A, principle
The nozzle of the electrostatic spray gun is connected with negative high-voltage static electricity. When the voltage reaches high enough, the air in the area near the nozzle will produce a strong corona discharge, forming a gas ion area. When the coating particles atomized by the electrostatic spray gun are in this area, the atomized particles of the coating have a negative charge. When the painted workpiece is suspended from the grounding line, the surface of the surface of the workpiece will have a positive charge. According to the electrostatic principle of the opposite charge phase attraction, with a negative charge of paint particles on the work surface movement to different order, adsorbed and deposited on the surface of the workpiece, forming a layer of uniform dense paint film, the workpiece is coated.
Second, the definition of
According to the principle of electrostatic field acting on electric charge, applying the physical phenomenon of electrostatic induction, the coating is sprayed on the surface of the workpiece.
1. Classification:
1) portable electrostatic spraying machine
2) rotary cup electrostatic spraying machine
3) rotary electrostatic spraying machine
Rotating plate type electrostatic spraying machine is commonly used
2. Equipment on the production line
1) electrostatic spraying room
Function: the solvent benzene and xylene volatilized from paint mist and paint are restricted to indoor environment and discharged from outdoor environment through ventilation system to reduce the pollution of workshop.
Type: type by type and "Ω"
Note:
A. The inner wall should be coated with butter or paint remover, and then affixed with wax paper or other paper, so as to replace and keep clean;
B. The air volume should not be too large at the ventilated place, 0.8-1.0m/s at the entrance and 0.3-0.5m/s at the exit;
C. All electrical components used in the room shall be explosion-proof and fireproof to ensure safety;
D. Ambient temperature is kept at ℃, RH<70%.
2) baking
Function: to dry the coating on the workpiece
Methods: convection drying, radiation drying, convection - radiation combination drying
Take infrared radiation drying as an example:
The temperature is below 120
Heating element: far infrared radiation heating element
Attention: consciously and regularly discharge the harmful gas in the baking path, should be equipped with rotation mechanism, in order to ensure that the workpiece in the baking path baking evenly.
3) high voltage electrostatic generator
Function: output enough voltage and power to ensure stable operation.
General technical performance:
The input current is 220V 50HZ
Power consumption ≤160W
Working environment T= RH ≤85%
Output voltage 30KV -- 150KV
Maximum output current above 700 mua
Structure: generator and double pressure box, double pressure rectifier by high voltage silicon reactor pressure.
4) others: spray gun, exhaust device, suspension conveying equipment, etc.
Iv. Process performance
Electrostatic spraying production process:
Pre-treatment of workpiece surface -- → drying -- → electrostatic painting -- → leveling -- → baking (heating into film) -- → cooling -- → remove the workpiece
1. Workpiece surface pretreatment
Degreasing, spray washing and phosphating treatment
2. Electrostatic spraying
A. The voltage is generally between 80KV and 120KV
B. Spacing between spray gun and workpiece should be 25-40cm
C. the distance between the spray guns should be at least 1m
D. spray gun speed: 1) the cup type 2800 r/min, Φ Φ 70-100 mm in diameter
2) disc: 3000 r/min, Φ Φ 200-300 mm in diameter
Five, the coating
1, thermoplastic plastic should not choose thermosetting coating, generally choose solvent volatile coating, thermosetting plastic should not choose high temperature curing class coating
PF can be used for polyacrylic coating, polyurethane two-component coating and amino coating.
3. Solvent: the solvent is general (xylene, diacetone alcohol, benzene, etc.)
But the use of solvents to consider: a, can dissolve paint and various additives
B no damage to plastic parts
C. It is better that the solubility parameter is located at the edge of the plastic solubility parameter region
4, choose coating to consider:
A. Good drain
B. Good atomization in electrostatic field has certain conductivity
C. Good fineness and low viscosity
D. Good hiding power and high viscosity
E. Surface tension is less than plastic surface tension
Brief process design
In rotating disc electrostatic spray the graph example, spray room for "Ω" type
Note:
A. A door shall be opened in the spray booth to facilitate access by staff;
B. Frame of spray chamber is strengthened with Angle steel and covered with plastic sheet;
C. The top cover of the skeleton is covered by hard PVC, on which two channel steels are traversed.
Environmental requirements: smooth ventilation, a good sewage system.
