Fastener Surface Treatment Processes And Their Applications in Electrical Terminals

As one of the most fundamental and widely used mechanical components, fasteners play an irreplaceable role in industries such as energy, electrical, electronics, machinery, metallurgy, molds, and hydraulics. Whether used in power equipment, control devices, or electrical connection components like screw terminal blocks and fuse terminal blocks, the quality of the fastener's surface treatment directly impacts product reliability and corrosion resistance.

In the modern electrical industry, components such as screw clamp terminals, screw clamps for fuse holder terminals, ground terminal blocks, and AMP terminal screws typically undergo rigorous corrosion protection and surface treatment to ensure long-term stability in high-humidity, high-temperature, and current-loaded environments. The following introduces several typical fastener surface treatment methods and their applications in electrical connectors.

Blackening (also known as bluing) is a classic rust-preventing process. By heating and oxidizing in a sodium hydroxide and sodium nitrite solution, a dense, ferroferric oxide (Fe₃O₄) film approximately 0.6–0.8μm thick forms on the fastener surface. This film provides certain rust and wear resistance, and is black or bluish-black in color with a uniform appearance.

In the electrical terminal industry, some M4 screw terminals and terminal screw blocks often undergo a bluing treatment to enhance the fastener's protective properties and maintain good electrical conductivity.

Phosphating is a process that forms a phosphate chemical conversion film on a metal surface. This film enhances corrosion resistance and serves as a primer before painting or electroplating, improving coating adhesion.

In high-end screw terminal wire connectors and block terminal electrical assemblies, the phosphate coating effectively prevents screw seizure and thread galling, enhancing smooth assembly and torque consistency.

Hot-dip galvanizing involves immersing derusted steel parts in a zinc bath at approximately 600°C, forming a thick zinc layer on the surface. This coating offers exceptional corrosion resistance and is commonly used for fasteners used outdoors or in high-humidity environments.

In distribution cabinets, transformers, and industrial terminal applications, such as screw clamps for fuse terminals and screw-type terminal blocks, hot-dip galvanizing effectively prevents terminal loosening and conductivity degradation caused by electrochemical corrosion.

Dacromet is a high-performance corrosion-resistant coating composed primarily of zinc powder, aluminum powder, and chromic acid. It offers excellent salt spray and heat resistance. Compared to traditional electroplated coatings, it is less susceptible to hydrogen embrittlement and is ideal for high-strength fasteners and precision terminal screws.

In the manufacture of electrical screw terminal blocks and fuse terminal blocks, Dacromet treatment maintains long-term corrosion resistance while ensuring torque consistency and electrical stability of screw clamp terminals.

Electrogalvanizing is a common process that deposits a metal layer on the surface of fasteners using electrolysis. The resulting coating is dense, bright, and cost-effective. Commonly used for surface protection of components such as screw terminals, AMP terminal screws, and ground terminal blocks.

Electrogalvanized coatings can be applied in various finishes, including white, blue, and colored zinc, depending on the intended use. In the electrical industry, galvanized screws are commonly found in screw clamps for fuse holder terminals and terminal screw blocks, offering both aesthetics and practicality.

In addition to the aforementioned processes, fastener surfaces can also be treated with a variety of other treatments, including electroplating with nickel, silver, chromium, sherardizing, and anodizing, depending on the operating environment. For example, in screw terminal wire connectors, which require high conductivity, silver plating not only improves conductivity but also prevents oxidation, ensuring long-term stability of the connection between the terminal and the wire.

With the development of industrial automation and new energy equipment, the reliability requirements for screw clamp terminals and screw terminal blocks are continuously increasing. Excellent surface treatment can significantly improve the corrosion life, torque consistency, and electrical conductivity of connectors. In new energy storage equipment, intelligent power distribution systems, rail transit, and electric vehicle charging devices, the use of fuse terminal blocks and electrical block terminals with superior corrosion resistance has become a mainstream trend.

In the future, fastener surface treatments will increasingly utilize environmentally friendly chromium-free coatings and nano-ceramic composite films to achieve green manufacturing and highly reliable electrical connections.

Although small, fasteners are critical components in electrical systems that perform both mechanical and electrical functions. Scientific surface treatment technologies can not only enhance the corrosion resistance of screw terminals and ground terminal blocks, but also ensure long-term electrical conductivity and stability, providing solid support for the safety and reliability of electrical connections.