NdFeB Magnet Scrap Recycling via Vacuum Refining and Fluoride Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The production of high-performance NdFeB rare earth permanent magnets from scraps is hindered by high impurity content, particularly manganese, which affects magnetic performance and increases production costs, and existing recycling methods are complex and inefficient, leading to reduced magnetic performance and increased resource consumption of scarce heavy rare earth elements like Dy.
Innovation Solution
The method involves adding rare earth fluorides, such as praseodymium, neodymium, and dysprosium fluorides, to control the vacuum degree and refining temperature, reducing manganese content to 0.011-0.027 wt% and incorporating specific phases and treatments to enhance magnetic performance and material toughness, while utilizing a multi-step process involving vacuum melting, hydrogen decrepitation, and nitrogen jet milling to produce high-density NdFeB magnets.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If NdFeB scraps are used as raw materials for remelting, then resource utilization is improved and raw material cost is reduced, but impurity content (particularly manganese) increases and magnetic performance deteriorates
Solution Approach 1:
The patent extracts harmful impurities (particularly manganese) from the molten alloy through selective removal processes. By taking out the detrimental elements while retaining the valuable rare earth components, the method resolves the contradiction between recycling scraps and maintaining magnetic performance.
Solution Approach 2:
The patent changes the chemical composition parameters of the alloy by controlling the addition of pure rare earth metals and adjusting the melting process parameters. This allows the impurity content to be reduced to acceptable levels while maintaining high resource utilization from scrap materials.
2Productivity
If conventional vacuum melting rapid-solidifying method is used, then production efficiency is improved, but precious raw materials volatilize and slags increase under high temperature
Solution Approach 1:
The patent performs preliminary purification of the scrap materials and pre-adjusts the composition before melting. By preparing the raw materials in advance and removing obvious impurities, the subsequent vacuum melting process experiences less material loss and generates fewer slags, maintaining high production efficiency.
Solution Approach 2:
The patent uses a composite raw material system combining NdFeB scraps with pure rare earth metals and other alloying elements. This composite approach allows the scraps to be utilized effectively while the pure materials compensate for losses and adjust the final composition, resolving the contradiction between productivity and material loss.
3Loss of substance
If scraps are processed without remelting (crushing and pickling only), then material loss during melting is reduced, but the process becomes complex and magnetic performance is greatly affected due to high oxygen content
Solution Approach 1:
The patent conducts the melting and processing operations in a vacuum or inert atmosphere environment. This prevents oxidation of the rare earth materials during processing, allowing the scraps to be remelted without significantly increasing oxygen content, thereby simplifying the process while maintaining magnetic performance.
4Reliability
If heavy rare earth elements (Dy, Tb) are increased to improve magnetic performance, then coercive force is enhanced, but resource consumption of scarce elements increases and cost rises
Solution Approach 1:
The patent optimizes the compositional parameters by precisely controlling the ratios of light rare earth elements (Nd, Pr) to heavy rare earth elements (Dy, Tb). Through parameter optimization rather than simple increase, the method achieves high coercive force with minimized heavy rare earth consumption, resolving the contradiction between performance and resource usage.
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 approach significantly improves the magnetic performance and reduces the content of manganese, increasing the practicality and cost-effectiveness of NdFeB magnet production, while minimizing the use of scarce heavy rare earth elements and reducing the rejection rate of products during machining.
Implementation Method 1
under a vacuum condition, sending a portion of raw materials, comprising pure iron, ferro-boron, the NdFeB scraps and rare earth fluorides, into a crucible of a vacuum melting chamber, heating the portion of raw materials to a temperature of 1400-1500° C., refining the portion of raw materials
Implementation Method 2
heating the portion of raw materials to a temperature of 1400-1500° C., refining the portion of raw materials, and obtaining a first melting liquid
Implementation Method 3
the alloy flakes after the hydrogen decrepitation process are sent into a nitrogen jet mill without discharging ultrafine powders
Implementation Method 4
the alloy flakes after the hydrogen decrepitation process are sent into a nitrogen jet mill without discharging ultrafine powders, milling the alloy flakes into powders by the nitrogen jet mill, and controlling an average particle size of the powders in a range of 1.6-2.8 μm
Implementation Method 5
under the protection of nitrogen, processing the powders with magnetic field pressing, and obtaining a pressed compact with a density controlled at 4.1-4.8 g/cm3; under the protection of the nitrogen, sending the pressed compact after magnetic field pressing into a vacuum sintering furnace, processing the pressed compact with vacuum sintering
Data Source
AI summary
A high-performance NdFeB permanent magnet produced with NdFeB scraps and a production method thereof are provided. The production method includes steps of: under a vacuum condition, sending a portion of raw materials, including pure iron, ferro-iron, the NdFeB scraps and rare earth fluorides, into a crucible, refining, and obtaining a first melting liquid; absorbing slags by a slag cleaning device, and moving the slag cleaning device out; sending a rest of raw materials into the crucible, refining the first melting liquid and the rest of raw materials in the crucible, and obtaining a second melting liquid; pouring the second melting liquid after refining onto a surface of a water-cooled rotation roller through a tundish, and forming alloy flakes; processing the alloy flakes with hydrogen decrepitation, milling the alloy flakes into powders by a jet mill, then magnetic field pressing, presintering and sintering.