The Cryoprocessing Equipment
Less is more
I’ve had discussions with customers whose experience extends back to WWII clays. I’ve learned from their oral history that a crude form of cryogenic processing had its origins at the Watertown Arsenal (Watertown, MA) during the war years.Under the guidance of Clarence Zener, who would go on to develop the Zener diode among other advances in solid-state physics. The method was straightforward; steel cutting tools were immersed in liquid nitrogen for a brief period of time, removed from the liquid, allowed to warm up and placed into service in the arsenal’s production lines. Occasionally tools would crack or chip as a result of the thermal shock associated with the rapid rate of cooling. Some tools might become brittle because of the newly formed and untempered martensite and chip in service. Of the tools that survived this crude quenching, many exhibited dramatically enhanced service life.
During the 1960’s, a few purveyors of cryogenic processing services started using multistage mechanical refrigerators in conjunction with insulated “cold boxes” to slowly cool tools to cryogenic temperatures. Rather than resorting to solid (tool) to liquid (liquid nitrogen) heat transfer they utilized gas kinetics to remove the latent heat from the tooling, a far gentler process. Not only did this avoid the problem of cracking during the cool-down, but also it yielded better wear resistance enhancement. This dependence of wear resistance upon cooling rate would later be quantified by Randall Barron (I). Post refrigeration tempering was also employed to toughen the fresh martensite to further improve the process.
With the growing acceptance of cryogenic processing today, several manufacturers now offer liquid nitrogen based processing equipment that attempts to mimic the slow cooling rates of mechanical refrigerators. Some are successful in this endeavor. Surprisingly, some still are proponents of the solid-to-liquid rapid cool down.
A crucial element of any system that purports to ensure freedom from thermal shock is a liquid-to-gas heat exchanger used in conjunction with a circulator fan. The heat exchanger contains the boiling liquid nitrogen (LN2 ) and absorbs the thermal shock while the fan circulates gaseous nitrogen over the heat exchanger (HE). and the payload to slowly remove the latent heat of the payload. Add a programmable controller and LN2 flow controlling solenoid valve, and a thermocouple to monitor gas temperature and you have a servo system that permits the execution of predetermined time-temperature profiles. Introduce electric resistance heating elements in front of the circulator fan, upgrade to a dual output controller and you can now cool and temper in the same machine. It seems simple enough, and yet equipment has been offered which departs from these essential principles with unfortunate results. Some equipment suppliers don’t bother with the heat and circulation or fan and simply provide a spray bar to rain down a “fine mist” of LN 2 droplets on delicate and expensive steel and carbide tooling having stress concentrations at their sharp edges. It’s not clear how “fine” this mist must be to avoid rapid cooling of the surface of the edges of such tooling while the core remains warm . This results in contraction of the surface with the generation of transient tensile stresses; chipping and cracking may follow.
At least one manufacturer slowly floods an insulated vessel containing the payload. The theory is that since the LN2 level rises slowly to envelop successively higher levels of tooling, that parts above the liquid will have time to cool clown before the e liquid actually hits so the e shock won’t be too great. Unfortunately, this scenario ignores stubborn physical realities. The temperature gradient above a quiescent pool of LN2 is very steep and the rate of heat transfer from a solid to LN2 is orders of magnitude greater than that between the same solid and gaseous LN2 at the same temperature as the liquid. This modified “dip” technique is risky business and should be avoided. In an attempt to reduce LN2 consumption, some equipment suppliers have resorted to hybrid systems that employ mechanical refrigeration with an LN 2 assist. In principle, this is a reasonable approach; its implementation, however, should be carefully scrutinized. The mechanical refrigerator component must provide a sufficient BTU removal rate to transfer out latent heat rapidly enough to get the temperature down in the time required by the programmed Controller. Larger payloads will require a greater BTU removal rate than a small payload running under control of the same program. Simply monitoring the chamber gas temperature may not ensure that the payload is getting cold. An underpowered mechanical refrigerator may have enough “oats” to cool a thermocouple, especially if it is located near the expansion coil, but not do much to a large mass of steel. Under this condition, when the LN2 “assist” kicks in to take the load down the rest of the way, you risk thermal shock. The controller thinks the payload is colder than it really is and unleashes enough LN2 to rapidly achieve a larger temperature drop than intended for a given time interval. Once again, thermal shock rears its ugly head.
From a purely practical point of view, hybrid systems may combine the worst of both worlds. You need a supply of LN2 and you also need to confront the maintenance of refrigeration compressors that are required to make repetitive deep temperature descents. These compressors are happier if they are required to merely maintain a low temperature in an insulated chamber to which relatively small masses are occasionally added; a good example would be a biological tissue storage refrigerator. Cryoprocessor service is very severe and requires heavy duty equipment if this approach is to yield reliable service.
Notice that the term cryogenic processing includes the word “cryogenic.” The principles of cryogenic engineering have been integrated into well-developed industrial practices and devices. Therefore, it is surprising that most manufacturers of cryogenic processing equipment have employed little use of these principles. The typical machine, even those designed to avoid thermal shock, is little more than a modified tempering oven, with ceramic insulation replaced by polyurethane foam. The engineering objective in designing an efficient cryoprocessor chamber is to minimize heat gain from the ambient surroundings. Such heat gains must be offset by LN2 consumption when compared to electricity or natural gas used for heating
The sign of an economical cryogenic system requires techniques not normally drawn upon in heating applications. Merely injecting foam insulation into the hollowed-out walls of a tempering oven won’t do the trick. Any solid insulation is subject to failure by means of thermal cycling fatigue. when the inside of the chamber gets cold, the inner layer of insulation starts to contract while the outer layer of insulation remains near room temperature. Differential contraction of the insulating mass leads to internal stresses. In machines that also temper, the stress distribution gets reversed. Repeat this cycling many times and the insulation will fatigue and crack and may crumble. Deteriorating insulation leads to increased LN2 consumption and also to thermal gradients within the processor. Polyurethane insulation is rated for a maximum operating temperature of +225 °F. and yet at least one equipment manufacturer uses polyurethane up against the inner chamber wall which gets to + 300 °F and higher. Of course, this slow deterioration occurs within a hidden space and so is not evident to the casual observer; only his LN2 distributor knows for sure!
The typical tempering oven and the typical cryoprocessor is constructed of thick steel members welded together to ensure structural strength. Consider the heat transport consequences of this approach. The outer walls of the device communicate thermally with the casketed surface against which a door closes. The gasketed surface communicates with the chamber interior.
During a cooling cycle, the outer walls absorb ambient room heat. It is , in effect, a giant heat absorber immersed in an infinite heat source, the atmosphere re. This heat travels through the gasketed surface into the inner ,vales, which act as a radiator. The rate of heat conduction is proportional to the cross sectional area of the members; the thicker the steel the more severe is this problem. This is called a “heat bridge” and is a bad thing because you must expend LN2 to offset these gains. Note: the typical cryoprocessor door is also a heat bridge and contributes about as much heat gain as that of the body of the machine . Other heat bridges , of less importance, would be fan shaft penetrations and even LN2 supply pipes.
But wait, there’s more. The same massive steel members that contribute to ambient heat gain also contain latent heat that must be removed with that of the payload to the tune of about 1/4 liter per pound. Unfortunately, there is no “pay” associated with this load; it’s strictly operating overhead. There is today a certain sense of pride expressed by some in owning a cryoprocessor built like a tank. It may inspire a feeling of machismo to own such a device. The operating cost associated with such an indulgence can be quite substantial and, like deteriorating insulation, is hidden from view
Cryogenics engineers have confronted these problems and provided clever solutions. Principal among these is the concept of vacuum insulation. Instead of relying upon the insulating value of trapped air pockets as in solid insulators, vacuum insulation relies on nothing . That is , you cannot have heat conduction or connection across a vacuum . The third possible transport mechanism, thermal radiation, can be mitigated by the insertion of an electromagnetic radiation reflector, aluminum foil, in the vacuum. Of course. the vacuum must be contained in something. This is, typically, a pair of concentric cylinders of nearly equal diameters, welded together around the perimeter of one set of circular ends with each opposite end capped with its own circular plate displaced slightly in the axial direction so that they don’t touch. Alternate layers of aluminum foil and fiberglass cloth fill the annular space between the cylinders, which is evacuated to about 10 -6 torr. This is essentially an industrial strength thermos bottle and is nearly perfect insulation..
The major mode of heat gain is via solid conduction from the outer cylinder through the junction between inner and outer cylinders and can be mitigated by careful design. Material thickness is intentionally kept to a minimum. The hoop stress resulting from the pressure differential between the evacuated region and the outside world is accommodated by the cylindrical geometry. The payload weight is supported at the junction between the inner and outer cylinders so that no support members, who would be heat bridges, are required. There is no solid insulation to fatigue or slowly burn up. The non-pay load is at a minimum. Vacuum insulation provides an example of less really being more. Less mass means less wasted LN2, which means more operating efficiency. Less solid insulation, really no solid insulation, means less heat gain and no degradation of thermal performance, which again means greater operating efficiency.
A numerical example comparing foam insulation to vacuum insulation with regard to heat gain is compelling. Consider a six inch slab of foam and a thin vacuum region containing reflective layers, each maintained with a temperature difference across their respective surfaces of 400 °F. The foam passes 15.3 BTU per hour per square foot while the vacuum passes 0.0080 BTU per hour per square foot. The vacuum is more than a 1900 fold improvement over the foam, is more durable than the foam and takes up considerably less space!
Continual incremental improvements over the years now enable us to offer highly refined, efficient, durable and reliable cryoprocessor embodying all of the positive features described above.
Reference: (I) Randall F. Barron, Cryogenic Treatment of AISI-T8
Cryogenic treatment is ineffective in properly heat treated components. No solid-state transformations occur below the martensite finish temperature (Mf). Non-ferrous materials are not affected by cryogenic treatment because they contain no retained austenite for transformation to martensite. It is also obvious, to even the casual observer that the earth is flat and the sun and stars rotate around us.
Fortunately, I was unaware of any of this conventional wisdom when I was first introduced to cryogenic processing thirty eight years ago. My background had been in physics; specifically non-linear spectroscopy and quantum electronics. A high school course in metallurgy in the ’60s provided the basis for my understanding of metals and consequently I didn’t realize that cryogenic treatment was essentially “snake oil.” I had only the observations, made by reasonable people who had availed themselves of treatment services that remarkable improvements in performance could result from cryogenic processing. Based on this admittedly non-scientific study, I undertook with a partner, Bruce Norian, a radical career change, forming our company to offer cryogenic treatment services and eventually to design, manufacture, and sell Cryo-processing equipment.
Having come from a sheltered academic background, I was ill prepared for the response of some prospective customers; even after we had demonstrated the technical and cost effectiveness of the process. A particular encounter, now over three decades old, remains vivid in my memory. We had successfully treated a guillotine bade for a major manufacturer; the engineer who supervised the test reported three times more production from the blade after treatment as compared to the identical untreated blade. When asked if he’d like to treat a meaningful quantity of tooling, the engineer replied, “If cryogenic treatment was so good, then we would have been doing it years ago.” Period. This otherwise rational individual was telling me that he was not about to believe his own eyes. He hadn’t learned about cryogenic treatment in school; his superiors (at the large multinational company) hadn’t either and he wasn’t going to fall into a trap set by some crafty salesman (me). Snake oil!
Years have passed since this sobering encounter and along the way there have been additional rebuffs; but there have also been many instances of courageous acceptance of this very cost effective technology. Scores of new service providers have entered the market in the past few years, spreading the message and helping to educate the manufacturing community. In the early days, when I’d make a sales call, carefully and conservatively explaining the known mechanisms and advantages of cryogenic processing, the responses ranged from restrained skepticism to outright dismay. We had trouble giving it away! Today, the situation has improved dramatically due to the collective effort of many “pioneers” to get the word out. We now routinely receive unsolicited requests for treatment services and for processing equipment. This increased activity has produced a wealth of feedback attesting to the validity of cryogenic treatment as a productivity enhancer. Novel and unexpected applications are discovered on a regular basis. Silver and brass instruments and instrument strings have their acoustic properties altered during treatment, and musicians like the change! Vacuum tubes become less microphonic and hence do their thing better when treated. High performance internal combustion engines yield higher performance. Guns shoot straighter and vegetable seeds germinate sooner. Figure skaters glide easier, surgeons cut cleaner and baseball players and golfers hit further. If this is snake oil, then someone ought to bottle the stuff!
Over two thousand years ago, Eratosthenes (Greek scientific writer, astronomer, and poet, who made the first measurement of the size of Earth) demonstrated that the earth is spherical and by using simple instruments, a protractor and measuring stick, was able to accurately estimate its diameter. Copernicus suggested and Johannes Kepler proved, by painstakingly constructing a mathematical model that accurately reproduced the best observations of the day, that the earth is not the center of the universe. In doing so, they gave us the foundation of celestial mechanics and ushered in a new, rational way of understanding nature, displacing mythology and astrology. Prior to the work of these remarkable men, the concepts they promulgated were derided as snake oil by the great authorities: Aristotle, Plato, Ptolemy, etc. Careful observation followed by rational thought and mathematical modeling is the essence of the scientific method which enables us to understand the world, turn nature to our benefit and improve our lives; it distinguishes us from all the other species on earth.
The benefits of cryogenic processing are established; the observation phase has proceeded for more than sixty years now. It’s time to move on to a better understanding of the underlying mechanisms by application of the methodology of science. In so doing, we gain intellectually, we hopefully refine the technology, and most importantly, help to dispel the skepticism that impedes widespread acceptance of a process that can help make better products available at reduced costs to everyone.
The ASM has wisely decided to foster this effort by establishing a committee on cryogenic processing whose initial effort will be to establish a data base of all existing research publications related to cryogenic treatment. By making this data base available to the academic and industrial research communities, we may stimulate additional research which will ultimately put cryogenic treatment on an equal footing with conventional heat treatment that occurs at super-atmospheric temperatures.
Some day, hopefully soon, cryogenic treatment will be a routinely specified manufacturing process to the benefit of all. Meanwhile, those whom have already adopted it have an edge.
Dr. Jeffery Levine.
We dive into the Cryogenic Processing and its origins and why it’s indispensable as a process.
The most visited page on our web site is the Cryogenic Myths page. As the process is new to many we thought we would clarify the process is its advantages.
What is Cryogenic processing:
Cryogenic processing is the process of cooling metal parts and some plastic gradually down to -315º F and holding that temperature (different for every type of metal) for a programmed amount of time. Once “soaking” is done we gradually raise the temperature to room temperature and above to finish the process.
What does it do to the parts to make them better?
Cryogenic processing makes changes to the crystal structure of materials. The major results of these changes are to enhance the following:
Abrasion resistance*(refers to the ability of materials and structures to withstand abrasion (a method of wearing down or rubbing away by means of friction.)
Fatigue resistance*(the highest stress that a material can withstand for a given number of cycles without breaking)
The changes we know about are:
- Change of Retained Austenite to Martensite in Hardened Steels.(Martensite is wanted more than Austenite to be brief)
- Reduction of Residual Stress.(Stress Causes your parts to crack or break prematurely)
- Precipitation(Cause more)of Fine Eta Carbides in Steel. (Formation of carbides is great for strength)
Reduction in point defects.
(Point defects are where an atom is missing or is in an irregular place in the 3d structure that is your part.)
Redistribution of alloying elements.
- Alloys are:
” A metallic solid or liquid that is composed of a mixture of two or more metals…metal elements, usually for the purpose of giving or increasing specific characteristics or properties: Brass is an alloy of zinc and copper.)”
What is gained by distributing all the elements in an alloy you are spreading all the elements more evenly so they have the intended effect on the entire piece. The effects are strength and durability
- Making the crystal lattice structure more orderly.Wood framed homes are built with studs at a certain distance on center from one another. Good spacing and enough of them make the entire structure stronger.
- Why do I need to do this, aren’t the parts good enough?
We can’t think of anyone that wouldn’t want to get the highest value possible from anything they own or just bought.
Getting 2-5 times the life out of anything is considered a huge success by any measure.
Deep Cryogenic Processing done correctly unlocks more strength, durability in Aerospace parts, racing engines, transmissions, Carbide tools, high speed steel, Aluminum, Magnesium, Titanium etc etc. If your parts are already made well, then our Deep Cryogenic treatment will make them HYPER-PERFORM.
NOTE: It won’t make parts indestructible. Used within their intended use, the parts will outperform untreated parts.
The Racer’s Edge article appeared in Heat Treating Progress, the official heat treating journal of ASM International. ASM International is the world’s premier metallurgical society. It appeared in the November, 2001 issue. This was the issue distributed at the ASM sponsored Heat Treat Trade Show in Indianapolis.
The article was written by Controlled Thermal Processing’s Roger Schiradelly and Frederick Diekman. It was written at the request of ASM who wanted some racing content in the issue due to the location of the show. We had little time to write it as the request came to us only several weeks before the publishing date. It seems that one of our competitors was originally going to write it but bowed out at the last moment. We dove into the project. We got pictures from Richard Petty’s race shop for the cover.
The article caused a great bit of interest in cryogenic treatment. Some of it was controversial. Metallurgists from a huge aerospace company demanded that the magazine apologise for publishing an article about voodoo science. Dr. Jeff Livine and Frederick Diekman wrote a reply to their rather vitriolic letter, stating scientific studies and giving them sources for our claims in the article. Nothin more was heard from that company. That is the way it was back in 2001.
Racing pushes engine and drive train components to the absolute limits of their durability. Extending those limits means more speed, better safety, and more races won. For this reason cryogenic processing is becoming a necessary part of the manufacturing process for racing components. This racing experience will serve as an example to manufacturing industries now similarly engaged in their own competition against manufacturing costs and waste, and the challenge to provide high quality products with superior performance.
Racer’s Edge Article
Using extremely low temperatures to make permanent changes in metal and plastic components, cryogenic processing is not the typical -84°C (-120°F) cold treatment most heat treaters use. It essentially involves exposing materials to temperatures below -184°C (-300°F). If done correctly, it creates a permanent change to the material that alters many wear characteristics.
The concept of changing metal through the use of low temperatures is relatively new and not well under- stood. Yet it is certain that exposure to very low temperatures does make permanent changes in virtually all metals and to some plastics. Observed changes include:
- Increased Resistance To Abrasion
- Increased Resistance To Fatigue.
- Precipitation of Very Fine Carbides
In ferrous metals that contain carbide forming elements:
- Transformation Of Austenite To Martensite In Ferrous Metals.
- Change In Vibrational Damping.
- Increased Electrical Conductivity.
- Anecdotal Evidence Of Changes In Heat Transfer.
- Stabilization Of Metals To Reduce Warping Under Heat, Stress, And Vibration.
In practice, cryogenic processing affects the entire mass of the part. It is not a coating. This means that parts can be machined after treatment without losing the benefits of the process. Additionally, cryogenics apply to metals in general, not just ferrous metals. For many years, it was assumed the only change caused by extreme cold was the transformation of retained austenite to martensite in steel and iron. Because of this, many misinformed engineers still believe that cryogenic processing is “just a fix for bad heat treat.” It is now known that cryogenic processing has a definite affect on copper, titanium, carbide, silver, brass, bronze, aluminum, both austenitic and martensitic stainless steel, mild steel, and others. It is also known that plastics such as nylon and phenolic show property changes.
Cryogenic processing is currently in use in every form of racing imaginable. It is used in virtually every class of NASCAR racing, IRL, CART, NHRA, IHRA, SCCA, IMSA, and ARCA, not to mention tractor pulls, go-karts, motorcycles, boats, and even lawn mower racing. Controlled Thermal Processing (CTP) has even done a fair number of axles for soap box derby cars. Over half of the cars competing at any given NASCAR Winston Cup race run parts that are cryogenically treated by CTP alone. Cryogenic processing can have a positive affect on virtually every engine, transmission, and drive line part, as well as many chassis parts.
Are there definitive tests and data on racing and cryogenic processing that we can point you to? Not yet. Racers do most of their testing on the race track or on the dynamometer. These are not controlled experiments in the classical sense, and in most cases they do not allow the results to be published because of the risk of losing competitive advantages. We do know that the use of cryogenic processing is on the upswing. Its use by manufacturers of racing components has been growing sharply. We also know that very experienced racing experts have examined the effects of cryogenic processing and have been very impressed.
Increasing the durability of components in the vehicles is the main reason for using cryogenic processing. Racing continually presents the engineer with the challenge of designing engine and chassis components that will survive long enough to win a race, but will not have any excess weight as a consequence. Put in too much mass, and a car will be slow and handle poorly. Make components too light, and they will not survive the race. There is al- ways this delicate balance: weight versus reliability. The great thing about cryogenic processing is that it allows an increase in durability without an increase in weight or major modifications to component design. In addition, the use of cryogenic processing has helped some racing teams reduce costs, enabling some expensive parts to survive the stresses of racing for use in subsequent races.
Cryogenic processing has become an integral part of the production process for many racing components. Many top racing teams have the process done if the manufacturer does not provide it. They do so because cryogenic processing has proven its worth time and again under extremely competitive conditions. Racers are generally people in a big hurry and would not take the time for cryogenic processing if there was no advantage to it. Applications that benefit from cryogenic treatment probably number more than anyone expects.
Brakes and Clutches
Brakes of a racing car take a real beating. It is not unusual for a racing vehicle to finish a race with the brakes totally worn out. This is especially true during road races and endurance racing, where brake rotors can get so hot they glow visibly at night. Cryogenic processing can be applied to both rotors and pads. The net result is two to three times the life of untreated components even under severe racing conditions. As a side benefit, the rotors are less prone to crack or warp. It is interesting that drivers report better braking action and feel. Some drivers are so sold on the concept that they have their street vehicle equipped with treated brakes.
Clutches are a form of brake, and the results are very similar. Drag racers have been doing some work on clutch plates to
measure the coefficient of friction in highly instrumented cars. They find that treated clutch facings will develop a higher coefficient of friction but exhibit significantly less wear.
As an offshoot of racing development, cryogenically treated rotors and pads are making their way into fleet operations on the road. The U. S. Postal Service specifies cryogenic processing for their rotors and is experiencing up to three times as many miles as they were getting on the unprocessed rotors. Similarly, many police fleets are starting to adopt treated rotors and pads. They, too, are experiencing large maintenance savings on both parts and labor. What is metallurgically interesting is that the brakes are a gray cast iron that has a pearlitic structure. This rules out the austenite to martensite transformation as the mechanism for increased life.
Springs fail in one of two modes. They either break or their spring constant starts to decline. Either way, it can have catastrophic effects on the performance of the vehicle. Most valve springs are made of specially made chrome silicon steel. The automotive valve spring is a fatigue failure waiting to happen. It typically can lose up to one third of its spring constant during a long race. In some forms of racing, it is just hoped that the valve springs will last through the race. Some drag racers routinely change the valve springs before every run down the drag strip to ensure consistent performance. Typically valve springs exhibit a longer life after cryogenic processing. How much depends on the type of racing, the type of spring, the manufacturing lot of the spring and the criterion for a failure.
Cryogenic processing of springs will usually triple the life before fatigue failure occurs, and it will reduce the amount of spring constant lost from 20 to 30% down to about 7%. This makes it easier to set up the engine, as there is not such a wide variation in the spring performance. It is difficult to determine absolute spring life increases, because the racers typically discard them long before they break. We do know one drag racer that used to change springs after each run: he now makes seven runs before changes. There is a caveat here. Occasionally we come across groups of springs that will not respond to cryogenics. Analysis of these springs usually discloses large inclusions in the wire, which become stress concentrators, causing failures at these locations.
A further advantage for cryogenic processing of springs is that the process seems to eliminate or reduce harmonic vibrations. If you have ever seen a high-speed movie of a valve spring at high engine rpm, you will notice that the spring does not simply move up and down. It does a very complex hula dance because of the harmonic vibrations. Racers typically have to design the spring and valve trains so that harmonics do not interfere with the valve action.
Not unexpectedly, chassis springs are also affected by cryogenic processing. Chassis springs lose their spring constant during a race. This can cause the chassis to lose its cornering ability, which drastically slows the car. Loss of spring constant also alters the height or road clearance of the vehicle. The vehicle height is critical at high speeds because it has a big affect on the aerodynamics of the car, and hence on the handling and the top speed of the car.
Other ramifications of springs sagging are evident. Watch the pit crew after a Winston Cup race as the car is pushed up on to a platform for inspection. If the springs have settled too much, the car may be disqualified. So the pit crew will often be lifting on the chassis as they roll it along to set it up a little higher. When they get the car to the measuring surface, they gently let it down so it does not bounce and settle farther than necessary. You have to know the tricks if you don’t want to lose.
The chassis itself is basically a very large, complex spring, having numerous welds and using not very precise tubing. The metals used here vary, depending on the type of racing. NASCAR frames are made from 1020 steel; other forms of racing use 4140 steel. Of course, other high strength, lightweight materials are also used.
As the chassis experiences vibration during the race, residual stresses in the welds and the tubing can start to relieve. This causes the chassis to change shape during the race, affecting the handling of the vehicle and therefore its speed. We are now working with several teams to do a heat stress relief on the chassis followed by a cryogenic treatment.
Gears, shafts, and assemblies. A study for the U. S. Army Aviation and Missile Command, by the Illinois Institute of Technology Research Institute concluded that cryogenic processing of carburized 9310 steel increased the gear contact fatigue life by 100%, and the ability of the gear to handle load by 10% over the sample material that had undergone a -84°C(-120°F) cold treatment per military specification. They also found that the conversion of retained austenite is only part of the effect on the gear. Most racing gears are 9310 carburized steel, although 8620 is also used. It is interesting to note that there is an experimental gear material under test that specifies cryogenic processing as part of its heat treat.
One major racing transmission maker, after inspecting numerous gearboxes after races, has ascertained that cryogenic processing cuts the gear wear dramatically. This also holds true for road racers of Porsches and BMW’s and other SCCA race cars who are now getting about three times the life on their gear boxes. The major problem all of these racers see is wear on the pitch line of the gear. Breakage is sometimes a problem, but that can usually be traced to driver error, bad heat treatment, or inferior material. Jerico Performance Products, a well-known producer of racing transmissions, supplies gearboxes to over 50% of the racers in Winston Cup, and to many other racers. The company currently has all of its gears and shafts cryogenically processed.
Cryogenic processing also increases the life of other heavily loaded gears. We see a doubling of the life of ring and pinion gears in differentials, even under such severe usage as tractor pulls. Quick-change gears also show dramatic increases in life. Axle shafts, universal joints, and constant velocity joints all show dramatic increases in durability. As the racing of front wheel drive cars becomes more popular, we begin to see more and more constant velocity joints being processed, as this is one of the weak points of the driveline. Axles are treated to stave off fatigue failures in the splines.
Virtually every part of an engine will respond to cryogenic processing, with all components exhibiting life in- creases. Several component manufacturers are starting to take advantage of this and are treating their racing components as part of their production. Some of the main applications are:
- Connecting Rods Usually Fail In Fatigue. This Occurs Because Of The High “G” Loading Of The Piston And Pin. Winston Cup Engines Currently Run Around 9300 Rpm. They Have A Stroke Of Around 86mm (3.375 In.) Pistons And Pins Typically Have A Mass Of Around 650 Grams (23 Oz.). Given These Figures, It Can Be Calculated That The Upward Force The Piston And Piston Pin Exerts On The Connecting Rod During The Exhaust Stroke Is Over 4800 G’s. Although This Calculation Ignores The Weight Of The Small End Of The Connecting Rod, It Can Be Seen That There Is A Repeated Stress On The Rod, Which Has A Cross Sectional Area Of Under 230 Mm2 (0.35 In.2). Cryogenic Processing Increases The Fatigue Life Of Connecting Rods Considerably. Dyer’s Top Rods In Forrest, IL, Claims That They Would Not Release A Rod From Their Shop Without Cryogenic Processing. We Process Steel, Titanium And Aluminum Rods. The Steel Rods Are Generally AISI 4340 Or 300M Steel; Aluminum Rods Are Usually 7075 T6.
- Cylinder Heads. Both Aluminum And Cast Iron Heads Usually Fail By Cracking, Which Results From Both Thermal Cyclic Fatigue And The Flexing Of The Head Under Combustion Pressures. Further, The Heads Are Often Subjected To The Extreme Pressures Created When The Fuel Mixture Detonates. All These Pressures Can Cause The Head To Flex So Much That It Is Not Unusual To Find Debris Such As Piston Coatings Under The Heat Gasket, Blown There During A Combustion Stroke.
Several Winston Cup teams have concluded that 356 T6 aluminum heads yield about double the life after cryogenic processing. Other racers have the heads (both aluminum and cast iron) treated as a matter of routine. Of course, treating the heads increases the life of valve seats and valve guides. It is interesting to note that the heads can be treated with the valve guides and seats installed.
- Camshafts And Lifters. Roller Lifters Usually Fail By Breaking, Some Of Which Is Just Poor Design With Sharp
Edges and stress risers all over. Even so, one customer reports that he gets about five runs down the drag strip unless he cryogenically processes his lifters. After cryogenic processing, he typically gets over 100 runs.
Winston Cup rules specify solid lifters. These cars are turning around 9300 rpm, so valve spring pressures have to be very high to slam the valve shut. The current practice is to create a cam profile that will actually loft the lifter. The lifter is thrown up in the air, forcing the valve to open very fast and then the spring slams the lifter down back against the cam. This creates extreme wear, but it gets the valve wide open as quickly as possible and leaves it wide open to the last possible microsecond.
The lifters start with a slightly convex surface and wear into a concave con- figuration. Typically, they are cast iron and heat treated to the mid 50’s HRC. In use, any wear increases the valve lash and delays valve lift, creating a loss of power. It also leaves a lot of wear particles in the oil. It can take up to three sets of lifters to get an engine through Dyno-testing and the race due to the extreme wear caused by these radical cam profiles and high spring pressures. Cryogenic processing reduces this wear by about half.
Camshaft wear is also a problem. Camshafts are generally carburized 8620 steel, but typical Winston Cup camshafts are 8620, with a layer of stellite welded or spray coated onto the lobes to help reduce wear. The stellite has a hardness of about 52 HRC. It wears and chips badly during a race, changing the valve lash and also the valve timing. In other forms of racing, camshaft wear is not as drastic, but still a definite problem, especially for racers who cannot afford a tear down after each race. Cryogenic processing has proven a boon to these racers because it reduces wear and therefore reduces camshaft replacement costs.
At least one racing-bearing manufacturer cryogenically treats babbited bearings as part of their production process. They found it increased the life of the bearings and also of the steel backing, which tended to fail in fatigue. It is interesting that Cryogenic Processing has an effect on the babbit metal of the bearings. Similarly, bronze bushings used on wrist pins also wear considerably less when treated.
Many racers are processing ball bearings and roller bearings (typically 52100 steel) because they get a three to five fold increase in life. Rod ends used in steering and suspension systems get the same treatment and performance gains.
Cylinders, pistons and rings
Cryogenic processing of piston rings and cylinder walls has been shown to reduce wear substantially. One go-kart racing customer claimed that he got a five-fold increase in engine life before he had to freshen the engine. Better ring seal was born out in pressure readings on a dynomometer. Apparently, this happens because the parts machine and hone better after treatment as a consequence of a more uniform hardness distribution over the surface of the part. (This fellow was a national champion, so he must know his business.) CTP has done tests that show a significant reduction in the standard deviation of hardness readings taken before and after cryogenic processing. In some cases, the standard deviation is one- third of what it was before the process.
Processed piston rings typically wear both less and more evenly than untreated rings. More tribologically compatible with the cylinder walls, they tend to flutter less due to the vibrational damping the process imparts into the material and due to the more even hardness of both the rings and the cylinder walls. All these factors combine to give better ring sealing, and therefore more power.
Cryogenic processing of engine blocks also stabilizes the blocks and reduces warping and distortion due to vibration and heat during use. The same is true for pistons. Several engine builders, who specify the process, have taken careful measurements of pistons before and after use, finding that cryogenically processed pistons distort less under use.
Cryogenics plays a vital role in a process developed by CTP to induction harden the bores of cast iron blocks. This process reduces friction and wear. Here, initial reports indicate substantial horsepower gains from this process.
Crankshafts benefit greatly from cryogenics. Several of the most respected names in the crankshaft business use cryogenics as a part of their thermal treatment. Cryogenic processing greatly decreases wear on crankshaft journals and stabilizes the crankshaft. We have treated every- thing from stock cranks through special racing nodular iron cranks and Racing cranks made of 4340 steel. Virtually all parts that are subject to stress or abrasion can benefit from cryogenic processing. Even head gaskets benefit because the armor around the combustion chamber is subject to both thermal cyclic fatigue and to Flexing fatigue.
Keys to the process
Success of cryogenic processing is critically dependent on the equipment in which the processing is done. The quality and function of the machines available varies from very poor to excellent. So does the ability of cryoprocessor manufacturers to support their machines with technical and processing advice. (More details on the equipment will appear in an up- coming HTP article.)
Cryogenic processing used to be fairly simple. Bring the part down to -184°C (-300°F) typically over an eight hour period. Hold the part at this temperature for eight to twenty hours, and bring it back to ambient temperature over a 15 h period, followed by tempering at a 149°C (300°F). This general formula can be used to good effect for many components, especially when all the previous thermal treatment specs are not known. As they say, though, the devil is in the details. The actual practice is harder than it looks. There are several large companies that have spent a lot of time trying to develop the process unsuccessfully. In fact, the idea that almost anyone can buy a cryogenic processing machine and set up a viable, reliable business is absurd. Metallurgical knowledge is not only helpful, but it is a requirement to achieve effective processing
The optimum process for any given part varies according to the metallurgy and the failure modes of the piece. Al- though “standard” processes will greatly improve components that are sent to us for processing, better results are achieved when the cryogenic process is part of an optimum package of material selection, production methods, heat treat and cryogenic processing . We even spend time analyzing component failures to allow us to optimize all factors in the thermal treatment of the part. This approach yields excellent results, especially for companies that do not have their own metallurgical staff.
Cryogenic processing is destined to become part of the standard production process as opposed to being an add-on process, as it now exists.
CTP selected Midwest Thermal Vac Inc., Kenosha, Wisc. For their unflagging attention to customers’ needs and their quest for doing things right. MTV’s president, Frederick Otto states, “It is becoming more and more obvious that cryogenic processing is a necessary and integral part of the thermal treatment of a quality component.”
By helping customers set up realistic standards and specifications, we have allowed them to develop sophisticated metallurgical standards to ensure the metallurgical performance of their product. According to Roger Friedman of Dyer’s Top Rods, “Integrating cryogenic processing with our materials selection, heat treat, and manufacturing methods has allowed us to make connecting rods that are both light and have a long service life under extreme racing conditions. The result? At the Eldora Million race, where there was a one million dollar prize for the winner, seven out of the first ten finishers used our rods, including the winner.”
The use of cryogenic processing is now starting to extend into the production processes of companies. Racing component manufacturers are beginning to treat their tooling and their cut- ting tools. This is reducing their tooling costs considerably. One firearms manufacturer currently saves over $3,000,000 annually by treating its tooling.
The Cryo future
More research into cryogenic processing is a certainty. When Illinois Institute of Technology created it’s Thermal Processing Technology Center in conjunction with the National Science Foundation earlier this year, it purposely used the term “Thermal Processing” in the name be- cause elevated temperatures are no longer the only means of thermal processing. One of the first proposed projects for this center is to study Cryogenic Processing to determine what factors cryogenic processing changed in metals. There is current interest in the use of the process on H13 steels.
Los Alamos National Laboratory, too, is very interested in doing more work on the subject. Their testing revealed that there were interesting things happening with steels that were cryogenically processed. They are eager to find industrial partners to help fund the research to delve into the process even further.
For more information:
Controlled Thermal Processing, Inc. – Url: www .ctpcryogenics.com
Car Racing Organizations
NASCAR, National Association of Stock Car Racers. This is the organizing body for “stock” cars. From the first race on the beach at Daytona in 1948, to last season’s door-to-door thriller at Atlanta between Dale Earnhardt and Bobby Labonte. NASCAR has provided 52 years of motorsports racing. www.nascar.com
IRL, Indy Racing League. This is the organization responsible for the Indianapolis 500 and similar races. Indy cars are Open-wheel, single-seat cars, open-cockpit and ground-effect underbody; outboard wings front and rear. www.indyracingleague.com
CART, Championship Auto Racing Teams. Open wheel racing in North America and around the world in 21 events. www.cart.com
NHRA, National Hot Rod Association. Drag racing. Now in its fifth decade, the NHRA is the world’s largest motorsports sanctioning body with more than 85,000 members, 144 member tracks, 32,000 licensed competitors, and nearly 4,000 member-track events. www.nhra.com
IHRA, Independent Hot Rod Association. Over 30 years of drag racing make the International Hot Rod Association a pioneer and trendsetter in the motorsports industry. Headquartered in Norwalk, Ohio, IHRA sanctions professional, sportsman, and bracket-racing competitions for drivers at all levels. www.ihra.com
SCCA, Sports Car Club of America. Sports cars of all descriptions. The Sports Car Club of America is a 55,000- member nonprofit organization featuring the most active membership participation organization in motor sports today, with over 2,000 amateur and professional motor sports events each year. www.scca.org
IMSA, International Motor Sports Association. Racing of Sports cars in the LeMans series and others. www. professionalsportscar.com
ARCA, Automobile Racing Club of America. The Automobile Racing Club of America (ARCA) was founded in 1953 in Toledo Ohio as a Midwest- based stock car auto racing sanctioning body. www.arcaracing.com
Controlled Thermal Processing
Figure 1: Typical Cryogenic Treatment Cooling Curve. Image: Republished with permission of ASM International, from ASM Handbook, Vol 4A, F. Diekman, “Cold & Cryogenic Treatment of Steel,” 2013; permission conveyed through Copyright Clearance Center, Inc.
Cryogenic treatment is the process of cooling materials to cryogenic temperatures temporarily to improve their material properties at room temperature. This is distinct from cooling materials down to cryogenic temperatures to take advantage of phenomena such as superconductivity that only occur at cryogenic temperatures. Cryogenic treatment, some- times also referred to as deep cryogenic treatment, is best thought of as an adjunct to other material processing steps such as heat treatment, quenching and cold work.
Depending on both the process applied and the material used, a number of material properties may be improved, including hardness, wear resistance (thus increasing lifetime), fatigue life and electrical conductivity. As an example, Barron (1982) described an increase of wear resistance of tool steel treated down to 77 K and ascribed the cause to a more complete transition from the austenite phase to the harder martensite phase.
While steel was one of the first materials to undergo cryogenic treatment—and the use of this technique to increase the lifetime of machine tools is one of its major applications—cryogenic treatment has been applied to a wide range of materials including Aluminum, brass, titanium, nickel alloys, some plastics and even carbon nanotubes.
Cryogenic treatment generally occurs at roughly 77 K (liquid nitrogen temperatures). Figure 1 shows a typical time versus temperature curve for cryogenic treatment. Some processes use dry ice temperatures (189 K) Which, while above the nominal 120 K limit of cryogenics, are also some times referred to as cryogenic treatment.
Cryogenic treatment is a very active area of research that has produced many reproducible and industrially useful results. However, cryogenic treatment is not a panacea and not all claims can be scientifically verified. Care must be taken in interpreting results in this area. Towards that end, the Cryogenic Society of America has established the Cryogenic Treatment Database (https://www.cryo- genictreatmentdatabase.org).
This database, updated quarterly, con- tains articles and scientific papers that have been vetted by an impartial committee of experts. Other good sources of information on cryogenic treatment include the proceedings of the International Cryogenic Materials Conference and the journal Cryogenics.
A related topic is cryogenic machining. Here the material is cooled to cryogenic temperatures during the machining pro- cess. This is done to optimize the machining or to optimize the final machined piece, for example in terms of its surface finish, porosity or hardness. Again, as in the case of cryogenic treatment, the resulting material is typically used at room temperature.
A detailed introduction to cryogenic treatment is given in “Cold & Cryogenic Treatment of Steel” by F. Diekman, ASM Handbook, Vol. 4A (2013). Other examples of cryogenic treatment include: ”Internal Friction Measurements of Phase Transformations During the Process of Deep Cryogenic Treatment of a Tool Steel,” Shaohong Li, et al., Cryogenics 57 (2013); “Cryogenic Treatment of Metals to Improve Wear Resistance,” R.F. Barron, Cryogenics, August (1982); “Effect of Cryogenic Treatment on the Plastic Property of Ti-6Al-4V Titanium Alloy,” K.X. Gu, et al.; Advances in Cryogenic Engineering (AIP Conf. Proc. 1574, 42 (2014)); and “Improvement of Carbon Nanotubes Using Cryogenic Treatment,” Dae-Weon Kim, et al. Japanese Journal of Applied Physics, Vol. 46, No. 45 (2007).
Applications of cryogenic machining are given in “Cryogenic Machining of Porous Tungsten for Enhanced Surface Integrity ,” J. Schoop, et al., Journal of Materials Processing Technology, 229 (2016); “Cryogenic Machining of Biomedical Implant Materials for Improved Performance, Life and Sustainability,” I.S. Jawahir, et al. Procedia CIRP (2016); and “Enhanced Surface Integrity of AZ31B Mg Alloy by Cryogenic Machining Towards Improved Functional Performance of Machined Components,” Z. Pu, et al., International Journal of Machine T ools and Manufacture, 56 (2012).
Using More of the Temperature Range
Cryogenic Processing of Metals is also known as Deep Cryogenic Treatment, DCT for short. DCT is an effective means of increasing industrial plant efficiency, increasing quality, and making products superior to competing products and making components perform better and last longer. DCT is a process that helps finish the heat treat that now is usually stopped at room temperature or slightly below.
We live in a very narrow temperature range between approximately -40o and 130oF. That is the temperature range in which we lived for thousands of years. Then we discovered fire and found that high temperatures were successful in helping us change materials. Fire helped us soften and harden metals. Fire helped us melt metals so we could shape them by casting. The effects of heat on metals and other materials were visible or easily detectable. A hardened piece resisted scratching and bending more. An annealed piece could be worked easier. A melted piece was liquid. Fire helped us turn metal ore into metallic form.
The lower temperature limit in the processing of metals stopped at a temperature in the life sustaining zone, and usually at ambient temperature for the day. Yes, the Swiss would bury watch parts in the snow to improve their wear resistance, and casting companies (and racers) would let castings “age” outside for long periods of time. They found that the aged castings did not distort so much in machining and in use and did have some better wear resistance. But there were big obstacles to using cold temperatures for treating metals. One was that until the late 1800’s it just wasn’t possible to get a lot of cold. The other was that people couldn’t conceive that a change could be made in a ‘frozen’ piece of metal.
It was the late 1800’s when people started to find ways of liquefying air. At first the amount that they could liquefy was extremely small. By the first decade of the 1900’s companies started to make liquid oxygen and liquid nitrogen in ‘industrial’ quantities. It took a while for them to get past freezing flowers and small animals. After all, what do you do with something you have never had before? Initial results on some metals that were dropped into liquid nitrogen produced negative effects.
Metallurgists were learning more about metals about this time. This was a time when metallurgists started polishing and etching metal samples and looking at them under a microscope. In steels they found that there were different ways the iron atoms related to the carbon atoms and the alloying atoms related to each other depending on the thermal history in both temperature and time of the part. You see, metals are crystalline. The way the atoms relate to each other depends on how hot or cold they have been and how fast the temperature changed. Crystal structure is what gives metals their metallic characteristics. So when someone tells you that a part failed because the metal crystallized you automatically know they do not know what they are talking about. By the way, metals are not molecular. So when someone tells you DCT affects the molecular structure of the metal you also know that they do not know what they are talking about.
A hard form of steel is called Martensite. Martensite was named after Adolph Martens, a German metallurgist who lived from 1850 to 1914. It has a distinctive structure when magnified. It is produced by heating steel to a high temperature. At that temperature (which is alloy dependent), the steel forms a structure named Austenite. Austenite is named for British metallurgist Sir William Chandler Roberts-Austen. When austenite is cooled quickly from its formation temperature, it forms Martensite. If it is cooled slowly, it remains Austenite. Cool it at some intermediate rate and some martensite forms but some austenite will remain. The remaining austenite is referred to as retained austenite. It turns out that if you bring the temperature way down, retained austenite will turn into martensite. Also, you can vibrate or cold work or temper (tempering is a mild heating process) or just age retained austenite and it will transform to martensite.
Certain things happen when transforming austenite to martensite. First, martensite is bigger because the atoms are farther away from one another. So the part grows. It doesn’t always grow evenly because metal grains are not all lined up evenly. This means the part can also warp. Also martensite needs to be tempered or it will be brittle. Now here is the kicker. If you have retained austenite (and you will) your part will change size, warp and have brittle areas because vibration, temperature change in use, and you cannot stop the passage of time. So tightly toleranced parts can change size and to some extent shape in use. This can make them unsuitable for use or require them to be designed with looser tolerances than ideal to allow for the change. A good example of this is with ejector pins in plastics molds. They have to have a close fit in order to reduce the possibility of the plastic going between the pin and the pin bore. We’ve found they can grow in use and then start to scrape and gall. DCT stops this.
Another problem with heat treated parts is that they can have residual stresses built up through the heat treat. Again, heat and vibration can release these stresses and cause warping and dimensional change. DCT relieves residual stresses and reduces this affect.
Besides transforming retained austenite, cold has other effects on crystal structure. It affects the concentration of point defects in the metal. For instance, the number of vacancies in the crystal matrix (areas where an atom should be but is not) are temperature dependent. The higher the temperature, the more vacancies can exist. Cold reduces the number of vacancies. It makes the atom to atom distance more uniform and more ideal. It affects where the alloying elements are in the crystal matrix. All these happen for reasons that are beyond the scope of this article, but are taught in the primary courses in metallurgy.
DCT offers a definite finish for heat treating through the use of more of the temperature range. We call that range cold only because it feels cold to humans, it is outside the temperature range that we are used to. It removes residual stresses, stabilizes materials, improves wear resistance, and increases fatigue life.
If you are looking for a technical explanation of Deep Cryogenic Treatment of Metals (or Deep Cryogenic Processing or Deep Cryogenic Tempering) stop reading. This is for the layman or the person who just wants to know the basics. Believe me, the basics are complicated enough as I will quickly demonstrate.
Deep Cryogenic Treatment or DCT for short is a process that uses cold to modify metals. It results in improvements in mechanical parts and electrical parts. These improvements result in considerably longer life of automobile components, and industrial tooling. For instance, valve springs last over six times longer, brake rotors over three times as long, industrial dies and tools over three times as long. DCT can also greatly improve electronics and musical instruments. The process works on most metals, some plastics, carbide and diamonds. Use of DCT can have a distinct effect on industrial plant efficiency.
- DCT Is A Process Where The Temperature Of An Item Is Reduced Slowly To 300oF Below Zero, Held There For A While And Then Slowly Brought Back To Room Temperature. There May Be An Above Room Temperature Tempering Cycle Added.
The main benefits of DCT are increased wear resistance, increased fatigue life, and a change in the vibrational characteristics of the material.
Most people know that heat can be used to change metals. You can use heat to harden, soften, and relieve stresses among other things. The thought that cold can make changes to metal is not so self-evident. For one thing, extreme cold was not easy to get until the early 1900’s. For another, people’s perception of a solid metal is that it is solid and nothing more could change without adding energy in the form of heat. While this perception seems logical, closer study of the structure of metals shows that it is not. Metals are crystals. That is how they get their metallic characteristics. Changing the temperature of a crystal changes the way the atoms in the crystal relate to each other. Some of those changes can be more or less permanent.
Most metallurgists will tell you the only thing freezing does to metals is that it causes retained austenite to become martensite. Hold on there. What are martensite and austenite? They are names of patterns you see when you polish a piece of steel and then etch it and look at it under a microscope. Martensite is a structure that results in steel being hard. It is made by heating the steel up until the steel forms an austenite structure and then cooling it quickly. Other patterns are called bainite, cementite, ferrite and pearlite. Don’t worry, there will not be a quiz.
- Most Hardened Steel Contains Martensite, Which Is Named After Adolf Martens, A German Metallurgist. Martensite Is Formed By Quickly Cooling Steel That Is Heated Above A Certain Point. The Faster The Metal Is Cooled (Or Quenched As It Is Called), The More Of The Steel Changes To Martensite. Some Austenite Usually Survives And Is Referred To As Retained Austenite. DCT Converts Most Of The Retained Austenite To Martensite.
All together, these patterns are called the microstructure of the metal, basically because they can be seen through a microscope. A lot of the properties of metals are caused by what microstructure they have. You can cause changes in the microstructure through heat, vibration, deformation, and get this, cold. The patterns are caused by how the atoms in the metals relate to each other. That is called the crystal lattice structure.
Let’s talk a bit about crystalline structure. This simply means that the atoms align themselves in an orderly pattern when the material is solid.
- This Also Means That There Are No Molecules. If Someone Starts To Tell You About The ‘Molecular Structure’ Of A Metal Just Walk Away Quietly.
Ideally, the pattern is perfect. Nothing is perfect and in the real world most metals are really pretty imperfect. In most metal crystals you will find:
- Places Where An Atom Is Missing
- Places That Have An Inappropriate Atom
- Places Where The Atoms Are Too Close Together
- Places Where The Atoms Are Too Far Apart
- Places Where There Is An Atom Where One Shouldn’t Be
Each of these raises the energy in the crystal. By slowly lowering the temperature, many of these defects are corrected or modified. The simplified version is that it takes the extra energy out of the crystal. The net result is that the crystal becomes more wear resistant and failure resistant. The real result is increased component life that creates many manufacturing efficiency solutions.