July 2005

Cryogenics Puts the Freeze on Tool Wear

Cryogenically-treated cutting tools reduce on abrasion and last longer.

By J.D. Piland
Cryogenically-Treated Cutting Tools

Cryogenic processing of cutting tools requires a "very gradual" drop in temperature to -300F or below, says Harold "Sandy" Stewart, who has researched the effects of cryogenically-treated cutting tools for Mississippi State and Purdue universities. The tools are kept at this temperature for a set amount of time - generally 24 hours - and then gradually returned to ambient temperatures. From there, they are tempered to about 300F to combat any brittle characteristics that may have been retained from the freezing.

The entire process creates a "phase transformation" in the chemical and crystalline structure of the material, Stewart says. The cobalt binders, which can be found in tungsten carbide tools, become stronger and bind the carbides together.

In the case of ferrous materials, the austenite, which is the original larger and softer crystalline structure, often is transformed to martensite, a smaller and more compact crystal, Stewart says.

The denser the molecular structure, the less abrasion occurs because the surface area of the tool is increased and the carbides are bonded tighter, which, in turn, reduces friction, heat and wear.

Most recently, researchers, including Stewart and Rado Gazo, associate professor at Purdue University's Department of Forestry and Natural Resources, tested cryogenically-treated and non-treated solid-carbide router bits on a CNC router. However, because the findings had not been published yet, the results of the tests are not available.

Cryogenic treatments have been applied to all kinds of products, including musical instruments, engine parts, electronics, gun barrels and even baseball bats.

Usually, when something is frozen, it becomes brittle and can be broken easily.

Usually.

This is not necessarily the case with cryogenically-treated cutting tools. Actually, the sub-zero treatment makes the tools that much more reliable, if done correctly. The -300F freeze the tools are subject to chemically and structurally change the materials the tools are made of. More often than not, the tool is made stronger and stays sharper for longer periods of time, thus, making them more reliable and more cost-effective.

Several companies that have had their tools cryogenically treated.

The Carbon, IN, location of Pike Lumber Co., a producer of hardwood lumber from ash and basswood to black walnut and yellow poplar, is one of those companies. It has used

cryogenically-treated chipper knives for about three years, plant supervisor Shane Johnson says.

The chipper knives are the only tools that are cryogenically treated at this Pike location. No saw blades are treated as of yet, but Johnson says the company may look into it soon.

"If you have a wear point, a spot where material constantly passes by it, that material basically wears through it," he says. "We've talked about the option of having a wear point treated to get it to last longer. But we haven't got to that point yet. I'm not saying we won't, we're just not there yet."

Though the knives are treated, Johnson admits that the quality of the chips produced did not factor into the decision to cryogenically treat the knives. "Instead of tearing, they are cutting, but we don't really look at the quality" because the chips go to paper production, Johnson adds.

The real issue was to address maintenance - and still is, Johnson says.

Sharpening the knives used to take place every day. Three years ago, a set of six knives, which is what is run on the chipper, would be replaced with freshly-sharpened ones every morning.

"Now, and of course this depends on what type of species we are running, we can go a week - five days," Johnson says.

"We change them in sets. In the application we are in now, we don't have to have as many sets. But, we probably won't have to replace that set right away because we will have that surplus of sets because we didn't have to replace the knives every day," he adds.

The knife maintenance never impeded on production time because it was scheduled before daily production even began. However, the fact that the maintenance workers no longer have to focus every day on the chipper knives is the key.

Cryogenics in cutting tools such as these are gaining popularity because the sub-zero process has been found to greatly extend tool life. Photo courtesy of CryoPlus Inc.

"That's the biggest benefit," Johnson says. "When you are focusing on those every day, you get maybe one or two days for other things. Now, you get more time to focus on something that might have been neglected before. That's going to trickle down to production, but we don't have any measurable results because of it."

And now, with the reduced knife maintenance, Pike can touch them up with our touch-up grinder if needed.

"But as far as longevity, I would say we have doubled - if not more - the time the tools will stay sharp and how long they will last."

                                                                                                                                                                                           

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