Frequently Asked Questions |
Magnets are universally used around us in many fields. Sometimes people may have kinds of questions related to magnets. Now we list several categories of questions which people often ask and the answers enclosed below for your reference. |
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Basics about magnets |
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Machining and handling magnets |
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Select and order magnets |
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Magnet-related Sketches |
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Basics about magnets
Which are the strongest magnets nowadays?
The most powerful magnets available today are the Rare Earths types. Of the Rare Earths, Neodymium-Iron-Boron types are the strongest. However, at elevated temperatures (of approximately 150C and above), the Samarium Cobalt types can be stronger that the Neodymium-Iron-Boron types (depending on the magnetic circuit).
What are Rare Earth Magnets?
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 and Samarium Cobalt types.
What are permanent magnets made of?
Modern permanent magnets are made of special alloys that have been found through research to create increasingly better magnets. The most common families of magnet materials today are ones made out of Aluminum-Nickel-Cobalt (Alnicos), Strontium-Iron (Ferrites, also known as Ceramics), Neodymium-Iron-Boron (Neo magnets, sometimes referred to as "super magnets"), and Samarium-Cobalt. (The Samarium-Cobalt and Neodymium-Iron-Boron families are collectively known as the Rare Earths.)
What is the Grade of a magnet?
The grade of a magnet directly refers to the Maximum Energy Product of the material that composes the magnet. It in no way refers to the physical properties of the magnet. Grade is generally used to describe how "powerful" a permanent magnet material is. The energy product is specified in the units Gauss Oersted. One MGOe is 1,000,000 Gauss Oersted. Grade N40 would have a Maximum Energy Product of 40 MGOe. The higher the grade the stronger the magnet.
Will magnets lose their power over time?
Modern magnet materials do lose a very small fraction of their magnetism over time. For Samarium Cobalt materials, for example, this has been shown to be less that 1% over a period of ten years.
What are the characteristics of magnets?
Magnets are characterized by three main characteristics. These are known as the:
1.) Residual Induction (given the symbol Br, and measured in Gauss). This is an indication of how strong the magnet is capable of being.
2.) Coercive Force (given the symbol Hc, and measured in Oersteds). This is an indication of how difficult it is to demagnetize the magnet.
3.) Maximum Energy Product (given the symbol BHmax, and measured in Gauss-Oersteds). This is an indication of what volume of magnet material is required to project a given level of magnetic flux.
How to measure the strength of the magnets?
Gauss meters are used to measure the magnetic field density at the surface of the magnet. This is referred to as the surface field and is measured in Gauss (or Tesla). Pull Force Testers are used to test the holding force of a magnet that is in contact with a flat steel plate. Pull forces are measured in pounds (or kilograms).
How to identify the poles of the magnets?
Three methods are listed as below can be used to distinguish the North and South poles of magnets.
1) Use a compass, the end of the needle that normally points North will be attracted to the South pole of the neodymium magnet.
2) Use another magnet that is already marked. The North pole of the marked magnet will be attracted to the South pole of the unmarked magnet.
3) Use a Gauss Meter.
Are there any Industry Standards for Magnets?
Yes. Two industry associations produce standards. The Magnetic Materials Producers Association (MMPA) publishes standards for the production of magnetic materials, and the Magnet Distributors and Fabrications Association (MDFA) produces standards on various ways of testing magnets and magnetic devices.
What are the maximum operating temperatures for different magnet materials?
The maximum temperature that a magnet may be effectively used at depends greatly on the 'Permeance Coefficient' - which is a function of the magnetic circuit - the magnet is operating in. The higher the permeance coefficient (the more 'closed' the circuit), the higher temperature at which the magnet may operate at, without becoming severely demagnetized. Shown here are approximate maximum operating temperatures for the various classes of magnet material. At temperatures close to those listed here, special attention may be needed in order to ensure that the magnet will not be demagnetized.
Material |
Approx. Maximum Operating |
Temperatures: |
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°C |
°F |
| NdFeB |
140 |
284 |
| SmCo |
300 |
572 |
| Ferrite |
300 |
572 |
| Alnico |
540 |
1,004 |
| Flexible |
100 |
212 |
Machining and handling magnets
Can I machine magnets?
Absolutely 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 is the machining process of sintered NdFeB magnets?
Basically the main machining process includes burdening, smelting, pulverization, molding, sintering, testing, machining, electroplating, magnetizing, final examining and packing.
What factors determine the cost of machine magnets?
Quantity - the larger the quantity, the lower the cost since set-up charges must be amortized over the quantity, and special tooling can be created to machine larger quantities;
Material - SmCo materials are more costly to machine since they are very brittle, flexible materials are very inexpensive to machine because of their physical characteristics;
Shape - complex shapes are more expensive than simple shapes; and,
Tolerances - the closer the required tolerances, the more expensive it will be to machine the magnets.
What might affect a magnet's strength?
The factors below can affect a magnet's strength:
Heat.
Radiation.
Strong electrical currents in close proximity to the magnet.
Other magnets in close proximity to the magnet.
Neo magnets will corrode in high humidity environments unless they have a protective coating.
Shock and vibration do not affect modern magnet materials, unless sufficient physically damage to the materials.
How can I block the 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, credit cards and computer monitors.
Store magnets in closed containers, so that they don't 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!
If a magnet which has lost its magnetism can be re-magnetized?
The magnet can be re-magnetized back to its original strength, provided that the material has not been damaged by extreme heat.
How to separate the magnets?
Small magnets can be part by hand, sliding bit by bit off other magnets. If they are of big size, you can separate them by using edge of desk or corner. Place magnets on the desk with a magnet hanging over ,then use your whole body to press the magnet down, but you should be careful at the same time, do not get off your balance. Now there are two easy ways, magnets are colored in grey.
1.Use two nailed sticks, put the magnets between the sticks, please refer to the sketch as below;
2.Use one object to press one magnet, then use another heavy object to push down the other magnet, please refer to the sketch as follows;
How to assemble magnets to a 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.
Select and order magnets
How to select a grade of magnets?
Selecting a grade is the next step, once you have decided which permanent magnet material is best for your application. Generally, a grade indicates the Maximum Energy Product of a magnet. For instance, Grade 32 implies the (BH) max is about 32 MGOe. A higher grade of permanent magnet has a better performance. However, higher grade is usually associated with a higher cost. Taking sintered Nd-Fe-B magnets as an example, the price of Grade 45 is twice and even more of that of Grade 33. Other property parameters, such as Br and Hci, also need to be considered in selecting a grade. One way to select the suitable grade for your application is "trial and error". You can purchase the several magnets with different grades (some suppliers have these magnets available on their shelves) and try each grade until you find one right for your application.
How do I order magnets?
To order magnets efficiently, you need to have a good idea of what you want to accomplish. Here are a few items that you should take into considerations:
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.
What factors are needed when you inquire magnets?
Please kindly provide us the following factors when you inquire magnets.
Material: Sintered NdFeB Magnet (our leading product), Bonded NdFeB Magnet, Ferrite Magnet, or SmCo Magnet...
Grade: N35, N45, N50, BNP-6, BNP-8, BNP-10, Y30, SmCo 5....
Size: If the size was very complicated, please offer me a drawing.
Coating: Ni, Zn. Gold, Cr, Ag...
Magnetization: Magnetized or not
Magnetization direction: through thickness, diameter and so on.
Quantity: It is very important for us to quote clearly.
How do you pack the magnets to ensure shipments safely?
We use carton and steel partition to pack the goods and ensure that every box is firm, secure and non-magnetic in accordance with national and international transportation regulations. If you have other specific packing requirements, please let us know in advance.
Magnet-related Sketches
Display of the lines of Magnetic flux
Lines of force are three dimensional, surrounding a bar magnet on all sides. Homopolar repels and heteropolar attracted.
When opposite poles are approaching, the lines of force join up and the magnets pull together.
But the same poles will repel when they close to each other.
Sketch of Magnetization direction
Different shaped magnets have different kinds of magnetization direction. Please refer to the enclosed sketch below:
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