How Sintered Neodymium Magnets are Made
We describe the steps concerned in manufacturing neodymium magnets, with some notes on what this implies for sensible magnet customers.
1. Prepare Materials for the Reaction
The fundamental compound for many Neodymium magnets is Nd2Fe14B. In observing, the precise chemical response used could be extra difficult. A generally used response is:
57 Fe + 8 B + 10 Fe2O3 + 7.5 Nd2O3 + 52.5 Ca -> Nd15Fe77B8 + 52.5 CaO
Notice that the powder fashioned by this response is barely completely different than the Nd2Fe14B ratio. Magnets are sometimes made each Nd-rich and B-rich, the place completed magnets sometimes comprise non-magnetic bits of Nd and B within the grain, inside that are extremely magnetic Nd2Fe14B grains.
For greater temperature magnet grades, further parts are added. When small quantities of Iron (Fe) are changed with Cobalt (Co), the properties enhance at elevated temperatures, however, the intrinsic coercivity decreases. If small parts of Neodymium (Nd) are changed with Dysprosium (Dy), the intrinsic coercivity is improved, however, the most power product (BHmax, the measure of a magnet’s power) decreases. It is not uncommon to make use of each Co and Dy collectively.
The chemical response described above happens in a vacuum induction furnace. The merchandise is heated by creating electrical eddy currents by it, all in a vacuum to maintain contaminants out of the response.
Jet milling turns the ensuing materials right into a powder with a really small particle dimension. The typical particle dimension is on the order of three micrometers.
The powder is pressed collectively to type a strong that has a most popular magnetization course. In a way often known as die-upsetting, the powder is pressed with a die right into a strong at elevated temperatures of about 725°C. The strong is then positioned in a second die, the place it’s compressed to a wider form that is about half it is authentic top. This aligns the popular course of magnetization parallel to the urgent course. For some shapes, there are strategies that embody a fixture that generates a magnetic area throughout urgent to align the particles.
Sintering is a typical course of in powder metallurgy. The fabric is compressed at elevated temperatures (as excessive as 1080°C) under the fabric’s melting level, till its particles adhere to one another.
The sintered magnets are minimized to the specified form utilizing a grinding course of. Much less generally, complicated shapes are made with electrical discharge machining (EDM). Due to the excessive materials value, materials losses because of machining are saved to a minimal. No efficient technique of recycling the waste has been developed.
The person magnets are electroplated with three layers: nickel, copper, and nickel. That is crucial as a result of un-plated neodymium magnets are extremely susceptible to corrosion, and can rapidly lose their magnetic properties within the presence of moisture.
At this level, the magnets have a “most popular” course of magnetization, however, they don’t seem to be magnetized. They’re positioned in a fixture that can expose the magnet to a really sturdy magnetic area for a quick second. It is mainly a giant coil of wire surrounding the magnet(s). The magnetizing tools make use of banks of capacitors and an extremely large voltage to get such a powerful present for a quick instantaneous.
The standard of the ensuing magnets is inspected for quite a lot of properties. A digital measuring projector verifies the scale. A coating thickness measurement system utilizing x-ray fluorescence know-how verifies the thickness of the plating. Periodic testing in salt-spray and pressure-cooker assessments additionally confirm the efficiency of coatings. A hysteresis graph measures the BH Curve of magnets, which confirms that they’re absolutely magnetized as anticipated for the magnet’s grade.
What all this implies for customers of neodymium magnets
- Neodymium magnets are fashioned by powder metallurgical strategies. Their mechanical properties extra intently resemble a ceramic, slightly than a metallic. They aren’t simply machined, and we do not suggest making an attempt to machine them. See our FAQ for extra particulars.
- Neodymium magnets are very onerous and brittle. Regardless of the metallic look of their nickel plating, they don’t seem to be sturdy as metal. If subjected to sharp impacts, comparable to permitting them to slam into each other, they will simply crack or break. Care and correct dealing with are vital.
- We do not suggest press-fitting neodymium magnets. Magnets are sometimes glued right into a pocket that’s barely bigger than the magnet, slightly than press-fitting.
- We do not suggest utilizing a threaded magnet. Whereas it is technically attainable to chop threads, they do not maintain up nicely below torque. A magnet hooked up to a component with metal threads works higher, like a few of our Mounting Magnets.
- Neodymium magnets cannot be made into very complicated shapes that supply like metal or aluminum permit. It is best to try to design half-complexity into different components and use extra easy shapes in your magnets.
- If you’re in search of a selected dimension or form that we do not supply as an inventory magnet, ask us about customized magnets.
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