November/December 1996
The use of powder metal products is growing. That’s the good news. The bad news is that these products pose potential recycling problems. Fortunately, the search is on for solutions to this complex situation.
By Eileen Zagone
If you’ve never heard of powder metals, join the club.
Even though products have been made via powder metallurgy for centuries—ancient Egyptian and Incan civilizations, for example, used this process to make tools and jewelry from powdered iron and precious metals—such products are virtually unknown and largely invisible to most people today, including scrap recyclers. The majority of metal processors, in fact, have probably handled powder metal parts without even knowing it. That’s because most such parts are small, they don’t look significantly different from forged or machined parts, and they are often enclosed in larger products, particularly automobiles.
But scrap recyclers are almost certain to become more aware of powder metal products—and run across them more frequently—in coming years. The reason is simple: Powder metallurgy is a relatively efficient, economical, and quick way to achieve a near-net-shaped part that requires little subsequent machining, thus saving time and money. Such attributes have made powder metals increasingly popular with many manufacturers, especially the cost-conscious auto industry, which has steadily boosted its use of powder metal parts in recent years, with plans to continue using more and more.
So what’s the problem?
According to some minimill executives, the copper content of ferrous powder metal parts can create problems in their melting process, potentially ruining heats and affecting their finished steel. In their view, some action needs to be taken to prevent the problem from escalating, and scrap recyclers could potentially be called on to be part of the solution.
Yet, with automakers and other industries set to use more powder metal parts in their products, the problem is almost sure to become more pronounced in the future.
The Life of the Part
The first fact to know about powder metals is that they come in a variety of types, including iron, tin, nickel, copper, aluminum, bronze, brass, stainless steel, titanium, tungsten, molybdenum, tantalum, and alloys. Iron powder metal is by far the most common, with shipments in 1995 totaling 347,170 tons, or about 79 percent of the 437,774 tons of powder metal shipped overall, according to the Metal Powder Industries Federation (MPIF) (Princeton, N.J.). That same year, copper was a distant second at 23,216 tons, accounting for about 5 percent of shipments.
Notably, powder metal can be produced from scrap or virgin raw material. To make the powder, the metallic feedstock is heated to its melting point in an electric-arc furnace. Then the molten stream of metal is blasted with water or gas to form individual particles, which are collected, then crushed and ground to remove contaminants and reduce each particle to a pure metal “microingot.”
Depending on the part to be formed, different powder metals can then be mixed to meet specific metallurgical requirements and achieve desired properties in the final product. Iron powder, for example, can be blended with small amounts of graphite, copper, and nickel.
To make a powder metal product, a die cavity is filled with the blended powder and pressure is applied—about 30 to 50 tons psi. (That pressure is equivalent to 50 compact cars stacked vertically on the die, says MPIF.) The compressed, preformed shape is then ejected from the die. At this stage, the product is compact and strong enough to maintain the form of the final shape while being moved to the next step of the process: sintering.
In sintering, the part is transferred to a controlled-atmosphere furnace that is hot enough to transform the powder’s mechanical bonds to metallurgical bonds, but not hot enough to melt the base metal. So in our iron example, the furnace temperature may be about 1,120ºC—hot enough that the graphite will rapidly dissolve, the copper will melt and partially diffuse, and the nickel will diffuse to form nickel-rich islands within the part.
Powder metallurgy reportedly affords a variety of distinct advantages for parts manufacturing, primarily offering an efficient, economical, and relatively quick means to produce complex-shaped parts at or near their final dimensions. Thus, the process usually eliminates the need for further machining of parts and enables manufacturers to mass produce products that would be too expensive, difficult, or impossible to make using any other process.
Powder Metals Apply Themselves
The first modern use of powder metallurgy techniques was for the production of tungsten filaments for electric light bulbs, followed shortly by the development of powder-based tungsten carbide cutting tools.
Since the 1920s, bearings manufacturers have taken advantage of the method’s ability to produce parts with “controlled porosity.” In this situation, tiny capillary-like pockets are distributed throughout the bearing to absorb oil or other lubricants. When the bearing is heated, the lubricants are released to the surface. When it cools, they are reabsorbed into the capillaries. These self-lubricating bearings eliminate the need for additional bearings and lubrication methods in a variety of bearing applications, including the fractional horsepower electric motors that raise and lower automobile antennas.
Today, powder metal parts can be found in such diverse applications as lock hardware, garden tractors, snowmobiles, washing machines, power tools, hardware, postage meters, offroad equipment, hunting knives, hydraulic assemblies, X-ray shielding, oil and gas drilling wellhead components, biomedical equipment, fishing rods, aerospace hardware, mineral additives in cereal and bread, and more. While these applications are vastly different, most powder metal parts have at least one common attribute in that they are generally small and intricate. That’s because fine metal powder can fill tiny die cavities, making the process ideal for creating complex parts of Lilliputian dimensions.
Those applications aside, powder metal’s largest single market by far is automotive parts, which accounted for more than 66 percent of powder metal parts usage in 1995, according to MPIF. In automobiles, powder metals have found homes as parts of overhead cam V8 and standard V6 engines, clutch assemblies, transmission components, connecting rods, ignition and fuel injection systems, shock absorbers, antilock brakes, air bag components, exhaust system flanges, camshaft lobes, main bearing caps, and more.
While the typical American-made passenger car or light truck currently contains about 30 pounds of powder metal parts, this amount will jump to about 50 pounds by 2000—an increase of more than 66 percent, MPIF projects.
Why are carmakers so in love with powder metal parts? In short, because the parts offer irresistible economic advantages, reportedly saving automakers up to 80 percent compared with traditional forged or cast parts. “Everything about powder metal parts speaks to the needs of the automobile manufacturing industry—efficiency, low cost, and performance,” says Brian Dodge, general sales manager of Metal Powder Products Co. (Indianapolis), reportedly one of the industry’s top-10 custom manufacturers of powder metal parts. “The auto industry depends on powder metal technology. Our industry offers them so much value.”
Driven by this burgeoning demand from automakers, as well as other industries, the powder metal industry will continue to exhibit strong growth, MPIF predicts, noting that powder metal producers are already expanding aggressively to meet existing as well as expected demand.
The iron powder sector, as the largest segment of the powder metal parts industry, is expected to grow particularly fast, swelling approximately 4 to 6 percent a year to reach shipments of 500,000 tons by 2005. This growth will be driven by increased demand from automakers and more-advanced technological developments that are allowing these parts to replace car parts that were traditionally forged or machined.
The Copper Conundrum
While all of this growth is great news for the powder metal industry and devout users of powder metal parts, it’s not-so-good news for minimills and, by association, the scrap recycling industry.
The problem is this: Ferrous powder metal parts reportedly have a copper content that can create problems when charged into an electric-arc furnace with other ferrous scrap.
Automotive ferrous powder metal parts contain anywhere from 0.5 to 5 percent copper, say manufacturers of iron powder, fabricators of powder metal parts, and minimill officials. The red metal is added in the powder metallurgy process to add strength to components and, depending on how much is used, a certain degree of process flexibility.
Though 0.5 to 5 percent may seem inconsequential, the fact remains that there is little tolerance for the red metal in the minimill steelmaking process. Some specialty steel manufacturers, for instance, have a tolerance for residual copper of about 0.25 percent, while producers of structural shapes have a higher threshold around 0.8 percent, with about 0.3 percent copper or less being the industry norm.
“High copper content has the effect of stiffening steel, which means increasing its strength and reducing ductility, with the result that it can become unsuitable for many applications, particularly when cold-working is involved,” explains Dick Jaffre, vice president of raw materials and transportation for Chaparral Steel Co. (Midlothian, Texas). “In addition, high copper can affect the surface quality of hot- and cold-worked steel, resulting in defects such as pits, cracks, and torn edges.”
And, once copper is melted, there is no way to extract it from molten steel. So, if the copper content is too high, says Jaffre, the steelmaker must sell the resulting products as a lower quality steel or set the heat aside and gradually add it to subsequent melts, thereby diluting the copper content to an acceptable level—options that put expensive burdens on the steelmaker.
With the use of powder metal parts in cars expected to skyrocket in the future, some minimills are raising red flags over fears that these cars, when scrapped, could add even more of a copper threat to their production.
Some minimills, in fact, have already formally adopted source control policies that exclude powder metal parts from their list of acceptable scrap. “Our company will not accept them at all,” says Stephen Farley, master raw materials analyst for Timken Co. (Canton, Ohio). “The presence of powder metal parts in any form is cause for automatic rejection of a load. As a producer of high-quality alloyed steel products, we just don’t want any powder metal parts—or any scrap that tends to have high copper content—coming into our plant.”
Other scrap-fed steelmakers are considering jumping on the bandwagon as well, with an executive of another domestic minimill saying that his company is considering warning its scrap suppliers of the high copper content of powder metal parts. “Over time,” he says, “I expect more and more steelmakers will not want to accept them.” Jaffre agrees, stating that “the utility of powder metal parts as a recyclable product is limited. Powder metal parts containing 2 percent copper are not designed for recycling.”
Far from being alarmists, most minimills are approaching the powder metal question with open-minded concern. “It’s not like we’re trying to change the fact that there is powder metal in cars,” says Farley. “We just want our scrap suppliers to be aware that it causes problems for us.” The underlying fear for Timken and similar companies is that if they don’t begin to address this problem now, Farley states, “it won’t be long until we can’t meet the requirements of our customers without dramatic changes to our scrap mix.”
A Processing Predicament
Looking beyond the effect of powder metals on steelmakers, other questions arise—namely, what effect will the growing presence of powder metal parts have on the recycling loop for automobiles, and how will scrap processors be affected?
The issue is tangled by the fact that most scrap processors have probably been handling the material for some time without even knowing it. This is happening largely because powder metal parts reportedly don’t look any different than other metal parts. Basically, they look like “good scrap,” as one steelmaker puts it. “It has always been a challenge to control and remove copper from the recycling loop, but powder metal parts make it more difficult for scrap processors,” asserts one scrap consumer.
So, how are scrap processors supposed to address this virtually invisible problem? While some recyclers—and more than a few minimill executives—would like to see powder metal parts eliminated from cars completely, that is highly unlikely. The domestic automobile industry has more than demonstrated its commitment to expand its use of these products now and in the future.
Others versed in the topic half-jokingly suggest that powder metal parts should be removed from cars prior to recycling, but this is an impractical and labor-intensive proposition to say the least, not only because it would be next to impossible to identify the powder metal parts, but also because they are dispersed throughout a car.
Among the practical options for scrap recyclers, shredding remains one of the best ways to distribute powder metal parts evenly throughout a load and thus avoid high densities of its copper content.
Others suggest that processors may want to step up their source control policies in the future, particularly if they accept scrap from engine and transmission rebuilders, as this material can potentially contain high concentrations of powder metal parts. The alternative is to risk penalties or rejections from consumers.
There is one other potential solution on the horizon, and that is for copper to be eliminated from ferrous powder metal parts in the future. Brian Dodge, as one powder metal producer, says that “copper probably could be eliminated from the process,” adding, in fact, that “the industry is moving in that direction.”
This would be a headache-saving change for scrap processors and—presumably—minimills. But, adding intrigue to the scenario, some powder metal sources suggest that minimills have a “veiled agenda” in stoking the copper controversy related to powder metal parts in automobiles. This purported agenda comes down to competition—or, rather, an effort to squelch it—as producers of powder metal parts compete directly for shares of some of the same markets that have traditionally been dominated by producers of steel parts. “We really cut into the supply margins of steelmakers in some applications,” explains one powder metal industry executive.
This intrigue aside, with the use of powder metal parts certain to grow and their recyclability becoming a more-vocalized concern of steelmakers and scrap processors, it looks as if this issue is poised to become a cause célèbre for several years to come. And the jury is still out on how this will play out in the end. Perhaps powder metal parts will change metallurgically to become more recyclable. Perhaps processors and steelmakers will find better ways to solve their copper concerns. Perhaps more drastic source control measures will be imposed.
Whatever happens, the only certainty is that this dialogue is just beginning. And for those in the industry who haven’t yet heard of powder metals, they soon will. •
Eileen Zagone is an associate editor of Scrap.