Permanent Magnet Applications Guide
How are magnets used? To answer this question, let’s review the key features of each of our product groups, identify specific applications for each product, and then go into detail about the operation of various magnetic devices.
Categories of Permanent Magnet Applications with Examples
Permanent magnet applications can be divided into four categories, as follows:
Applications that make use of the tractive and/or repelling force of the magnet, i.e., the attraction between a magnet and a soft magnetic material, such as a piece of iron or steel, or the attraction or repulsion between two magnets, is used to do mechanical work. The following applications are in this category:
- Magnetic separators, magnetic holding devices, such as magnetic latches.
- Magnetic torque drives
- Magnetic bearing devices
Applications that make use of the magnetic field of the magnet to convert mechanical energy to electrical energy. Some of these applications are:
- Generators and alternators
- Eddy current brakes (used widely for watt-hour meter damping). (This application could be listed under electrical to mechanical energy conversion; but as mechanical energy is used to create the eddy currents, it will be discussed with this group.)
Applications that make use of the magnetic field of the magnet to convert electrical energy to mechanical energy. Some of these applications are:
- Actuators, linear, and rotational
Applications that use the magnetic field of the magnet to direct, shape and control electron or ion beams. Some of these applications follow:
- Magnetic focused cathode-ray tubes
- Traveling Wave Tubes
- Magnetrons, BWO’s, Klystrons
- Ion Pumps
Matching Arnold Products to Applications
The purpose of a permanent magnet is to produce flux in the working gap of a device. Obviously all permanent magnetic material will produce flux, but depending upon the working application, certain material types, grades and shapes will be more efficient than others. The following is a breakdown by product line applications that are most suitable for a material’s characteristics:
The key attributes of Cast Alnico are:
- Mechanically strong
- Cast to a variety of shapes
- Very temperature stable
- Can change magnetic orientation
- High Br and Bhmax characteristics compared to ceramic materials.
The key attributes of Sintered Alnico are:
- Mechanically strongest of the Alnicos
- Close tolerance pressing/typically minimum grinding
NOTE: Both cast and sintered Alnico have low Hc when compared to ceramic or rare earth materials.
General applications for both cast and sintered Alnico are:
- Electron tubes, radar, traveling wave tubes.
- Separators, holding magnets, coin acceptors, clutches and bearings.
- Magnetos, motors, generators, meters, instruments, controls, relays, watt-hour meters (bearings and dampeners).
- Communications, receivers, telephones, microphones, bell ringers, musical instruments (guitar pickups).
- Automotive sensors, loudspeakers, cow magnets, distributors.
FERRITE (CERAMIC) MAGNETS
Key attributes of ceramic magnets & Arnold’s products are:
Economical High Hc and Hci compared to Alnico
On the negative side, ceramics are good for simple shapes only, very fragile, require expensive tooling, and temperature sensitive (0.2%°C.)
FERRITE MAGNET APPLICATIONS
Generally ceramic magnets are used in:
DC permanent magnet motors used in the automobile industry for blowers, window lifts, windshield wipers, etc. (NOTE: Many of the motors come from outside sources not tied directly to the auto company itself). Separators to remove ferrous materials from liquid powder and bulk commodities.
Magnetic Resonate Imaging, MRI
Magnetos used on lawnmowers, garden tractors and outboard motors.
DC brushless motors with controllers for speed and direction.
While being quite expensive, samarium cobalt magnets are:
High Hc and Hci
Very good temperature stability
Powerful for size
On the negative side, samarium cobalt is price sensitive due to cobalt supply and demand.
SAMARIUM COBALT APPLICATIONS
Samarium Cobalt is used in these general applications:
Traveling wave tubes
Computer rigid disc drives
D.C. Motors (where temperature stability is vital, such as, Military use-satellite systems, small military motors) sensors, growing automotive applications and linear actuators.
Key reasons for using Neodymium are:
High energy for size
More economical than Samarium Cobalt
Good in ambient temperature situations
Very high Hc and Hci output
On the negative side of neodymium are relatively high price, corrosion that can result in loss of energy, and temperature coefficient of .13%/ degree centigrade.
Some of the ever-growing list of uses are:
Computer rigid disc drives
DC Motors & Automotive starters
While we make every effort to ensure that the information contained in these documents is complete and accurate, we make no warranty regarding this. Please see our disclaimer statement. We would appreciate your input, so please contact us regarding corrections, additions and suggestions for improvement.