- September 24, 2020
- Cryogenic Processing
There’s immense benefit to be reaped from cryogenically treated materials when compared against heat treated parts that are conventionally used in most industries. Parts that are heat treated tend to have residual stresses built up.
With enough heat and vibration, these stresses can cause warping and dimensional change in the materials. Cryogenic treatment helps eliminate this limitation as it can relieve the residual stresses and thus reduce the risk of warping or dimensional change further down the line.
Cryogenically treated steel parts must be conventionally heat treated prior to treatment at sub atmospheric temperatures. Parts are typically heated to the “austenitizing temperature” and then quickly cooled to room temperature by quenching in oil, water or air. The quench is normally, and historically was, always terminated at room temperature because it was convenient to do and yielded good results. Extending the quench to extremely low, sub-atmospheric temperatures, yields substantially better results. Early attempts at cryogenic treatment involved dropping hardened steel components into liquid nitrogen.The modern embodiment of the process is actually far more complex than simply dipping the materials in liquid nitrogen and then forgetting about them for a day. Cryogenic treatment is actually a very finely-tuned process that needs to be controlled through specialized computers and equipment.
This also needs to be tailored to each metal so that the appropriate crystal structure can properly develop. The work is carried out in multiple stages that can take up to 24 hours to complete.
What are superconducting wires?
Superconducting wires are widely used for cryogenic systems. Wires that are made of superconductive material are called superconducting wires. These materials have physical properties that eliminate electrical resistance and expel magnetic flux fields from the material.
Therefore, superconducting wires don’t suffer from the limitation that conventional wires do, in that their resistance drops to zero when the temperature is lowered to temperatures approaching absolute zero. Superconducting wires have a characteristic critical temperature and if the temperature drops below that, the resistance immediately drops to zero. This is what enables an electric current to persist indefinitely without a power source in a loop of superconducting wire.
Niobium–titanium, an alloy made of niobium and titanium, is conventionally used for fabricating superconducting wire in an aluminium or copper matrix. It has a critical temperature of around 10 kelvins. For more high-temperature superconductivity, Yttrium barium copper oxide is now being used. It becomes superconducting above the boiling point of liquid nitrogen.
How much current can a superconductor carry?
Remember, a superconducting wire does not have any electrical resistance. The resistance abruptly drops to zero when the temperature drops below the critical temperature of the wire. This means that the wire doesn’t heat up when electrical current is passed through it.
Conversely, wires that are non-superconducting can be damaged if too much current is passed through them as they can get hot and melt.
What this doesn’t mean is that superconducting wires can carry an unlimited amount of current. The fact is that as per Ampere’s law, any flowing current will create a magnetic field circling around it.
Ampere’s law dictates that the magnetic field that’s created by an electric current is proportional to the size of that electric current and has a constant of proportionality that’s equal to the permeability of free space.
A superconductor is capable of expelling the magnetic fields from inside itself but that just leaves several magnetic field lines bunched up together outside the surface of the superconductor. This creates a very strong magnetic field on the outside of the surface.
Superconductivity can be affected by magnetic fields, particularly when the critical field of the superconductor is breached. If that breach happens, the superconductor will stop superconducting and that’s when the magnetic field produced by the flowing current becomes too much for the superconductor.
This results in what’s called a “quench,” whereby the superconductor abruptly stops superconducting and the energy that’s flowing in the current quickly turns into heat. Therefore, the current at which the magnetic field is going to reach the critical value depends on the configuration of the wire itself as well as the material.
Superconductors and cryogenic treatment
The practicality of a superconductor is predicated on its ability to sustain a usable current, even if cryogens are required. Many cuprate high-temperature superconductors can be superconducting when they’re immersed in a cryogen like liquid nitrogen. All superconducting materials require a temperature far below ambient temperatures to work. Therefore, they need to be cooled.
Materials that behave as superconductors at temperatures above 73.15K need to be cooled in a very specific manner. None of them can be cooled using dry ice. This is actually the lowest temperature that’s reachable by liquid nitrogen, it’s one of the simplest and most widely available coolants in cryogenics.
Superconducting wires and related components that are made from materials like Nb-Ti and Indium are widely used for conductor applications in cryogenic environments for aerospace, science and industrial use cases.
Since superconducting wire can conduct more electrical current than conventional copper wire of the same dimension, this can help to significantly reduce the size and weight of equipment in addition to more power throughput and efficiency.
How superconducting wires contribute to our cryogenic treatment
Controlled Thermal Processing Cryogenics uses state-of-the-art very precise equipment to improve the crystalline structure of most metal equipment. The company has an experienced leadership at the helm that has been a part of this industry for almost four decades.
The cryogenic treatment is very carefully applied to the metal equipment at extremely cold temperatures of -310° F and below. This helps improve the reliability of treated components and enables it to perform for much longer than it would have otherwise.
Cryogenic treatment is a great way to increase the life of production equipment and any machine that is life- limited by abrasive wear. With a longer run time there’s less routine maintenance which results in a lot of money saved over the years.
Even though the process might seem simple enough to people, it’s actually not that simple. Cryogenic treatment is something that you shouldn’t try to perform at home. CTP Cryogenics has developed proprietary processing techniques that are available for a variety of metals like steel, iron, aluminum, titanium, and other alloys.
CTP has three processing locations in the United States so we are well positioned to provide fast and reliable service across the country.
If you’re interested in learning more about our process, do contact us today and we’ll be happy to also provide you with a custom quote for your project.