Expanded Magnet Coating With Porous Structure for 170 °C Durability
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Solution Overview
Problem
Existing expandable coatings for rare earth permanent magnet synchronous motors lack sufficient thermal stability and mechanical performance at high temperatures, leading to potential damage and poor corrosion resistance when exposed to operating conditions exceeding 150 °C.
Innovation Solution
The coating composition is optimized with a specific ratio of spheroid pores (53%-57% cross-sectional area) and a combination of chemical and physical foaming agents, achieving a stable structure with high shear and tensile strengths, enhanced corrosion resistance, and improved thermal stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If conventional expandable coatings are used, then the coating can fill the magnetic steel groove and fix the magnetic steel pieces, but the coating lacks sufficient thermal stability and mechanical performance at high temperatures (>150°C)
Solution Approach 1:
The patent uses a composite coating system comprising a thermosetting resin matrix (epoxy, polyester, or vinyl ester resin) combined with specific filler materials (oxidized polyethylene crosslinked beads, expandable microspheres, and inorganic fillers). This composite structure provides both high-temperature thermal stability and enhanced mechanical strength, with the crosslinked polymer network maintaining integrity at temperatures above 150°C while the filler particles contribute to shear strength and rigidity.
Solution Approach 2:
The coating incorporates a controlled porous structure with porosity of 30%-70%, created through the inclusion of expandable microspheres and oxidized polyethylene crosslinked beads that form voids upon expansion. These pores improve thermal stability by reducing thermal conductivity and preventing thermal stress concentration, while the surrounding resin matrix maintains mechanical strength. The pore distribution and size are controlled to balance thermal and mechanical properties.
2Manufacturing precision
If the coating is expanded to fill the magnetic steel groove, then assembly precision is improved, but the coating may be sheared along the groove under centrifugal force at high temperatures
Solution Approach 1:
The patent optimizes several key parameters: the filler bead size distribution (0.1-2.0 mm oxidized polyethylene crosslinked beads mixed with 10-100 μm expandable microspheres), the resin-to-filler ratio, the curing agent content (0.5-5.0 phr), and the expansion temperature profile. These parameter changes ensure the coating expands sufficiently to fill grooves with 0.05-0.5 mm clearance while developing a crosslinked network that resists shear forces. The gradual curing process at 80-150°C followed by post-curing at 100-200°C creates a dense, stress-resistant structure.
Solution Approach 2:
The coating is applied to the magnet surface before assembly, allowing it to cure and pre-expand in a controlled manner before experiencing operational stresses. The preliminary curing process at 80-150°C for 1-24 hours establishes the basic structural integrity, followed by post-curing at higher temperatures to maximize crosslinking density. This preliminary action ensures the coating is already bonded and structurally sound before the magnet assembly undergoes centrifugal forces during motor operation.
3Volume of stationary object
If the coating expands at high temperature, then the magnetic steel groove is filled, but the corrosion resistance and oil resistance may deteriorate
Solution Approach 1:
The patent creates local quality differences within the coating structure through the heterogeneous distribution of filler materials. The oxidized polyethylene crosslinked beads and expandable microspheres create localized expanded regions with high void content for groove filling, while the thermosetting resin matrix in between maintains continuous protective coverage. The inorganic fillers (such as aluminum oxide, aluminum hydroxide, or calcium carbonate) are distributed to provide localized corrosion resistance. This local quality variation allows the coating to simultaneously achieve groove filling and maintain corrosion/oil resistance.
Solution Approach 2:
The expandable microspheres and oxidized polyethylene crosslinked beads act as sacrificial expansion agents that decompose or expand during the curing process to create the porous structure, then become part of the permanent coating matrix. These materials are consumed during the expansion process to achieve the desired volume and structural properties, while the thermosetting resin matrix provides the lasting protective function against corrosion and oil. The expandable particles are replaced by the cured resin structure that provides long-term protection.
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 optimized coating exhibits shear strength greater than 2 MPa, tensile strength greater than 2 MPa, oil resistance exceeding 1800 h, and neutral salt spray performance greater than 288 h at 170 °C, ensuring durability and reliability under high-temperature conditions.
Implementation Method 1
the foaming agent is a chemical foaming agent
Implementation Method 2
The foaming agent does not prematurely react with the substrate of the coating
Implementation Method 3
a thermosetting resin is used
Implementation Method 4
the expanded coating has relatively high magnet-substrate binding force and neutral salt spray test performance at room temperature after expansion
Implementation Method 5
The expandable coating can be expanded by thermal treatment
Implementation Method 6
expandable microspheres in a controlled ratio to enhance thermal stability
Data Source
Figure 1~2
AI summary
The present disclosure provides an expanded coating, a preparation method and use thereof, and a permanent magnet comprising same. The expanded coating described herein comprises pores and a filler resin arranged among the pores; the pores comprise at least a spheroid pore having a cross section with a long diameter and a short diameter; in the cross section of the expanded coating, the area of the spheroid pores accounts for 50%-60% of the cross-sectional area of the expanded coating. The permanent magnet of the present disclosure comprises the expanded coating. The expanded coating has high strength and can exhibit excellent mechanical properties and corrosion resistance at high temperatures (such as 170 °C), with a shear strength greater than 2 MPa, a tensile strength greater than 2 MPa, an oil resistance greater than 1800 h and a neutral salt spray performance greater than 288 h at 170 °C.