Popular Woodworking 2001-12 № 125, страница 39
• Warmer Cryo: Some labs use dry ice to cool the tools. Dry ice will take the temperature down to -109° Fahrenheit. This process works, but you won't get a full transformation of austenite to martensite. • Quick Dip: Some labs dip the tools into liquid nitrogen (-320°), leave it there for a short period of time, remove the tools and let them return to room temperature. This process can cause the tools to shatter from thermal shock. It also can transform only the outer layer and leave the core untreated. Many of the experts we talked to do not recommend this procedure. • Long Bath: Other cryo labs use gaseous nitrogen to reduce the temperature slowly; they keep it there for 20 hours or more (using either gas or liquid nitrogen), and then slowly return the tools to room temperature. Bryson says he's tried a variety of methods, and the equipment he prefers (and sells to other cryo labs) takes the temperature down using gas and then soaks the tools in liquid nitrogen. Either process works, however. One of the keys to getting the best results is to choose a lab that has some knowledge of heat-treating and metallurgy and is willing to soak the tools for a long time, says Randall Barron, professor emeritus at Louisiana Tech University's Department of Mechanical Engineering. Barron's pioneering research in the 1970s, 1980s and 1990s helped convince many industries to use the process in manufacturing. Barron's studies showed that bringing the temperature down to -320° created a more durable tool. Plus, his research showed that soaking the tools for hours was what led to the creation of the micro-carbides, which lend additional wear resistance. No matter which process is used, after the tools return to room temperature, the tools need to be retempered because the new martensite is fragile and can shatter, experts say. This retempering process is almost always included in the price for the cryo treatment. Bryson recommends that the tools be tempered at 300° to 350° for two hours for every inch of thickness of the tool. He also says you should make sure that the items are not stacked on top of one another during tempering. How Well Does it Work? This, of course, is the big question. Some of the claims seem outright outrageous. A dowel maker claimed his A2 knives lasted 800 percent longer. A titanium aircraft bit that once lasted for 15 holes was replaced by a common bit that had been cryogenically treated that would last for 200 holes. Most cryogenic labs will tell you it's reasonable to expect your tooling to last two or three times longer between sharpen-ings. Considering how inexpensive cryogenic treatment can be, you'll make your money back after one sharpening. In August, we sent a batch of tooling from our shop here at Popular Woodworking to a cryo lab for treatment — everything from a chisel to 12" jointer knives. We're going to compare the durability of these tools with the identical untreated tooling we recently installed in our machinery. Next year, we'll let you know what we found. But even if we find out that cryogenic processing really works, don't be surprised if you don't see cryogenic planer blades for sale in woodworking catalogs. Professor Barron says that one of the studies he did in the early days was for a manufacturer of razor blades. The company wanted to see if the cryogenic process could improve the dies they used in making the blades. "I asked if they wanted to treat the razor blades to make them last longer," he says with a chuckle. "They said no, because then they might not make as much money." PW IN SEARCH OF PROOF CRYO REALLY WORKS To many people, cryogenics sounds too good to be true. So we went looking for some stories to back up the claims we'd read so much about. Ron Hock, the founder of Hock Tools, began offering A2 plane blades this year that have been cryogenically treated — in addition to his line of high-carbon steel blades that he's offered for years. He says he began offering the A2 tools after other plane blade manufacturers, such as Veritas of Canada, began selling A2 blades. Hock says he isn't entirely convinced that A2 can be made as sharp as his high-carbon blades, but it does appear to wear longer and be slightly more corrosion-resistant. "It was adding the cryo that tipped it for me," Hock says. "Without the cryo improvement, I wouldn't use the A2." Hock says he's getting good reports back from customers who are seeing longer edge life. Thomas Lie-Nielsen, the founder of Lie-Nielsen Toolworks in Warren, Maine,was also looking for answers. During the summer, he was considering switching to a different type of blade for his line of high-quality planes. For years he's used a high-carbon steel that he carefully heat treated. Lie-Nielsen was considering switching to A2 that was cryogenically treated. So he took three A2 blades (some of which had been cryogenically treated) and three high-carbon blades and made 300 identical cuts with each. He then sent them to an independent lab to examine the blades. Lie-Nielsen says it was obvious that the A2 blades retained their edge longer than the high-carbon blades.And he hopes the lab will be able to tell him how the cryogenically treated blades fared. We promise to share the results with you in a future issue. Ron Hock's A2 blades and Thomas Lie-Nielsen's planes are both available from Woodcraft (800-225-1 153), Japan Woodworker (800-537-7820) and Garrett Wade (800-22l-2942).The products are also available directly from the manufacturers: • HockTools 888-282-5233 www.hocktools.com • Lie-Nielsen 800-327-2520 www.lie-nielsen.com |
