Cryogenics And Heat Treatment

NITESH. Y

N. MAHESH

Mechanical Department Sri indu college of engineering and technology 2nd Year

INTRODUCTION  Cryogenics

may be defined as the branch of physics which deals with the production of very low temperature and their effect on matter.  It may also be defined as the science and technology of temperatures below 120K.  The word “cryo” is derived from a Greek word “kruos” which means cold.

Through the advent of Boltzmann’s statistical thermodynamics, which explains temperature in terms of microscopic structure and dynamics, the entropy formulae was postulated as, S = kB ln W Where, kB=1.38*10-23 J/K.

Boltzmann also found that the average thermal energy of a particle in a system in equilibrium at temperature T can be given, E ~ kB T . Consequently, a temperature of 1 K is equivalent to a thermal energy of 10-4 eV or 10-23 J per particle.

Superconductivity  Superconductivity is a phenomenon

occurring in certain materials generally at very low temperatures, characterized by exactly zero electrical resistance and the exclusion of the interior magnetic field(the Meissner Effect).  Superconductors have peculiar properties unlike normal materials.  Helium is considered to be the most efficient and widely used superconductor.  Helium-4 exhibit the property of flowability from lower to higher altitude at 2.2K temperature.

Cryogenic Heat Treatment  This is a process of treating metals,

plastics, ceramics at temperatures below 120K to their crystal structures and properties.  This increases their wear resistance, and life of metals and plastics.  They are used in the field of super conductors, cryomicrobiology, and space programs.  Unlike other processes here permanent coating is completely impart through the metal surface.

The symbol used to represent cryogenic heat treatment

Deep Cryogenic Process  Deep cryogenic treatment system and process

 

is capable of treating a wide variety of materials, such as ferrous and non-ferrous metals, metallic alloys, carbides, plastics (including nylon and Teflon) and ceramics. The entire process takes between 36 to 74 hours, depending on the weight and type of material being treated. The technology revolves around a sophisticated processor and time-temperature software which contains several ramp and soak phases, where each phase catering to certain specific characteristic changes in the material, resulting in drastically improved performance and longer useful life for both metal and non-metal products.

In alloy steels:In this process the alloy steels are treated to convert the entire austenite into a martensite matrix such it changes the molecular structure of the steel and forms an entirely new, more refined grain structure which partly relieves the thermal stresses.  The number of countable carbides increase from 30,000 to 80,000 per square millimeter which forms a “super hard” surface on the metal. 

After deep cryogenic heat treatment

Before CI Processing

After CI Processing

Comparative microphotographs (1000x) of steel samples show the change in microstructure produced by the controlled deep cryogenic process. Uniform, more completely transformed microstructure and less retained austenite at right, is related to improvements in strength, stability and resistance to wear. *Cryogenics International's Cryogenics International (CI) was granted a U.S. patent for its revolutionary new computerized deep cryogenic treatment systems. Cryogenics International now makes dramatic cost savings and increased productivity available to many people and industries around the world.

Methods to Produce Low Temperatures  Magnetism

produces low temperatures. When a material is magnetized it becomes warm and cold when demagnetized in controlled atmosphere thus producing low temperatures.

 By

compressing the gas, the gas is cooled releasing heat and later allowed to expand producing ultra low temperatures.

Advantages of Cryogenic Processing The following properties are attained to the materials treated: Increases wear resistance  Increases corrosion resistance  Good dimensionality  High strength  Good quality  Cost reduction in the material manufactured  Lower stress corrosion Cryogenic heat treatment helps to reduce the stored stress in the metal by creating a unified bond between the crystals.

 This

process is eco friendly in nature  There is no waste deposition  The nitrogen which used in the process is liquefied from the atmosphere and later released back into it thereby creating no imbalance to the ecosystem.

APPLICATIONS OF CRYOGENIC TECHNOLOGY  The major application of cryogenics the fractional distillation of air to produce oxygen, nitrogen, and other gases.  This process requires cooling the air to low temperatures to liquefy the gases in it. Natural gas, oxygen, nitrogen, and other gases are often liquefied for storage and transport because the liquid form occupy lesser space than the gaseous form.  The cryogenic technology can be used to liquefy gases as Liquefied gases are used as coolants in various industrial processes.  Liquid nitrogen is used to freeze foods quickly.

Cryogenics in Industries  Cryogenics is used to produce super high strength steels, better machinability, greater corrosion resistance, greater impact resistance and lower stress corrosion.  It improves the quality, dimensional stability and helps in cost reduction.  Several materials like 316SS, 410SS, 4142 CR-MO steel, S-2, M1 tool steel show improved corrosion resistance between 30% and 80% in highly corrosive environment of H2S.  It is used for close tolerance machining with high quality finish.  Treated copper electrodes serve 400% longer, milling tools, drill bits, piston rings, exhibit 100% to 1200% increase in service life. Dies after outlast non treated ones by 2 to 8 times.  Cryo treated automobile engine components exhibit 50% to 200% increase in service life.

 Ball and roller bearings show 200% to 700% improvement in load and wear characteristics. Cryogenically treated carbide tools performance increased by 400%. Therefore the entire industry including tools and dies significantly benefit from this technology.

Cryogenic Rocket Engines Cryogenic rocket engines are one of the important applications in the field of cryogenics. The higher thrust levels required for a rocket engines are achieved when liquid oxygen and liquid hydrocarbons are used as fuel. But at atmospheric conditions, LOX and low molecular hydrocarbons are in gaseous state. Therefore these are stored in liquid form by cooling them down using cryogenics. Hence the name Cryogenic Rocket Engines.

Cryogenic fuels

Cryogenics has made possible the commercial transportation of liquefied natural gas. Without cryogenics, nuclear research would lack liquid hydrogen and helium for use in particle detectors and for the powerful electromagnets needed in large particle accelerators. Such magnets are also being used in nuclear fusion research.

Cryogenic cooling is often used in space telescopes that observe objects in infrared and microwave wavelengths. More efficient and compact cryocoolers allow cryogenic temperatures to be used in an increasing variety of military, medical, scientific, civilian, and commercial applications, including infrared sensors, superconducting electronics, and magnetic levitation trains.

Cryogenics in biology Cryogenic temperatures are also used in cryobiology—the study of life and life processes at very low temperatures.  One such use in bio field is Cryosurgery. Cryosurgery sometimes is referred to as cryotherapy or cryoablation. It is a surgical technique in which freezing is used to destroy undesirable tissues.  Liquid nitrogen, which boils at -196°C, is the most effective cryogen for clinical use. Temperatures of -25°C to -50°C can be achieved within 30 seconds if a sufficient amount of liquid nitrogen is applied by spray or probe.

Other uses of cryogenics IN SPORTS:Cryogenics are also used to treat many types of sports equipment, the most common being golf clubs. Because cryogenics increases the molecular density of treated materials, it improves the distribution of energy (in this case kinetic energy) through the object. The treatment also increases the rigidity of the metal, which in this case might affect the shaft of the golf club. Combined, the increases in kinetic energy distribution and rigidity of the shaft make for a longer and straighter drive.

Use in musical instruments: Cryogenics is also used to treat

many types of musical instruments. Because treated materials are denser, the surface area of an object is affected.  Inside the instrument, the surface is smoother than an untreated instrument. This change in surface characteristics changes the quality of sound that the instrument can produce.  In most cases, a crisper, clearer sound is achieved, especially amongst the brass section of instruments. The same type of effect can also be useful in stringed instruments by treating the strings themselves.

Future of Cryogenics Cryogenic rocket engine which will be used by NASA for its next manned moon mission.

ICICLES

CONCLUSION From this presentation it can be concluded as cryogenics can be applied to almost everywhere in every field. It finds its application in military, tooling industry, agricultural industry, aerospace, medical, recycling, household, automobile industry, cryogenics is found to improve the grain structure of everything treated be it metal or plastic or coils or engines or musical instruments or fiber. This field could be put to many other applications in various fields. Its reaches in the mentioned industries hold a good chance of extension. Hence Cryogenics proves to be very promising for the future in this world of materials.

REFERENCES: Websites: www.pdfcoke.com, www.google.com, www.hubpages.com. Papers and Books: •Research Paper on Cryogenic pumping System by, Ralph P. Hill. (U. S. Patent no:4,704,876) •Manufacturing engineering and Technology (4th edition) by, Serope Kalpakjian and Steven R. Schmid.