Chapter 6: Paint Spraying by Electrostatic Charge
Basic of Electrostatic for Painting
Electrostatic carry material paint through the electric field. The particles are classified into 3 types. 1. Positively charged particles 2. Negatively charged particles 3. Neutral particle. With 3 different particle. It will be attracted each other. That is the basic of electrostatic procedure.
Electrostatic Spray Gun
Electrostatic Powder Spray Gun
Rotary Bell Atomizer
The movement of electric particle must require electric field as the road between electrostatic spray gun and work piece. Electric field will be exist from a charged object. That's why work pieces are required to attach with ground.
Therefore, electric charge within material paint will support to move into ground object and occur "wraparound effect" which support to reduce material cost and operating time.
It's means the gravitational attraction through the electric current in order to bring paint particle attach the workpiece automatically by using high voltage as the driving force to push the paint which input the charge particle into workpiece surface through out the electric field. There have the method of wraparound effect are following as below;
1. Create Charge particle by Electrode (Corona Charge)
Liquid Coating GM5000 Series and PEM X1 Powder Coating Spray gun are the corona method which create charge particle and input to paint by electrode in order to create electric field with high voltage and separate ion around between spray gun and workpiece which is attached by ground cable. Electrode is developed to be better quality; create charge particle which push precisely paint into workpiece, reduce overspray, reduce time and provide the good wrap around quality.
High voltage cascade
2. Create electrostatic field by high speed rotary
Rotary bell atomizer (Evobell and Top Finish) generates an electrostatic field of force via the applied high voltage. The paint particles atomized by the rotating bell are now transported by kinetic and electrostatic energy to the grounded work piece and distributed finely across the entire sprayed object.
Rotary Bell cup which create electrostatic field.
Wrap around by high speed rotary.
3. Create charge particle from Friction
Use of friction between the powder paint and air mix in powder tube of gun to create electrostatic charge, which uses the principle of electrostatic induction by bringing two objects with positive and negative electrodes into contact with the friction until a particle occurs. With non-conductive objects, the Tribo's WAGNER powder spray gun uses this principle by using non-conductive PTFE (Teflon) materials. Then it will be sprayed out from spray gun and absorbed into workpiece surface immediately.
The friction between powder paint and air mix within powder tube.
Tribe Powder Spray gun from WAGNER
Material Paint Resistant
Paint Resistant is the compatible requirement of material paint for using with electrostatic gun. If paint resistant rate is too high, electrostatic can not perform effectiveness. It can not bring material to attract work piece. If paint resistant is too low, electrostatic also lack of effectiveness. Each of electrostatic spray gun series require the paint resistant rate already so user may contact paint supplier to make material paint follow the paint resistant rate requirement. The measurement unit is kilohm (kOhm).
Example of using electrostatic electrostatic gun
The main objective is material paint saving, operating time saving. Therefore, manufacturer where use high quantity of paint and large production volume use electrostatic gun to save cost and get the efficient return to investment.
Liquid Coating Application
Electrostatic Powder Spray Gun
Rotary Bell Paint Atomizer
Spraying with electrical workpiece
In case of Plastic, wood, Glass, and fiberglass. All of them are electrical insulation workpiece that electrostatic gun might not spray for these workpiece. However, there are many woodwork factories around the world that use electrostatic spray guns, which can be divided into cases as follows:
1. Wood workpiece must be the wood categories that it have inherent moisture inside material which is electrical conductor. For example, rubber wood for furniture maker. The wood is porous and has moisture inside, so this spray gun can support to effectively coat around the workpiece. While other types of wood such as teakwood are solid wood and have no natural moisture, so electrostatic spray gun can not be used.
2. Plastic Glass and Fiberglass. There have conductive material which is used to coat these workpiece before painting by electrostatic spray gun.