The power’s in the pulse
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Corona guns are one of the most common spray application techniques for powder coatings. Like other methods, use of corona guns requires pumping of powder from a vibrating box feeder, fluidized hopper or gravity hopper. Powder volume and transport speed are adjusted at the spray apparatus control panel, and particles are atomized and directed into a well-dispersed cloud.
The powder within this cloud is then electrostatically charged, and in the case of corona guns this is accomplished using an electrostatic generator to create an electrostatic field between the gun and the grounded part. The powder particles accept the electrostatic charge as they move through this field and are attracted to the grounded part.
Corona guns are probably the most commonly used type of spray application equipment in general powder coating applications, and they all work basically as just described. But Parker Ionics (Westland, MI) says its GX131 Pulse Power guns offer an improvement to standard corona equipment.
According to the company, the guns are the first and only corona charging units that pulse the charge to the external electrode several times a second. Parker Ionics says the continuous pulsing prevents a buildup of free ions on the electrode, resulting in a smoother transfer of powder and higher first-pass transfer efficiency for increased production, lower maintenance costs, less powder to recover and savings in time and energy.
The company also claims several other benefits for the system. The rapid on/off-on/off of the charge is said to allow the powder to be carried into recessed or Faraday cage areas on complex parts by reducing free ions in the air. The result is better coverage and more uniform film build over the entire part surface. Reducing free ions is also said to minimize back-ionization for an even smoother, higher quality finish.
According to Parker Ionics, the system also simplifies operation by enabling use of a single setting for a variety of tasks, including recoating operations, spraying of very thick coatings and application of specialty powders such as metallics. With conventional guns, operators would have to adjust voltage and powder flow parameters to handle a variety of parts and situations.
The company first marketed Pulse Power guns in 2003. Parker says the current new generation of guns uses a much faster pulsing frequency than previous versions, resulting in an optimal charge to mass ratio without overcharging, which would produce excess free ions.
Available with two different interchangeable grip sizes for improved operator comfort, the guns work with a dedicated controller developed specifically for them. The GX355 controller guns provide full diagnostics with alarms for abnormal main solenoid conditions, powder valve solenoid, fluidizing air solenoid and gun voltage. Built-in measurement of accumulated run time allows monitoring and scheduling of preventive maintenance, and the unit allows fast adjustments of voltage and air with the ability to preprogram up to 20 coating recipes.
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