Knowledge and technology of hot galvanizing

Galvanization of hot galvanization steel of use galvanization just is useful extensive, in extensive national economy each have a few. The use of galvanizing talents primarily focuses on building, cars, appliances and containers. The following table shows the primary use of galvanized steel.

Function of hot-dip galvanized steel

Main mechanical function

Galvanized steel sheet needs to be formed when used, so it is required to have certain strength, but also should have excellent deep drawing function. The internal annealing of normally low carbon steel plate using Sendzimir production line does not meet this request. However, for goods that are usually lightly processed by deep drawing, the method of reducing the speed of the steel strip operation (that is, extending its stay in the recovery furnace) can be chosen.

Input corrosion resistance

Galvanized steel has excellent atmospheric corrosion resistance. This is because zinc has a lower potential than iron, and the zinc layer is positive for the steel matrix and negative for iron. In the electrolyte, the zinc layer dissolves to maintain the steel matrix from corrosion. In addition, the zinc layer in the ordinary atmospheric environment, its corrosion product is usually basic zinc carbonate [ZnCO3?Zn(OH)2], it has certain maintenance effect on the zinc layer. However, in the sulfur-bearing industrial atmosphere, the corrosion product is the water-soluble zinc sulfate salt, which is easy to be washed away by rain, and cannot prevent further corrosion of zinc layer. Thus, the zinc layer corrodes rapidly in the industrial atmosphere.

Welding function

Galvanized steel sheet has excellent weldability, can spot welding and seam welding. When spot welding, its welding strength and low carbon steel spot welding close. But the welding current should be increased by 10% ~ 15%.

Zinc pot and heating heat source

1. The zinc pot

Zinc pot is a key equipment for hot galvanizing steel.

Contour scale and shape

(2) material

(3) the thickness of the

ichnoid

2. Heating source

Look out for a few headlines when choosing a heat source:

Discharge high thermal power

Outstanding adjustable rationality

The temperature of the outer wall of the pot can be maintained

Heat uniformly along the outer wall of the pot, without cooling and over-heating.

Hot galvanizing of steel structure and malleable steel

There are many kinds of steel parts, and the shape is mixed. As a result, its hot galvanizing skills can only be selected by flux method.

Due to the various shapes of steel structural parts, full attention should be paid to its spreader planning. The following factors should be considered when planning the spreader: easy operation, less zinc liquid, strong suspension, component non-deformation, workpiece not suffocating (holes should be punched in the difficult part of air discharge, air free discharge when dipping zinc), zinc liquid backflow dredge, etc.

The pretreatment of malleable steel parts is usually first shot to remove the moulding sand adhering to the appearance. Then, put into the pickling roller for rolling pickling. The roller is immersed in the pickling tank below the ground. When the rolling time is certain, discharge the acid wash, and then pass into cold water for rolling washing. The cleaned malleable steel parts will be funneled into the flux treatment rotor. The rotating cylinder is immersed in the flux tank, discharged from the outlet with a screw propeller, and automatically enters and lands in the basket to prepare for galvanization.

A frame basket with malleable steel parts is hoisted into a zinc pot. The surface residue of the zinc liquid should be removed before dipping and removing the zinc pot. After hoisting out the zinc pot, it should immediately put on the rotary table of the centrifuge, start the centrifuge, by the effect of centrifugal force to get rid of the malleable steel surface and internal residual zinc liquid. And then water cooling.

Galvanized steel pipe

Steel tube hot galvanizing skill mostly chooses flux method. Over the years, hydrogen recovery has been announced as a new skill developed on the basis of continuous hot galvanizing of the Sendzimir steel strip. But because of some skill titles, it has not yet been implemented.

Flux steel tube galvanizing process is the same as single sheet steel flux galvanizing process. Because the original pipe is usually free of oil and does not require degreasing process, directly into the pickling process. When pickling, the control is first hoisted into the first pickling tank for prepickling. Then it is hoisted into a second pickling tank for pickling to remove all iron oxide. Usually choose hydrochloric acid or sulfuric acid heated to 50 ~ 60 ℃. The concentration of acid wash solution is 10% ~ 20%, which has good effect. The pickling time shall be determined according to the condition of the oxidized iron sheet on the outer surface of the steel pipe. Often string the steel pipe, can speed up the pickling process. As a result, the bottom of the pickling trough and the side wall device protruding the wooden bar, facilitates the steel pipe to roll in the pickling liquid.

In the normal galvanized temperature scale (445 ~ 465 ℃), zinc liquid temperature, can increase the activity of the zinc liquid. The surface quality of the zinc layer can be advanced and the reflux of the zinc solution can be improved to decrease the coating component. In addition, can also shorten galvanizing time, forward the output power of zinc pot. However, the galvanizing temperature is too high, which will lead to the deformation of steel pipe.

Hot-dip galvanized steel wire is divided into mild steel wire of usual use and medium high carbon steel wire of special use. Hot galvanizing of steel wire is usually by flux method and hydrogen recovery method is rarely used. The process of hot-dip galvanization of low carbon and medium high carbon steel wire is slightly different. The skills flow is as follows:

Hot dip galvanized steel sheet

1. Hot-dip galvanizing skills

First choice flux method hot galvanizing skill

Flux method sheet sheet hot galvanizing process is as follows:

2. Continuous hot galvanizing production line of steel belt

There are four main production lines: non-oxidizing furnace production line, American steel link production line, Wheeling production line and Selas production line

3. Type of galvanized steel sheet

The first type is; Large galvanized sheet, small galvanized sheet, poor thickness galvanized sheet, single side galvanized sheet

4. Alloy galvanized steel sheet

For more than ten years, because the car industry and home appliance industry use galvanized steel sheet a lot, and put forward higher request to the function of galvanized steel sheet, that is, besides should have good corrosion resistance, also should have good stamping forming, welding and coating. As a result, the economic prosperity of the country has conducted a lot of research on the composition of the steel base, the structure and function of the hot-dip galvanizing layer and so on.

It is well known that hot dip galvanized steel, which usually calms and eases steel, can only satisfy the general need for construction, vessels, etc. But regarding the automobile industry and the household appliance industry, because to the board deep to rush the request high but cannot satisfy. To this end, the IF steel (no interstitial atomic steel) was announced in the 1970s. It has excellent stamping properties. After hot-dip galvanizing and alloying, it has better welding, corrosion resistance and coating property, and is suitable for the surface of cars and household appliances. During the process, the most important effect on its function is its forming and welding. Hot dip galvanized steel sheet is also the main topic for discussion in recent ten years.

Hot dip galvanizing of hot rolled steel sheet

It is well known that the strips of steel are continuously hot-dip galvanized with a uniform cold rolled sheet. Over the years, hot rolled sheet is gradually selected as the original plate.

Elements influencing the functions of hot galvanizing layer

In the process of hot galvanizing, the primary influencing factors are:

(1) zinc liquid temperature and dipping time

In the normal galvanized temperature scale (445 ~ 465 ℃), zinc liquid temperature, can increase the activity of the zinc liquid. The surface quality of the zinc layer can be advanced and the reflux of the zinc solution can be improved to decrease the coating component. In addition, can also shorten galvanizing time, forward the output power of zinc pot. However, the galvanizing temperature is too high, which will lead to the deformation of steel pipe.

In the process of hot galvanizing, the zinc liquid temperature (or galvanizing temperature) and the time of galvanizing have the main influence on the galvanizing layer. Iron loss from galvanizing is usually used as a parameter of fe-zn reverberation rate. Iron loss refers to the amount of iron that forms the alloy layer with the reaction of iron and zinc, and that layer falls off and becomes some of the iron in the zinc slag.

(2) chemical composition of steel matrix

Generally speaking, the higher the carbon content in steel, the stronger the response of fe-zn, the greater the iron loss, and the thicker the naturally formed alloy layer.

The effect of silicon on hot galvanizing is most prominent in steel. Carbon steel is usually rich in a small amount of silicon.

C. The influence of copper due to the mineral material, some carbon steels may be rich in a small amount of copper, while a small amount of copper has no obvious influence on the structure of galvanized layer. The galvanizing layer of copper - containing steel has good atmospheric corrosion resistance.

[d]. Impacts of manganese, sulfur and phosphorus are generally rich in required quantities of manganese and a few sulfur and phosphorus in low carbon steel. In general, manganese and sulfur have no obvious effect on the structure of the galvanized layer.

(3) composition of zinc liquid

A. The influence of aluminum on the structure and function of the coating is mainly affected by the increase of aluminum in zinc liquid.

B. the influence of lead zinc ingots is often rich in a small amount of lead, about 0.003% ~ 1.75%. The solubility of lead in zinc liquid is about 1.2% under 450 ~ 455 ℃. This small amount of lead has no effect on the composition of fe-zn alloy. But it can drop the melting point of zinc.

C. Effect of iron on iron solubility in zinc solution is small.

D. The influence of cadmium in zinc ingots is usually rich in small amounts of cadmium, about 0.001% ~ 0.07%.

E. The effect of tin on the zinc solution by adding tin can also decrease the melting point of the zinc solution and extend the solidification time to obtain a beautiful large zinc-flowered zinc coating.

F. antimony and bismuth affect both antimony and bismuth in zincal solution by lowering the melting point of zinc and obtaining a zinc coat of large zinc flowers.

G. Effect of copper the addition of copper to zinc is beneficial for corrosion resistance of the progressive zinc coating

Composition of hot galvanizing layer:

During hot galvanizing of steel, a series of disordered physical and chemical processes occur between zinc solution and steel. For example, the infiltration of zinc solution to steel surface, the dissolution of iron, the chemical reaction between iron atoms and zinc atoms, and the diffusion of iron atoms and zinc atoms.

As a result of this process, Fe-Zn alloy layers of iron and zinc are formed on the surface of the steel.