Chemical surface treatment


product name
Blue and black, phosphating, pickling, anodizing, electrochemical polishing, electroplating, electrophoresis, TD treatment, QPQ treatment, chemical oxidation, chemical surface treatment
Chemical treatment of hardware parts: It mainly uses acid-base or alkaline solutions to react with oxides and oil stains on the surface of hardware parts to dissolve them in acidic or alkaline solutions to remove rust and scale on the surface Oil stains can be cleaned up with a brush roller made of nylon or 304# stainless steel wire (a steel wire brush roller made of acid and alkali solution).

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The process of heating steel or steel parts in air-water vapor or chemical drugs to an appropriate temperature to form a blue or black oxide film on the surface. Also called black and blue. The oxide film formed on the surface of ferrous metal after "bluing" treatment, the outer layer is mainly ferroferric oxide, and the inner layer is ferrous oxide.
In order to improve the anti-rust ability of steel parts, the surface of steel parts is oxidized into dense and smooth Fe3O4 (Fe3O4) with a strong oxidizer. This Fe3O4 thin layer can effectively protect the inside of the steel from oxidation. Fe3O4 oxidized at high temperature (about 550°C) is sky blue, which is called bluing treatment. Fe3O4 oxidized at low temperature (about 130°C) is dark, and it is called blackening treatment. In the weapon industry, blue treatment is commonly used; in industrial production, black treatment is commonly used.

Phosphating (phosphorization) is a process in which metal iron, zinc, aluminum and their alloys undergo a chemical reaction in an acidic phosphate solution to form a non-metal or non-conductor conversion film. . The main purpose of phosphating is: to provide protection to the base metal and prevent the metal from being corroded to a certain extent; it is used for primer before painting to improve the adhesion and anti-corrosion ability of the paint film layer;
(1) Impregnation and phosphating
  Suitable for high, medium and low temperature phosphating. Features: The equipment is simple, only a heating tank and corresponding heating equipment are needed. It is best to use stainless steel or rubber lined tanks. Stainless steel heating pipes should be placed on both sides of the tank.
(2) Spray phosphating
  It is suitable for medium and low temperature phosphating process, and can process large-area workpieces, such as automobile, refrigerator, washing machine shells. Features: Short processing time, fast film-forming reaction speed, high production efficiency, and the phosphating film obtained by this method has dense, uniform crystals, thin film, and good corrosion resistance.
(3) Brush coating and phosphating
  When the above two methods cannot be implemented, this method is used to operate at room temperature, easy to paint, and can remove rust. After phosphating, the workpiece is naturally dried and has good rust resistance, but the phosphating effect is not as good as the first two.
Phosphating treatment

Electroplating processing
Electroplating is a process in which a thin layer of other metals or alloys are plated on the surface of certain metals using the principle of electrolysis. It is a process in which a metal film is attached to the surface of a metal or other material by electrolysis.
Function: Prevent metal oxidation (such as rust), improve wear resistance, electrical conductivity, reflectivity, corrosion resistance (copper sulfate, etc.) and enhance aesthetics.
1. Copper plating: used for primer to improve the adhesion and corrosion resistance of the electroplated layer. (Copper is easy to oxidize. After oxidation, the patina no longer conducts electricity, so copper-plated products must be protected by copper)
2. Nickel plating: used for primer or appearance to improve corrosion resistance and wear resistance (among which, chemical nickel is more wear-resistant than chrome plating in modern technology). (Note that many electronic products, such as DIN head and N head, no longer use nickel as a primer, mainly because nickel is magnetic, which will affect the passive intermodulation in the electrical performance)
3. Gold plating: improve conductive contact impedance and enhance signal transmission. (Gold is the most stable and the most expensive.)
4. Palladium nickel plating: Improve conductive contact resistance, enhance signal transmission, and have higher wear resistance than gold.
5. Tin-lead plating: to improve soldering ability, soon to be replaced by other substitutes (because of lead, most of them are now plated with bright tin and matte tin).
6. Silver plating: improve conductive contact impedance and enhance signal transmission. (Silver has the best performance, easy to oxidize, and also conducts electricity after oxidation)

The method of using acid solution to remove oxide scale and rust on the surface of steel is called pickling. It is a way to clean metal surfaces. It is usually carried out together with pre-passivating treatment.
Generally, the parts are immersed in an aqueous solution such as sulfuric acid to remove oxides and other thin films on the metal surface. It is the pre-treatment or intermediate treatment process of electroplating, enamel, rolling and other processes.
Method Applicable scope Advantages and disadvantages
Dipping method is used for parts that can be put into pickling tank or passivation tank, but not suitable for large equipment
  Pickling liquid can be used for a long time, with high production efficiency and low cost;
Large-volume equipment is filled with acid and immersion consumes too much liquid
Brushing method Suitable for internal and external surface and local treatment of large equipment Manual operation, poor working conditions, acid can not be recovered
Paste method is used for installation or maintenance site, especially for welding part treatment. Manual operation,
Poor working conditions and high production cost. Spraying method is used at the installation site, and the inner wall of the large container has low liquid consumption, low cost and high speed.
But need to be equipped with spray gun and skewer ring
System circulation method is used for large-scale equipment, such as heat exchanger, tube and shell treatment. Easy construction, acid liquid can be reused, but pipes and pumps are required to connect
The electrochemical method of the circulatory system can not only be used for parts, but also can be used for the surface treatment of field equipment by the electric brush method. The technology is more complicated and requires a DC power supply or a potentiostat.
Anodic oxidation
Anodic oxidation, the electrochemical oxidation of metals or alloys. Aluminum and its alloys form a layer of oxide film on aluminum products (anode) under the action of applied current under corresponding electrolyte and specific process conditions. This oxide film has protective, decorative and other functional properties. If anodizing is not specified, it usually refers to sulfuric acid anodizing.
Anodizing process:
Mechanical polishing-degreasing-washing-chemical polishing-washing-anodic oxidation-washing-sealing-mechanical bright
Types of anodizing Anodizing has long been widely used in industry. There are many ways to assign different names, and can be summarized into the following classification methods:
According to the current type, there are: direct current anodizing, alternating current anodizing, and pulse current anodizing that can shorten the production time to the required thickness, the film is thick, uniform and dense, and the corrosion resistance is significantly improved.
According to electrolyte, it is divided into sulfuric acid, oxalic acid, chromic acid, mixed acid and natural color anodizing with organic sulfonic acid solution.
According to the nature of the film, it is divided into: ordinary film, hard film (thick film), porcelain film, bright modification layer, semi-conductor barrier layer and other anodic oxidation.

Electrochemical polishing
Electrochemical polishing is also called electrolytic polishing. Electrolytic polishing uses the polished workpiece as the anode and the insoluble metal as the cathode. The two poles are simultaneously immersed in the electrolytic cell, and direct current is applied to produce selective anode dissolution, thereby achieving the effect of increasing the surface brightness of the workpiece.
Electrolytic polishing is mainly aimed at the surface brightening treatment of stainless steel workpieces. Stainless steel workpieces are divided into 200 series, 300 series, and 400 series materials. For each series of materials, targeted electrolytic polishing liquid must be used. For example, the 200 series of stainless steel must use the 200 series formula, which cannot be adapted to the 300 series or 400 series stainless steel materials. This has always been a major problem in China, because some manufacturers use composite parts, including 200 series stainless steel and 300 or 400 series stainless steel.

TD processing
TD coating treatment is a kind of metal carbide coating of several micrometers to tens of micrometers formed on the surface of the workpiece through high temperature diffusion.
TD mold surface super-hardening treatment technology, using the principle of TD (Thermal Diffusion Carbide Coating Process), is to place the workpiece in borax molten salt and its special medium at a certain processing temperature, and pass it in the special molten salt. The metal atoms in the workpiece chemically react with the carbon and nitrogen atoms in the workpiece, and diffuse on the surface of the workpiece to form a metal carbide layer of vanadium, niobium, chromium, titanium, etc., ranging from a few microns to more than twenty microns. High workpiece wear resistance, seizure resistance, corrosion resistance and other properties
TD processing

Electrophoresis electrophoresis processing
Electrophoresis is that the electrophoretic paint is applied to the anode and cathode, and the charged paint ions move to the cathode under the action of voltage, and interact with the alkaline substance generated on the cathode surface to form insoluble matter and deposit on the surface of the workpiece. Electrophoresis is generally used for spray painting, that is, a layer of paint on the surface, which is often used in the automotive industry.
Electrophoresis paint film
Electrophoretic paint film has the advantages of fullness, uniformity, flatness and smooth coating. The hardness, adhesion, corrosion resistance, impact performance and permeability of electrophoretic paint film are significantly better than other coating processes.
(Decomposition) At the beginning of the cathode reaction is an electrolysis reaction, generating hydrogen and hydroxide ion OH. This reaction causes a high alkaline boundary layer to form on the cathode surface. When the cations and hydroxide radicals react to become water-insoluble substances, the coating film is deposited , The equation is: H2O→OH+H.
Migration, migration) Cationic resin and H+ move to the cathode under the action of an electric field, while the anion moves to the anode.
(Precipitation) On the surface of the coated workpiece, the cationic resin reacts with the surface of the cathode to neutralize and precipitate non-sediment, which is deposited on the coated workpiece.

QPQ processing
QPQ treatment refers to putting ferrous metal parts in two salt baths with different properties, and forming a composite permeated layer through multiple elements infiltrating the metal surface, so as to achieve the purpose of modifying the surface of the parts.
It has not been quenched, but has achieved the effect of surface quenching, so it is called QPQ at home and abroad. The newest improved process is called optical nitridation. Compared with QPQ, this process has the advantages of no deformation at all, higher hardness, deeper depth, high efficiency, no polishing, high nitriding accuracy, non-standard and large parts. After QPQ treatment, the wear resistance of the product is more than 16 times higher than conventional quenching and high-frequency quenching, more than 9 times higher than 20# steel carburizing and quenching, and more than 2 times higher than hard chromium plating and ion nitriding.