Embedded Reinforcing Coil for Brittle Magnet Fracture
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Solution Overview
Problem
Conventional magnets in electrical machine rotors are brittle and prone to fracture under excessive tensile stress, limiting the speed of the machine, and compressive forces applied to counteract radial forces can lead to creep and eventual magnet failure over time.
Innovation Solution
A composite magnet body with a reinforcing coil embedded within, where the coil surrounds the bore and is formed from a ribbon to enhance radial stiffness and tensile strength, eliminating the need for pre-stressing and minimizing eddy currents and thermal expansion issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the speed of the electrical machine is increased, then the productivity is improved, but the magnet is subjected to excessive tensile stress and will fracture
Solution Approach 1:
The magnet is constructed as a composite structure combining a magnetic powder body with an embedded reinforcing element (metal sleeve or mesh). This composite design allows the magnet to maintain its magnetic properties while gaining enhanced tensile strength from the reinforcing element, enabling operation at higher speeds without fracture.
Solution Approach 2:
The reinforcing element is strategically positioned within the magnet body at locations where tensile stresses are most critical during rotation. This localized reinforcement provides strength exactly where needed, allowing the magnet to withstand high-speed operational stresses without requiring uniform strengthening of the entire magnet structure.
2Force
If an outer sleeve is used to apply compressive force to the magnet, then the radial forces are opposed, but the magnet undergoes creep and the compressive force decreases with time
Solution Approach 1:
Instead of applying compressive force from the outside (outer sleeve), the reinforcing element is embedded within the magnet body itself. This internal reinforcement structure provides continuous support against radial forces without relying on external compression, eliminating the creep problem associated with time-dependent deformation under sustained compressive load.
Solution Approach 2:
The external mechanical compression system (outer sleeve applying compressive force) is replaced with an internal structural reinforcement system. The embedded reinforcing element provides structural support through its inherent strength and bonding with the magnet body, rather than through time-dependent compressive force application.
3Strength
If the reinforcing element is made thicker in radial direction, then the radial stiffness is increased, but the axial thickness increases and more eddy currents are induced
Solution Approach 1:
The reinforcing element is designed with non-uniform thickness, being thickest in the radial direction where it needs to provide maximum stiffness and strength, and thinner in the axial direction to minimize eddy current paths. This localized variation in thickness optimizes both mechanical performance and electrical performance.
Solution Approach 2:
The reinforcing element is configured as a mesh or lattice structure rather than a solid block. This three-dimensional arrangement provides radial stiffness through the geometry of the mesh while creating discontinuities that interrupt eddy current paths, thereby reducing harmful electromagnetic effects.
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 reinforced magnet can operate at higher speeds without fracturing and maintains its ability to withstand radial forces over time, reducing the risk of creep and internal stresses, while allowing for a lighter and cheaper rotor design.
Implementation Method 1
radial forces stress the magnet
Implementation Method 2
the reinforcing element has a greater radial stiffness and radial tensile strength than that of the composite body and thus acts to oppose radial and circumferential stresses
Implementation Method 3
the resulting stresses may cause the magnet to creep. As a result, the magnitude of the compressive force may decrease with time
Implementation Method 4
If the magnet is subjected to a rotating magnetic field (e.g. from a stator of an electrical machine), eddy currents may be induced in the reinforcing element if formed of an electrical conductor. The eddy currents will tend to circulate in loops parallel to the axis of rotation. The reinforcing element, being a helical shape, does not include any continuous paths in the axial direction. As a result, any eddy currents induced in the reinforcing element will be relatively small.
Implementation Method 5
a larger interface is created between the reinforcing element and the composite body. As a result, tensile stresses may be better transferred from the composite body to the reinforcing element
Implementation Method 6
The magnet may undergo thermal expansion and contraction during use and/or manufacture
Data Source
Figure 1
Figure 2(a)~2(c)
Figure 3
AI summary
A magnet (1) comprising a composite body (2) and at least one reinforcing element (3,16) embedded within the body (2), the reinforcing element (3,16) surrounding a bore (4) in the body (2). Additionally, methods of manufacturing the magnet (1).