MOVED TO: http://www.eskimo.com/~billb/weird/unusual/e-wall.html SESSION 7: SPECIAL SESSION, 17th Annual EOS/ESD Symposium THURSDAY, SEPTEMBER 14, 1995, 8:00 am SESSION 7: SPECIAL SESSION: ELECTROSTATIC CONSIDERATIONS IN INDUSTRY MODERATOR: D. Swenson, 3M 7.7 CASE STUDY - LARGE PLASTIC WEB ELECTROSTATIC PROBLEMS, RESULTS AND CURE, D. Swenson, 3M Company Tremendous static charge generation on a plastic web causes unique physical phenomena and special problems. Solution was simple and cost effective. David Swenson of 3M describes an anomaly where workers encountered a strange "invisible wall" in the area under a fast-moving sheet of electrically charged polypropelene film in a factory. The "wall" was strong enough to prevent humans from passing through. A person near this "wall" was unable to turn, and so had to walk backwards to retreat from it. This occurred in late summer in South Carolina, in extremely high humidity. Polypropelene (PP) film on 50K ft. rolls 20ft wide was being slit and transferred to multiple smaller spools. The film was taken off the main roll, went upwards 20ft to overhead rollers, passed horizontally 20ft and then downwards to the slitting device, where it was spooled onto shorter rolls. The whole operation formed a cubical shaped tent, with two walls and a ceiling approximately 20ft square. The spools ran at 1000ft/min, or about 10MPH. The PP film had been manufactured with dissimilar surface structure on opposing faces. The generation of surface charge imbalance during unspooling was therefor not unexpected, and is a common problem in this industry. On entering the factory floor and far from the equipment, a 200KV/ft handheld electrometer was found to slam to full scale. When Mr. Swenson attempted to walk through the corridor formed by the moving film, he was stopped about half way through by an "invisible wall." He could lean all his weight forward but was unable to pass. He observed a fly get caught in the web. The production manager did not believe Mr. Swenson's report of the strange phenomena. When they both returned to the factory floor, they found that the "wall" was no longer there. But the production workers had noticed the effect as occurring early in the morning when humidity was lower, so they agreed to try again another day. The second attempt was successful, and early in the morning the field underneath the "tent" was strong enough to raise even the short, curly hair of the production manager. The "invisible wall" effect had returned. He commented that he "didn't know whether to fix it or sell tickets." - Bill Beaty A thought: unspooling of film typically generates higher net charge on the film than on the spool. The unequal imbalance indicates that charge is being lost through some unseen path, most probably as ionized air. So, if the charged "tent" of film is negative in the above situation, and if large quantities of positively charged air are being generated, then perhaps the "invisible wall" is a pressure gradient created by ionized air trapped under the tent by electrostatic attraction. Yet this effect would be expected to create a diffuse zone of increasing force, not a "wall" which can trap flies. - B.B. Reference: Article about the "Wall" in ESD Journal MORE THOUGHTS: From: Beaty, William J Subject: Ion cushion Date: Monday, August 12, 1996 4:02PM Also: I wonder if the (I assume) huge quantity of air ions had anything to do with your weird phenomenon. Maybe the "wall" effect involves a plug of ionized air which is held in place by the opposite charge on the film. If so, your repulsion phenomenon would not occur if the "tent" of film was replaced with highly charged metal plates, since the source of oppositely-polarized ions would then be missing. I'm still convinced that the charged film should produce an attractive force upon a human body. Repulsion requires that the human be charged with the same polarity as the PP film, yet induction should produce an *opposite* body charge, so attraction is expected. But if a plug of oppositely-charged air was strongly attracted into the "tent" of PP film, it might produce a significant pressure-gradient in the surrounding air. A fraction of a PSI per foot would be more than enough to prevent someone from walking forward. If this is the origin of the effect, then the repulsion forces you experienced involved air pressure rather than electrostatic attraction/repulsion. This might be an entirely new way to accomplish levitation. Attract a blob of ionized air to an oppositely-charged plate, then use the resulting pressure gradient to lift and manipulate uncharged objects. Sort of like a fluidized bed, but using charged air instead of sand. Speculative, untried experiments: CAN FULL OF AIR: Generate a high-density cloud of negative air ions. Place a large positive potential upon a metal can or bucket. Direct the air ions into the bucket. This should form a charged capacitor, with the air being one plate and the bucket the other. Ground the bucket and see if the contained ionized air is affected. (Once the ion/metal capacitor effect has commenced, you should be able to remove the power supply without destroying the effect.) Drop small, light objects into the bucket to test for pressure-gradient repulsion forces. Inject smoke into the bucket to observe possible "ion wall" effects. Connect the bucket to a large negative potential and observe whether the contained ionized air is disrupted. ION COATED WIRE: Hang a long piece of thin wire from a source of large positive potential, so the wire swings freely like a pendulum. Bathe the wire in the output of a negative ion generator. Remove the ion generator and bring a neutral object near the wire to see if a transparent "ion shell" repels the wire from the object via its pressure gradient. Swing the wire as a pendulum, see if it swings slower because of the extra mass of entrained air. Remove the positive potential from the wire and test to see if the repulsion vanishes (it might not, if the air/metal capacitor is not disrupted!) AIR-THREADS: Connect a single needle to the positive terminal of a source of large potential, so that ion-wind is generated. Bath the needle in the output of a negative-ion generator. Use a Schlerien optical system to observe the needle and its surroundings. The positive ion-wind from the needle will attract a surrounding negative sheath and build a "thread" structure of oppositely charged air. The pressure gradients within the "thread" will be observable in the Schlerien image as optical distortions, and an image of a long thread-like structure will appear. The "thread" will be found to be of neutral polarity. Try building another "thread" generator, but of opposite polarity. What happens when "threads" of opposite polarity interact? Try injecting smoke or water-mist into the thread, and see if it can be made directly visible. Try immersing the thread-generator within a pool of CO2 mist and see if an upwards- directed thread will entrain and transport mist along with it. The "Thread" phenomena was discovered by C. Yost, but the (possible) involvement of opposite ions is my untested speculation. ALIEN SPACECRAFT: Build a low-mass disk-shaped device having negative ion generators around its rim and a large central foil disk on the bottom which is insulated from the rest of the device. Connect power supplies to the ion generators via an umbilical. Connect a large positive potential to the central plate. A region of negative ions will form adjacent to the positive plate, and a pressure gradient will appear. If the total weight of the device is low enough, the device will lift into the air and hover on top of its transparent ion-bubble. If a large enough device could be built, the power supplies could be placed onboard! "THICK" AIR: Suppose a volume of air was entirely composed of equal numbers of ions of opposite charge. They would attract each other and might form a low-density semisolid, like a cross between aerogel and ionic crystal (such as sodium chloride.) Suppose a 3-dimensional array of small volumes of ionized air could be produced. Volumes of opposite polarity would experience attraction forces and the array as a whole would be neutral, and would be at higher pressure than ordinary air. The array might act like a sort of invisible "solid" which would cohere together, resist disruption, eject intruding objects, and would move as a unit when pushed. It would act somewhat like an invisible semi-solid mass. The organized-ion air could take the form of positive threads in a negative medium, positive spheres in a negative medium, alternating layers of positive and negative, various close-packing arrays of opposite polarity, etc. A gas composed mostly of positive and negative air ions (few neutral molecules) might exhibit a behavior very different than ordinary air. It would exhibit increased pressure, density, and refractive index. It would be heavier than normal air, and might be directly visible as an area of optical distortion in the air. The increased attraction between ions might raise the boiling and freezing temperatures to anomalously high values. BURST A BALLOON: Fill a large plastic bag with air, connect the two ends of a hollow plastic pipe to the bag, then install a small fan and an ion generator inside the pipe. When the ion generator is operated, the ionized air within the bag will self-repel and exert force upon the walls of the bag. The pressure should increase linearly as long as the ionizer is operating, and the bag should burst from electrical pressure. DIPOLE AIR: Build two of the above 'bag' devices, but having opposite polarities. When operated, the attraction forces between them should grow to a large value, until the bags tear loose from their moorings and slam together. ELECTRIC DIRIGIBLE: Fill a hot-air balloon with air, then install a negative ionizer and let it run until the contents of the balloon become highly charged. The balloon should experience a lifting force as the positively charged sky attracts it and the negatively charged earth repels it. Is the force too feeble to lift a dirigible? Then try charging soap bubbles? ((((((((((((((((((((( ( ( ( ( (O) ) ) ) ) ))))))))))))))))))))) William J. Beaty SCIENCE HOBBYIST website billb@eskimo.com www.eskimo.com/~billb EE/programmer/sci-exhibits science projects, tesla, weird science Seattle, WA 206-762-3818 freenrg-L taoshum-L vortex-L webhead-L