Cryogenics Comes of Age

Conducted properly, and by a knowledgeable professional, cryogenic processing alters material characteristics to increase strength, life, and reliability.

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Manufacturing innovations that impart better performance, cost savings, and longer component life are typically expensive, require new equipment, and new or complicated manufacturing techniques to fully realize their benefits. In this light, a simple and cost effective means of actualizing value for dollars seems impossible. Promising technological advances most often have prohibitive upfront costs that make them inaccessible to smaller companies, or require a substantial commitment for those companies that have the financial resources to explore them.

While largely underutilized in many industries, there is an alternative to the standard sea of expensive, uncertain and complex experiments. It is a technology that can make machine parts, machine tooling and other components wear less and last longer. Moreover, it has a record of real-world success. That technology is cryogenic processing.

Science in Space
Cryogenic processing uses temperatures in the range of -310° to -316° Fahrenheit to create molecular changes in tool steels, carbides, cast steels, cast irons, non-ferrous metals, and some plastics. This is a treatment technique few people recognize, and few have tried. Cryogenic processing has had a bumpy maturation. Plagued with unfulfilled promise and the promises of unscrupulous service providers, cryogenics slid into the realm of snake oil and pseudo science. For one thing, the very act of freezing objects to make them perform better has no purchase in our technological paradigm. Our thermal treatment choices have been limited to heat treating, electroplating, and other applied surface coatings. This cryogenic technology of using extremely cold temperature to create positive changes in materials seems at best a fairy tale, or maybe brings to mind old tales of changing base metals into gold. We have all heard about star athletes and other celebrities being frozen after death with the thought that when a future cure for the cause of their demise is discovered, they will be thawed out and healed. This pseudo-science/religion is called cryonics, and it has no relationship to industrial cryogenic processing cryogenics.

With its origins in NASA rocket science, cryogenic processing became a sci-fi comic book technology. That is, until Dr. Randall F. Barron at Louisiana Tech began experiments and research into the validity and application of cryogenic science. Through rigorous scientific study, Dr. Barron has proven the viability of cryogenic processing. His groundbreaking research proved without a doubt that cryogenic processing is a valuable and practical technology. The current evolution of cryogenic science is based on Barron’s work.

Increased Stability
Cryogenically cold temperatures, typically colder than -310° Fahrenheit, induce changes in the molecular lattice of tool steels, other metals, and some plastics. These changes create greater resistance to wear, relieves stress, reduces stress cracking, and creates smoother surfaces that have significantly lower coefficients of friction. Entire structures become more electrically and thermally conductive. The increased thermal conduction allows quicker dissipation of heat and cooler running parts.

As I’ve mentioned, NASA first observed the cryogenic alteration of metal. Spacecraft recovered from orbit that had been subjected to the deep cold of outer space exhibited changes in component metals. One of the most striking changes observed was the increased stability of recovered aluminum parts as they were being machined for re-use.
Unfortunately, translating lab science to viable commercial enterprise has been frustrating and fraught with failure. Attempts to make short cuts, circumvent the realities of physics and otherwise trying to fiddle with Mother Nature have produced results that have been far short of commercial viability for either the cryogenic service provider or customer.

Occasional successes have for the most part kept cryogenic processing alive. For example, aluminum ball bats that make big sluggers out of Little Leaguers, golf drivers that get increased yardage off the tee, razors that shave seven or eight hundred percent longer with comfort, panty hose that are extremely run resistant, fishing line that loses curl memory and lays flat on the water, lawn mower blades that stay sharp much longer, and string trimmer line that is much more durable. Unfortunately, these amazing cryogenic achievements don’t have much commercial applicability unless you’re a Little League coach, or you operate a municipal park.

Recent Advances
In the last few years, advances in cryogenic technique and technology have begun to reveal astounding benefits for the users of cryogenic processing. For example, a company manufacturing automotive components involving stamping out brass parts found that the stamping tooling for one part went from 44,000 hits to well over a quarter of a million after being cryogenically processed. Another of their progressive die sets went from 60,000 hits to well over a million. More amazing was that after use these tooling components were re-machined, and when returned to service they retained and operated with the same striking results without further cryogenic processing. Sawmills using cryogenically processed knives have realized extended knife life of three or more times. Other benefits imparted by the cryogenic process include reduced galling, elimination of the need for wear resistant coatings, reduction of stress cracking, and reduced maintenance attention.

Cryogenically processed gears not only double or triple in-use life, they run quieter and smoother. Splined components last longer and function more smoothly, even with the typical axial and radial loading these items are subjected to. Roller chain quits stretching, and sprockets run much longer. Of course the manufacturers of gears and machined parts have benefited the most by how much longer their machine tooling lasts. Hobs, mills, drills, keyway cutters, broaches, carbide inserts, collets, and chucks are some of the items successfully cryogenically processed. Customers report that a dollar invested in cryogenic processing returns three to four dollars in benefits.

Cryogenic Conversion
Most companies considering cryogenic processing have a few predictable concerns. Contrary to what one might think, cryogenic processing does not impart brittleness or dramatically affect hardness. Hardness is not increased or decreased by more than two Rockwell C scale points (see Figure 1). There are changes in the crystalline lattice that produce observable phenomena including greater thermal and electrical conductivity, stress relief, structural stability, smoother and cooler running mating surfaces, and improved wear resistance.  Cryogenic processing penetrates throughout the part and can’t be worn away (Figure 2). The cryogenic effect is not a coating or surface treatment. It is a physical change in the molecular structure. The cryogenic effect lasts as long as the component lasts.

By comparison, heat-treating steels has a primary objective of achieving greater hardness, thus creating parts that wear less and last longer. A large part of the heat-treating process involves converting austenitic grain structure to martensitic grain structure. This conversion creates greater resistance to wear and longer tool life. Due to the necessary constraints of commercial heat-treating, this conversion is seldom more than 65 percent complete.  Cryogenic processing brings this conversion much closer to 100 percent. In addition to the austenite to martensite conversion, research has suggested that fine carbide particles are formed in the microstructure boundary lines and in different areas rod-like carbides are formed, adding to the increased wear resistance of the component being cryogenically processed. These and other structural changes are the progenitors of creating greater wear resistance characteristics. To achieve maximum results, ferrous metals should be heat-treated before being cryogenically processed.

The cryogenic process is both simple and rigorously prescribed. Materials are placed in a cryogenic processor (see Figure 3, Figure 4). Most of these devices look very similar to large chest type deep freezers, but there are some cylindrical processors. The cold temperature is produced by the use of liquid nitrogen. Through computer control the nitrogen is first injected into the cryogenic chamber as a vapor. The temperature in the cooling chamber is reduced at a rate of one degree a minute, or even slower for parts with larger cross sections.

As the temperature nears -160° C the vapor becomes a mist, and then at -194° C the injection stream is liquid nitrogen. At this point the chamber is filled with liquid nitrogen and the chamber’s contents are left to “soak” in the liquid nitrogen for a minimum of 32 hours. After the cold soak and the liquid nitrogen has gassed off, the parts are removed from the cryogenic processor and placed in a tempering oven (Figure 5) and tempered to lock in the cryogenic effect. The complete details of the cryogenic process are proprietary knowledge and are the property of my employer, Down River Cryogenics.

There are some cryogenic service providers who use equipment that is both cryogenic processor and tempering oven in one unit. As with most multipurpose devices, these units don’t perform either job very well. A separate cryogenic processor and tempering oven produce results that are clearly superior. This two-unit technique requires more equipment but the benefits justify the methodology.

Methods Matter
There is a form of cryogenic processing where the parts being processed are subjected to temperature cycling. This involves taking the temperature down to a temperature in the range of -260° F for a period of an hour or two, then increasing the temperature to around +300° F for a couple hours before repeating this cycle several times as prescribed by an esoteric formulary of little scientific origin. Results are as good as the science behind this roller coaster scheme.

Then there are cryogenic processors who “cold soak” for just a short time, often less than eight hours. As with heat treating, cryogenic processing requires specific time and temperature formulation. These are critical factors in achieving satisfactory results. The cryogenic process is in some respects similar to heat treating in that by using different temperatures and soak times, different results can be obtained. Tempering, case hardening, normalizing, and annealing are normal results that are all heat treatments but not full heat treating. Using very low but not deep cryogenic processing temperatures and shortened processing cycle times can induce some positive changes. Some cryogenic practitioners temper cryogenically processed metals for only two to three hours or less, some not at all. As a result, many cryogenic service providers have consequences that are bounded by the 80/20 rule. About 20 percent of the processed items show some positive results, the other 80 percent show little or no improvement. There are cryogenic processors who generate successful results 95 percent of the time or more. Applied science and scientifically developed cryogenic technique make the difference.

The major reason cryogenic processing has had such a varied history of results is the disparity between the various cryogenic and near cryogenic processing techniques. It took a long time and a lot of experimentation for heat treating to evolve into the science that it is now. The “recipes” for the heat treatment of all the various steels and other metals are set out in specific detail and were developed over years of experimenting. The heat-treating results obtained depend on how well the heat treater followed the recipe. This same recipe-following procedure is also applicable to cryogenic processing. In its current state the proprietary, the recipe book for cryogenics is held by very few operators in the cryogenic processing business. For someone wishing to try cryogenics, find a cryogenic processor and ask for a free test. If tested items exhibit the desired outcome, wonderful. If they don’t, try another cryogenic processor. You will eventually find one who owns the recipe book.

When selecting a cryogenic service provider, choose one that will either provide free test processing or will agree that if results aren’t cost effective or as otherwise needed and agreed to, you won’t have to pay. Look for a processor who has references in a broad industry base.

Buyer Beware
Cryogenic processing is still plagued by those who promise results they can’t deliver. One company has a Web site claiming they invented cryogenic processing, have thousands of customers, and are a major player in the scientific development of cryogenic science. The reality is that they are a telephone boiler-room sales outfit with a lot of promises and little performance. Looking at their Web site one would conclude they invented ice cubes. What they really want to sell is a setup of their cryogenic equipment, a lot of blue-sky promises, and very little success for the naive buyer. The fact of the matter is that its not so much the equipment as it is the processing technique. Almost anyone could come up with a large insulated metal box and say that’s all a cryogenic processor is. What counts is how the cryogenic process is executed. Remember when your high school science teacher immersed a banana in a flask of liquid nitrogen and then whacked it on the tabletop? Pieces flew everywhere. This was not cryogenic processing.

Experienced, successful cryogenic processing companies with business built on repeat customers, ethical practices, and cost-effective results are out there. You just have to look for them, but it’s well worth the search.