The electroplating process
The dimensions of our baths are in the 800 x 500 x 250 mm range. This determines the maximum size of processable workpieces.
Stable suspension is ensured by copper wires, stringed clips and plastic covered proprietary electroplating fixtures. We are specialising in large series batches.
The purpose of electroplating – i.e. surface protection with inorganic coating – is to protect the plated pieces from corrosion and ensure an attractive glossy finish.
The electroplating process uses electricity to deposit a metal layer on the surface of metal or plastic objects. The coating decorates the plated objects, makes them resistant to environmental and chemical effects, and give them specific properties to fulfil various technical criteria (wear resistance, electric conductivity, etc.). Electricity for electroplating is provided by external power supplies. The technology is based on the principles of electrochemical processes in the aqueous solutions of various chemicals.
In order to understand the processes, let’s briefly overview the key electric and electrochemical concepts.
Some materials conduct electricity (e.g. copper wire), while others do not (e.g. plastic). Materials that conduct electricity are called conductors.
Conductors can be divided into two groups:
- Primary conductors (e.g. metals). In this case electricity is conducted via the movement of ions in the metal.
- Secondary conductors (aqueous solutions of electrolytes). In this case electricity is conducted via the positive and negative elementary particles, i.e. ions in the bath solution. Electric flow (current) is produced by way of the so-called electric force.
The force to produce electric current is the electrical voltage. Its unit is one volt, its sign is “V”.
Amperage:: the electrical flow passing through a conduction in one unit of time (second). Its unit is one ampere, its sign is “A”.
Ohm’s law applies to the relation between the current and the voltage in the conductor, which states that:
The current through a conductor between two points is directly proportional to the voltage across the two points and inversely proportional to the resistance subject to the material quality of the conductor. The unit of resistance is one ohm, its sign is “Q”.
The resistance of a conductor is subject to:
- the length of the conductor,
- the cross-section and the material quality of the conductor
Steps of the technological process:
The first step of electroplating is always the assessment and needs analysis. This step precedes each treatment process. It is key to know the baseline condition and the desired goal to offer you the process that best suits your needs.
Excellent quality, beautiful coating.
A well-chosen technology saves you money and energy. We hope that you will be pleased with our workmanship and spread the reputation of our company.
Chrome coating deposited by electroplating is hard, abrasion-proof and has good corrosion resistance. Oxidants create a thin oxide layer on the surface that reduces corrosion.
The wear resistance and hardness of chrome coating deposited for engineering purposes are decisive factors. Chrome coating has good resistance to the corrosive effects of gases, acids (save for hydrochloric and hydrofluoric acid), salts and alkali liquors.
Main areas of application:
- decorative chroming,
- industrial chroming (hard chroming).
A thin chromium layer is deposited – usually on an intermediate nickel layer for decorative chroming applications. Plating has a dual role here: it reduces the matting of the nickel layer and increases its resistance to corrosion.
Chromium compounds usually have trivalent or hexavalent chromium in them. Chromium may be separated by plating from the aqueous solution of both types of compounds. The physical and chemical properties of the deposited layer greatly depend on the composition of the electrolyte used, the temperature and the conditions of deposition. Chromium is mostly deposited from its hexavalent compounds, although the process with trivalent chromium requires less electricity. The reason is that chrome coating from bath solutions containing trivalent chromium can only be made under strict conditions. Cathodic current efficiency also depends on the foreign acid used and its concentration. By increasing the concentration of foreign acid, cathodic current efficiency first increases steeply, reaches a maximum and then decreases again. Therefore, extreme care needs to be taken to control these proportions and to make the necessary corrections. If the foreign acid content of the electrolyte is low, a spotted rainbow chromium layer is deposited. When the foreign acid content exceeds certain limits, chromium deposition decreases and then disappears completely.
The hardness and gloss of the deposited chrome coating depends on the electrolyte temperature, and the cathode current density. In chrome plating electrolytes, cathodic current efficiency of between 10 … 25% is determined by the following factors:
- the chromic acid content of the electrolyte
- type and concentration of the foreign acid used, – the cathodic current density,
- the operating temperature.
In practical chroming, the uniform thickness of the deposited coating (dispersion) and the covering capacity of the electrolyte are of utmost importance.
The dispersion of the electrolyte depends on:
- the primary current distribution,
- the temperature and current density used.
Electrolyte dispersion is degraded by rising temperatures, and improved by increasing cathodic currents.
It is a well-known fact that the dispersion of chrome plating electrolytes is bad. This is particularly problematic when chrome plating parts with large surface area and profiled parts. Therefore, the depositing of a chromium coating on peaks, edges and other surfaces that is thicker than necessary must be prevented by shielding and by special suspension technology. At the same time, it is necessary to ensure, using auxiliary anodes, that the required layer thickness of chromium coatings will also be formed in the recesses.
When chroming profiled objects, especially when making decorative coatings, chromium deposition can be realized in the recesses so that chroming is carried out with an electrolysis using a current density of 60 … 20 A/dm2 for 30 s (after precipitation, current density is reduced so that it does not exceed the required current values permanently at other places on the workpiece).
The covering capacity of chrome plating electrolytes depends on the surface condition of the part to be processed. Copper and brass parts can be chrome-plated more easily than similar steel or cast iron components.