Adhesive Recommendations for Powder Cores
Powder core assemblies often require adhesive bonding when creating larger magnetic structures such as block core assemblies, stacked toroids, or assembled E-cores. Selecting the proper adhesive helps ensure mechanical strength, dimensional stability, and reliable performance throughout the life of the component.
Because powder core surfaces are rougher and more porous than ferrites, adhesive requirements can differ from those commonly used for ferrite assemblies.
Recommended Adhesives
Magnetics has evaluated several adhesive systems for powder core assemblies.
| Assembly Type | Recommended Adhesive |
|---|---|
| Block Assemblies | ResinLab EP950G |
| Alternative Evaluated Materials | ResinLab EP950NMF, ResinLab EP950MF |
| Stacked Toroids | 3M™ DP420 |
| E Core Sets | 3M™ DP420 |
Powder Core Block Assemblies
Powder core block assemblies require sufficient adhesive to penetrate and bond the textured mating surfaces. In some applications, a larger volume of adhesive may be required than would typically be used for ferrite cores.
Magnetics has successfully utilized ResinLab EP950G in combination with Nordson EFD dispensing systems to achieve repeatable adhesive application and preserve adhesive quality during use.
Typical I Core Assembly Process
- Inspect mating surfaces and remove any loose powder or contaminants with acetone
- Bring the adhesive to room temperature before use
- Apply a continuous bead of EP950G along the stamped face of one block using the EFD dispenser (recommended settings: 60 PSI air pressure, 5 PSI vacuum drawback, 1 second timer)
- Press the mating block firmly into place with stamped faces oriented inward
- Clamp the assembly using a constant-force spring clamp
- Verify that edges remain flush and properly aligned
- Cure at 350°F (177°C) for 40-45 minutes
- Allow the assembly to cool below 120°F (49°C) before removing the clamp
Proper adhesive application should produce full bond-line coverage with minimal squeeze-out. Excess adhesive can create raised surfaces that complicate subsequent assembly operations.
Typical U Core Assembly Process
After the I cores have cured and cooled:
- Assemble two cured I cores into a U-shaped structure
- Apply EP950G to the mating surfaces before joining the components. Dispensing time should be slightly less than when gluing just the I cores.
- Use a fourth I core as an alignment fixture during assembly
- Add a reinforcing bead of adhesive at the inside right-angle joints
- Cure at 350°F (177°C) for 55-60 minutes
- Allow the assembly to cool below 120°F (49°C) before removing clamps
Stacked Toroid Assemblies
For stacked toroid configurations, Magnetics commonly uses 3M™ DP420 two-part epoxy. This adhesive provides strong structural bonding between stacked components and has proven effective in production assemblies where multiple toroids are combined to achieve larger effective cross-sectional areas.
E-Core Assemblies
For powder E-core assemblies, Magnetics typically uses 3M™ DP420. The adhesive provides durable mechanical bonding while supporting precise alignment of the assembled core structure during curing.
Assembly Considerations
- Apply adhesive immediately before assembly to prevent material flow.
- Use a continuous bead rather than a large adhesive spot.
- Verify alignment before curing.
- Avoid using expired adhesive materials as it loses cured break-strength when it is too old.
- Cure assemblies according to adhesive manufacturer recommendations.
- Changes in ambient temperature can affect adhesive viscosity and dispensing characteristics.
Need Assistance Selecting an Adhesive?
Magnetics engineers can provide guidance on adhesive selection for powder core block assemblies, stacked toroids, E-core assemblies, and custom magnetic structures. Contact our engineering team to discuss your application requirements and assembly process.