Industry Knowledge
What is the function of the surface treatment process of bimetal contact rivets
The core role of surface treatment process
The design philosophy of bimetallic rivets is to combine highly conductive metals (such as silver, copper) with high-strength metals (such as tungsten, molybdenum) to achieve excellent electrical properties and mechanical strength. However, due to the significant differences in physical and chemical characteristics of the two materials, problems such as interface corrosion and contact resistance fluctuations frequently occur, which seriously affects the overall performance of the rivets. Nantong Rongxin Electrical Control Technology's surface treatment process effectively solves these industry pain points through multiple mechanisms.
In terms of corrosion resistance, considering the easy oxidation of the tungsten-molybdenum matrix, Nantong Rongxin Electrical Control Technology adopts cyanide-free electroless nickel plating process to form a nickel-phosphorus alloy layer with a thickness of 2-3μm on the surface of the rivet. The coating has a density of more than 98% and exhibits excellent corrosion resistance of 720 hours without red rust in the neutral salt spray test (NSS), significantly exceeding the 96-hour standard of traditional galvanizing processes.
To optimize the conductivity, Nantong Rongxin applied a silver alloy conductive coating on the nickel layer using vacuum sputtering technology, with a thickness of 1-2 μm. Through fine regulation of components, Ag-Cu-Sn ternary alloy is used to stabilize the contact resistance at a level less than 3mΩ, meeting the needs of low-voltage signal transmission, and effectively suppressing the short circuit risk caused by silver migration.
In terms of wear resistance, in response to the problem of insertion and removal wear, Nantong Rongxin Electrical Control Technology sprays nano-grade molybdenum disulfide (MoS₂) as a solid lubricant to form a composite coating with a thickness of 0.5-1μm. The friction coefficient of the coating was reduced to 0.03, a 70% reduction compared to conventional graphite lubricants. After 100,000 plug-and-removal tests, the rate of change of contact resistance remains below 5%, ensuring the stability of the rivets during frequent use.
Process innovation
Nantong Rongxin Electrical Control Technology's surface treatment process is based on the collaborative design concept of materials, process and performance, and has built a triple protection system, further improving the reliability and durability of the product.
The bottom passivation treatment removes the oxide film at the composite interface through pickling and activation processes, thereby enhancing the binding force of the plating. To ensure surface cleanliness meet ISO 8502-3 standards, Nantong Rongxin has also introduced ultrasonic cleaning technology to ensure that every detail meets high standard production requirements.
In terms of middle layer strengthening, adding rare earth elements (such as cerium) during electroless nickel plating can effectively refine the grains to below 10nm, significantly increase the hardness to above HV800, while maintaining the toughness of the material and avoiding the risk of brittle fracture. This design not only enhances the mechanical properties of the rivets, but also improves its service life under extreme conditions.
The top layer functionalization accurately controls the thickness of the silver alloy layer through magnetron sputtering technology, and at the same time, the surface energy is improved in combination with plasma treatment technology, so that the adhesion of the lubricant coating can be increased to 8N/cm. This design ensures the stability and reliability of rivets in the automated assembly process, and meets the requirements of modern manufacturing for high efficiency and precision.
What impact does environmental factors have on the performance of bimetal contact rivets?
In modern industrial applications, the performance of bimetallic rivets is affected by a variety of environmental factors, especially temperature, humidity, vibration and impact, and corrosive gases. These factors not only affect the mechanical properties of the rivets, but also may lead to a significant decline in electrical properties.
Temperature influence
Temperature is an important environmental factor affecting the performance of bimetallic rivets. In high temperature environments, Nantong Rongxin's research shows that there is a significant difference in thermal expansion coefficient between the tungsten-molybdenum matrix and conductive layers such as copper and silver. The thermal expansion coefficient of tungsten and molybdenum is about 4.5×10⁻⁶/℃, while copper is about 17×10⁻⁶/℃. This difference can lead to interfacial stress concentration, thereby accelerating creep failure of the material. In automotive engine compartment applications, unoptimized rivets may rise to more than three times the initial value after continuous operation at 200°C for 1000 hours.
To cope with this problem, by designing an interface gradient structure, i.e. introducing a tungsten-copper transition layer between tungsten and molybdenum and copper layer, Nantong Rongxin successfully reduced the thermal stress by 60% and controlled the rate of change of contact resistance to within 5%. This innovation significantly improves the reliability of rivets in high temperature environments.
In low temperature environments, conditions below -40°C may cause material embrittlement. Nantong Rongxin's low-temperature impact test shows that the impact toughness of ordinary rivets at -60℃ is 70% lower than that of normal temperature. The rivets that use nanocrystallation have improved the toughness retention rate to more than 90% by refining the grains to below 5nm, which can meet the needs of extreme working conditions such as aviation and polar equipment.
Humidity effect
Humidity is a key factor in the corrosion resistance of rivets. In an environment with a relative humidity of more than 80%, the results of Nantong Rongxin's salt spray test showed that rivets without surface protection showed red rust within 72 hours. The rivets that have been protected by double protection from cyanide-free electroless nickel plating and vacuum sputtered silver alloys showed excellent performance of 720 hours of red rust-free in the neutral salt spray test, and the corrosion resistance is seven times higher than that of the traditional galvanizing process.
Humidity may also penetrate into the composite interface through capillary action, resulting in electrochemical corrosion. Therefore, Nantong Rongxin designed an interface closed-cell structure to form dense tungsten oxide nanopores between the tungsten-molybdenum and the copper layer, successfully reducing the moisture permeability to 10⁻¹⁰g/(cm²·s), effectively blocking the corrosion channel and significantly improving the durability of the rivets.
Vibration and impact
In fields such as rail transit and industrial automation, rivets need to withstand high-intensity vibration and impact. Nantong Rongxin's vibration test shows that the contact resistance fluctuates by unoptimized rivets after 100 hours at 10 g vibration acceleration. Through the multi-axial stress dispersing structure design, a wavy buffer layer is introduced between the nail head and the nail foot, which improves the vibration stability by 50%, ensuring that the contact resistance change rate is controlled below 5%.
In the impact test, ordinary rivets are prone to breaking their nail feet under 50J energy impact. However, rivets using high-strength toughness tungsten alloy matrix have an impact toughness of more than 120J/cm², meeting international standards such as IEC 61373, ensuring safety and reliability in high-strength environments.
Corrosive gases
In special environments such as chemical industry and oceans, corrosive gases such as hydrogen sulfide and chlorine pose a potential threat to the performance of rivets. Nantong Rongxin's accelerated aging test shows that ordinary rivets have a contact resistance of 50% in an environment containing 0.1ppm H₂S. The corrosion resistance of rivets using rare earth doped coating (adding 0.5% cerium to nickel-phosphorus alloy) has been improved by three times, and the contact resistance change rate is controlled within 10%, greatly extending the service life of the product.
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