Science

How did a 3m tape manufacturer create an “invisible wall”?

American writer Kurt Vonnegut wrote that “science is magic that works.” It opens up a world of realities and opportunities waiting to happen. One such scientific incident involves a story told by David Swenson of the 3M adhesive tape factory, in which workers experienced a glitch and encountered an invisible wall that wouldn’t let humans through. No, it’s not a Hollywood science fiction movie. This supposedly happened in South Carolina during a late summer day in 1980 and can be explained entirely by the laws of physics.

What was going on in the factory before the invisible wall was built?

How did a 3m tape manufacturer create an "invisible wall"?
3M facility PP film manufacture set up.

It was a very wet August day of 1980, and business was going on as usual. Simply put, plastic films were run at high speed and cut into huge rolls to be coated with adhesive to make a tape. But to explain it in more detail, 50,000-foot polypropylene (PP) film was cut in 20-foot-wide rolls (about the width of three lanes for highway traffic) and transferred onto many smaller spools. This PP film was ejected from the master roller at a very high speed, flowing upwards 20 feet to the upper rollers, passing 20 feet horizontally, and finally traveling down towards the shredder. There, they were wrapped in much shorter rolls.

According to Swenson, this entire process formed a dynamic, cube-shaped tent with two walls and a roof of about 20 square feet. The speed of these rollers was 1,000 feet/minute, or about ten miles per hour. The invisible wall in the area below the fast-moving sheet of electrically charged film was created in the middle of the tent.

How did David Swenson describe the invisible wall?

How did a 3m tape manufacturer create an "invisible wall"?
Invisible wall

David Swenson of 3M Electrical Specialties in Austin visited the 3M South Carolina plant to investigate. According to Swenson, when he entered the factory floor and was still 20 feet away from the equipment, he blasted his hand-held electrometer to the full 200 kV/ft range. His hair also began to stand on end, and sparks could be felt hitting him from all sides. When he tried to walk down the aisle of the moving movie, he ran into an invisible and impenetrable wall.

She felt an invisible force field blocking her. Although he could lean his weight forward, he could not pass. Anyone near the wall was unable to turn around and had to walk backwards to get far enough from its impact. Swenson also observed a fly being pulled into the electrically charged field. In his report, he stated that the force was strong enough even to suck in birds.

“I didn’t know whether to fix it or sell tickets,” said the production manager.

How did a 3m tape manufacturer create an "invisible wall"?
Static electricity

Mr. Swenson described the phenomenon in his report, but the factory production manager did not believe it. The wall was gone by the time he arrived, but the factory workers were able to recreate the same event another day during the same early morning hour. It was the same conditions as the previous day. The experiment was a success, and the invisible wall appeared again, this time even stronger! With electric charging, even the production manager’s short, curly hair has become straight! With a laugh, he exclaimed that he didn’t know whether to fix it or sell tickets. But of course they fixed it.

How was the invisible wall created?

Experts are divided on the veracity of the Invisible Wall story. Some say that no matter how amazing it may sound, science has a reasonable explanation for it. But there are others who think it’s weird for a wall to push humans back because electric charges can attract neutral objects, but they shouldn’t repel them. Whatever the case, most experts believe that, under ideal circumstances, it is possible.

One dangerous aspect of these mills, apart from the fast-moving rollers, is the huge static charge that is produced when the plastic sheets are loosened. This explains why Swenson’s meter is bound at 200 kV/ft as soon as it approaches the field. The amount of static electricity has to be in the megavolt range for this to happen.

This phenomenon can be explained with the help of a phenomenon called “Coulomb forces”, or electrostatic force, which is the law of constant attraction and repulsion of particles and objects due to their electrical charges. A balloon sticking to a wall, nylon clothing that emits static electricity, a photocopier, a comb that attracts pieces of paper, or we bump into a car door on a dry day are all examples of Coulomb forces.

In the case of the 3M factory, the electric charge was moving at a very high speed. Two stationary objects with the same charge repel each other, but when moving, they create magnetic fields around them that attract each other. This process eventually creates a vortex charged envelope, which is a perfect position to create an invisible wall.

Ionized air and static electricity may have helped create the invisible wall.

How did a 3m tape manufacturer create an "invisible wall"?

In the 3M factory incident, a high-velocity drum was delivering a steady supply of the same charge to the dynamic tent-like structure created on the factory floor by a high-velocity moving film. Inside the tent, friction caused air to circulate with the same charge as the plastic film. Since the particles were experiencing repulsion due to the same charge, the sheath could not contract there. Nor can it expand outward because this electrically charged air begins to create attractive forces between parallel moving particles as it draws more charges from the moving plastic web.

This creates a tightly bound sheath of air molecules and charged particles. And every second, newly charged particles are added. Also, due to the constant movement, discharge also does not occur. This tight casing is usually invisible and feels like a solid wall with a defined edge and a soft center. On the day of the invisible wall, the temperature was 80 degrees Fahrenheit with a relative humidity of 75 to 80%, which also created the ideal conditions for this phenomenon. The wall removal solution was easy and cost effective. The workers fixed the grounding problem on the machine, and the invisible wall was gone.

Swenson later stated in a talk at the Electrostatic Discharge Seminar Sessions in 1995 that despite many inquiries, explanations and numerous attempts, the Invisible Wall has never been recreated – at least to his knowledge! Even the US Department of Defense was interested in monitoring the phenomenon, but it never succeeded!

Smith

Tricare west is a global news publication that tells the stories you want to know.

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