Corona charging guns work by bombarding powder particles sprayed from the gun with charged particles called ions. The corona charging process begins with a potential or voltage applied to one or more electrodes near the front of the gun. A high-voltage generator is used to produce up to 100,000 volts. For spraying most types of finishing powders, a negative polarity voltage is produced in the generator and results 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 a 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. Some powder powder particles may be shielded from other particles in the charging zone and therefore not accumulate a charge. For these particles, aerodynamic forces might propel them toward the part. Ions which don’t become attached to powder particles in flight are known as excess ions or free ions. Ions, being charged particles, also tend to follow the electric field and many are deposited onto the part.