Basic knowledge of continuous electrogalvanized cold-rolled steel sheets and strips

Consecutive Zinc Plating Cold-rolled Steel Sheet and Strip Basics

Cold-rolled steel sheet and strip are metal products produced from hot-rolled sheet steel, formerly cooled and rolled down to the required sheet thickness and width at room temperature. The cold-working process produces sheet steel with higher strength and higher hardness in comparison to hot-rolled sheet steel, due to the interstitial dislocation motion in the crystal lattice and the strain hardening of the metal itself.

Since cold-rolled steel products are characterized by thin thicknesses, high strength and hardness, they are most commonly and widely used in the production of electrical appliances, auto parts and containers. The processing and manufacture of these features require uniform coverage and corrosion resistance of the surface, which can be obtained through metal plating. Additionally, the electroplating process provides properties such as low coefficient of friction, increased fatigue strength and improved wear resistance, as well as improvements in appearance.

Zinc plating is the most commonly used metal plating process for the production of cold-rolled steel sheet and strip. Zinc plating offers low cost and excellent corrosion protection, and is especially suitable for products consisting mainly of steel. Zinc plating also improves the appearance of cold-rolled steel sheet and strip products, as it has a bright, glossy finish.

The continuous zinc plating process consists of three main steps. The first step is the cleaning of the steel surface. This includes degreasing and an acid pickling process to remove oils, other organic contaminants and oxides from the steel surface. The second step is the electroplating process itself, in which a zinc anode electrode is placed in a plating tank and a current is applied to the steel samples via the anode, which deposits a thin layer of zinc on the samples. The third step is a post-treatment process, unwhich a thin chromium layer is applied to the processed samples. This thin chromium layer adds on top of the zinc layer and forms a layer of corrosion protection on the steel surface.

The success of any continuous zinc plating process depends on several factors. These include the acid concentration of the pickling bath, the voltage and current applied during electroplating, pH control in the solution, temperature control, agitation and air bubbles, and the use of acid flux or other chemicals in the solution. The most important factor in the process is the concentration and quality of the zinc anode used in the plating tank. The higher the purity and concentration of zinc in the anode, the higher the resulting layer of zinc deposits on the steel surface.

In conclusion, cold-rolled steel sheet and strip production requires a surface coating for improved appearance and corrosion protection. Continuous zinc plating is the most common plating process used for this purpose, and is characterized by low cost and excellent protection from corrosion. To successfully complete the process, several factors have to be taken into account, such as the acid concentration of the pickling bath, the voltage and current applied during electroplating, pH control in the solution, temperature control, agitation and air bubbles, and the use of acid flux or other chemicals in the solution. Finally, the quality of the zinc anode is the most critical parameter for successful plating.

Continuous galvanizing technology is used to provide ultimate protection against rust and corrosion for steel strip and plate products. Hot-dip galvanizing is the most common and cost-effective process used for this purpose. This process is often used for cold-rolled steel sheets and steel strips, as hot-rolling strips would damage the zinc layer.

Cold-rolled steel strips and plates undergo a series of processes before they can be hot-dip galvanized. Cold-rolling is one of the most important processes, and allows for tight control of the steel’s shape, size, and thickness. After cold rolling, steel sheets and strips go through a pickling process to clean the surface of any rust or oxidation. The pickling process also leads to a rougher surface which helps increase the adhesion of the zinc.

The steel strips and plates are then immersed in a zinc bath to coat the material with zinc. This bath is composed of liquid zinc and various chemicals that help protect the zinc from oxidation or other unforeseen circumstances. The steel plates or strips are heated to a temperature above 860° F in order to ensure a zinc coating is properly applied and adhered.

Once galvanization is complete, the sheets and plates are passivated to ensure a pristine finish. Passivation removes any remaining chemicals and impurities on the outermost layer of the zinc to ensure that the material is ready for use. Cold-rolled galvanized steel strips and plates have excellent corrosion-resistant properties and other known benefits, making them ideal for many applications such as in automotive and construction.