Rare-Earth Magnet Binder Decomposition for Sintering Precision
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Solution Overview
Problem
The powder sintering method for manufacturing rare-earth permanent magnets results in porosity issues, leading to deformations, inhomogeneous density, and degradation of magnetic properties due to the presence of carbon and oxygen-containing substances in the binder, which affect the sintering process and magnetic performance.
Innovation Solution
A manufacturing method involving milling magnet material into powder, mixing with a binder made of long-chain hydrocarbons or polymers without oxygen atoms, forming a green sheet, decomposing the binder in a non-oxidizing atmosphere, and sintering at high temperatures to reduce carbon and oxygen content, thereby preventing magnetic property degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If powder sintering method is used to manufacture permanent magnet, then manufacturing process is established, but deformations such as warpage and depressions occur due to non-uniform contraction during sintering
Solution Approach 1:
The invention applies preliminary magnetic field orientation to the magnet powder before sintering. By orienting the magnetic particles in the desired direction prior to sintering, the magnet achieves both the required magnetic performance and dimensional stability, preventing warpage and depression during the sintering process.
Solution Approach 2:
The invention controls the porosity parameter of the magnet powder within a specific range (3-15%) to optimize both sintering behavior and magnetic field orientation. This parameter control ensures uniform contraction during sintering while maintaining adequate space for magnetic field alignment.
2Ease of manufacture
If powder sintering method is used to manufacture permanent magnet, then manufacturing process is established, but surface distortion occurs due to pressure unevenness during pressing
Solution Approach 1:
The invention optimizes the porosity parameter of the magnet powder to a specific range (3-15%), which ensures uniform pressure distribution during pressing and prevents surface distortion. This parameter control eliminates the need for subsequent diamond cutting and polishing operations.
3Ease of manufacture
If binder containing carbon or oxygen atoms is used in green sheet formation, then green sheet can be formed, but magnetic performance degrades due to carbide formation and gap creation during sintering
Solution Approach 1:
The invention uses a binder composed exclusively of hydrogen and carbon atoms (such as polyethylene, polypropylene, or polyvinylidene fluoride) that contains no oxygen atoms. This inert composition prevents oxidation reactions during sintering, eliminating carbide formation and gap creation, thereby preserving magnetic performance.
Solution Approach 2:
The invention employs a specific composite binder material with a molecular structure containing only hydrogen and carbon atoms (or fluorine in the case of PVDF). This specialized composite binder provides both green sheet formation capability and chemical inertness during high-temperature sintering.
4Shape
If thin-film magnet is cut from bulk body, then desired shape is achieved, but material yield decreases and manufacturing time increases
Solution Approach 1:
The invention performs preliminary shaping of the magnet powder into the exact desired geometry before sintering by applying magnetic field orientation in the specific direction required for the final product. This preliminary action eliminates the need for post-sintering cutting operations, maximizing material yield and reducing manufacturing time.
Solution Approach 2:
The invention controls the porosity parameter within 3-15% to enable direct forming of thin-film magnets with precise dimensions during the sintering process itself, eliminating the need for subsequent cutting and polishing operations.
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
This method ensures uniform contraction and dimensional accuracy of the magnets, reduces the number of manufacturing steps, and prevents the separation of alpha iron, leading to improved magnetic performance and coercive force by minimizing carbon and oxygen content.
Implementation Method 1
decomposing the binder from the green sheet by holding the green sheet for a predetermined length of time at binder decomposition temperature in a non-oxidizing atmosphere
Implementation Method 2
sintering the green sheet from which the binder has been removed by raising temperature up to sintering temperature
Data Source
AI summary
There are provided a rare-earth permanent magnet and a manufacturing method thereof capable of preventing deterioration of magnet properties. In the method, magnet material is milled into magnet powder. Next, a mixture is prepared by mixing the magnet powder and a binder made of long-chain hydrocarbon and/or of a polymer or a copolymer consisting of monomers having no oxygen atoms. Next, the mixture is formed into a sheet-like shape so as to obtain a green sheet. After that, the green sheet is held for a predetermined length of time at binder decomposition temperature in a non-oxidizing atmosphere so as to remove the binder by causing depolymerization reaction or the like to the binder, which turns into monomer. The green sheet from which the binder has been removed is sintered by raising temperature up to sintering temperature. Thereby a permanent magnet 1 is obtained.