July/August 1993
Many scrap processors want to improve their sorting capabilities. Here's a look at what's up with optical emission and X-ray fluorescent alloy analyzers designed to help.
BY JEFF BORSECNIK
Jeff Borsecnik is assistant editor of Scrap Processing and Recycling.
If you were to describe your perfect alloy sorting tool, you'd probably specify that it be easily portable, perhaps the size of a transistor radio. It would be simple to use, require no programming, and be able to simultaneously and instantly identify any alloy or any number of elements in a sample.
Unfortunately, if there were such an instrument it would probably be infinitely expensive. But fortunately, if you want something that comes close to that idea and are willing to make a manageable investment, there's a growing number of handy portable sorting tools available that allow you to put a bit of the laboratory in your sorter's hand. Of course, these analytical tools do not typically provide the same sort of performance as their laboratory kin, but, then again, they are designed for a different, less-exacting task—quickly identifying alloys, rather than providing precision chemical analysis. Portables even have some advantages over lab units, including greater speed and more leeway in terms of sample preparation, cleanliness of the environment where the sample is to be tested, and operator skill.
Such portable alloy-identification analyzers generally use one of two technologies—X-ray fluorescence (XRF) or optical-emission spectroscopy (OES)—both of which rely on the fact that every element releases a unique pattern of electromagnetic radiation when energized, providing a sort of fingerprint that can be identified. Here is simple summary of how they typically work: A hand-held probe is placed against a sample whose surface is clear of rust, paint, or scale. A trigger or button is activated, directing the probe to "excite" the sample using a high-voltage spark like a welding burn, in the case of OES systems, or a beam of X-rays released from one or more small radioactive sources, in XRF units. The energy transmitted causes electrons in the atoms of the sample to change their energy levels or "orbits," and in doing so, various wavelengths of light—X-rays and/or visible and ultraviolet light—are released.
The X-rays or UV light are collected by the probe, separated by wavelength, and converted into electronic pulses, which are then transmitted to a central processing unit. This computer sorts through and analyzes the information to determine what elements are present and in what concentrations. It then compares this analysis to a stored library of dozens or even hundreds of alloys and displays the alloy name or number on a screen located on the probe or computer. In some cases, the system will note how closely the sample matches the most similar alloy in the library, list the approximate "chemistry" of the piece, or simply reveal whether the sample matches a certain reference alloy.
In all, the process may vary from a few seconds to a few minutes, depending on the type of analyzer used, the accuracy desired, the particular alloy being tested, the shape and condition of the sample, and other factors.
Pick Your Portable
Equipment makers as well as their scrap recycling customers are quick to point out that neither technique is perfect. Paul Penney, president of Arun Technology Ltd. (Dearborn, Mich.), which manufactures portable XRF analyzers, puts it this way: "To date, no one has come up with the ideal instrument that can do anything and everything perfectly. So, like a tailor, you cloth to your pocket," satisfying your needs as best you can on your budget.
Although portable XRF and OES analyzers perform similar tasks and their abilities do broadly overlap, each has its strengths and weaknesses. For instance, according to Bob Nowkoff, vice president of MMA Labs (Los Angeles), which uses a variety of portable and laboratory analyzers, OES machines "see" more elements, and can more precisely identify low concentrations of lightweight elements such as silicon, aluminum, carbon, and magnesium. On the other hand, some OES units are "not as forgiving in operation," he says. XRF units, meanwhile, can easily adjust to read concentrations of most elements across a broad range, while OES systems have a rougher time with widely varying concentrations.
These differences mean, for example, that XRF systems are good for quick verification of alloys or for examining high-alloy steels, says Jim Pasmore, director of sales and marketing for Outokumpu Electronics Inc. (Bend, Ore.), which makes portable XRF as well as wheeled mobile OES systems. But OES analyzers have the edge for low-alloy or carbon steels as well as aluminum alloys.
Other distinctions between the two technologies include the fact that XRF units perform "nondestructive" testing, while the arc of OES systems, which actually vaporize a tiny amount of the sample, leave a mark. This doesn't appear to be a concern for most scrap processors, however, and some point out their clients welcome such mars as a sign of positive material identification.
In addition, because of their need for a substantial power source to create their arc, OES systems are somewhat bulkier and less portable than the XRF units, many of which reportedly can operate on a replaceable battery pack for up to 12 hours before recharging, allowing them to be taken and used almost anywhere. OES analyzers typically require access to an electric outlet or generator; nevertheless at least one manufacturer, Arun Technology, produces an OES unit that can operate for a few hours on a battery that weighs about as much as the analyzer.
Finally, XRF analyzers use radioactive sources, which means they must be government-regulated, while OES systems are not. In many cases, the XRF tools are covered by a general license in which the regulators merely need to be kept informed about the whereabouts of these tools. In some states, however, operators must obtain a license. (The weak radioisotopes in the XRF analyzers pose virtually no health risk, according to various sources.)
This last factor could have particular significance to those who want to travel with their XRF units. One experienced user who takes his XRF analyzer on road trips points out that airlines may require advance warning of such baggage. But a manufacturing representative suggests not advising the airline since pilots have discretion to refuse such baggage and may do so out of ignorance. Passengers traveling with an XRF unit are merely required to make sure the probe container is labeled as a radioactive source as required by law, he explains.
Technology Improving
Portable XRF and OES systems have been developing since at least the late 1970s and have seen gradual improvement over the years, manufacturers report. As a matter of fact, most units can now identify multiple elements simultaneously, while earlier models were limited to one, and many can now display and/or transfer to an external computer or printer an approximate chemical analysis of the sample.
Solid state detectors have enabled manufacturers of some portable XRF analyzers to substantially cut the bulk of their machines. Meanwhile, a few of the newest portable OES analyzers, including systems manufactured by Outokumpu and Arun, have switched to detectors using compact photodiode arrays in place of the older, bulkier photomultiplier tubes, allowing better performance in a smaller package.
In addition to the evolution in computer hardware, which has benefited these analyzers, the software used to analyze the data collected and provide the user interface has dramatically improved in recent years, according to manufacturers. It now can either take over almost all of the operator's decision-making or allow the user to easily program the unit to add alloys to its memory.
Operating Options
There may be as many ways to use portable analyzers as there are alloys to sort, judging from a sampling of processors using one or both types of portable analyzers.
Some portable machines are used in tandem with laboratory OES or XRF analyzers, whereas others operate at facilities that have never used lab equipment. For certain large items or high-value grades, users may analyze every piece, while others only check the occasional sample, relying on other means for the bulk of sorting. And some analyzers are used on the road to help prepare bids, with others working only in a single spot.
Monico Alloys Inc. (Los Angeles) uses several OES units as complements to its laboratory analytical equipment, says the plant's manager, Elmer Aguilar. The mobile tools are used in several ways, including double-checking the identity of materials received; "go/no-go" sorting, such as separating "commercially pure" titanium from Ti-6-4; or determining the composition of materials too large to take inside to the firm's lab.
Portable XRF analyzers are used by Midwest Steel and Alloy Corp. (Cleveland) both on the road for purchasing and in the plant, where they serve as laboratory units, operated in a stationary position to check samples cut from large scrap and brought to them, notes Robert Wallens, the vice president of sales and purchasing for the firm. In most cases, the analyzers are used to determine the actual chemistry of samples, not simply identify grades.
At Lake Erie Recycling Corp. (Buffalo, N.Y.), a facility that processes a wide variety of nonferrous materials, portable XRF and OES analyzers are used on buying trips as well as back at the shop, where they are typically paired with more elementary sorting techniques, says Howard L. Goldman, president of the company. For example, samples from mixed loads might be analyzed to determine exactly what alloys are present, after which time the bulk of the materials are simply sorted by shape or use of a spark test.
Why Buy?
Where once upon a time only the largest processors were equipped with laboratories to analyze their materials, smaller processors are increasingly investing in some sort of analytical equipment. Rick Booth, manager of analytical sales for TN Technologies Inc. (Round Rock, Texas), which produces portable XRF analyzers, predicts that most medium-size firms will eventually go with XRF or OES units—or both—while smaller players will at least step up to sorting aides such as chemical and thermoelectric tests.
No matter what the size of the firm, the most obvious benefit of portable analyzers is the ability to use them anywhere in the plant or outside it when bidding on scrap, improving the ability to bid aggressively with limited risk.
Also, the increasingly strident quality demands from scrap consumers are pushing processors to invest in more-sophisticated analytical equipment so they can improve the quality of the scrap they provide—or simply retain customers. In addition, more scrap players are finding economic advantages to portable analyzer use, such as allowing them to sell more-segregated grades, such as low-copper instead of just mixed clips.
For those who must carefully test their scrap piece by piece, portable analyzers may be a big time-saver. Terry Will, vice president and treasurer of Western Smelting and Metal Inc. (Dallas, Ore.), says his firm has been able to speed its sorting of high temperature alloys by a factor of five or six since it began to use portable OES equipment for the job.
Several users also note that portable analyzers can ease reliance on highly trained human scrap sorters. Brad Thompson, president of Thompson Metal Services Inc. (Piney Flats, Tenn.) says portable XRF units don't suffer the same limits as a skilled sorter, noting, "A good spark-tester can sort stainless very accurately—but he must work in the dark and do it all time. You almost have to be retrained after being off 30 days." Another scrap processing executive expresses relief that his portable analyzers have saved him from being "at the mercy" of scrap sorters who, jealously guarding their jobs, sometimes refuse to train other sorters. In addition, he points out that the analyzers can do away with the acids needed for chemical tests and their related safety concerns, as well as cut the use of outside lab services—representing savings in convenience, if not always cost.
Speaking of Cost...
Well, they're not as steep as their high-brow laboratory kin—that's the good news. Lab-quality XRF and OES systems might begin at about $65,000 and $100,000, respectively, and run to as much as $250,000, according to various manufacturers. In contrast, most portable XRF units cost $40,000 to $60,000, while the OES systems go for around $50,000 to $80,000. (These are ballpark figures, and actual costs vary widely depending on capabilities and how each machine is programmed to meet the customer's needs.)
Surprisingly, the handful of portable analytical tools aimed specifically at the scrap recycling industry tend to fall toward the lower end of the scales, perhaps because they are generally built for very limited, specific needs. One new entry to the market, for example, is a niche XRF alloy analyzer with a domestic list price of around $13,000 from ASOMA Instruments Inc. (Austin, Texas). On the OES side, Arun is selling scrap alloy analyzers with prices of $22,000 to $40,000, according to Penney.
Processors and equipment makers say those shopping for portable analyzers need to begin by carefully defining their needs. Next, advises Thompson, "Get demos of all units." All the analyzers can "do just about anything in a lab on certified samples," he says, but it may be another thing out in the field on scrap covered with scale. In choosing a machine, Goldman emphasizes the importance of easy portability as well as versatility—in order to avoid the necessity of buying additional units to fill performance gaps.
And, say several experienced users, don't expect costs to end once you've plunked down the money. Although manufacturers stress that the tools are becoming ever-easier to use, operators still need to be trained, and the sophistication of the training will depend on the machine and how it is to be used, such as whether the operator will need to program new alloys into its memory. "Make sure you are willing to spend the money to train your people to operate the machine correctly," says Wallens, warning: "Remember, garbage in, garbage out." Thompson agrees, suggesting that both XRF and OES techniques require "a sharp operator to know when to believe the machine and when not to believe it. In neither case can you just pump out the money and start sorting." •
Many scrap processors want to improve their sorting capabilities. Here's a look at what's up with optical emission and X-ray fluorescent alloy analyzers designed to help.