Chrome plating can be used both for decorative purposes and to improve the technical and operational properties of the workpiece. For metal products, this coating method is especially relevant, as it reduces the risk of corrosion damage. The technology is used not only in industry, but also in the private sector - for example, to decorate and protect the exterior of a car. How to chrome metal at home? There are several relatively affordable methods, each of which provides its own implementation nuances, but there are general rules for organizing this process.
Preparing a part for chrome plating
The quality of the coating directly depends on the condition of the work surface. It should not only be cleaned of dirt and dust, but subjected to mechanical cleaning with abrasives. Sanders should eliminate specific details for problematic defects as small lesions, scale, rust and old paint. On the surface should remain directly the base structure of the product. This is a basic preparation condition under which it is possible to chrome metal in a home environment, expecting a positive result. Moreover, special attention is paid to persistent fat stains, which also impede the processes of applying chromium. At a minimum, aggressive chemical solvents, white spirit, or gasoline should be used for this treatment. For a more reliable effect of cleaning fat and oil films, experts also recommend the use of compositions based on caustic soda, silicate glue and soda ash, pre-heating them with a temperature regime of 85-90 º
Conditions of the treatment
In the process of chromium plating, irrespective of the processing method used, the emission of harmful fumes is inevitable, therefore, living quarters should immediately be abandoned. The best place is a garage, utility room or other technical room. But that is not all. Stable ventilation should be considered with an efficient exhaust hood. It is impossible to hope for natural weathering, since harmful substances can have an effect already in the course of work. How to chrome metal at home without harming your health? Even with ventilation, personal protective equipment should be prepared. The required kit includes construction glasses, a respirator, an apron, and rubber-coated gloves.
Preparing a Chrome Tank
In any case, to perform the procedure, a conditional bath will be required to keep the part in the working solution. Depending on the size of the part, a 3-liter can, basin, tank or classic bathtub can be used. The only limiting parameter of choice is the material of manufacture - glass or metal, which does not enter into chemical reactions with the electrolyte. Next, you should deal with the arrangement of the selected tank. Firstly, it must be installed on a flat surface and fixed in a stable position so that the chromed metal gets a uniform coating. Secondly, during the cold required insulation capacity as fiberglass which can be used mineral wool or granular material (sand, expanded clay). At this stage thought out device or structure to easily hold the workpiece and the functional devices to be used at different stages of the operation.
Sources of electric current
When performing metallization at home, electrodes are needed that will be connected to the workpiece to provide an electrochemical reaction. A negative cathode must be connected to the product, and a positive anode to the solution. The shape of the electrodes is selected according to convenience; both rod and plate elements can be used. But how to chrome a metal so that the contact does not open throughout the operation? For a circuit with a current supply to the part, a crocodile wiring clamp should be provided. He will reliably capture the workpiece in the desired position. If you plan to process a compact lightweight part, this grip will replace the tool-retaining equipment in the solution. An ordinary rheostat can act directly as a current source with sufficient voltage. For small workpieces, wires with a cross section of up to 2.5 mm2 will be sufficient.
Electrolyte solutions
Active motorists for the procedure using a simplified structure based on chromic anhydride (250 g / l) and sulfuric acid (up to 3 g / l). It is important to keep in mind that the above-mentioned anhydride acts as the main ingredient of hexavalent chromium, and chromium chloride or sulfate acts as the trivalent one. The second scheme is used less often, since such a composition has a significant impact on the textured and textural properties of the part. With regard to temperature, the chrome-plated metal quality can be obtained at 45-60 ° C, but this range could widen depending on the chosen technology. Now we can take a closer look at the methods for implementing the task.
electrochemical technology
The most common method that is widely used in the domestic field. Instructions for its use look like this:
- The prepared container is filled with water by about 60-70%. It is important to note that the liquid must be pre-filtered - it is best to use the settled distilled water.
- The tank warms up until the temperature of the contents reaches approximately 60 ° C.
- The estimated volume of chromic anhydride falls asleep. It should be thoroughly mixed in water.
- At this stage, you may encounter the problem of lack of the required amount of water. How to chrome metal at home, if there is a need to correct the proportion of the solution? It is advisable to avoid this, but in any case, amendments are recommended to be made in the direction of increasing the volume of water to fill the desired level of capacity.
- Sulfuric acid is added in the right amount.
- After stirring the solution again, it should be allowed to stand for 3-4 hours while applying current at the rate of 6.5 A per 1 liter. As the reaction progresses, the electrolyte will gradually acquire a dark brown hue.
- The power source is turned off, after which the capacity is insisted for another day.
Possible defect when performing chrome plating
If the operation is performed for the first time, then there are big risks to get all sorts of defects. How to chrome metal at home to exclude such a possibility? To do this, you need to know the specific reasons for the appearance of marriage:
- There are small sinks on the surface - insufficient machining of the part with abrasives was carried out.
- Peeling of the coating - the current source was supplied with voltage drops.
- The chromium layer is softened - the temperature is too high and the current is reduced.
- There is no characteristic gloss on the surface - evidence of an overestimated current strength or an excess of the chromium component in the solution.
- The gloss is uneven on the surfaces - a lack of temperature or a sign that the solution was poorly mixed.
- Brown spots - a small proportion of acid against the background of an excess of chromium.
Alternative Chrome Plating Technologies
Another way to apply chromium is diffuse. But it is used specifically for modification of surfaces due to the combined effects of silicon, carbon, aluminum and nitrogen at high temperature. How to chromium metal at home by diffusion? The technology involves wetting in hydrochloric acid, after which it is laid with powder mixtures followed by exposure to gases. A subspecies of this method is the condensation treatment with chrome chloride vapors, but it is usually performed on technologically sophisticated equipment. Also worth noting is a method called “silver mirror”. Its essence lies in the deposition of silver salts in an alkaline solution. Further, it is necessary to use auxiliary solutions containing hydrazine and invert sugar. To give the coating a specific color at the final stage of processing, special paints and varnishes can be used.
How to restore a chrome coating on metal?
Technically, it is only possible to restore the structure of a given coating by a decapitation operation. It is to re-immersing the items in the solution with sulfuric acid and hydrochloric acid at the desired concentration, which depends on the dimensions and details of the current state of the chromium layer. After this procedure, the workpiece is washed with warm water and infused for several hours in a dry place. More affordable methods for the restoration of a chrome-plated coating on a metal involve the use of special pastes produced by car chemical manufacturers. Such means literally rubbed into the structure microfiber coating, forming a protective film and filling the fine pores of defects. Sanding procedures also help to correct the imperfections of the chrome surface, but their effect erases the coating over time. For this reason, it is recommended to use additional protective equipment as a prophylaxis. Among them, the simplest folk recipes based on crushed chalk and ammonia. However, rubbing these materials should only be soft sponges and napkins.
Is it possible to chrome parts from other materials?
Theoretically, any materials having a porous structure on the surface can be subjected to electrochemical metallization, which will provide sufficient adhesion. Unlike metals, plastics and ceramics are chrome plated in less aggressive temperature conditions. This nuance applies to all products that are sensitive to temperature effects. Otherwise, the conditions remain the same - both in terms of technical preparation, and in terms of the preparation of an electrolytic solution.
Conclusion
The result of applying chromium plating is equally valuable both in aesthetic effect and in the creation of a protective coating. In the first case, you can expect to receive attracting attention gloss, referred to above, and the second - the extension of the working life details. Even metals chromed at home add to the properties of wear resistance, strength and hardness. For additional hardening of critical parts, special heat treatment of the coating is sometimes applied with exposure to temperatures up to 200 ° C. On the other hand, chrome metallization also has weak points. Over time, the coating wears away, and in a minor mechanical effects, which is why experts strongly recommend since the beginning of operation of renovated surface to take care of its protection. As for the processing method itself, with all the accessibility for home use, it also has a big minus. It is expressed in the toxicity of the electrolytes used, which necessitates compliance with and appropriate safety measures.