Permanent Magnet Options: How To Select The Optimum Solution For Your Application
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The objective of this presentation is give a flavor of the material options available and highlight some of the important factors and point out a few misconceptions when it comes to selecting the best magnet option.
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Permanent Magnet Options: How To Select The Optimum Solution For Your Application
- 1. Permanent Magnet Options: How To Select The Optimum Solution For Your Application. Dr. John Ormerod Senior Technology Advisor Magnet Applications, Inc.
- 2. Presentation Outline • Introductions. • Major permanent magnet materials and types. • Key permanent magnet characteristics. • Be careful of $/kg. • Thermal and environmental considerations.
- 3. Introduction: John Ormerod • BSc, MSC and PhD in Metallurgy from the University of Manchester (1972 – 1978). • Magnetics career began with Philips (UK and Holland) - 1979 – 1990. • Developed and commercialized SmCo5, 2:17 and NdFeB magnets • Joined Arnold Engineering (US) responsible for soft and hard magnetic materials development and GM for permanent magnets ( 1990 – 2002). • 2002 - 2014 President of Res Manufacturing in Milwaukee. • Metal stamping and value added assemblies to the automotive market (Toyota, GM, Nissan) • Major supplier to Tesla Motors for Model S and future Model X • Founded business and technology consultancy for magnetics and metals related industries in 2015 – JOC LLC (www.jocllc.com). • Recently provided expert testimony on issues of invalidity during the rare earth magnet ITC investigation and currently advising the Rare Earth Magnet Alliance on prior art relative to Hitachi Metals key patents. • Advisory Board member for Bunting Magnetics, Senior Technology Advisor for MAI and Technology Advisor for Niron Magnetics.
- 4. Introduction: Magnet Applications, Inc. • Visit the latest website at: http://magnetapplications.com. • A Bunting Magnetics Company: https://buntingmagnetics.com/. • Only North American manufacturer of compression bonded NdFeB and injection molded ferrite, NdFeB and hybrid magnets. • Supply full range of engineered magnets and magnetic assemblies. • Located in DuBois, PA – Originally established in UK over 50 years ago – sister company located in Berkhamsted, UK. • Primary applications are BLDC motors and sensors in the automotive, medical, defense and industrial markets.
- 5. Introduction: Magnet Applications, Inc. • Pre-production magnetic design services including 3D magnetic modeling. • State of the art manufacturing capabilities including in-house coating and complete magnetic testing suite. • Investing in R & D for next generation of magnetic materials e.g. high Br compression bonded, 3D printed magnets. • The backing of strong family ownership – in business for over 55 years. • ITAR / DFARS registered for Defense Industry. • ISO-9001 Certified Quality System with a strong continuous improvement culture. • Very strong international supply chain for the complete range of permanent magnet materials.
- 6. Presentation Outline • Introductions. • Major permanent magnet materials and types. • Key permanent magnet characteristics. • Be careful of $/kg. • Thermal and environmental considerations.
- 7. Historical Development Of Permanent Magnets Strain Shape Magnetocrystalline
- 8. Commercially Important Permanent Magnets 10 20 30 40 50 (BH)max-MGOe Ferrite Alnico Bonded NdFeB SmCo Sintered NdFeB Gap Magnet
- 9. Manufacturing Methods • Powder Metallurgy - Sintered Magnets • Most NdFeB Magnets and SmCo • Foundry - Casting • Alnico • Ceramic Magnets - Oxides • Ferrites • Compression Bonded Magnets (thermoset binder) • Mainly Isotropic NdFeB • Injection Molded Magnets (thermoplastic binder) • Isotropic NdFeB or Ferrite • Flexible Magnets (elastomeric binder) • Mainly Ferrite but also some NdFeB • 3D Printed Magnets?
- 10. Permanent Magnet Market – My Guess Material Weight (000’s kg) Value ($ Millions) NdFeB 137,500 10,300 Ferrite 750,000 5,300 Bonded NdFeB 10,000 900 SmCo 4,000 400 Alnico 6,000 350 Total Approximately $17 B
- 11. Market ($) Dominated By NdFeB And Ferrite
- 12. Market By Major Application Type
- 13. Automotive Applications – NdFeB Is Gaining Ground! Source: TDK Tech Notes
- 14. Presentation Outline • Introductions. • Major permanent magnet materials and types • Key permanent magnet characteristics. • Be careful of $/kg. • Thermal and environmental considerations.
- 15. The Three Magnetic Vectors • H - Magnetic field (from current). • B - Magnetic flux density or Induction. • M – Magnetization (a material property). • These vectors are not independent, but are related. • Induction is the combination of magnetization and magnetic field.
- 16. How are B, H and M related? B=H + 4M cgs units B= 0 (H+M) SI units 0=4 10-7 Source: http://spontaneousmaterials.com/index.htm
- 17. Hysteresis Loops – Normal and Intrinsic Applied field Inducedfield Normal curve (B-H) Intrinsic curve (4πM-H) + H + B or 4πM - B - H Bsat. Jsat. or Msat. H at saturation 2nd Quadrant Demagnetization Curves typical of a permanent magnet
- 18. Permanent Magnet Key Characteristics 2nd Quadrant Demagnetization IHc Intrinsic Curve Normal Curve BHc Br - H Bm Hm B, 4πM Load line
- 20. Key PM Magnetic Properties • Br, Remanence or Remanent Induction – indicates available flux output from the magnet after magnetized to saturation. • IHc (or Hcj), Intrinsic coercivity or BHc, normal coercivity – indicates the magnet’s resistance to demagnetization. • (BH)max, Maximum Energy Product – a figure of merit for how much potential magnetostatic energy is available in a circuit.
- 21. What Is (BH)max? • Hg 2 = (BmHm)Vm/Vg – Hence, Vm is minimum when BH is maximum • Eg = Hg 2Vg/8π– Energy in airgap is proportional to BH (see Culity and Graham, 2nd Ed) IHc Intrinsic Curve Normal Curve BHc Br - H Bm Hm B, 4πM Load line HgBm Hm
- 22. What Is (BH)max? • Hg 2 = (BmHm)Vm/Vg • Eg = Hg 2Vg/8π • Hence in order to minimize magnet volume (Vm) the magnet is designed to operate at (BH)max. • It’s possible for static applications but not for dynamic applications. • (BH)max Br 2/4 HgBm Hm
- 23. Many Other Important Characteristics • Br • BHc • IHc • Hk • Recoil permeability • Rate of change of B and BHc with temperature • Maximum operating temperature • Ease of magnetizing • Resistivity • Mechanical properties • Machinability • Shape availability • Raw material cost and availability • Corrosion resistance • Manufacturability and ease of device/sub assembly integration • Economics of total raw materials and manufacturing process • Process Control and Quality Assurance
- 24. Major Functions Of A Magnet Application Category Physical Law System Function is Proportional to Application Examples Electrical to Mechanical (with solid conductor) Lorentz Force law B Loudspeakers, PM motors, HDD/ODD VCM Mechanical to Electrical Faraday’s Law of Induced voltage B Generators, Alternator, Tachometer, Magneto, Microphone, Eddy current devices, sensors Magnetostatic Field Energy to Mechanical Work Coulomb Force Principles B2 Magnetic Chucks, Conveyors, Magnetic Separators, Reed Switches, Synchronous Torque Couplings Electrical to Mechanical (with free charged particles) Lorentz Force law B Travelling Wave Tubes, Magnetrons, Klystrons, MRI
- 25. Presentation Outline • Introductions. • Major permanent magnet materials and types. • Key permanent magnet characteristics. • Be careful of $/kg. • Thermal and environmental considerations.
- 26. $/kg – What Are The Problems? • From first principles the field produced in a airgap (Hg) is a function of the volume of magnetic material (Vm). Hg 2 = (BmHm)Vm/Vg (see Culity and Graham, 2nd Ed) HgBm Hm
- 27. $/kg – What Are The Problems? • By experience we specify magnets by dimensions and geometry not weight. • We buy and use a volume of magnet material.
- 28. $/kg – What Are The Problems? • Different magnet materials have different densities. • On a volume basis Ferrite has a price performance ratio of approximately 50% better than NdFeB. Material Density (g/cm3) NdFeB 7.5 Ferrite 5.0 Bonded NdFeB 5.1 SmCo 8.4 Alnico 7.3
- 29. Normalized Price/Performance Based On Weight and Volume ( Ferrite is 1.0) Material Average (BH)max (MGOe) Average price ($/kg) Price/Performance (Unit Weight) Price/Performance (Unit Volume) Ferrite 3.8 7.1 1.0 1.0 NdFeB 40 75 1.0 1.5 Bonded NdFeB 8 90 5.9 6.1 SmCo 25 100 2.1 3.5 Alnico 7 58 4.4 6.4
- 30. Presentation Outline • Introductions. • Major permanent magnet materials and types. • Key permanent magnet characteristics. • Be careful of $/kg. • Thermal and environmental considerations.
- 31. Types of Thermomagnetic Effects Thermal flux loss Description 1. Reversible Change in flux output as a function of temperature – dependent on reversible temperature coefficient of B – α. Function of Curie temperature of the material. 2. Irreversible (But Recoverable) Critical conditions exceeded, magnet becomes partially demagnetized – controlled by reversible temperature coefficient of coercivity – β. Can be recovered by remagnetizing. 3. Structural (Irreversible-Unrecoverable) Permanent loss of flux due to corrosion or excessive temperature (or radiation) causing structural/phase change.
- 32. N42 Thermal Properties With Different Load Lines (Pc) Reversible Irreversible
- 33. Thermal Properties: Comparisons Max Use Alpha Beta Tc Material Grade Min ºC Max ºC ºC α β ºC Alnico, cast 5 20 100+ 520 -0.02 -0.01 900 Alnico, cast 8 20 100+ 520 -0.02 -0.01 860 Sm2Co17 27 MGOe 20 120 350 -0.035 -0.20 810 SmCo5 20 MGOe 20 120 250 -0.04 -0.40 700 NdFeB, Bonded MQP-A, O 20 100 110, 140 -0.13 -0.40 310 NdFeB, Bonded MQP-B 20 100 110 -0.11 -0.40 360 NdFeB, Bonded MQP-C, D 20 100 125, 110 -0.07 -0.40 470 NdFeB, Sintered L-38UHT 20 180 180 -0.10 -0.50 350 NdFeB, Sintered N38UH 20 180 180 -0.12 -0.65 310 NdFeB, Sintered N48M 20 100 100 -0.12 -0.65 310 Ferrite C-5, 8 20 120 400 -0.20 0.27 450 Temp. Range Source: Magnetics & Materials LLC
- 34. Corrosion of NdFeB 1990’s NdFeB magnets with excess Nd content Current NdFeB magnets with optimized composition and microstructure
- 35. Typical Coatings For NdFeB Coating Thickness Range (microns) Salt Fog Resistance (35○C/5% NaCl) Electroless Nickel 25 max. > 500 hours Ni-Cu-Ni 10 to 20 > 500 hours Epoxy (E-coat) 15 to 60 >240 hours Parylene (C/D/HT) 7 to 50 >100 hours Aluminum IVD 7 to 25 >500 hours Zinc 25 max. >96 hours Epoxy Powder Coat 50 to 125 >500 hours
- 36. Thank you for your attention Any Questions? Dr. John Ormerod Senior Technology Advisor Magnet Applications, Inc. DuBois, Pennsylvania, USA +1 414 899 2859 John_ormerod@magnetus.com
Editor's Notes
- Good morning ladies and gentlemen. My name is John Ormerod and today I am representing Magnet Applications Inc as their Senior Technology Advisor Title of presentation is……….. Introduce a somewhat different perspective on our traditional way of thinking about permanent magnets options Provide an alternative way of selecting the optimum magnet type based on the market and application requirements. First I always like to start my presentations with an interesting quote.
- Here are the subjects I would like to cover in today’s presentation. First a disclaimer; all the content of this presentation assumes the use of cgs units. I leave it up to those interested in SI to make the appropriate conversions and mu0 factors as appropriate. Start with introduction to MAI Then build on an idea I wrote about on LinkedIn last year….is there an optimum price/performance metric for PM’s. 2 commonly used metrics to evaluate PM options – discuss some of their limitations.
- A few words about myself: Graduated in the UK in metallurgy Began magnetics career with Philips developing RE magnets Joined Arnold Engineering in 1990 and ran their PM buisnesses 2002 left the industry and ran a manufacturing business became a major supplier to Tesla Motors Expert witness for the ITC and RE Magnet Alliance challenging the validity of the HML NdFeB patents Senior Technology Advisor for MAI Founded JOC LLC
- Here are the subjects I would like to cover in today’s presentation. First a disclaimer; all the content of this presentation assumes the use of cgs units. I leave it up to those interested in SI to make the appropriate conversions and mu0 factors as appropriate. Start with introduction to MAI Then build on an idea I wrote about on LinkedIn last year….is there an optimum price/performance metric for PM’s. 2 commonly used metrics to evaluate PM options – discuss some of their limitations.
- Let’s start with the chart that you have seen numerous times in various guises at this or other magnet conferences and shows the development of permanent magnets based on the (BH)max. The only thing that is unique in my chart is it’s in various shades of green. It shows the dramatic improvement in magnetic performance from magnet steels (strain induced mechanism of Hc), to Alnicos (Hc based on shape anisotropy) and finally hard ferrites and rare earths exhibiting high coercivities through strong magnetocrystaline anisotropy. This explains the change in slope from the earlier 1970’s.
- While it’s true that most magnet material are still being used (even PtCo) there are only 5 classes of PM materials/types that are commercially important. A similar chart was shown at last year’s conference by Alex King of the CMI and the case was made that their as a gap in material properties ((BH)max) between bonded NdFeB at say 12 MGOe and SmCo at say 18 MGOe and hence here is an opportunity for a new magnet material. Well that got me thinking that this simple chart is missing a very important factor; namely the relative market share (and commercial importance) of each of these magnet options.
- Obviously it’s easy to poke holes in other people’s efforts so I decided to take a stab at estimating the market myself. It turns out that if you don’t mind subjecting yourself to criticism if not downright ridicule posting articles on LinkedIn is actually a very effective method of receiving good information. After I posted my Price/Performance article last year I did get a lot of input from many active industry sources that I then used to formulate the above data and adjust my estimates from the original article. I will point out that my total market of $17 billion actually falls halfway between Walt and Steve's estimates.
- So here are those estimates shown as market share segmentation for each of the material classes. This dramatically illustrates that the market is dominated by NdFeB and ferrite magnets (over 90%) What I find intriguing is how these two material types which are at the opposite ends of both the price and performance spectrum can dominate the applications for permanent magnets. This got me thinking is there a magic or optimum price/performance metric that helps to explain this market dominance.
- However in terms of the market share the majority of applications are dependent on B and therefore Br.
- Here are the subjects I would like to cover in today’s presentation. First a disclaimer; all the content of this presentation assumes the use of cgs units. I leave it up to those interested in SI to make the appropriate conversions and mu0 factors as appropriate. Start with introduction to MAI Then build on an idea I wrote about on LinkedIn last year….is there an optimum price/performance metric for PM’s. 2 commonly used metrics to evaluate PM options – discuss some of their limitations.
- The point at which increasing the applied field results in no additional contribution by the magnet material is called saturation. When referenced to the Normal curve, it is the B-saturation point. On the Intrinsic curve it is called either J-saturation or M-saturation. The value of H is the same for both curves. The curves shown here represent a “straight line” permanent magnet material such as ferrite, neo or SmCo. The term “straight line’ derives from the straightness of the Normal curve in the second quadrant. We also refer to straight line materials as “square loop” when reffering to the intrinsic curve.
- Here are the subjects I would like to cover in today’s presentation. First a disclaimer; all the content of this presentation assumes the use of cgs units. I leave it up to those interested in SI to make the appropriate conversions and mu0 factors as appropriate. Start with introduction to MAI Then build on an idea I wrote about on LinkedIn last year….is there an optimum price/performance metric for PM’s. 2 commonly used metrics to evaluate PM options – discuss some of their limitations.
- HANDOUT These key properties are used to gauge magnetic suitability and quality. They are sometimes referred to as “figures of merit.”
- (BH)max is an universally quoted metric we all use to compare magnet options. So I thought it would be interesting to remind ourselves both the origin and some of the limitations of this measure Let’s start by getting back to first principles which unfortunately do involve some elementary calculus Same toroidal ring magnet I showed earlier into which we have machined a gap of know volume, Vg. On the right you see the intrinsic and normal demagnetization curve for this magnet. Based on the geometry of the magnet it is operating at the load line shown with a magnet flux of Bm at a field of Hm. Here is the same equation I showed before but this time note that for a given air gap, Vg the volume of magnet to generate the field in the gap, Hg, is a minimum when Bm times Hm is maximum.
- Hence in order to minimize the magnet volume the circuit is designed to operate at the (BH)max point on the demagnetization curve. Also added this second equation where Eg is the magnetostatic energy of the air gap field and by substituting Hg2 in these equations it can be shown that Eg is proportional to B times H; hence the product of B H is known as the energy product. But it’s not often practical to design for (BH)max conditions e.g.dynamic applications, high performance motors
- The main point I want to make is that there are lots of other material characteristics (other than (BH)max or Br) that have to be considered when choosing the optimum magnet type for an application. (BH)max is one parameter but not necessarily the most important one.
- The only role of a permanent magnet is to provide a magnet field in a substance or vacuum. How the field interacts with a conductor, field, charged particle or another magnetic material is the how a magnet provides a useful function. Here is a table of the 4 major applications and the physical law and the magnet parameter that determines the functionality. As can be seen most are dependent on B which assuming a straight line high coercivity magnet (rare earths and ferrite) is proportional to Br rather than (BH)max. For holding type applications the function of the system is proportional to B2 and in these applications (BH)max is important.
- Here are the subjects I would like to cover in today’s presentation. First a disclaimer; all the content of this presentation assumes the use of cgs units. I leave it up to those interested in SI to make the appropriate conversions and mu0 factors as appropriate. Start with introduction to MAI Then build on an idea I wrote about on LinkedIn last year….is there an optimum price/performance metric for PM’s. 2 commonly used metrics to evaluate PM options – discuss some of their limitations.
- $/kg……what are the issues with this oft used metric? First let’s start from first principles which does require a bit of algebra. Consider a toroidal ring magnet which into which we have machined a gap of know volume, Vg; incidentally this is the type of circuit that was used in a traditional moving coil meter before we move to digital devices. The only function of a permanent magnet is to establish a magnetic field that then interacts with another field, electrical charge or magnetic material. In this example it creates a field Hg in the airgap. Assuming no leakage or fringing fields, using Ampere's law and some basic magnet circuit equations it’s relative easy to arrive at the above equation. For rigorous mathematical treatment I refer you to the text book by Culity and Graham. What we find is for a given air gap, field in the air gap, Hg, is proportional to the volume of magnet in the circuit.
- From everyday working with magnets I don’t think anyone has bought magnets like we by potatoes by the pound or kg.
- The reason why comparing magnet materials on a unit weight basis is an issue is because each material type has a different density with a wide range of values.
- So I’ve attempted to show the effect of density on my price/performance metric on a volume basis. In this case I have normalized the price/performance ratio to ferrite and defined ferrite as 1.0 on both weight and volume basis. Remember from my previous analysis on a weight basis ferrite ad NdFeB have the same ratio…..so the obvious question is why does anyone use hard ferrite? Well on a volume basis NdFeB is at a 50% price disadvantage over ferrite. All other materials are significantly less efficient in converting $ to magnetic performance on a volume basis than ferrite.
- Here are the subjects I would like to cover in today’s presentation. First a disclaimer; all the content of this presentation assumes the use of cgs units. I leave it up to those interested in SI to make the appropriate conversions and mu0 factors as appropriate. Start with introduction to MAI Then build on an idea I wrote about on LinkedIn last year….is there an optimum price/performance metric for PM’s. 2 commonly used metrics to evaluate PM options – discuss some of their limitations.
- When a magnet suffers loss in output, it may be one of several types. Reversible: a change in output which is temporary - - when the temperature is returned to room temp, the magnet properties are returned to their original state. Irreversible: the change is output is permanent. Irreversible, recoverable: the magnet may be re-magnetized and all output recovered. Structural loss (irreversible, unrecoverable): there is permanent change in output which cannot be recovered except by reprocessing the magnet. An example of reversible change is the change in output as a magnet is raised to a higher temperature within the recommended maximum for the material and then returned to room temperature. An example of irreversible, unrecoverable loss is that due to corrosion of the magnet. Reversible losses can almost always be accommodated in the design. However, un-planned large irreversible losses are not acceptable. To accommodate exposure to temperatures at which mild de-magnetization occurs, magnets are sometimes “pre-stabilized”, that is partially de-magnetized. Structural loss is not acceptable and can result in system failure. For example, corrosion not only results in lower magnetic output, but can also result in physical destruction of the device.
- A comparison of some Alpha and Beta values for common magnet materials is listed here in order of increasing Beta – with the exception of Ferrite. Ferrite magnets are ferrimagnetic and exhibit a positive change in Beta with temperature. This makes them excellent for higher temperature use, but limits their low temperature use. A typical lower temperature limit for Ferrite is -40 ºC (-40 ºF). Unfortunately, Ferrite has a high Alpha resulting in large reduction in flux output as temperature increases. A practical upper use temperature is 250 ºC. However, in motor applications, 150 ºC may be the maximum practical use temperature due to system design limitations.
- On early NdFeB magnets, the grain boundaries were heavily laden with rare-earth-rich phase. The corrosion of NdFeB magnets tended to occur along the grain boundaries where this phase exists. As the grain boundary material is corroded away, the grains themselves become loose. The magnet would quickly disintegrate into loose particles. More modern alloys minimize this phase at the grain boundary; as a result, corrosion proceeds slowly through the material. The resulting magnet is less likely to disintegrate due to the effects of corrosion. However, not all companies have learned to produce stable alloy structures. Therefore, it is advised to establish a corrosion specification when purchasing NdFeB and to work closely with the supplier to ensure that it is consistently met.
- Various coatings are compared in environmental testing: temperature-humidity chamber, autoclave and salt spray testing as applied to NdFeB magnets. Electrolytic nickel plating or nickel with an overcoat of epoxy performs best. Improvements in electroless nickel plating have allowed this non-magnetic form of nickel to replace the (magnetic) electrolytic plating in many applications. A shortcoming of electrolytic nickel is the “dogbone” effect where the nickel plate is thicker at the edges and corners of the magnet. Only ferrite magnets have exhibited good resistance to corrosion in salt spray testing. Magnets are often encapsulated within assemblies and are not directly subjected to salt spray in use. Other coatings include: IVD Aluminum, Aluminum Chromate and Nickel Chromate.
- Thank you for attention and happy to take any questions