Neodymium

Goudsmit UK markets its range of NdFeB magnets under the Neoflux^TM name.

There are two main ranges of magnet :

1. Normal grade magnets which have grade names starting with GSN
2. S-series magnets with increased heat and corrosion stability

Normal Neoflux range

These magnets have been developed in the last ten years with standard alloy characteristics. Energy products range from 28MGOe to 48MGOe. Operating temperature ranges from 80^oC to 140^oC. The magnets are susceptible to corrosion and rusting and as such need to be coated. Our range of coatings is outlined below.

Neoflux S-series range

As a result of a lengthy R&D project by the Goudsmit Group a high energy corrosion resistant magnet has been developed which operates up to a maximum temperature of 200^oC and has a maximum energy product of 53MGOe.

The corrosion behaviour of the new Neoflux S-grade magnets is close to being similar to the corrosion behaviour of mild steel. The microstructure has been adjusted using suitable additive elements, leading to the replacement of the inter-granular Nd-rich phase by other corrosion stable inter-granular phases.

The corrosion weight losses under the very severe conditions of a HAST test (Highly Accelerated Stress Test or Pressure Cooker Test, 120-130ºC, 100% humidity and 2.5-3 bar pressure) are insignificant after several days of testing.

The typical weight losses of the Neoflux S-grades after 7 days of testing are approximately 1-2 mg/cm². Figure 1 compares Goudsmit GSNS-grade magnets to traditional GSN-permanent magnets of Goudsmit and customary Chinese GSN-35SH permanent magnets.

The typical measured weight losses of the S-grade magnets are about 20-50 times lower than the weight losses of customary  Chinese GSN-35SH permanent magnets.

Figure 1: the typical weight losses under HAST conditions specified for maximum operating temperatures of 150ºC.

Another very important advantage of the Neoflux S-grade magnets is the increase of the Curie-temperature of the RE₂FE₁₄B  compound ( RE = Rare-Earths), causing improved  thermal coefficients of the remanence and coercivity.

A magnetic grade is called “thermal stable” at a given temperature if the irreversible losses for a working point B/µ₀H ~ -1 are lower than 3%. The new Neoflux S-grades S30EH, S32UH, S35SH and S38H can be used at high operating temperatures of 200ºC, 180ºC, 150ºC and 120ºC, respectively without considerable irreversible magnetic losses ( see Table 1)

Table 1

* The operating temperature depends partly on the dimensions of the magnet and the system design.

Table 1: typical magnetic specifications of NdFeB S-grade material at 20ºC and 150ºC

Figure 2: The typical demagnetisation curve of a permanent magnet in GSNS-30EH quality at high temperatures.

Coatings

Magnets can be coated with the following finishes:

• Nickel plated
• Double Nickel Plated
• Zinc
• Zinc yellow passivate
• Nickel Copper Nickel
• Cadmium Chromate
• Aluminium Chromate
• Epoxy
• Copper Chrome
• Silver
• Gold
• Tin

All the coatings have different properties and different corrosion resistances. For advice please talk to our sales team who will be happy to advise which coating is best for which application.

Magnetisation

As Neoflux is a sintered anisotropic material it can be magnetised only along its axis of anisotropy. Mostly the magnets are sold in block, ring or disc form and the available patterns for each are shown below. A more detailed explanation of each pattern can be found in the section on magnetisation.

Packing and handling

Neoflux magnets are extremely strong and quite dangerous to handle. When planning a project with such a magnet it is worthwhile to consider how the magnets will be unpacked and handled. Goudsmit UK can supply the magnets with spacers between them and can pack the magnets in clear plastic tubing to make separation simple and efficient.

In certain applications magnets need to be marked for their polarity either north or south. Goudsmit UK can do this to client requirements.