The Electroplating Process for High-end Quality Products
When electroplating, the coated metal or other insoluble materials serve as the anode, and the workpiece to be plated serves as the cathode. The cations of the coated metal are reduced on the surface of the workpiece to form a coating. To eliminate interference from other cations and make the coating uniform and firm, a solution containing the coated metal cations is used as the electroplating solution to maintain the concentration of the coated metal cations unchanged. The purpose of electroplating is to coat the substrate with a metal coating, change the surface properties or dimensions of the substrate. Electroplating can enhance the corrosion resistance of the metal (the coated metal is mostly corrosion-resistant), increase hardness, prevent wear, improve conductivity, smoothness, heat resistance, and surface aesthetics.
Electroplating method
Electroplating can be divided into hanging plating, rolling plating, continuous plating, and brush plating, which are 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. Rolling plating is suitable for small parts, fasteners, washers, pins, etc. Continuous plating is suitable for batch production of wire and strip. Brush plating is suitable for local plating or repair. Electroplating solutions include acidic, alkaline, and acidic and neutral solutions with chromium agents. Regardless of the plating method used, plating tanks, hangers, etc. in contact with the products to be plated and plating solution should have a certain degree of universality.
Coating classification
According to the composition of the coating, it can be divided into three categories: single metal coating, alloy coating, and composite coating.
If classified by purpose, it can be divided into:
① Protective coating;
② Protective decorative coating;
③ Decorative coating;
④ Repair coating;
⑤ Functional coating
Single metal electroplating
Single metal electroplating has a history of over 170 years, and there are 33 types of metals on the periodic table that can be electrodeposited from aqueous solutions. More than 10 commonly used types include zinc plating, nickel, chromium, copper, tin, iron, cobalt, cadmium, lead, gold, silver, etc. The coating formed by simultaneously depositing two or more elements on the cathode is an alloy coating. The alloy coating has a structure and properties that are not present in a single metal coating, such as amorphous Ni-P alloy, various Sn alloys that are not present in the phase diagram, as well as alloy coatings with special decorative appearances, high corrosion resistance, excellent weldability, and magnetic properties.
Composite plating
Composite plating is the process of adding solid particles to a plating solution and co depositing them with metals or alloys to form a metal based surface composite material, in order to meet special application requirements. According to the electrochemical properties between the coating and the substrate metal, the plating layer can be divided into two categories: anodic plating and cathodic plating. When the potential of the coating metal relative to the substrate metal is negative, the plating layer is the anode when forming a corrosive microcell, so it is called anodic plating, such as the galvanized layer on steel parts. When the potential of the coating metal relative to the substrate metal is positive, the plating layer is the cathode when forming a corrosive microcell, so it is called cathodic plating, such as the nickel and tin plating layers on steel parts.
Classified by purpose:
① Protective coatings: coatings such as Zn, Ni, Cd, Sn, and Cd Sn, used as corrosion-resistant coatings for atmospheric and various corrosive environments;
② Protection. Decorative coatings: such as Cu Ni Cr, Ni Fe Cr composite coatings, etc., which have both decorative and protective properties;
③ Decorative coatings: such as Au, Ag, and Cu. Sun imitation gold coatings, black chromium, black nickel coatings, etc;
④ Repair coating: such as electroplating Ni, Cr, and Fe layers to repair some expensive and easily worn parts or parts with poor processing quality;
⑤ Functional coatings: conductive coatings such as Ag and Au; magnetic coatings such as Ni Fe, Fe Co, Ni Co; high-temperature oxidation resistant coatings such as Cr and Pt Ru; reflective coatings such as Ag and Cr; anti reflective coatings such as black chromium and black nickel; wear-resistant coatings such as hard chromium and Ni. SiC; Ni. VIEE, Ni. C (graphite) anti wear coatings, etc.; welding coatings such as Pb, Cu, Sn, Ag; anti-seepage carbon plating Cu, etc.
Material requirements
The plating layer is mostly a single metal or alloy, such as titanium palladium, zinc, cadmium, gold or brass, bronze, etc.; there are also dispersed layers, such as nickel silicon carbide, nickel fluoride graphite, etc.; there are also composite layers, such as copper nickel chromium layer on steel, silver indium layer on steel, etc. The substrate materials for electroplating are not only iron-based cast iron, steel, and stainless steel, but also non-ferrous metals, or ABS plastic, polypropylene, polysulfone, and phenolic plastic. However, before plastic electroplating, special activation and sensitization treatment must be carried out.
