In many fields such as machinery manufacturing and construction engineering, non-standard nuts are widely used and critical. Since nuts are exposed to different environments for a long time and are susceptible to corrosion by moisture, acid and alkali substances, their anti-corrosion performance is crucial. Surface treatment process is the core means to improve the anti-corrosion ability of non-standard nuts. There are significant differences in the effects of different processes on the anti-corrosion performance of nuts. Reasonable selection of processes requires comprehensive consideration of multiple factors.
The surface treatment processes of non-standard nuts are rich and varied, and each process has its own unique principles and characteristics. Galvanizing is a more commonly used process, which is divided into hot-dip galvanizing and electro-galvanizing. Hot-dip galvanizing is to immerse the nuts in molten zinc liquid to form a thicker and denser zinc layer; electro-galvanizing is to deposit a zinc layer on the surface of the nut by electrolysis. The nickel plating process forms a uniform nickel layer on the surface of the nut by chemical or electroplating. There is also Dacromet treatment, which is to immerse the nuts in a special coating solution containing zinc powder, aluminum powder, etc., and form an inorganic coating after high-temperature baking. In addition, there are processes such as blackening, cadmium plating, and coating with organic coatings, which are different in process and application scenarios.
The galvanizing process is widely used in non-standard nut processing due to its good anti-corrosion effect. The zinc layer formed by hot-dip galvanizing is relatively thick, generally up to tens of microns. The zinc layer is firmly combined with the nut matrix, which can effectively isolate air and moisture and play a physical protective role. At the same time, the chemical properties of zinc are more active than iron. When the zinc layer is damaged, the zinc will be corroded first, thereby protecting the nut matrix. This sacrificial anode protection method greatly improves the nut's anti-corrosion ability. The electroplated zinc layer is relatively thin, usually between a few microns and more than ten microns. Although the anti-corrosion performance is slightly inferior to hot-dip galvanizing, it is suitable for general environments where the anti-corrosion requirements are not particularly high because of its smooth surface, beautiful appearance, and low cost.
The nickel plating process also has unique advantages in the anti-corrosion of non-standard nuts. The nickel layer has good chemical stability and corrosion resistance, and can resist the erosion of a variety of chemical substances, especially in neutral and weakly alkaline environments. The surface hardness of the nut after nickel plating increases, and the wear resistance is also improved, which reduces the surface damage caused by friction, thereby reducing the risk of corrosion. In addition, the cadmium plating process has been widely used in high-strength non-standard nuts. The electrochemical properties of the cadmium layer are similar to those of zinc, which can provide sacrificial anode protection, but its toxicity is relatively high, and its application is gradually limited. The chrome plating process can form a hard and bright chromium layer on the surface of the nut, enhance the surface wear resistance and corrosion resistance, and is often used in occasions with high requirements for appearance and corrosion resistance.
The inorganic coating formed by Dacromet treatment has excellent anti-corrosion properties. The coating is composed of countless tiny zinc flakes, aluminum flakes and chromates, which has a good shielding effect and can effectively prevent the penetration of corrosive media. At the same time, the chromate in the coating has a passivating effect, which can form a protective film on the metal surface, further improving the anti-corrosion ability. Dacromet-treated nuts can still maintain good anti-corrosion effects in harsh environments such as high temperature, high humidity, and salt spray. Applying organic coatings is also a common anti-corrosion method, such as epoxy resin coatings, polyurethane coatings, etc. Organic coatings can form a continuous film on the surface of the nut to isolate the nut from the external environment, and coatings with special functions can be selected according to different use environments, such as acid-resistant and alkali-resistant coatings, high-temperature-resistant coatings, etc.
Different surface treatment processes have different anti-corrosion properties for non-standard nuts, which are mainly affected by a variety of factors. Parameter control in the process is crucial, such as temperature, time, zinc liquid composition during galvanizing, electroplating solution concentration and current density during nickel plating, etc. These parameters directly affect the thickness, uniformity and density of the coating, and thus determine the anti-corrosion performance. In addition, the properties of the nut base material will also affect the surface treatment effect. Different materials have different bonding abilities with the treatment layer, and their resistance to corrosive media is also different. Environmental factors should not be ignored. In harsh environments such as high humidity, high salt spray, strong acid and alkali, the anti-corrosion requirements for the surface treatment process are higher, and a more targeted treatment method needs to be selected.
When selecting a non-standard nut surface treatment process, many factors need to be considered comprehensively. The first is the use environment. If the nut is used in a highly corrosive environment such as marine engineering and the chemical industry, hot-dip galvanizing, Dacromet treatment or high-performance organic coating with excellent anti-corrosion performance should be preferred; in general indoor environments, electrogalvanizing or blackening treatment can meet the needs. The second is the cost factor. The cost of different processes varies greatly. For example, the cost of Dacromet treatment and chrome plating is relatively high. Under the premise of meeting the anti-corrosion requirements, a lower-cost process should be selected to control the production cost. In addition, the mechanical performance requirements, appearance requirements and environmental protection requirements of the nut should also be considered. For example, in the food, medical and other industries, a non-toxic and environmentally friendly surface treatment process should be selected.
The surface treatment process of non-standard nuts plays a decisive role in their anti-corrosion performance. Understanding the characteristics, influencing factors and selection basis of different processes can help us choose the most suitable surface treatment method for non-standard nuts according to actual needs, thereby improving the anti-corrosion ability of nuts, extending service life, and ensuring the safe and stable operation of mechanical equipment and engineering structures.
