The Cryogenic Question

Cryogenic tempering, which supercools material to -300 degrees F and below, promises to make wear parts stronger and longer-lasting—but does it work? 

By Robert L. Reid

Remember that old experiment from high-school science class in which a rose gets dipped into a container of liquid nitrogen? After a moment, the frozen flower is removed from the liquid and dropped, shattering like glass into a thousand pieces.
   A neat trick, sure, but one that has a more practical side for scrap processors. That’s because liquid nitrogen can be used to strengthen wear parts. It’s part of a process called cryogenic tempering, which involves “soaking” or “quenching” ferrous, nonferrous, and even plastic components in liquid-nitrogen gas for extended periods at -300 degrees F and below.
   The resulting molecular changes can increase the durability and useful life of wear parts—and perhaps even lead to dramatic reductions in downtime and maintenance costs. The cryogenics industry certainly sees it that way and promotes liquid-nitrogen treatments for a host of scrap-equipment applications, including shear blades, granulator knives, shredder hammers, liner plates, gears and motor parts, even the rotors and brake drums on trucks and other vehicles.
   Of course, this assumes that cryogenic tempering actually works—a point that’s very much open to debate, at least as far as scrap processors are concerned.

Chilling Out
First, a quick overview of what happens during cryogenic tempering:
   In the process, the parts being treated are placed in a sealed chamber and slowly chilled with liquid-nitrogen gas to roughly -300 degrees F at a descent rate of 1 degree or less a minute. At that rate, it takes five or more hours to cool the parts to the desired supercool temperature.
   Once the target temperature is reached, the parts are held there for 24 hours or longer. Then the process is reversed, with the parts being brought to room temperature at a similar ascent rate of 1 degree or less a minute, again over multiples hours, with computers controlling and monitoring the temperature throughout.
   Many cryo firms then temper or “draw” the parts by heating them to roughly +300 degrees F, a step that reportedly fixes and stabilizes the effects of the cryogenic treatment. (This tempering stage should not be confused with the initial heat-treating done by the original manufacturer of the part.) 
   Metallurgically, the cryogenic supercooling and tempering process converts a relatively weak molecular structure in ferrous metal known as austenite into martensite, which is a “more desirable hardened, finer-grain structure,” says Atlantic Cryogenic Solutions Inc. (Joppa, Md.). As much as 25 percent of a ferrous wear part’s metal structure could be austenitic, even after the manufacturer’s original heat-treating, notes Arnie Breidenbaugh, vice president of Atlantic Cryogenic. So, in essence, the cryogenic process simply finishes the job, resulting in benefits such as “improved wear resistance, stress relief, improved dimensional stability, and increased tool life,” he asserts.
   Supercooling also strengthens parts made from nonferrous metals and plastics (which do not undergo the heat-tempering portion of the process). Instead, the cryogenic treatment alone “allows the molecules in the materials to compress, expand, and realign to become denser and more evenly spaced throughout the material,” Atlantic Cryogenic explains. “This molecular bonding and readjustment eliminates weak voids in the structure and results in improved toughness, strength, and an increase in density.”
It’s important to note that the parts being treated are exposed only to liquid-nitrogen vapors—the material never comes into contact with the supercooled liquid itself. All the major cryo firms seem to use this “dry” cryogenic approach, which eliminates the potential for thermal shock that can occur when parts are immersed in liquid nitrogen. That, combined with the slow computer-controlled chilling and reheating, helps explain why treated parts don’t shatter like the aforementioned frozen rose.

Computerized Cooling
Cryogenic treatment has been around in various forms for more than a century and has been used by NASA and the defense industry for decades. Before cryo firms widely adopted microprocessors in the 1990s, however, the cooling and reheating process had to be controlled manually, which produced inconsistent results.
   “Years ago, a guy would send in a part, and it would come back after being treated and work great,” says Breidenbaugh. “But when he sent in another part, it would come back and work terribly—the results were all over the place because the cryo firm didn’t have the level of control that we have today.”
   Thanks to computers, modern cryo companies can point to numerous success stories and satisfied customers in fields ranging from aerospace to manufacturing and sporting goods. They’ve successfully treated industrial parts such as industrial shear blades, hammermills, and granulator knives, along with more exotic items such as NASCAR racing engines, musical instruments, and golf clubs. 
   One industrial company that cryogenically treated its band-saw blade went from replacing the blade every two or three shifts to getting at least 14 shifts out of the blade, yielding $6,700 in annual savings, claims Breidenbaugh. Plus, he adds, customers often find that “the big money is in the additional throughput and increased efficiency in production because they don’t have to take the machinery down to change parts nearly as often.”
   Meanwhile, 300 Below Inc. (Decatur, Ill.)—one of the nation’s oldest and largest cryo firms—has treated brake rotors and pads for various vehicles, noting that the customers report improvements ranging from 333 to 1,400 percent. Indeed, doubling or tripling the useful life of cryogenically treated wear parts is quite common, at least for nonscrap customers—and theoretically the benefits can be even greater, various cryo firms note.
Depending on the metal being treated, cryogenics can improve performance life anywhere from 98 percent for C1020 carbon steel up to 817 percent for D2 high-carbon/chromium die steel, according to tests conducted by Louisiana Polytechnic Institute (Ruston, La.).
   Remember, though, that these results were obtained under laboratory conditions. Atlantic Cryogenic—which touts the Louisiana Polytechnic stats on its Web site—advises customers to “conduct independent tests to confirm treatment compatibility for your specific applications.”
   And that’s one problem for interested scrap processors: Few cryo firms have much experience with the specific—and often exceptionally tough—conditions that wear parts undergo in recycling operations.
What About Scrap?
   Where a scrap-related track record does exist with cryogenic treatments, the results have been mixed (see “Cryo Cases” on page 19). Of the handful of scrap processors who have cryogenically treated their shear blades, for instance, a few vow that the process resulted in improved performance. Others say the initial benefits didn’t last or didn’t make economic sense given the cost of the cryogenic process. 
   Speaking of cost, cryogenic treatment is usually priced based on the weight, in pounds, of the parts being treated, with volume discounts available. Scrap processors contacted for this article paid $1.75 to $4 a pound, depending on how much material they had treated at a time. In several cases, processors said the treatment cost nearly as much as the price of a replacement part.
   Moreover, in situations where third parties—such as wear-part manufacturers—have tried to reproduce the performance improvements reported by satisfied scrap processors, the manufacturers say they didn’t get similar results. Why such variation?
   The reasons, not surprisingly, vary as well. As the Louisiana Polytechnic study indicates, the metal itself matters, with certain metals offering better results than others.
   “Cryogenic tempering doesn’t work on all materials,” confirms John Koucky, vice president of 300 Below. “It’s very material-dependent rather than application-dependent. If we have the right materials, we’re going to increase the wear-resistance.”
   Tool steels with designations such as D2 and A2 are prime candidates for improvement, along with any higher-carbon, higher-alloy ferrous metals, according to cryo firms. The process also works well on gray and cast iron plus martensitic stainless, though not as well on austenitic stainless, Koucky says. Likewise, some—but not all—forms of manganese steels show promise. Meanwhile, cold-rolled steel products are unlikely to see the truly dramatic improvements that cryogenics offers, though they could enjoy a 50-to-100-percent improvement in useful life, says Breidenbaugh.
   Thus, one reason why some recyclers have had inconsistent cryo results could be the metallurgical makeup of their wear parts. Certain shear blades and granulator knives are made from the tool steels that cryogenics reportedly can improve while other products are not. Even an ideal steel for cryogenics such as D2 can experience a wide range of improvement depending on how well the part was originally heat-treated, says Garry Crabtree, president of cryo firm TechSpec Inc. (Kansas City, Mo.).
   So processors interested in trying cryogenics should first determine the metallurgical content of their wear parts and whether a cryo treatment could improve performance.
Unfortunately, about the only source for finding cryo-treatment results is a cryogenics provider—and, of course, these firms are eternal optimists about their process.
   One provider, for instance, conceded that he’d never treated any scrap wear parts yet stated confidently that he could save processors “a lot of money.” (He added, though, that two different scrap processors could get entirely different results from similarly treated wear parts based on how well they maintain their machinery and what they’re processing.) Another cryo firm that had treated one scrap company’s shear blades—with mixed results—suggested that perhaps the blades were chipping away under the rough conditions of cutting scrap rather than wearing away. And a third provider—whose work for a scrap processor had fallen short of expectations—suggested that processors simply don’t keep good enough records to realize how much their blade performance has improved.
   Scrap processors should also be forewarned that some cryogenics providers firmly believe that manufacturers of wear parts are undermining cryogenics to avoid losing sales from longer-lasting parts.
   “A lot of people are bad-mouthing the cryogenics process because we make the parts live too long,” says one provider. Another notes: “My gut feeling is that parts manufacturers may not be interested because they don’t want to see a 50-percent reduction in their consumables sales—if it doesn’t wear, they don’t sell parts.”

Testing the Treatment
While it’s true that some parts manufacturers show little or no interest in cryogenics, others are working with cryo providers to treat their products, even if just on a test basis.
   The American Shear Knife division of ASKO Inc. (Homestead, Pa.), for one, has experimented with cryogenics on all its product lines, notes Chuck Churchill, vice president of technology. Some of ASKO’s scrap customers are arranging on their own to have their ASKO knives cryogenically treated, while other customers are asking ASKO to arrange for their knives to be treated, he notes. According to Churchill, though, such requests are “extremely infrequent,” involving less than 1 percent of ASKO’s customers, and seem to involve processors who are simply experimenting with cryogenics. Still, he asserts, “We certainly feel there’s a possibility that the process has merit, and we want to make sure that we’re in a position to pass any benefits along to our customers.”
   Zenith Cutter Co. (Loves Park, Ill.), an after-market blade producer, cryogenically treats all the blades it sells for use in tire shredders made by Columbus McKinnon Corp.—primarily because its competitors do the same, explains Todd Gaines, a Zenith sales representative. Zenith has “no quantitative evidence” to prove that cryogenic treatment improves blade life, he says, nor does the company promote the fact that its blades are cryogenically treated. Even so, Zenith is thinking about entering the mobile shear blade market and, as part of that move, intends to at least experiment more with cryogenics, Gaines says. 
   MTB Recycling (Trept, France), which sells shredders and granulators in the United States, is also looking into cryogenics. MTB got interested in the process when one of its U.S. customers said that cryogenics had increased blade performance up to 200 percent on his MTB shredder. Though MTB’s own tests failed to show similar results, the company asked its European blade supplier to conduct additional tests, says Jean-Philippe Fusier, MTB’s general manager. Those second tests did show a “small improvement” in blade wear life of perhaps 5 to 10 percent—enough to convince MTB to explore the issue further, he says. Currently, the company is testing some 200 cryogenically treated granulator blades.
Another equipment manufacturer, though, noted that the current cost of cryogenic treatment is simply too high. “The cost is on a per-pound basis—and our stuff is very heavy,” he asserts, adding that “if cryogenics comes down in price, it would bring our interest up.”

Wanted: Cold Hard Facts
   So, what’s the future for supercooling scrap wear parts? Clearly, there’s some interest from both scrap processors and equipment suppliers, and the cryo firms themselves are definitely interested in the recycling market.
   One provider has even taken a small, mobile cryogenic chamber to various high schools to treat band instruments—which at least raises the possibility of scrap processors someday being able to have parts treated on-site rather than having to ship them off-site for treatment. Indeed, one new firm—Cryogenic Chambers L.L.C. (Delphi, Ind.)—is manufacturing cryo equipment that users can buy to treat their own wear parts. Kenn Workman, one of the new firm’s founders, believes that larger scrap processors represent about 5 percent of the potential market for such equipment, which costs as much as $60,000 and can treat approximately 500 pounds of parts at a time.
   Still, a common complaint from potential users is that there’s no hard evidence—only testimonials—that cryogenics works. As one notes: “A lot of people consider cryogenics to be snake oil. Show me exactly how this works, show me the statistics behind this working.”
   Unfortunately for cryogenics, that empirical evidence might be hard to find. “No one’s sure exactly why some of this happens,” explains Atlantic Cryogenic’s Arnie Breidenbaugh. “We can observe the benefits of the changes, but we can’t put our finger on what causes them.”
   For the time being, then, scrap processors and their equipment suppliers will likely take a cautious approach to cryogenics. That’s the attitude even of a satisfied scrap customer who has started off by testing a single cryogenically treated part in a single piece of equipment.
   “We didn’t want to jump into this because I know no one personally who has tried this,” he says. “I’ve read articles about it. I’ve talked with people in the business. But we weren’t going to jump into it with both feet. So, if for some reason it doesn’t work, we’ve got the experience and it hasn’t cost us an arm and a leg.” 

Cryo Cases
Though the list of scrap processors who have experimented with cryogenics isn’t long, it does offer an interesting range of experiences. Here are some examples:
• OmniSource Corp.’s granulator division (Fort Wayne, Ind.) tested several styles of cryogenically treated blades on its granulators about two years ago. Now, the division uses only treated blades from a supplier in Ohio for its wire-chopping line, says Jerry Colley, maintenance supervisor. While these pretreated blades cost a little more than other blades, they require roughly 50-percent less grinding to resharpen, which represents a substantial cost savings in manpower and downtime, Colley says.
   OmniSource also experimented with cryogenically treated alligator-shear blades but didn’t get the same improvement in performance, possibly because the blades were made from different steels, Colley says.
• Before Tube City Inc.’s Gary, Ind., facility—which processes scrap from U.S. Steel’s Gary Works—started cryogenically treating the blades for its Vezzani 1600 shear, it went through about a set and a half of blades every month, says Peter Gage, equipment analyst, with each blade changeover taking nine or 10 hours to complete. Now, one set of cryogenically treated blades can last as long as two months before needing replacement. Plus, the treated blades enable Tube City to process heavier material in larger volumes, 
Gage says.
   “Basically, the cost of the shear blades and the price of the cryogenic process break about even as far as savings compared to what we paid for noncryogenic blades,” Gage notes. “But in maintenance costs and from an operating standpoint, we’re more than ahead.”
   Over the past three to four years, Tube City has worked with two commercial cryogenic firms to treat its blades, including its current provider, Cryocool Inc. (Crown Point, Ind.). In addition to shear blades, Tube City has tried cryogenically treating “everything under the sun”—from other cutting tools to the wear edges 
of wheel-loader buckets, Gage says—but has not been as pleased with the results.
• Mallin Bros. Co. Inc. (Kansas City, Mo.) had its granulator blades treated and initially noted a 75-to-80-percent improvement in wear life. Those results quickly fell off, though, after subsequent sharpenings. “By the time we’d sharpened the knives two or three times, we were back to where we were originally,” says Jeffrey Mallin, president. 
   Mallin’s cryogenic provider—TechSpec Inc. in Kansas City—worked closely with the company to solve the problem, but in the end Mallin decided that cryogenically treating granulator blades just didn’t make economic sense. The cost of the treatment basically equaled the cost of a blade, thereby doubling the investment, Mallin says. Also, the chance that a contaminant in the scrap would damage a whole set of expensively treated knives was always a threat.
   Despite his granulator-blade experience, Mallin does see possible uses for cryogenics—perhaps with shear blades or shredder knives. “The concept is fantastic,” he asserts, even if “so far the results haven’t been extraordinary.”
• At Sturgis Iron & Metal Co. Inc. (Sturgis, Mich.), cold weather was causing the spindles on its Link-Belt mobile cranes to snap. The company tried to solve the problem by cryogenically treating the parts. Working with cryo provider All-American Inc. (Plymouth, Ind.), Sturgis had four spindles treated, installed one last February or so, and made it through that winter without a breakage, says Joe Turpin, purchasing manager. That winter was fairly mild, however, so the company hasn’t fully evaluated the results.
   Still, the potential savings are attractive since each spindle costs about $400 to treat compared with $12,000 for a new part, says Turpin, who is willing to try cryogenics further. “If this works for us,” he says of the treated spindles, “we’re certainly going to look at doing our shear blades.”

Robert L. Reid is managing editor of Scrap.