Electrostatic discharge on the rewinder of a blown film extrusion line
How does blown film extrusion work?
A blown film is a film made of a thermoplastic material, which is produced with the help of a special blown film extrusion line. The way it works is that molten plastic is blown out of a ring-shaped nozzle with the help of air. The solidified tube is collapsed at a height of 10-20 meters by a pair of rollers. At the end of the line, the film is cut lengthwise and usually wound separately on two winders. Typical machine speeds are around 10-20 m/min. These continuous films are mainly used for packaging of food, medical products or in the pharmaceutical sector.
During the winding of blown films, problems arise due to electrostatic charges.
The blown films are usually made of a high-resistance polyethylene which becomes electrostatically charged through contact and separation with other machine parts. The electrostatic charge very often amounts to several thousand volts at the winder, so that dangerous discharges to persons can occur. Persons can be injured by direct contact with the winder, but accidents due to startle reactions also occur time and again. In addition to the danger to persons, highly charged film winders attract dust, dirt and insects from the immediate vicinity. This is a particular problem for films used in the food, pharmaceutical or medical sectors. The electrostatic charges on the rewinder must therefore be removed. The two rewinders were equipped with 2 pcs ionSTAR RX3 and 2 pcs blueBAR directly after the corona treatment. The maximum distance between the ionSTAR RX3 electrode and the foil was 800 mm. The charge on the foil was 5 – 10 kV, which did not yet meet the requirements.
The highly charged plastic wrap is reliably discharged with unique ionization bars. The bars can be installed at a large distance from the winding surface.
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The high-performance discharge power supply POWER IONIZER impresses with its flexibility. The simple operation, the LED display for visualization of the current values and the integrated function and malfunction monitoring characterize the power supply unit. The POWER IONIZER can be operated with the Eltex AC discharging bars, ion blower nozzles and ion blower pistols. Lowest residual charges can be achieved by different adjustable parameters. Operation is possible as single unit or in a network.
Protocol/device description files of the fieldbus interfaces for integration into the machine control: Information fieldbus integration
HIGH-END discharge for highest discharge performance
The VARIO discharging bar flexBAR R60L with its free-standing, air-assisted spring tips has a very high passive discharge effect, which enables active operation even at low AC high voltage. To increase the range, a small amount of air optionally flows through the hollow spring tip. The air flow additionally serves the continuous cleaning of the emission tip.
The robust all-rounder bar
The VARIO discharge bar blueBAR R50 creates a significantly higher active discharge capacity than most discharge techniques. The isolated ground conductor enhances the E-field at the active tips, contributing to increased production and velocity of charge carriers. Thus, significantly more positive ions and free negative electrons are available than with conventional bars. At the same time, the bars have a high passive discharge capacity. The resistance-decoupled tips ensure good discharge performance and make the bar absolutely short-circuit and touch-proof.