Sintered magnets

Magnete besitzen faszinierende physikalische Eigenschaften. Als die Magnet-Experten nutzen wir diese Eigenschaften, um daraus individuelle technische Magnetlösungen für unterschiedlichste Aufgabenstellungen zu entwickeln. Gesinterte Magnete kommen in unterschiedlichen Anwendungen zum Einsatz. Beispielsweise werden Seltenerdmagnete verwendet, wenn höchste Magnetkräfte auf kleinstem Raum gefordert sind. Hartferritmagnete erfüllen dagegen höchste Anforderungen an die Beständigkeit.

01Sintered magnets

Sintered magnets feature magnetic material in its highest performance composition. No additional material is mixed in with the base material (e.g. NdFeB) of sintered magnets. That is a contrast to plastic-bonded magnets, which are very popular nowadays.

Magnets reach their greatest attractive force (remanence) as well as their greatest consistency (coercivity) in their sintered form and they also achieve their highest performance. Homogeneity as well as consistency are the primary indicators of high quality.

Among sintered magnets, a distinction is made between robust hard ferrite magnets and the high-performance rare earth magnets.

02Sintered hard ferrite magnets

Hard ferrite magnets are made from iron oxide and barium carbonate or strontium carbonate. According to a recipe, the individual raw materials are mixed, granulated and calcinated (pre-sintered). Via different intermediate phases, a hexagonal ferrite phase (BaFe12O19 or SrFe12O19) is created. The pre-sintered granulate is ground further and can be pressed or sintered in the magnetic field – either wet or dry (anisotropic) or without magnetic field (isotropic). As ceramic materials, hard-ferrites have the proper mechanical properties with regard to hardness and brittleness. They can be machined, e.g. by grinding via diamond discs.

03MAGNETIC AND MECHANICAL CHARACTERISTICS

A typical data sheet for a permanent magnetic material contains its key magnetic and mechanical characteristics. The magnetic characteristics are usually measured in accordance with DIN EN 60404-5. In addition to magnetic values, the data sheet also contains mechanical characteristics such as density, hardness and strength properties.

About the magnetic characteristics

04Additional product information

Type of material

Ceramic material

Production process

Pressing and sintering process in oxidising atmosphere

Mineral deposits

The main components of hard ferrite magnets are iron oxide and barium carbonate or strontium carbonate. Sufficient amounts of iron oxide and the alkaline earth materials barium and strontium are naturally available. Iron oxide is also produced during the industrial processing of steel.

Defining features

The main distinguishing features of hard ferrite magnets are:

cheap raw materials
very good corrosion and chemical resistance
easy to magnetise

 

 


05The path from raw material to hard ferrtite magnet

Production process

  1. Iron oxide and barium or strontium carbonate
  2. Inspection of incoming raw material
  3. Mixing
  4. Presintering
  5. Milling
  6. Wet pressing with magnetic field (anisotropic magnets)
  7. Drying/granulating
  8. Axial and transverse field pressing with magnetic field (anisotropic magnets)
  9. Pressing without magnetic field (isotropic magnets)
  10. Sintering
  11. Magnetising, marking, coating according to customer specifications
  12. Outgoing goods inspection

02Sintered rare earth magnets

Rare earth magnets mainly consist of intermetallic compounds of rare earth metals (samarium, neodymium) and transition metals (e.g. cobalt, iron). In contrast to hard ferrite magnets, the grinding, pressing and sintering take place in an inert gas atmosphere. The magnets are either pressed in an oil bath (isostatic) or in a tool (axially or diametrical). They can then be further machined, e.g. by grinding at diamond discs.

Samarium-cobalt (SmCo) and neodymium-iron-boron (NdFeB) are important base alloys for rare earth magnets. The microstructure of sintered NdFeB materials is characterised by Nd2Fe14B grains as the magnetic main phase and the intermetallic grain boundary area. In the case of conventional NdFeB materials, the grain boundary area consists of free neodymium prone to corrosion. In the case of our NdFeB materials, this free neodymium is replaced by a stable intermetallic phase if possible, as well as corrosion-stabilised. This significantly decreases the susceptibility to corrosion of the materials. Principally, NdFeB is relatively stable to solvents and has a strong corrosive reaction to salts and acids. Hydrogen makes the material brittle. The corrosion-stabilising NdFEB magnets can be used unprotected for many applications.

03MAGNETIC AND MECHANICAL CHARACTERISTICS

A typical data sheet for a permanent magnetic material contains its key magnetic and mechanical characteristics. The magnetic characteristics are usually measured in accordance with DIN EN 60404-5. In addition to magnetic values, the data sheet also contains mechanical characteristics such as density, hardness and strength properties.

About the magnetic characteristics

04Additional product information

Type of material

Metallic material

Production process

Pressing and sintering processes in an inert gas atmosphere

Mineral deposits

The main components of SmCo are samarium and cobalt, and neodymium and iron for NdFeB. The rare earth metals samarium and neodymium are abundant in the form of ores and they are part of the rare earths in the periodic table. Cobalt is a natural raw material that is also available in sufficient amounts.

Raw material extraction

Neodymium, samarium and cobalt are mined in different parts of the world.

Defining features

Rare earth magnets feature a very high energy density and are used when high forces or top magnetic flux densities are needed in the smallest of spaces. Due to the high energy densities, a miniaturisation, e.g. in the area of sensor technology, or a reduction of the assembly size, e.g. in motor construction, is possible.


05The path from raw material to rare earth magnet

Production process

  1. Alloying
  2. Inspection of incoming raw material
  3. Breaking up/filtering
  4. Milling
  5. Mixing
  6. Isostatic pressing
  7. Axial and transverse field pressing with magnetic field
  8. Sintering
  9. Surface finishing
  10. Magnetising, marking, coating according to customer specifications
  11. Outgoing goods inspection

06Additional product areas

The requirements of our customers are very diverse, as is our product portfolio. More than 5,000 custom-developed products stand for quality and reliability.

Plastic-bonded,
pressed magnets

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Plastic-bonded,
injection-moulded magnets

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plastic-bonded magnets
with plastic

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magnet assembly

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Holding magnets

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07Your points of contact

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