Common Failure Modes of Bimetal Rivet Contacts

Bimetal rivet contacts are crucial in electrical systems, but several failure modes can undermine system performance and reliability. Understanding these modes helps manufacturers and users take preventive steps.

►Electrical - related Failures
⇔Contact Resistance Increase
Contact resistance often rises over time. Oxidation, corrosion, or contaminant buildup can degrade contact surfaces. In humid conditions, metal surfaces form an oxide layer, increasing resistance. As resistance goes up, more heat is generated according to Joule's law (\(P = I^{2}R\)). Excessive heat can damage the contact material, and in extreme cases, cause melting or welding, leading to complete electrical failure.
⇔Electrical Arcing and Erosion
Electrical arcing occurs when contacts open or close, especially under high - current conditions. The resulting high - temperature plasma discharge erodes contact surfaces, reducing material thickness. Repeated arcing creates pits and grooves, further increasing resistance and the likelihood of more arcing. Severe erosion can make it impossible to maintain a reliable connection, causing intermittent or complete power loss.

►Mechanical - related Failures
⇔Rivet Loosening
The tightness of the rivet connection is vital for mechanical integrity. Vibration, thermal cycling, or excessive mechanical stress can loosen the rivet. In applications with continuous vibrations, like industrial machinery, the rivet can gradually come loose. Once loose, bimetal components may move, affecting electrical contact and potentially causing intermittent or complete disconnection.
⇔Fatigue Failure
Repeated mechanical stress, common during cyclic operations like relay opening and closing, can cause fatigue failure. Micro - cracks form at stress - concentrated areas, such as rivet edges or the interface between bimetal materials. As the number of cycles increases, these cracks grow and eventually lead to contact failure. Fatigue failure is hard to detect early but can seriously impact system reliability.

►Environmental - related Failures
⇔Corrosion
Exposure to corrosive environments is a major failure cause. Chemicals in the air, water, or the operating environment react with metal surfaces. In marine or industrial settings with high salt or acidic gases, bimetal materials corrode quickly. Corrosion weakens mechanical strength and increases contact resistance due to non - conductive corrosion products. In extreme cases, it can destroy the contact structure.
⇔Thermal Expansion and Contraction Issues
Bimetal materials have different thermal expansion coefficients. Temperature changes cause differential expansion and contraction, putting stress on the rivet connection and contact surfaces. Over time, this can lead to cracking, rivet loosening, or damage to the contact interface. In outdoor equipment with large temperature variations, this is a significant failure factor.
In summary, bimetal rivet contact failures are due to electrical, mechanical, and environmental factors. Awareness of these modes allows for design improvements, better material choices, and preventive maintenance to boost reliability and lifespan in electrical systems.