(1) Master the correct electrostatic spraying operation procedures
The electrostatic spraying operation includes two procedures of starting and stopping. The following takes rotary cup electrospraying as an example to illustrate the starting and stopping procedures of electrostatic spraying.
1. Boot procedure
First start the rotary cup motor to make the rotary cup rotate, observe whether the rotating speed of the rotary cup is normal, then first turn on the low-voltage switch of the high-voltage electrostatic generator, and then turn on the high-voltage switch, at this time the high-voltage indicator light will be on, and the insulating oil in the high-voltage generator will be slightly vibration. The high-voltage value on the Spray Gun cannot be measured by instruments at present, so it can only be judged by experience. In order to judge whether the Spray Gun has high voltage, you can hold a well-insulated rod, wind a grounding wire on one end of the rod, and let the wire gradually approach the Spray Gun. If there is a high voltage, spark discharge will occur. When the distance between the arcs is 1cm, the estimated voltage is 10kV. When the voltage increases, the distance of the arc will increase, and the maximum can be extended to 8~12cm. After turning on the high-voltage generator, pay attention to prevent people from being shocked. Then start the paint pump and observe whether the paint mist is sprayed from the rotary cup. After everything is normal, the paint pump can be turned off, and the paint pump can be turned on after the workpiece is sent to start painting.
2. Shutdown procedure
After spraying, first turn off the paint delivery pump, stop the delivery of paint to the rotary cup, then turn off the high-pressure generator, connect the paint delivery pipe to the solvent barrel with thinner, and pour it into the thinner to clean the pipeline. After cleaning the equipment, turn off the power of the rotary cup. The operating procedures of other electrostatic spraying are roughly the same. During the operation, special attention should be paid to checking whether the Spray Gun has high voltage and whether the workpiece is well grounded. After spraying, the equipment must be cleaned with solvent.
(2) The workpiece needs to be well grounded
In the electrostatic spraying production line, the workpiece is usually connected to the ground through the connection mode of workpiece-slinger-transportation chain-house steel part-grounding. Except for the workpiece, the spreader is the most likely to adhere to the paint in the electrostatic spraying. After repeated use, the paint It will accumulate thicker and thicker on the spreader, which will lead to poor grounding of the spreader and poor grounding of the workpiece, which will not only affect the coating effect, but also cause the danger of spark discharge due to the accumulation of charges, so check the grounding of the spreader in time. One method of inspection is to measure with a 1000V withstand voltage meter. If the insulation resistance between the earth and the workpiece exceeds 1Ma, it means that the workpiece is not well grounded, and the paint attached to the spreader should be stripped immediately. Another method is to use a non-contact electrostatic charge Detector to measure the surface potential of the coated workpiece that has just been painted. If it is not zero potential, it can be judged that the grounding is poor.
(3) Do a good job of cleaning the equipment
The discharge electrode on the Spray Gun is the key part of cleaning. During the use of electrostatic spraying equipment, the paint will adhere to the discharge electrode, which will reduce the charging efficiency. Clean the nozzles. The discharge electrode should be grounded before scrubbing, and the charged charge should be discharged to prevent the flammable solvent from igniting. If the paint is attached to the electrical insulators such as the shell of the electrostatic Spray Gun, the bracket fixing seat, the paint delivery pipe, the gas delivery pipe, and the high-voltage cable, not only leakage will occur, but also surface discharge and insulation resistance will be burned to cause spark discharge. Dangerous, so after spraying, these parts should be cleaned with cotton gauze dipped in solvent and allowed to dry to keep them dry and clean.
(4) Pay attention to safety during operation
The main safety hazards in electrostatic spraying are combustion and explosion caused by electric sparks. Combustion and explosion need to meet three conditions: the presence of oxygen, flammable or combustible and detonating fire. Since it is impossible to isolate oxygen in the electrostatic spraying environment, we can only avoid the occurrence of combustion by removing flammable and combustible materials and avoiding the ignition of the fire.
1. Types of combustibles
In the process of electrostatic spraying, there are two types of combustibles in the coating: one is powder coating, when the concentration of its dust in the air reaches a certain level, it will burn and explode, and because the powder coating is in the air It is in a fluidized state and is evenly dispersed in the air, so once it burns and explodes, it will be very fast. Generally, the lower limit of dust explosion concentration is 30g/m³, as long as it exceeds this value, there is a possibility of explosion. Therefore, when using powder coatings for electrostatic spraying, special attention should be paid to the danger of dust explosions, and the paint dust in the air should be carefully filtered and removed. The other type is solvent-based paints. In addition to water-based paints, most of the liquid paints contain very flammable organic solvents. They will volatilize during the electrostatic spraying process, and they will easily cause combustion and explosion after reaching a certain concentration in the air. Explosion, so must do a good job of ventilation, equipped with a good exhaust system. Most of the solvents used in cleaning are flammable. Improper use will cause fire when encountering electric sparks. Therefore, special care should be taken when using them. Waste paint and waste solvents should not be accumulated in the painting area, and the ground should be cleaned. To avoid burning of the solvent during the cleaning process, only enough cleaning solvent should be brought into the spray area. The solvent should be packed in a metal container with a cover and grounded. The tools used for cleaning need to use materials that will not generate electrical sparks. production. After cleaning, the rags and cotton yarns with paint and solvents should be properly disposed of in time to avoid natural occurrences. And smoking must be strictly prohibited in the spraying area.
2. Sources of sparks that cause fires and how to avoid them
The sources of electric sparks in electrostatic spraying are as follows.
①Due to the poor grounding of the workpiece, electric sparks will be generated during spraying, so the workpiece must be well grounded.
②The distance between the discharge electrode of the electrostatic Spray Gun and the workpiece is too close to generate discharge sparks, so the minimum safe distance between the Spray Gun electrode and the workpiece should be kept above 2.54cm/10000V.
③Electric sparks will also be generated if the objects, equipment, and human body around the spraying area are not well grounded, so all substances (except high-voltage systems) need to be grounded during electrostatic spraying. When operating the portable electrostatic Spray Gun, the hands need to be bare, and gloves cannot be worn, and the finger covers of the gloves should also be cut off when wearing gloves. Workers should not wear rubber shoes with good insulation. Wearing leather shoes can better send charges to the ground and prevent static charges from accumulating in the human body (the paint delivery system cannot be grounded when spraying conductive paint, but insulation work must be done).
④ Improper use of tools during the cleaning process will generate electric sparks due to friction, so the friction between tools should be reduced as much as possible.
⑤ If the temperature of preheating or drying equipment is too high, exceeding the ignition point of the solvent in the paint will cause combustion, so temperature control must be done well.
⑥The electrostatic spraying system uses a variety of electrical appliances and has a high-voltage power supply, so electric sparks may be caused when switching electrical appliances. Therefore, as soon as the electrostatic spraying operation stops, the high-voltage power supply should be cut off immediately and grounded for discharge.
(5) Common faults and solutions of electrostatic spraying
Common failures of electrostatic spraying include poor spray atomization and deposition, poor operation of the Spray Gun, etc. See Table 4-13 for the causes and solutions of these failures.
