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> MAGNETIC THEORY |
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MAGNETIC
THEORY
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There are 5 main types of magnetic materials as follows
1 - Alnico
2 - Ferrite
3 - Neodymium Iron Boron
4 - Samarium Cobalt
5 - Magnetic rubber
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Within each type of material, there are many grades and variations to provide a variety of different magnetic properties.
The following details are simplified to give someone with minimal magnet knowledge, an insight into the typical properties of each material....
© Copyright e-magnets UK 2004 |
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| 1 - Alnico |
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Alnico is usually manufactured in a foundry by a casting process, patterns are needed and these can be expensive.
Alnico can also be sintered to form small, intricate and accurate shapes.
The Alloy consists mainly of Aluminium, Nickel, Cobalt and Iron.
Strengths - High temperature ability, high corrosion resistance, good magnetic stability.
Weaknesses - Poor resistance to demagnetisation, high cost
The most common grade is Alnico 5 and it has the following properties |
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| Br (Gauss) |
12,500 |
(The amount of magnetism) |
| Hc (Oersteds) |
640 |
(It's resistance to demagnetisation) |
| BH max (MGOe) |
5.5 |
(Derived from the above two) |
| Density (gm/cm3) |
7.3 |
weight in grams per cm3 |
| Max operating temp |
540 |
(Degrees C) |
| Temp. coefficient |
-0.02 |
loses 0.02% of its Br value per degree C rise in temperature |
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| 2 - Ferrite |
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Ferrite is manufactured using powder sintering technology and is sintered using special tooling into standard disc, rings and block shapes.
These can then be cut into smaller magnets or ground to tight tolerances using diamond cutting tools.
Ferrites are the most cost effective of all magnets and are used extensively in loudspeakers and security systems.
Strengths - Medium temperature ability, high corrosion resistance, good magnetic stability, inexpensive.
Weaknesses - Low magnetic flux density means that magnets have to be relatively big to be effective
The most common grade is Ferrite 8 and it has the following properties |
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| Br (Gauss) |
3,900 |
(The amount of magnetism) |
| Hc (Oersteds) |
3,200 |
(It's resistance to demagnetisation) |
| BH max (MGOe) |
3.5 |
(Derived from the above two) |
| Density (gm/cm3) |
5.0 |
weight in grams per cm3 |
| Max operating temp |
300 |
(Degrees C) |
| Temp. coefficient |
-0.2 |
loses 0.2% of its Br value per degree C rise in temperature |
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| 3 - Neodymium Iron Boron |
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Neodymium Iron Boron is manufactured using powder sintering technology and is sintered using special tooling into standard disc, rings and block shapes.
These can then be cut into smaller magnets or ground to tight tolerances using diamond cutting tools.
Neodymium Iron Boron (NdFeB) the one of the most powerful magnets per unit volume and is used where ever a small size and maximum power are needed.
Strengths - High flux density, high resistance to being demagnetised, high power to weight ratio.
Weaknesses - Poor temperature resistance, poor corrosion restistance, although most are nickel plated.
Nd35H and it has the following properties |
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| Br (Gauss) |
11,900 |
(The amount of magnetism) |
| Hc (Oersteds) |
10,900 |
(It's resistance to demagnetisation) |
| BH max (MGOe) |
35 |
(Derived from the above two) |
| Density (gm/cm3) |
7.5 |
weight in grams per cm3 |
| Max operating temp |
120 |
(Degrees C) |
| Temp. coefficient |
-0.11 |
loses 0.11% of its Br value per degree C rise in temperature |
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| 4 - Samarium Cobalt |
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Samarium Cobalt is manufactured using powder sintering technology and is sintered using special tooling into standard disc, rings and block shapes.
These can then be cut into smaller magnets or ground to tight tolerances using diamond cutting tools.
Samarium Cobalt (SmCo) the one of the most powerful magnets per unit volume and is used where ever a small size, maximum power and high temperatures are needed.
Strengths - High flux density, high resistance to being demagnetised, high power to weight ratio. Medium temperature resistance.
Weaknesses - high cost
A common grade is SM27H and it has the following properties |
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| Br (Gauss) |
11,000 |
(The amount of magnetism) |
| Hc (Oersteds) |
10,300 |
(It's resistance to demagnetisation) |
| BH max (MGOe) |
28 |
(Derived from the above two) |
| Density (gm/cm3) |
8.4 |
weight in grams per cm3 |
| Max operating temp |
350 |
(Degrees C) |
| Temp. coefficient |
-0.04 |
loses 0.04% of its Br value per degree C rise in temperature |
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| 5 - Magnetic Rubber |
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This is produced by heavily loading ferrite powder of Barium or Strontium base into a synthetic rubber or PVC matrix and either extruding to shape or calendering into thin sheets.
Magnetic rubber can be cut with scissors and can be supplied with adhesive backing, bright coloured vinyl facing and is easily cut into special shapes using form cutters.
Strengths - Flexible, easy to cut, good corrosion resistance.
Weaknesses - Low magnetic flux density, poor temperature resistance.
A common grade is Y grade material and it has the following properties |
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| Br (Gauss) |
2,000 |
(The amount of magnetism) |
| Hc (Oersteds) |
1,600 |
(It's resistance to demagnetisation) |
| BH max (MGOe) |
0.8 |
(Derived from the above two) |
| Density (gm/cm3) |
3.5 |
weight in grams per cm3 |
| Max operating temp |
80 |
(Degrees C) |
| Temp. coefficient |
-0.2 |
loses 0.2% of its Br value per degree C rise in temperature |
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