What is chrome plating

Galvanic chrome plating

Electroplated chrome plating has become very widespread because... It is characterized by high wear resistance, hardness, strength, chemical and thermal stability. Galvanic chrome coating has high decorative properties (it does not fade or change color even when heated). Chrome plating is not affected by sulfur compounds (which are very harmful to many other coatings).

When exposed to strong oxidizing agents or simply exposed to open air, the surface of the chromium coating goes into a passive state (a thin film of oxides forms on it). Chromium dissolves quite quickly in hot sulfuric acid and hydrochloric acid. It is insoluble in solutions of sulfuric and nitric acids. A significant disadvantage of the protective galvanic chrome coating is that if it contains pores, scratches, cracks, etc.

it does not provide electrochemical protection against corrosion, because has positive potential.

Electroplated chrome coatings are used:

- in the manufacture of reflectors, mirrors, spotlights, etc. (the coating has high reflective properties, which are second only to aluminum and silver, but these properties are more stable due to chromium’s good oxidation resistance);

— for protective and decorative purposes (with a sublayer of nickel and copper, the chrome coating perfectly protects steel from corrosion and gives the product an attractive appearance). Protective and decorative galvanic chrome plating is used to form layers on some parts of cars, devices, motorcycles, bicycles, etc.);

— to restore dimensions (for example, a chromium layer is built up on the worn surface of heat-treated shafts and bushings, which makes it possible to extend the service life of products and restore original dimensions);

- to increase the wear resistance of critical parts.

The thickness of the galvanic chrome coating is set depending on its purpose and operating conditions. The thickness of the layer intended to restore worn dimensions can reach 500 microns.

The protective and decorative layers applied to parts made of copper and alloys based on it are about 6.0 - 9.0 microns in thickness, and on the nickel sublayer - 0.5 - 1.5 microns. If it is necessary to increase the wear resistance of dies, molds, etc.

, then the thickness of the chromium layer can vary from 9 to 60 microns.

Modes of galvanic chrome plating

The modes of applying galvanic chrome coating have a very large impact on the quality of the finished chrome coating and its protective and decorative properties (including corrosion resistance). Immediately after loading the parts into the sulfate electrolyte, a current is supplied that is one and a half times the calculated current value (and is maintained for 15 - 30 seconds).

This is the so-called “push” of current, which is necessary in order to improve the covering ability of sulfate electrolytes. Then the current decreases to the rated value. Such a “push” of current is especially necessary if galvanic chromium coating is applied to cast iron products.

If the coating is applied to parts made of steel, then first a countercurrent is applied (for anodic dissolution of oxide films), and then a “push” of the current in the forward direction.

Coatings obtained in sulfate electrolytes at a temperature of 330 – 332 K and a current density of 30 – 50 A/dm2 will be highly wear-resistant. Protective and decorative chromium coatings in sulfate electrolytes are obtained at a temperature of 320 – 325 K and a current density of 15 – 20 A/dm2. The milky (matte) layer is formed at a current density of 25 – 35 A/dm2 and a temperature of 342 – 344K.

Porous chrome coatings. Pores and cracks form on the surface of chrome coatings (except for “milk”) during their application, which significantly reduce their protective properties. But sometimes it is simply necessary for these cracks and pores to be present.

  In addition, the chrome-plated part is subjected to additional anodic treatment in the same electrolyte in which the coating was applied. This is done to expand the pores in the coating. Large pores allow lubricants to enter and remain trapped.

At a cathode current density of 40 – 60 A/dm2 and a temperature of 325 – 331 K, the most developed network of channels and pores is obtained on the surface of the chrome-plated part. Anodic treatment is carried out for 10 – 12 minutes.

Features of galvanic chrome plating

During the application of galvanic chromium coating on the surface of the insoluble anode, intense oxygen evolution occurs, and hydrogen evolution occurs on the cathode surface, because the process is carried out at low cathode current output. The gases released during electrolytic chrome plating rise upward and carry droplets of electrolyte with them into the ventilation ducts.

This leads to quite large losses of working fluids and creates the need to equip galvanic baths with exhaust systems. To improve the working conditions of workers in electroplating workshops and reduce electrolyte losses, a special drug “Chromin” is introduced into it. It reduces the surface tension of the electrolyte, thereby reducing its losses.

It is necessary to administer Chromine in the exact quantities specified in the instructions and constantly monitor its content in the electrolyte. It is also necessary to pay attention to the fluorine content in the preparation, which has a destructive effect on the lead lining of galvanic chromium plating baths. If titanium is used as a lining material instead of lead, the service life of the bath will be extended.

The presence of floating inert particles (for example, fluoroplastic, polyethylene, polypropylene, etc.) on the electrolyte surface (on the bath mirror) also leads to additional losses of the working solution.

To form a chromium coating on the internal surfaces of parts, additional anodes are required. They must be mounted so that they do not come into contact with the cathode surface and are not an obstacle to the escape of gases. Additional anode materials may include lead-coated steel, pure lead, and (in some cases) uncoated steel.

When installing parts on suspension equipment, you should pay attention to the fact that they do not shield each other and have a fairly rigid contact. To avoid overheating of the pendants, the current must pass through elements with a sufficiently large cross-section.

When current passes, a fairly large amount of heat is released, which affects the temperature of the electrolyte. To avoid problems with the quality of the finished chrome coating, it is necessary to correctly set the degree of loading of the galvanic bath with parts.

The ratio of the current that passes through the bath to its volume (volume current density) should not exceed 1 A/l.

During galvanic chromium plating, hydrogen released on the surface of the cathode partially penetrates the structure of the steel (the material of the parts to which the coating is applied) and creates internal stresses. This can lead to corrosion cracking of parts.

In some cases, the internal stresses that arose during galvanic chrome plating can be added to the stresses that arose during preparatory operations and the parts may crack (especially if they have fairly thin walls).

In order to remove hydrogen formed after the galvanic chromium plating process from steel and heat-treated parts, they are heated in air or oil for 1 - 1.5 hours at a temperature of 445 - 455 K.

Two-layer combined coatings

Two-layer combined coatings are formed in order to give the chrome layer both wear resistance and protective properties. A good option is a combination of non-porous milky chrome and wear-resistant one. First, at a temperature of 343K and a cathode current density of 30 A/dm2, a layer of milky chromium, about 9 microns thick, is applied. This process lasts about 20 – 30 minutes.

Next, the electrolyte is cooled to an operating temperature of 323 - 328 K and the product is further chrome-plated at a cathode current density of 45 - 55 A/dm2. The duration of the second chrome plating process depends on the thickness of the layer that needs to be obtained, and therefore on the purpose of the chrome-plated part.

In order for the milky chromium and wear-resistant layers to adhere well to each other, after applying the first, additional treatment is carried out at 5 A/dm2.

Black chrome plating

Black chrome plating is used to form protective layers on parts that must have good heat transfer (for example, radiators) and optical systems. The black chrome layer has a fairly small thickness - 1.5 - 2 microns. To protect metals from corrosion, a layer of black chrome is combined with milk chrome. If the part is made of non-ferrous metal, the thickness of the sublayer should be at least 3 – 6 microns. And if it’s made of black – at least 9 microns.

Black chrome coating is characterized by increased wear resistance (unlike coatings obtained as a result of oxidation or black nickel plating). It also has good heat resistance and retains its properties up to a temperature of 773K.

Black chrome plating can be carried out in several electrolytes. The result will be equivalent (the properties of the deposited galvanic chromium layer will not differ). The choice of electrolyte composition is dictated only by the availability of the necessary materials.

Removing low-quality galvanic chrome coating

The defective coating is removed using an electrochemical or chemical method. Electrochemical removal of galvanic chromium coating involves anodic dissolution in an electrolyte that contains 150 - 200 g/l sodium hydroxide. The process is carried out at a current density of 3 – 10 A/dm2 and room temperature. During chemical removal, the chrome-plated part is immersed in a solution of hydrochloric acid and water in a 1:1 ratio and at a temperature of 300 - 314K.

Source: https://www.okorrozii.com/galvanicheskoe-hromirivanie.html

How to chrome metal correctly?

To protect metal structures from corrosion, increase strength characteristics and improve the aesthetics of their appearance, chrome plating technology is used. It is relatively simple and easy to master, but before chrome plating any metal, you need to carefully study the processing technology to avoid mistakes.

What is chrome plating?

Chrome plating of parts involves applying a special coating to a metal surface. There are two main methods:

1. Saturation of surface layers by diffusion method. The maximum number of chromium atoms penetrates into the metal crystal lattice.
2. Electrolytic method. It involves the cathodic deposition of chromium onto a steel structure under the influence of an electric current.

Chrome plating is carried out only on a clean, prepared surface. A feature of the process is the application of a uniform layer of a certain thickness to structures of various shapes. The coating can perform a decorative or protective function.

The thickness of the formed layer is from 0.075 to 0.25 mm. Hardness - 66–70 HRC. The surface has roughness and the thicker the applied coating, the more defects there are. Therefore, after chrome plating, polishing of the workpieces is required.

The technology involves the use of solutions:

• with chromic anhydride;
• with chromium sulfate or chloride.

Why is chrome plating needed?

The chrome plating process is carried out for the following purposes:

1. Protecting metals from corrosion and sudden temperature changes.
2. Restoring the metal surface. It is possible to increase the service life of structures, provided that the surface is worn to a depth of up to 1 mm.
3. Increased wear resistance. Chrome coating can withstand friction, mechanical stress, and thermal expansion. Allows you to protect the base metal from negative external factors.
4. Improvements in reflective properties. The chrome layer has reflective properties. Used in lighting devices to improve the visibility of body elements or signs.

Source: https://metalloy.ru/obrabotka/zashhita/kak-hromirovat-metall

Galvanic chrome plating – SPG-Composite

Today, chrome plating is one of the most common types of galvanic coatings. It is used to protect metal products from corrosion, wear, and adhesion of contacting materials to the surface.

Depending on the application technology and modes, chromium coatings reach microhardness of up to 950 - 1100 HV.

Even despite the small thickness of the layer, chromium significantly increases the corrosion resistance of the product and gives the surface a beautiful shiny appearance. Products coated with chrome have high hardness and wear resistance, low friction coefficient, high heat resistance and good chemical resistance.

And what is very important is that chromium provides parts with a long service life in any operating conditions. Therefore, chrome plating is widely used to increase the hardness and wear resistance of various measuring and cutting tools, rubbing parts of devices and machines.

A large and visible effect is achieved by chrome plating of molds in the manufacture of products from plastics, rubber, and in powder metallurgy.

The thickness of the chrome coating, depending on the purpose of the products, can be in the range from 5 to 350 microns or more.

Hard chrome plating with minimal thickness variation is required on cylinder rods, piston rings, liners and other cylindrical surfaces. Our unique technology allows us to apply a coating of 200 microns thick on a cylindrical surface with a spread of 5 microns.

When using different electroplating modes, chromium coatings with different properties can be obtained, namely:

• “milk chrome” is an elastic and non-porous coating characterized by low hardness - it is deposited at a temperature of 65-80°C and relatively low current densities (15-25 A/dm2);
• “shiny chrome” - a chrome coating that has a mirror shine and has the highest hardness and wear resistance - at a temperature of 45-60°C and average current densities (30-100 A/dm2);
• “hard chrome” is a gray coating characterized by high hardness and brittleness - at low temperatures (up to 40°C) and high current density.

Chrome coatings are characterized by high hardness and wear resistance compared to other galvanic coatings, which ensures the widespread use of galvanic chromium plating for hardening and repairing parts.

Chrome plating of parts allows:

• increase the service life of equipment,
• save on repairs.

Another most important properties of chromium coatings are their low wettability (low adhesion to other materials) and low coefficient of friction, which can significantly reduce the adhesion of the processed material to the surface of the product.

We repair, restore chrome coatings and increase the service life of chrome coatings of forming parts of extrusion and other equipment (dies, calibrators, gauges, mandrels, molds, etc.) We use chrome restoration technology in our production, we carry out high-quality repairs, in no way inferior to factories - to manufacturers.

In order to maintain a long service life and prevent carbon deposits and sticking of the molding mass on the working surface of the extrusion tool, a protective chrome coating is applied to the surfaces in contact with the heated mass using an electrochemical method.

Over the years, under the influence of external factors (such as foreign objects entering the mass, frequent cleaning, etc.), the chrome coating wears out.

This leads to production defects (in the form of longitudinal stripes, scorch marks) and, as a consequence, a stop in production and the need to restore the tool, and in some cases even to purchase a new one.

Hardening kits for the production of glass products allows not only to extend the service life of equipment made of heat-resistant cast iron or alloy steel, but also to obtain glass surfaces with a beautiful textured pattern.

The cost of work and terms are calculated individually, based on the current condition of the products and coating requirements.

Chrome plating technology

The quality of the resulting chrome coating depends on the ratio of the amount of chromic anhydride and sulfuric acid. Its value should be 100:1. A decrease in the ratio (50:1) leads to a deterioration in scattering and covering power.

To ensure good adhesion strength, it is necessary to keep the parts in a bath without current so that they accept the temperature of the electrolyte and at the initial moment of chrome plating give a so-called “current push” for 0.5-1 min, increasing the current density by 2-3 times compared with working, and then gradually reduce it to normal value.

An increase in trivalent chromium in the electrolyte leads to a deterioration in the quality of the coating, which becomes dark and brittle. Iron impurities have approximately the same effect as trivalent chromium. Nitric acid is a very harmful impurity. When it is contained in an amount of 1 g/l, it is necessary to significantly increase the current density, and with an increase, the normal implementation of the chrome plating process is no longer possible.

When chrome plating, anodes made of pure lead or a lead alloy with 4-6% antimony are used. Recently, the use of platinized titanium anodes has become popular. Anodes are made from rods with a diameter of 10-15 mm or sheets.

It is not advisable to use soluble anodes, since chromium dissolves predominantly in the form of trivalent ions. The ratio between the surface of the anodes and cathodes should be in the range from 1:2 to 2:3. During operation, lead anodes are coated with a layer of lead chromate, which makes work difficult.

During breaks between work, the anodes are removed from the bath and immersed in water. Platinized titanium anodes do not require such cleaning.

There are a large number of additives in chrome plating electrolytes, both standard and self-regulating, which significantly increase the covering and dissipating ability of the electrolyte.

Additives are based on inorganic or organic components; some additives increase the deposition rate, others increase the microhardness or corrosion resistance of chromium coatings.

There are no universal additives, so you have to select the technology based on the requirements for the final product and its operating conditions. Removing chrome coatings from parts

Removing defective chrome coatings from the surface of a part

There are several ways:

• chemical dissolution of the chrome coating applied to parts made of steel, copper, brass, nickel in a 10-20% solution of hydrochloric acid, but at the same time the steel is etched;
• electrochemical dissolution of chromium coating from parts made of steel, brass and copper in a 10-15% solution of caustic soda at an anodic current density of 10-20 A/dm2 and a temperature of 25-30°C. Steel is used as the cathode. The electrolyte has no effect on steel. To remove the chromium coating from aluminum and zinc alloys along with the nickel sublayer, anodic dissolution in a 60% sulfuric acid solution with the addition of glycerin at a current density of 5-10 A/dm2 is recommended.

Source: http://spg-kompozit.ru/services/galvanicheskoe-khromirovanie/

Technologies of chrome plating of parts

Various metal products require a protective layer to be applied to them to prevent early destruction and give them a beautiful and elegant look. Electrochemical chrome plating of parts is a long-established and widespread method of corrosion protection.

Various metal fittings, plastic items, car wheels, many items from the food, sanitary, medical and many other industries are subject to chrome plating, as a result of which the parts are literally “ennobled” and acquire an aesthetically impeccable appearance and strength.

The service life of objects treated with hard chrome plating increases significantly; they become virtually invulnerable to corrosion processes and the accumulation of dust, dirt, and other aggressive deposits on them.

Areas of application

Electroplating with chromium is characterized by certain properties, such as:

• resistance to chemical attack;
• microhardness (up to 1100 units);
• porosity, heat resistance;
• friction set;
• coverage depth.

For all of the above characteristics, chrome-plated parts have no equal; they have found the widest application not only in domestic conditions, but also in various branches of industrial production.

Chrome plating technology is used in industries such as:

• powder metallurgy;
• production of aluminum, rubber, metal, plastic products (for example, chrome-plated molds);
• automotive industry;
• machine tool industry;
• shipbuilding and many other industries that are impossible to list.

In some industries, chrome plating of aluminum is especially widespread. This is an indispensable type of processing of this metal to increase its stability and durability.

In the optical-electronic industry, a special type of chrome plating is common - black chrome plating, which has irreplaceable properties of heat transfer, heat resistance and wear resistance. And chrome plating of rods, for example in the automotive industry, cannot be replaced with anything at all.

Main types of chrome plating

Chromium plating using the electrochemical diffusion method can be carried out in three ways, as a result of which the following types of chrome plating are distinguished:

• Hard chrome. It runs at a denser current (above 100A/dm2) and a low temperature (below 40/C), and the part acquires hardness, but becomes brittle.
• Shiny chrome. The chrome plating process takes place at a current density of less than 100A/dm2 and a temperature of up to 60/C, the product acquires increased wear resistance, hardness, and an excellent mirror shine.
• Milky chrome. The minimum current density (25A/dm2) in this case gives the parts a unique hardness.

Source: https://GidPoKraske.ru/spetsialnye-materialy/diffuzionnoe-nasyshchenie/hromirovanie-detalei.html

Chrome plating of parts: technology of chemical and galvanic chrome plating of metal

Chrome plating is a series of processes of diffusion saturation of the surfaces of metal workpieces with chromium, as a result of which they acquire a mirror surface. In the official literature, this technology is also called “metallization” . However, the latter name most likely summarizes all methods of changing the surface characteristics of metallic and non-metallic objects using a thin metal layer.

Having mastered the technology of chrome plating, you will be able to carry out a number of unique works at home. This will allow you to change the appearance of a motorcycle or car, as well as make many stylish and modern things, for example: handles for cabinets or doors, stands, fasteners, cornices, flowerpots and other decorative items that will turn your interior into something incredible.

Brief description of the process

And although the standards of modern life dictate their own rules, people still take special interest in beautiful and shiny things, as their ancestors did many centuries ago. Elegant parts of vehicle bodies, shiny products in bathrooms and kitchens , original figurines and bright coatings of houses - all this is very popular, so the demand for chrome plating of parts is steadily growing.

Currently, several methods of metallization of workpieces are practiced. Among them:

• Galvanizing;
• Chrome coating;
• Aluminum coating.

The use of zinc has a positive effect on the anti-corrosion properties of steel and metal workpieces, as a result of which their service life is rapidly increasing.

Aluminum also improves anti-corrosion properties, so it is applied to equipment that is forced to operate at temperatures up to 900 degrees Celsius. Such devices include parts and mechanisms for extracting oil products and pumping gas, components for furnace systems, as well as many other products.

As for chrome plating, this technique is a good way to create beautiful decorative coatings, allowing you to hide all manufacturing defects and give the product a more elegant look. In addition, chrome plating improves a number of performance characteristics , namely:

• Improves anti-corrosion properties;
• Increases metal hardness;
• Improves protective characteristics against erosion;
• Increases heat resistance;
• Improves wear resistance;
• Makes the appearance of the product more attractive;
• Allows you to create high-quality coatings with specified parameters.

Features of the technology

The application of chromium to metal workpieces is commonly called chemical chrome plating. The technology is used to improve the decorative and functional properties of metal products. The process itself can be performed using the following techniques:

1. Galvanic method.
2. Chemical.
3. By spraying.

If we talk about applying chromium to the surface of the workpiece using the first method, then this can be done in two ways: diffuse and electrolytic. To introduce both types of electroplating, you need to stock up on special tanks with acid-resistant coating and water jackets.

Electrolytic chrome plating is based on the principle of metal electrolysis. During the processing process, electric current is supplied through an electrolyte, presented in the form of a special solution of chromium, acid or alkali salts. As the current passes, chromium cations are released. As a result, they remain on the treated surface.

The average parameters of chrome plating by galvanic method are as follows:

1. Chromic anhydride 250 g/l.
2. Sulfuric acid - 2.5 g/l.
3. Temperature indicators are 50 degrees Celsius for decorative processing, and 55-60 degrees Celsius to improve functional qualities.
4. Current density is 25 A/dm2 for decorative processing, as well as 60 A/dm2 to achieve functional properties.

To perform high-quality electroplating, you need to correctly select the electrolyte temperature and current density. Such parameters influence the appearance and functional properties of the applied layer.

Remember that any increase in temperature reduces the current efficiency of chromium, and an increase in density has the opposite effect.

At low temperatures and constant current density, the resulting coating turns gray. If the current density does not change and the temperatures remain high, this allows a milky tint to be obtained.

Apply the method of heat treatment of steel using chrome plating, which has a positive effect on the operational properties of the surface, giving the material strength, hardness, toughness, wear resistance, elasticity, heat and corrosion resistance.

Subject to a certain temperature regime, the surface of a particular workpiece is susceptible to the action of reagents, and through diffusion, the surface layer is saturated with chromium.

Diffusion treatment is indispensable when applying silicon, carbon, nitrogen and aluminum to the surface layer.

Thermal chrome plating using powders involves the use of mixtures that consist of ferrochrome and fireclay. Such a composition is usually called solyanka acid. Another type of diffusion treatment is the condensation of chromium vapor.

Chemical chrome plating

When performing chemical treatment, a number of the following reagents are used:

• Chromium chloride;
• Sodium hypophosphate;
• Sodium citrate;
• Glacial acetic acid;
• Twenty percent sodium hydroxide solution;
• Water H2O.

During the reaction, the temperature is maintained at 80 degrees Celsius. Before applying chrome plating to a steel workpiece, they are first coated with a layer of copper. As a result, the workpieces are washed in water and dried thoroughly. Using an acid-base solution, chemical metallization of dielectrics is carried out.

In addition, another type of chemical metallization is widespread in the modern world - vacuum chrome plating or PVD process. The method provides complex condensation of chromium vapor on the surface layer of the workpiece.

This happens in special vacuum chambers, where the metal is heated to an evaporation temperature, and then settles in the form of fog on a specific part. The thickness of the chrome layer is so tiny that it is additionally coated with varnish to protect it from scratches.

A similar technique is used for chrome plating aluminum products.

Sputtering of parts with chromium (catalytic chromium plating) is carried out using the “silver mirror” reaction. Complex silver layers in alkaline ammonia solutions are used as reagents. The role of the reducing agent is performed by a solution of invert sugar, hydrazine or formalin.

With the simultaneous deposition of silver and a reducing agent, the metal workpiece acquires a beautiful snow-white mirror coating.

Such products are characterized by excellent reflectivity. At the next stage of catalytic chrome plating, the workpiece is coated with a protective varnish with the addition of a light-resistant coloring toner. This product is obtained by mixing purple, blue and black colors in a ratio of 3:1:1.

Silver mirror processing consists of several processes:

1. Analysis and preparatory stage. It is necessary to prepare the surface of the part by cleaning it and rinsing it with a special product. To improve adhesion, the surface is pre-grinded using sanding paper with a grit rating of P500−600.
2. Using a glossy base. The prepared material is coated with a black glossy coating, which completely eliminates the yellowness of the mirror layer. Drying of applied varnishes is carried out at a temperature of 20−25 degrees Celsius without the use of additional drying devices. To dry, the workpiece is left for 8 hours. If we are talking about drying in a paint-drying environment with a temperature of 60 degrees, then 45 minutes of drying is enough.
3. The next step is drying.
4. Then the surface of the workpiece is etched to improve the adhesion of silver, as well as the material is cleaned with distilled water.
5. Next, sensitization or special treatment of the surface layer is performed using an activator. Thus, the surface is covered with a protective film.
6. At the next stage, metallization is carried out using silver.
7. Then a protective varnish is applied to the workpiece, which reliably protects the treated surface from tarnishing and loss of performance properties due to prolonged use and aggressive influences.

Preparation for chrome plating of metal

The preparatory stage consists of performing several mandatory actions:

1. Preparation of the workpiece surface by grinding and polishing.
2. Cleaning from dirt using a special product and distilled water and wiping with a rag.
3. Complete insulation of surfaces where chrome does not need to be applied, sealing of holes (if internal cavities do not need to be coated).
4. Installation of the product on a special suspension.
5. Complete degreasing.
6. Washing with water.
7. Picking.

The role of hexavalent chromium is played by chromic anhydride, trivalent chromium is played by chromium sulfate or chloride.

The galvanic bath is coated with sulfuric acid, and after placing the workpiece to be processed into the solution, a current with certain density indicators is applied.

It is also necessary to observe a suitable temperature regime for the solution in the bathroom, which is set taking into account the characteristics of chrome plating.

When using thermal mode, you must adhere to the same temperature values ​​throughout the entire event. Any deviations from the established standard can lead to a deterioration in the adhesive properties of the coating, as a result of which the electroplating will lose its correct structure, and various defects will appear on the surface layer, such as stains, growths and stalactites.

The duration of galvanic treatment is determined by the required thickness of the chrome layer.

During the processing process, a number of harmful vapors are released from the solution, so all measures must be carried out taking into account all the subtleties of safety precautions and using personal protective equipment.

Under certain conditions, metallization is carried out only after etching or applying another metal, for example, copper or nickel, to the workpiece. This way the resulting layer is strengthened.

To seal the formed chrome pores, the part is additionally coated with oil or varnish. The resulting chrome film is additionally protected by heat treatment, during which the workpiece is exposed to high temperatures (about two hundred degrees Celsius) for some time.

Subtypes of chrome plating

As mentioned above, galvanic chrome plating allows you to create an effective protective and decorative layer and give the surface special properties.

Chromed metal is also decorated with other metals , including copper or nickel. In this case, performance indicators, namely the service life and preservation of the shine of chrome, are significantly improved. The material also acquires excellent anti-corrosion properties, so it is not susceptible to harmful influences.

Hard chrome plating is indispensable when it comes to the desire to improve wear resistance and hardness by reducing friction on the workpiece.

In this case, there is no need to use another metal. The soaking time in the bath is long, which is necessary to obtain a certain layer thickness.

In contrast to decorative metallization, hard metallization involves the additional use of special varnishes or oils.

Now you know what all the features of metalizing parts with chromium are. If you follow the sequence of actions, you can successfully carry out such an event at home.

Source: https://tokar.guru/metally/tehnologiya-hromirovaniya-detaley.html

Chrome plating of parts

Today, a large number of substances are used as decorative finishing for individual parts. A considerable number of them are made on the basis of chromium.

Chrome plating process

Chrome plating is the process of saturating metal surfaces with chromium. Also, this process may mean the formation of a chrome deposit on the surface of individual parts made of metals, which is necessary for decorative purposes. Chromium is deposited on the surface of metals under the influence of electric current.

Important: The use of chrome plating is necessary not only to make the surface of individual parts more attractive from an aesthetic point of view, but also to protect metals from corrosion.

Thanks to chrome plating, a thin layer of a protective substance is formed on the surface, which makes the metal structure more durable. This is why chrome parts can last for many years. Decorative chrome plating can last a long time.

The process of chrome plating parts

The chrome plating process is quite time-consuming because everything must be done carefully.

The whole process can be divided into several stages, which are as follows:

At this stage of chrome plating, heavy contaminants are removed from the surface of the metals so that the chromium layer lays flat and neat.

This step involves removing remaining traces of contamination so that they do not interfere with further work.

• Preliminary preparation.

Depending on the material to which the chromium composition will be applied, it depends on what measures should be taken to prepare it for further work.

• Place in a bath with the prepared solution.

At this stage of chrome plating, metal products are placed in a bath with a prepared composition consisting of chromium and other auxiliary elements. This is where temperature equalization takes place.

This step involves connecting a current of a certain strength to the solution containing the chrome plating material. Current treatment occurs to form a layer of chromium of a certain thickness on the metal surface.

During chrome plating, a large amount of toxic substances are released that can harm human health.

Attention: Today there are a large number of countries in the world in which this chrome plating process is under careful control.

Compounds for chrome plating

The following types of solutions are used for chrome plating:

• Hexavalent chromium solution. Its main component is chromic anhydride.
• Trivalent chromium solution. It mainly contains chromium sulfate or chromium chloride. This solution is used quite rarely. This situation arises due to the fact that there are some restrictions on the thickness of the coating, its shade and color saturation.

Table 1. Compositions of electrolytes for chrome plating

ComponentsElectrolyte compositions, g/lDilutedUniversalConcentrated

chromic anhydride	150	250	350
sulfuric acid	1,5	2,5	3,5
cathode current density, A/dm2	45–100	15–60	10–30
solution temperature, °C	55–60	45–55	35–45

Table 2. Composition of chromium plating mixtures for steel

MaterialComposition of chrome plating mixture (mass fraction, %)Chrome plating temperature, °С Exposure, hDepth of chrome layer, mm

Medium carbon alloy heat resistant. steel (springs, labyrinth seals)	60% chromium metal, 39% alumina, 1% ammonium iodide	1020–1050	8	Not less than 0.01
Low-carbon alloy steel (parts of turbine steam distribution units)	1020–1080	8–10	Not less than 0.025
Heat-resistant alloys (O-rings, bushings, valves, nuts, studs)	70% chromium metal, 29% alumina, 1% ammonium iodide	1100–1150	5–10	0,02–0,03

Types of chrome plating

In the modern world there are a large number of varieties of chrome plating.

The following types of this process are distinguished:

• Galvanic chrome plating

This method of chrome plating is a method of applying a special coating to the surface of metals or plastic materials using electric current. Thanks to this, the equipment of the processed material achieves unique properties.

They consist of: thickening the surface, resistance to rust, and acquiring an attractive appearance. When using galvanic chrome plating, a three-layer application of a metal substance is used.

Because chromium reacts with other metals, it settles on the surface and gives it a shiny appearance.

When using this chrome plating method, no electric current is used. The entire process is based on a reaction that occurs between reactants. In this case, it is very important to apply a thin layer of copper before processing individual parts using the chrome-plating method.

For this purpose, a mixture of: copper sulfate, concentrated sulfuric acid, distilled water is used.

For chrome plating, the following composition is used: chromium fluoride, sodium hypophosphate, chilled acetic acid, sodium hydroxide solution, sodium citrate, distilled water.

This type of chrome plating involves applying a thin layer of gold metal to the surface of metals. This is done not only to achieve the best decorative effect, but also to protect the material from corrosion. Gilding makes the material more dense and wear-resistant.

Chrome plating at home

In the modern world there are a considerable number of people who carry out home chrome plating. Thanks to this, you can significantly save on chrome processing of individual metal or plastic parts.

Important: The electroplating process is not available in our country for home use. Its use is criminally punishable.

From a theoretical point of view, it is possible to chrome plating at home, but this will require a lot of effort. For this purpose, it is necessary to purchase a large number of baths and solutions for the process. This will take a lot of time and money. It is not recommended to carry out the chrome plating procedure at home by treating solutions and materials with electric current, because this releases toxins that can harm the environment.

At home, you can use chemical chrome plating. In this case, it is very important to prepare a copper-chromium solution. Only after this can you begin processing metal and non-metal products.

During the chrome plating procedure, it is necessary to take care of safety precautions, as in an industrial environment.

Chrome plating at home video

Source: http://lkmprom.ru/clauses/tekhnologiya/khromirovanie-i-osobennosti-khromirovaniya-v-domas/

Hard chrome plating

Hard chrome plating has found wide application in the manufacture of parts subject to high wear, active corrosion in aggressive environments, in the restoration of metal parts, to increase the service life of tools (cutting, measuring), as well as for decorative finishing of products made from non-metallic materials.

Hard chrome plating is carried out using the following methods:

• galvanic (described above);
• catalytic, in which chromium is reduced on the surface from ammonia and silver salts;
• vacuum, in which the reagent applied to the surface being treated exhibits diffusion activity under negative pressure;
• thermochemical, which can be compared to the cementation of products.

Using the thermochemical method, chrome plating is carried out in a carburizer consisting of crushed chromium and kaolin in a proportion of 55-45%. To prevent oxidation of chromium at high temperatures, hydrogen is blown through the boxes with parts and carburizer. The duration of chrome plating is three hours. During this time, the layer thickness reaches 0.15 mm at a temperature of 1300°C, and 0.8 mm at a temperature of 1400°C.

Chrome plating by electrolysis

Chrome plating by electrolysis involves the easy removal of hydrogen compared to chromium from the electrolyte. The electrolyte is chromic acid. The baths are equipped with insoluble lead anodes.

A sulfate electrolyte based on chromic anhydride with sulfuric acid CrO3:H2SO4 is widely used.

The concentration of the solution is selected based on the nature of the coating and the complexity of the part’s shape.

At a low metallization temperature (not higher than 35°C), the chrome surface has a matte gray tint. The intensity and current density does not affect the process. When the temperature increases to 65°C and the current density, the surface becomes shiny. With a further increase in temperature and current density (up to 30 A/dm2), chromium has a milky tint.

Also, the quality of the coated surface depends on the electrolyte concentration. The chrome coating obtained using a concentration of up to 150 g/l is characterized by high hardness and wear resistance. Highly concentrated electrolytes, up to 450 g/l, are used for decorative coatings.

Galvanic chrome plating

Galvanic chrome plating is the most common modern method of chrome plating. It is carried out in two ways: in an electrolyte environment and by diffusion. The electrolytic method is similar to chrome plating by electrolysis; they differ only in the modes of the process.

The diffusion method is the process of saturating a surface under certain conditions from applied reagents. Finished parts have: strength and hardness, viscosity and elasticity, wear, heat and corrosion resistance.

Equipment for chrome plating

The market offers a variety of equipment for applying a chrome layer, both domestic and foreign. Private foreign entrepreneurship prompted developers to create compact installations that can be easily placed in a garage or small workshop.

Non-professional equipment only imitates high-quality chrome plating, but the quality is not so good. The work is carried out in the following sequence:

cleaning of old coating; grinding; degreasing; applying primer; spraying chrome; drying;

protection from damage with varnish.

Electrolytic (galvanic) chromium plating is widely used in production. For this purpose, special baths, electrical installations, ventilation systems, washing and drying installations are used. The hot method of applying chromium uses furnaces and vacuum units.

But regardless of the type of equipment used, during the chrome plating process, physical and chemical reactions occur, which are accompanied by the release of decomposition products.

Scope of technology application

Decorative chrome plating of parts allows you to improve the visual characteristics of products made from both metals and various types of plastics, glass and other materials. For everyday use, chrome is used for coatings:

• furniture fittings;
• interiors and design projects;
• souvenirs;
• plumbing.

Chrome plating of car parts

Plumbing equipment must be chrome-plated to protect against water oxidation (corrosion), be it inexpensive silumin or expensive brass and bronze.
Industry uses chrome plating to increase the durability of parts operating under high friction conditions:

• pistons;
• compression rings;
• rollers;
• axes.

Chrome plating is also used in the manufacture of tools and equipment:

• press dies;
• cutting tool;
• measuring tool.

Chrome plating technology allows you to extend the life of mechanism elements or give products an attractive appearance.

Source: https://stankiexpert.ru/spravochnik/materialovedenie/hromirovanie-detaley.html

Chrome plating – decorative coating of metal with chromium: technology, types

The term “chrome plating” can be understood as both diffusion saturation of the surface of the workpiece with a layer of chromium, and the application of chromium using galvanic technology. There is also a more general term - “metallization”. It means applying a layer of metal to the surface being treated, which can include chromium.

True fans of chrome plating are not averse to covering everything they can with chrome.

Among the electroplating methods of metal deposition, chrome plating is the most popular. That is why the term “metalization” is often used as a synonym for the word “chrome plating”.

What is the chrome layer for?

Applying a layer of chromium can be performed to improve the decorative characteristics of a metal product (decorative chrome plating), as well as to protect the metal part from corrosion and give its surface greater hardness. Thus, by chrome plating it is possible not only to improve the mechanical and decorative characteristics of the product, but also to significantly extend its service life.

A wide variety of chrome-plated products can be found both in everyday life and in various industries. The use of metal products with a layer of chromium applied to their surface is relevant in cases where they will be used under conditions of constant exposure to aggressive environments and intense friction.

Restoring the chrome plating restores its original appearance and extends the service life of the structure.

In domestic conditions, the following products with chrome coating are most actively used:

• furniture fittings;
• elements for decorating home and office interiors;
• car rims and vehicle parts;
• souvenir products;
• plumbing equipment.

In industry, chrome plating technology is used for the following purposes:

• in the production of products using powder technology;
• in the manufacture of molds used for the manufacture of products made of rubber and polymer materials;
• in the production of reflectors for various purposes;
• to increase the hardness of the surface layer and wear resistance of cutting, as well as special measuring tools;
• to impart exceptional decorative characteristics to body and other parts of vehicles;
• for processing parts operated under conditions of constant friction and negative influence of the external environment (elements of steam equipment and heating networks, parts of automobile engines and marine vessels).

Industrial electroplating line designed for applying hard chromium to steel and non-ferrous metal products

Chrome parts have the following characteristics:

• highly resistant to corrosion;
• microhardness, the values ​​of which reach 950–1100 units on the HV scale;
• high porosity of the coating, its wear and heat resistance;
• low coefficient of friction of the formed coating;
• large variation in the thickness of the chromium layer (5–300 μm or even more).

The listed characteristics, which can be achieved using chrome plating of steel and other metals, make this technology so popular. It would take quite a long time to list all the areas where the chrome plating process is actively used.

Types of metallization according to the method of interaction of the metallized surface with the applied metal (click to enlarge)

Basic methods

Today, the following types of chrome plating are distinguished, each of which has its own advantages and disadvantages:

• chrome plating performed using galvanic technology;
• diffusion chromium plating, carried out in a sealed container at high temperature;
• vacuum chrome plating, which requires the use of a special chamber in which a vacuum is created;
• catalytic chrome plating, which involves applying special liquids without acids to the surface of the workpiece;
• chemical chrome plating of steel and other metals, which is similar in technology to conventional painting;
• chrome plating using galvanic technology.

How to prepare the product

The technology of decorative chrome plating (as well as the application of a layer of chrome for protective purposes) requires careful preparation of the product. Such preparation consists of performing procedures such as:

• grinding the surface to be treated, as well as its thorough polishing;
• washing the product and wiping it with a soft cloth;
• insulation of those surface areas where chrome plating is not required;
• degreasing the chrome-plated part;
• pickling of the product, which improves the adhesion of the applied chrome layer to the base metal;
• placing the product in an electrolytic solution using a special bracket.

Polishing the product before chrome plating

In some cases, decorative chrome plating technology involves preliminary etching of the surface being treated and applying a layer of another metal (copper or nickel) to it, which helps to increase the strength of the chrome coating.

How to carry out the chrome plating procedure

The technology of decorative chrome plating itself is as follows.

• After preliminary preparation, the product is placed in a container with an electrolytic solution, which already contains the anode.
• The solution into which the product is immersed must be preheated to the required operating temperature. It should be borne in mind that the operating temperature of the electrolytic solution must be maintained throughout the entire chrome plating process. This is necessary in order to ensure good adhesion of the applied layer, as well as its uniformity in structure and thickness.
• Depending on how thick the chrome layer should be, determine the time the product is in the electrolytic solution.

Recommended drying modes for chrome-plated products

The technology of decorative chrome plating also involves heat treatment of the part (this stage is necessary to make the chrome coating harder and more durable). The product, on the surface of which a layer of chromium has already been applied, is kept for several hours in a heating furnace at a temperature of about 200°.

Source: http://met-all.org/obrabotka/prochie/hromirovanie-detalej-dekorativnoe-pokrytie-hromom-tehnologiya-2.html

What is chrome plating: do-it-yourself technology for processing or coating parts and metal and equipment for this at home

Various metal products require a protective layer to be applied to them to prevent early destruction and give them a beautiful and elegant look. Electrochemical chrome plating of parts is a long-established and widespread method of corrosion protection.

Various metal fittings, plastic items, car wheels, many items from the food, sanitary, medical and many other industries are subject to chrome plating, as a result of which the parts are literally “ennobled” and acquire an aesthetically impeccable appearance and strength.

Chrome plating with electrolyte

Electrolytic chromium plating is based on the use of tri- and hexavalent chromium, depending on the type of coating.

When using trivalent chromium, the main component of the electrolyte is chromic anhydride, when using hexavalent chromium, chromium sulfate, and the electrolyte solution in this case consists of sulfuric acid, anhydride in a ratio of 1/100 (2.5 and 250 g/liter, respectively).

If this proportion or ratio is violated, the result of galvanic chrome plating will be far from expected and, instead of an even, ideal coating, we will get a part with obvious peeling of the protective layer, with varying dullness and the presence of stains.

When the above ratio is reduced by half (1/50), the covering and scattering properties of the product will significantly decrease. And violation of the parameters of current density (more than 300 A/dm2) and electrolyte temperature leads to the formation of dendrites on the corner and end parts of products, unsightly in shape and appearance.

Anodes used in the process of chrome plating parts must be almost 100% pure lead, with no more than 6% antimony added.

When the chrome plating process is completed, the lead anodes must be cleaned of the resulting chromate deposits and stored in a water bath in case of a long break in use. Recently, anodes made of platinized titanium have been widely used, the use of which does not require cleaning them after chrome plating.

Chrome restoration

Restoring parts by chrome plating involves the use of one of two types – shiny or milky. The last type of chrome plating is used in cases of increased loads and friction affecting the part, shiny - for less intense loads.

The application of chromium must be performed only after a number of operations:

• washing the workpieces in water;
• removal of dust, dirt, and other deposits;
• preliminary polishing of the surface or grinding it.

Restoring self-passivating parts (titanium, aluminum) involves preliminary cleaning of their surfaces by etching and applying a nickel or copper underlayer to the metal.

To eliminate the risk of corrosion when using a nickel sublayer, it is recommended to saturate this film with oils or varnishes at high temperatures (up to 200C) on the surface to be chromed.

Chrome decoration

Many people are interested in decorative chrome plating, the possibility of chemical metallization in domestic conditions in order to protect plastic, metals, and alloys using spraying. To find out, you need to understand the essence of metallization. In a nutshell, chemical metallization is the process of applying a metal layer to the surface being treated.

Both metallic and non-metallic materials can be used as a base. These can be plastic parts, wood, glass, aluminum, etc.

Methods for applying a protective layer can also be different, depending on our goals and the equipment used.

The most widely used method is using a bath with an electrolytic solution when chrome plating a product.

In addition, spraying with a gas burner is often used when applying components in their dispersed form and the cladding method by hot rolling the applied metal on one or more sides.

The diffusion method is also used, in which deep penetration of the molecules of the protective layer into the surface being treated occurs under strong heating, as well as the hot coating method by immersing the workpiece in molten metal.

Chemical metallization

The purpose of carrying out this type of chrome plating of products is most often the desire to give them the necessary external decorative appearance, remove various surface damage in the form of cracks, microchips, increase anti-corrosion properties, and improve other characteristics of parts, such as durability, hardness, and anti-erosion resistance.

In fact, we can talk about the possibility of using this method for applying a coating with predetermined properties to products not only made of metal, but also plastic.

At the molecular level, chemical metallization is a process in which atoms of higher potential are raised to the surface of the metal under the catalytic influence of specially applied reagents.

In this case, there is a clear change in the shade, and sometimes the color of the workpiece.

The use of various combinations of reagents makes it possible to obtain coatings of a wide variety of colors and shades until they smoothly transition into each other.

In essence, this is catalytic chrome plating, intended for any metal, a fairly simple method, it can be compared to applying a paint coating.

Electroplating

If the necessary precautions and safety precautions are taken, galvanic chrome plating can be carried out at home.

One has only to remember that this work is carried out with rather aggressive chemical materials and their various components, but with the correct, verified organization, you can engage in galvanic chrome plating of any objects - from ordinary buttons to complex, voluminous curved surfaces such as statues, busts, etc.

The product is pre-washed, cleaned of dust, dirt and primed with a special type of primer. Next, you need to apply reagents, which, by analogy with printing photographs, have the properties of an activator and a reducer.

After surface treatment with reagents, the part is covered with a protective layer of paint and varnish to ensure the protective function of the metallization produced.

This metal chrome plating is characterized by a high degree of hardness and wear resistance.

Using a pre-selected toner will allow you to obtain the desired color, as well as the shade of the treated surface.

The use of a special primer is highly recommended, as this improves the adhesive characteristics of the object.

To remove the coating applied during the galvanization process, you can use a special substance to wash it off and re-process the part.

As you can see, this method of galvanic chrome plating is quite simple and similar in its implementation to the process of conventional varnishing, where chrome painting can also be used.

The main thing is to observe the necessary sequence of technology, all precautions, while paying special attention to the ventilation of the workroom, the use of personal protective equipment, which is quite achievable at home.

The technology of decorative chrome plating does not represent any extremely complex operation, but you must always remember that the process of chemical metallization is accompanied by a large amount of gases released, creating gas fog from harmful chemical compounds, so the room must be open, well ventilated or have reliable forced ventilation.

Source: https://xn----8sbna6aihebzq3cl.xn--p1ai/kuzovnoj-remont/kak-ponyat-chto-takoe-hromirovanie.html