Since its incorporation in 1961, Dura Magnetics has been a leading manufacturer of fabricated alnico magnets. Alnico is an acronym used to reference the three primary elements used in the manufacturing process; aluminum, nickel, and cobalt. Prior to the 1970’s and the advent of rare earth magnets, alnico was the strongest type of permanent magnet. Although rare earth magnets such as samarium cobalt and neodymium may offer higher magnet strength, and ceramic magnets feature lower costs, alnico magnets still offer unparalleled high heat performance when compared to other available magnet grades. Alnico magnets are ideal for high heat applications due to the unique crystalline bonding between aluminum, nickel, and cobalt and the length to diameter ratios achieved during manufacture.
Find the Ideal Material for Heat Resistant Magnets
Manufactured using casting and sintering, Alnico magnets are primarily comprised of the following family of material grades: alnico 2, alnico 5-7, alnico 8, and alnico 5. Alnico 5 is the most commonly produced and fabricated material type. The once ubiquitous horseshoe magnet is typically manufactured using alnico 5. The image below left represents common surface finishes, both ‘as cast’ and ground. The image on the right shows the end of an alnico rod and its crystalline structure.
In some instances, the geometry of fabricated alnico is as critical as material grade when it comes to the ultimate performance of a magnet. Characteristically, the longer the magnetic axis, the better the magnet will perform within a given application. A general rule of thumb is that the magnetic length to diameter ratio should be 4:1. Although this is true for alnico 5, alnico 8 offers a higher resistance to demagnetization, and thus shorter magnetic axes are common and practical for use. In essence, certain grades of alnico lend themselves appropriate to specific applications. The costs of custom parts can vary greatly based on the size, material grade, quantity, and intricacy of the shape. Limitations exist based on the physical characteristics of the magnetic material; however a short consultation with a member of our technical team and a description of the application is all that is needed to hasten the quoting process. The reference tables below offer technical information on available grades and the physical characteristics of alnico offered by Dura Magnetics:
| Sintered Alnico - Available Grades | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Dura Magnet Grade | Residual Induction Br | Coercive Force Hc | Intrinsic Coercive Force Hci | Maximum Energy Product (BH)max | Max. Operating Temp.* |
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| Nominal | Nominal | Minimum | Nominal | Nominal | ||||||
| k-Gauss | Tesla | Oersted | kA/m | Oersted | kA/m | MGOe | kJ/m3 | °C | °F | |
| Alnico 2 | 7.0 | 0.7 | 500 | 40 | 540 | 43 | 1.5 | 12 | 450°C | 840°F |
| Alnico 5 | 11.0 | 1.1 | 600 | 48 | 600 | 48 | 4.25 | 34 | 450°C | 840°F |
| Alnico 8 | 8.8 | 0.88 | 1,530 | 121 | 1.600 | 127 | 5.25 | 42 | 450°C | 840°F |
| * The listed maximum operating temperatures are based on an adequate Length to Diameter ratio or a properly designed magnetic circuit. The listed values are for reference and validation must occur before one chooses a design path. Please consult a Dura technical representative before selecting or designing with Alnico magnet alloy. | ||||||||||
| Cast Alnico - Available Grades | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Dura Magnet Grade | Residual Induction Br | Coercive Force Hc | Intrinsic Coercive Force Hci | Maximum Energy Product (BH)max | Max. Operating Temp.* |
|||||
| Nominal | Nominal | Minimum | Nominal | Nominal | ||||||
| k-Gauss | Tesla | k-Oersted | kA/m | k-Oersted | kA/m | MGOe | kJ/m3 | °C | °F | |
| Alnico 5 | 12.2 | 1.22 | 600 | 48 | 630 | 50 | 5.0 | 40 | 500°C | 930°F |
| Alnico 5B | 12.2 | 1.22 | 650 | 52 | 660 | 53 | 5.5 | 44 | 500°C | 930°F |
| Alnico 5 DG | 12.5 | 1.25 | 690 | 55 | 700 | 56 | 6.5 | 52 | 500°C | 930°F |
| Alnico 5-7 | 13.0 | 1.3 | 700 | 56 | 740 | 59 | 7.5 | 60 | 525°C | 980°F |
| Alnico 8-HC | 7.0 | 0.7 | 1,750 | 139 | 1,750 | 139 | 4.5 | 36 | 525°C | 980°F |
| Alnico 8 | 8.2 | 0.82 | 1,500 | 119 | 1,600 | 127 | 5.0 | 40 | 525°C | 980°F |
| Alnico 8B | 8.8 | 0.88 | 1,500 | 119 | 1,650 | 131 | 5.5 | 44 | 525°C | 980°F |
| Alnico 8C | 9.0 | 0.9 | 1,380 | 110 | 1,440 | 115 | 7.5 | 60 | 525°C | 980°F |
| Alnico 9 | 10.5 | 1.05 | 1,410 | 112 | 1,440 | 139 | 9.0 | 72 | 525°C | 980°F |
| * The listed maximum operating temperatures are based on an adequate Length to Diameter ratio or a properly designed magnetic circuit. The listed values are for reference and validation must occur before one chooses a design path. Please consult a Dura technical representative before selecting or designing with Alnico magnet alloy. | ||||||||||
| Reversible Temperature Coefficient for Cast and Sintered Alnico | ||
|---|---|---|
| Temperature Range (°C) | Induction Br (α) (%)/°C | Intrinsic Coercivity Hci (β) (%)/°C |
| 20°C to 150°C | -0.02 to -0.03 | -0.02 to -0.03 |
| α = Δ Br / Δ T * 100 (Br @ 20°C) [ΔT = 20°C - 150°C] β = Δ Hci / Δ T * 100 (Hci @ 20°C) [ΔT = 20°C - 150°C] |
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| Alnico Magnets - Physical Properties | |||
|---|---|---|---|
| Property | Units | Value Sintered Alnico | Value Cast Alnico |
| Vickers Hardness | Hv | 440 | 440-620 |
| Density | g/cm3 | 6.8 - 7.0 | 6.9 - 7.3 |
| Curie Temp TC | °C | 810 - 860 | 740 - 860 |
| Curie Temp TF | °F | 1,400 - 1,580 | 1,460 - 1,580 |
| Specific Resistance | μΩ⋅Cm | 50- 70 | 45 - 75 |
| Bending Strength | kN/mm2 | 0.35 - 0.76 | 0.05 - 0.31 |
| Tensile Strength | kN/mm2 | 0.35- 0.45 | 0.02 - 0.15 |
| Thermal Expansion | °C-1 | +11.0 to +12.4 x10-6 | +11.0 to +13.0 x10-6 |
| The listed values are approximate and should be used as a reference. Any magnetic or physical characteristics should be substantiated before selecting a magnet material. Please engage Dura's Design / Development team members before selecting a design path. | |||
Today, most suppliers of magnets are simply that–suppliers of magnets. Dura maintains the ability to produce alnico magnets specified on drawings dating back to the 1950’s. Our proprietary and expert fabrication methods set us apart from other suppliers relying solely on an import, buy/resell business model. As a custom fabricator maintaining in-house manufacturing, we can integrate features such as grooves, slots, chamfers, and holes into alnico magnetic alloy. To learn more about Alnico magnets, or to discuss your project, contact Dura Magnetics for further assistance.