Magnetics Business & Technology - Winter 2012 - (Page 10)

WHITE PAPER Magnet Materials and Their Properties Magnet Materials, Their Composition, Applications and Technical Capabilities Permanent, soft and electro-magnets are a vital part of everyday life. They are found in or used to produce almost every modern convenience today. Magnet channels and products continue to advance with the changing needs of the marketplace. Through the years, customer requirements have become more advanced, from the magnet distribution needs of the early 1950s to the custom permanent magnet machining required for today’s applications. There are a number of major families of permanent magnets available for designers, ranging from ferrite, known for its low cost and low energy, to rare earth materials, which are more expensive and offer higher performance. Designers need to analyze magnetizing field strength and magnetic output of magnetic materials prior to deciding on the appropriate magnet. As seen in Figure 1, magnetizing intensity for each material is shown verses that material’s magnetic flux density. Below is a general overview of select magnet materials addressing technical and application requirements. Magnet Materials and Their Applications Alnico - As one of the first magnet ma- Figure 1. Figure 2. terials, Alnico was developed in the early 1930s. During World War II it was used in military electronic applications and after the war it quickly spread into civilian versions of applications and replaced magnet steel in many applications. High induction levels with good resistance to demagnetization and stability, due to its low temperature coefficient (0.02 percent /°C), at a reasonable cost made Alnico the material of choice. Alnico magnet material is made by alloying aluminum, nickel and cobalt with iron. Some grades also contain copper and/or titanium. The alloying process used is casting or sintering. The process and the heat treatment needed to optimize magnetic properties produces hard (Rc45) and brittle parts that are best shaped or finished by abrasive grinding. Cast parts are gen- erally under 70 pounds and may be used as-is, but polar surfaces are usually ground flat and parallel. Sintering is confined to high volume parts in sizes under one cubic inch and an effective press length to diameter ratio under four. A high working temperature limit (550°C/1,020°F) makes Alnico well-suited for sensitive automotive and aircraft sensor applications. Alnico is produced in many grades to fit the requirements of these applications, from Alnico 1 to Alnico 12, but the most popular grades are 2, 5 and 8. By comparison to newer materials, the coercivity of Alnico is low. Where Alnico is appropriate, magnet size can be minimized if it can be magnetized after assembly into the magnetic circuit. If used independent of other circuit components, as in security applications, the form factor (related to the permeance coefficient) must be great enough to cause the magnet to work above the knee in its second quadrant demagnetization curve. For critical applications, Alnico magnets may be calibrated to an established reference flux density value. A by-product of low coercivity is sensitivity to demagnetizing effects due to external magnetic fields, shock and application temperatures. For critical applications, Alnico magnets can be temperature stabilized to minimize these effects Ceramic (Hard Ferrite) - Ferrite magnets, sometimes referred to as ceramic because of their production process, are the least expensive class of permanent magnet materials. The material became commercially available in the mid 1950s and has since found its way into countless applications including arc shaped magnets for motors, magnetic chucks and magnetic tools. The raw material, iron oxide, for these 10 Magnetics Business & Technology • Winter 2012

Table of Contents for the Digital Edition of Magnetics Business & Technology - Winter 2012

Magnetics Business & Technology - Winter 2012
Editor's Choice
Permanent Magnet Industry Outlook - 2013
Magnet Materials and Their Properties
Magnets • Materials • Measurement
Application • Component Developments
Magnetics 2013: Conference Preview
Research & Development
2012 Resource Guide
Industry News
Advertising Index
Spontaneous Thoughts: Retired, Senile and Dead

Magnetics Business & Technology - Winter 2012