plating
1. The concept of electroplating is to plate one or more metal layers on the surface of the workpiece by electrodeposition to give the workpiece a beautiful appearance or specific functional requirements. During electroplating, the plated metal or other insoluble material is used as the anode, and the metal product to be plated is used as the cathode. The cations of the plated metal are reduced on the metal surface to form a plating layer. In order to eliminate the interference of other cations and make the coating uniform and firm, a solution containing the metal cations of the coating layer should be used as the plating solution to keep the concentration of the metal cations of the coating layer unchanged. The purpose of electroplating is to plate a metal coating on the substrate to change the surface properties or dimensions of the substrate. Electroplating can enhance the corrosion resistance of metals (corrosion-resistant metals are mostly used for plating metals), increase hardness, prevent wear, improve conductivity, lubricity, heat resistance, and beautiful surfaces.
2. Principle In the plating tank containing the plating solution, the cleaned and specially pretreated parts to be plated are used as the cathode, and the anode is made of plated metal, and the two poles are respectively connected to the negative electrode and the positive electrode of the direct current power supply. The plating solution is composed of an aqueous solution containing a metal to be plated, a conductive salt, a buffer, a pH adjuster, and an additive. After the current is applied, the metal ions in the plating 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 plating solution to maintain the concentration of metal ions being plated. In some cases, such as chromium plating, it is an insoluble anode made of lead and lead-antimony alloy, which only plays the role of transmitting electrons and conducting current. The chromium ion concentration in the electrolyte needs to be maintained by periodically adding chromium compounds to the plating solution. During electroplating, the quality of the anode material, the composition of the plating solution, the temperature, the current density, the energization time, the stirring intensity, the precipitated impurities, and the power waveform will all affect the quality of the plating layer, which needs to be controlled in a timely manner.
3, the purpose is to obtain a metal layer with certain characteristics, such as: hardness, brightness, corrosion resistance and the same shape in electroforming.
4.Conductive medium in which metal ions move between the anode and the cathode in the plating solution.
How to maintain the plating solution? Continuous chemical analysis, Hershey’s bath plating test, adding chemicals, removing contaminants, regular cleaning, routine inspection of defects / defectives, physical testing
5, PH value is used to measure the pH; pH range is between 0-14; less than 7 is acidic, greater than 7 and less than 14 is alkaline, 7.0 is neutral.
Two basic electrochemistry
1.Plating cell 2.Cathodic reaction Ion reduction reaction Absorbs electrons from external circuit Typical reaction: Ni ++ + 2e- → Ni (metal) 2H + + 2e- → H24H2O + 4e- → 2H2 + 4 (OH)-3, Anode The reaction metal oxidizes into cations and releases electrons to the external circuit. Typical reactions: Ni → Ni ++ + 2e-4OH- → O2 + 2H2O + 4e-2H2O → O2 + 4H + + 4e- 3. Cleaning 1. The purpose of cleaning is to ensure subsequent coating Get the high-quality perfect coating; the coating has various desired characteristics. 2. The influence of incorrect cleaning and the poor adhesion between the substrate (material) metal, peeling of the coating, missing plating, micro-roughness, Foaming, poor corrosion resistance, contamination of the plating solution3, pre-cleaning options, mechanical cleaning, dry blasting / peening solvent cleaning, degreasing, emulsification, solid-liquid separation. 4. How the cleaning agent works 1) Dispersion is a method in which solid particles are dispersed into small particles by the action of a surfactant and other components in the cleaning agent. This principle is effective for cleaning the residues left during polishing.
2) Saponification
Saponification is the conversion of fatty acids / fatty oils or other reactive soils into a water-soluble mixture (soap). Increasing the temperature, concentration and pH will promote the speed and completion of the reaction.
3) Emulsification
Emulsification is a chemical process in which surfactants penetrate oils and dirt and disperse them in solution into tiny, dispersible water-soluble beads and suspensions.
4) Type of cleaning
Solvent degreasing is suitable for the mixing of solvents and surfactants; it is used in steam degreasing; it should be used as little as possible due to health and environmental considerations. Alkaline washing main body: Sodium hydroxide (or potassium hydroxide) Silicate carbonate Concentrated phosphate additives: Chelate can eliminate the effects of hard water and metal ions. Surfactant: Displace and disperse dirt, reduce the surface of metal The surface tension of the cleaning agent allows the metal surface to be completely covered by the cleaning solution. The galvanic cathode releases hydrogen, which is twice the amount of oxygen released by the anode, activates the surface, and reduces some oxide films. The disadvantage is that metal ions can The anode in the form of loose dirt is deposited on the surface of the workpiece, and the anode releases oxygen. This form of cleaning can remove dirt, metal contaminants will not be deposited on the surface of the workpiece, produce oxide films, and passivate the surface. The device is used to generate sound waves, which are converted into mechanical energy in the solution. Ultrasonic waves can selectively compress and expand the liquid, causing it to have several simultaneous effects. Due to the cavitation caused by high frequencies, dirt is removed by physical methods. Spray cleaning Depending on the substrate, the solution often contains slightly alkaline, through a series of tubes and spray equipment, Pumps are usually used to transport cleaning agents. Physical shock and chemical reactions remove dust, metal dust, carbides, and other residues. Why should acid be soaked with acid? The oxide film on the metal surface is removed, so that the subsequent metal plating layer has a good bonding force; the alkaline film remaining on the surface is neutralized.
Three copper plating
1.The advantages of copper plating are bright, good filling, good ductility, no stress, fine coating crystal, easy to control, fast plating, easy polishing, good ductility, good micro-plating, good machining performance. Good electrical conductivity
2. Copper plating effect
Provide good adhesion and good adhesion after polishing / polishing; provide a good coating platform for post-process coating. 3. Filling level 1. The ability of uniform plating on the macroscopic scale to distribute the coating relatively uniformly over a wide range of current density
2.Microscopic ability to deposit coatings on grooves, small holes, cracks and other surface micro-defects.
Four nickel and chrome
1. Type of nickel solution: Pre-plated nickel, semi-bright nickel, high sulfur nickel, bright nickel, microporous nickel (nickel seal), positive nickel layer, nickel sulfamate, chemical nickel precipitation
Pre-nickel: Initial nickel layer for enhanced adhesion, activation for electroplating and replating on stainless steel, low pH, pH <1.0
Semi-bright nickel: anti-corrosion, high filling, good ductility, columnar structure, positive coating potential, low sulfur content <0.005%
High sulphur nickel: anti-corrosion protective layer for sacrificing, lateral corrosion instead of vertical nickel sulfamate electroforming, very good ductility, low stress chemical nickel: electroplating on aluminum, electroplating on plastics, corrosion resistance Uniform hardness and thickness distribution and wear resistance. Chrome plating: In decorative plating, chromium is used as the final coating due to darkening resistance. It has hardness, thickness between 0.1-0.5 u, and durability.
Five plating test
1.Type binding force, bendability, corrosion resistance, hardness, porosity, residual stress, surface roughness, thermal shock, optical characteristics, appearance, contact resistance, ductility, thermal resistance, purity, solderability, thickness, Abrasion resistance
2.Test methods: bending, sawing, filing, impact, peel strength, friction, chiseling, splitting, scraping
3, typical salt spray experiments, neutral salt spray experiments, acetate salt spray experiments, copper accelerated acetic acid experiments, CASS, and corrosion paste experiments
Salt spray box
Neutral salt spray test:
In a closed box, spray 5% sodium chloride strictly according to the required temperature and spray speed, and the pH should be controlled between 6.5-7.2.
Acetic acid salt spray test:
This test is similar to the neutral salt spray test (B-117) except that the pH is between 3.1 and 3.3. It is suitable for ferrous and non-ferrous metal coatings, as well as organic and inorganic coatings.
Copper accelerated salt spray test:
Evaluate the corrosion resistance of copper / nickel / chrome coatings on stainless steel, aluminum, plastic and zinc alloys in a closed box under controlled temperature, spray speed and pH. The solution contains sodium chloride, copper chloride and acetic acid with a pH of 3.1-3.3
4, ductility test
The ability of a material to be plastic without cracking
Bend test, expansion test, tension test, shaft test, micrometer test Bend test
ASTM – B-489 Bend Test for Measuring the Ductility of Electrodeposited and Autocatalytic Deposits on Metals ASTM B-490 Quantitative Micrometer Bend Test for Measuring the Ductility of Electrodeposits (CHRYSLER Ductility Test) To test for ductility, a piece of plated sample strip was bent back and forth 90 degrees at the jaws of the clamp until it broke. The number of bends indicates how good the ductility is. Micrometer test
Shaft test A portion of the nickel-plated workpiece was bent around the shaft and continuously wound to a smaller diameter until cracks were visible on the plating.
The dilatation test allows accurate ductility results. This test can also be used to test the tension and ductility of the coating peeled from the substrate.
Surface roughness refers to defects and imperfections in the shape of the surface. Roughness may come from substrate treatment or from electroplating. It can be measured by moving the stylus on the surface of the sample according to the amount of vertical movement recorded. Internal stress Internal (residual) stress is the distortion of the lattice of the plating layer, where the atoms are tighter than normal, and tensile stress is generated; when the atoms are looser than usual, compressive stress is generated. Internal stress can be tested with a steel bar or a spiral stress meter. Spiral Stress Tester
Thickness is an important factor for both corrosion and abrasion resistance. There are two destructive and non-destructive test methods for thickness.
Thickness test
Peeling and reweighing, Coulomb method, eddy current test, magnetic test, micrometer test, micro test, X-ray test.