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Annual designedcapacity of the plant is 12,800 tons.
Energy used is electrical energy.
Galvanizing temperature is 440-450 degrees Celsius.
Dimensions of the baths are 7000mm x 2200mm x 1800mm.
Cranes load is 2 x 2 tons.
Standards EN ISO 1461, ASTM A-123, ASTM A-385

 

HOT DIP GALVANIZING TECHNOLOGY

Hotdip galvanizing process consists of:
- Inspection and charging structure to the batch, chemical preparation and the process of galvanizing.
Chemical treatment is a series of actions of sinking construction into different solutions. Drying in the dryer at temperature up to 150° Celsius. After chemical preparation is done construction is dipped into molten zinc at a temperature of 440-450° Celsius. Dipping it in molten zinc coating creates a protective layer of Zn and Fe alloy and the zinc layer, which protects the structure from corrosion.
After galvanizing is done structure is cooled in the bathtub with water. Then the structure is immersed in a solution for passivation, which is used to stabilize the coating and the prevents  the formation of "white rust".
Then the construction is rinsed with water and inspection of galvanized construction is done.

The factorycontrols all the parameters of the technological process:
- Temperature of the solution in the bath
- Concentration and density of solution
- The amount of ferric salts and acids an the amounts of iron in the flux
- The temperature of zinc in the furnace-permanent
- Testing the solution of zinc in zinc and other metals
- Look and coating thickness


CHEME OF TECHNOLOGICAL PROCESS OF HOT-DIP GALVANIZING

 

Bathtub dimensions:
Dimensions that can be galvanized at once depend primarily on the dimensions of the bathtubs.
Dimensions of our bathtubs:
- Length 7000 mm, width 1800 mm, height 2200 mm;
It takes two times to galvanize pieces up to 9500 mm long.
The maximum weight of construction for galvanizing may be up to 3800 kg.

Purchasershould consult on dimensions and weight of constructions he wants to galvanize.

MATERIALS SUITABLE FOR HOT GALVANIZING
Prior to the preparation of construction designer needs to know whether the material could be galvanized and therefore must use materials that are suitable for hot-dip galvanizing.


Most of the material containing iron, hot rolled steel, cold rolled steel, steel casting can be successfully protected against corrosion by hot dip galvanizing.


For hot galvanizing particularly suitable are unmitigated and reassured aluminum steels. In these steels normal coating is produced (coating which contains iron alloy layer iron- zinc and a layer of pure zinc).

Chemical composition of  material affects the quality of the zinc coating.
Steel which is used for galvanizing in its chemical composition should have:
- Carbon (C <0.25%), silicon (Si <0.32%), phosphorus (P <0.04%), manganese (Mn <0.25%).
If there is a surplus of these elements it would lead to the formation of coating different from normal. These elements have an effect on the rapid growth of the layer alloy steel - zinc, while the growth of pure zinc layer may be missing.

Such acoating is visible as matt gray surface opposite the usual glossy appearance and smooth galvanized coatings, and these are more brittle and unstable than normal coating.


Galvanized coatings are specified for their resistance to corrosion, and not by their looks. Relative corrosion resistance of normal and abnormal coatings in practical terms is the same.


Structural part of the construction should be made ​​up of elements from the steel of similar chemical composition and surface condition.

TABLE OFCOATING THICKNESS FOR NOT  CENTRIFUGED SAMPLES  ACCORDING TO EN ISO 1461

PRODUCT AND THICKNESS

LOCAL  THICKNESS OF THE LAYER µm (minimum)

MID THICKNESS OF THE LAYER µm (minimum)

STEEL≥6mm

70

85

STEEL≥3mm to< 6 mm

55

70

STEEL≥1,5mm to< 3mm

45

55

STEEL< 1,5mm

35

45

CASTS≥ 6mm

70

80

CASTS< 6mm

60

70

 

COMBINATION OF DIFFERENTMATERIALS AND COMBINATIONS
Different manufacturing methods, the combination of different materials can make it difficult to get uniform coating.
You should avoid the combination of old and new steel, as well as casted and rolled in the same construction.
Various parameters of immersion in solutions (immersion time, solution concentration) are required for:

- Extremelycorroded surfaces;
- Machined surface finish;
- Castings;
- Hot-rolled steel;
- Cold-rolled steel;
- Cast iron;
- Wrought iron;
- Steel with higher content of C, Mn, P, Si;

Rusty, embossed, or forged steels should not be used in conjunction with new or machined surfaces due to the difference in the above parameters.


Manufacturer of cast parts must know in advance that they will be galvanized, and that it is necessary to perform a quality sandblasting and cleaning of surfaces, and graphite and sand must be completely removed from the surface.


If there is a need for the combination of different materials then sandblasting of the surface is needed and is necessary to remove all the sand.
There should be no mistakes of double plasticity, rolled cunder, rolled emulsion or dirt.

 

 

GALVANIZINGHOLLOW BODIES, TANKS
Since it is not possible to follow the process of galvanizing on the inside, there is a need to clean  internal surfaces in order to prepare them better for galvanizing. Otherwise, outside zinc coating can be perfect but it does not mean it is the same inside.

DEFORMATIONS OF CONSTRUCTION
The cause of the construction deformation so called contortions is the release of internal stresses during the galvanizing temperature to 450 degrees Celsius.
Self strains are represented in each construction in the form of:
- Stress of rolling
- Stresses of cold treatment
- Stresses from welding

Thesestresses are in balance so there is no deformation. By entering the heat balance is disturbed and deformations can occur.
When welding there special attention should be taken to avoid unnecessary stress, which later in galvanizing can lead to deformities.
Internal stresses caused by improper welding during hot dip galvanizing can cause material  deformation.
Joining elements of varying thickness can also be the cause of deformation since cooling and heating rate of different thickness are different.

EXAMPLESOF THERMAL DEFORMATIONS  ARE:
- Thin sheets of larger dimensions
- Structures where sheets of various thicknesses were welded
- Fixed mashes in frames or individual
- Long tubes and profiles


Deformations of the structures can not be controlled in galvanizing. Therefore galvanizing process is not responsible for any deformations that occur as a result of temperature fluctuations.

Deformation can be reduced or avoided in the following manner:
- Proper welding to balance stress on the entire construction
- Symmetrical welding as close to the median line and no more than necessary
- Avoiding sporadic or spot welding, especially when connecting plates of different thicknesses and profiles
- Previous annealing - easing tension in the material
- Provide openings for filling and emptying in the required format to facilitate rapid immersion of tube elements

- Insertingreinforcement which must be of the same material and the more uniform thickness
- Hanging construction in several places to prevent the bending (if the shape of the structure allows it)
When galvanizing welded assemblies, weld zone and metal composition may affect the characteristics of the coating.
When welding uncoated electrodes should be used, when possible, to fight against the formation of slag on a piece that is welded.
When welding slag residues are chemically inert in acid solution and their existence produces the rough surface and the lack of a protective coating of zinc.

If youare using coated electrodes, residues (slag) must be removed mechanically.


Welding process MIG, TIG, CO2 are recommended until the product costs. Welding electrode rich in silica can cause darkening of the surface area of ​​the weld.


Welds must be compact and clean. In the porous and incomplete weld after galvanizing oxide leaks occur from these places to galvanized pieces. In the presence of moisture in the atmosphere  these places become a source of corrosion.

Severalexamples of possible sources of corrosion in case ofhardening structures:

- Angle profiles

 

- U profiles

 

Stiffeningnew plateswithinsured zinc circulation. 

 


 

 

Weldsmustbe compact, cleaned ofslag, sand...

 

 

Carriers   

 

 

 

Welding should bedone according to the regulations for the hot dip galvanizing. Leaning area is limited.
On welded pieces there openings for air vents should be predicted. Otherwise, there is the possibility to open the weld 1 - 2 cm, and air which can not get out can cause dangerous explosions during the galvanizing process. Welded reinforcement should be avoided as much as possible in these constructions.