The direction of Magnetisation, DoM
NdFeB magnets are sintered anisotropic materials − they have a preferred direction of magnetization locked in their structure.
So the magnet can only be magnetized in one axis − any attempt to magnetize in another axis results in very little performance.
Each NdFeB magnet has a Direction of Magnetisation (DoM). In drawings, the poles are labeled (with a North or a South).
Or the magnet shape has an arrow inside it − this arrow points to the North pole face (the other end is the South pole face).
Sometimes one dimension in the description ends in a letter ˆA˜. The A (Alignment or Axis) indicates the DoM axis it is magnetized in.
The value ending mmA or inch A is the distance between the North and South Pole faces.
e.g. D10mm x 2mmA is an axially magnetized magnet; 40mm x 20mm x 10mmA has 10mm between the North and South faces.
The North pole face of a permanent magnet is a North-seeking pole (it seeks the geographic North). By scientific definition
of unlike poles attracting, the Earth’s geographic North pole is actually a magnetic South pole. We use this definition for DoM.
Temperature Ratings (Please note − your application will affect the performance available)
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MAGNET TYPE SUFFIX
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Rev. Temp. Coef. of Induction (Br), α,%°C (20−100°C)
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Rev. Temp. Coef. of Intrinsic Coercivity (Hci), β,%/°C (20−100°C)
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Max. Working Temperature
(based on a High working point)
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−0.120
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−0.70
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80 0C = 176 0F *
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M
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−0.115
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−0.65
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1000C = 212 0F *
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H
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−0.110
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−0.60
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1200C = 248 0F
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SH
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−0.105
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−0.55
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150 0C = 302 0F
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UH
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−0.100
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−0.55
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180 0C = 356 0F
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EH
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−0.095
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−0.50
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200 0C = 392 0F
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VH / AH
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−0.090
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−0.49
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230 0C = 446 0F
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* Please note that N52, N50, and N50M are rated to a maximum of 60°C (140°F).
Coatings Available
NdFeB should always be given a protective coating to minimize corrosion risk. There are currently over 40 options for magnet finish.
Nickel Copper Nickel (NiCuNi) is the standard (default) coating. This NiCuNi coating is applied unless otherwise requested.
A Zinc (Zn) coating is sometimes used as an alternative to NiCuNi − it is not as shiny as the Nickel finish and is not as good on corrosion resistance.
Nickel Copper Nickel plus Epoxy provides a double coating with improved corrosion-resisting properties.
Gold and Silver plating is actually a Gold or Silver layer on top of standard NiCuNi. The black nickel finish is a dull grey/black color.
Undamaged coatings will prolong the magnet's lifetime but only if the magnets are used in good environmental conditions (e.g. warm, dry, no humidity).
It is impossible to guarantee that NdFeB magnets will be free from long-term corrosion.
For such requirements consider plated SmCo and any Ferrite magnets. When using glue you are bonding onto the plating or coating rather than the material itself. If the plating or coating fails, the magnet may become free to move.
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Nickel−Copper−Nickel (Ni−Cu−Ni) [standard coating]
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Everlube (6102G)
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Nickel (Ni)
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Zinc (Zn)
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Nickel−Copper plus Black Nickel
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White Zinc
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Black Zinc
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Epoxy (Black)
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Epoxy (Grey)
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Copper (NiCu)
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Copper (NiCuNiCu)
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Tin (Sn)
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Gold (Au) [this is actually NiCuNi plus Gold]
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Ni−Cu−Ni plus Rubber
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Zn plus Rubber
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Zinc Chromate
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Silver (Ag) [this is actually NiCuNi plus Silver]
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Parylene C
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Ni−Cu−Ni plus Parylene C
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Ni−Cu−Ni−Au−ParyleneC
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Phosphate Passivation
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PTFE ("Teflon®") in white
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PTFE ("Teflon®") in silvery
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PTFE ("Teflon®") in grey
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PTFE ("Teflon®") in black
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Titanium (Ti)
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Titanium Nitride (TiN)
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Chrome (bright/standard)
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Chrome (black)
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Ni−Cu−Ni plus Everlube
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Ni−Cu−Ni plus Epoxy
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Ni−Cu−Ni plus PTFE
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Zn plus Everlube
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Tin (Sn) plus Parylene C
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Rhodium
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Potted (various)
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Colored (red, green, blue, pink, purple, etc)
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Uncoated (bare ˘ recommend vacuum packing as well)
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Plastic encased (this fits around pre−coated magnets to give additional protection and is not hermetic)
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Other coatings may be possible − please let us know your requirements.
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Relative Coating Performance − Examples (your application and its environmental condition may give different results)
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PLATING APPLIED6 commonly coating examples given
(other coatings exist)
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Overall Thickness
(1 micron = 1/1000th mm)
(1 micron = 0.03937 mil)
(1 inch = 1000 mil)
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Pressure Cooker Test (PCT)
Test is:− 2 bar, 120°C and 100% RH
(hours until corrosion could start to be
noted)
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Salt Spray Test
The test is:− 5% NaCl solution at 35°C
(hours until corrosion could
start to be noted)
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Nickel Copper Nickel (NiCuNi)
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15−21 microns
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48 hours
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24 hours
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NiCu + Black Nickel
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15−21 microns
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48 hours
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24 hours
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NiCuNi + Black Epoxy
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20−28 microns
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72 hours
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48 hours
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NiCuNi + Gold
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16−23 microns
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72 hours
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36 hours
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NiCuNi + Silver
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16−23 microns
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48 hours
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24 hours
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Zinc
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7−15 microns
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24 hours
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12 hours
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Physical Characteristics (Typical)
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Characteristic
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Symbol
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Unit
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Value
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Density
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D
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g/cm3
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7.5
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Vickers Hardness
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Hv
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D.P.N
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570
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Compression Strength
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C.S
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N/mm2
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780
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Coefficient of Thermal Expansion
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C//
|
10-6/°C
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3.4
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C⊥
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10-6/°C
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−4.8
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Electrical Resistivity
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ρ
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µ Ω cm
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150
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Temperature coefficient of
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resistivity
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α
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10-4/°C
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2
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Electrical Conductivity
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σ
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106S/m
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0.667
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Thermal Conductivity
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k
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kCal/(m h °C)
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7.7
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Specific Heat Capacity
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c
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kCal/(kg. °C)
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0.12
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Tensile Strength
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σUTS, or SU
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kg/mm2
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8
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Young’s Modulus
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λ / E
|
1011N/m2
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1.6
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Flexural Strength
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β
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10- 12m2/N
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9.8
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Compressibility
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σ
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10- 12m2/N
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9.8
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Rigidity
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E.I
|
N/m2
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0.64
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Poisson’s Ratio
|
ν
|
|
0.24
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Curie Temperature
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Tc
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°C
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310
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Dimensional Tolerances
The standard NdFeB magnet tolerance is +/−0.1mm. It is possible to produce most shapes to +/−0.05mm tolerances but the magnet may cost more.
For tighter tolerances, we would have to review the shape to inform you of the tolerances we could achieve (in most applications +/−0.05mm is the best).
The shape and finish determine the tolerances that can be achieved. Please contact us for a free and without obligation quotation.
Example of a BH (second quadrant demagnetization) curve
NdFeB - N42 grade
Conversions:-
1kA/m=12.5665Oe, 1kOe=79.5775kA/m 1T=10kGauss, 1 Gauss=0. 1mT
Additional Notes
The magnet shape, its environment, and the actual application affect how the NdFeB magnet will perform. Temperature is important as well as damp or wet conditions.
When determining suitability, you should analyze the Intrinsic curve, not the Normal curve.
By keeping the intrinsic working point above the ’knee’ and ideally at the BHmax working point maximum performance is possible.
If you have any more questions, require technical assistance and would like a quotation, simply contact us.
ALL
Callers:+86 13646720020
WHATSAPP:+86 13646720020
Although we have made every attempt to provide accurate information, we do reserve the right to change any of the information in this document without notice. We cannot accept any responsibility or liability for any errors or problems caused by using any of the information provided.
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