No.46: Electrostatic Spray Coating

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Key Notes

Proper use of the electrostatic spray method improves coating efficiency, and powder particles become charged through their interaction with air, allowing for uniform coating. 

The electrostatic spray method can be broadly categorized into the following three methods: 

1. Corona Pin Method

The Corona Pin method involves applying high voltage (-30,000 to -100,000V) to particles that have been atomized using air or airless spray. In this method, the charged paint particles adhere to the grounded object being painted due to the electrostatic attraction, leading to improved coating efficiency. 

2. Disc Rotation Method or Cylinder Cup Rotation Method (Bell Type)

This method is commonly used in automotive paint lines and achieves paint atomization without the use of air. Paint is supplied into a bell-shaped cup, and by rapidly rotating it (15000~40000rpm), the paint is thinly stretched and released from the cup’s edge, forming atomized particles. These particles are charged with approximately -90000V. This method results in narrower particle size distribution and improved appearance of the finish. 

3. Powder Electrostatic Method

The powder electrostatic method includes both the Corona Pin method and the friction-charging Tribogun method. However, the Corona Pin method is more commonly used in practical applications. The cylinder walls can be made of Teflon or nylon, and they are not affected by external electric fields, allowing charged particles to be supplied precisely where needed, even in recesses and complex-shaped objects. In the Tribogun method, a high-voltage generator is not required, and powder particles become charged through friction as they flow and collide with the inner cylinder walls of the painting machine. However, the tribocharging method’s effectiveness depends on the paint’s characteristics and is influenced by factors such as climate and humidity. 

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