Electrolytic processing
A method of shaping metal by an electrochemical reaction where the anode is dissolved.
When the cathode tool is continuously moved towards the workpiece, the highest current density is achieved and the workpiece anode dissolves the quickest at the point where the gap is the smallest. This is because the gap between the two surfaces is not uniform.
As a result, the metal material is continuously dissolved in the shape of the cathode profile of the tool. At the same time, the electrolysis product is flushed away by the electrolyte until the surface of the workpiece forms a shape that is roughly the opposite of the cathode profile of the tool. This is when the desired surface of the part is machined.
Electrolytic processing utilizes a low-voltage DC power supply, ranging from 6 to 24 volts, and a high operating current.
To ensure a continuous and smooth flow of electrolyte to the electrolysis zone with an appropriate flow rate and temperature, the processing is usually performed in a sealed device.
Conductive grinding
Also referred to as Electrolytic Grinding.
It combines the process of electrolysis with mechanical grinding.
In conductive grinding, the workpiece is connected to the anode of the DC power supply, while the conductive grinding wheel is connected to the cathode. Both maintain a certain level of contact pressure and an electrolyte is introduced into the processing zone.
When the power is turned on, the metal surface of the workpiece undergoes anodic dissolution and a thin oxide film is formed. This film has a much lower hardness compared to the workpiece, making it easily removed by the high-speed rotating grinding wheel.
A new oxide film is then formed and polished by the grinding wheel, repeating the process until the desired results are achieved.
Electrochemical polishing
Also referred to as Electrolytic Polishing.
This process involves directly improving the surface finish of mechanically processed parts through anodic dissolution in an electrochemical reaction.
Electropolishing is more efficient than mechanical polishing, offers higher precision, and is not influenced by the hardness or toughness of the material. It has gradually become the preferred method over mechanical polishing.
The basic principle of electropolishing is similar to that of electrolytic machining, but in electropolishing the cathode is fixed, the distance between the poles is larger (1.5 to 200 mm), and a smaller amount of metal is removed.
When electropolishing, it is important to control the current density. If the current density is too low, the metal surface will be corroded and production efficiency will suffer. On the other hand, if the current density is too high, a discharge of hydroxide ions or oxygen-containing anions can occur, leading to the precipitation of gaseous oxygen and reducing current efficiency.
Electroplating
Electrolysis is used to deposit metal onto the surface of conductors (such as metal) or non-conductors (such as plastic, ceramic, fiberglass, etc.) to improve wear resistance, increase electrical conductivity, provide corrosion protection, and serve decorative purposes.
For non-conductive materials, proper treatment (such as using graphite, conductive paint, electroless plating, or vapor phase coating) is necessary to form a conductive layer before electroplating can be performed.
During electroplating, the item being plated is connected to the cathode, and the metal to be deposited is attached to the anode. The electrolyte is a solution containing ions of the metal to be plated.
Upon energization, the anode gradually dissolves into metal cations, and an equal number of metal ions in the solution receive electrons from the cathode and precipitate onto the surface of the item being plated, forming a metal plating layer.
For instance, nickel plating is performed on a copper plate using an aqueous solution containing nickel sulfate as the plating solution. Upon energization, the nickel on the anode dissolves into positive ions, and nickel is continuously deposited onto the surface of the copper plate (the cathode).
Electroetching
Also referred to as Electrolytic Etching.
This process uses the principle of electrochemical anodic dissolution to etch a desired pattern or text onto a metal surface.
The basic processing principle is similar to that of electrolytic machining.
Since only a small amount of metal is removed during electroetching, there is no need to use a high-speed flowing electrolyte to wash away the dissolved product from the workpiece.
During the process, the cathode is fixed.
Electroetching has the following four processing methods.
① To engrave a pattern or text, the punch is processed as a cathode with a metal material and the metal workpiece to be engraved is used as an anode. The two are placed together in an electrolyte. When the power is turned on, the surface of the workpiece will dissolve into the same pattern or text as the punch.
② A conductive paper (or metal foil) is cut or engraved with the desired pattern or text, then pasted on an insulating sheet. The unconnected lines in the pattern are connected to wires on the back of the insulating sheet to serve as the cathode. This method is suitable for workpieces with simple graphics and low precision requirements.
③ For complex workpieces, the technology used for making printed circuit boards can be utilized. This involves creating a positive pattern of the desired engraving on one side of a double-sided copper clad plate, with each isolated line in the pattern connected to the other side of the copper clad plate as the cathode. This method is not suitable for processing fine and disconnected graphics.
④ A layer of photoresist is applied to the surface of the metal to be engraved, and a negative photographic film is made on the photosensitive adhesive or a photolithography technique is used to expose the portion to be engraved. In this case, the workpiece still serves as the anode, while the cathode can be made of a metal plate.
Electrolytic smelting
Refining and purifying colored and rare metals using the principle of electrolysis.
It is divided into two types: Aqueous Electrolytic Smelting and Baked Salt Electrolytic Smelting.
Aqueous Electrolytic Smelting is widely used in the metallurgical industry to extract and refine metals such as copper, zinc, lead, and nickel. For example, the electrolytic purification of copper: Crude copper (99% copper) is first made into a thick plate as the anode, pure copper is used as a thin plate as the cathode, and a mixed solution of sulfuric acid (H2SO4) and copper sulfate (CuSO4) serves as the electrolyte.
When electrified, copper dissolves from the anode into copper ions (Cu2+) and moves towards the cathode. At the cathode, the ions receive electrons and pure copper (also known as electrolytic copper) is precipitated. Impurities in blister copper, such as iron and zinc, which are more active than copper, dissolve into ions (Zn2+ and Fe2+) along with copper. These ions are less likely to precipitate than copper ions, and can be prevented from depositing on the anode by adjusting the potential difference during electrolysis appropriately. Impurities such as gold and silver, which are less active than copper, are deposited at the bottom of the electrolytic cell.
Baked Salt Electrolytic Smelting is used to extract and refine active metals (such as sodium, magnesium, calcium, aluminum, etc.). For example, the industrial extraction of aluminum: purified ore containing alumina (Al2O3) is placed into molten cryolite (Na3AlF6) to create a molten electrolytic body, and a carbon rod serves as the electrode. The electrochemical reaction at the two poles is:
4Al3++6O2-+3C─→4Al+3CO
