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CRYOGENICS BOOK DETAIL |
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Price: $36.95 + $4.05 S&H |
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This book covers the two major types of processes (wet versus dry), types of equipment, pros and cons, dangers and proven techniques in its discussion of the subject. It gives an overview of heat treating basics, grounding the reader in proper heat treat processes, enabling them to get a better understanding of what and how Cryogenics works.
It answers all the pertinent questions of how to perform the process, step by step, learn how the parts should be treated, the dangers of not following the rules, but also the gain if a short cut is taken.
It deals with deep cryogenic stress relief in all types of materials and shows how you can get stabilized components for fussy, critical, applications such as optically sensitive parts. It teaches about the multitude of different materials that are effected by cryogenics and what it will do for them.
The following pages are excerpts taken from the book, titled:
CRYOGENICS(Put the freeze on wear) published by Hanser Gardner Publications.
This transcript is Copyrighted Feb. 1999 by Advisor In Metals and was transferred to Hanser Gardner Publications in June 1999. No portion of this transcript can or should be used without written permission by the publisher and the author.
THIS IS A PARTIAL SELECTION TAKEN FROM THE INTRODUCTION
Cryogenic treatment of metals is not really a new process as you’ve seen in the preface titled ‘EVOLUTION OF THE PROCESS’. But, its emergence in industry to improve wear characteristics is still considered a relatively new engineering field. The cryogenic process produces considerably longer wear life for most heat treated tools or parts subject to wear and abrasion if measured and judged fairly. Here are just a few key questions to get you thinking.
How does it work? What makes it work? We’ll cover that in more depth later in the book but for now, consider this as a starting point ....... Cryogenic processing increases the wear resistance of metals and various other materials by creating a denser metallurgical structure. For heat treated metals, it completes the heat treating process by the continuation of transforming grain structure into usable, life extending structure. In non-ferrous metals, carbides and in some man made plastics and fiber materials, it allows the molecules to readjust their position in relation to each other and close ranks, (increasingly denser structure) eliminating the weak voids in the structure.
Does that mean that all materials should be cryogenically processed to improve them? NO! It means there is a definite change taking place in materials subjected to cryogenics, but does not mean it would always be economically feasible, or dimensionally smart to perform the process. Low Carbon steels (with no heat treatment for case hardening) show almost no increased wear resistance. That doesn’t mean the structure hasn’t changed, but alludes to the fact there is very little wear resistance to begin with. The chemistry wasn’t designed for and doesn’t support wear resistance. The only thing cryogenics will accomplish for low carbon steel, that’s worth the cost of processing, is a very thorough residual stress relief.
Can the increase of wear be predicted? No! Contrary to some bad marketing concepts the increase in wear resistance from a tool cannot be predicted accurately, neither by grade or by application as some claim. It will vary depending on how good the initial heat treatment process was to begin with. In non-ferrous application the same will hold true. It’s going to depend on the crystal structure that you’re beginning with.
Is it necessary to cryogenically reprocess the tools after resharpening? The cryogenic process is a one time application. The tool, if properly processed and soaked for enough time to produce transformation into the center of its mass, will exhibit the wear resistance increase from the first cut to the last cut regardless of how many times the tool is re-sharpened.
Can I replace some of the higher cost tool steels with lower cost, easier to machine tools with Cryogenic processing? That is entirely possible for some applications. However, you should not try to change the rules. Every application must first be evaluated on its own merit. These parameters can then be evaluated in order to chose the right steel grade to accomplish that specific application. It is fool hearty to ask a steel grade to do what it isn’t best suited for, although this happens everyday.
To get optimum properties for any application, careful selection of the grade of metal and heat treatment procedure is paramount for success.
To get optimum properties for any application, careful selection of the grade of metal and heat treatment procedure is paramount for success. If you’re interested in more information on this subject, we would suggest you look at “Heat Treatment, Selection and Application of TOOL STEELS” published by Hanser Gardner Publications in Cincinnati, Ohio in book or video format.
What can be successfully cryogenically treated? Commonly treated metals are the ferrous grades of heat treated steel alloys of all grades. But, it effects more than wear in just ferrous metals. It has an impact on wear, toughness and strength in non-ferrous materials, such as: Copper Alloys, 300 series Stainless Steels, Carbides, Aluminum, Titanium, Magnesium and on and on the list goes. It also effects many plastics, rubber compounds, solder connections on PC boards, various engine parts and many stress effected parts.
Does the processed tool hardness increase? This subject is covered in more detail in the text, but a simple answer is .... Yes, there is usually a very slight hardness increase in all heat treated ferrous metals processed. It may be too small to measure accurately in most shops, but a ¼ point, or even 1 point increase is normal. Be mindful it is not an increase in hardness that contributes to the increased wear resistance which we’ll cover this subject in depth in later chapters. Large, very significant hardness increases (2 to 5 points) will be observed if the heat treatment process was poor to start with. In fact, by asking customers to freeze tools overnight just in their refrigerator freezers always revealed if good heat treatment procedures were being used by customers doing their own heat treatment. If a part even under those simple low temperatures (-0oF) showed hardness changes, we could count on it that there was a heat treat problem. Tensile and yield strengths will for most metals, remain the same or achieve their published optimums. In some cases the strength of certain metals and plastics is increased. The yield strengthening of 300 series Stainless is well documented when used in a stretch forming operation utilizing deep cryogenic treatment.
Does the cryogenic process change the look of the parts after processing? Unfortunately, no it doesn’t. It has been said if cryogenically treated parts were yellow after processing, customers would use it without hesitation. But the process is invisible to the unaided eye.
Today the cryogenic fever is speeding into many various fields and applications, such as....
.... cutting tools that last from 100% to 500% longer. .... welding electrodes that double and triple their life expectancy. .... PCB solder connections become stronger and electrical conductivity is increased. .... carbide inserts that double or triple in life. .... racing engines that wear better and make race cars, motorcycles and boat racers go faster. .... rifles that hold target pattern accuracy better. .... musical instruments produce better tonal quality and the valves slide more smoothly .... baseball bats hit balls 2% - 4% further. The 65 home run record could fall again.
Some scoff at the idea that there has been promotion of cryogenics for razor blades, golf balls or pantyhose, but those examples have been used to get people’s attention. It is because people have been talking about the subject that its reemerged after the poor beginning of the 70s. Let a lady try a pair of cryogenically treated pantyhose and she’ll be the best advocate for the process. Get someone who has a tough beard and save him money and you get his attention.
But still the biggest payoff at the present time is the tremendous wear resistance increases experienced in industries using cutting tools. But, even now we’re starting to see that change to everyday needs. All types of tools, equipment and metals are being improved when the process is applied properly and measured. Again the question, Why? What’s going on? The book goes on to describe the process, the cause and the results in depth.
FROM CHAPTER 6 WHICH DEALS WITH EQUIPMENT SELECTION. This is just a few sections of the transcript.
EQUIPMENT
What has emerged from this crude beginning is just now beginning to be recognized as a valuable and crucial tool for industry. There are still several schools of thought developing about the process even as the process equipment producers push and shove to grab the early windfall of the market. Unfortunately, some of these producers are selling inferior products, built to barely get the job done for the sake of a sale and a pocket full of cash. The majority of the manufacturers don’t even understand clearly what is actually transpiring in their processors and they then write instruction manuals based on poor technical knowledge which could potentially hurt the whole industry just as those did in the 70s. But take heart. There are other good producers that are trying to produce superior products by putting good materials and fabrication techniques into their product to give their customers the very best product available. It is critical to anyone about to enter the cryogenic market as a processor, or buying equipment to perform in house processing, to study and investigate the available equipment and procedures in depth before laying down hard cash for a product. In simple terms, Caveat Emptor! (BUYER BEWARE)
Caveat Emptor! (BUYER BEWARE)
One thing you are likely to see offered in today’s market from many equipment manufacture is the lack of sufficiently thick enough material in the inner chamber walls to endure the long term thermal stress from repeated cryogenic cycles. In the same vein, many manufacturers don’t stand behind their equipment and have very weak or no warranty to cover their product from weld cracks, which is the major cause of catastrophic failure that takes place in processors. The cracked welds stem from the expansion/contraction in different planes where side walls meet the bottom of the chamber. When thin walls are used, they go through constant expansion and contraction causing sever flexing of the walls, in turn causing tremendous fatigue and stress conditions in the welds. Thick walls also expand and contract but the flexing is reduced, plus the weld penetration can be greatly enhanced on the thicker wall weld joints. There are chambers on the market that use 1/16” thick walls, and processors with ¼” thick walls. There are some offering no warranty type units (for weld cracks) and some processors with 3 year warranties against any weld cracks. Another area to be on the watch for is special design features that tend to eliminate weld cracks. There are some proprietary designs, tightly guarded, in the market that because of their design, totally or very close to totally eliminate any possible weld cracks in the bottom corners and the design enhances the side corner welds as well. For these few suppliers, you must dig and pry for the feature since they want to safe guard their idea for as long as possible.
Another poor design (in the writer’s opinion) in processor equipment that some manufacturers offer and promote, is the use of heating elements within the cryogenic chamber design for the purpose of heat tempering. There are a host of reasons for this concern and here are just a few:
1. If a processor is heated while there is still coolness in the load, condensation will form on the parts, potentially allowing oxides to form on the surface. If the moisture is driven off by the heat, the oxide still exists unless there is a pure nitrogen (N) atmosphere maintained through the cycle under a partial or positive pressure controller. Also, any moisture will remain as moisture somewhere within the insulation, where it does not get driven off by the heat, also causing potential early catastrophic failure of the insulation through deterioration. A good working system keeps a positive nitrogen (N) atmosphere in the chamber until it reaches room temperature. This eliminates dew point moisture from attacking metal surfaces. So if you’re looking for a processor, find out if there’s a water problem in the chamber from end users or if the manufacture promotes using oil to prevent oxidation. In a meeting with one processor recently, he said he always sprays all the parts generously with anti-oxidation chemicals (oil or rust inhibitor) to protect from the water formation in his processor. A good designed and procedurally correct process will see no water in the inner chamber, not only after processing a load, but during any of the processing stages. The condensation doesn’t need to be heated or dried off because there isn’t any created.
Item 2 & 3 not shown.
4. Some of the units on the market are dangerous. There are units on the market that allow operators to be exposed to these high temperatures as much as 1200oF or (649oC) or even transferred -300oF (149oC) temperatures on the outside surfaces of the unit. Poor for operators, seals and any semblance of efficient operation.
5. Depending how the load is packed, this tempering process can either produce proper tempering temperatures or in many cases, little or no temper due to stacked up or piled parts. It is too risky to the life of a tool to treat the cryogenic processor as an answer to all things. Tempering should be done in equipment designed for tempering and proven metallurgical tempering cycles must be used!
Tempering should be done in equipment designed for tempering and proven metallurgical tempering cycles must be used!
Processing operators need to know what tempering is all about. They need to understand the needs of the metal, the application and either their own or their customer’s needs.
CONTROLS
A good programmable temperature controller makes the job easy. For the most part you only need one that has the ability to store a few programs. Four programs will pretty much take care of anyone’s needs There are computer controlled processors on the market but add little but dollars that are not really necessary for good temperature and process control. The temperature control and process used in cryogenics is simple enough that a low cost single program controller for under $250 works just as well as anything else on the market. And these units are simple enough to program that changes can easily be made on the fly, should it dictate. A $600 controller with 8 programs is bordering on overkill for the most part as long as you establish good loading techniques. The computer controlled units on the market do offer touch screen or push button selection for which program will handle certain size loads. But it still demands the processor be loaded properly and the operator make a judgment on what’s needed. As simple as the process is there appears to be no need for this bell or whistle. If you really need computer monitoring an RS 232, RS 485 or RS 422 communications card can be added to most all controllers on the market today for computer generated temperature profiles. But again a chart recorder works fine and doesn’t require a computer dedicated to gathering simple information.
The temperature recorder is often sold as an option by most processor manufactures. It should be a standard. It’s worth its weight in gold. It gives proof positive verification of what’s taking place inside the processor. Since processing is a three day process it just makes good sense to monitor the process and have a record of what the processor did during the middle of the night. It’s also a preventive maintenance tool as you can compare the repeated process in reference to gas consumption to make sure your processor is not failing.
Thermocouples or RTDs can be used as you prefer. It appears there are lots of false claims about the subject of temperature accuracy. Some processor manufacturers rave that their units will hold accuracy to one half of one degree. Temperature controllers are typically not that accurate nor are thermocouples or RTDs, so it is baffling how anyone can make this claim. It’s not very impressive and should prompt a buyer to wonder what else is stretched in the sales fluff. Even higher end controllers costing thousands of dollars are typically accurate within 1 ½ degree F at best, and thermocouples depending on type used are good for 1 to 2oF. That could be a range of 3 1/2oF. Now the load, type of product in the unit, flow of gas, etc. will all effect the temperature uniformity in a processor. Plus or minus 5oF is likely doable, but guaranteed? At a recent ASM convention, one of the shoe exhibitors had a sign stating this accuracy, so he was asked if the company really could deliver that accuracy? He admitted it was not possible but one government supplier required that guarantee in order to make a sale possible. So it stuck in the sales fluff.
If you’re going to buy a processor or send your parts to a processor, it cannot be emphasized enough that you really need to find a processor that knows what they’re doing. If you’re buying a processor, it would behoove you to at least work with a manufacturer that does processing. This type of processor has to perform correctly in order to build their business.
As mentioned, this is just a small portion of the book. The rest of the book deals with these chapters:
Chapter Chapter Subject Dedication Preface Evolution of the Process Introduction Cryogenics, The Basics 1 Cryogenics for Ferrous Metals, Non-ferrous and Plastics 2 Liquid Nitrogen 3 The Process 4 Thin Film Layer Phenomena 5 Stress Relieving 6 The Equipment 7 Target Items for Processing 8 Grinding Guide Lines 9 Wear 10 Stress Metallurgical Glossary (This glossary will cover roughly 1000 words) Useful information
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