Cold, hard facts on cryogenics, Solutions!, Online Exclusives, November 2004

Cryogenic processing—the deep chilling of tool steel to bring the molecular structure of the metal to “cryogenic stillness” in order to improve wear characteristics—is not a new technology. In the past, tool makers would bury components in snow banks for weeks or even months to improve their wear resistance. Castings were left outside in the cold to age and stabilize.

A chipper knife is loaded into the chamber for cryogenic processing. The equipment will maintain a temperature of -300F.

Today’s dry process is computer-controlled, using a prescribed schedule and maintained at -300F for a predetermined time before slowly returning the parts to room temperature. Prior to the deep cryogenic step, many tool steels require a preconditioning step consisting of a short temper. After being subjected to the deep freeze, the materials must be tempered to about +300F. This temperature varies for different materials, and the processing time varies for different material cross sections.
          Production facilities can improve performance and increase the life of metal cutting tools, blades, punches, dies, slitters, shears and knives with cryogenic processing. Cryo processing increases abrasive wear resistance, raises the tensile strength and decreases brittleness with only one permanent treatment. It creates a denser molecular structure and closes the grain’s structure, resulting in a larger contact surface area that reduces friction, heat and wear. Cryogenic treatment changes the entire structure, not just the surface. Subsequent refinishing or regrinding operations don’t affect the permanent improvements of the processing.
          Today’s limited acceptance and use of cryogenic treatment is largely attributed to a lack of understanding about the technology. Changes to the material micro structure are not visible with a standard laboratory metallograph or any other standard mechanical testing. Material hardness remains about the same.
          When the cryo treated tool does wear, the degree of wear reportedly is less severe, slower and more uniform. Therefore, less material must be removed to re-sharpen it. Customers have reported a material removal rate of less than half the normal material removed in re-sharpening. Cryo treating reduces the cost of the product by having longer tool life, less scrap, fewer rejections, and reduced downtime.
          Darl Bolyard of Bruce Hardwood Floors noticed a 200-300% increase in life of his Wisconsin straight flooring machine knives. After using cryogenics, Pike Lumber in Akron, Indiana said there was a noticeable difference in wear, less time changing knives, 2-3 times longer life and less grinding to resharpen. Chipper knives would usually last for one shift which would make 20-25 tons of chips. The cryo treated knives made 45-60 tons of chips.

According to John Blake at Brookville Wood Products in Brookville, Pa., “when changing the knives I’ve seen fewer nicks in the blades and they didn’t show any signs of burning.”
          It looks as if cryogenics finally may be getting the attention, in terms of metallurgical research, that many of its proponents have been seeking. Cryogenics is an exciting and important frontier that has already led to major discoveries and holds much promise for future applications in the industrial sector.

About the author:
Kathi Bond is with CryoPlus, Inc., Wooster, Ohio. Visit www.cryoplus.com to learn more.