HANGZHOU TENGYE MAGNETIC MATERIALS CO., LTD.

Sintered Neodymium Magnets | Comprehensive Introduction for Industrial Buyers

Table of Contents

Neodymium magnets, also known as NdFeB magnets or neo magnets, are the third generation of rare earth magnet, which were developed in early 1980s independently by General Motors and Sumitomo Special Metals. According to manufacturing process, they are divided into sintered neodymium magnets, plastic bonded neodymium magnets, and hot-pressed neodymium magnets. Sintered neodymium magnets have the highest energy product among all types of permanent magnets. Tengye Magnetic is a leading neodymium magnet manufacturer in China that produces high quality sintered neodymium magnets.

Geometry of Sintered Neodymium Magnets

neodymium ring magnet
ring magnet
neodymium disc magnet
disc magnet
neodymium cylinder magnet
cylinder magnet
neodymium square magnet
square magnet
neodymium rectangular magnet
rectangular magnet
neodymium bar magnet
bar magnet
arc motor magnets
arc motor magnets
neodymium wedge magnet
wedge magnet
countersunk neodymium magnet
countersunk magnet
neodymium sphere magnets
sphere magnets

Grade of Sintered Neodymium Magnets

According to remanence (Br) and coercivity (Hc), the grade of sintered neodymium magnets can vary in two ways. Take N42UH grade as an example, N represents Neodymium, 42 remanence, and UH coercivity (resistance to demagnetization). Generally, magnet grade can range from N30 to N55 in the perspective of remanence, N to TH in the perspective of coercivity or resistance to demagnetization. There are a variety of neodymium magnet grades that are suitable for different application requirements.

GradeRemanence
(Br)
Intrinsic Coercivity
(Hcj)
Coercivity
(Hcb)
Maximum Energy Product
(BH)max
Temperature  Coeffcient
(α)
Max.Working Temp.
TkGskA/mkOekA/mkOekJ/m3MGOeαBrαHcj°C
MaxMinMaxMinMinMinMinMinMaxMinMaxMin%/℃%/℃(L/D=0.7)
N541.501.4515.014.58761183610.54374145552-0.12-0.7660140
N521.471.4214.714.28761183610.54223905349-0.12-0.7680176
N501.441.3914.413.99551286010.84063745147-0.12-0.7680176
N481.421.3714.213.79551286010.83903584945-0.12-0.7680176
N451.371.3213.713.29551289911.33663424643-0.12-0.7680176
N421.321.2813.212.89551289911.33423184340-0.12-0.7680176
N401.281.2512.812.59551289911.33263024138-0.12-0.7680176
N381.251.2212.512.39551289911.33102873936-0.12-0.7680176
N351.221.1712.211.79551286010.82872633633-0.12-0.7680176
N331.171.1311.711.39551283610.52712473431-0.12-0.7680176
N301.131.0811.310.89551279610.02472233128-0.12-0.7680176
N52M1.471.4214.714.2111414103513.04223905349-0.12-0.68100212
N50M1.441.3914.413.9111414103513.04063745147-0.12-0.68100212
N48M1.421.3614.213.6111414102712.93903584945-0.12-0.68100212
N45M1.371.3213.713.211141499512.53663424643-0.12-0.68100212
N42M1.321.2813.212.811141495512.03423184340-0.12-0.68100212
N40M1.281.2512.812.511141492311.63263024138-0.12-0.68100212
N38M1.251.2212.512.311141489911.33102873936-0.12-0.68100212
N35M1.221.1712.211.711141486810.92872633633-0.12-0.68100212
N33M1.171.1311.711.311141483610.52712473431-0.12-0.68100212
N30M1.131.0811.310.811141479610.02472233128-0.12-0.68100212
N52H1.471.4214.714.2127416104313.14223905349-0.12-0.66120248
N50H1.441.3914.413.9135317103513.04063745147-0.12-0.66120248
N48H1.421.3614.213.6135317102712.93903584945-0.12-0.66120248
N45H1.371.3213.713.213531799512.53663424643-0.12-0.66120248
N42H1.321.2813.212.813531795512.03423184340-0.12-0.66120248
N40H1.281.2512.812.513531792311.63263024138-0.12-0.66120248
N38H1.251.2212.512.313531789911.33102873936-0.12-0.66120248
N35H1.221.1712.211.713531786810.92872633633-0.12-0.66120248
N33H1.171.1311.711.313531783610.52712473431-0.12-0.66120248
N30H1.131.0811.310.8135317796102472233128-0.12-0.66120248
N52SH1.441.4214.414.2159220107613.54223905349-0.12-0.66140284
N50SH1.421.3914.213.9159220105313.24063745147-0.12-0.66140284
N48SH1.401.3614.013.6159220103513.03903584945-0.11-0.56150302
N45SH1.371.3213.713.215922099512.53663424643-0.11-0.56150302
N42SH1.321.2813.212.815922095512.03423184340-0.11-0.56150302
N40SH1.281.2512.812.515922093911.83263024138-0.11-0.56150302
N38SH1.251.2212.512.215922090711.43102873936-0.11-0.56150302
N35SH1.221.1712.211.715922087611.02872633633-0.11-0.56150302
N33SH1.171.1311.711.315922084410.62712473431-0.11-0.56150302
N30SH1.131.0811.310.815922080410.12472233128-0.11-0.56150302
N28SH1.091.0410.910.41592207889.92231992925-0.11-0.56150302
N50SHT1.421.3914.213.9175122105313.24063745147-0.11-0.56150302
N48SHT1.401.361413.6175122103112.93903584945-0.11-0.56160320
N45SHT1.371.3213.713.2175122100312.63663424643-0.11-0.56160320
N42SHT1.321.2813.212.817512297112.23423184340-0.11-0.53160320
N40SHT1.281.2512.812.517512294711.93263024138-0.11-0.53160320
N38SHT1.251.2212.512.217512292311.63102873936-0.11-0.53160320
N35SHT1.221.1712.211.717512288411.12872633633-0.11-0.53160320
N33SHT1.171.1311.711.317512286010.82712473431-0.11-0.53160320
N30SHT1.131.0811.310.817512281210.22472233128-0.11-0.53160320
N50UH1.421.3914.213.9199025105313.24063745147-0.11-0.53170338
N48UH1.401.3614.013.6199025103112.93903584945-0.11-0.53180356
N45UH1.361.3213.613.2199025100312.63663424643-0.11-0.50180356
N42UH1.321.2813.212.819902597112.23423184340-0.10-0.50180356
N40UH1.281.2512.812.519902592311.63263024138-0.10-0.50180356
N38UH1.251.2212.512.219902590711.43102873936-0.10-0.50180356
N35UH1.221.1712.211.719902586010.82872633633-0.10-0.50180356
N33UH1.171.1311.711.319902585210.72712473431-0.10-0.50180356
N30UH1.131.0811.310.819902581210.22472233128-0.10-0.50180356
N48VH1.401.3614.013.6214927103112.93903584945-0.10-0.50180356
N45VH1.361.3213.613.2214927100312.63663424643-0.10-0.50190374
N42VH1.321.2813.212.821492797112.23423184340-0.10-0.50190374
N40VH1.281.2512.812.521492794711.93263024138-0.10-0.50190374
N38VH1.251.2212.512.221492792311.63102873936-0.10-0.50190374
N35VH1.221.1712.211.721492788411.12872633633-0.10-0.50190374
N33VH1.171.1311.711.321492786010.82712473431-0.10-0.50190374
N30VH1.131.0811.310.821492785210.72472233128-0.10-0.50190374
N48EH1.351.4013.514238830105113.23903584945-0.10-0.45200392
N45EH1.361.3213.613.2238830103112.93663424643-0.10-0.45200392
N42EH1.321.2813.212.823883097012.23423184340-0.10-0.45200392
N40EH1.281.2512.812.523883094711.93263024138-0.10-0.45200392
N38EH1.251.2212.512.223883091511.53102873936-0.10-0.45200392
N35EH1.221.1712.211.723883088411.12872633633-0.10-0.45200392
N33EH1.171.1311.711.323883086010.82712473431-0.10-0.45200392
N30EH1.131.0811.310.823883082010.32472233128-0.10-0.45200392
N45FH1.361.3213.613.2254732103112.93663424643-0.10-0.45210410
N42FH1.321.2813.212.825473297012.23423184340-0.10-0.45210410
N40FH1.281.2512.812.525473294711.93263024138-0.10-0.45210410
N38FH1.251.2212.512.225473291511.53102873936-0.10-0.45210410
N35FH1.221.1712.211.725473288411.12872633633-0.10-0.45210410
N33FH1.171.1311.711.325473286010.82712473431-0.10-0.45210410
N30FH1.131.0811.310.825473282010.32472233128-0.10-0.45210410
N42AH1.321.2813.212.827863597012.23423184340-0.10-0.45230446
N40AH1.281.2512.812.527863594711.93263024138-0.10-0.45230446
N38AH1.251.2212.512.227863591511.53102873936-0.10-0.45230446
N35AH1.201.1712.011.727863588311.12872633633-0.10-0.45230446
N33AH1.171.1111.711.127863584410.62712393431-0.10-0.45230446
N30AH1.131.0711.310.727863581210.22472153127-0.10-0.45230446
N28AH1.091.0210.910.22786357729.72311992925-0.10-0.45230446
N38TH1.251.2212.512.231824091511.53102873936-0.10-0.42260500
N35TH1.221.1712.211.731824086710.92872633633-0.10-0.42260500
N33TH1.171.1111.711.131824085110.72712393431-0.10-0.42260500
N30TH1.131.0811.310.831824082010.32472233128-0.10-0.42260500

Coating (surface treatment)

Coating (sintered NdFeB magnets)Abbreviationcolorthickness (µm)corrosion resistance (rating 1 to 10)Recommended working Temp. (℃)Surface Tension (γ)
SSTHHTPCT
   Nickel (barrel)  NiCuNi  Bright silver10-20555≤26036
   Nickel (rack)  NiCuNi  Bright silver10-20455≤26036
   3+Cr Zinc (barrel)  Zn  Blue&white5-10433≤16038
   3+Cr Zinc (rack)  Zn  Blue&white5-10333≤16038
   3+Cr Color Zinc (barrel)  Colored Zn  Bright color5-10333≤16038
   3+Cr Color Zinc (rack)  Colored Zn  Bright color5-10333≤16038
   Electroless nickel plating (barrel)  Electroless Ni  Dark silver12-20554≤26036
   Electroless nickel plating (rack)  Electroless Ni  Dark silver12-20454≤26036
   Nickel+Chromium  Cr  Dark black12-20455≤26036
   Teflon  PTFE  Dark grey 333≤26036
   Nickel+Black Nickel  Black Ni  Black12-20555≤26036
   Nickel+Tin  Sn  Bright silver12-2045536
   Nickel+Silver  Ag  Silver12-2045536
   Nickel+Gold  Au  Golden10-2045536
   Epoxy  Epoxy  Black10-20554≤16036
   Nickel+Epoxy  NiCu+Epoxy  Black15-25553≤16036
   Passivation/Phosphorization  Phosphate  Dark grey1-3≤24037
   Nano Coating  Nano  Gray/Black15-30667≤30033

Manufacturing Process of sintered NdFeB magnets

Sintered neodymium magnet (Neodymium-Iron-Born or Nd-Fe-B) is an alloy consisting of neodymium, iron, boron, cobalt, varying levels of praseodymium, dysprosium or terbium and other transition metals. The manufacturing process for sintered neodymium magnets are divided into two main stages: powder metallurgy and mechanical processing. There are are six critical manufacturing steps involved in the powder metallurgy stage.

Raw material including PrNd alloy, iron, copper, DyFe, etc. are mixed and melted together according to a certain proportion. These are heated in a vacuum furnace and a stream of molten metal is forced under pressure onto a cooled drum where it is rapidly cooled at approximately 100,000 degrees-per-second. As a result, strip cast NdFeB ingot is produced for further processing

After melting and casting, the NdFeB alloy ingot is subject to hydrogen atmosphere. Hydrogen slowly absorbs into the solid alloy and makes it brittle, which upon milling becomes fine powder.

The NdFeB powder produced from hydrogen decrepitation is protected in an inert gas atmosphere and handled in glove boxes before going to the automated press. The powder are then fed into a grinding chamber, where the high-velocity gas streams are introduced to cause particles clash violently against each other. As a result, extremely fine powder having a size ranging from 3 to 5 μm is produced.

The powder from jet milling is pressed. During the pressing, a strong magnetic field is applied in order to rotate the powder particles so that their main crystal axes are aligned. That’s required to achieve anisotropy, which means that every piece of powder in the finished magnet will contribute to the magnetic field. Without the alignment, the c-axis (crystal axis) would be more or less randomly distributed, and only those particles which are roughly in the direction of the magnetization field would be magnetized, resulting in a significantly weaker magnet.

The pressed NdFeB block is bagged and immersed into a cold isostatic press (CIP) under huge pressure. This process intends to remove the remaining air gaps within the block. NdFeB blocks coming out of CIP become a bit smaller than it was before it goes in.

The pressed blocks are placed in a sintering furnace at an extremely high temperature just below the melting point of the NdFeB alloy. At this temperature of over 1000 degree, the individual atoms have a lot of motion, which enables the NdFeb alloy to develop their full magnetic and mechanical properties. The magnetic domains maintain the same orientation they had before sintering. At this temperature, shrinkage of NdFeB blocks takes place and full density is achieved. 

After sintering, there are pent-up stresses in the metal from all the movement during sintering, so the blocks are heat-treated again in a step fashion at lower temperatures to reduce the stresses. The blocks are ramped up to a high holding temperature for a set time and then they are ramped down to a lower holding temperature. Once the holding time is achieved, the now stress-free blocks are slowly cooled to room temperature.

Direction of Magnetization

Sintered neodymium magnets are anisotropic and can only be magnetized in the predetermined direction. Generally, the magnets are axially magnetized (magnet in round shape) or magnetized through thickness (magnet in square or rectangular shape). However, it’s not uncommon to find a neodymium disc magnet diametrically magnetized because it’s used as rotary position sensor. Besides simple two-pole magnetization, sintered neodymium magnets can also be magnetized in sectors. Examples of different magnetization patterns are given below. (Sinter neodymium magnets in ring shape can have axial, diametrical, or radial magnetization. Arc magnets are usually diametrically magnetized in pair since they are used in electric motors. Thus the name, arc motor magnets.

magnetization patterns tengye magnetic (magnetization direction)

Maximum Working Temperature of Neodymium Magnets

Sintered neodymium magnets are characterized by their excellent magnetic performance at room temperature. However, they have the least temperature resistance compared to other permanent magnets. N grade magnet only has a theoretical temperature limit of 80°C. (The practical maximum operating temperature is related to the L/D ratio of the magnet.) For higher temperature resistance, high-cost heavy rare earth elements (HREEs) are needed to increase the magnet coercivity. Even with the help of grain boundary diffusion (GBD) technology, less heavy rare earth is needed to increase the coercivity, the cost to produce sintered neodymium magnets that can withstand temperature over 200°C is still very high. That’s why the market for Sm2Co17 magnets still widely exists in e.g. aerospace, military industry, etc.

Chart by Visualizer
Temperature Characteristics of sintered NdFeB magnets and Sm2Co17 magnet
sintered NdFeB magnets vs. Sm2Co17 magnets

Raw Material "NdPr Price" | Neodymium Magnet Price

Neodymium magnets are known for its high price, but more importantly for its price volatility. Rare earth alloy – NdPr alloy is the determining raw material for the price change of all types of neodymium magnets, especially sintered neodymium magnets. PrNd price is of vital importance to the production and cost of any type of neodymium magnets. It’s also an indictor of price trend of neodymium magnets.

ndpr price

About Tengye: Tengye Magnetic supplies finest neodymium magnet materials and custom magnetic assemblies to world industry. We work closely with our customer from designing stage to mass production. 

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