The Metalworking Idea Magazine

Cryogenic Tempering Boosts Parts Life Up to 400%
By Larry Olson, MAN editor
 
 

Rings and pinion gears, valve springs made of H-11 or H-13 steel, and brake rotors for heavy haulers and race cars, have lasted two to four times longer after cryo treatment. Cryo processing has three benefits, specifically increased dimensional stability, stress relief, especially for aluminum, titanium, composite materials, and improved wear or abrasive resistance.

The process completes the austenite to martensite transformation that occurs during heat treat in steel alloys.  Heat treating increases hardness in tooling, while post-heat treat cryo processing with a mild draw increases hardness by an additional 1% - 2%.

The process uses Liquid nitrogen to cool parts from room temperature to –300F at a rate of ½ to 1F per minute for maximum stress relief.  Then, maintaining the parts at –300F for 18 to 36 hours completes the austenite transformation.   The more carbon in the material, the colder and longer the parts are kept at low temperature, according to the customer’s specific needs.  After the “cold soak,” the parts are returned to room temperature at ½ to 1-minute rate.  Usually, three heating and cooling stages (called a “triple draw”) are included, depending on the material, with a one-hour hold at the temperature extremes.

Cutting tools are the largest market for the process, including drill bits, endmills, slitter knives, punches and dies.  Cryo processing also is used to treat TiN coated tooling, HSS (high-speed steel) saw blades – bandsaws, circular saws, jig saws, M-series blades – and carbide-tipped saws (C-2, C-3 and C-4).   In the 1995 ASM heat treater's guide, 67 out of 77 tool steels listed have cryogenic stabilizing specified as the only method to increase dimensional stability after heat treat.

Cryo processing also is used to stabilize aluminum and titanium, since they are often hard to handle during machining.  In aerospace applications, cryogenic tempering conditions the metal in aluminum optical benches, so that large temperature variations can be tolerated with minimal distortion.  Once a part has been cryo treated, additional cryogenic processing will not usually make any difference.  When a tooling manufacturer has included cryogenic treatment as part of the process, additional treatment by the end user will usually have no effect.

Multifaceted tools or materials need to be separated into it individual components for cryo processing, since the rates of cooling may vary slightly between different grades of metal.  Smaller items and more intricate tooling process better if disassembled.  It is less critical on the larger items; for example, processing is not a problem for a cast iron or aluminum engine block with steel sleeves without disassembly.

Consistent Results for a Wide Range of Applications:
 

Calsonic Yorozu Corporation, a Tennessee subsidiary of Isuzu, uses a large HSS twist drill to manufacture chassis.  The drill is about 1’ long by 7/8” diameter and costs about $80.  Two drills are mounted on a robotic arm in an assembly line and usually last for only 100 holes.  Cryo treating the drills costs about $10 and increases the tool’s life between 20% and 50%.  Production is now getting between 120 and 150 holes from a single drill with less downtime. Hexell is said to be the world’s largest manufacturer of composite materials.  The company has been cryo treating the tooling used to cut Kevlar, titanium and aluminum during production.  They are a large tool buyer, and the 300% increase in tool life from cryogenic tempering saved them about $1/2 million in tooling cost during 1197.  The treated tooling includes ¼” and ½” endmills, about half of which are coated, and a scissors shear.

The teeth of the backhoes (called “frosties”) used to dig frozen perma-frost in Alaska were wearing out too quickly.  After cryo treating, the life of the teeth increased from about four hours to 16 hours.  In another heavy-duty application, a paving equipment manufacturer builds and supports paving equipment to mix asphalt.  The company uses 12 flute endmills, called “slugger bits,” to cut stainless steel.  The bits, some of which are coated, cost $20 to $50 each.  After cryo processing the tooling life increased by two to three times.

Gears in heavy equipment or transmissions, cast iron or forged items also can benefit from processing.  When the military tested cryo treating helicopter gears in the 70’s, they found that the process improved durability and reduced noise, which turned out to solve several problems in combat.  Noisy working environments are improved through cryo treatment by providing greater longevity and safety for gears and moving parts.

The process has also become popular on the race car circuit among such well known names a Cale Yarborough and Tony Furr in the John Andretti car, and NHRA professionals, such a Kurt Johnson, Larry Morgan, Allen Johnson and Roy Johnson of ProStock. Race car owners and drivers are always looking for any performance advantage.  In cryogenic treatment of their cars’ parts and engines, if one of the materials in a metal-to-metal contact surface is carbon-bearing, it is a good candidate for cryo treating.   This is especially true if it has already been heat-treated.

In an experiment in another sport, golf balls were dropped from 8’, before and after cryo treatment.  The balls rebounded 2” higher (about 2%) after treatment.  In another test, cryo treated golf clubs showed a 3% to 5% improvement over untreated clubs.  Also, One Cryo is offering its own special line of softball bats, tempered with cryo treatment.

Equipment, Service and Processing Support:

Although the operation is only three years old, the process dates back over 50 to 60 years with many practical innovations and improvements since the 60s.  One Cryo consists of three separate service centers located in Orlando, FL, Seattle, WA and Wasilla, AK.  Regional market variations have meant that the parts usually handled for processing in Alaska are different from the parts processes in Florida.

Every area of the country has much to offer especially the Midwest corridor from Cincinnati to Detroit, the heavy industry areas of the eastern US and the racing areas along the eastern seaboard.   Companies in Oregon, UK and Australia have also shown an interest in setting up franchisee operations.   The western US is also an active area in supporting aerospace manufacturing Boeing subcontractors are involved in discussing the cryo treatment of their in-house tooling for increasing tool life.

This relatively undiscovered industry has also developed its service side to provide cryogenic processing in response to specific regional niches.  One Cryo is equipped to provide an in-house design and manufacturing capability, with engineers on staff for design and fabrication of individual processing systems specific to their customer’s production needs.