First, electrolytic polishing
Electropolishing is a relatively new process for metal surface finishing. It is applied to pre-plating and post-plating finishing of metal parts, and can also be applied to metal surface processing alone. For example, electropolishing is often used for decorative parts and surface finishing of complex metal parts, special tools and instruments, and various coatings. Under certain conditions, electropolishing can also be used to replace heavy mechanical polishing. Electropolishing has the advantages of high production efficiency and convenient operation. The disadvantages are high cost, short service life and difficulty in regeneration.
The mechanism of electropolishing is complicated. Among them, the mucosa theory believes that an adhesive film having a high electrical resistivity is formed on the surface of the anode during electropolishing. The thickness of the mucosa at the microscopic protrusion is smaller than the thickness of the concave portion, the current density is higher, and the dissolution is faster; while the current density at the concave portion is lower, the dissolution speed is slower, so that the position of the convex and concave is constant after a period of time. The conversion gradually reached the goal of leveling and brightening.
The electropolishing liquids currently used in production mainly include:
a polishing solution consisting of sulfuric acid, phosphoric acid and chromic anhydride;
a polishing solution consisting of sulfuric acid and citric acid;
A mixed polishing solution consisting of sulfuric acid, phosphoric acid, hydrofluoric acid, and glycerin or the like.
Electrochemical polishing of steel parts
(1) Influence of material types There are many types of steel materials, and different polishing liquids should be used for different steel materials.
(2) Effects of various factors Phosphoric acid is the main component of the polishing liquid. The phosphate formed by it adheres to the surface of the anode and plays an important role in the polishing process. Sulfuric acid can increase the polishing rate, but the content should not be too high to avoid corrosion. Chromic anhydride can improve the polishing effect and make the surface bright.
The current density has a great influence on the polishing quality. Different current densities should be used for different solutions. The current density is too low, and the leveling effect is poor. If it is too high, it will cause over-corrosion. Temperature has a certain effect on the quality of the polishing, but it is not the main factor.
(3) Operational precautions
1 The newly prepared solution should be energized in the case of a large cathode area (the cathode area is several times larger than the anode area) to reduce a part of the hexavalent chromium to trivalent chromium. If the trivalent chromium is excessively increased during use, the opposite is true, that is, in the case of a large anode and a small cathode.
2 Frequently measure the density of the solution, and add water or heat the concentrated solution in time. The contents of phosphoric acid, sulfuric acid and chromic anhydride and trivalent chromium in the solution should be analyzed and adjusted periodically.
3 During the use, the content of dissolved iron in the anode gradually increases, and when the content of iron (calculated as Fe2 03) reaches 7% to 8%, it is partially replaced, or the solution is completely replaced.
4 Preparation First, the phosphoric acid and sulfuric acid are mixed, the chromic anhydride is dissolved in water, and then the acid mixture is poured into a chromic anhydride aqueous solution and heated to 80 ° C. The gelatin is slowly added under constant stirring (the reaction is intense). After (after about 1 h) the solution became a uniform grass green.
Electropolishing of other metals
Electrolytic polishing of copper and its alloys, the use of phosphoric acid electrolytes is widely used. Electrolytic polishing of aluminum and aluminum alloys is carried out using a solution of phosphoric acid monosulfate-chromic acid.
Electropolishing of aluminum and aluminum alloys is widely used in production. If the polished parts are subjected to a short-time oxidation treatment, not only can a flat and bright appearance be obtained, but also a complete oxide film can be formed, corrosion resistance can be improved, and the surface gloss can be maintained for a long period of time.
For the preparation method of the solution, reference can be made to the relevant content of electropolishing of steel parts.
When the aluminum content in the solution exceeds 5%, the solution should be partially replaced or completely replaced.
When the chloride ion content exceeds 1%, the surface of the part is prone to speckle corrosion. The chloride ion content in the water used to prepare the solution should be less than 80 mg/L.
Second, chemical polishing
Chemical polishing is the process of etching and leveling a part in a specific solution.
The chemical polishing equipment is simple and can handle parts with more complex shapes. Disadvantages The quality of chemical polishing is not as good as electrolytic polishing. The adjustment and regeneration of the solution is also difficult and limited in application. In particular, during the chemical polishing operation, nitric acid emits a large amount of yellow-brown harmful gas, which is very serious to the environment.
Electropolishing is a relatively new process for metal surface finishing. It is applied to pre-plating and post-plating finishing of metal parts, and can also be applied to metal surface processing alone. For example, electropolishing is often used for decorative parts and surface finishing of complex metal parts, special tools and instruments, and various coatings. Under certain conditions, electropolishing can also be used to replace heavy mechanical polishing. Electropolishing has the advantages of high production efficiency and convenient operation. The disadvantages are high cost, short service life and difficulty in regeneration.
The mechanism of electropolishing is complicated. Among them, the mucosa theory believes that an adhesive film having a high electrical resistivity is formed on the surface of the anode during electropolishing. The thickness of the mucosa at the microscopic protrusion is smaller than the thickness of the concave portion, the current density is higher, and the dissolution is faster; while the current density at the concave portion is lower, the dissolution speed is slower, so that the position of the convex and concave is constant after a period of time. The conversion gradually reached the goal of leveling and brightening.
The electropolishing liquids currently used in production mainly include:
a polishing solution consisting of sulfuric acid, phosphoric acid and chromic anhydride;
a polishing solution consisting of sulfuric acid and citric acid;
A mixed polishing solution consisting of sulfuric acid, phosphoric acid, hydrofluoric acid, and glycerin or the like.
Electrochemical polishing of steel parts
(1) Influence of material types There are many types of steel materials, and different polishing liquids should be used for different steel materials.
(2) Effects of various factors Phosphoric acid is the main component of the polishing liquid. The phosphate formed by it adheres to the surface of the anode and plays an important role in the polishing process. Sulfuric acid can increase the polishing rate, but the content should not be too high to avoid corrosion. Chromic anhydride can improve the polishing effect and make the surface bright.
The current density has a great influence on the polishing quality. Different current densities should be used for different solutions. The current density is too low, and the leveling effect is poor. If it is too high, it will cause over-corrosion. Temperature has a certain effect on the quality of the polishing, but it is not the main factor.
(3) Operational precautions
1 The newly prepared solution should be energized in the case of a large cathode area (the cathode area is several times larger than the anode area) to reduce a part of the hexavalent chromium to trivalent chromium. If the trivalent chromium is excessively increased during use, the opposite is true, that is, in the case of a large anode and a small cathode.
2 Frequently measure the density of the solution, and add water or heat the concentrated solution in time. The contents of phosphoric acid, sulfuric acid and chromic anhydride and trivalent chromium in the solution should be analyzed and adjusted periodically.
3 During the use, the content of dissolved iron in the anode gradually increases, and when the content of iron (calculated as Fe2 03) reaches 7% to 8%, it is partially replaced, or the solution is completely replaced.
4 Preparation First, the phosphoric acid and sulfuric acid are mixed, the chromic anhydride is dissolved in water, and then the acid mixture is poured into a chromic anhydride aqueous solution and heated to 80 ° C. The gelatin is slowly added under constant stirring (the reaction is intense). After (after about 1 h) the solution became a uniform grass green.
Electropolishing of other metals
Electrolytic polishing of copper and its alloys, the use of phosphoric acid electrolytes is widely used. Electrolytic polishing of aluminum and aluminum alloys is carried out using a solution of phosphoric acid monosulfate-chromic acid.
Electropolishing of aluminum and aluminum alloys is widely used in production. If the polished parts are subjected to a short-time oxidation treatment, not only can a flat and bright appearance be obtained, but also a complete oxide film can be formed, corrosion resistance can be improved, and the surface gloss can be maintained for a long period of time.
For the preparation method of the solution, reference can be made to the relevant content of electropolishing of steel parts.
When the aluminum content in the solution exceeds 5%, the solution should be partially replaced or completely replaced.
When the chloride ion content exceeds 1%, the surface of the part is prone to speckle corrosion. The chloride ion content in the water used to prepare the solution should be less than 80 mg/L.
Second, chemical polishing
Chemical polishing is the process of etching and leveling a part in a specific solution.
The chemical polishing equipment is simple and can handle parts with more complex shapes. Disadvantages The quality of chemical polishing is not as good as electrolytic polishing. The adjustment and regeneration of the solution is also difficult and limited in application. In particular, during the chemical polishing operation, nitric acid emits a large amount of yellow-brown harmful gas, which is very serious to the environment.
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