Neodymium magnet processing steps
In the manufacture of high-quality, high-tech neodymium magnets, there are many major production steps, plus many sub-steps. Every step is very important, and every step is an important part of a highly refined operation.
This is the main step. In fact, the alloy used to make the magnets is called PrNd because the two elements are so chemically similar that not only are they too similar to separate, but they are also so similar that they contribute only a small amount to the mass of the magnet Impact.
The following are the main steps.
Step 1: Mining rare earth ore
First, rare earth mines are discovered and then mined. Since rare earth mines are mostly open-pit mining, large-scale equipment is required to remove the ore after removing the soil cover.
Step 2: Ore Processing and Refining
Next, the rare earth ore is crushed and milled. The ore is then mixed with water and special chemicals to separate the rare earth elements from the tailings. Depending on the source of the ore, concentrates can also be electrorefined. Rare earth metals can be refined and extracted by electrochemistry, distillation, ion exchange or other techniques. Concentrates (refined ore) are then smelted. This means that it is heated to very high temperatures (~1500°C) so that valuable metals can be separated from useless materials in the ore.
Rare earth elements are often found along with other valuable metals, such as precious metals, and even large amounts of base metals, such as copper and nickel, so multiple steps are required to separate them.
The extraction of rare earths is very difficult because many rare earths have very similar properties, which makes extraction a challenge. This is one of the cost factors; because this refining method requires the use of expensive chemicals and time-consuming processes.
For example, it's not well known, but about 20-30% of the neodymium in neodymium magnets is true praseodymium. In fact, the alloy used to make the magnets is called PrNd because the two elements are so chemically similar that not only are they too similar to separate, but they are also so similar that they contribute only a small amount to the mass of the magnet Impact.
Step 3: Alloying
During the alloying process, small amounts of other metals are added to the NdFeB alloy to refine and modify the microstructure of the final product, improve its magnetic properties, and enhance the effect of other processes.
Step 4: Cast Strip
The alloy NdFeB is now ready for melting and strip casting. It's heated in a vacuum furnace, where a stream of molten metal is forced under pressure onto a cooling drum, where it cools rapidly at about 100,000 degrees per second. High cooling rates produce very small metal particles, which help simplify and enhance downstream processing. In addition, small particles are an important part of producing high-quality magnets.
Vacuum belt furnace rapidly solidifies NdFeB magnet material to form very small grains
Step 5: Hydrogen Fragmentation
Although the grains of tape casting are very small, the material from tape casting comes out of the casting machine in flake form, which must be reduced to powder to make magnets. The next step after this is hydrogen cracking - a process in which hydrogen is introduced to purposefully break down the magnet material. The metal is now brittle and can easily be broken into smaller pieces, which is why it is called hydrogen cracking. When machining most metals, processors avoid introducing hydrogen into the metal.
Hydrogen embrittlement is a major problem for many metals. In this case, hydrogen is deliberately introduced in order to decompose the material. Then it's easy to grind it down smaller in subsequent operations. The crushed material is now ready for the next step.
Hydrogen cracking is a step in the production of neodymium magnets that produces extremely small particles in the material.
Step 6: Jet Mill
A jet mill uses a high-speed flow of inert gas to grind NdFeB metal blocks into powder. The metal hits other metal powders inside the cyclone. Cyclone automatically classifies the particle size as they pass through the system, so a narrow and very favorable particle size distribution is maintained.
Due to the different aerodynamic characteristics of particles with different particle sizes, the cyclone airflow makes the particles naturally separate due to the pressure and speed of the airflow, so that the material cannot be in contact with both sides of the pressure vessel.
Jet Milling is a very clean and efficient method of grinding NdFeB metal into powder
Step 7: Forming Orientation
The powder is kept in an inert gas atmosphere and handled in a glove box before entering the automatic printing press. The powder enters the mold and is pressed between the plates under the action of a strong magnetic field, forming a block of material. The magnetic field orients the grain, keeping the magnetic domains in the designed orientation through all subsequent processing steps.
The magnetic field has two orientations: 1) aligned with the block, 2) perpendicular to the block. Sintered neodymium magnets are usually pressed vertically against the block to achieve the highest anisotropy (strongest north-south magnetization)
Step 8: Isostatic Pressing
The bulk material is bagged and immersed in a Cold Isostatic Press (CIP) under enormous pressure. This eliminates any remaining voids in the stone, and the air coming out of this pressure is much smaller than when it went in.
Step 9: Sintering
The compacts are removed from the bag and sintered. Sintering involves placing a metal block in a furnace at a very high temperature, just below the melting point of the metal. At temperatures >1000 °C, there is a large motion of individual atoms, which enables the bulk to have adequate magnetic and mechanical properties.
The magnetic domains maintain their orientation before sintering. At this temperature, full density is achieved and the block has shrunk to its final size.
Neodymium magnet material reaches full density in sintering furnace
Step 10: Temper
After sintering, there are pent-up stresses in the metal due to all the movement during sintering, so at lower temperatures, the block is heat treated in stages to reduce the stress.
The blocks are raised to a high hold temperature for a set time, then they are lowered to a lower hold temperature. Once the hold time is reached, the now stress-free block is slowly cooled to room temperature.
Step 11: Cutting, Machining and Grinding
Due to all the previous steps, NdFeB magnets already have a lot of added value. Cutting, machining and grinding are carried out according to a strict control plan, designed to minimize waste.
Wire cutting is performed with very fine wire to minimize kerf loss. In previous processes, machining and grinding were minimized through tight controls. Waste is reused and recycled.
Wire cutting machine for precise and economical cutting of magnets
Step 12: Surface Treatment
Most neodymium magnets now have a final finish before leaving the factory. The baseline treatment is nickel-copper-nickel plating, which protects the magnets from corrosion in most typical usage environments.
For a variety of reasons, some end users require no coating at all. Other coatings provide greater protection than Ni-Cu-Ni. Aluminum-zinc alloys provide better protection than NiCuNi. IVD aluminum is another option specified by the end user. Epoxy is an excellent coating for harsh environments and is specified by end users for applications where magnets may be exposed to salt spray.
JDM's corrosion-resistant coatings for all types of environments. This is a continuous spraying aluminum zinc coating production line.
Step Thirteen: Test
Magnet materials are tested and evaluated at nearly every process step, and records are kept for every data point. Faced with such intensive testing demands, BJMT maintains a large inventory of testing equipment internally to maintain and improve product quality, production efficiency and cost.
Rigorous testing ensures that only high-quality products are delivered to customers
Step 14: Magnetization
One of the final steps is magnetization. The material is placed inside an energized coil that generates a strong magnetic field for a short period of time. After the coil is de-energized, the magnetic field in the magnet remains.
Composition and process differences of NdFeB
High temperature neodymium magnets often require the addition of heavy rare earth elements (HREEs) such as dysprosium and terbium. Heavy rare earth elements improve the magnet's resistance to demagnetization in the presence of high temperature and reverse magnetic field.
The relative scarcity of heavy rare earth elements has led some leading NdFeB companies to develop methods and processes to reduce or eliminate the need for heavy rare earth elements in high temperature NdFeB magnet grades.
