strong magnetic field
attract the iron and other magnetic matters around them greatly.
Under common condition, the manual operator should be very careful
to avoid any damage. Due to the strong magnetic force, the big magnet
close to them takes the risk of damage. People always process these
magnets separately or by clamps. In this case, we should ware the
protection gloves in operation.
2. In this circumstance of strong magnetic field, any sensible
electronic component and test meter may be altered or damaged. Please
see to it that the computer, display and magnetic media , for example
the magnetic disc ,magnetic cassette tape and video record tape
etc., are far from the magnetized components, say farther than 2m.
3. The collision of the attracting forces between two permanent
magnets will bring enormous sparkles. Therefore, the flammable or
explosive matters should not be placed around them.
4. When the magnet is exposed to hydrogen, it is prohibited to
use permanent magnets without protection coating. The reason is
that the sorption of hydrogen will destroy the microstructure of
the magnet and lead to the deconstruction of the magnetic properties.
The only way to protect the magnet effectively is to enclose the
magnet in a case and seal it.
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