A little history....
The ancient Greeks and Chinese discovered that certain rare stones possessed mysterious and attractive properties. These stones could attract small pieces of iron in a magical way, and were found to always point in the same direction when allowed to swing freely, suspended by a piece of string, or floating on water. Early navigators used these magnets for the first compass to help them determine their direction while at sea.
The name MAGNET comes from Magnesia, a district in Thessaly, Greece where it is believed that these first "lodestones" were mined.
Over the millennia magnets have evolved into the high strength materials we have today. It was discovered that by creating alloys of various materials we could create similar effects to those found in lodestones, and increase the level of magnetism. It was not until the 18th century that the first man-made magnets were created, and progress in creating stronger magnetic alloys was very slow until the 1920s when Alnico (an alloy of nickel, aluminum and cobalt) was formulated. Ferrites (also known as Ceramics) were created in the 1950s and the Rare Earths in the 1970s. Since then, the science of magnetism has exploded exponentially and extremely powerful magnetic materials have made possible the myriad devices that we have today.
What is the strength of the Earth's magnetic field?
The surface field strength of the Earth is about 0.75 gauss, but it varies by as much as 10% depending on the strength of the "crustal field". A range from 0.85 to 0.60 can be found across the globe. Geomagnetic storms can cause changes of between 1% to 5% that last from hours to a day or so.
What are Magnetic Poles?
Magnetic Poles are the surfaces from which the invisible lines of magnetic flux emanate and connect on return to the magnet.
What are the standard industry definitions of "North" and "South" Poles?
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, the North Pole of a magnet seeks the North Pole of the Earth. Similarly, the South Pole of a magnet seeks the South Pole of the Earth.
How can you tell which is the North Pole if it is not marked?
You can't tell by looking. You can tell by placing a compass close to the magnet. The end of the needle that normally points toward the North Pole of the Earth would point to the South Pole of the magnet.
How do lines of magnetic flux behave?
The general answer is "Predictably"!
Lines of force are three dimensional, surrounding a bar magnet on all sides.
|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.|
What does "orientation direction" mean?
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.
Is there such a thing as a temporary magnet?
Soft iron and certain iron alloys 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 that are used, for example, in telephones and electric motors.
What are electromagnets?
Electromagnets are produced by placing a metal core (usually an iron alloy) inside a coil of wire carrying an electric current. The electricity in the coil produces a magnetic field, which is conducted through the iron core. Its strength 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.
What is a magnetic assembly?
A magnet assembly consists of one or more magnets, and other components, such as steel, that generally affect the functioning of the magnet.
How should I assemble magnets to my device?
If a magnet needs to 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, you will need an adhesive with plenty of "body" 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.
We can supply Flexible magnets with an adhesive already attached to the magnet: all you need to do is to peel off the liner and attach to your product.
As with all adhesive applications, it is very important to ensure that all surfaces being bonded are clean and dry before bonding.
Can I machine magnets?
Magnets can be machined. However, hard magnet materials - as opposed to the flexible or rubber type magnet materials - are extremely difficult to machine. Magnets should be machined using diamond tools or soft grinding wheels, and in the unmagnetized state as far as possible. In general, it is best not to try to machine hard magnet materials unless you are familiar with these specialized machining techniques.
What can I use to block a magnetic field?
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.
Tips on handling and storing magnets
- Always take care! Magnets can snap together and injure personnel or damage themselves.
- Keep magnets away from magnetic media - such as floppy discs and credit cards - and computer monitors.
- Store magnets in closed containers, so that they do attract metal debris.
- If several magnets are being stored, they should be stored in attracting positions.
- Alnico magnets should be stored with "keepers" (iron or magnetic steel plates that connect the poles of the magnet) since they can easily become demagnetized.
- Magnets should be kept away from pacemakers!
What do magnets cost?
The costs of different magnet materials vary significantly from one to the other. Here is an approximate guide as to what magnets cost.
* Note: the costs shown here are relative costs based on high volumes of magnet materials that have no special machining or other characteristics.
|Material||BHmax (MGOe)||Relative Cost|
On a cost-per-pound basis, Neodymium magnets seem very costly. However, on a cost per BHmax basis, they do not seem so costly. Often by using a more powerful magnet, the entire device that the magnet goes into can be miniaturized, yielding cost savings that favor the more powerful magnet materials.
How do I order magnets?
To efficiently order magnets, you need to have a good idea of what you want to accomplish. Here are a few items that you will need to consider:
- General nature of application - Holding, moving, lifting, etc.
- Shape of magnet desired - Disc, Ring, Rectangle, etc.
- Size of magnet desired - Diameter, length, width, height, etc.
- Tolerances - what variation in dimensions is allowed.
- Conditions magnet will be used in - Elevated temperature, humidity, outside, inside, etc.
- Strength of magnet required - In pounds of holding force, Gauss, etc.
- Magnet should cost no more than? - This will eliminate certain materials from consideration.
- Quantities you will need
Contact MagnetShop today for answers to all of your custom magnet questions!