A CENTURY AGO, WHEN THE AGE OF THE AUTOMOBILE WAS JUST BEGIN ning, few people worried about what would happen when cars began to wear out. After all, there were plenty of junkyards, where horse carts and carriages and all the other conveyances of premotorized America ended their days. If anyone did think about it, they probably figured that old automobiles would be taken apart and sold for scrap, just like their predecessors. The problem, if it was a problem, would be small in any case, since autos were still a luxury item that sold in tiny numbers.
Sometime around 1927, when Ford sold its fifteenmillionth Model T even while losing its status as the world’s largest car manufacturer to General Motors, Americans began to notice that their country was accumulating an awful lot of worn-out auto bodies. Some were dumped in rivers or lakes; others were put in landfills or abandoned mines or quarries; but most were simply piled up in unsightly heaps. More cars were being sold than ever before, and they tended to be bigger and heavier than the old models. The scrap market absorbed some of the bodies but far from all. Something had to be done.
In scrapyards, auto wreckers were using the same basic process they would continue to follow for most of the century. First they removed salable parts, including engines, transmissions, batteries, wheels, and some nonferrous diecast components, such as copper radiators. Next the glass was smashed and sent to a landfill, and what was left of the hulk, containing large amounts of upholstery, wood, and rubber, was set on fire. Finally the unburned remains were cut up and sold as scrap.
Every step along the way created dreadful eyesores and polluted the air and water. Moreover, since the car-wrecking business was dispersed and labor-intensive, it could easily become unprofitable when the price of scrap metal dropped. Following downturns in the market, car bodies piled up even higher. Auto wreckers and scrapyards sometimes charged a fee to accept them, leading frustrated car owners to simply abandon their jalopies in the street.
The 1930s saw the first step toward large-scale, systematic recycling of cars. As before, the immediately salable components were salvaged; glass, cushions, and other easily removed items were stripped; and what remained was burned. But now, instead of being cut up, the hulk was crushed into a “bundle”—a compact block that might weigh half a ton to a ton or more. Some of these blocks were sold to steelmakers, who mixed them with raw iron in their furnaces. Under the open-hearth process, which was then prevalent, six to eight hours were needed to process a batch of steel. During this time, most of the nonmetallic impurities either went up the smokestack or were removed in the form of slag.
A typical pre-World War II steel mill used 40 to 60 percent scrap, but most of it came from sources other than cars. Many steelmakers refused to accept automotive scrap because of its high levels of copper, which is present throughout a car’s body in wiring, fuel lines, and instruments. Removing the copper before compacting was too expensive, so No. 2 bundles (as those made from automobiles were called) had to be sold at the low end of the scrap market.
During this era the Ford Motor Company, which had already embraced vertical integration to the point of buying its own mines, forests, and rubber plantations, extended the concept to the other end of the product cycle by going into the car-disposal business. Ford paid $20 for each old car traded in on one of its new models, thus promoting sales in the bargain. Dealers shipped the bodies to Detroit, where Ford had engaged the German firm of Logemann to build the world’s largest automobile baler. This enormous machine could crush an entire automobile, with the resulting bales fed into an open-hearth furnace. Unfortunately, the baling plant could not reduce the nonmetallic components to acceptable levels, so the experiment was abandoned after six months. Ford eventually sold the baler to the Proler Steel Corporation of Houston, which persuaded Lone Star Steel to modify its furnace to accept the baler’s output.
During the 1950s, as post-World War II cars started to be replaced, several factors combined to make No. 2 bundles even less attractive to steelmakers. First, design changes increased the fraction of nonmetallic components and nonferrous metals in cars. Particularly troublesome were lead, chromium (which was in vogue as a decorative element), and tin (which was used for repairing dents). Even in small amounts, these elements can seriously alter steel’s performance. At the same time, the basic oxygen furnace began to replace the open hearth across the steel industry. (Today open-hearth furnaces have virtually disappeared everywhere outside the old communist bloc.) In contrast to the open hearth’s slow simmer, a basic oxygen furnace processes a batch of steel in less than an hour, since most of its starting material is molten iron direct from an on-site blast furnace.
Together, these changes allowed steelmakers less time to remove more impurities. The problem was especially great with contaminants that lay buried deep inside a densely compacted bundle. For these and other reasons, most basic oxygen furnaces in the 1950s and 1960s used only 10 to 35 percent scrap. Faced with a shrinking market, the scrap industry grew desperate for ways to separate the steel from the rest of a car’s body, purify it, and break it into small pieces that would melt more readily.
Another innovation that lent urgency to the problem was more positive for scrap dealers: the advent of hydraulic “auto sizers” small enough to be mounted on trailers. These units flattened car hulks down to a manageable size for hauling, so that a single trailer could transport as much as 10 tons of scrap. Auto sizers allowed a dealer to cover a circuit of auto wreckers and salvage yards, collecting hulks for recycling at a large, central facility. Scrap processors liked the way sizers increased their supply of hulks and decreased the need for storage space. However, the pre-crushing of hulks made it even harder to remove contaminants before processing, so it became all the more important to find ways of removing them afterward.
To meet this challenge, the industry developed new equipment and technologies. For example, a 1960s Japanese invention, the Carbeque, baked a car hulk rotisserie-style at successively higher temperatures to melt out different metals. A similar scheme was invented by Harris Press & Shear of Cordelle, Georgia. As with many clever engineering solutions, neither of these processes was cost-effective.
When regulations banned the open incineration of scrap automobiles, processors switched to enclosed furnaces with emission controls that greatly reduced the smoke problern. Even so, incineration of automobile hulks was a risky business. The combination of paint, plastics, aluminum, and other materials that burn or evaporate turned the exhaust into a witch’s brew. The need was clear for a solution that did not require incineration.
Industry leaders began to recognize the potential of machines that would cut scrap into pieces and separate out the steel. Such machines are known as shredders, and the first ones had been invented decades earlier as specialty items to serve a market that had nothing to do with steel: copper production. When dealing with low-grade ores, the most efficient way to extract the copper is to leach it out with acid and then add iron to the solution. The iron displaces the copper, causing it to precipitate. This method is also used to extract small concentrations of copper from water that has been used for washing and processing ore.
Scrap is the usual source of iron for this process. Clearly, the greater the surface area of the scrap, the more effective it will be. So in the 1920s a Los Angeles firm, L.A. By-Products, developed machines that would tear chunks of scrap steel—from any source, not just auto bodies—into smaller pieces. Tin-coated steel cans were the most common feedstock.
Besides serving copper processors, this firm also sold shredded scrap to steelmakers. Since the open-hearth method still dominated, ease of melting was not a priority, and the shredded pieces were often compressed back into bundles for transportation. But thanks to the company’s pioneering work in magnetically separating ferrous from nonferrous material, these bundles were purer than those made from untreated car hulks. The market for such scrap was still small, and since cars were not the only source of raw material for shredding, there was no reason to build a machine that could process entire cars at once. Instead, they were cut up beforehand.
Except for a brief flurry of interest during World War II, shredding remained a minor corner of the scrap industry. As the postwar building boom kept demand for steel high, even small dealers found a ready market for minimally processed scrap through the mid1950s. But the good times came to an end with the recession of 1957-58. As automobile hulks piled up and the shift to basic oxygen furnaces continued, a few scrap processors began to appreciate the possibilities of shredder technology.
The pioneer was Proler Steel Corporation of Houston, the same company that had earlier bought Ford’s surplus auto baler. Its chairman, Israel Proler, had learned shredding at L.A. By-Products as part of a wartime government assignment. Building on that experience, he and his brother Sam designed a shredder specifically to serve the steelmaking industry, one that would turn car bodies into scrap suitable for basic oxygen furnaces. In 1958 the company opened its first shredding plant, with the revolutionary machine hidden behind thick steel walls to prevent industrial espionage.
After the shredder was patented, Israel Proler described its workings at a 1960 meeting of the Institute of Scrap Iron and Steel (today the Institute of Scrap Recycling Industries, or ISRI). It used a modified hammer mill, of the sort that crushed rocks in quarries, to tear the cars apart and magnetic and other methods to separate the steel. Proler said his scrap not only came out of the shredder in convenient pieces, fist-sized and weighing roughly a pound, but was 90 percent steel, as opposed to regular bundled automobile scrap, which was in the 65 to 80 percent range. He was already selling “Prolerized” scrap to Armco Steel of Houston for $8 to $10 a ton more than conventional scrap.
Other scrap processors using their own technologies flocked to the market. The biggest of them was Luria Brothers & Company, which started with a plant in the junked car capital of the world—Los Angeles—and expanded during the 1960s to Detroit, Cleveland, and other industrial cities. Newell Industries of San Antonio and Universal Engineering of Cedar Rapids, Iowa, were other early entrants, along with German and Japanese firms.
Shredding technology can be applied to any kind of scrap, but by far the biggest source today is automobiles. A successful automobile shredder must do three things: reduce a huge hulk of steel—often consisting of high-strength alloys, as in engine blocks and axles—to small pieces; separate the ferrous metal from the nonferrous; and remove the small metallic fragments, known as fines, from the residue, which includes plastics, rubber, foam, fabric, wood, insulation, glass, and dirt. A typical shredding system might be 1,000 feet long and cover an acre or more. The shredder’s housing and the removable liners in the main shredding area are made of steel plate as much as 4 inches thick. The machinery weighs a total of several hundred tons, and its cost may run into the tens of millions of dollars. Supplemental equipment includes magnetic separators, air knives, cyclones, trommels, cranes, and other accessories. Additional millions must be spent on noise abatement, waste treatment, antivibration, and other environmental compliance measures.
Before an auto body enters the shredder, salable parts are removed, its fluids are drained, and the interior and trunk are inspected to see if any irregular items (especially tires and lead batteries) have been left there. The hulk is then flattened and fed into the shredding apparatus on a conveyor. Inside, many hammers (several dozen in the larger models) attached to a rotor beat the hulk into pieces against a breaker bar or grates. The rotor, which can weigh 25 tons or more, typically turns at several hundred revolutions per minute. The banging continues until the pieces are small enough to fall through a grating. The parts that perform the shredding are made of especially tough alloy steel, but even so, a shredder will typically lose a total of half a pound off its hammers with each car that it processes.
The original shredders required welders to enter the unit every night to renew the hammer edges. Then in the 1970s new designs were developed with removable hammers that could be replaced and have their edges renewed in the shop. Terry M. Francis of Riverside Products, a division of the Sivyer Steel Corporation, was one of the chief innovators in this area. (Riverside also produced a 60-ton rotor for the largest shredder in the world, which processes 1,600 autos in a day.) The most popular installation in use today has a 3,500-horsepower electric motor and removable hammers that weigh 270 pounds apiece. No welding is necessary to replace them. After the hammers have been used for 500 tons on each of their two sides, they are sent to the manufacturer to be melted and recycled into new hammers.
With all types of shredders, inexpert maintenance can be disastrous. At the official inauguration of one machine, for example, 5 tons of scrap were fed in, but 10 tons came out. An inspection revealed that the wear plates, which had not been bolted properly, had been ripped out of place by the violence of the shredding process and extruded as scrap.
As a car is being shredded, dedusting apparatus extracts smoke and small particles of dirt and other nonmetallic components. This apparatus may be either dry (relying on air currents and filters) or wet (spraying in water to precipitate the dust). An operator monitors the entire shredding process to see that it is running smoothly. If the main rotor jams, he can reverse its direction, and if a large, unshreddable piece appears, he can eject it. Operators usually rely on sound to tell them when something is wrong.
After the car has been reduced to pieces of manageable size, the next step is to separate the ferrous portion from the nonferrous metals and nonmetallic material. Some of the nonmetallic portion will already have come off as dust, and most of the rest can be extracted with blasts of air that leave the metal behind. After that happens, or sometimes before, the steel is magnetically separated from the rest of the scrap and diverted to a conveyor belt, where workers visually inspect it and pick out nonmetallic and nonferrous pieces that have slipped through. Copper, often in the form of wiring entangled with the steel, is of particular concern, since most steel mills require a copper content well under .5 percent in their scrap.
The materials left behind are known collectively as auto shredder residue (ASR). A typical composition might be 33 percent fabric and batting; 22 percent plastic; 20 percent sponge and foam; 19 percent glass, sand, and dirt; and 6 percent small-mesh metal fragments (mostly brass and zinc). Over the last three decades, much work has been done in salvaging as many useful components as possible from ASR. These methods take advantage of the different properties of different components, including size, density, melting point, and coefficient of friction.
A unique approach to separating the wheat from the chaff was patented in 1975 by Prof. Richard D. Stafford of Vanderbilt University and installed at a scrap-processing facility in Nashville. It was a steel tower with a series of curved descending troughs that operated on gravity and friction. The exit conveyor of an on-site shredder fed ASR into the top of the tower, and the troughs separated the metallic components into various grades according to their densities. The remaining material fell to the bottom and was removed for disposal at a landfill. The Stafford Slide was a clever solution, but in the end its friction-based separation method was not complete enough to be reliable.
In 1979 a Dutch firm, Dalmeijers Metalen bv, developed a system known informally as “sink and float” to recover aluminum scrap. It used liquids in a centrifuge to separate materials based on their specific gravity. Other firms experimented with water elutriation (which amounts to mixing ASR with water and skimming off the materials that float to the top, sometimes with the aid of an upward air current) and other density-related methods. By the 1980s it was possible to remove the metals from ASR so thoroughly that the remaining material, called fluff, was acceptable in several states for use as daily cover in landfills.
As the industry grew, the development of shredders split into two directions. Newell, Universal, and other firms concentrated on building larger and more powerful machines, with motors up to 6,500 horsepower. These behemoths, which sometimes must be enclosed in air-conditioned rooms, can take in a complete car, flatten it, and reduce it to “corn flakes” in one minute. Other manufacturers developed smaller units to process cars that have received a rough preliminary chopping from a machine called a ripper.
All these advances in processing scrap have been crucial to the biggest development in steelmaking of recent years, the shift to mini-mills. As the name implies, mini-mills are much smaller than the huge integrated works of traditional steelmaking, which take in raw ore and coal and turn them into finished steel products. Mini-mills rely entirely or almost entirely on scrap as their input, eliminating the need to process these raw materials. The price of scrap is usually higher than that of iron ore pellets, but mini-mills more than make up the difference on other costs. Little or no coke is required, and since their furnaces run on electricity, mini-mills burn no fuel.
The first few mini-mills were opened in the 1930s, often to produce alloy or specialty steels in small amounts. After World War II, their number increased slowly but steadily. Most of them concentrated on turning out one or two finished products, unlike integrated works, which make a whole range of goods. The most common mini-mill product was (and remains) reinforcing bars for concrete, which allow fairly generous tolerances for impurities. In recent years, mini-mills have diversified into structural steel shapes, wire rods, sheets, tubes, and other products.
The growth of mini-mills picked up during the 1960s, and when the American steel crisis hit in the 1970s and 1980s, they proved much better able to adapt to changing times than old-line plants. Among other advantages, mini-mills do not need to be located near supplies of ore and coal, because their raw material, scrap, can be found virtually anywhere. Mini-mills can thus be established wherever there is demand for their products, giving them a great advantage in transportation costs over integrated facilities. Today electric furnaces turn out nearly half the steel produced in America, and the great majority of them are located in mini-mills.
To be sure, not all the scrap used by mini-mills comes from automobiles or other postconsumer uses. Part of it—more than half, in some cases—is “home” scrap left over from the mill’s own operations. As production methods become more efficient, including a shift to continuous casting, this becomes less plentiful. Another source is industrial (or “prompt”) scrap from other companies’ manufacturing processes, and a third source is postconsumer (or “obsolete”) scrap.
Mini-mill operators use computers to mix and balance the various items in the feedstock, and depending on a variety of factors, a heat in an electric furnace may take one to two hours. Whatever the source of scrap, uniformity and a low level of impurities (or, in the case of certain alloys, carefully controlled levels of specific impurities) are important. Big, unwieldy chunks of varying composition are not acceptable for these plants. Shredded steel, with its small size, free flow, and warranted specifications, has been a vital factor in the success of the mini-mills.
Although car hulks account for 90 percent of shredded steel, the shredding industry has an impressive record in dealing with another potential solid-waste problem—appliances. Refrigerators, ovens, washers, and dryers, known in the trade as “white goods,” have long been a problem because of their porcelain or durable paint finishes. These resist corrosion so well that appliances can last for centuries in landfills. For a long time, however, it was impractical to process them as scrap by conventional means because of their bulk and low steel content.
Shredding made it possible to recycle these items, though it required some accommodations. One popular colored finish contained cadmium, and most electrical controls contain mercury, both of which are health hazards even in small amounts. The shredding industry persuaded appliance manufacturers to eliminate the cadmium, and processors learned to remove electrical controls by hand before shredding. With these changes, steel from white goods can be recycled, and the residue is acceptable in landfills, where it takes up much less space than whole appliances. Some of the many other items that are processed in shredders are bicycles, office furniture, structural forms, and vending machines.
Even beyond these areas, shredder technology has greatly advanced the recycling and solid waste management industry. The mechanical reduction of many types of waste into manageable sizes has been a great asset in decreasing the space it occupies, making it easier to dispose of, and converting parts of it into useful products. Today shredders are used to recover usable material from demolition waste and old pavements. Other types can recover materials from used tires. Inverse magnetic separation systems, which remove aluminum cans from the refuse stream, depend on shredders to cut large items into bits so that they will flow easily in conveyors. Similar methods are used to shred plastic items before separating and recovering the different types.
As the amount of aluminum in car bodies increases, recyclers are concentrating on improving their techniques for recovering that metal. One goal is to separate cast aluminum from wrought aluminum, which has a lower level of impurities. A method currently yielding good results is the “hot crush” technique, in which mixed aluminum scrap is heated to just below its melting point and then subjected to pressure. If the temperature is properly controlled, cast pieces will soften to the point where they are easily fractured, while wrought pieces will hold their shape. The smaller cast fragments can then be separated out by their size. Heating also works to remove paints and coatings from the aluminum. This method depends on having pieces of similar size to begin with, which requires a shredder.
Other changes and challenges lie ahead for the shredding field. The steelmaking industry, still its biggest partner by far, is now seeing a convergence between mini-mills and the traditional integrated works. Mini-mills are getting larger and diversifying their product lines, sometimes using pig iron or specially treated iron ore pellets in place of scrap as their feedstock. Diversified works, meanwhile, are adopting electric furnaces and eliminating coke and blast furnaces from their processing, allowing them to run smaller units economically. With the trend in all areas of manufacturing toward smaller lots and greater customization, the scrap industry will be pushed even harder to meet changing specifications and environmental regulations.
A growing challenge to the scrap industry is the introduction of new combinations of materials, such as plastic bumpers with steel inserts, that will require modified techniques or apparatus. Another concern is radioactive scrap; even a small amount can contaminate an entire heat in a steel mill. Many processors pass all loads of scrap before a detector that sounds an alarm if it detects any radioactivity. It may be jarring to think of huge, noisy industrial plants playing a key role in preserving the environment. Yet by converting an ugly disposal problem into a valuable resource, automobile shredders have contributed to this end in three ways: reducing the quantity of solid waste, reducing the need to mine iron ore, and decreasing coke production by steelmakers, another abundant source of pollution.
The advent of shredders caused the scrap industry, long a haven for small-to-medium-sized firms, to become much more centralized. In so doing, it has helped the steel industry become much less so. The results have benefited all sectors of the economy. In 1997 some 15.4 million new vehicles were sold while 13 million old cars were destroyed in America’s more than 200 shredders. Each shredded car yielded about a ton of scrap, amounting altogether to about 20 percent of the nation’s total scrap consumed. These figures help explain why the automobile, despite its bad reputation among environmentalists, should be appreciated as the most successfully recycled item in history.