Why is aluminum in Alnico magnets

Alnico magnets and custom assemblies

Arnold offers a full range of cast and sintered Alnico products including:

  • Rotors
  • Solid and hollow cylinders
  • C-shaped
  • Multipole holding magnets
  • ring
  • Special parts
  • Rod
  • Die-cast aluminum
  • pole
  • Dipped in plastisol
  • Horseshoe-shaped
  • Painted (painting according to military standard)

Some commercially available Alnico magnets are available on our e-commerce website.

Cast Alnico grades

  • Alnico 2
  • Alnico 8B
  • Alnico 3
  • Alnico 8H
  • Alnico 4
  • Alnico 8U
  • Alnico 5
  • Alnico 9
  • Alnico 6
  • ArKomax®
  • Alnico 8
  • ArKomax® 800

Sintered alnico

Sintered Alnico magnets, which are primarily manufactured according to your specifications, are available in grades 2, 5, 6, 8B and 8H.

ALNICO MAGNETS AND customer-specific assemblies

We offer custom Alnico assemblies using Arnold's magnetic materials. We are able to manufacture your assembly entirely in-house, manufacturing both the magnetic and non-magnetic components and assembling these parts so that you have a finished sub-assembly. In addition, we can work with your and our component suppliers to develop the most cost-effective solution for your requirements.

Download our Cast Alnico and Sintered Alnico Permanent Magnets catalogs for more information on our capabilities.

General properties

Alnico permanent magnets are made of alloys, the main components of which are iron, aluminum, nickel and cobalt, although other elements (e.g. copper and titanium) may be contained in small quantities. Alnico grades vary in terms of cobalt content, which ranges from zero (Alnico 3) to 40% (Alnico 8). The lower grades (2, 3 and 4) are not aligned, with the magnetic properties being isotropic and the same in all directions. Their magnetic performance is relatively low. Anisotropic grades (Alnico 5, 6, 8 and 9) are designed to produce high magnetic power in a specific direction. Alignment is achieved during the heat treatment by cooling the product from a temperature of about 1093 ° C (2,000 ° F) at a controlled rate within a magnetic field corresponding to the preferred direction of magnetization.

Alnico 5, the most widely used quality class, supplies the energy for a magnetic circuit more economically than any other Alnico quality class. In addition to the highest coercive force of all Alnico grades, Alnico 8 has excellent volume energy and a low reversible temperature coefficient. It is recommended for applications that are exposed to strong demagnetizing fields or where a short magnetic length is required for reasons of space.

ArKomax® 800 and Alnico 9 are premium grades of Alnico 5 and 8. The superior magnetic performance of these grades is generated by crystal orientation in the molten state in the desired direction of magnetization.

Design considerations

Alnico magnets are coarse-grained, hard and brittle and usually cannot be drilled using conventional means. Arnold has developed a process that enables Alnico to be drilled.

Because of these mechanical properties, Alnico parts are not normally used as components. When you have a choice, go for simple shapes. Slots are preferred over holes. Cross sections less than 3.18 mm (0.125 ″) should be avoided. If necessary, finished surfaces can be made by grinding. In many applications, however, the “cast” or “sintered” surface provides a satisfactory result at significantly lower costs. To facilitate assembly and to adequately protect the magnet, special assemblies such as rotors and magnetron magnets can be provided with an aluminum jacket. In addition, low carbon steel pole pieces can be attached to magnetic pole faces by gluing or by means of bolts or screws. Plastisol or paint can be applied to improve the appearance.

magnetization

In order to be able to use Alnico as efficiently as possible, it must be magnetized after the magnet with its pole pieces has been mounted in the final magnetic circuit. Shipping the non-magnetized product also eliminates the need for special packaging and prevents contamination from stray iron filings, etc. The magnetic saturation at the point of use requires the application of a magnetizing force that is 4 to 5 times greater than the coercive force of the material. A magnetizing force of 3,000 Oersted (240 kA / m) is recommended for Alnico 5. With Alnico 8, the magnetization force should be at least 7,000 Oersted (560 kA / m). The magnetizing force only needs to be exerted for a short time. Pulse magnetizers with a capacitor discharge are therefore used as a rule. DC magnetizers are also effective.

Stability and temperature influences

Alnico magnets offer excellent stability in the event of temperature fluctuations: the reversible change is 0.02% per degree Celsius. Heating can lead to an irreversible loss of magnetic force. The amount of loss depends on the dimensions of the magnet and its composition, but is usually less than 5% and can be restored by re-magnetization. At temperatures above 538 ° C (1,000 ° F), a metallurgical change occurs that causes the magnetic force to decrease rapidly. This change cannot be restored by re-magnetization.

External magnetic fields can also cause a certain degree of demagnetization. In some critical applications it is desirable to stabilize the magnet by deliberately reducing the magnetic power by 5% to 10%. Such stabilization can reduce or even eliminate the effect of scattered outside fields.

Certifications

Download our Alnico Certifications here.