Cryogenic hardening can only take place at very low temperatures. It’s not possible to reach such temperatures with conventional cooling methods. That’s why cryogenic gases are so vital to the process. It wouldn’t be possible to achieve the intended result without them.
One does need to exercise a fair bit of caution when handling these gases. That’s because of the extremely low temperatures involved and the high rates of conversion into gas for all cryogenic liquids. In most cases, specific precautions also need to be followed as a particular liquid might react with contaminants and present other hazards like asphyxiation or flammability.
It’s because of these extremely low temperatures that cryogenic liquids and their vapors can rapidly freeze human tissue. That’s why special protective equipment should be worn when handling these gases. Such liquids in containers at temperatures at or below the boiling point of liquefied air –318°F can condense the air around them and create a localized oxygen-enriched atmosphere.
What are cryogenic gases?
Cryogenic liquids are liquids that have a normal boiling point below –130°F. They happen to be some of the most commonly used industrial gases that are handled, transported and stored in the liquid state at cryogenic temperatures. These include nitrogen, hydrogen, oxygen, helium, and argon.
All of the cryogenic liquids can produce very large volumes of gas when they vaporize. For example, a liter liquid nitrogen can vaporize to 694 liters of nitrogen gas at 68°F and 1 atm.
Cryogenic liquids can’t be maintained as a liquid indefinitely even if they are stored in containers that are properly insulated. If these liquids end up vaporizing in a sealed container, they can create a significant amount of pressure that can rupture the container.
How cold do they get?
Some of the most common cryogenic gases include nitrogen, helium, hydrogen, argon, and oxygen. These are extremely cold gases that have boiling points below -238°F. That’s colder than what most conventional cooling systems are capable of achieving. As you can imagine, they can get very, very cold. The boiling points of the aforementioned gases are -320.4°F, -452.1°F, -423.2°F, -302.5°F and -297.3°F respectively.
Types of cryogenic gases
Liquid nitrogen is one of the most commonly used cryogenic gases. In a liquid state, nitrogen is a low viscosity liquid that’s colorless. It’s primarily used as a coolant. Liquid nitrogen’s temperature can be instantly reduced to its freezing point of −346 °F by placing it inside a vacuum chamber and reducing the pressure over the liquid surface. However, its efficiency as a coolant is limited because of the fact that it boils immediately when it comes into contact with a warmer object, thereby enveloping the object in insulating nitrogen gas. This is called the Leidenfrost effect.
The liquid state of carbon dioxide doesn’t occur under atmospheric pressure, it can only exist at a pressure in excess of 5.1 atm. It’s a form of highly compressed and cooled carbon dioxide in gaseous state.
Liquid CO2 only forms at specific pressure and temperature. The gas itself is transparent and odorless. Liquid carbon dioxide is commonly used in fire extinguishers, as a coolant, and even for the extraction of virgin olive oil.
Liquid argon is extremely cold, tasteless, colorless, and odorless gas. It’s also non corrosive and nonflammable. It’s actually a rare gas but happens to be the most plentiful as it makes up approximately 1 percent of the Earth’s atmosphere. It’s an inert gas so it’s not known to form any chemical compounds.
This cryogenic liquid has a boiling point of -302.5°F. It’s most commonly used in its gaseous state for filling bulbs. Liquid argon is also used with combinations of other rare gases for filling special bulbs and tubes in order to achieve special colors effects. Argon is also used in the welding industry as a shielding gas to protect metal from oxidation during the welding process.
Helium can exist in liquid form only at the very low temperature of y−452.1°F, its boiling point, provided that it’s at standard pressure.
It’s widely used as a cryogenic refrigerant for use in cryocoolers. It’s also produced commercially for use in superconducting magnets like the ones that are used in magnetic resonance imaging, nuclear magnetic resonance and for experiments in physics.
Liquid oxygen happens to be the liquid state of diatomic oxygen. The gas has a pale blue color and is very paramagnetic so it can be suspended between the poles of a powerful horseshoe magnet. It’s slightly denser than liquid water and has a boiling point of −297.3 °F.
Since it’s a cryogen, liquid oxygen can make the materials that it touches very brittle. It’s also a very powerful oxidizing agent, causing organic materials to rapidly burn. It’s used commercially as an industrial gas. Liquid oxygen is also the most common cryogenic liquid oxidizer propellant for rockets. It was used as an oxidizer for the first liquid fueled rocket invented in 1926.
How they are used in cryogenic processing
Cryogenic hardening requires the use of cryogenic gases to reach the extremely low temperatures required for the hardening process. Gases like liquid nitrogen, helium, and others are utilized in a cryogenic refrigeration system for the cold station. A cold station can either be a bath of cryogenic liquid or a conductive surface that’s cooled to the bath temperature with the materials to be processed fastened to it.
The complex refrigeration systems include insulation that’s meant to minimize heat leaks into the extremely cooled parts. This requires the use of high-vacuum technology, structural materials that have a low thermal conductivity, and radiation shields.
Cryogenic gases and metal treatment
Cryogenic processing is increasingly being used to improve the durability and enhance the lifecycle of materials. For example, valve springs that have been cryogenically hardened can last over six times longer and brake rotors can see a 3x improvement in their lifecycle. The process of cryogenic hardening works on most metals, some plastics, carbide, and even diamonds.
Through this process, changes can be caused in the microstructure of the metal, think of it as the building block of the metal. Many of the metal’s properties are due to the microstructure that they have. Through extremely cold temperatures, a change can be made to this microstructure. With this treatment, the metal can thus be more wear and failure resistant.
How to handle cryogenic gases safely
Given the very low temperatures and high rates of conversion into gas for cryogenic liquids, there are several general precautions and best handling practices that must be followed. It goes without saying that one must always handle cryogenic liquids very carefully.
That’s because their very low temperatures can cause cryogenic burns of the skin and even freeze the underlying skin tissue. If they’re spilled on a surface, the liquids tend to spread as far as the quantity of liquid spilled and the physical dimensions of the area. The vapors that emerge from these liquids are also extremely cold and capable of producing burns.
More delicate tissues such as eyes are at a greater risk of damage when exposed to these cold gases. One such stand clear of boiling and splashing liquid and the associated cold vapors. The boiling and splashing of these liquids occurs when a warm container is charged or when objects are immersed in the liquid.
No unprotected part of the body should touch uninsulated pipes or vessels that contain cryogenic liquids. At such low temperatures, even nonmetallic materials are dangerous to the touch. Therefore, nonmetallic materials should be used to immerse and remove objects from cryogenic liquids.
At Controlled Thermal Processing Cryogenics, we know a thing or two about cryogenic gases. We are an industry leader in cryogenic processing and treatment of metals and plastics. Operating from three locations in the United States, we use state-of-the-art equipment to help our customers improve the quality of their tools and parts.
The company was founded in 1980 by race car driver Jim Birks, who had accidentally cryo-treated his engine and had discovered that this actually improved the engine’s performance and lifespan. See below.
Rick Diekman, an engineer who had previously worked on projects for companies like Ford and General Motors, was later introduced to cryogenic processing and Jim Birks. We would eventually take a stake in Controlled Thermal Processing.
Our company has almost four decades of experience in this industry and it offers thermal processing of metal parts, metallurgical advising, and micro polishing services. We also deal in the sales of cryogenic treatment equipment. Our list of clients includes NASA’s Space Shuttle Program, the US Postal Service, Remington Firearms, Dupont, and more.
Require cryogenic treatment services? Our services are available to clients from coast to coast in the United States. Simply reach out for your free quote today and our team will be happy to assist you.