How a Corona Treating System Works
How a Corona Treating System Works
Components in a corona treating system:
- The Generator
The generator is the power source. Consisting of a high frequency generator and a high voltage output transformer, the purpose of the generator is to supply a sufficient amount of power to the treater station to generate a corona. The job of the high frequency generator is to take low frequency power, commonly supplied by the local utility, and convert it to high frequency ranging between 3-340 kilohertz (kHz) depending on the generator. Solid state generators, which are the most common, range between 3-40 kHz.
Once the power is converted to high frequency, it then travels to the high voltage output transformer. It is at this point that the power is sent to the “hot” electrode in the treater station and across the air gap in the form of a corona.
- The Treater Station
Basically a mechanical fixture; the treater station’s main components are the two electrodes and most often the dielectric covering. Auxiliary components vary based on need. Often included is a zero speed detection switch, which is used to shut off the generator automatically should the web stop. Other options include completely or partly enclosed cabinets with built-in exhaust ports to prevent the ozone which is produced from entering the plant’s atmosphere; safety interlock switches which turn off the high voltage when a door is opened; a variety of easy web threading methods such as manual or pneumatic electrode lifts, air purging systems for operation in combustible environments, and a number of other custom features along these lines.
Components in a corona treating system:
Each corona treating system consists of:
1) Power Supply
2) Treater Station
3) Exhaust System
1) Power Supply is composed of:
- Input transformer: The primary function of the input transformer is to raise or lower the input voltage. A secondary function of the input transformer is to isolate the power supply from the incoming power line so that it can be utilized as a filtering device. The input transformer raises and lowers the input voltage to the power supply. It also smooths out any power surges present and isolates the power supply from the incoming power line.
- Control box: The control box takes incoming power (in watts) and converts it to direct current. This is a conversion from low frequency, high current, low voltage, to direct current and finally is chopped into very high frequency ranging from 3kHz to 50kHz. Essentially, the control box converts the incoming power from low frequency to high frequency. The control box also has monitoring functions of operation.
- High voltage transformer: High current, low voltage is converted to low current, high voltage ranging from 10,000 to 30,000V
2) Treater Station is composed of:
- High voltage electrode: The sole function of this device is to present the high voltage electrical field across the air gap and the substrate. This is where high voltage potential is created or produced. It can be a metal or a dielectrically covered conductor.
- Ground path/source: This is typically a roller that can be metal or dielectrically covered depending on the specific system. It is used to provide an electrical path to the ground.
- Dielectric: The dielectric materials’ sole function is to evenly distribute the HV field across the substrate. A dielectric material is any material which is non conductive. The dielectric is used to buffer the voltage field to create a capacitor.
- Air gap: The air gap is one of the most critical componenets of the treater station, since it is the air gap where the ionization (corona) occurs. Corona will occur anywhere air is present between the two electrodes. The distribution of power across the gap will only be even if the distances between the two electrodes is even. This is the area where corona is generated
- Housing: The main function of the housing is to capture and contain any of the ozone or gas by products that are produced. The second function is to protect the operators from the high voltage and to capture any byproducts and for safety purposes. The housing acts to isolate for safety so that operators do not have access to high voltage/currents.
3) Exhaust System
- Piping
- Exhaust blower: There are several byproducts that come off of corona. The main one being ozone (O3). In some instances, the byproducts are released into the air. Otherwise, something such as an ozone destruct unit will exhaust byproducts through a filtration process.
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