With the development of the automobile industry, the annual production capacity is 250,000-300,000 car body painting workshops. Its production cycle has reached 0.75-1.0min/unit, and the chain speed of the production line has reached 6-7m/min. Such a high Chain speed, manual spraying operation has been difficult to adapt, and can not guarantee the stability of quality. With the progress of electrostatic coating technology and computer control technology, high-speed cup-type automatic electrostatic spraying machine (ESTA) and manipulator spraying machine have completely replaced manual spraying and general-speed cup-type electrostatic spraying machine, realizing the middle coating and topcoat Full automation or basic automation of spraying (automatic electrostatic spraying has been basically realized on the outer surface of the car body, while manual spraying is still required on the inner surface). At present, the intermediate coating topcoat production lines with an annual output of more than 100,000 units basically use high-speed cup-type automatic electrostatic spraying machines.
(1) Characteristics of high-speed cup-type electrostatic spraying High-speed cup-type electrostatic spraying (Es-TA) has become the mainstream of today's automobile body mid-coat and topcoat coating technology, and it has the following characteristics.
① Good decoration and stable quality. Due to the use of electronic computer operation, the mechanical movement, spraying distance and angle, and the amount of paint spraying are precisely controlled, and the error of the coating film thickness can be controlled within ± 5 µm, ensuring stable quality. Since the maximum speed of the cup-shaped nozzle can reach 60000r/min, the strong centrifugal force makes the paint atomized very finely, and the diameter of the paint droplet can be as small as 50~100µm, and the smaller the diameter of the paint droplet, the smoother and fresher the paint film will be. The higher the reflection, the decorative effect far exceeds that of air spraying, airless high-pressure spraying and general electrostatic spraying with coarser atomization fineness. Moreover, the automatic production line eliminates the dust brought in by painters and pipelines during manual spraying, reducing the possibility of paint surface contamination and defects.
②High coating efficiency, saving paint. Due to the high-speed cup-type electrostatic spraying with 90,000-120,000 volts of high voltage, the environmental protection effect is improved, and the coating efficiency can reach more than 90%. When using air spraying, the coating efficiency is only 30%~40%, and the general electrostatic Spray Gun is only 50%~60%. Because the coating efficiency is greatly improved, the paint consumption is greatly reduced.
③Energy saving and labor saving, good environmental protection effect. Due to the automatic spraying production line, the demand for manpower is greatly reduced, the labor intensity of workers is reduced, and the working environment of workers is greatly improved. Moreover, the wind speed of the spray booth can be reduced from 0.4~0.5m/s during manual air spraying to 0.2~0.3m/s, and the air supply energy of the air conditioner is also greatly reduced. Due to the stable coating quality, the repair work for defective products can be greatly reduced. With the improvement of coating efficiency, the amount of solvent emitted from the painted surface is also greatly reduced, which reduces the harm of volatile organic compounds to the environment, and is more in line with the requirements of environmental protection.
④ Significantly improve the production efficiency of the body painting line. High-speed cup-type electrostatic spraying is suitable for large-volume assembly lines. The chain speed of the spraying line for intermediate coating and natural color topcoat spraying can reach 7.5m/min. Spray topcoats of different colors, and can meet the needs of multi-variety mixed-flow production of car bodies. Due to the high centrifugal force generated by the high-speed spray cup, the coating with high solid content and high viscosity can be atomized well. Therefore, when the chain speed is 4m/min, the film thickness of one spray can reach 35~40µm, while air spray One time spraying can only form a paint film of about 20µm.
(2) Composition of high-speed cup-type electrostatic spraying (ESTA) equipment ESTA equipment is composed of top spraying machine, side spraying machine, paint supply system, high voltage generator, related safety facilities and control equipment. Among them, the top spraying machine and side spraying machine are arranged in the 7~8m long spray booth section.
①The side spraying machine is arranged on both sides of the car body in the forward direction, and sprays the side of the car body. It is divided into two types: fixed type and reciprocating type. The fixed type is to fix the high-speed cup-type electrostatic Spray Gun on the support or hanger. In order to expand and uniform the spray width of the sprayer, the Spray Gun head can swing up and down within a certain angle. Generally, three Spray Guns are arranged on both sides of the car body to spray the upper, middle and lower parts of the car body. This side spray machine is suitable for large-scale flow production lines with high chain speed. The electric Spray Gun of the reciprocating side spray machine can reciprocate up and down and follow the shape during spraying, and the spray width is relatively fixed, which is more suitable for medium and small batches of various car body coatings with medium and low chain speeds.
②The top spraying machine is arranged on the top of the car body to spray the upper surface of the car body and the front and rear end faces of the car body. It is divided into two types: suspension type and gantry type. The former can be hung in the spray booth. The electric Spray Gun of the top spray machine can not only reciprocate up, down, left, and right according to the stroke, but also rotate forward and backward by 45°~90°, so as to meet the needs of spraying the front and rear end faces of the car body.
At present, the automatic electrostatic spraying station composed of top spraying machine and side spraying machine has been replaced by a more professional automatic electrostatic spraying station composed of 3~4 manipulator electrostatic spraying machines. The automatic production line speed of manipulator electrostatic spraying can exceed 1m/s, and the paint output rate of the Spray Gun can exceed 800m1/min.
③Paint supply system. In order to ensure the stable quality of automatic electrostatic spraying, the amount of paint delivered must be accurately measured. Common methods for measuring paint volume include paint pressure adjustment method, paint volume adjustment method, and gear metering method. Among them, the paint pressure adjustment method is a simple one, which measures the paint by measuring the pressure change of the flowmeter. It has the advantages of simple structure, small size and easy cleaning. The disadvantage is that the error is large and is greatly affected by the viscosity of the paint. Except for two-component paints, other coatings can be measured by this method. The paint volume adjustment method is an accurate but more complicated measurement method. The flow of paint is sensed by the sensor installed at the outlet of the paint pressure regulator, which is less affected by the change of paint viscosity. The gear metering method controls the amount of paint delivered by controlling the motor speed. This kind of metering has high accuracy and is basically not affected by the viscosity of the paint. It is suitable for various paints, especially for the metering of two-component paints.
Each electric Spray Gun is equipped with an automatic color-changing device with simple structure and good cleaning performance. When the paint of the first color stops spraying, its color paint valve will be closed, and the pulse compressed air and solvent control valves will be activated alternately. Let the air-solvent mixture enter and clean the residual paint in the paint pipeline, open the high-speed cleaning valve, and use solvent to clean the residual paint in the rotor cup. After cleaning, start the paint valve for the next spray paint to make the color The paint enters the spray cup and enters the spraying of the next color paint. The time required for color change depends on the structure of the system, the type of paint and the performance of the cleaning solution. Usually, the color change can be completed within 8-15 seconds.
④ High voltage generator and related safety equipment. The high-voltage generator is generally installed outside the paint spraying room. Generally, a medium-frequency high-voltage generator is used to convert the 10,000-volt AC high-voltage power into a 100,000-120,000-volt high-voltage direct current through frequency conversion and double voltage, which can generate Hui’an-level high-voltage current. An ESTA system generally needs to be equipped with several high voltage generators. In order to ensure the safety of equipment operation, overvoltage and overcurrent detection circuits are installed in the high voltage generator. When the upper and lower limits are exceeded, the high voltage generator will be automatically shut down, and the high voltage device will be grounded.
⑤ control equipment. Spraying control equipment is generally composed of an electric control box, an air control box, an operating console and a TV monitor, and realizes electronic computer program control, which can identify the vehicle model and spray color, control automatic color change, and control the speed of the spray cup and spray Adjust the range, and control and adjust other operating parameters of the electrostatic spraying equipment.
The process flow of using professional robots or high-speed rotary cup electrostatic spraying in the automatic production line of intermediate coating and topcoat spraying of automobile body is shown in Figure 7-1.
