Selecting the correct magnet for your application can be challenging due to the variety of magnetic materials available. This guide simplifies the process by explaining key considerations and the differences between magnet grades, focusing on the strongest rare earth magnets: Neodymium (NdFeB) and Samarium Cobalt (SmCo).

Key Questions for Magnet Selection

When choosing a magnet, consider the following:

  1. Maximum Operating Temperature: What temperature will the magnet be exposed to?
  2. Materials Nearby: Will the magnet be next to steel, aluminum, plastic, etc.?
  3. Size and Tolerances: What are the size requirements and tolerances?
  4. Operational Context: Is the magnet part of an assembly or used independently?
  5. Coating Requirements: Are there specific coating needs due to environmental factors like humidity, corrosive chemicals, or exposure to water?

These questions help narrow down the magnet options suitable for your application.

Understanding Magnet Strength and Grades

Magnet Strength (BHmax)

  • Neodymium Magnets: BHmax ranges from 30 MGOe to 55 MGOe. Higher numbers mean stronger magnets. Common grades include N35, N38, N40, N42, N45, N48, N50, N52, and N55.
  • Samarium Cobalt Magnets: BHmax ranges from 16 MGOe to 32 MGOe. Common grades are 16, 18, 20, 22, 24, 26, 28, 30, and 32. Neodymium magnets are generally stronger than Samarium Cobalt magnets.

Magnet Coercivity (Hci)

  • Coercivity measures a magnet's resistance to demagnetization. It is often represented by letters:
    • M: Up to 100°C
    • H: Up to 120°C
    • SH: Up to 150°C
    • UH: Up to 180°C
    • EH: Up to 200°C
    • TH: Up to 220°C
  • Higher letters indicate better resistance to demagnetization forces like heat.

Considerations for Magnet Selection

Strength Needs

  • The strongest magnet isn't always the best choice. For example, sensor magnets may require a specific magnetic field, and using a too-strong magnet could cause malfunctions.

Cost

  • Higher grades and higher coercivity magnets generally cost more. For instance, an N48H will be more expensive than an N48, and an N48SH will cost even more.

Coating Requirements

  • Depending on the environment, specific coatings might be necessary to protect the magnet. For example, if the magnet will be exposed to moisture or corrosive chemicals, a coating like nickel, epoxy, or gold might be required to prevent corrosion and ensure longevity.

Application Context

  • The final application might allow for combining magnets or using other materials to optimize performance, possibly allowing for lower-grade magnets.

Size and Shape

  • The physical dimensions of the magnet affect its performance. For very thin or small magnets, choosing a material with higher coercivity might be necessary to ensure durability.

Trade-offs in Magnet Selection

Balancing strength and coercivity is essential. For instance, if you need a magnet that can handle 180°C, a UH material will be necessary. A technical expert can help determine the best magnet based on your specific needs.

For more detailed assistance, contact a magnet specialist who can guide you through the selection process based on your unique application.

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