Eye on electronics

Motor,  Nov 2002  by Dale, Mike

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Advances in electronic automotive material recycling methods ensure that even more of what goes around will come around (again and again) in new-car production.

When it comes to recycling, the automobile is a genuine success story. For those vehicles that are recycled, more than 75% of the material is made reusable. Almost half the steel currently made in the U.S. is made of recycled scrap metal. Because this steel goes into new cars, today's vehicles already have a significant content of recycled materials in them.

There are new goals on the horizon. The European Union is pushing for vehicles to be 95% recyclable by 2007. So there's talk of adding $100 to the purchase price of each vehicle to make sure there's money to recycle it at the end of its useful life. Under their new laws, manufacturers will have to take back their vehicles and recycle them.

Electronics has a major role to play in all of this. On the one hand, sophisticated electronics is being used to separate the various materials used in the vehicle. On the other hand, it's the electrical system of a vehicle that's one of the hardest parts to recycle. Let's look at some of the neat things being done to change that.

The first step in vehicle recycling is the salvage yard. As you might guess, these places make their money by selling parts from late-model wrecks. A working alternator has a much higher value as a used part than it ever will have for its metal content. Trouble is, for the average 15-year-old vehicle, there really isn't much that's worth selling. What would you be willing to pay for a used engine with 175,000 miles on it?

The second step in the process is the automotive shredder. The tires and battery are removed and the vehicle is drained of all fluids. Everything that remains is dropped in the shredder. One located near Detroit can shred a car down to pieces smaller than your hand in less than a minute.

What comes out on a conveyor is a mix of plastic, steel, iron, aluminum, rubber, copper, etc.-- all the materials you know to be in the vehicle. Electromagnets make separating the ferrous scrap-iron and steel-easy.

It's the separation of the nonferrous metals that makes use of electronic technology. The device that does this is called an eddy current generator, a rollerlike device that can be located near the end of the conveyor belt that carries what's left of the debris stream after the iron and steel have been removed. Inside the roller are a series of powerful rare earth magnets, which induce currents in the electrically conductive particles of aluminum and brass. This current in the nonferrous metals causes a magnetic field to form around the particles. Since this field has the same polarity as the magnets, the particles are repelled up and away from the main debris stream.

The trajectory of the particles depends on many factors, including their size and shape and relative electrical conductivity. If the particle sizes are reasonably uniform, it's possible to separate the different metals by using metal shields or splitters that separate the trajectories.

What's left after the metals are removed is called ASR, or automotive shredder residue. This consists mostly of plastics, but also contains some window glass, dirt, rubber moldings and other odd items. There are a half-dozen major types of thermoplastics and many, many subvarieties. When they're mixed together like this, they're unfit for reuse.

The Argonne National Laboratory has been experimenting with something called froth technology to reclaim some of this material. The basic idea has been around for a while and has been used in the mining industry. In the case of plastics, it turns out that each major type has its own unique "surface energy." Surface energy is a way of measuring how easily a drop of water will wet to a given surface. If you put a drop of water on the surface of some plastics, it will remain in the shape of a drop. In other plastics, the drop will flatten out and "wet" the surface.

What the folks at Argonne did was start with plastic residue that had been ground to some uniform particle size. They put the residue in a large tank with water and detergentlike materials. Then they introduced from the bottom a stream of bubbles whose size is carefully controlled. When things are set up correctly, a certain size bubble will stick to the ABS plastics in the tank and float them to the surface, where they can be scooped off A different size bubble will float off high-impact polystyrene. Yet another size bubble can then be used to float off other types of plastics. The resulting purity of each group that's separated is reported to be in the 99%-plus range.

The issue of purity is hugely important. If there's such a thing as a dirty little secret of the recycling world, it's the question of what truly is meant by "recycled." If the definition is that the materials are good enough to be put back into new car parts, the sad truth is that there isn't nearly as much of that going on as folks would like you to believe.