What is rich neodymium phase?
Except main phase Nd2Fe14B, NdFeB have another important composition like rich boron phase and rich neodymium phase. Rich boron phase is harmful. Rich boron phase plays an important role in the magnetism formation of the sintered magnet alloys. It will promote the Hcj of the NdFeB magnet with proper rich neodymium phase.
What is HD strip?
HD strip is the NdFeB alloy pieces which are produced through the vacuum induction strip casting furnace. The thickness of strips is more uniform than the traditional casting craft alloys, and the phase composition ratio is higher. Rich neodymium phase scattered disperse. α-Fe is eliminated.
Why does powder size and oxygen content need to be controlled?
The smaller the NdFeB magnetic powder size is, the higher the corresponding coercivity and corrosion resistance will be, but future process is difficult to control. The narrower the powder size distribution is, the higher the property will be. The oxygen content mainly exists in rich neodymium phase. The oxygen in NdFeB has a destructive effect on the coercivity.
How should I detect the quality of coatings?
Check the appearance of coatings. Check the thickness of coatings. Drop test (mainly among the Zinc coated magnets), crosscut test (mainly among the Nickel coated magnets), PCT test, SST test, constant temperature and humidity test etc.
How should I shield the magnetic field?
Ferromagnetic materials can be used to shield the magnet field, and generally we use the ordinary iron sheets. We need to pay attention to the thickness of the iron sheet. If the sheet is too thin or its magnetic is in saturation, it can only shield part of the magnetic field and part of magnetic lines will spread out in all directions. The key to conduct magnetic field to form into magnetic circuit is to choose a high permeability material with proper size and shape to reduce the magnetic flux leakage.
What are the different types of magnets available?
There are 2 types of magnets: permanent magnets and electro-magnets. Permanent magnets emit a magnetic field without the need for any external source of power. Electro-magnets require electricity in order to behave as a magnet. There are various different types of permanent magnets, each with their own unique characteristics. Each different magnet has a wide range of grades that have properties slightly different from each other, though based on the same composition.
The below chart illustrates the types of magnets: Magnets highlighted in blue are what we are manufacturing now.
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 NdFeB and SmCo types.
What does a magnet do?
- Mechanical to mechanical - such as attraction and repulsion
- Mechanical to electrical - such as generators and microphones
- Electrical to mechanical - such as motors and loudspeakers
- Mechanical to heat - such as eddy current and hysteresis torque devices
- Special effects - such as Hall effect devices and magnetic resonance
- How permanent is a magnet's strength?
If a magnet is stored away from power lines, other magnets, high temperatures, and other factors that adversely affect the magnet, it will retain its magnetism essentially forever.
Will magnets lose their power over time?
Modern permanent magnets do lose a very small fraction of their magnetism over time. For SmCo magnet, for example, this has been shown to be less that 1% over a period of ten years.
What is a magnetic assembly?
A magnetic assembly consists of one or more magnets, and other components, such as steels, that generally affect the functioning of the magnets.
How should I assemble a magnet to my device?
If the 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. You should select the proper adhesives and adhesion method to ensure that there will be no mechanical distortions after adhesion. In addition, you must carefully test and examine the type, quantity, conditions, strength, and other properties and characteristics of the adhesives, and test for reliability.
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.
As with all adhesive applications, it is very important to ensure that all surfaces being bonded are clean and dry before bonding.
Do all grades of NdFeB still need to be coated?
NdFeB magnets have improved dramatically over the last 10 years. But they still contain iron and other reactive phases, and will rust. NdFeB is a blended powder before it is pressed into a magnet. The better the powder is mixed, the less "free" iron is available (small clumps of iron that do not mix with the other chemicals).
We recommend that NdFeB magnets be coated. This greatly extends the lifetime of the magnets. The benefit over time is great. Uncoated NdFeB materials can be used for prototypes and experiments as long as there is not an expectation that the material will remain rust free, particularly in harsh environments.
When does SmCo require coating?
SmCo is typically coated for medical applications to give a "sealing" coat of nickel. This is extra insurance against the rare flake of iron. Nickel can be good insurance against such flaking, by making the surface tougher. It also protects the magnet from sterilizing chemicals and other contaminates.
What's the difference between an open circuit and a closed circuit in a magnet application?
A magnet operating by itself is referred to as an open circuit application. There are a lot of open circuit applications, like permanent magnets used to actuate Hall effect devices and reed switches. Helmholtz coil measurements are open circuit tests since no other magnetic materials are in the flux path during the test. The permeance coefficient of an open circuit magnet is determined by the magnet’s geometry alone. For example, a magnet with a length equal to its radius will have a PC close to 1.0.
A true closed magnetic circuit would have the poles joined by a high permeability material and a Bd/Hd ratio of infinity, since Hd=0. This condition is approximated when a steel magnetizing fixture is used, or when magnets are tested in a permeameter. A true closed magnetic circuit has little practical value as no external flux is available to perform a function. However, many functional magnetic circuits are more closed than open, i.e. they have a high PC value. An estimate of the PC value for a magnetic circuit is the magnetic length of the magnets in the circuit divided by the length of the working gap. For a motor, this might be a 12.7mm thick magnet divided by a gap length of 0.635mm for an estimated PC value of 20.
Why are attraction forces stronger than repelling forces? Shouldn't the magnetic forces be equal and opposite?
Magnets in attraction produce an increasing field strength in the gap between them as they approach, and therefore greater force. The reason is that the effective system permeance coefficient (PC) increases as the magnets get closer. As they approach, more flux lines flow from one magnet to the other, rather than taking a path from North to South pole of the same magnet. This causes them to act increasingly more like a single, longer magnet with a greater load line slope, increasing the value of Bd and decreasing Hd for both magnets. (PC = Bd/Hd)
Since flux lines can not cross each other, the bucking magnetic fields of magnets in repulsion are compressed. Flux density in the radial component of the bucking fields increases in amplitude as the magnets approach each other, and more of their own external field (Bd) is pushed back into the magnets themselves, where it becomes part of the self demagnetizing field (Hd). Since Bd decreases while Hd increases, the PC value decreases as repelling magnets get closer and there is less external field available to create a repelling force. A repelling magnet arrangement can apply intense cross fields where magnetic domains have the least resistance to external influences, so some level of demagnetization may occur, depending on magnet geometry and the coercivity of the magnet. |