PU Paint Coating Line

PU paint, namely polyurethane paint, is widely used in numerous industrial and civil fields due to its excellent abrasion resistance, chemical resistance, and good decorative properties. The PU paint coating line is a professional production equipment specifically designed to evenly coat PU paint on the surface of various objects, achieving the purposes of protection and decoration.

Basic Composition

• Pre-treatment Equipment: Before coating, the surface of the workpiece needs to be cleaned and pre-treated. Common pre-treatment steps include degreasing, where specific chemical solutions are used to remove oil stains on the surface of the workpiece to ensure good adhesion of the paint. Rust removal operations are aimed at metal workpieces to prevent rust from affecting the coating quality. In addition, there may also be processes such as phosphating and passivation, which form a conversion film on the surface of the workpiece to further enhance the bonding force between the coating and the workpiece.

• Painting Equipment: This is the core part of the PU paint coating line. Common painting methods include air spraying, high-pressure airless spraying, and electrostatic spraying. Air spraying equipment atomizes and sprays the PU paint onto the surface of the workpiece through compressed air. It is easy to operate and suitable for workpieces of various shapes and materials. High-pressure airless spraying uses a high-pressure pump to directly spray the paint from the spray gun, resulting in finer paint mist particles, a more uniform coating, and high painting efficiency. Electrostatic spraying relies on electrostatic attraction to make the paint mist particles evenly adsorbed on the surface of the workpiece, which can effectively improve the utilization rate of the paint, reduce waste, and is especially suitable for products with high requirements for appearance quality.

• Drying Equipment: After the PU paint is coated, it needs to go through a drying process to cure it. According to the heating method, the drying equipment can be divided into hot air circulation drying, infrared drying, and ultraviolet drying, etc. Hot air circulation drying makes the workpiece evenly heated through the circulation of hot air in the drying chamber, and it is suitable for workpieces of various shapes and sizes. Infrared drying uses infrared radiation to directly heat the surface of the workpiece, with a fast heating rate and high drying efficiency. Ultraviolet drying is for special photocurable PU paint, which can achieve rapid curing in a short time and has extremely high production efficiency.

• Conveying System: It is responsible for smoothly transporting the workpieces between various processes of the coating line. Common conveying methods include overhead conveying chains, ground chain conveyors, and belt conveyors. Overhead conveying chains are suitable for workpieces with regular shapes and light weights, which can make full use of space and realize continuous production. Ground chain conveyors are suitable for heavier or larger workpieces and have good conveying stability. Belt conveyors are often used for workpieces with high requirements for surface flatness to avoid damaging the workpieces during the conveying process.

• Waste Gas Treatment Equipment: Since organic solvents will volatilize during the coating process of PU paint, generating harmful waste gas. For environmental protection and safe production, the coating line is equipped with waste gas treatment equipment. Common waste gas treatment methods include the adsorption method, where adsorbents such as activated carbon are used to adsorb the organic solvents in the waste gas; the combustion method, which burns and decomposes the waste gas at high temperatures, converting it into harmless carbon dioxide and water; and the catalytic oxidation method, which uses a catalyst to reduce the oxidation temperature of the organic matter in the waste gas, making it decompose more efficiently.

Workflow

• Workpiece Loading: The workpieces to be coated are first placed on the conveying system, and the conveying system smoothly sends them to the pre-treatment area.

• Pre-treatment: The workpieces go through pre-treatment processes such as degreasing and rust removal in sequence to ensure that the surface is clean and free of impurities, preparing for the subsequent coating. After being rinsed with clean water and dried, the treated workpieces enter the painting stage.

• Painting Operation: According to the material, shape, and coating requirements of the workpiece, select appropriate painting equipment and process parameters for painting. During the painting process, the viscosity of the paint, the spraying pressure, and the distance between the spray gun and the workpiece need to be strictly controlled to ensure that the uniformity and thickness of the coating meet the requirements.

• Leveling: After painting, the workpiece stays for a certain period of time under certain temperature and humidity conditions to allow the paint layer to level naturally, eliminating defects such as orange peel and sagging on the surface and improving the flatness of the coating.

• Drying and Curing: The leveled workpiece enters the drying equipment. Under the set temperature and time, the solvent in the PU paint volatilizes, and the resin crosslinks and cures to form a hard and wear-resistant coating. The control of the temperature and time during the drying process is crucial and directly affects the performance and quality of the coating.

• Quality Inspection: The dried workpieces are sent out through the conveying system for quality inspection. The inspection items include coating thickness, adhesion, hardness, glossiness, etc. For unqualified products, rework treatment is required.

• Workpiece Unloading: The qualified workpieces after inspection are unloaded from the coating line and enter the subsequent packaging or assembly process.

Application Areas

• Furniture Manufacturing: Coating PU paint on the surface of furniture can endow the furniture with good abrasion resistance and a beautiful gloss, protect the wood from wear, moisture, etc., extend the service life of the furniture, and at the same time improve the appearance quality of the furniture.

• Automotive Parts: Interior parts, exterior parts, and engine parts of automobiles often use PU paint coating to improve the weather resistance, corrosion resistance, and appearance decoration of the parts, meeting the high requirements of the automotive industry for product quality and appearance.

• Electronics Product Enclosures: The plastic enclosures of electronic products such as mobile phones, computers, and tablets are coated with PU paint, which can not only enhance the appearance texture of the products but also strengthen the abrasion resistance and scratch resistance of the enclosures, protecting the electronic products from damage during daily use.

• Building Materials Industry: After building materials products such as doors and windows, floors, and decorative panels are coated with PU paint, their water resistance, moisture resistance, and insect resistance can be improved, and at the same time, the decorative effect of the surface can be improved, making the building materials products more beautiful and durable.

Advantages

• Excellent Coating Performance: The coating formed after PU paint coating has excellent abrasion resistance, chemical resistance, and adhesion, which can effectively protect the surface of the workpiece and extend the service life of the product.

• Good Appearance Effect: It can achieve coating effects with various glossinesses and colors, from high gloss to matte, with bright and lasting colors, meeting the diverse needs of different customers for product appearance.

• High Production Efficiency: Through automated painting equipment and continuous production processes, the PU paint coating line can quickly and efficiently complete the painting operations of a large number of workpieces, improving production efficiency and reducing production costs.

• Improved Environmental Performance: With the continuous development of environmental protection technology, the PU paint coating line is equipped with advanced waste gas treatment equipment, which can effectively reduce the emission of harmful waste gas during the coating process, comply with national environmental protection standards, and realize green production.