Ceramic (ferrite) magnets are composed of strontium carbonate and iron oxide. Not sure if ceramic is the best material for your application? Review our Permanent Magnet Materials comparison for more information.
Manufacturing -A powdered mixture of strontium carbonate and iron oxide is injected into a wet or dry press for forming. During this process, a magnetic field is applied in the direction of preferred magnetization to orient the material and increase the magnet’s performance potential. This magnet is considered “oriented” (anisotropic). If not exposed to a magnetic field at time of formation, it is called “non-oriented” (isotropic).
After the molding process, the magnetic material is then sintered at about 2,000°F. The sintering process is similar to that of kilning ceramic pottery, thus the popular name “ceramic” magnet.
Lastly, the magnet is finish-ground to size with a diamond-bladed grinding wheel, magnetized, and inspected for shipment.
Tolerances -Pressed dimensions are either +/– 2% or +/– .025”, whichever is greater. Cut dimensions are either +/– 3% or +/– .025”, whichever is greater. Thickness tolerances are normally ground to +/– .005”, according to International Magnetics Association (IMA).
Visual imperfections such as cracks, porosity, voids, surface finish, etc. (commonly found in sintered ceramic magnets) do not constitute cause for rejection. Chips are acceptable if no more than 5% of the pole surface is removed. Cracks are acceptable, provided they do not extend across more than 50% of the pole surface.
Magnetizing and Handling -Ceramic magnet material is extremely brittle and can chip or break if dropped on a hard surface, or if allowed to “jump at” an attracting object.
The weakest grade of ceramic material is grade 1, which is typically non-oriented. Grades 5 and 8 are oriented ceramic material. When making magnetic assemblies with ceramic, it is typically easier to magnetize the product after assembly.
Machining - Since ceramic material is so brittle, it requires special machining techniques and equipment. Lead times may vary, but we offer cutting and grinding of ceramic material to meet your specifications. Contact us for more information.
Typical Magnetic and Physical Properties of Ceramic
|Ceramic Material||Density||Max. Energy Product |
|Typical Residual Induction Br (max)||Coercive Force Hc (min)||Intrinsic Coercive Force (Hci)||Maximum Operating Temperature||Curie Temperature|
Note: Unshielded open circuit ceramic magnets should not be subjected to more than 400°F or they will require re-magnetization.
Applications of Ceramic Magnets
- Speaker magnets
- DC brushless motors
- Magnetic Resonance Imaging (MRI)
- Magnetos used on lawnmowers and outboard motors
- DC permanent magnet motors (used in cars)
- Separators (separate ferrous material from non-ferrous)
- Used in magnetic assemblies designed for lifting, holding, retrieving and separating
Attributes of Ceramic Material
- Least expensive material compared to alnico and rare earth magnets
- High intrinsic coercive force
- Available in simple shapes only due to manufacturing process
- Lower service temperature than alnico, greater than rare earth
- Finishing requires diamond cutting or grinding wheel
- Lower energy product than alnico and rare earth magnets
- Most common grades of ceramic are 1, 5 and 8 (1-8 possible)
- Grade 8 is the strongest ceramic material available
- Tooling can be expensive