Cryogenics: Deep Freeze, Deep Secret?

Could this be a deep, dark snowmobile racing secret that someone hopes never gets out? If the opportunity were opened to inexpensively treat your engines and other sled components so they would last three to five times longer, would you be interested?

Deep cryogenics is a relatively new process for hardening metal to resist wear. The process is not a coating, but a permanent, irreversible change completely through the metal structure. It is applicable to all the metal in a snowmobile from the studs and carbides to the engine. Deep cryogenic processing is a computer controlled process that very slowly lowers the temperature of metal parts to -310°F below zero. Think of it as an extension to heat treating. The end results are engines that refuse to wear out and other applications where the treated parts wear many times longer than normal. The process increases performance and cuts repair costs significantly by reducing wear for both new and used parts. Already in use by NASA, Indy car racers, and in other racing applications - but it is, (as far as we know) totally new to snowmobiling. Cryogenic processing would allow a racer to cross the finish line more often by significantly increasing durability and reliability at a nominal cost. To finish first, you must first finish.

The word, "Cryogenics" comes from two greek words - "kyros" which means cold or freezing, and "genes", meaning born or generated. DEEP cryogenics (below -300°F) has created many new applications for racing as well as ultra-cold physics. It is a space age process that significantly extends the productive life of metal tools, machine parts, and engine components.

The idea of rapidly cooling heated metal to strengthen it isn't new by any means. Heat treating is what gives metal its hardness, toughness, wear resistance, yet retain its ability to be molded - its "ductility". Anyone that has frequented old blacksmith shops probably remembers the sound of the sizzle and the steam created when a red hot part was plunged into a barrel of water.

However, the term "heat treating" is actually misleading. It really should be called "cold" treating. The beneficial changes don't actually take place from the heating, but rather the cooling from high temperature. Nor do the good changes stop at room temperature. They continue to grow to absolute zero.

Racers and manufacturers have experimented with applying dry ice to heat treated metals (-120°F) to change the molecular structure of the part. Studies have found that the effect of such shallow cryogenic treatments is minimal, unless performed as a part of the initial heat-treatment cycle. However, even when performed properly, this type of shallow treatment would change only 85% of the retained austenite (large, softer particles of iron) to martensite (a denser, harder, and more refined material.)

Deep cryogenic temperatures of below -300°F are required to effect a complete molecular change in most alloy steels, and convert an additional 8-15% of the remaining austenite to martensite.

Because the deep cryogenic process makes no visible changes to the metal, metallurgists (metal scientists) have been skeptical of the process. Since the deep cryogenic process converts such a small percentage (8-15%) in comparison to normal heat treating (85%), it was thought to be an inefficient process. True statements, but an inaccurate conclusion.

The subjected metals develop a more uniform, refined microstructure with greater density. "Carbide fillers" are pre-

cipitated as a result of the deep cryogenic processing. (US snowmobilers are familiar with the durability of carbide!) The amount of carbide would actually triple in the structure, filling the open spaces (micro-voids) resulting in a much denser, coherent structure of the steel.

The increase in the amount of "carbides" is where the great increases in durability and wear resistance come from. The change is uniform throughout the material, unlike a coating, and will last the life of the material regardless of any finishing operations. It should be noted however that the benefits from this process do vary and depend on the exact type of metal being treated.

Various studies, including one per-formed by the Department of Mechanical Engineering at Louisiana Tech University support the increased life claim. Their scientists found that for various metal samples processed at -320°F, the wear resistance was approximately 2-5 times greater than that for samples processed at -120°F.

Previous (unsuccessful) attempts at cryogenic treatments were made by dropping a motor part into liquid nitrogen, which would CREATE thermal stresses rather than relieve them. (Like dropping an ice cube into a cup of hot coffee. The stress created on the exterior of the ice cube by the hot coffee while the interior of the ice cube is still frozen causes the cube to crack as a result of the stress shear due to differing rates of "thermal growth".)

The dry deep cryogenic tempering process doesn't expose the material to liquid nitrogen, thus eliminating the risk of thermal shock. The material being treated is cooled very slowly at a rate of less than one degree per minute. The computer controlling of the process brings a measure of accuracy and consistency to the process.

TOUGH ENGINES:

The deep cryogenic process has been used successfully on crankshafts, camshafts, cylinder heads, connecting rods and blocks. It is also effective on cylinder heads and blocks after they have been welded. Welding creates stress within the metal. Cryogenic processing returns metal to its relaxed state by stress relieving and stabilizing the metal, making it more durable and less susceptible to micro cracking in

the weldment areas. Normally when engine parts are assembled, they will "move" as engine heat builds, creating undue eccentric wear as a result of warpage. Parts which are "finish machined" after deep cryogenic processing will not move, hence there is less wear and abnormal tensions.

Automobile and motorcycle racers report being able to run significantly more races between rebuilds. A small block Chevy treated ran at over 8000 RPM for an entire racing season. When disassembled, normal cylinder wear was expected to be from two to four thousandths. The motor showed less than one-fourth of one thousandths wear. Bill Barnes, a kart racer and owner of BKM racing in North Creek, NY, treated his kart racing engine and advanced the timing to really make it run hot. After racing for an entire season (over 2,000 laps) the wear in the cylinder consisted of only four ten-thousandths of taper. There was no wear on the rod or crank journals, and when the cylinder was honed for the rebuild it took LESS than one-thousandths to remove the taper and bring the cylinder back into perfectly round condition.

HELP FOR SNOWMOBILERS:

The potential for cryo-processed products for snowmobile racing are numerous and can be of great benefit, even for racers on a tight budget. While the major durability increases come from treating alloy steels, aluminum components such as engine cylinders can be treated cryogenically. Machinists working with go-kart and motorcycle racers (including Yamaha, Rotax, and Suzuki motors) report significant gains in machinability and in the finish of the aluminum. Processed engines machine much cleaner and act more like a piece of "aircraft aluminum". Perhaps the greatest benefit is that the treatment raises the distortion temperature of the aluminum, and racers claim they are able to run even leaner and hotter, making quicker lap times. Another clue that the cylinders are harder is that it takes 4-5 times longer to finish hone a processed engine than an un-processed one. The stress relief allows for tighter tolerance machining and dimensional stability. Treated heads would resist warping. Crankshafts would be stronger, and crankshaft failure has been a subject of more than one racer going home empty handed. Cylinder studs, pistons, rings, and all metal engine components would be stronger and last longer.

Suspension components, rod ends, chains, and all of those steel parts that typically break during racing could benefit from the process. The weak areas created during the welding of the entire front and rear suspension arms would be strengthened. How about the appeal of lightweight components with no sacrifice in strength? It is possible that almost every heat treated component in a snowmobile could be made lighter, and remain as strong (if not stronger) by using the deep cryogenic process.

What about studs and wear bars? Since we don't know of anyone actually using the process on any of these materials, we can only speculate and apply the increases in durability experienced in industrial and other racing applications. It is difficult to know if durability increases of four to five times are possible in this application, but would a racer have an advantage if his studs and carbides lasted, say, twice as long? Not unlike the condition of the tires on an Indy car, when you start to lose control of your vehicle you are at a disadvantage. Considering some of the brutal conditions that races were conducted in last season, we would tend to think that he who had the most durable traction products throughout the race would have an advantage.

Would more durable studs and carbides appeal to the trail rider? The big question here is the cost of the treatment. The base price is determined on the amount of poundage. It you have $250 invested in a set of carbides and a bag of studs, how much would you be willing to pay to increase their durability? It would be far more economical for manufacturing (volume) applications, but the amount of parts each dealer sells in a season could make for their own "custom order" and remain cost effective, say $5.00 per pound.

300 Below Inc. cryogenically processed over a half million pounds in 1995 of high performance racing engines, tooling, dies, cutters, and drills. They also process such diverse items as musical instruments, razor blades, rifle barrels, guitar strings, camera mounts for NASA, and hundreds of thousands of knife blades. The Deep Cryogenic Processing of Racing Engines appeared on the Discovery Channel's high technology show "Next Step" that aired nationwide twice during October 1995.