Case of the Completion of Installation of the Powder Coating Line for Hydraulic Cylinders of Construction Machinery

Information about the Powder Coating Line for Construction Machinery Cylinder

I. Basic Components of the Coating Line

1. Pretreatment System

• Degreasing Tank

• Function: To remove oil and grease from the surface of the hydraulic cylinder. Construction machinery cylinders get contaminated with grease during the manufacturing process. If not removed, this grease will affect the adhesion of the powder coating. The degreasing tank usually uses an alkaline degreaser to clean the surface through immersion or spraying. The grease reacts chemically with the degreaser and is thus removed.

• Example: A commonly - used alkaline degreaser contains components such as sodium hydroxide and sodium carbonate. For example, when the cylinder is immersed in a degreasing tank solution at a temperature of 50 - 60°C for about 10 - 15 minutes, the oil and grease can be effectively removed.

• Pickling Tank

• Function: To remove rust and scale from the surface of the cylinder. Construction machinery cylinders are mostly made of metal and are prone to rust during storage or processing. The pickling tank generally uses acidic solutions such as hydrochloric acid or sulfuric acid. The acid reacts chemically with the rust, dissolving it and restoring the clean surface of the cylinder.

• Example: Using a 10% - 15% hydrochloric acid solution to pickle the cylinder at room temperature for about 5 - 10 minutes can effectively remove rust. However, after pickling, thorough water rinsing is required to prevent acid residue.

• Phosphating Tank (or Passivation Tank)

• Function: To form a phosphating film (or passivation film) on the surface of the cylinder, enhancing the adhesion of the powder coating to the cylinder surface. The phosphating film (or passivation film) serves as a transition layer, enabling the coating to adhere better and also improving the corrosion resistance of the cylinder.

• Example: During phosphating treatment, in a phosphating tank containing a zinc - based phosphating agent, with the temperature controlled at 55 - 65°C and the treatment time of about 3 - 5 minutes, a uniform phosphating film can be formed on the surface of the cylinder.

2. Powder Spraying System

• Electrostatic Spray Gun

• Principle: The electrostatic spray gun is the core equipment for powder coating. During the spraying process, the spray gun charges the powder coating electrostatically, while the cylinder is grounded as an anode. The electrostatically - charged powder coating is adsorbed onto the cylinder surface under the influence of the electric field force. This method can improve the utilization rate of the coating, reduce coating waste, and enable a more even distribution of the coating.

• Example: For a certain brand of electrostatic spray gun, the powder coating particles it sprays carry a negative charge. Under an electric field strength of 40 - 60kV, the powder - collecting rate of the coating can reach 80% - 90%.

• Powder - feeding Device

• Components: It includes a powder hopper, a powder pump, and a powder - conveying pipeline. The powder hopper is used to store the powder coating, the powder pump transports the coating from the powder hopper to the spray gun, and the powder - conveying pipeline ensures the stable transmission of the coating.

• Features: The powder - feeding device needs to have good fluidization performance so that the powder coating can enter the spray gun evenly. At the same time, to ensure the quality of the coating, the powder hopper usually has a stirring device to prevent the coating from caking.

• Recovery System

• Function: To recover the powder coating that is not adsorbed by the cylinder. During the electrostatic spraying process, some of the coating does not adhere to the cylinder. The recovery system collects this coating through cyclone separation and filter cartridge filtration. After treatment, the recovered coating can be reused, which not only reduces production costs but also reduces environmental pollution.

• Example: The cyclone separator uses centrifugal force to separate large - particle coatings, and the filter cartridge filter can filter out finer particles. The recovered coating can be reused for spraying after screening and adding new coating.

3. Curing and Drying System

• Drying Oven

• Type: A tunnel - type drying oven is usually used. There is a conveyor belt inside this drying oven, and the cylinder passes through the drying oven on the conveyor belt. The drying oven can be divided into electric - heated, gas - heated, etc., according to the heating method.

• Temperature Control: For the powder coating curing of construction machinery cylinders, the temperature of the drying oven is generally controlled at 180 - 200°C. Within this temperature range, the powder coating can be fully cured to form a hard and wear - resistant coating.

• Time Control: The residence time of the cylinder in the drying oven depends on the type of coating and the coating thickness, usually about 20 - 30 minutes. Appropriate time and temperature control can ensure complete curing of the coating and good performance of the coating.

• Ventilation System

• Function: During the curing and drying process, organic waste gas is generated. The ventilation system exhausts this waste gas from the drying oven and introduces fresh air to ensure the air quality inside the drying oven and also helps to maintain the stability of temperature and humidity inside the drying oven.

• Components: It includes an exhaust fan, an air inlet, and a waste gas treatment device. The waste gas treatment device can adopt methods such as activated carbon adsorption and catalytic combustion to treat the exhausted waste gas and reduce environmental pollution.

II. Advantages of the Coating Line

1. High - Quality Coating

• The coating formed after the powder coating is cured has high hardness and good wear resistance, which can effectively protect the construction machinery cylinder from wear and corrosion in harsh working environments. For example, in mining machinery and other working conditions, the cylinder needs to withstand a lot of friction from sand and gravel and chemical erosion. The coating of the powder - coated cylinder can significantly extend its service life.

2. Good Environmental Performance

• Compared with traditional liquid coatings, powder coatings contain little or no solvent. During the spraying and curing process, the emission of volatile organic compounds (VOCs) is greatly reduced, meeting the increasingly strict environmental requirements. At the same time, the powder coating recovery and reuse system also reduces coating waste and environmental pollution.

3. Economic Efficiency

• Although the initial investment in the powder coating line is relatively high, including equipment purchase, installation, and commissioning costs, in the long run, due to the high utilization rate of powder coatings, lower maintenance costs (such as reducing the solvent recovery process), and longer coating service life, it can save a lot of costs for enterprises. For example, in large - scale production of construction machinery cylinders, powder coating can reduce the coating cost per unit product by 10% - 20%.

III. Technological Process of the Coating Line

1. Workpiece Conveyance: The construction machinery cylinder is conveyed to the pretreatment area of the coating line through a hanging conveyor chain or a pallet conveyor system.

2. Pretreatment: The cylinder is treated in the order of degreasing → water rinsing → pickling → water rinsing → phosphating (or passivation) → water rinsing to ensure that the cylinder surface is clean and has a good adhesion base.

3. Spraying Preparation: The pretreated cylinder is conveyed to the spraying booth. The parameters of the electrostatic spray gun, such as voltage, current, and powder spraying amount, are adjusted. At the same time, the powder - feeding device and the recovery system are started.

4. Powder Spraying: The powder coating is evenly sprayed onto the surface of the cylinder through the electrostatic spray gun. During the spraying process, attention should be paid to the distance and angle between the spray gun and the cylinder. Generally, the distance between the spray gun and the cylinder surface is maintained at 20 - 30 cm, and the angle is adjusted appropriately according to the shape of the cylinder to ensure the even coverage of the coating.

5. Inspection and Repair: After spraying, the coating on the cylinder surface is inspected to see if there is any missed spraying or uneven coating thickness. If there is a problem, it is repaired in a timely manner.

6. Curing and Drying: The inspected - qualified cylinder is conveyed to the drying oven of the curing and drying system and cured and dried according to the set temperature and time to form a hard coating of the powder coating.

7. Cooling and Packaging: After drying, the cylinder is cooled naturally or by air - cooling, then undergoes quality inspection. The qualified products are packaged and ready for shipment.