Position : Fecrco > FAQ

FAQ

What's the Inspection standard for permanent magnet?

1) When the permanent magnet is not supplied with specific size and shape, the properties of material should be tested. The test standard is as per GB/T3217-95 permanent magnet (hard magnet) material test trial method ,GJB2453-95 rare earth permanent magnet material general criterion and relevant enterprise standard. GB/T3217 stipulated the test method. Enterprise standard stipulated the test process and sampling method.

2) When the permanent magnet is supplied with specific size and shape, the properties of the magnetic component should be tested. The properties of the material are only tested for reference.

3) For different permanent magnetic components, the test parameters and test methods are different. For magnetic ring, the test parameter is diametric flux density. For magnetic segment and block, the parameters can be surface field, magnetic flux etc. The magnetic flux is better.

A digital tesla meter can test diametric flux density

With a transverse sensor. Magnetic flux can be tested by permanent magnet tesla meter and Helmholtz coil.

For more information about the international standard, you may urn to the following reference:

IEC 404-5(1982) magnetic material Part 5: test measure for hard magnet (permanent magnet) material properties.

JISC 2501-1989 Test method for magnetic material(Japan)

What are the maximum recommended operating temperatures for different magnet materials?

The maximum temperature that a magnet may be effectively used at depends greatly on the 'permeance coefficient' - which is a function of the magnetic circuit - the magnet is operating in. The higher the permeance coefficient (the more 'closed' the circuit), the higher temperature at which the magnet may operate at, without becoming severely demagnetized. Shown here are approximate maximum operating temperatures for the various classes of magnet material. At temperatures close to those listed here, special attention may be needed in order to ensure that the magnet will not become demagnetized.

Material Approx. Maximum Operating Temperatures
  °C °F
NdFeB 140 284
SmCo 300 572
Ferrite 300 572
Alnico 540 1,004
Flexible 100 212

What are the design considerations one faces with AlNiCo magnets?

Alnico magnets cannot be conventionally drilled or machined because they are coarse-grained, hard and brittle. These mechanical properties of alnico magnets makes them a bad choice as structural members. Instead of holes, slots are used. Cross sections of less than 3.18 mm are avoided.

Finished surfaces if the need arises, can be produced by grinding. However, the industry has found that for most applications the cast alnico magnet or sintered alnico magnet is satisfactory as it is and the cost is significantly lower.

What about stability and temperature effects on AlNiCo magnets?

Alnico magnets offer exceptional stability with temperature changes. Heating may sometimes produce an irreversible loss of magnet strength but the loss is less than 5% and can be recovered by remagnetization. At temperatures exceeding 10000C, a metallurgical change takes place which causes magnetic strength to reduce rapidly. This change will not be recovered by remagnetization.

What is the proper method of storing AlNiCo methods?

Alnico magnets have a low resistance to demagnetization and loose power quickly, if stored improperly; they should be stored in a low humidity and mild temperature environment. The magnetized alloy will attract ferrous particle 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 and keepers 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. Most of all, never stored alnico magnets with the unlike pole repelling each other, for best results, alnico must be stored with the like pole attracting each other. A steel keeper may also be used.

How should we packing AlNiCo magnet?

Alnico magnets are very susceptible to demagnetization. They will even partially demagnetize each other if like poles are forced together. To combat this effect Alnico magnets are usually packaged with keepers or attracting in rows. Some assemblies are magnetized in rows and the mild steel component of one assembly acts as a keeper to the neighboring assembly. It is imperative that magnets with keepers or that are attracting in rows be stored as such. This attracting condition should only be changed when the magnets are to be used or integrated into the end application.

The packaging methods of magnetized alloy are dependent upon the magnet size and the customer requirement. A brief overview of Dura Magnetics standard packaging is listed below. Please alert your Dura contact if you require a deviation from these methods.

Quarter sized or smaller magnets are usually put attracting in rows. They may or may not have plastic spacers between them in order to reduce the attracting force between the magnets. These rows may be wrapped in corrosion inhibiting paper (VCI) and the wrapped rows are arranged attracting in a brick. The bricks may be skin package on cardboard or wrapped in foam.

Magnets up to 2"square will be arranged attracting in rows with sizable spacers and keepers on each magnet. The rows can be arranged attracting with spacers running the length of the rows or individually wrapped in foam. Smaller quantities of these large magnets can go into an appropriate cardboard box, but larger volumes must be crated.

Large magnets, arrays, or assemblies will be packaged in wooden crates. Many times these products must be shipped via a LTL carrier.

Alnico Shipping

A majority of our products are shipped ground by UPS, Fed Ex Ground, or LTL carriers. FAA guidelines consider magnetized material as hazardous goods when the field density emanating from the package sides exceed a specified value. Many air carriers will not accept magnetized material for air shipments. Dura Magnetics is able to ship via air, but a packing/handling charge may be applied for larger volumes. These charges are only applied in extreme cases to cover the cost of extra shielding and packaging material, labor, and necessary paperwork.