Introduction of liquid coating and solid coating self-coating process
Paint is inseparable from people's lives. It is because of his existence that he has a colorful world around him. The paint commonly referred to in people's mouths is only one type of paint. Today's paints are divided into solid and liquid. They are generally classified into solvent-based paints, water-based paints and powder coatings. The coating on the surface of the object has other functions such as protection (anti-corrosion, waterproof, oil-proof, chemical-resistant, light-resistant, temperature-resistant, etc.), decoration (color, gloss, pattern and flatness, etc.). With the development of science and technology, the construction process of coatings is also changing. After the author's collection and collection, the following will introduce you one by one.
First, liquid coating technology
1, brushing
Painted coatings are the most widely used, but the coating efficiency is low, the production scale reaches a certain level, and manufacturers with certain requirements for production efficiency cannot tolerate this original coating method. Although the cumulative use of small and medium-sized enterprises is large, but the market is scattered, the judgment of coating quality is subjective, and it is not the most intense field for foundry paint manufacturers. Moreover, the quality of the core coating is not good, the surface of the coating has brush marks, the coating waste is large, and the painting technique is required to be high.
2, spraying
Spraying is the most widely used coating technology in the mechatronics industry and the most polluting process in all coating processes. It is a method of atomizing a liquid coating into a mist and spraying it onto the surface of the object to form a coating. They are divided into air spray and airless spray depending on the principle of the tools used. Airless spraying, also known as high pressure airless spraying, uses a high pressure piston pump to cause the paint to form an atomizing airflow on the surface of the object (wall or wood surface). Airless spray is uniform and has no graininess compared to air spray. Air-spraying, also known as low-pressure air-spraying, relies on low-pressure air to cause the paint to form an atomizing airflow on the surface of the object (wall or wood surface) after it is ejected from the muzzle. Compared with the hand brush, the air spray has no brush marks, and the plane is relatively uniform, and the unit working time is short. It should also be noted that if the metal surface is sprayed, it is best to use metal paint (magnetic paint). During the spraying process, due to the action of compressed air, a large amount of "flying paint" will be generated, floating in the space of construction work; "flying paint" adheres to the roof and wall of the workplace, and settles to the ground to form "paint residue". The utilization rate of the coating process for the coating is about 50%.
3, dip coating
Dip coating is mainly suitable for small cores. Dipping paint is a coating method in which all of the immersion paint is immersed in a container containing the paint, taken out of the tank for a short period of time, and the excess coating liquid is returned to the tank. There is no "flying paint" problem in the dipping paint, but there is a problem of solvent evaporation and a small amount of paint on the ground. The dipping process has a high utilization rate of the coating, which is 70% to 80%. The thickness of the dip coating should not be guaranteed, and the thickness of the coating above and below the sand core is significantly different, which is not suitable for the mold. The coating concentration is strict. Dip coating a large number of applications in the fish car industry, the automotive industry is China's key industry to develop into a pillar industry, a series of industries represented by it, will enable the foundry industry to develop the future of dip coating.
4, flow coating
Flow coating is widely used in sand core and medium and small mold coatings. The flow coating is performed by using a pump to extrude paint from a nozzle at a pressure of 0.02 MPa to 0.2 MPa and coating the workpiece on the conveyor. Excessive paint, overflow dripping back to the storage tank for recycling. The flow coating has no brush marks, smooth surface, high surface quality, saves paint, and has little environmental pollution. It is suitable not only for sand core but also for casting. However, the flow coating has the problem of solvent volatilization, and the flow coating process has a utilization rate of up to 95%.
5, roll coating
For single or double-sided high speed continuous mechanical coating of sheet or strip. It will "transfer" the coating onto the surface of the workpiece by a rotating coating roller with a coating to form a film of the desired thickness.
Coil coating can increase production capacity and output, reduce production cost, rich color, consistent quality of different batches of products, can obtain a variety of surface effects, and have good flexibility during processing, but strict controllable release film thickness.
6, curtain coating
Curtain coatings are primarily used for sheet or strip coating. The paint is pumped or gravity overflowed to form a "lacquer curtain" through the adjustable gap, which is applied to the surface of the workpiece. Curtain coating is a high speed coating process with minimal coating loss.
7, roller coating or rotating drum coating
Roller coating or rotating drum coating can more effectively control the accuracy and flatness of the sheet, and successfully eliminate the irregularities and wrinkles caused by the traditional. Therefore, it is often used for small parts such as screws, nuts and small screws with a single weight of less than 0.5kg. It is a process in which a certain amount of paint is sprinkled on a drum or a rotating drum for holding a workpiece to uniformly coat the coating onto the surface of the workpiece.
8, electrophoretic coating
It mainly refers to "cathode electrophoresis coating", which is widely used in the automotive industry, and is applied to the surface anti-corrosion and decoration of building materials, light industry, household appliances and other industrial fields as well as hardware and handicrafts. Cathodic electrophoresis is a positively charged cationic resin that moves to the cathode after being energized. As the pH near the cathode rises, particle exchange occurs and the cathode coating precipitates over the test piece. The cathodic electrophoretic coating film has strong adhesion, strong hiding power and high corrosion resistance (neutral salt spray test for 1000 h). The electrophoretic paint is a water-based paint, and the commonly used cathodic electrophoretic paints are epoxy paint, acrylic paint and polyurethane paint. There is no solvent evaporation problem in electrophoresis.
Second, solid coating technology
Solid coating is a "powder coating". Instead of using a solvent, it coats the fine powder of the coating material on the workpiece and melts it at a temperature exceeding the melting point of the powder to form a paint film on the workpiece. Powder coating includes three processes of "electrostatic spraying", "flow bed" and "electrostatic fluid bed". The utilization of the powder coating is almost 100% under the conditions in which the powder is collected and reused. "Electrostatic spraying" adsorbs the powder coating on the workpiece at room temperature by electrostatic adsorption, and then heats and melts to form a paint film. The "flow bed" is to place a workpiece that has been preheated above the melting point temperature of the coating into the fluidized suspended coating powder, and the coating powder in contact with the workpiece is melt-coated on the workpiece to form a paint film. The "electrostatic fluidized bed" is an electrode placed in a powder chamber to adsorb a negative charge of the fluidized bed coating powder onto a grounded workpiece. There is no solvent contamination problem in powder coating, mainly the problem of recycling and utilization of coating powder. Companies that specialize in the production of complete powder coating equipment are equipped with a complete powder recycling system and an explosion prevention system.
With the increasing awareness of environmental protection, environmentally friendly coatings will be more and more widely used. Suitable construction techniques should be adopted for different coatings to reduce the construction cost while ensuring the protection and decorative effects of the coatings.
It is believed that in the future market, people not only put forward high requirements on the quality of coatings, but also put forward corresponding environmental protection requirements for the coating construction process.
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