راية الأنابيب الفولاذية

Carbon Steel, Galvanized Steel, Alloy Steel, Stainless Steel Pipe Coating Services

Gnee Steel provides a variety of protective coating and lining services. The most common coating and lining services are FBE, Synergy Wrap, Spiral Wrap, and Galvanizing. The common lining types are FBE & Cement Lining. These protective layers help prevent corrosion. The pipe size range for these services is normally 1/8″ OD and up.

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تضمن Gnee أن متطلبات العملاء مفهومة بوضوح وقادرة على توفير حلول الطلاء التي تلبي المعايير. ويشمل نوع الطلاء (مثل الطلاء المضاد للتآكل، والطلاء المضاد للصدأ، والجلفنة بالغمس الساخن، وما إلى ذلك)، وسمك الطلاء، ومواد الطلاء، ومتطلبات معالجة السطح، وما إلى ذلك.

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تقوم Gnee باختيار تقنيات ومواد الطلاء المناسبة. قد يشمل ذلك طرق طلاء مختلفة مثل الرش، والطلاء بالغمس، والطلاء الكهربائي، والجلفنة بالغمس الساخن، وما إلى ذلك. وفي الوقت نفسه، نختار مواد طلاء عالية الجودة تلبي المعايير والمتطلبات ذات الصلة لضمان متانة وأداء الطلاء.

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Gnee ينشئ عملية مراقبة الجودة الصارمة. نحن نضمن أن كل أنبوب فولاذي يخضع لعمليات التنظيف والمعالجة المسبقة والطلاء المناسبة، وكذلك يخضع لفحوصات واختبارات الجودة اللازمة.

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Introduction Of Hot-dip Galvanizing Process

What Is The Process Of Galvanizing?

Galvanizing is a metallurgical process. The most common method of galvanizing is hot-dip galvanizing. Hot-dip galvanizing process generally refers to the process of placing black carbon steel pipes and fittings into a zinc bath to coat the pipes or fittings with a layer of zinc. In recent years, with the rapid development of high-voltage power transmission, transportation, communication and other industries, the requirements for steel product protection are higher and higher. The demand for hot-dip galvanizing is increasing.

Hot Dip Galvanizing Process: Workpiece → degreasing → water washing → pickling → water washing → dipping auxiliary plating solvent → drying and preheating → hot-dip galvanizing → finishing → cooling → passivation → rinsing → drying → inspection

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Galvanizing Process
Galvanizing Process

Protective Properties Of Hot-Dip Galvanized Layer

Usually the thickness of galvanized layer is 5~15μm, while the thickness of hot-dip galvanized layer is generally above 65μm, even up to 100μm. hot-dip galvanized has good covering ability, dense coating and no organic inclusions. As we all know, the mechanism of zinc resistance to atmospheric corrosion, including mechanical protection and electrochemical protection, in the atmospheric corrosion conditions, the surface of the zinc layer has ZnO, Zn (OH) 2 and alkaline zinc carbonate protective film, which can slow down the corrosion of zinc to a certain extent, and if this layer of protective film (also known as white rust) is destroyed, a new film will be generated. When the zinc layer is severely damaged, endangering the iron substrate, zinc provides electrochemical protection to the substrate. The standard potential of zinc is -0.76 V, and the standard potential of iron is -0.44 V. When zinc and iron form a microcell, the zinc is dissolved as the anode and the iron is protected as the cathode. Obviously hot-dip galvanizing has better atmospheric corrosion resistance to the base material iron than electro-galvanizing.

Hot-Dip Galvanized Layers Formation Process

The process of forming a hot-dip galvanized layer is the formation of an iron-zinc alloy between the iron matrix and the outermost layer of pure zinc. The formation of an iron-zinc alloy layer on the surface of the workpiece during hot-dip galvanizing results in a good bond between the iron layer and the pure zinc layer. The process can be described simply as follows: When an iron workpiece is immersed in a molten zinc solution, a solid melt of zinc alpha iron (body core) is first formed at the interface. This is a crystal formed when the zinc atoms dissolve in the solid state of the base metal iron. The two metal atoms are fused together and the attraction between the atoms is relatively small. Therefore, when the zinc is saturated in the solid melt, zinc, iron two monomers atoms diffuse into each other, diffusion (or infiltration) into the iron matrix of zinc atoms migrate in the matrix lattice, and gradually with the formation of iron alloy. Iron and zinc diffused into the molten zinc solution form the intermetallic compound FeZn13, which sinks to the bottom of the hot-dip galvanizing pan and forms zinc slag. When the workpiece is removed from the zinc dip solution, a layer of pure zinc is formed on the surface as hexagonal crystals. Its iron content shall not exceed 0.003%.

Consult For our sTEEL PIPE Process
Galvanizing Process

Process Description Of Hot-Dip Galvanizing

Step 1

Degreasing

The workpiece can be degreased using chemical degreasing or a water-based metal degreasing cleaner until the workpiece is fully immersed in water.

Step 2

Pickling

Acid washing can be carried out with H2SO4 15%, thiourea 0.1%, 40~60℃ or HCl 20%, hexamethylenetetramine 1~3g/L, 20~40℃. Adding corrosion inhibitor can prevent excessive corrosion of the substrate and reduce the hydrogen absorption of the iron substrate. Poor degreasing and pickling treatment will result in poor adhesion of the plating, failure to apply zinc or zinc peeling off.

Step 3

Dip Plating Auxiliary Agent

Also known as adhesive, it can make the workpiece maintain a certain activity before dip plating, in order to enhance the bonding of the plating layer and the substrate.NH4Cl 15%~25%, ZnCl2 2.5%~3.5%, 55~65 ℃, 5-10 minutes. To reduce the volatilization of NH4Cl, glycerol can be added appropriately.

Step 4

Drying Preheating

In order to prevent the workpiece from deformation caused by the sharp rise in temperature during dip plating, remove the residual moisture, and prevent the phenomenon of zinc explosion, resulting in zinc splash, the preheating temperature is generally 120~180℃.

Step 5

Hot-Dip Galvanized

It is necessary to control the temperature of zinc liquid, dip plating time, the speed of the workpiece from the zinc liquid. Low temperature, the liquid liquid fluidity of zinc is poor, the coating is thick and uneven, easy to produce hanging, poor appearance; high temperature, liquid fluidity of zinc is good, the liquid is easy to detach from the workpiece, hanging wrinkles to reduce, strong adhesion, thin coating, good appearance, high productivity; but the temperature is too high, the workpiece and zinc pot iron damage is serious, produce a large number of zinc slag, affect the quality of the zinc layer dipping, resulting in high zinc consumption, or even can not be coated with zinc. At the same temperature, the dip galvanizing time is long and the coating is thick. When the same thickness is required at different temperatures, high-temperature dip galvanizing takes a long time. In order to prevent high temperature deformation of the workpiece, reduce iron loss caused by zinc slag, general manufacturers use 450 ~ 470 ℃, time 0.5 ~ 1.5 min. Some factories use higher temperatures for large workpieces, cast iron parts, but need to avoid the peak temperature range of iron loss. In order to improve the fluidity of the hot dip plating solution at lower temperatures, to prevent excessive thickness of the plating layer, improve the appearance of the plating layer, often adding 0.01% ~ 0.02% of pure aluminum. Aluminum should be added in small quantities several times.

Step 6

Organization and Passivation

The main task of finishing the workpiece after plating is to remove the residual zinc and zinc tumor on the surface, which can be carried out by vibration method or manual method.
The purpose of passivation is to improve the atmospheric corrosion resistance of the surface of the workpiece, reduce or extend the time of white rust, and maintain the good appearance of the plated layer. Passivation with chromates and dichromates, such as Na2Cr2O7 80 ~ 100g / L, sulfuric acid 3 ~ 4ml / L.

Step 7

Cooling

Generally use water-cooled, but the temperature should not be too low, in order to prevent the workpiece, especially castings due to quenching contraction and cracking of the matrix organization.

Step 8

تقتيش

The appearance of the plating is bright, fine, no hanging, wrinkle phenomenon. Thickness checking can be carried out by plating thickness gauge, which is a relatively simple method. The thickness of the coating can also be converted to the amount of zinc adhesion. The bonding strength can be used to bend the specimen 90-180 ° bending machine, there should be no cracks, coating flaking and other phenomena. It can also be checked by hitting with a heavy hammer.

Display Of Galvanizing Equipment

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