Features of the structure and use of hot-dip galvanizing baths

Electroplating is the application of various metal and chemical coatings to metal surfaces. The most common electroplating method is galvanizing.

Galvanic galvanizing is the process of applying a thin layer of zinc to the surface of metal products in an electrolyte solution. During the electrolysis process, zinc dissolves, and its ions with a positive potential are deposited on the surface of the base metal to form a layer with a thickness of 4 to 20 microns, which accurately follows the contours of the product. The coating during galvanizing is particularly precise and smooth.

Working principle of galvanizing

The rust protection method is based on the chemical oxidation process. Most metals in air react with oxygen, as a result the surface is covered with a film, which begins to play a protective role. The exception to this series is iron and its alloys; they form a film of loose composition, which does not protect, but, on the contrary, promotes further oxidation of the material and its destruction. Zinc is used to protect steel and other iron-based metal materials. It forms a galvanic couple with Fe, and due to its greater activity, it begins to oxidize first, forming a film that serves as surface protection.

The thickness of the film varies depending on the technology; it can be thin - from 6 microns or dense - up to 1.5 mm.

Main design features of galvanizing baths

There are also various types of baths on sale, specially designed for both pre-product preparation and galvanizing.

The design of the products is created in such a way as to ensure a high level of quality of work. Special protective metal casings, aspiration systems and much more are provided. All this allows us to guarantee that the level of product preparation, as well as the quality of the work results, will be at a truly high level.

Areas of application of galvanized structures

• Construction work of various profiles: road, bridge, construction of buildings and structures.
• Oil production and oil refining.
• Gas production and gas processing industry.
• Energy sphere.
• Connection.
• Automotive industry.
• Agriculture and other areas.

The method is applicable for structures that are operated under different conditions

• Supports of high-voltage transmission lines.
• Supporting metal structures of bridges and pipelines.
• Various equipment.
• Valves and locks of hydraulic systems.
• Frames of houses and fences.
• Piles supporting various types of floors.
• Stair steps and flights.
• Pipes of various systems, including ventilation.
• Ship hulls.
• Monuments and architectural structures.

What affects the service life of a galvanizing bath?

It is worth paying attention to what determines the service life of such a container.

On average, one bath lasts for 20-25 years.

At the same time, it is important to ensure compliance with operating requirements and prevent it from reaching an emergency condition.

It is also worth monitoring what compounds are filled inside. The use of different types of chemically active substances can affect how long a similar galvanizing tank will be used.

Choosing the correct composition of the galvanizing bath ensures that even in contact with aggressive chemical environments, there will be no violation of the integrity of the structure or tightness.

Galvanizing production processes

Several galvanizing methods are used in metallurgical and chemical production.

1. Galvanic galvanizing
2. Hot galvanizing of metal
3. Cold galvanizing method.
4. Diffuse galvanizing method.
5. Shoping.
6. Gas-dynamic method.
7. Duplex processing methods

A phosphating method can be used, which, in addition to the main method, provides additional protection to the surfaces of metal objects and parts. Most often used for non-ferrous metals.

The widespread use of galvanizing is associated with the coating’s resistance to aggressive environments, temperature changes, and high anti-corrosion properties.

Galvanic galvanizing

Electroplating is an electrochemical method of coating metal structures with zinc. It is carried out in large containers with zinc-containing electrolyte. The complexity of this method lies in the effect of two processes on the metal at once: electrical physical influence and chemical method.

In the galvanic method, an active process of adhesion of elements of metal material and zinc occurs. Adhesion involves the adhesion of dissimilar substances at the intermolecular level.

Electrogalvanic production technology

Metal products, structures or parts are immersed in electrolytic baths equipped with an anode - a zinc plate, from which, with the help of an electrolyte - zinc sulfate and zinc chloride, the anions of this metal pass to the surface, covering it with a uniform layer.

The galvanizing process is influenced by the composition of the electrolyte and the temperature maintained in the containers. Coloring additives and shine-forming components are added to the solution. This is done to give objects a decorative appearance.

Electrolytes used in the production process are:

• Acidic and slightly acidic: sulfates, borofluorides, chlorides.
• Ammonia: alkalis and neutral solutions.
• Cyanide and zincate: alkaline electrolytes with cyanide and sodium zincate in sodium hydroxide solution.

Before carrying out work, it is necessary to prepare metal products: cleaning and degreasing surfaces, fluxing - applying a film to prevent oxidation.

Characteristics of zinc electroplating: the surface is distinguished by such properties as ductility, continuity on parts that must work under conditions of cyclic deformation. For example, steel springs.

Hot galvanizing of metal structures

The hot-dip galvanizing method is usually used for ferrous metals, primarily steel. This is the most common method of covering surfaces with zinc film.

The technology boils down to lowering parts or structures into a bath of molten zinc. The temperature is maintained at 460 degrees. C. The process takes place under the influence of oxygen from the atmosphere, it reacts with the metal to form ZnO - zinc oxide, which combines with carbon dioxide CO2. As a result, zinc carbonate is formed - ZnCO3. It has a characteristic matte gray shade.

Before lowering into the bath, a stage of cleaning, degreasing and etching the surface of the parts is necessary.

After being in the bath, the products are centrifuged to remove excess metal. To remove sagging, threaded areas on large parts are ground; small parts, such as fasteners, are not subjected to such treatment.

As a result, products with an increased service life, resistant to aggressive environments, do not require additional coating with a paint layer.

Negative characteristics include unevenness of the surface with high consumption of zinc, and the dimensions of the products are limited by the dimensions of the container. Production is considered harmful. Further processing becomes more difficult, the parts are poorly connected by welding.

Features of the hot galvanizing process

• The technological process is simple.
• High productivity is noted, it passes quickly.
• Highly trained employees are not required.
• The equipment is quite simple.
• The zinc layer has a thickness of 30 to 100 microns.

Compared to galvanic methods, hot-dip galvanizing is a more expensive method, but also more effective.

Cold galvanizing of metal

The method consists of applying zinc-rich paints, compositions and primers to the surface. Not the entire surface of the product is covered, but the designated areas.

It is widely used for processing individual structures and large areas.

Positive aspects of cold galvanizing

• You can process products and surfaces of any size, there are no restrictions on area and shape.
• There is no need to carry out preliminary dismantling work in order to immerse it in a container for electrolysis or hot-dip galvanizing.
• The process is characterized by productivity.
• Temperature range: from minus 20 degrees. From to positive 40 gr. WITH.
• The zinc layer after the cold method allows welding; it does not destroy the zinc surface. After welding, the seam can be covered with an additional protective layer.
• The structure of the coating is flexible and reliable.
• Zinc silicate paint has adhesion characteristics that are compatible with metal and finishing paints.
• The method is quite simple and does not require special professional training.
• Can be used to repair parts and areas that have previously undergone a galvanizing process.
• A convenient way to apply a touch-up layer under varnish or chemical-resistant paint for double protection. This is a combined coating method.
• You can process the entire structure without disassembling it into individual components.
• Economical way.

The composition for cold galvanizing contains highly dispersed zinc powder - up to 95%. Before carrying out work, it is necessary to prepare the surface and strictly comply with the technological requirements of the work.

In the production process, a necessary stage is quality control to ensure the absence of defects in the zinc layer. At the end of the process, the coated products are allowed to “rest” for several days to harden the layer.

The resulting coating is waterproof, electrically conductive, and fireproof.

Thermal diffusion galvanizing method

The diffusion method was called “Sherardization” after the inventor, a specialist from Great Britain, Sherard.

Thermal-diffusion coating is an anodic coating, covering ferrous metals with a dense film of zinc. The name is associated with the process of diffusion of metals, zinc and iron. It takes place in passivation solutions, which are necessary to provide protection from exposure to atmospheric oxygen.

Thermal diffusion coating is similar to the galvanic method, but surpasses it in anti-corrosion characteristics.

Products processed by thermal diffusion are characterized by a uniform surface coating from 30 to 80 microns. For small areas of parts, subject to precise production, thicknesses from 5 to 150 microns can be achieved. When structures with complex surfaces are processed, the variation in coating thickness is large - up to 80 microns.

The technology consists of saturating the area of ​​parts and structures with zinc in a powder medium.

Zinc-containing fine powder is diluted with absorbents such as charcoal. The temperature is maintained at 400-500 degrees. C. Temperature conditions are different for different types of products, the characteristics of steel that are fixed in its grade, and production requirements.

A hermetically sealed container in which surfaces are enriched with zinc is a prerequisite for the technology. After the main process, finishing is carried out on products that will be used in conditions of high humidity, sea or other salt water, during periods of condensation and drying.

Features of thermal diffusion coatings

• The technological process of processing at low temperatures, in addition to anti-corrosion properties, gives the metal increased ductility.
• Treated products are resistant to abrasive wear, which is formed as a result of cutting, deforming, and scratching effects. Occurs during processing and transportation.
• The coating accurately reproduces the relief of the structure.
• Increased hardness distinguishes the processed products; the property of fragility does not arise.
• Zinc coating can be applied to pre-assembled units.
• Preparation of the thermal diffusion galvanizing process does not require complex operations.

Shoping

Metal shopping refers to metallization, or spraying processing. For work, a special apparatus is used, which is sometimes called a pistol. Molten zinc is sprayed onto the surface under compressed air pressure. The method owes its name to the inventor G. Schoop.

The metallization method is applicable for large structures, as well as for the restoration of worn parts made of steel of various grades. The zinc layer applied by shopping forms a stable film, which acts as a primer for applying the paint layer.

Gas-dynamic galvanizing

The gas-dynamic method is galvanizing using the kinetics of finely dispersed metal in a gas stream, carried out by a supersonic flow.

The starting material is zinc powder with ceramic or metal particles. It is accelerated by a jet of gas from a high-temperature nozzle and welded to the surface towards which the flow is directed. Additional material - metal and ceramic - increases the density and reduces the porosity of the surface.

The equipment for the gas-dynamic method is a portable heater for compressed air, which is equipped with a supersonic nozzle. This is a kind of atomizer. Gas at t 500-600 gr. C draws in the powder and directs it to the surface.

Advantages of the method

• Processing of products and parts of any size.
• The adhesion of the composition is higher than that of any paint and varnish layer – 40-100 N/mm2.
• The thickness of the layer can be different; the layer can be thickened in areas of increased risk of corrosion.
• The porosity of the zinc layer is less than 1%.

Combined – duplex processing methods

Duplex coatings involve a combination of zinc material with polymer or paint.

The combination of the electrochemical effect of zinc protection with the waterproofing effect of the paint layer creates a double protective effect.

Characteristics of duplex systems

• Provides galvanic or cathodic protection and at the same time barrier protection.
• It is as easy to apply as a paint coating.
• A special type of zinc is used in production - atomized.
• Increases resistance to mechanical damage
• It does not require complex preparation of the source material for the coating process - it is enough to treat it with a solvent.
• Can be applied over hot-dip galvanized and metallized surfaces.
• Non-toxic and environmentally friendly.

Features of using containers for chemical preparation of products

Our company pays great attention to the process of preliminary preparation of products immediately before hot-dip galvanizing. This allows you to remove from the surface all contaminants that could potentially pose a threat to the quality of the final galvanization.

They remove organic contaminants and also do everything to increase the level of adhesion and stabilize the quality of adhesion of the zinc coating.

There are several main types of baths that can be used in the product preparation process. These include the following:

• Containers for degreasing. Typically, for such a task, the use of special polypropylene containers with different characteristics is allowed. They are available with a wall thickness of approximately 20 mm. When placing steel in such a bath, alkaline solutions are poured inside. At the same time, organic contaminants are removed from the surface, which could affect the final quality of galvanizing.
• Washing baths. Water is actively used in preparation work. This is necessary in order to remove all remnants of chemical solutions from the surface. In this case, it is possible to use polymer materials for the manufacture of containers.
• Pickling bath. Another action that was created specifically for preparing metal is etching. There are many material options that can be used in the process. The main requirement for them is a guarantee of a high level of protection against destruction due to prolonged contact with hydrochloric acid.
• Containers for fluxing. To increase the adhesion of the material and make the zinc coating much better and more stable, the fluxing procedure is also used in the work. The materials used to create the bathtub have a high level of resistance to contact with ammonium chlorides and zinc.
• Cooling baths. To continue working with a part after it has been fully galvanized, polymer or steel baths are used in which the temperature of the material gradually drops to the specified characteristics.

Our production is equipped with all modern hot-dip galvanizing baths, as well as properly selected containers for preparation. The entire production line strictly meets the established industry requirements.

Do-it-yourself metal galvanizing

Most galvanizing methods are production methods that require industrial equipment and special metal processing.

Some of them are available to craftsmen in workshops. Most often they talk about “garage galvanizing,” since they are the ones who need to restore car parts and components.

The most accessible method is cold galvanizing.

There is a possibility of galvanic processing of parts. It allows you to form patterns and decorative elements on the surface of products.

DIY galvanizing

To work with this method, an electrolyte is required. This can be zinc chloride (ZnCl), hydrochloric acid (HCl), zinc sulfate (ZnSo4). Formulations require maximum care; chemical components have a tendency to explode or enter into unexpected reactions.

The zinc composition involves the extraction of zinc from salt batteries, galvanized metal objects, Soviet-made fuses, or purchase at the auto or radio market.

How to work:

• The bathroom can be a plastic or glass container.
• The anode is a zinc plate with a positive charge supplied.
• The workpiece plays the role of a cathode. It must be prepared - cleaned, degreased, activated. It is located equidistant from the anode.
• Power source - battery, power supply. The precaution is to avoid active boiling. If the process is smooth, long-term galvanization will provide a thick protective layer of zinc.

How to perform the procedure at home

Galvanizing at home is carried out mainly by the electrochemical method or using cold galvanizing technology, which is explained by the simplicity of these methods. To perform galvanizing yourself using the electrochemical method, you must carefully prepare the surface of the workpiece. Such preparation consists of cleaning and degreasing, as well as acid etching and subsequent rinsing with water.

Diagram of a galvanic installation for self-galvanizing

Your own device for performing galvanic galvanizing can be made from a direct current source that produces a voltage of about 6–12 V with a current strength of 2–6 A, a container made of dielectric material and a device with which the electrode and the workpiece will be fixed. The electrolyte in this case can be a solution of any salt containing zinc. You can prepare such a solution from battery electrolyte by placing zinc in it for a while and waiting for the dissolution reaction to complete. The resulting composition should be filtered before use for galvanizing.

When performing galvanizing with your own hands, you should keep in mind that the following factors influence the thickness and quality of the coating formed:

• current density per unit area of ​​the workpiece;
• temperature of the electrolytic solution used;
• density of the electrolyte used;
• geometric parameters and complexity of the shape of the processed product.

Place an order for high-quality hot-dip galvanizing

The production line of our company is equipped with various options for the design of hot-dip galvanizing baths and the correct preparation of materials for processing. We carry out quality galvanizing work and ensure that the metal receives a good level of protection against most potential external loads.

Among the advantages of working with us are:

• Good level of modern equipment.
• Official quality guarantees for all types of work.
• Fast execution even of urgent orders.
• Affordable prices.
• Work even with the largest parts.

We are ready to answer all clients’ questions and calculate the cost of completing the task.
To find out more details about working with us, leave a request or call the numbers provided. Return to articles Share article