Electroplating:

The technology of depositing well-adhered metal coatings on mechanical products by electrolysis, but with different properties and substrate materials. The electroplating layer is more uniform than the hot-dip layer, and is generally thinner, ranging from several microns to tens of microns. By electroplating, decorative protective and various functional surface layers can be obtained on mechanical products, and workpieces that are worn and machined incorrectly can also be repaired. Most of the coatings are single metal or alloy, such as titanium target, zinc, cadmium, gold or brass, bronze, etc.; there are also dispersed layers, such as nickel-silicon carbide, nickel-fluorinated graphite, etc.; and cladding layers, such as steel copper-nickel-chromium layer on steel, silver-indium layer on steel, etc. In addition to iron-based cast iron, steel and stainless steel, there are also non-ferrous metals, such as ABS plastic, polypropylene, polysulfone and phenolic plastics, for electroplating base materials, but plastics must undergo special activation and sensitization treatment before electroplating.

Electroplating principle

In the plating tank containing the electroplating solution, the cleaned and specially pretreated part to be plated is used as the cathode, and the anode is made of plated metal, and the two poles are respectively connected with the positive and negative poles of the DC power supply. The electroplating solution is composed of an aqueous solution containing metal-plating compounds, conductive salts, buffers, pH adjusters and additives. After electrification, the metal ions in the electroplating solution move to the cathode under the action of the potential difference to form a plating layer. The metal of the anode forms metal ions into the electroplating bath to maintain the concentration of metal ions being plated [1]. In some cases, such as chrome plating, it is an insoluble anode made of lead and 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 regularly adding chromium compounds to the plating solution. During electroplating, the quality of the anode material, the composition of the electroplating solution, temperature, current density, energization time, stirring intensity, precipitated impurities, power waveform, etc. will affect the quality of the coating, which needs to be controlled in time.

Electroplating method

Electroplating is divided into rack plating, barrel plating, continuous plating and brush plating, which are mainly related to the size and batch of the parts to be plated. Rack plating is suitable for general-sized 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 mass-produced wire and strip. Brush plating is suitable for partial plating or repair. The electroplating solution includes acid, alkaline and acid and neutral solutions with chromium compound. No matter what kind of plating method is used, the plating tank and hanger in contact with the product to be plated and the plating solution should have a certain degree of resistance. Universality.

Plating classification

Coatings are divided into decorative protective coatings and functional coatings.

Decorative protective coatings are mainly chrome coatings on ferrous metals, non-ferrous metals and plastics, especially copper-nickel-chromium layers on steel, nickel-chromium layers on zinc and steel. In order to save nickel, people have been able to plate copper-nickel/iron-high-sulfur nickel-nickel/iron-low-solid nickel-chromium layer on steel. Tin/nickel plating similar to chrome plating, used on analytical balances, chemical pumps, valves and flow measuring instruments.

There are many types of functional coatings, such as: ① sliding bearing cover coating to improve compatibility and embedment with journals, lead-tin, lead-copper-tin, lead-indium and other composite coatings; ② for resistance Hard chrome coating on the piston rings of the milled medium and high-speed diesel engines, this coating can also be used on plastic molds, with the characteristics of non-stick mold and long service life; ③Copper plating on the sliding surface of large herringbone gears can prevent Early roughening of the sliding surface; ④ galvanizing to prevent atmospheric corrosion of steel substrates; ⑤ copper-tin plating to prevent nitriding; - Zinc plating. Engineering coatings suitable for repair and manufacturing, such as chromium, silver, copper, etc., are relatively thick, and the hard chromium layer can be as thick as 300 microns.

The process of electroplating is basically as follows

1 Connect the plated metal to the anode

2 Connect the plated part to the cathode

3 The cathode and anode are connected by an electrolyte solution composed of positive ions of the plated metal

4 After the DC power supply is applied, the metal of the anode will undergo oxidation reaction (loss of electrons), and the positive ions in the solution will be reduced (gain electrons) into atoms at the cathode and accumulate on the surface of the negative electrode.

The aesthetics of the plated objects after electroplating is related to the magnitude of the current. The smaller the current, the more beautiful the plated objects will be; otherwise, some uneven shapes will appear.

The main uses of electroplating include preventing metal oxidation (such as rust) and for decoration. The outer layers of many coins are also electroplated.

Effluents from electroplating, such as spent electrolytes, are a significant source of water pollution.