Positive Identification

Technological progress continually allows for a variety of improvements in metals analyzers, increasing the speed of analysis and the durability and portability of the instruments.

But technology cannot change one fundamental thing: The alloy detection capabilities of the two most common types of analyzers, X-ray and arc/spark. Therefore, most sources reached for this story agree: The search for a metals analyzer should begin with the question, Which alloys must be detected?

David Jarzinski, regional sales manager of stationary metal analyzers, Spectro Analytical Instruments Inc., Leominster, Mass., says, “Today, mills are lowering allowable limits and tightening down on specifications and allowable tolerances. Therefore, nearly everything needs to be tested sooner or later before it gets re-melted.”

Jarzinski says that analysis is especially critical for some alloys. “High-temp alloys come to mind first due to the significant money that can be lost or made with everyday decisions dealing with these metals. Second are aluminum and copper alloys due to the many possible tramp elements or poisons that can quickly devaluate or even make the material worthless. Lastly, titanium stands out due to the many new uses for titanium alloys in safety related products.”

THE CRUCIAL CRUCIBLE

For Bob Rappaport of Universal Metal Corp., Worcester, Mass., analysis is absolutely critical. Rappaport says, “as an approved vacuum processor of high temperature alloys, when we sell the alloy, we have to be dead-on. We have to know what we are selling.”

In many cases, Rappaport says that Universal Metal Corp. does 100 percent sortation. “Being able to get a reading that is accurate and timely is very important for us to be able to process our metal,” he says.

At some locations, a variety of materials are dealt with. At SLC Recycling, a division of Ferrous Processing and Trading, Detroit, vice president of quality control Clarence Watts says, “We purchase and sell recyclable scrap for the steel melting as well as the nonferrous melting business. So, our analyzers have the capability of checking both ferrous and nonferrous materials.”

Margo Myers, director of analytical marketing for Thermo MeasureTech, Round Rock, Texas, says, “By making the analysis and assuring the alloy type, the dealer can appropriately price his product. Since we provide XRF (X-ray fluorescence) systems, more of these are sold into non-ferrous, non-aluminum yards. But even aluminum dealers may want an XRF as it will tell them groups of aluminums: 2000 series versus 7000 series.”

Jarzinski says, “The analysis requirements must be carefully matched together with the capability of the instruments available before purchasing.”

WHICH METHOD?

Optical emission systems (OES), also called arc/spark, and XRF are the two basic methods used for metal analysis.

OES uses an arc or a spark to vaporize the sample, exciting the atoms and ions into emission of radiation. This emitted radiation then passes through an optical fiber and is dispersed into its spectral components. A photo-multiplier tube (PMT) measures the range of wavelengths emitted.  

The OES system is essentially two techniques in one machine. Jarzinski explains, “Arc is a very fast sorting tool that typically does not require sample preparation. Many grade/alloy IDs can be performed between 0.5 to 3 seconds. Spark on the other hand is a more finite analysis tool when close alloys need to be separated, such as 6061 and 6063 aluminum, or better chemistry is needed to maximize profits, as with nickel alloys. A spark analysis typically requires some light grinding or sample preparation and has an analysis time of 13 seconds.”

Jarzinski adds, “Only OES can determine such elements as carbon, phosphorous and sulfur, which can be important in stainless steels, certain copper alloys and a few nickel alloys.” In addition, OES can analyze silicon and magnesium. He also says that the ownership cost for OES is lower because the system does not need to be licensed, therefore saving the associated fees, and that no nuclear sources need to be replaced.

Tom Anderson of Niton Corp.’s Bend, Ore., office, says, “The arc/spark technology really shines for aluminum alloys.” However, Anderson says, “With arc/spark, you have to know what the base material is in order to know which analysis program to use.” Anderson also says that OES systems are not as adept with high-temperature alloys.

XRF uses X-rays emitted from an X-ray tube or a radioisotope to excite the atoms of the sample material. An electron is ejected, causing a second to fall into its void and energy is released. A detector within the instrument uses the energy level to determine the element.

Anderson says that XRF’s strengths lie in high temp and titanium alloys, nickel and cobalts. “That’s where their strengths really are—materials with higher concentrations of alloying elements. And that’s the limitation of arc/spark.”

With regard to aluminum alloys, Anderson says that Niton systems “can easily separate some grades within a series, such as 7050 and 7075. It can also distinguish series in most aspects.” Anderson adds that XRF has some limitations with regard to aluminum bronzes and silicon bronzes because of the inability to detect aluminum or silicon.

John Patterson, president of Metorex, Ewing, N.J., says that XRF doesn’t work “when you need information about some of the light elements, like carbon, sulfur, phosphorous and things like that. But anything that falls in the X-ray range, people are going to use X-ray every time.”

Patterson adds, “The pros of X-ray are that it’s easy, it’s fast, and it’s non-destructive.”

Lynn Shepherd, marketing communications specialist, Oxford Instruments, Scotts Valley, Calif., says that XRF comes into its own when analyzing high-quality stainless steels. “XRF has a very broad scope. It’s quite a versatile analysis technique, really,” Shepherd says.

However, she says that some of the drawbacks associated with XRF are the need for licensing and the decay of the radioisotope source. “As it decays, it takes longer to analyze and you get less of a consistency or a constancy.” Oxford offers XRF analyzers with a digital cathode tube rather than radioisotopes, which means that there are less stringent licensing requirements on it, she says.

SIZING UP THE POSSIBILITIES

Analyzers are typically available in three sizes: stationary, bench-top and hand-held. Stationary systems are usually more sensitive and capable of detecting alloys in lower concentrations. They are also capable of detecting a wider range of elements. However, a trained technician is required to operate a stationary system.

Hand-held analyzers can be carried out into the yard, but cannot detect the same breadth of elements as stationary systems. A bench-top resides between the others in terms of breadth of analysis and portability. 

Jarzinski says that stationary systems have not been the most prominent in the recycling industry because of their high price and the complexity of operation. However, he says that the flexibility of the SpectroLAB-Jr. allows it to grow as its end users’ requirements grow and expand to meet the changing demands of the scrap industry.

“Traditional stationary spectrometers have a price range of $60,000 to $140,000,” Jarzinski says. However, the SpectroLAB-Jr. bench-top analyzer ranges from $37,000 to $50,000, depending on the analytical configuration, he notes. 

Peterson says that the hand-held models are most popular with scrap recyclers. “It’s just easy,” he says. Prices on the hand-held systems can range from $20,000 to $82,000 depending on configuration Jarzinski says.

Niton Corp. is generally credited with introducing and popularizing hand-held models with recyclers. The company’s demonstration of it’s hand-held model at the 1998 ISRI (Institute of Scrap Recycling Industries Inc.) convention drew curious throngs of potential buyers, and hastened the trend toward smaller analyzers.

Tom Bloomer, vice president of marketing for Spectro Analytical, which has its headquarters in Fitchburg, Mass., says, “The larger the system, of course, the better the sensitivity and precision. But for this type of application, the hand-helds are much more popular because people are climbing on top of piles of metals and such. It’s much easier to carry around an analyzer that weighs two pounds versus 30 pounds.”  Bloomer adds that the hand-held systems are typically very rugged and designed to be operated by a novice.

Bloomer also says that the accuracy of the hand-held analyzers is increasing in comparison to the stationary systems, but “they are never going to be as accurate.”

Myers says, “Scrap processors like the ability to analyze in the yard and on the bench. Many of our systems are used back in an office and occasionally taken into the yard, while others are used 100 percent in the yard. Our instrument provides this flexibility with a true bench-top or field configuration. We have the ability to position our probe under a counter and operate the unit with the electronics placed some distance away. This mode can be set up somewhat near the shaker table in the warehouse, for instance. Or you can place the system in a field pack and use the smallest probe on the market to fit into tight spots and make measurements on parts in a crowded barrel in the yard.”

Myers adds that some of the hand-held devices available in a one-piece design do not provide the flexibility for bench-top usage of software user-defined features. Thermo MeasureTech provides a hand-held system that can easily be configured for desk-top use, Myers says.

Patterson says that Metorex’ X-MET can also be easily configured for hand-held or bench-top use.

Watts says SLC Recycling uses a stationary OES by Angstrom Inc. “It fit our business because our samples are generated by our melt shop. Most hand-held systems that I looked at are limited in how many elements they can check at one time. We can check 16 elements at one time at our stationary unit. Most of the hand-held units that I looked at can be calibrated to check two or three accurately in a remote situation.”

Rappaport says Universal Metal Corp. uses some hand-held units in its operation. However, he adds, “because of our specialty in the business, the hand-helds take too long to do a reading.” Universal Metal Corp. recently bought two hand-held Niton systems to perform spot-checks for quality control post processing. “For the specific application that we use the Niton hand-held for, it works for us,” Rappaport says. “But it’s not for production use because of the time factor.”

The company also relies on Kevex units that they have been updating themselves since Thermal Electron Corp. acquired the brand and the line for the scrap recycling industry was discontinued. “But we know we’ll probably be going [eventually] to the other analyzers that are more readily available as new units,” Rappaport says.

Niton Corp.’s Anderson says that some people swear by these older Kevex units, and for that reason Niton has introduced a unit designed to offer a modern replacement and upgrade of the old Kevex machines.

“The Niton XRT-800 is designed to address that market,” says Anderson. The data display is also similar to that of a Kevex, “to keep a comfort level there,” Anderson says. The XRT-800 sells for $70,000. The unit is built to be durable, he says, so it can analyze something as heavy as a helicopter blade, for example.

The new Niton model features an X-ray tube rather than an isotope source, Anderson says. “The X-ray tube will probably need to be replaced every three to five years. But you don’t have the reduction in speed [that you would experience from decay of a radioisotope].” Niton disposes of the isotopes used in its portable models for the processor, he adds.

TECHNO TRENDS

The X-ray tube is an attractive alternative to radioisotopes and is appearing in more and more analyzers. In the next two to five years, I think probably that most of the instruments will have X-ray tubes in them instead of a source.”

Myers says she has heard that the tubes are fragile, bringing reliability into question. “The last thing anyone would want to do is trade off licensing headaches for reliability headaches. For licensing, once it’s done, it’s done,” she says.

Shepherd, however, says that the tubes in Oxford instruments analyzers are “practically indestructible. They are covered with these carbon fiber nanotubes so they are very, very robust. If you dropped our analyzer, for example, you might shatter the case, but nothing inside would break.”

Some contend that the most prominent development in OES analyzers is that CCD (charge couple device) detectors, are replacing PMT detectors. “CCD detectors are slowly replacing PMT detectors due to their lower manufacturing costs and resulting lower cost instrumentation,” Jarzinski says. “CCD detector optics are designed with all the hardware necessary to capture the entire optical range with every spark, therefore allowing future elements to be added or even entire families of alloys to be added very easily and affordably.”

Bloomer says that the CCD detectors give Spectro more flexibility. “Again, you’re not working with these huge optics anymore,” allowing Spectro to pack more into a smaller analyzer, he says.

Adaptability and upgradeabilty of analyzers is key, as it can determine the life cycle of the machine. As Bloomer says, not only does an analyzer have to function mechanically, it has to function to the needs of the scrap recycler.

Niton Corp.’s Anderson believes this demand has not been lost on analyzer makers. “Most manufacturers, when they introduce a product, they want it to be upgradeable.” He says offering a decent trade-in value is another way to offer upgradeability to customers.

In addition to upgrade capabilities, scrap recyclers also need to consider the performance they require in regard to specific elements, their need for portability as compared to accuracy and speed, and the cost and customer support they will receive to ensure that the analyzer they select will accommodate their needs for years to come.  RT

The author is a staff member of Recycling Today and can be reached at dtoto@RecyclingToday.com.