1. Surface treatment is a process of artificially forming a surface layer on the surface of the base material that has different mechanical, physical and chemical properties from the base material;
2. The purpose of surface treatment is to meet the corrosion resistance, wear resistance, decoration or other special functional requirements of the product;
3. For metal castings, our more commonly used surface treatment methods are: mechanical grinding, chemical treatment, surface heat treatment, spray surface treatment, which specifically include cleaning, sweeping, deburring, degreasing, and descaling the workpiece surface.
1.One is surface treatment in a broad sense, which includes many physical and chemical methods such as pre-treatment, electroplating, painting, chemical oxidation, thermal spraying, etc.
2. The other is surface treatment in a narrow sense, which only includes sandblasting, polishing, etc., which is what we often call pre-treatment.
1.During the processing, transportation, and storage of workpieces, the surface is often covered with oxide scale, rust, residual molding sand, welding slag, dust, oil and other dirt.
2. In order for the coating to adhere firmly to the surface of the workpiece, the surface of the workpiece must be cleaned before painting. Otherwise, it will not only affect the bonding strength and corrosion resistance of the coating and metal, but also cause the base metal to continue to corrode even with coating protection, causing the coating to peel off and affecting the mechanical properties and service life of the workpiece.
3. Therefore, surface treatment of the workpiece before painting is an important guarantee and measure to obtain a high-quality protective layer and extend the service life of the product.
1. Surface treatment before painting
In order to remove various foreign matter (such as oil, rust, dust, old paint film, etc.) attached to the surface of the object, provide a good base suitable for the coating requirements, and ensure that the coating has good anti-corrosion properties, decorative properties and certain special functions , the surface of the object must be pretreated before painting.
2. Chemical treatment
It mainly uses acidic or alkaline solutions to chemically react with oxides and oil stains on the surface of the workpiece, making them dissolve in the acidic or alkaline solution to remove rust, oxide scale and oil stains on the surface of the workpiece, and then use a brush roller made of nylon or 304# stainless steel wire (a wire brush roller made of acid and alkali solution resistant) to clean it to achieve the purpose.
Chemical treatment is suitable for cleaning thin plates, but its disadvantages are: if the time is not properly controlled, even if corrosion inhibitors are added, the steel can still be over-corroded . For more complex structural parts and parts with holes, after pickling with acidic solution, the residual acid that has penetrated into the gaps or holes is difficult to completely remove. If not handled properly, it will become a hidden danger of future corrosion of the workpiece. In addition, chemicals are volatile and costly, and the chemical discharge work after treatment is difficult. If not handled properly, it will cause serious pollution to the environment.
3. Mechanical treatment
It mainly includes sand blasting, wire brush roller polishing, shot blasting and shot peening.
1. Electrochemical method
This method uses electrode reaction to form a coating on the surface of the workpiece. The main methods are:
(1) Electroplating
The process of forming a coating on the surface of a workpiece in an electrolyte solution with the workpiece as the cathode under the action of an external current is called electroplating.
(2) Oxidation
In an electrolyte solution, the workpiece acts as the anode. Under the action of an external current, the process of forming an oxide film on its surface is called anodic oxidation, such as the anodic oxidation of aluminum alloy.
2. Chemical Methods
This method uses the interaction of chemical substances to form a coating on the surface of the workpiece without the action of electric current. The main methods are:
(1) Chemical conversion film treatment
The process of forming a coating on a metal workpiece's surface by the interaction of chemical substances in an electrolyte solution with the workpiece in the absence of an external current is called chemical conversion coating treatment. Examples include bluing, phosphating, passivation, and chromium salt treatment of metal surfaces.
(2) Chemical plating
In an electrolyte solution, the workpiece surface is catalytically treated without the action of external current. Due to the reduction effect of chemical substances in the solution, certain substances are deposited on the workpiece surface to form a coating. This process is called chemical plating, such as chemical nickel plating, chemical copper plating, etc.
3. Thermal processing method
This method is to melt or diffuse the material under high temperature conditions to form a coating on the surface of the workpiece. Its main methods are:
(1) Hot dip galvanizing
The process of placing a metal workpiece into molten metal to form a coating on its surface is called hot-dip coating, such as hot-dip galvanizing and hot-dip aluminum.
(2) Thermal spraying
The process of atomizing molten metal and spraying it onto the surface of a workpiece to form a coating is called thermal spraying, such as thermal spraying zinc, thermal spraying aluminum, etc.
(3) Hot stamping
metal foil to form a coating layer on the surface of a workpiece is called hot stamping, such as hot stamping aluminum foil.
(4) Chemical heat treatment
The process of bringing a workpiece into contact with chemical substances, heating it, and allowing certain elements to enter the workpiece surface at high temperatures is called chemical heat treatment, such as nitriding and carburizing.
