SINTERED 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.

Sintered
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.

MAGNETIC 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

ADDITIONAL PRODUCT INFORMATION

Ceramic material

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.

The main distinguishing features of hard ferrite magnets are:

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

THE PATH FROM RAW MATERIAL TO HARD FERRTITE MAGNET


  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 / Surface finishing
  11. Magnetising, marking, coating according to customer specifications
  12. Outgoing goods inspection

Sintered 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.

MAGNETIC 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

ADDITIONAL PRODUCT INFORMATION

Metallic material

Pressing and sintering processes in an inert gas atmosphere

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.

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

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.

THE PATH FROM RAW MATERIAL TO Sintered rare earth magnets

  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

ADDITIONAL 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 magnets - pressed

Plastic-bonded, pressed magnets offer a filling level of up to 97% NdFeB powder and thus higher magnetic values than injection-molded magnets.

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Plastic-bonded, injection-moulded magnets

Plastic-bonded, injection-molded magnets have an enormous variety of shapes and allow the tightest tolerances.

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Sintered or plastic-bonded magnets with plastic

Since the 1980s, we have been overmolding sintered and plastic-bonded magnets with plastic and manufacturing functional elements for integration into assemblies.

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System solutions

For magnet assemblies, we process sintered and plastic-bonded permanent magnets into a customer-specific magnet system.

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Holding magnets

Our standard holding solenoids with holding forces from 5N to 900N such as pot magnet and bar magnet systems offer the right solution for every need.

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