Ferrite magnets, sometimes referred to as ceramic because of their production process, are the least expensive class of permanent magnet materials. Ferrite magnets became commercially available in the mid 1950’s and has since found its way into countless applications including arc shaped magnets for motors, magnetic chucks and magnetic tools.
The raw materials of ferrite magnets are mixed in the correct proportions, granulated, and calcined (presintered). After going through several intermediate phases, a hexaferrite phase (BaFe12O19 or SrFe12O19) is achieved. The presintered granulate is ground to a powder. It can then be pressed wet or dry in a magnetic field (anisotropic) or in the absence of a magnetic field (isotropic) and sintered. The nature of the manufacturing process results in ferrite magnets that frequently contains imperfections such as cracks, porosity, chips, etc. Fortunately, these imperfections rarely interfere with a magnet’s performance.
Ferrite magnets are inherently brittle, and it is highly recommended that they NOT be utilized as structural elements in any application. Their thermal stability is the poorest of all the magnetic families, but ferrite magnets may be utilized in environments up to 300 °C (570 °F). The dimensional repeatability of ferrite magnets that as pressed components is difficult to control, consequently, components requiring tight tolerances necessitate secondary grinding operations to assure conformity.
CERAMIC (HARD FERRITE) MAGNETS
Ferrite magnets, sometimes referred to as ceramic because of their production process, are the least expensive class of permanent magnet materials. The material became commercially available in the mid 1950’s and has since found its way into countless applications including arc shaped magnets for motors, magnetic chucks and magnetic tools.
The raw material – iron oxide – for these magnets is mixed with either strontium or barium and milled down to a fine powdered form. The powder is then mixed with a ceramic binder and magnets are produced through a compression or extrusion molding technique that is followed by a sintering process. The nature of the manufacturing process results in a product that frequently contains imperfections such as cracks, porosity, chips, etc. Fortunately, these imperfections rarely interfere with a magnet’s performance.
To enhance a ceramic magnet’s performance, the ferrite compound may be biased by a magnetic field during the pressing process. This biasing induces a preferred direction of magnetization within the magnet, significantly reducing its performance in any other orientation. Consequently, ceramic magnets are available in both oriented (anisotropic) and non-oriented (isotropic) grades. Because of its lower magnetic properties, the isotropic grade of ferrite, ceramic 1, is typically utilized where complex magnetization patterns are required, and in process biasing would be cost prohibitive.
Ceramic magnets are inherently brittle, and it is highly recommended that they NOT be utilized as structural elements in any application. Their thermal stability is the poorest of all the magnetic families, but they may be utilized in environments up to 300 °C (570 °F). The dimensional repeatability of as pressed components is difficult to control, consequently, components requiring tight tolerances necessitate secondary grinding operations to assure conformity.
Machining and tolerances
Machining must be performed with a diamond wheel, preferably before magnetization. Standard tolerances are +/-.005” for ground dimensions and +/- 2% of feature size for sintered dimensions. Due to their brittle nature, these magnets will not withstand impact or flexing. They are also not recommended to be used as structural components in assemblies. Ceramic magnets are chemically inert non-conductors, which is a benefit in many applications but eliminates the use of the EDM process to produce samples or special shapes.
Temperature constraints and methods of magnetization
Due to Ceramic’s positive temperature coefficient of Hci high temperatures are not generally a major concern with respect to irreversible magnetic loss. Low temperatures, however, pose a much greater risk for permanent demagnetization. For example, a ceramic 5 grade with a permeance coefficient of 1 will start to experience permanent losses below -20°C.
Isotropic ceramic grades can be magnetized in any direction, while anisotropic grades have a preferred direction of magnetization and will only meet their full magnetic potential when magnetized along the “easy axis.”
Gauss Calculations of Ceramic Magnets
LECMAG will help you calculate magnetic field strength measured in Gauss, on the centerline of a disc magnet or ring magnet magnetized through its thickness, at a distance of X from the surface of the magnet.
LECMAG carries a large inventory of ceramic disc, block (rectangular & square), and ring magnets, available for immediate purchase in a wide range of shapes and sizes. Ceramic magnets are part of the permanent magnet family, and the lowest cost, hard magnets available today.
Ceramic magnets are used for many consumer & commercial applications such as craft projects, refrigerator magnets, badge holders, latches, display boards, motors, lifting magnets, science projects, toys, games, POP displays, advertising giveaways & much more.
We can also custom manufacture ceramic magnets to fit your exact specifications using our in-house global manufacturing facilities and experienced team of engineers. Just let us know what you are looking for by sending us a request for quote or contact us today, and we’ll work with you to determine the most economical solution for your project.
Magnetic and Physical Properties for Sintered Ferrite magnet
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Features & Characteristics of Ceramic / Ferrite Magnets
What are the main characteristics for ceramic magnets? Ceramic magnets are medium in magnetic strength, and can be used at fairly high temperatures. They are low cost, making them ideal for applications such as automotive sensors, magnetic separators, craft projects, badge holders, latches, display boards, science projects, toys, games & more.
What grades & shapes are available for ceramic magnets? Grades 5 (most commonly used) through 8 are available in disc, block (rectangle & square) and ring shapes, and can be custom manufactured to meet your specialty requirements.
What are the temperature constraints for ceramic magnets? Ceramic magnets can be used at fairly high temperatures, although their magnetic properties drop with temperature. At 175°C (350° F), approximately 75% of their room temperature magnetic properties are retained.
How are magnets rated? Magnets are typically rated by their residual induction, coercive force & maximum energy product. This refers to the maximum strength that the magnetic material can be magnetized to.
What are some common applications for ceramic magnets? Common applications for ceramic magnets include raft projects, refrigerator magnets, badge holders, latches, display boards, loudspeakers, security systems, motors, generators & alternators, lifting magnets, eddy current devices, brakes, clamps, switches & relays, sweeper magnets, science projects, toys, games, motors, magnetic couplings, POP displays, advertising giveaways, promotional items, novelties & more.
Are there machining constraints for ceramic magnets? Ceramic magnets require special machining techniques, and should be machined in an “un-magnetized” state. We are fully equipped to machine these materials to your specifications, just let us know what you are looking for by sending us a special request.
Are surface treatments required for ceramic magnets? Ceramic magnets do not need to be protected for surface rust. A thin film of magnet powder on the surface is common.
What are some bonding applications for ceramic magnets? Ceramic magnets are often assembled into products using “superglues” such as Loctite 325 or other epoxies. Please always ensure that bonding surfaces are clean and dry prior to bonding.
What safety precautions should be taken into consideration when working with ceramic magnets? Ceramic Magnets are hard & brittle, and they can chip or break if dropped or snapped together, so please take special care when handling these magnets!
Ceramic or Ferrite Magnets are produced by calcining a mixture of iron oxide and strontium carbonate to form a metallic oxide. A multiple stage milling operation reduces the calcined material to a small particle size. The powder is then compacted in a die by one of two methods. In the first method, the powder is compacted dry which develops an isotropic magnet with weaker magnetic properties, but with better dimensional tolerances. Oftentimes, a dry pressed magnet does not require finish grinding. In the second method, the powder is mixed with water to form slurry. The slurry is compacted in a die in the presence of a magnetic field. The applied field creates an anisotropic magnet which exhibits superior magnetic properties, but usually requires finish grinding.
The compacted parts which approximate the finished geometry are then sintered at high temperatures to achieve the final fusion of the individual particles. Final shaping is achieved by diamond abrasives. Usually the pole faces of the ceramic (ferrite) magnets will be ground and the remaining surfaces will exhibit “as sintered” tolerances and physical characteristics.
Large Ceramic (Ferrite) magnets are very strong and brittle and appropriate handling and packing is required. Most receiving departments are not familiar with the strength of Ceramic magnets and this can result in injury or broken parts. All personnel that may come in contact with this alloy should be made aware of the dangers of handling Ceramic magnets. The brittle nature of the alloy can lead to flying chips if the magnets are allowed to impact each other or a solid surface. Larger magnets can become a pinching hazard if caution is not exercised. We urge all customers to discuss handling techniques pertinent to their magnets.
Although Ceramic magnets are fairly inert, all Ceramic magnets should be stored in a low humidity and mild temperature environment. The magnetized alloy is very strong and it will attract ferrous particles from the air and surrounding surfaces. These particles will accumulate and appear as small “hairs” on the surface of the magnet or packaging. To combat the accumulated debris, the magnets should be kept in closed, clean containers and left in their original Dura wrapping. The magnets should remain in the attracting condition with all spacers intact. Metal shelving with poor clearance may cause the magnets to jump or shift as they are accessed. Do not store any magnetic material near sensitive electronics, equipment with cathode ray tubes (CRT), or magnetic storage media. Magnets which are not of the same alloy may need to be buffered from each other because of demagnetizing effects.
LECMAG offers a wide selection of Ferrite / Ceramic magnet products. Views on your desired product types.
Ferrite / Ceramic Ring Magnets
Our stock ceramic ring magnets are Grade 5, magnetized through the thickness.
Ferrite / Ceramic Discs
View a small sampling of our stock ceramic disc magnets in Grades 1, 5 or 8.
Ferrite / Ceramic Rectangles
We stock ceramic bar magnets in Grade 5, magnetized through the thickness.
Ferrite / Ceramic Block Magnets
We stock ceramic block magnets in Grade 8, magnetized through the thickness