Electroplate
Electroplating is a process that uses electrolysis to attach a metal film to the surface of metal or other materials. It can prevent corrosion, improve wear resistance, conductivity, reflectivity and enhance aesthetics.
The concept of electroplating
It is the process of using the principle of electrolysis to coat a thin layer of other metals or alloys on the surface of certain metals. During electroplating, the coated metal is anointed and oxidized into cations into electroplating solution; The metal products to be plated are animated, and the cations of the coated metal are reduced on the metal surface to form a coating. In order to exclude the interference of other cations, and make the coating uniform and firm, it is necessary to use a solution containing the coated metal cation as the electroplating solution to keep the concentration of the metal cation of the coating unchanged. The purpose of electroplating is to coat the substrate with a metal plating layer (deposit) to change the surface properties or size of the substrate, electroplating can enhance the corrosion resistance of the metal (the coated metal is mostly corrosion-resistant metal), increase hardness, prevent wear, improve conductivity, lubricity, heat resistance, and surface beauty
Plating
The technology of using electrolysis to deposit a well-adhered metal cladding on mechanical products, but the properties and substrate materials are different, and the electroplating layer is more uniform than the hot-dip layer, and is generally thinner, ranging from a few microns to tens of microns. Through electroplating, decorative protection and various functional surface layers can be obtained on mechanical products, and most of the workpiece plating layers that can repair wear and processing errors are single metals or alloys such as zinc, cadmium, gold or brass, bronze, etc.: there are also diffuse layers, such as nickel-silicon carbide, nickel-fluoride, etc.: there are also cladding layers, such as copper-nickel-chromium layers on steel, silver-indium layers on steel, etc. In addition to iron-based cast iron, steel and stainless steel, the base material of electroplating also includes non-ferrous metals such as ABS plastic, polypropylene, polysulfone and phenolic plastic, but the activation and sensitization of plastic must be carried out before plating
Principle of electroplating
In the plating tank containing electro-hydraulic, the parts to be plated after cleaning and pre-treatment are used as yin and made of metal-coated parts
Positive, two are positively and negatively connected to the DC power supply. Plating solutions consist of aqueous solutions containing coated metal compounds, conductive salts, buffers, pH adjusters, additives, etc. After the electricity is applied, the metal ions in the electroplating solution move to the yin to form a plating layer under the action of the potential difference. The positive metal forms metal ions into the plating solution to maintain the concentration of the metal ions being plated. In some cases, such as chrome plating, it is an insoluble yang made of lead, lead-antimony alloy, which only plays the role of transferring electrons and conducting current. The concentration of chromium ions in the electrolyte is maintained by the regular addition of chromium compounds to the bath. During electroplating, the quality of the positive material, the composition of the electroplating solution, temperature, current density, stirring strength during the energizing time, precipitated impurities, and power supply waveform will affect the quality of the plating layer, and it is necessary to control it in a timely manner.
Plating method
Electroplating is divided into hanging plating, barrel plating, continuous plating and brush plating, which is mainly related to the size and batch of the parts to be plated. Hanging plating is suitable for general size products, such as car bumpers, bicycle handlebars, etc. Barrel plating is suitable for small parts such as fasteners, washers, pins, etc. Continuous plating is suitable for wire and strip produced in batches. Brush plating is suitable for spot plating or restoration. The electroplating solution has acidic, alkaline, acidic and neutral solutions with chromium mixture, and the plating tank and hanging device in contact with the products to be plated and the plating solution should have a certain degree of versatility regardless of the plating method.
Plating classification
Plating is divided into two categories: decorative protective coating and functional coating
Decorative protective coating is mainly the chrome plating layer on ferrous metals, non-ferrous metals and plastics, especially the copper-nickel-chromium layer of steel, the nickel-chromium layer on zinc and steel. In order to conserve nickel, it has been possible to plate the steel with a copper-nickel/iron-high-sulfur nickel-nickel/iron-low solids nickel-chromium layer. Tin/nickel plating, similar to chrome plating, can be used on analytical balances, chemical pumps, valves, and flow measuring instruments. There are many types of functional plating, such as: 1. Sliding bearing cover coating to improve compatibility and embedding with the shaft journal, lead-tin, lead-copper-tin, lead-indium and other composite coatings; 2. The hard chrome plating on the piston ring of the wear-resistant medium and high-speed diesel engine can also be used on the plastic mold, which has the characteristics of non-stick mold and long service life; 3. Copper plating on the sliding surface of large herringbone gears can prevent early brushing of the sliding surface; 4. Galvanizing used to prevent the steel matrix from atmospheric corrosion; 5. Copper-tin plating to prevent nitriding; 6Tin-zinc plating for brazing in the manufacture of radios and televisions and to prevent corrosion of galvanic cells between steel and aluminum. Engineering coatings suitable for repair and manufacturing, including chromium silver, copper, etc., are relatively thick, and the hard chrome layer can be up to 300 microns thick.
The process of electroplating is basically as follows
1.I connect the metal which I plating on
2. The object to be plated is connected to the negative
3. The positive and negative are connected by an electrolyte solution composed of positive ions of the coated metal
4. After the direct current power supply is applied, the positive metal will oxidize (lose electrons), and the positive ions in the solution will be reduced (electrons obtained) into atoms and accumulated on the negative surface.
5. The aesthetics of the electroplated object after electroplating is related to the size of the current, the smaller the current, the more beautiful the electroplated object will be; Otherwise, some uneven shapes will appear.
6. The main uses of electroplating include preventing metal oxidation (such as rust) and decorating. The outer layer of many coins is also plated.
7. Effluent from electroplating (e.g. electrolytes that have lost their effectiveness) is an important source of water pollution.
