Rare Earth Magnet Powder Classification for Grain Size Control
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Solution Overview
Problem
Existing methods for producing rare earth magnets result in magnetic powders that are chemically reactive, leading to powder fires and poor orientation, which impairs the remanence and coercive field strength of the magnets due to high volumes of fine and coarse particles.
Innovation Solution
A method involving the comminution of rare earth metal alloys, followed by classification based on particle size and density using dynamic and static classifiers to produce a starting material with a targeted particle size range of 2-8 μm, reducing the volume percentage of fine and coarse particles to ≤2%, thereby enhancing the magnetic properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If magnetic powder is produced by grinding alloys in fluid bed jet mills, then fine grinding with defined upper grain limit is achieved, but high volume percentage of fine particles causes chemical reactivity and powder fires
Solution Approach 1:
The harmful fine particles are extracted and separated from the magnetic powder using classification devices such as air classifiers or hydrocyclones. This removes the reactive fine fraction that causes powder fires while retaining the desired magnetic properties in the coarser fraction.
Solution Approach 2:
The particle size distribution is changed by implementing multiple grinding stages with intermediate classification. The process transitions from producing fine powder to producing a controlled mix of particle sizes, specifically reducing the fine particle fraction below 10 μm while maintaining adequate overall fineness for magnetic properties.
2Manufacturing precision
If magnetic powder contains high volume percentage of fine particles, then defined fine grinding is achieved, but orientation of particles is poor which impairs remanence
Solution Approach 1:
Different particle size ranges are assigned different functions: coarser particles (10-50 μm) provide structural integrity and good orientation, while a controlled amount of finer particles fills voids. This local differentiation of particle sizes optimizes both orientation and magnetic properties.
Solution Approach 2:
The particle size distribution is dynamically optimized by adjusting classification parameters during production. The process adapts the ratio of fine to coarse particles based on specific magnet requirements, balancing orientation needs with filling efficiency.
3Stability of the object's composition
If magnetic powder contains high volume percentage of coarse particles, then chemical stability is improved, but opposing field stability and coercive field strength require improvement
Solution Approach 1:
The magnetic powder is designed as a composite of different particle sizes and compositions. Coarser particles provide chemical stability and structural framework, while finer particles enhance magnetic properties and fill interstices, creating a synergistic composite material that achieves both stability and magnetic performance.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The process produces rare earth magnets with improved remanence, coercive field strength, and reduced chemical reactivity, resulting in higher quality magnets with enhanced temperature stability and corrosion resistance.
Implementation Method 1
at least one dynamic classifier for separating a fraction from the powdery intermediate product which forms the starting material intended for the production of rare earth magnets via classification of the powdery intermediate product based on particle size and/or density
Implementation Method 2
A first step of the method involves comminution of an alloy comprising at least one rare earth metal, with a powdery intermediate product being formed from the alloy comprising at least one rare earth metal
Data Source
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AI summary
The invention relates to a method for producing a powdered starting material (AM) intended for the manufacture of rare-earth magnets. The method comprises the following steps: - comminution of an alloy comprising at least one rare-earth metal, wherein a powdered intermediate product (ZP) is obtained from the alloy comprising at least one rare-earth metal, and - performing at least one classification of the powdered intermediate product (ZP) based on particle size and/or density, wherein a fraction of the powdered intermediate product (ZP) formed by the at least one classification constitutes the starting material (AM) intended for the manufacture of rare-earth magnets. At least one dynamic classifier is also provided.A portion separated from the powdered intermediate product (ZP) by means of the at least static classifier is fed to at least one dynamic classifier (10), which performs at least one classification based on particle size and/or density for the portion separated from the powdered intermediate product (ZP) by means of the at least one static classifier and thereby separates the fraction from the portion which forms the starting material (AM) intended for the manufacture of rare earth magnets.