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Fowler Associates Labs

 

 

Static Fire Stories Articles & Technical Papers Current News

The Final Frontier

Paraphrased and dramatized by Cynthia Waters

In August of 1980 in the southeast United States, problems were being experienced at a polypropylene plant. Strange things were happening around a film slitting machine.

David Swenson of 3M Electrical Specialties Division in Austin, Texas was called in to investigate. Little did he know that he was about to enter the final frontier. When Dave asked what type of problem they wanted him to look at, he was told that he would have to come to the plant. They could not explain it over the telephone. They did tell him that they were experiencing problems with contamination of wide web film as it was being run at high speed, converted (split) into "film jumbos" with a width of 3' x 5' for coating with adhesive to make tape. Dave didn't see what was so unusual about film being contaminated by dust, flies, other insects and... birds. "Birds"?

Now they had Dave's attention and he didn't hesitate to go to the plant to see for himself how birds could be caught up in film.

The Polypropylene web was 21 feet across - almost the width of three lanes of traffic on the interstate.  The film ran from one roller up 20 feet to another roller; across 15 feet to a third roller; down 20 feet to a splitter; and was then wound onto two rolls. It formed a huge dynamic "tent". On the morning that Dave intended to measure the static electricity inside the web tent , the temperature was 80F with a relative humidity of 75 to 80%.

As he walked toward the web with his field meter in hand, the machine operator said "I wouldn't do that if I were you. Strange things happen inside the web tent this time of day."

Dave paused and thought about what the man had said but he was there to do a job and that was what he intended to do. You see, Dave is a very brave guy. Besides, it was just film running on a splitting machine. He had seen that many times and nothing seemed particularly unusual that morning. That is, until he looked down at his static field meter.

With a 200kV @ 12" measurement device, the voltage measurements were off the scale and he was still 20 feet away from the web! For the meter to be pegged at that distance, the amount of static electricity had to be in the Megavolt range. He thought to himself "Van de Graaff would be proud!"

Since he had come this far, Dave decided to enter the web anyway. As he did so, the hair on his head, arms and entire body began to stand on end. Even worse, he began to feel like sparklers were hitting him all over his body. It felt like burning sensations at hundreds of points all over his being. (brave? - hummm?) At exactly one-half way into the web, David slammed into a wall that was both invisible and impenetrable. It felt like he had hit a force field like he had seen on Star Trek.

Although he knew this was Coulomb's Forces - the law of static attraction and repulsion - he was held in place for what seemed like ages as he tried to grasp what was actually happening to him. It's one thing to know about Coulomb forces, but it is quite another to feel them with such gusto. When he finally came to his senses, he had to literally "peel" himself off of the invisible wall.

As he backed out of the web, he saw a fly drawn right up into the film and wondered if conditions ever existed inside that web that could actually draw a person up there as well. Dave hurried to talk with the Plant Manager and excitedly explained what had just happened to him. The Plant Manager agreed to go to the web to see for himself what was going on. By the time he was able to go, however, it was later in the day and the temperature and relative humidity had risen. He was able to walk into the web and from one side to the other without experiencing anything at all unusual. He told Dave that he thought he was simply hallucinating. When the machine operator corroborated Dave's story, the Plant Manager agreed to meet early the next morning to see if the same conditions would exist as they had experienced earlier in the day. They met bright and early the next day. As the Plant Manager entered the web, his curly gray hair immediately straightened. As he strutted toward the center of the web, his confident gait suddenly came to a complete stop as he hit the wall of invisibility.

Once he peeled himself off of the force field wall, a shaken Plant Manager came out of the web and exclaimed...

that he "didn't know whether they should fix it or sell tickets".

They decided to fix it.

Conclusion Static Electricity can cause some very strange and often difficult to explain phenomena. It is easily controlled if a commitment is made. This nuisance can be reduced to a non-nuisance level by proper analysis and installation of suitable equipment, at a very low cost.

 

Corrective Action An induction static eliminator was installed across the web at the unwind. The static electricity was immediately reduced throughout the process to less than 50kV (from MV's). It was then possible to make measurements in the rest of the area. Additional induction units were also installed at the jumbo wind-up areas which resulted in less than 5kV at conclusion.

Editor's Note We would like to hear your explanations for Dave's adventure. Please give us any similar experiences you may have had. We will publish these in the next issue. Maybe this will become a series - "Weird Phenomena."

 

Response received via e-mail September 22, 2001 from reader Melissa Georgiou

I was searching the internet to find a similar situation that I had encountered and your article on the invisible wall is very interesting. I encountered an invisible wall, but it felt more like a cushion which was vertical and got denser the farther I pushed on it. It lasted for about 30 secs and I could not walk through it. It happened at dusk in England during fog and high sunspot activity. I've been trying to explain it since. I am so glad some one else has experienced a "star trek" like force field and I hope you will encourage your engineers to perfect the effect instead of fixing it by decreasing static.

Sincerely, Melissa Georgiou

 

Response received via e-mail June 7, 2001 from reader Peter Thomson

EUREKA - I have found it. I have been studying the implications of charge being moved at high speeds. The math is very complex so it is hard to predict what sort of experimental setup is required to demonstrate different aspects of the phenomenon. But I think your members have practical experience of this phenomena, and my theory may provide insight into practical ways of predicting and preventing problems.

First, a little bit of basic physics, often overlooked. When you consider two charged particles with the same charge, when stationary they will repel each other, but when moving in parallel each moving charge creates a circular magnetic field round itself that results in mutual attraction. This is normally demonstrated in the attraction between two wires where negative charge is moving in parallel, but applies equally to charge moving in a paper or plastic film on a production line or in a moving charged dust cloud, or a thunder storm.

The forces created by an electrical current in a wire are produced in proportion to the speed of electrons through a wire. Because of collisions and random movements of electrons in the wire, the overall speed of the electrons, or drift speed is quite slow. http://hyperphysics.phy-astr.gsu.edu/hbase/electric/ohmmic.html (but the density is high). A 1 volt potential in a pure copper wire will produce a drift speed of 0.0043m/s This is less than half a centimeter in a second. One definition of the amp and force is based on this. 1 amp produces a force of 2*10^-7 Newtons per metre of wire when the parallel wires are 1 meter apart. By contrast production line speeds for paper and plastic film can be over 100 times faster and air flow in a tornado can exceed 1000 m/s.

Because electrostatics and electric current are often taught separately in schools, the effects of moving charge are often forgotten about. The effects of moving single charge become most dramatic when a charged vortex is created. Charged particles in front of or behind another particle will experience strong forces of repulsion, but the charged particles moving in parallel are very strongly attracted together! The net result is to form a charged sheath vortex, where a sheath of particles rotates about an open core. The sheath cannot contract into the core because of repulsion round the core, and the opposite sides flowing in opposite directions repel, Neither can it expand outwards from the sheath because of the attraction between particles moving in parallel. The result is a very tightly bound sheath of particles and air molecules. If new charged particles are being delivered to this rotating sheath vortex they will be bound into the sheath with the build up of huge electrical potential that doesn't discharge because of the forces of attraction generated by the movement of charged particles.

Your article describes the ideal situation for setting up a charged sheath vortex. The high speed
web is delivering a constant supply of the same charge to the tent created by the web flowing up and over the tensioning rollers. Within this tent, friction with the moving film causes the air to start rotating and initially this air will be given the same charge as the film. The rotating charged air will now start to create the attractive forces between particles moving in parallel and will draw in more charge from the moving plastic web. This process will continue and will produce a charged vortex sheath spinning in the middle of the tent. This would normally be invisible and could also feel like a solid wall with a well defined edge (and a soft center). You certainly wouldn't push it out of the way!

The charged sheath vortex could be made visible by releasing smoke streamers into the area.

Reference http://uk.geocities.com/tornadodrive/

 

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