Galvanizing refers to a surface treatment technology that coats the surface of metal, alloy or other materials with a layer of zinc for aesthetics and rust prevention. The main method used is hot dip galvanizing.
Zinc is easily soluble in acid and alkali, so it is called an amphoteric metal. Zinc changes little in dry air. In humid air, a dense basic zinc carbonate film will form on the zinc surface. In atmospheres containing sulfur dioxide, hydrogen sulfide and marine atmospheres, zinc has poor corrosion resistance. Especially in atmospheres with high temperature, high humidity and organic acids, the zinc coating is easily corroded. The standard electrode potential of zinc is -0.76V. For steel substrates, zinc coating is an anodic coating. It is mainly used to prevent corrosion of steel. Its protective performance is closely related to the thickness of the coating. After the zinc coating is passivated, dyed or coated with gloss protectant, its protective and decorative properties can be significantly improved.
basic introduction
Galvanizing refers to a surface treatment technology that coats the surface of metal, alloy or other materials with a layer of zinc for aesthetics and rust prevention. The main method used now is hot dip galvanizing.
galvanized
In recent years, with the development of galvanizing technology and the adoption of high-performance galvanizing brighteners, galvanizing has moved from pure protective purposes to protective-decorative applications.
There are two types of galvanizing solutions: cyanide plating solution and cyanide-free plating solution. Cyanide plating solutions are divided into micro-cyanide, low cyanide, medium cyanide and high cyanide. Cyanide-free plating solutions include alkaline zincate plating solutions, ammonium salt plating solutions, sulfate plating solutions and ammonia-free chloride plating solutions. Cyanide zinc plating solution has good throwing ability and the resulting coating is smooth and delicate, so it has been used in production for a long time. However, due to the highly toxic nature of cyanide and serious environmental pollution, in recent years there has been a tendency to use low-cyanide, micro-cyanide, and cyanide-free zinc plating solutions.
main feature
1. Smooth appearance, no zinc tumors or burrs, and silvery white in color;
2. The thickness is controllable and can be selected arbitrarily within 5-107μm;
3. No hydrogen embrittlement or temperature hazard, ensuring unchanged mechanical properties of the material;
4. It can replace some processes that require hot-dip galvanizing;
5. Good corrosion resistance, neutral salt spray test up to 240 hours.
Application scope Steel nails, iron nails, fasteners, water pipe joints, scaffolding fasteners, wire rope horse steel chucks, etc.
working principle
In the plating tank filled with galvanizing liquid, the cleaned and specially pretreated parts to be plated serve as the cathode, and the anode is made of plated metal. The two poles are connected to the positive and negative poles of the DC power supply respectively. The galvanizing solution consists of an aqueous solution containing metal plating compounds, conductive salts, buffers, pH adjusters and additives. After energization, the metal ions in the galvanizing solution move to the cathode under the action of potential difference to form a coating. The metal of the anode forms metal ions into the galvanizing solution to maintain the concentration of metal ions being plated. In some cases, such as chromium plating, an insoluble anode made of lead or lead-antimony alloy is used, which only serves to transfer electrons and conduct current. The concentration of chromium ions in the electrolyte needs to be maintained by regularly adding chromium compounds to the plating solution. When galvanizing, the quality of the anode material, the composition of the galvanizing solution, temperature, current density, energization time, stirring intensity, precipitated impurities, power supply waveform, etc. will all affect the quality of the coating and need to be controlled in a timely manner.
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