Electrostatic. powder coating process

Transcription

1 powder coating process Electrostatic The process of applying electrostatic powder coating to a grounded part until heat is added to flow the powder and complete the process. The powder may cling to the grounded part for several hours before baking/heating process is done. If uncured powder coat is damaged before baking/heating process the electrostatic powder may be blown off and re-coated. Four basic pieces of equipment commonly comprise an electrostatic powder spray coating system. They are the powder feeder, power unit, electrostatic gun, and powder booth recovery system. Powder is supplied to the spray gun from a feeder unit where the powder is diffused by compressed air into a fluid-like state. The fluidized powder is then siphon out by movement of high velocity air flowing through a venturi. It is propelled through the powder feed tubing to the spray gun. The powder feeder is an essential part of the powder coating process because without this no powder would come out of the electrical static gun and cling to the grounded part. The powder

2 feeder has provides a controlled air pressure and powder feed which lets you put your desired thickness and smoothness of the job. The powder feeder with its electric static charge, coverage can be attained depending on size of part feet away from grounded part. The powder unit, or electrostatic voltage generator, has sufficient voltage to assure maximum wraparound. Voltage is variable up to 1000 kv so that is may be; (1) reduced to combat Faraday "cages" encountered in spraying inside corners; (2) increased as necessary to provide wraparound, surface coverage, and efficient deposition of powder on convex surfaces and flat panels; and (3) adjusted for the powder being sprayed Powder leaves the spray gun in a form of a diffused cloud being propelled toward the work piece. A high voltage, low amperage power unit supplies a charging electrode at the front of the spray gun. The charging electrode emits a field charge which is imparted to the powder particles. This causes them to seek out and attach themselves to the grounded work piece. Corona powder coating guns use a high-voltage generator to disassociate air and produce a stream of negative or positive

3 ions, which in turn imparts a like charge to the powder cloud. The potentials of the charged cloud and gun electrode combine to generate an electric field with the opposite pole (the part). Charged powder particles at the gun seek the lower potential of the opposite pole (the part). The term "100 kv" applies to Corona guns and refers to the 100,000 high-voltage generator that produces the arc to disassociate air and generate an electron cloud. The electrode of the gun typically has a negative polarity relative to the piecework. Polarities must be reversed for nylon powders, which require a positive charge.

4 a negative polarity voltage is produced in the generator and results

5 in the powder particles accumulating a negative charge. Positive polarity generators are also typically available as an option and are used primarily for charging nylon powders. As the voltage on the electrode is increased, an electric field is produced between the gun and grounded part. When the electric field in the vicinity of the electrode reaches strength of about 30 kv per centimeter, the field is strong enough to break down the air in the vicinity of the electrode. This electrical breakdown of air results in the creation of charged molecules or ions in the form of a continuous discharge known as a corona discharge. Powder particles exiting the gun travel near the electrode where many are bombarded by ions and accumulate a negative charge. These powder particles are influenced by the electric field between the gun and part and tend to follow the electric field to the part.

6