Advantages of adhesives in electric motor production

Bonding electric motors offers benefits that mechanical connections cannot provide:

• Prevention of Friction and Contact Corrosion: Adhesives minimize friction and contact corrosion in sensitive motor components such as rare earth magnets.
• Noise Reduction through Vibration Damping: The damping effect of adhesives minimizes vibrations and reduces operational noise.
• Thermal Stress Compensation: Differences in coefficients of thermal expansion between the stator and housing in an electric motor cause thermal stress. Adhesives compensate for this and prevent damage.
• Slack and Slip Prevention: Adhesives effectively prevent slack and slip in driveshaft connections, particularly when bonding the driveshaft, efficiently stabilizing them.
• Cost Reduction in Manufacturing: The use of adhesives allows for a simplified production process and reduced costs. Adhesives offer flexibility in their application, allowing for larger manufacturing tolerances compared to mechanical methods. Additionally, bonding often requires fewer production steps, saving time and simplifying automation. Modern adhesives can also speed up production, achieving rapid UV-light curing within seconds.

Choosing the right adhesives for electric motors

Selecting the right adhesive is crucial for the performance and longevity of motors. The variety of individual components and their requirements makes it essential to consider the properties of different adhesive groups. Here are the three most common groups of adhesives for bonding electric motors and their strengths.

One-component epoxy resins

Single-component epoxy resins from the DELO MONOPOX family maintain excellent strength even at continuous temperatures of up to 220 °C. These adhesives are ideal for high-temperature applications and are suitable for motors within insulation class C.

Their excellent adhesion to nickel-plated surfaces makes them perfect for magnet bonding. Besides their high chemical resistance, they also offer excellent gap bridging, which is particularly important for compensating uneven surfaces and ensuring reliable connections. A significant advantage of gap bridging is its ability to compensate for mechanical tolerances, thereby increasing the load capacity of the adhesive joint.

However, a challenge with using one-component epoxy resins is the need for heat during curing. Curing typically takes between 20 and 40 minutes. This time can be reduced to about a minute using induction heating, but this method is limited to electrically conductive components.

Two-component epoxy resins

Two-component epoxy resins from the DELO-DUOPOX family offer a more flexible solution. The mixing ratio can be adjusted to optimize properties such as curing time, flexibility, and hardness. These adhesives fully cure at room temperature, reducing energy costs and processing times. With heat application at 80 °C, components can be further processed after five minutes, achieving a fully cured state after ten minutes. Using induction heating at 100 °C, components can be fixed with a strength of 10 MPa within 60 seconds. The adhesive then achieves its final strength at room temperature.

These adhesives are particularly suitable for structural bonds and offer strong connections, even under harsh chemical or thermal conditions. Two-component adhesives also excel in gap bridging and stress-relieving properties, providing excellent production and automation possibilities. Moreover, they are easy to store, with strength remaining unchanged at high temperatures and humidity, as long as the components are unmixed.

Metal adhesives

Metal adhesives that cure at room temperature are another modern solution. They are highly heat-resistant and can withstand temperatures up to 200 °C. DELO-ML adhesives achieve excellent adhesion on smooth surfaces and are ideal for driveshaft bonding. This is because the adhesive networks with the metal surface under air deprivation and the presence of metal ions. Metal adhesives also offer better thermal and electrical conductivity, which are crucial for securing magnets on the rotor or stator. Bonding housing materials and heat sinks is another typical application area.

One challenge here is that modern-day materials like neodymium magnets contain few metal ions, as do simple motor ferrite cores. Activators, which can be sprayed or applied by dipping, enhance the adhesion of methacrylates and accelerate curing. Functional strengths can be achieved within 30–60 seconds.

For even shorter cycle times, dual-curing urethane acrylates are recommended, curing under UV light in less than 10 seconds and allowing further processing immediately. The adhesive then gains full strength under air deprivation, potentially eliminating a process step and negating the need for mechanical fixation common with thermosetting adhesives.