Mary pipe pieces to use as a water pipe in the important parts, since the normally exposed to water and air, so that the corrosion resistance is important. Malleable iron pipe fittings commonly used in the product surface galvanized way to do anti-rust treatment. Which is divided into galvanized and hot-dip galvanizing cold galvanizing categories. So, how to distinguish between hot and cold galvanizing it?
To distinguish from the outside, since the cold galvanized coating evenly, so close to the surface of the blank, the product has a unique rough surface concavity, it looks smooth and bright. Since the electrical shielding phenomenon, cold plating layer is generally no internal galvanized (except for special galvanizing techniques). The hot dip galvanized pipe due later than the layer, and the liquid zinc illiquid, so the surface of the zinc layer is thicker, and because the hot-dip galvanizing layer surface will produce a layer of white protective oxide layer, so the color is generally more gloomy but nowhere near the degree of surface smoothness and cold plating products.
Now there are some manufacturers use some not galvanized black member in the surface coating layer of silver paint after posing galvanized pipe fittings sold. Its distinction is also very simple, with two tubes mutual knock, silver paint will come off the surface of the pipe. In addition, to distinguish from the color, silver paint off the pipe if it is not the case, paint is very bright, cold galvanized pipe was dark then bright, generally no internal zinc coating, and hot-dip galvanizing in a period of time after the factory will turn dark gray.
So cold and the hot dip plating pipe fittings in the end what kind of performance is more excellent it?
From the galvanizing process the product to specific analysis:
HDG also known as hot-dip galvanizing is a method of covering the metal layer of the tube immersed in the molten zinc was obtained.
Principle: galvanized coverage is good, dense coating, organic-free inclusions. As we all know, the mechanism of resistance to atmospheric corrosion of zinc mechanical protection and electrochemical protection, under atmospheric corrosion conditions zinc coating surface ZnO, slow down corrosion of zinc Zn (OH) 2 and basic zinc carbonate protective film, to a certain extent, this layer protective film (also known as white rust) damage will form a new film. When the zinc layer severely damaged, jeopardizing the iron matrix, the matrix of zinc produce electrochemical protection, standard potential -0.76V zinc standard potential -0.44V iron, zinc and iron to form micro-zinc battery as the anode are dissolved iron as the cathode is protected. Clearly galvanized resistance to atmospheric corrosion of the base metal than galvanized iron.
Hot-dip galvanizing layer forming process is iron matrix between the outermost layer of pure zinc and iron formation - process zinc alloy, iron surface is formed when hot-dip - zinc alloy layer between the iron and makes very pure zinc layer good combination of the process can be simply described as: when the workpiece is immersed in the molten iron liquid zinc, zinc is first formed and α iron (body-centered) solid solution in the interface. This is the base metal of iron dissolved in the solid state to form a crystalline zinc atom, a fusion between the two metal atoms, the atoms of gravity is relatively small. Therefore, when saturated in solid zinc melt, two elements of zinc, iron atoms interdiffusion spread to (or called infiltration) iron matrix of zinc atoms in the substrate lattice migrate gradually form an alloy with iron, and diffusion molten zinc liquid iron to form the intermetallic compound FeZn13, sunk galvanized pot, that is dross and zinc. When the workpiece is removed from the surface of molten zinc dip pure zinc layer.