Modern magnet materials are made through casting, pressing and sintering, compression bonding, injection molding, extruding, or calendaring processes. Once manufactured, magnets often need to be further processed by grinding or other machining processes, and then assembled into a next-level assembly.
There are three types of magnets: permanent magnets, temporary magnets, and electromagnets
There are many different types of permanent magnet materials, each with their own unique characteristics. Each material has a family of grades that have properties slightly different from each other, though based on the same composition
Modern permanent magnets are made of special alloys that have been found through research to create increasingly better magnets. The most common families of permanent magnet materials today are made out of aluminum-nickel-cobalt (alnicos), strontium-iron (ferrites, also known as ceramics), neodymium-iron-boron (a.k.a. neodymium magnets, or "super magnets"), and samarium-cobalt-magnet-material. (The samarium-cobalt and neodymium-iron-boron families are collectively known as the rare-earths).
Rare Earth magnets are magnets that are made out of the rare-earth group of elements. The most common rare-earth magnets are the neodymium-iron-boron (neo magnets) and samarium cobalt (SmCo magnets).
Soft iron and certain iron alloys, such as permalloy (a mixture of iron and nickel) can be very easily magnetized, even in a weak field. As soon as the field is removed, however, the magnetism is lost. These materials make excellent temporary magnets, like those used in telephones and electric motors
Electromagnets are used when very strong magnets are required. Electromagnets are produced by placing a metal core (usually an iron alloy) inside a coil of wire that carries an electric current. The electricity in the coil produces a magnetic field. The strength of the electromagnet depends on the strength of the electric current and the number of coils of wire. Its polarity depends on the direction of the current flow. While the current flows, the core behaves like a magnet, but as soon as the current stops, the magnetic properties are lost. Electric motors, televisions, maglev trains, telephones, computers, and many other modern devices use electromagnets.
These are electrical currents that are induced when a magnetic field moves in relation to an electrical conductor that has been placed within reach of the magnetic field. In turn, these eddy currents create a magnetic field that acts to stop the relative motion of the original magnetic field and electrical conductor
If stored away from factors that adversely affect the magnet such as power lines, other magnets, high temperatures etc., a magnet will retain its magnetism essentially forever.
Factors that can affect a magnet's strength include:
Shock and vibration do not affect modern magnet materials, unless sufficient to physically damage the material.
Modern magnet materials do lose a very small fraction of their magnetism over time. With samarium cobalt magnets, for example, this has been shown to be less than 1% over a period of ten years.
Once a magnet is fully magnetized, it's "saturated" and cannot be made any stronger. In that sense, magnets are like buckets of water: once they are full, they can't get any "fuller".
Provided that the material has not been damaged by extreme heat, most magnets can be re-magnetized back to their original strength.
Most commonly, Gaussmeters, magnetometers, or pull-testers are used to measure the strength of a magnet. Gaussmeters measure the strength in Gauss; Magnetometers measure in Gauss or arbitrary units (making it easy to compare one magnet to another); pull-testers measure pull in pounds, kilograms, or other force units. Helmholtz Coils, search coils and permeameters are also used to make sophisticated measurements of magnets.
No. The Br value is measured under closed-circuit conditions. A closed-circuit magnet is not of much use. In practice, you will measure a field that is less than 12,300 Gauss close to the surface of the magnet. The actual measurement will depend on whether the magnet has any steel attached to it, how far away from the surface you make the measurement, and the size of the magnet (assuming that the measurement is being made at room temperature).
For example, a 1" diameter Grade 35 neodymium magnet that is ¼" long will measure approximately 2,500 Gauss when 1/16" away from the surface, and 2,200 Gauss when 1/8" away from the surface.
The strength of a magnetic field drops off more or less exponentially over distance.
Here is an example of how the field (measured in Gauss) drops off with distance for a samarium cobalt Grade 18-disc magnet which is 1" in diameter and 1/2" long:
For a circular magnet with a radius of R and length L, the field Bx at the centerline of the magnet at distance X from the surface can be calculated by the following formula, where Br is the residual induction of the material):
There are additional formulae that can be used to calculate the field from a rectangular magnet and magnets in other configurations.
Only materials that are attracted to a magnet can "block" a magnetic field. Depending on how thick the blocking piece is, it will partially or completely block the magnetic field.
Magnetic poles are the surfaces from which the invisible lines of magnetic flux emanate and connect on return to the magnet.
The north pole is defined as the pole of a magnet that, when free to rotate, seeks the north pole of the earth. In other words, a magnet's north pole will seek the earth's north pole. Similarly, the south pole of a magnet seeks the south pole of the earth.
Lines of force are three-dimensional, surrounding a bar magnet on all sides.
Like poles repel and unlike poles attract. When opposite poles of a magnet are brought together, the lines of force join up and the magnets pull together.
When like poles of a magnet are brought together, the lines of force push away from each other and the magnets repel each other.
Most modern magnet materials have a "grain" in that they can be magnetized for maximum effect only through one direction. This is the "orientation direction", also known as the "easy axis", or "axis".
Un-oriented magnets (also known as "Isotropic magnets") are much weaker than oriented magnets, and can be magnetized in any direction. Oriented magnets (also known as "Anisotropic magnets") are not the same in every direction - they have a preferred direction in which they should be magnetized.
Yes, magnets can be machined. However, hard magnet materials are extremely difficult to machine, unlike flexible or rubber-type magnet materials. Magnets should be machined in the unmagnetized state as much as possible, using diamond tools and/or soft grinding wheels. In general, it is best not to try to machine hard magnet materials unless you are familiar with these specialized machining techniques.
Magnetic Assemblies consists of one of more magnets, along with other components, such as steel, that generally affect the functionality of the magnet.
If a magnet must be fastened to a device, you can use either mechanical means or adhesives to secure the magnet in place.
Adhesives are often used to secure magnets in place. If magnets are being adhered to uneven surfaces, an adhesive with plenty of "body" is required so that it will conform to the uneven surface. Hot glues have been found to work well for adhering magnets to ceramics, wood, cloth, and other materials. For magnets being adhered to metal, "super glues" can be used very effectively.