Spraying is a coating method that is dispersed into uniform and fine droplets by means of pressure or centrifugal force through a spray gun or disc atomizer and applied to the surface of the object to be coated. It can be divided into air spraying, airless spraying, electrostatic spraying and various derivatives of the above-mentioned basic spraying forms, such as high-flow and low-pressure atomizing spraying, thermal spraying, automatic spraying, multi-group spraying, etc.
A processing method in which paint is atomized by a spray gun and applied to the surface of an object. There are many kinds of compressed air spray painting, high pressure airless spray painting and electrostatic spray painting. Painting operations use flammable paints that contain large amounts of solvents, and solvent vapors that evaporate into the air under conditions that require rapid drying can easily form explosive mixtures. In particular, electrostatic spraying is carried out under a high voltage of more than 60 kV, and the distance between the spray nozzle and the painted workpiece is less than 250 mm, which is prone to spark discharge, which will ignite flammable vapors.
At present, there are four main types: arc spraying, flame spraying, plasma spraying and explosive spraying. Using spraying technology, coatings with wear resistance, corrosion resistance, heat insulation, electrical conductivity, insulation, sealing, lubrication and other special mechanical physical and chemical properties can be obtained on various substrates. The application range is very wide, involving all sectors of the national economy and various fields including cutting-edge technology.
hand spray
Through the front-line operators, the surface of the product is directly sprayed with oil, and now it is currently used for manual spraying of defective products after automatic spraying.
Fully automatic spraying
Fix the product that needs to be sprayed on the rotatable bracket, and then lock the bracket on the assembly line. Through the movement of the assembly line and the continuous rotation of the rotatable bracket, 100% uniform spraying on the surface of the product has been achieved.
The spraying operation has high production efficiency and is suitable for manual operation and industrial automation production. It has a wide range of applications, mainly in the fields of hardware, plastics, furniture, military industry, ships, etc. It is the most commonly used coating method today; spraying operation requires environmental requirements There are dust-free workshops ranging from one million to one hundred. The spraying equipment includes spray guns, spray booths, paint supply rooms, curing ovens/drying furnaces, spraying workpiece conveying equipment, fog elimination and waste water, waste gas treatment equipment, etc.
The main problem in spraying is the highly dispersed paint mist and volatilized solvent, which not only pollutes the environment, is not conducive to human health, but also wastes paint and causes economic losses.
High-flow and low-pressure atomizing spraying is characterized by low atomizing air pressure and low air jet velocity, and the low atomized paint running speed improves the rebound of the paint from the surface of the coating. The paint rate is increased from 30% to 40% of ordinary air spraying to 65% to 85%. In light leather finishing, spray the finish on the leather surface with a spray gun or sprayer.
Common problems and solutions for spraying operations:
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1. Phenomenon: granulation
Reasons: The job site is unclean, and dust is mixed into the paint; the paint and curing agent have produced copolymerized particles after the paint has been prepared for too long; too close
Solution: Clean the spray booth and cover the paint bucket; the paint is well prepared and should not be left for too long; adjust the spray gun to make it in the best working state, and make sure that the distance between the gun muzzle and the object surface is 20-50CM.
2. Phenomenon: vertical flow
Reasons: Too much thinner makes the paint viscosity too low and loses its viscosity; too much oil output, too close to the object surface or too slow spray operation; too much oil injection each time too thick or too short interval between re-spraying; object surface Uneven, especially the streamline shape is easy to sag
Solution: Proportion as required; control the oil output to ensure that the spray paint is separated from the spray gun and increase the speed of the spray gun; each injection should not be too thick, it is best to control the interval spraying time in two times; control the oil output and reduce the thickness of the paint film; press Instructions for use
3. Phenomenon: orange peel
Reason: too much curing agent, the paint film dries too fast and reacts violently; the spraying pressure is too high, and the wrinkled paint film cannot be leveled; the temperature at the job site is too high, so the paint film should be violent
Solution: Proportion according to the instructions for use; adjust the air pressure, not too high; pay attention to the site temperature, and slow-drying diluent can be added to suppress the drying speed
4. Phenomenon: whitening
Reason: The temperature and humidity at the job site are high, and the paint film reacts violently, which may combine with the moisture in the air to cause whitening; excessive curing agent, too much and too thick spraying at one time
Solution: Pay attention to the on-site humidity, you can add anti-white water to prevent the occurrence of whitening; adjust according to the proportion, and one spray should not be too thick
5. Phenomenon: Foaming
Original solid: The compressed air is mixed with water on the paint film, the temperature at the job site is high, and the paint dries too quickly; the moisture content of the object surface is high, and the air humidity is high; one spray is too thick
Solution: separate oil and water, pay attention to drainage; add slow-drying thinner; clean the surface, add anti-white water to the paint; one should not be too thick
6. Phenomenon: shrinkage
Reason: The primer or intermediate coat is not dry before applying the topcoat
Solution; spray at the recommended thickness of each gun spray layer
7. Phenomenon: wrinkling
Reasons: The drying time is too short or the paint film is too thick; the curing agent in the primer or putty is improperly selected; the primer putty is incomplete; when the topcoat is sprayed, a gun goes too thick, the internal deep agent is not volatilized in time, and the outside is dry and the inside is dry. Don't do it.
Solution: Allow enough drying time between each coat; only spray the second coat or wet spray after hard drying.
Notes Edit Voice
Safety technical measures for spraying operation
1. Spraying operators must undergo safety technical training, and are not allowed to work without training.
2. Before painting, all painting equipment and tools must be fully inspected to confirm that there is no problem before work.
3. The ventilation and purification of painting workplaces should meet the requirements of GB 6415.
4. During the operation, the safety technology department of the enterprise should set up special personnel to regularly measure the oxygen content and combustible gas concentration in the air in the confined space. The oxygen content should be above 18%, and the combustible gas concentration should be lower than 10% of the lower explosion limit.
5. At least two people are required to work together for painting in the cabin. If the workplace is too small and can only accommodate one person to operate, another person should be responsible for supervision.
6. The high-altitude painting operation shall comply with the "Safety Regulations for Ship Construction at Heights".
7. When multiple spray guns work at the same time, the distance must be widened (about 5m), and the spraying should be carried out in a certain and the same direction.
8. For special coating operations, the spraying equipment and hoses should be managed by special personnel. If the equipment fails or has abnormal conditions, first notify the personnel in the cabin to withdraw from the cabin, and the maintenance personnel will overhaul.
9. The high-pressure jet and leakage of airless spray paint can lead to serious injury accidents. The operation should be done as follows:
a. Do not point the nozzle of the spray gun at others and yourself at any time;
b. Do not touch the nozzle with your fingers, or peep at the muzzle;
c. When cleaning the spray gun, it is necessary to cut off the pump driving source, release the pressure, and sell the safety device to the spray gun before cleaning;
d. When the spray gun is out of use, the safety latch must be locked.
10. After the operation is completed, the spray gun must be withdrawn from the cabin in time, and ventilation should be continued until the paint film is completely cured.
11. After the painting operation is completed, the workplace should be cleaned up in time, and the remaining paint and solvent should be returned to the warehouse in time.
12. Operators must wear protective masks, rubber gloves, eye masks and other related protective equipment.
