Whether in automation systems, grippers or sensors: magnetic systems must function reliably even under high mechanical and thermal stresses. Adhesive technology plays a key role in this. It permanently bonds magnets to steel pots, pole shoes or housings made of stainless steel, plastic and brass.

At BRUGGER Magnetsysteme GmbH, bonding is therefore far more than a simple assembly step. It is only through the precise interplay of materials, surface preparation, bonding gap, dispensing, positioning and curing that a robust bond is created. Depending on the geometry, quantity and technical requirements, BRUGGER applies the adhesives either by hand in a craft-like process, using an adhesive robot, or in an automated potting process.

Why are magnets bonded?

In principle, magnets can also be clamped, screwed or mechanically fastened in other ways. However, bonding offers several design and manufacturing advantages. As no drilling is required, no additional weak points are created in the component. At the same time, work steps such as drilling and deburring are eliminated.

A further advantage is the large-area bond. Whilst screws and other mechanical fasteners take up space and transfer forces at specific points, an adhesive can utilise almost the entire available bonding surface. This allows loads to be distributed more evenly across the joined components.

In BRUGGER’s magnetic systems, the adhesive bond often serves a purpose beyond simply securing the magnet pellet in the steel pot.

Depending on the product and design, it can also:

• compensate for gaps,

• dampen vibrations and shocks,

• seal the joint,

• protect against corrosion and

• prevent the ingress of dirt.

In some magnetic systems, the bonding surface or existing gaps are additionally covered with adhesive or potting compound. This creates sealed surfaces in which less dirt can accumulate.

Which adhesive is suitable for a magnetic system?

There is no single universal adhesive suitable for all magnetic systems. The choice depends, amongst other things, on the type of magnet, the surface of the housing, the bonding gap and the subsequent operating conditions.

BRUGGER, for example, processes magnets made of ferrite, neodymium-iron-boron (NdFeB), samarium-cobalt (SmCo) and aluminium-nickel-cobalt (AlNiCo). Suitable counterparts include steel pots, stainless steel and brass housings, and plastic shells, amongst others. Each of these material combinations places different demands on the bonding technology.

For recurring tasks, BRUGGER offers 16 different adhesives for various standard applications. An application table containing technical specifications is used to determine which system is suitable for the task at hand. Two-component epoxy resins and anaerobic adhesives are frequently used. For certain applications, BRUGGER also uses cyanoacrylates – i.e. fast-curing adhesives – or radiation-curing adhesives.

‘2K’ stands for ‘two components’: the resin and hardener are combined in a defined ratio. Mixing triggers the chemical reaction and thus the curing process. However, for new or particularly demanding tasks, selecting a product based solely on existing experience is not always sufficient. In such cases, BRUGGER investigates further adhesive systems and tests them in application-specific test series.

Temperature, vibration and environmental influences

BRUGGER’s magnetic systems are used in a wide variety of fields – for example, in automation and plant equipment, in gripping systems or in sensor applications. The stresses that the bonded joints must withstand are correspondingly diverse.

In addition to tensile and shear forces, impacts, vibrations and cyclic loads may occur. Added to this are potential effects from splash water, moisture, oils or chemicals. For outdoor applications, exposure to salt spray may also be a factor.

Temperature resistance is particularly important. Many polymers and epoxy resin systems used in industry can – depending on the specific product and application – be designed for temperature ranges up to around 280 °C. Inorganic high-temperature adhesives are available for extreme thermal requirements. Other systems cure in a manner similar to cement or ceramics and, depending on the formulation, can withstand temperatures of up to 1,000 °C.

It is not just the maximum temperature that is crucial. Repeated temperature cycles can also put a strain on the bond, as the magnet, housing and adhesive expand to different degrees. BRUGGER therefore assesses the suitability of an adhesive on the basis of the application as a whole, rather than on the basis of a single temperature value alone.

The surface determines the bond strength

A high-performance adhesive bond requires carefully prepared surfaces. The parts to be joined must be clean, dry and free from grease, oil, dust and release agent residues. Contaminants can prevent the adhesive from wetting the surface evenly and bonding to it reliably.

Furthermore, magnets are often coated with metallic or organic protective layers. NdFeB magnets in particular often require a coating due to their susceptibility to corrosion. Steel pots and pole shoes may also be bare, galvanised, coated or otherwise treated. The adhesive must therefore be compatible not only with the base material but also with the actual surface present.

Depending on the combination of materials, the components are cleaned, degreased, roughened or pre-treated using a suitable process at BRUGGER. Only then does the actual bonding process begin.

Bonding gap, dispensing and positioning

The bonding gap defines the thickness of the adhesive layer. Its geometry influences both the amount of adhesive required and the mechanical properties of the joint. At the same time, the gap must be designed in such a way that it does not unnecessarily impair the magnetic function of the system.

In BRUGGER’s in-house assembly process, care is therefore taken to ensure a uniform distance between the magnet and the steel pot. Pole shoes, for example, can be inserted using hand-operated lever presses to align them precisely and fix them in place in a controlled manner. The position of the components to be joined must not change until the adhesive has cured sufficiently.

The amount of adhesive applied must also be precisely matched to the intended bonding gap. Too much adhesive can be squeezed out of the joint, alter component dimensions and – depending on the adhesive system and the layer thickness – impair curing. If there is too little adhesive, the surfaces may not be fully wetted. This can result in voids and areas with insufficient bonding, which reduce the load-bearing capacity.

An additional challenge is posed by the forces exerted by components that are already magnetised. These can pull the magnet out of its intended position during assembly. BRUGGER therefore uses suitable non-magnetic tools as well as mechanical guides and devices. Where the manufacturing process permits, the magnets are initially bonded in a demagnetised state. Only once the adhesive has fully cured is the finished magnetic system magnetised.

Manual work or adhesive robots?

At BRUGGER, manual bonding and automated dispensing are not competing processes. Both have their place, depending on the product, geometry and quantity.

Craft-like manual work offers advantages when flexibility is more important than maximum speed and repeatability. This applies in particular to small batch sizes, frequently changing variants or special geometries. Experienced staff can flexibly adapt the process to the respective assembly and implement bespoke solutions.

For high production volumes and where there are high demands on precision and cycle time, BRUGGER uses an adhesive application robot. Among other things, it controls:

• the application quantity,

• the mixing ratio of two-component adhesives,

• the dispensing and travel speed,

• the positioning of the parts to be joined, and

• the angle of the dispensing tool.

Volumetric dispensing systems enable a constant and reproducible adhesive volume down to the milligram range. This ensures that the specified layer thickness can be reliably maintained across a large number of components. Automation therefore not only increases processing speed but, above all, enhances process stability and repeatability.

At BRUGGER, some magnet systems are also automatically potted. Potting can secure components, seal gaps and protect the assembly from moisture, dirt or other environmental influences. Here too, the amount of material, positioning and curing must be precisely tailored to the respective design.

Different methods of curing

How an adhesive cures is determined by its chemical composition. In two-component (2K) systems, the reaction begins once the two components are brought together and mixed. Many of these adhesives can cure at room temperature. Anaerobic adhesives, on the other hand, typically react in the absence of air and in contact with suitable metallic surfaces.

Other specialist adhesives are activated by atmospheric humidity or UV light. A targeted application of heat can significantly accelerate the curing of certain systems. Some inorganic high-temperature adhesives require a defined thermal curing process. Some adhesives are cured in an oven at temperatures above 100 °C to achieve the required cross-linking and heat resistance.

Curing is therefore not merely a waiting process, but a technically defined production step. At BRUGGER, temperature, time and environmental conditions are defined to suit the respective adhesive system.

How does BRUGGER test the quality of the bond?

It is not possible to assess whether an adhesive bond will function reliably in the long term by visual inspection alone. That is why BRUGGER tests new or particularly demanding bonds using in-house testing equipment. The test series can extend over periods of up to one year.

A compressive shear test is used to determine the maximum static strength of the bond. The results also provide an indication of whether the bond gap and surface pretreatment have been selected appropriately.

A dynamic impact test on an eccentric press simulates cyclic shock loads. It reveals how impact-resistant or brittle the adhesive used behaves under repeated stress. In addition, long-term tests examine ageing resistance and resilience to climatic conditions, humidity and temperature fluctuations.

These tests are particularly important for new material combinations or specialised applications. This is because the technical suitability of an adhesive cannot be determined solely from its data sheet. What is crucial is its behaviour within the specific component geometry and under realistic operating conditions.

Precise dispensing saves resources

A controlled bonding process not only improves quality but also reduces material consumption. If the required amount of adhesive is dispensed precisely, there is less surplus and less waste. Unavoidable production waste is recorded and disposed of properly at BRUGGER.

When selecting adhesives, the company also specifically opts for systems that are as harmless to health as possible and low-odour. At BRUGGER, sustainable bonding thus combines health and safety, resource efficiency and process reliability.

Conclusion: At BRUGGER, it is the entire bonding process that counts

Reliable magnet bonding is not achieved solely by choosing a high-performance adhesive. A coordinated overall process is crucial: the type of magnet and its coating must be taken into account, as must the housing material, surface preparation, the bonding gap and the subsequent loads.

Precise assembly procedures prevent magnets and pole shoes from shifting during curing. For high-volume production, adhesive robots ensure reproducible dispensing and positioning. For small batches and special geometries, manual processing offers the necessary flexibility.

The combination of many years’ application expertise, in-house assembly, automated dispensing technology and comprehensive testing procedures enables BRUGGER Magnetsysteme GmbH to tailor bonding processes specifically to the requirements of the respective magnet system.