Gluing magnets - which glue to choose?

What are you really bonding – the magnet or its coating?

This is one of the most important questions before adhesive selection.

Many NdFeB neodymium magnets are protected by an external coating. Depending on the supplier and application, this may include:

• nickel or multilayer Ni-Cu-Ni,
• zinc,
• epoxy coating,
• another manufacturer-specified protective system.

The adhesive then bonds to the outer protective layer, not directly to the NdFeB material.

The durability of the complete joint can therefore be limited by several different interfaces:

1. adhesion of the adhesive to the magnet coating,
2. cohesive strength of the coating itself,
3. adhesion of the coating to the magnet material,
4. cohesive strength of the adhesive layer,
5. adhesion of the adhesive to the second component.

Neodymium, ferrite and other magnets – what changes when bonding?

The actual surface is more important to adhesive selection than the magnetic classification alone.

For production engineering, a change of magnet supplier or coating can be a bonding-process change even if dimensions, magnetic force and drawing number remain unchanged.

Which adhesive should be used for magnets?

The best technology depends on joint geometry, the real surfaces and the operating conditions.

LOCTITE AA 326 – a dedicated direction for magnets and ferrites

LOCTITE AA 326 is listed by Melkib specifically for bonding magnets and ferrites. It is used together with LOCTITE SF 7649 activator and is intended for close-fitting rigid surfaces.

The adhesive and activator should be applied according to the validated process and product documentation. Activator quantity, adhesive dose, gap and assembly timing still need to be controlled in production.

LOCTITE 480 – for impact and peel resistance

Henkel describes LOCTITE 480 as a black, rubber-toughened, low-viscosity cyanoacrylate for close-fitting parts. It offers improved peel, impact and shear strength compared with a conventional rigid instant adhesive and is suitable for metals, elastomers and plastics.

It is a good candidate for small magnet assemblies where rapid fixture is required and the joint can experience impact or edge loading.

LOCTITE 496 – very tight gaps and metal surfaces

Henkel describes LOCTITE 496 as a very low-viscosity instant adhesive particularly suited to metal substrates. It is intended for close-fitting assemblies and very small gaps.

It should not be used as a substitute for a gap-filling structural adhesive when the magnet sits loosely in a pocket or housing.

LOCTITE 401 and 454 – general assembly options

LOCTITE 401 is a low-viscosity general-purpose cyanoacrylate used on a broad range of materials. It can be considered for small, simple magnet assemblies after substrate compatibility is confirmed.

LOCTITE 454 is a gel cyanoacrylate. Its consistency makes application easier on vertical and porous surfaces such as certain wood assemblies.

When is a 2K adhesive a better choice?

A 2K structural adhesive is often a more natural direction when:

• the joint gap is larger,
• the component needs more positioning time,
• the assembly is larger,
• the joint must tolerate greater dimensional variation,
• serial production requires controlled mixing and dispensing.

Melkib MMA Power 10 is an example of a two-component methacrylate system used for structural multi-material bonding. It should still be validated for the specific magnet coating and second substrate.

Adhesives, activator and surface-preparation products used in magnet-bonding applications

Bonding magnets to plastics or wood

Plastics

The word “plastic” is not enough for adhesive selection. ABS, PC and rigid PVC behave very differently from low-surface-energy plastics such as PE, PP and PTFE. POM can also be difficult to bond.

For difficult plastics, a standard metal adhesive or universal cyanoacrylate should not be assumed to work without a suitable primer, surface treatment or dedicated adhesive system.

Wood

Wood is porous, so low-viscosity adhesive can be absorbed into the surface and starve the joint. A gel or higher-viscosity adhesive may be easier to control, but the wood should first be dry, dust-free and mechanically stable.

How should a magnet be prepared for bonding?

Surface preparation often decides whether the process becomes repeatable.

1. Identify the coating. Determine whether the adhesive will contact nickel, zinc, epoxy, ferrite or another surface.
2. Clean both bonding surfaces. Remove oil, fingerprints, dust and processing contamination with a cleaner compatible with the magnet coating and second substrate.
3. Do not abrade automatically. Mechanical preparation should only be used when it is justified and validated for the actual coating.
4. If abrasion is required, remove all dust afterwards.
5. Apply the adhesive in a controlled quantity. Too much product can create squeeze-out and an uncontrolled bond line.
6. Control the joint gap. Cyanoacrylates require close-fitting parts; larger gaps may need a different technology.
7. Stabilise the component until sufficient handling strength is reached.

Temperature, vibration and thermal cycling

A magnet assembly can fail even when the initial room-temperature bond strength is high.

For industrial applications, assess:

• continuous and peak temperature,
• thermal cycling,
• vibration and impact,
• fatigue loading,
• humidity or process fluids,
• centrifugal force in rotating components,
• creep or long-term static load.

Bonding magnets in electric motors

Electric-motor rotor applications require much more than a simple room-temperature pull-off test. The adhesive joint may experience high rotational speed, centrifugal load, vibration, temperature changes and repeated thermal cycles.

In addition, strong magnets can move abruptly during assembly. If the magnet snaps into a steel pocket, it may squeeze most of the adhesive out of the bond line or move out of the intended position.

A repeatable motor-magnet process should therefore define:

• magnet and coating specification,
• rotor material and surface preparation,
• joint gap and adhesive quantity,
• positioning or assembly tooling,
• fixture and cure conditions,
• temperature and rotational-speed validation,
• change control for magnet or coating suppliers.

How to make magnet bonding repeatable in production

1. Define the magnet specification, including coating.
2. Define the second substrate.
3. Set the acceptable joint gap.
4. Standardise cleaning and any activation or primer.
5. Control adhesive dose.
6. Use tooling where magnetic force can disturb positioning.
7. Define fixture and full-cure requirements separately.
8. Validate the joint under real temperature and mechanical loads.
9. Treat a coating or supplier change as a potential process change.

If a magnet begins to detach in service, do not start by searching for a “stronger adhesive”. First inspect both fracture surfaces and identify which interface actually failed.

Video: magnet bonding in practice

The three videos from the existing article are retained because they show practical application, adhesive selection and comparison. They are presented one below another for better readability.

Practical assembly – step by step

Adhesive selection and common mistakes

Practical test and comparison

FAQ – bonding magnets

What is the best adhesive for magnets?

There is no single best adhesive for every magnet. For industrial bonding of magnets and ferrites, LOCTITE AA 326 with SF 7649 is one useful starting point. For small close-fitting parts, an appropriate cyanoacrylate may work well, while larger gaps can require a 2K structural system.

Which adhesive should be used for a neodymium magnet?

First determine the external coating of the magnet. With a coated NdFeB magnet, the adhesive bonds mainly to the nickel, zinc, epoxy or other protective surface rather than directly to the NdFeB material.

Should a neodymium magnet be roughened before bonding?

Not automatically. Aggressive abrasion can damage the protective coating and expose corrosion-sensitive magnet material. Start with controlled cleaning and validate adhesion before introducing mechanical preparation.

When should LOCTITE 480 be considered?

For small close-fitting joints where fast fixture is required and improved impact or peel resistance is useful. Henkel describes LOCTITE 480 as a rubber-toughened, low-viscosity instant adhesive for close-fitting parts.

When is LOCTITE 496 a better option?

When the parts are very closely fitted and metal bonding is a priority. Its very low viscosity is not intended to compensate for a large gap.

Why can magnets come loose even when a high-strength adhesive was used?

Possible causes include contamination, failure of the magnet coating, excessive gap, insufficient adhesive, squeeze-out during assembly, incorrect cure, impact, vibration, temperature or failure of the second substrate. Inspect the fracture surfaces before changing products.

Summary – how to select an adhesive for magnets

The most important step is identifying what the adhesive will actually bond to. With a neodymium magnet, the bonding surface may be nickel, zinc or epoxy rather than NdFeB itself.

For professional magnet and ferrite bonding, LOCTITE AA 326 with SF 7649 is a useful starting point. For small and close-fitting components, LOCTITE 480 or 496 may be considered. For larger gaps, larger parts or assemblies requiring more positioning time, a 2K system such as Melkib MMA Power 10 may be more appropriate.

In serial production, coating condition, cleanliness, adhesive quantity, bond-line thickness, positioning and cure are just as important as the adhesive name.