Round head rivets, as key components in mechanical connections, have their surface treatment processes directly impacting the friction, durability, and overall structural stability of the riveting. To enhance the friction between the round head rivets and the connecting parts, a comprehensive design considering surface roughness, chemical stability, and mechanical interlocking is necessary. The following analysis examines different process principles.
Sandblasting uses a high-pressure airflow to propel abrasive particles onto the surface of the round head rivets, creating a uniform micro-pitted structure. This treatment significantly increases surface roughness, resulting in a mechanical interlocking effect when the rivet contacts the connecting parts. For example, in automotive chassis riveting, the surface roughness of sandblasted rivets can reach Ra3.2-6.3μm, increasing the coefficient of friction by more than 40% compared to polished surfaces. Simultaneously, sandblasting removes the oxide layer and oil from the rivet surface, providing an active surface for subsequent coating adhesion and further enhancing the composite friction performance.
Zinc plating deposits a zinc layer on the rivet surface through electrochemical processes. Besides its anti-corrosion function, the micro-rough structure of the zinc layer improves frictional stability. The zinc oxide protective film formed by the zinc layer in the air has porous properties, allowing it to absorb moisture from the environment and form a lubricating film, thus dynamically adjusting the coefficient of friction under dynamic loads. This characteristic makes galvanized rivets particularly suitable for structural connections in humid environments, such as bridge steel structure riveting, preventing electrochemical corrosion while maintaining long-term stable friction performance.
Dacromet coating, an inorganic zinc-aluminum composite coating, forms a dense protective structure through the interlocking of multiple layers of lamellar zinc-aluminum flakes. While providing excellent corrosion resistance, its microscopic surface protrusions significantly increase the contact area. Experiments show that Dacromet-treated rivets maintain a coefficient of friction above 0.35 after 1000 hours of salt spray testing, a 25% improvement over ordinary galvanized rivets. This characteristic makes it the preferred solution for riveting in marine engineering equipment.
Mechanical plating forms a dense coating on the rivet surface through a cold welding process using metal microparticles. Its unique deposition method results in a uniform granular protrusion on the coating. This structure creates numerous friction contact points at the microscopic level, resulting in a more uniform load distribution. Compared to electroplating, mechanically plated rivets exhibit a 30% reduction in the fluctuation range of the coefficient of friction, making them particularly suitable for precision instrument riveting, such as lightweight structural connections in aerospace equipment.
Blackening treatment generates a black iron oxide (Fe3O4) film on the rivet surface through chemical oxidation. This film has a porous structure. During riveting, the film deforms under pressure, forming a micro-interlocking structure. Simultaneously, the porous structure stores lubricating media, enabling dynamic adjustment of the coefficient of friction. This treatment method keeps the coefficient of friction fluctuation within ±0.05 under alternating loads, significantly improving connection reliability.
Composite treatment processes achieve synergistic performance by combining different surface treatment technologies. For example, sandblasting increases surface roughness, followed by the application of a Dacromet coating to form an anti-corrosion friction layer, and finally a sealing treatment to fill the micropores. This three-layer composite structure allows the rivet to maintain a high coefficient of friction while achieving corrosion resistance exceeding 1000 hours according to ISO 9227 standards, meeting the requirements of harsh environments such as rail vehicles.
The selection of surface treatment processes must comprehensively consider the operating environment, load characteristics, and cost factors. For dynamic load scenarios, sandblasting or mechanical plating processes that can form a mechanical interlocking structure should be prioritized; in corrosive environments, Dacromet or composite treatments are more advantageous; and for precision connection scenarios, the relationship between the coefficient of friction and surface finish needs to be balanced. Through targeted process design, the connection performance of round head rivets can be significantly improved, providing a reliable guarantee for the safe operation of mechanical structures.
