Surface treatment is a process of artificially forming a surface layer with different mechanical, physical, and chemical properties from the substrate on the surface of the substrate material. The purpose of surface treatment is to meet the requirements of corrosion resistance, wear resistance, decoration, or other special functions of products. Here is everything you should know about a detailed explanation of the surface treatment process of hardware die castings.

 

For metal castings, our common surface treatment methods are mechanical grinding, chemical treatment, surface heat treatment, and spraying surface. Surface treatment is to clean, clean, deburr, degrease and scale the workpiece surface.

 

In the process of processing, transportation and storage, the surface of workpieces often contains oxide scale, rust, molding sand, welding slag, dust, oil and other dirt left in mold making. To ensure that the deep layer can be firmly attached to the workpiece surface, the workpiece surface must be cleaned before coating. Otherwise, it will not only affect the adhesion and corrosion resistance between the coating and the metal, but also make the base metal continue to corrode even with the protection of the coating, make the coating peel off, and affect the mechanical properties and service life of the workpiece. Therefore, the surface treatment of the workpiece before painting is an important guarantee and measure to obtain a high-quality protective layer and prolong the service life of the product.

 

In order to provide a good workpiece surface, the following points need to be paid attention to in surface treatment:No oil stain and moisture

-No rust and oxide

-No adhesive impurities

-No acid, alkali and other residues

-The workpiece surface has a certain roughness

 

Surface treatment method:

Manual processing:

Such as scraper, wire brush or grinding wheel. The rust and oxide scale on the surface of the workpiece can be removed by hand, but the manual treatment has high labor intensity, low production efficiency, poor quality and incomplete cleaning.

 

Chemical treatment:

It mainly uses the acid-base or alkaline solution to react with the oxide and oil on the surface of the workpiece to dissolve it in the acid or alkaline solution, so as to remove the rust, oxide scale and oil on the surface of the workpiece, and then clean the brush roller made of nylon or 304# stainless steel wire (steel wire brush roller made of acid-base resistant solution).

 

Mechanical treatment:

It mainly includes wire brush roller polishing method, shot blasting method and shot blasting method. Polishing method is that driven by the motor, the brush roller rotates at high speed on the upper and lower surfaces of the strip in the opposite direction to the movement of the rolled piece to brush off the iron oxide scale. The brushed iron oxide scale shall be washed off by a closed circulating cooling water flushing system. Shot blasting cleaning is a method of using centrifugal force to accelerate the shot and shoot it to the workpiece for rust removal and cleaning.

 

Shot blasting is divided into shot blasting and sand blasting:

Surface treatment by shot peening has great striking force and obvious cleaning effect. However, the treatment of thin plate workpiece by shot peening is easy to deform the workpiece, and the steel shot strikes the workpiece surface (whether shot blasting or shot peening) to deform the metal substrate. Because Fe304 and Fe203 are not plastic, they are stripped after crushing, and the oil film is deformed together with its material, shot blasting and shot peening cannot completely remove the oil stain on the workpiece with oil stain.

 

According to the different methods used, the surface treatment technology can be divided into the following categories.

Electrochemical method

This method uses electrode reaction to form a coating on the surface of the workpiece. The main methods are:

 

Electro plating

In the electrolyte solution, the workpiece is the cathode, and the process of forming a coating on its surface under the action of external current is called electroplating. The coating can be metal, alloy, semiconductor or contain various solid particles, such as copper plating, nickel plating, etc.

 

Oxidation

In the electrolyte solution, the workpiece is an anode, and the process of forming an oxide film on its surface under the action of external current is called anodic oxidation, such as the anodic oxidation of aluminum alloy. The oxidation treatment of steel can be carried out by chemical or electrochemical methods. The chemical method is to put the workpiece into the oxidation solution and form an oxide film on the surface of the workpiece by chemical action, such as the bluing treatment of steel.

 

Chemical method

This method is to form a plating layer on the surface of the workpiece by using the interaction of chemical substances without the action of current. The main methods are:

 

Chemical conversion membrane treatment

In the electrolyte solution, the process of forming a coating on the surface of the metal workpiece without the action of external current and the interaction between the chemical substances in the solution and the workpiece is called chemical conversion film treatment. Such as bluing, phosphating, passivation and chromate treatment of metal surface.

 

Electroless plating

In the electrolyte solution, the workpiece surface is catalytically treated without external current. In the solution, due to the reduction of chemical substances, some substances are deposited on the workpiece surface to form a coating, which is called electroless plating, such as electroless nickel plating, electroless copper plating, etc.

 

Hot working method

This method is to order material melting or thermal diffusion under high temperature conditions to form a coating on the surface of the workpiece. The main methods are:

 

Hot dip coating

The process of putting a metal workpiece into molten metal to form a coating on its surface is called hot-dip galvanizing, such as hot-dip galvanizing, hot-dip aluminizing, etc.

 

Thermal spraying

The process of atomizing molten metal and spraying it on the workpiece surface to form a coating is called thermal spraying, such as thermal spraying zinc, thermal spraying aluminum, etc.

 

Hot stamping

The process of heating and pressurizing the metal foil to cover the surface of the workpiece to form a coating layer is called hot stamping, such as hot stamping aluminum foil.

 

Chemical heat treatment

The process of contacting and heating the workpiece with chemical substances and ordering certain elements to enter the workpiece surface at high temperature is called chemical heat treatment, such as nitriding, carburizing, etc.

 

Surfacing

The process of forming a welding layer by accumulating deposited metal on the surface of the workpiece by welding is called surfacing, such as surfacing wear-resistant alloy, etc.

 

Vacuum method

This method is the process of ordering the material to be gasified or ionized and deposited on the surface of the workpiece in a high vacuum state to form a coating. The main method is.

 

Physical vapor deposition (PVD)

Under vacuum conditions, the process of vaporizing metal into atoms or molecules, or making its ions into ions, which are deposited directly on the surface of the workpiece to form a coating is called physical vapor deposition. The deposited particle beam comes from non chemical factors, such as evaporation plating, sputtering plating, ion plating, etc.

 

Ion implantation

The process of surface modification by implanting different ions into the workpiece surface under high voltage is called ion implantation, such as boron implantation.

 

Chemical vapor deposition (CVD)

Under low pressure (sometimes also under atmospheric pressure), the process of gaseous substances forming solid deposition layer on the workpiece surface due to chemical reaction is called chemical vapor deposition, such as vapor deposition of silicon oxide, silicon nitride, etc.

 

Other methods

Mainly mechanical, chemical, electrochemical and physical methods. The main method is.

 

Painting

The process of coating by spraying or brushing the coating (organic or inorganic) on the surface of the workpiece is called coating, such as painting, brushing, etc.

 

Impact plating

The process of forming coating layer on the surface of workpiece by mechanical impact is called impact plating, such as impact galvanizing, etc.

 

Laser surface treatment

The process of irradiating the workpiece surface with laser to change its structure is called laser surface treatment, such as laser quenching, laser remelting, etc.

 

Ultra dural technique

The technology of preparing super hard film on the surface of workpiece by physical or chemical methods is called super hard film technology. Such as diamond film, cubic boron nitride film, etc.

 

Electrophoresis and electrostatic sprayingIn electrophoresis, the workpiece is put into a conductive water-soluble or water emulsified coating as an electrode to form a solution circuit with the other electrode in the coating. Under the action of electric field, the coating solution has been dissociated into charged resin ions, the cations move to the cathode and the anions move to the anode. These charged resin ions, together with the adsorbed pigment particles, are electrophoresed to the surface of the workpiece to form a coating. This process is called electrophoresis.

 

Electrostatic spraying, under the action of DC high-voltage electric field, the atomized negatively charged paint particles are directed to the positively charged workpiece to obtain the paint film, which is called static spraying. Edit other classifications in this paragraph.

 

The common application of wire brush is the cleaning of castings, including ferrous and non-ferrous; Cleaning of spatter and welding slag during welding; As long as the base material is strong enough to withstand brushing, dust, corrosion and paint can be removed. The wire brush can produce a beautiful surface and can also be used to make decorative surfaces.

 

The division of all the above categories is not absolute. For example, surface treatment technology can also be divided into three technologies: surface modification technology, film technology and coating technology. The significance of surface treatment: it can effectively improve the hardness and wear resistance of workpiece surface.