How to remove zinc coating from metal

Removal of low-quality zinc coatings. Zinc is more active than most metals (iron, copper, etc.), so removing it is not particularly difficult.
In this case, the value of the corrosion potential of zinc varies from -0.76 to -1.26 V. The zinc coating from steel and magnesium is removed in cyanide solutions, and from copper and brass - in alkali or sulfuric acid solutions. To remove zinc from aluminum, use sulfuric acid (1.33) at 20-40 °C. The most widely used are 20% NaOH solution, 10% H 2 SO 4 solution and 10% ammonium nitrate solution. Typically, in such solutions the rate of zinc removal reaches 100 µm/h at room temperature. For anodic removal of zinc coatings, use a solution containing 90 g/l NaCN (t=20÷25°C, U = 6 V) or 100-120 g/l NaOH (t = 20 ÷ 40°C; i a = 2 A /dm 2; cathode - made of steel).

Galvanizing is recognized throughout the world as the most effective way to protect metal structures, pipes, wires, bolts, nuts and other hardware products from the negative effects of the environment. Due to the relative cheapness of galvanizing technology, prices for galvanized products are much lower than prices for stainless steel hardware. But if you need to connect the elements by welding, then the zinc coating can become a serious problem.

How to remove galvanizing from a pipe

Due to the relative cheapness of galvanizing technology, prices for galvanized products are much lower than prices for stainless steel hardware.

But if you need to connect the elements by welding, then the zinc coating can become a serious problem.

Options for welding galvanized pipes - advantages and disadvantages of methods

Pipes made of galvanized steel are very widely used for laying various communications and constructing all kinds of metal structures, since they have good performance qualities.

Installation of such products can be done in several ways. This material will tell you how to weld a galvanized pipe, and what features of this process may be important during the work.

Features of welding galvanized metal

The need to remove zinc coatings from metals usually arises during welding operations. Every welder knows that welding galvanized surfaces is problematic and even the thinnest layer of zinc can greatly deteriorate the strength properties of the weld. An admixture of zinc that gets into the weld pool leads to pore formation and the appearance of crystallization cracks in the seam, that is, it does not allow a dense and uniform seam to be obtained. In addition, during welding, zinc begins to evaporate under the influence of a high-temperature arc, and its toxic fumes can cause severe poisoning and even suffocation of the welder, especially when working in a poorly ventilated area.

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There's too much sealant here. Remove with a brush until bare metal. Then: Step 1. Carefully sand the seams until they are flat. Ideally, tap the seams with a rounded striker until a small groove is formed, but after overlap welding, this method will not allow normal deformation of the metal, and the seam may crack. Step 2. Treat the entire surface where the zinc was removed before welding or burned during welding several times with a Zinkar-type compound until a clearly defined zinc layer appears. The more times it is processed, the thicker the zinc layer. It's a long way from hot priming, but still better than nothing. Step 3. Cover with an insulating epoxy or acrylic primer suitable for zinc. Step 4. Puttying. Step 5. Acrylic primer. Step 6. Painting with base paint. Step 7. Varnish. Step 8. Polishing. Step 9. MUST! Anti-corrosion treatment of the internal surface of replaced elements and seams. Preferably good formulations: Dinitrol, Tectil, Body. In two stages: Stage 1. Penetrating ML composition in 2-3 layers. Stage 2. Using the main product in 2-3 layers.

Methods for removing zinc from welded surfaces

Mechanical. Unwanted zinc coating can be removed from metal surfaces using an abrasive grinding wheel. Sometimes it is enough to clean the part to a metallic shine with a brush with stiff wire bristles (cord brush).

Thermal. An effective way to remove metal coating is to burn off the zinc with a high-temperature flame, such as using a torch. At the same time, you should remember the toxicity of zinc and take all safety measures.

Chemical. When welding critical structures, it is better to pre-clean surfaces from zinc in a weak solution of hydrochloric acid (5%). Zinc is more active than steel, so it reacts effectively with acid and is easily removed from hardware. To prevent acid corrosion of steel, 1% methenamine can be added to the solution. The part to be welded is immersed in a bath of dilute acid at room temperature. The cleaning process (etching) lasts several minutes. When it is complete, and this will be evident from the attenuation of the hissing, the metal is treated with an alkali to neutralize the acid, for example, a soda solution (1g / 50ml), then washed with water and dried until the moisture has completely evaporated.

For chemical etching of galvanized parts being welded, many welders use a proven and effective product - spent acid battery electrolyte, which is nothing more than an aqueous solution of sulfuric acid. Just a few minutes in such a bath and not a trace will remain of the zinc coating on the metal.

At hot-dip galvanizing enterprises, for various technological reasons, defects occur (depending on the qualifications of the technologist, its share ranges from a few percent to tenths of a percent); in this case, it is necessary to perform the so-called “galvanizing” and re-galvanizing. For galvanizing, one of the baths with a technological solution is most often used, which is no longer suitable for pickling, but is suitable for galvanizing. In addition, not all products are galvanized on wires - long products (pipes, angles) are galvanized in special cassettes or using grips that are immersed together with the galvanized products in molten zinc. After several dozen dives, these cassettes must be freed of zinc to check their performance and routine repairs.

Using a spent solution from one of the pickling baths as a bath for galvanizing defective products and equipment requiring repair has both positive and negative sides.

It can be considered positive that no additional equipment is required to carry out this technological operation, which allows the existing equipment to be concentrated on improving other hot-dip galvanizing operations. It must be borne in mind that with the qualified work of a technologist, the amount of defects at an enterprise is usually calculated in tenths and even hundredths of a percent, therefore the concentration of zinc in OTP is calculated in values of the order of several grams per liter (with an iron concentration of about 80-120 g/l). And these values make it possible to use ferric chloride obtained as a result of HCl regeneration operations with qualifications that make it possible to use it as a coagulant for the treatment of municipal waters even with strict standards of EU countries. In the case of neutralization, the resulting iron hydroxide precipitate in some cases can even be sent to storage sites.

The disadvantage of the galvanizing method in one of the OTR baths is the loss of zinc, which is the most expensive reagent. And in the preface it was already indicated: in order not to create additional problems for yourself with the processing of mixed wastewater, do not allow different wastewaters to be mixed, but process them separately.

In a significant part of European galvanizing industries, they follow the second path - there are special “dezincating” baths, where hydrochloric acid, rather than OTP, is used. As with pickling baths, pickling inhibitors are added to minimize acid-iron interactions. As a result, we obtain an OTR that is fundamentally different from the OTR of pickling baths: it contains over 100 g/l of zinc and only a few g/l of iron.

The obtained data are summarized in table 13.4.

Table 13.4 . Approximate composition of OTP galvanizing baths.

Prevention of white rust on zinc coating

1. Store galvanized products in a clean, dry, closed room at a constant temperature (the temperature in the storage area should be above the dew point), away from doorways.
2. Laying of large zinc coated products on special wooden devices to eliminate contact with the ground. 3. Packaging of galvanized products during transportation and storage must be done in a special way: gaskets are placed between the contact surfaces, and the stacks are tied using belts. This method allows air to circulate, which prevents the accumulation of moisture. 4. When storing, place packaged products at a slight angle to each other (the slope should be 5 mm per 1 m of product length). This facilitates the drainage of water and condensation. 5. Transport and store only clean galvanized products, since dirt and chips provoke the formation of white corrosion. 6. After the galvanizing process, carry out:
Additional surface treatment with a water-repellent agent, apply a protective barrier coating.

7. When storing galvanized products outdoors, cover them with waterproof material with the possibility of air circulation.

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How to clean zinc from rust

Zinc is one of the materials widely used to protect steel from corrosion. This study concludes the effectiveness of the two systems in removing white rust and re-passivating the cleaned zinc surface. It is enough to soak a sponge or food foil crumpled into a loose ball in the indicated drinks and treat the rusted area. We promised that for you, dear hostesses, we will have information that will help you overcome this worst “red-haired enemy”! I don't know the chemical formula of the compound.

Lemon juice together with vinegar. To do this you will need: In the case of a small rusty spot, you just need to sprinkle the cut potatoes with salt and the next treatment of the affected area can be done for about 15 minutes.

White rust on zinc coatings: causes, action and methods of combating

Treat the steel with soapy water and a brush. Wipe the zinc coated steel with a damp cloth. Often such products are made from a phosphorus-based acid, tannin. Afterwards, I immediately wiped it dry with a rag, since cleaned bare metal, and even wet metal, immediately begins to rust. Galvanized rust is steel coated with zinc, which protects the metal from corrosion and increases the wear resistance and durability of the steel.

Next, you need to thoroughly sprinkle the surface with rust with table salt, then apply liberally of lemon juice. on galvanized steel there are traces of corrosion, or the so-called “white rust”. Fortunately, most rust does not adhere well to zinc, so after drying, thoroughly wash off any residual traces of paint remover when the steel is cleaned.

Smooth alloy surfaces are perfectly cleaned by electrochemical methods, with a slight “patina” of rust on your cap. It's probably better to clean it with coral. It is suitable, for example, if a nut, due to corrosion, has stuck to a bolt and cannot be unscrewed. Then clean the surface of this mixture, and at the same time of rust.

How to clean a copper coin can be found here. Afterwards, wipe the coin with a piece of foil and wash with water. A zinc layer is applied to the product. Body shine for a year without polishing! Coca Cola.

Rust remover, how to clean it from alloy, coins, skates, cars, plumbing fixtures?

How to clean rust from metal? Galvanization is often used. You cannot use such aggressive acids without inhibitors: In addition, there is conflicting information on the Internet, for example, on some websites they write: Removing rust from metal using lactic acid. Lactic acid. Iron products are placed in acetic acid or cleaned with baking soda.

Zinc chloride. Cleaning the alloy from rust with potatoes and salt. How to clean rust from metal, how to clean zinc, if you use professional products?

Methods for removing rust at home. There is another method of removing rust - sulfuric acid and zinc. It is necessary to squeeze the lemon juice into a glass container. Zinc is one of the materials widely used to protect steel from corrosion. This study concludes the effectiveness of the two systems in removing white rust and re-passivating the cleaned zinc surface.

To remove fresh paint from the surface of zinc-coated steel, you can use a nylon brush and paint thinner. Add baking soda to make a homogeneous mixture. Experiments on rusty corners are good, BUT the problem is that the cars are assembled and the iron is 0.5 - 1.00 mm... What can be done on the corner is a hole on the car... And the rust on the car is rushing inside, and the bugs are a secondary consequence, so that this method is like a poultice for the dead...And the creator can’t easily treat the rusty bottom of a car with this method?

Zinc is inexpensive and has good adhesion to steel. Then they must be degreased and treated with anti-corrosion chemical compounds.

Metal rust remover

"White" rust. Mechanism of formation of lesions

The durability of the zinc layer depends on the film coating formed on the surface. The film formation process takes place in several stages.

1. Oxidative stage

. As a result of the interaction of zinc and oxygen, an unstable compound is formed - zinc oxide.

2. Hydration process

. In the presence of moisture, oxygen depolarization occurs - diffusion between zinc anions (Zn^(2+)) and hydroxide cations (OH^-). At the anodic areas of the surface, zinc dissolves with the release of two electrons. At the cathode sites, an oxygen reduction reaction occurs with the formation of hydroxyl ions. As a result of the interaction, a poorly soluble precipitate of zinc oxide hydrate (zinc hydroxide) is obtained. The reaction occurs at an acidity level of 5.2 and above (neutral or alkaline environment). Hydration formulas:

3. Carbonate formation phase.

At this stage, poorly soluble basic zinc carbonate is formed. Reaction formula:

The finally formed film coating provides reliable anti-corrosion protection to the zinc layer under the negative influence of moisture. However, the film formation process takes a certain period of time. “White” rust is the result of a violation of the technological process. Foci of damage most often occur in places where there is no film coating on freshly galvanized products when actively exposed to moisture (water):

Rain, dew, condensation.

The presence of negative effects of sulfates and chlorides in the environment accelerates the corrosion process.

The zinc coating reacts quickly with clean water to form zinc hydroxide. If, after galvanic galvanizing, the product is continuously exposed to moisture in conditions of lack of oxygen, then the water, reacting with zinc, gradually destroys (corrodes) the zinc layer. Foci of white rust form in places where moisture accumulates when galvanized products are tightly packed.

Method for removing zinc from galvanized steel

Owners of patent RU 2599061:

The invention relates to the field of non-ferrous metallurgy and can be used for processing galvanized steel waste. The method involves treating galvanized steel waste with an aqueous solution containing 250 g/l hydrochloric acid and 2.5 g/l hexamethylenetetramine, in which the galvanized steel waste is kept at a temperature of 10-40°C for 20-30 minutes, after which the aqueous solution saturated with zinc the solution is drained and the steel waste is removed. The method ensures the removal of zinc from galvanized steel to a content of no more than 5% of the original in the conditions of foundries of engineering production, taking into account the protection of the metal base of the waste from dissolution in acid during the reaction.

Possibility of eliminating white rust spots on zinc coating

Minor damage to zinc coating

Visually, such a lesion consists of small areas of white plaque, powdery composition, clearly visible on ground or polished surfaces.

The cause may be a violation of the integrity of the passivation film due to direct exposure to rainwater.

The filmy coating of white rust is removed mechanically: with a sponge, a soft brush or by thorough weathering.

Moderate focal lesion

Large affected area relative to the area of the galvanized product. Corrosion areas are characterized by darkening. In the affected areas, there is a lack of a zinc layer with a partial violation of the integrity of the matrix base. The thickness of the zinc coating is determined for each specific area. Corrosion zones are cleaned with special metal brushes. In this case, about 5% of the zinc coating is removed.

To preserve the appearance of a damaged galvanized product after mechanical cleaning (brush, abrasive tool) with a mild cleaning agent, which can be used as weakly concentrated acid solutions:

Phosphorus, acetic acid, glycol, citric,

Additional processing is carried out - aluminum paint is applied to the rust spots. As a result, a thin protective layer is formed. This treatment allows you to localize the affected area and associate it with the intact zinc coating.

Severe form of corrosion damage to zinc coating

Extensive areas of salt deposits. Areas with slight darkening turn black. Corrosion zones are characterized by the presence of red rust. In places of close contact, galvanized products stick together (stick to corroded areas). The degree of damage is determined by measuring the thickness of the zinc coating.

Stages of restoration of areas damaged by white corrosion

1. Mechanical cleaning of corrosion zones with a metal brush.
2. Polishing the cleaned areas to completely remove rust and oxidation products. 3. To create a protective barrier, a polymer coating is applied to the prepared surface - zinc, epoxy paint or zinc primer.

Chemistry plus battery. We chase “bugs” and do galvanic galvanization using garage methods