Plating from hexavalent chromium baths: the deposition of chromium electrowinning is widely used both as decorative plating that functional. The most commonly used electrolyte is a solution of hexavalent chromium but, given its characteristics of toxicity, have developed environmentally friendly alternative processes based on trivalent chromium, which allow to solve / reduce environmental health issues (Perterbilt chrome).
Plating baths of trivalent chromium: the deposition of trivalent chromium, also known as Trichromium, today it is proposed as a viable alternative substantially for decorative applications or for applications where they are not required thickness of chromium exceeding microns. The process differs from the traditional one (hexavalent chromium) for the chemical composition of solution and to anodes employed.
Deposition of chromium may be deposited directly onto workpiece according to its use. For cylinders it is advisable to perform a sub-layer of nickel 20 microns to limit corrosion. You should know that the chromium deposit has a low cathode efficiency (15%) and cathode occurs a release of hydrogen which weakens the steel and reduces resistance to fatigue. Degassing treatment is to return to mechanical characteristics of part.
To increase the fatigue strength, shot peening can also be performed before plating. Improvements were made to process, to avoid the appearance of microcracks in deposits, to get some micro-porosity supports the retention of lubricants to replace hexavalent chromium by the less toxic trivalent chromium, etc. The electrodeposition under pulsed currents dramatically improves the deposition rate and the cathode efficiency.
Plating obtained by galvanic process, to give a certain thickness to an object, always, of iron or steel, consummated during use and making it suitable for reuse, using the hardness of chromium, after correction of piece itself. This procedure is used for example, in inserts of movable molds for the extrusion of clay, brick industry, which will consume for the continuous rubbing with mixture of ground extruded at high pressures.
Plating of steels containing more than 0.3-0.4% of C, also increases the hardness and wear resistance. The hardness of chromium is from 66 to 70 HRC. The thickness of plating layer is generally from 0.075 to 0.25 mm, but there are thicker and thinner layers. Superficial defects are amplified and plating surface is subject to further processing as the chromium does not effect the alignment.
In recent years, in addition to hexavalent chromium, is used more and more trivalent chromium, defined 'environmentally friendly'. There is then the chromium satin (matte) for which the process is similar except for the last bath where, with use of special oils, you create microbubbles uniformly distributed on the surface of workpiece which give the characteristic matt appearance to surface same.
Chromate flash: this technique allows the storage of small thickness of chromium (0003-0007 mm), without the need for subsequent grinding operations. The process requires very high currents, but less time than the traditional chromium. This allows a productivity quite high (300-400 pcs / hour) and the use of much smaller tanks (also 30 l). It is used for plating of small parts (eg. Valves intake / exhaust of engines).
Plating baths of trivalent chromium: the deposition of trivalent chromium, also known as Trichromium, today it is proposed as a viable alternative substantially for decorative applications or for applications where they are not required thickness of chromium exceeding microns. The process differs from the traditional one (hexavalent chromium) for the chemical composition of solution and to anodes employed.
Deposition of chromium may be deposited directly onto workpiece according to its use. For cylinders it is advisable to perform a sub-layer of nickel 20 microns to limit corrosion. You should know that the chromium deposit has a low cathode efficiency (15%) and cathode occurs a release of hydrogen which weakens the steel and reduces resistance to fatigue. Degassing treatment is to return to mechanical characteristics of part.
To increase the fatigue strength, shot peening can also be performed before plating. Improvements were made to process, to avoid the appearance of microcracks in deposits, to get some micro-porosity supports the retention of lubricants to replace hexavalent chromium by the less toxic trivalent chromium, etc. The electrodeposition under pulsed currents dramatically improves the deposition rate and the cathode efficiency.
Plating obtained by galvanic process, to give a certain thickness to an object, always, of iron or steel, consummated during use and making it suitable for reuse, using the hardness of chromium, after correction of piece itself. This procedure is used for example, in inserts of movable molds for the extrusion of clay, brick industry, which will consume for the continuous rubbing with mixture of ground extruded at high pressures.
Plating of steels containing more than 0.3-0.4% of C, also increases the hardness and wear resistance. The hardness of chromium is from 66 to 70 HRC. The thickness of plating layer is generally from 0.075 to 0.25 mm, but there are thicker and thinner layers. Superficial defects are amplified and plating surface is subject to further processing as the chromium does not effect the alignment.
In recent years, in addition to hexavalent chromium, is used more and more trivalent chromium, defined 'environmentally friendly'. There is then the chromium satin (matte) for which the process is similar except for the last bath where, with use of special oils, you create microbubbles uniformly distributed on the surface of workpiece which give the characteristic matt appearance to surface same.
Chromate flash: this technique allows the storage of small thickness of chromium (0003-0007 mm), without the need for subsequent grinding operations. The process requires very high currents, but less time than the traditional chromium. This allows a productivity quite high (300-400 pcs / hour) and the use of much smaller tanks (also 30 l). It is used for plating of small parts (eg. Valves intake / exhaust of engines).
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