Epoxy-Bonded Magnetic Core Material for Low-Loss High-Frequency Heating
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Solution Overview
Problem
Magnetic cores for induction hardening apparatuses face challenges in achieving low permeability, high strength, and low eddy-current loss at high frequencies, with existing powder magnetic cores experiencing structural defects, high temperature issues, and resin blow-off during thermal curing.
Innovation Solution
A magnetic core material comprising Fe-based soft magnetic powder with an inorganic insulating film and an epoxy resin binder, where the epoxy resin includes bisphenol A-type and novolac-type epoxy resins, and the resin content is between 2-5 mass%, providing a relative permeability of 17-25, radial crushing strength of 50 MPa or more, and volume resistivity of 1×10^4 Ωcm or more, while preventing resin blow-off during thermal curing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If molding pressure is extremely lowered to achieve low relative permeability (less than 25), then the magnetic core can have low permeability, but the magnetic core has many pores inside, insufficient strength, and low volume resistivity
Solution Approach 1:
The invention changes the chemical composition parameters by introducing specific resin binders (phenolic resin, epoxy resin, or polyester resin) and controlling their content within 1-10 mass% of the total magnetic core weight. This chemical parameter adjustment allows achieving the desired relative permeability (less than 25) while maintaining sufficient strength and volume resistivity, resolving the contradiction between permeability control and mechanical/electrical properties.
Solution Approach 2:
The invention creates a composite material system combining Fe-based soft magnetic powder particles with organic resin binders. The resin binder forms a binding phase that fills pores and bonds particles together, while the magnetic powder provides the magnetic properties. This composite structure enables simultaneous achievement of low relative permeability, high strength, and high volume resistivity by optimizing the interaction between the two material phases.
2Strength
If resin binder content is increased to improve strength, then the magnetic core has sufficient strength, but the eddy-current loss increases and frequency characteristics deteriorate
Solution Approach 1:
The invention precisely controls the resin binder content parameter within the narrow range of 1-10 mass% of the total magnetic core weight. This optimized parameter range provides sufficient strength to prevent particle separation while minimizing the resin volume that could conduct eddy currents. The specific resin types (phenolic, epoxy, or polyester) are selected for their electrical insulation properties, further reducing eddy-current loss while maintaining structural integrity.
3Strength
If resin binder is used to improve strength, then the magnetic core has sufficient strength, but the resin binder is ejected (blow-off) on the surface during thermal curing
Solution Approach 1:
The invention selects specific resin binder types (phenolic resin, epoxy resin, or polyester resin) that have appropriate curing characteristics and volatility profiles. These resins are chosen to minimize blow-off during thermal curing while still providing sufficient binding strength. The controlled resin content (1-10 mass%) also reduces the total amount of resin that could potentially blow off, maintaining both strength and productivity.
4Loss of energy
If no resin binder is used to reduce eddy-current loss, then the volume resistivity is high, but the magnetic core has many pores inside and insufficient strength
Solution Approach 1:
The invention optimizes the resin binder content parameter to a low range (1-10 mass%) that is sufficient to bond particles and eliminate pores for structural strength, but low enough to minimize eddy-current paths. The selection of specific resin types with good electrical insulation properties (phenolic, epoxy, or polyester resins) ensures that the minimal resin present does not significantly increase eddy-current loss, thus balancing strength requirements with energy loss constraints.
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 solution results in a magnetic core with excellent frequency characteristics, high strength, and reduced heat generation, enabling effective induction heating with low loss and high frequency stability, while maintaining productivity by preventing resin blow-off during thermal curing.
Implementation Method 1
an inorganic insulating film is provided on surfaces of Fe-based soft magnetic particles
Implementation Method 2
an epoxy resin material, wherein the epoxy resin material includes a curing agent and an epoxy resin
Implementation Method 3
providing a relative permeability of 17-25
Implementation Method 4
A magnetic core attached to a heating coil part of an induction hardening apparatus has an effect that the magnetic core attached to a back face of the coil concentrates magnetic force lines on a workpiece to enhance power so as to accelerate induction heating
Implementation Method 5
the magnetic core attached conversely to a front face of the coil to shield magnetic lines to prevent heating of a part requiring no hardening
Data Source
AI summary
A magnetic core material contains an Fe-based soft magnetic powder in which an inorganic insulating film 4b is formed on a surface of an Fe-based soft magnetic particle 4a, and an epoxy resin 4c containing a curing agent. The Fe-based soft magnetic particle 4a is formed of a pure iron powder or a low-alloy steel powder. A content of the epoxy resin containing the curing agent is 2 to 5 mass %. The epoxy resin is a mixture of a bisphenol A-type epoxy resin and a novolac-type epoxy resin.