Endothermic gas (CO/H₂/N₂) is often used as a ‘neutral’ protective gas or carrier gas during heat treatment process. Monitoring and controlling the furnace gas composition is essential to ensure metallic products retain their desired properties.
Full Answer
What is endo gas used for in a furnace?
· Endothermic atmospheres are commonly used during the heat treatment of steel. It is used as a carrier gas for atmosphere additions for carburizing or carbonitriding. Using an endothermic generator, either natural gas or propane is used. If nitrogen-methanol is injected in the furnace, then methanol is the carbon source.
What is endothermic gas used for?
Endothernnc gas, or "Endo" is quite commonly used for "neutral" hardening and as a carrier gas for gas carburizing and carbonitriding. The endothermic reaction requires heat to be supplied and this is accomplished in an Endothermic Gas Generator. These units, as illustrated in Figure 1 are the most widely
What gases are used in heat treatment?
· Surface ® Combustion RX ® Endothermic Atmosphere Gas Generators provide onsite generation of endothermic gas for controlled atmosphere furnaces performing metallurgical heat treatments such as carburizing, carbonitriding, ferritic nitrocarburizing (FNC), hardening, and annealing. Industries using RX gas include Automotive, Energy, Mining, …
What gas is used for hardening and tempering?
· Endothermic gas (aka RX ® or endo gas) is primarily used for neutral hardening and as a carrier gas for gas carburizing and carbonitriding. Today, endo gas is typically supplied to the furnace so that the furnace atmosphere is essentially neutral to the surface of many steels and can be made chemically active by the addition of enrichment (hydrocarbon) gas, ammonia …
How does an endothermic gas generator work?
Endothermic gas is produced when a mixture of air and fuel is introduced into an externally heated retort at such a low air-to-gas ratio that it will normally not burn. The retort contains an active catalyst, which is needed for cracking the mixture.
What is endothermic gas generator?
The endothermic generator creates an atmosphere to provide a positive pressure in a heat treating furnace, and a platform on which a carburizing or decarburizing environment can be formulated, by addition of enriching gas or dilution air. Generator maintenance scheduling, operation, and control are discussed.
What is exothermic gas?
Exothermic gas or exo gas is used for the thermal treatment of metals as a protective gas. It is the cheapest shielding gas available and can be generated in an exothermic gas generator by burning natural gas, consisting mainly of methane or other hydrocarbons with some lack of oxygen.
What gas is used in heat treatment?
The inert gases most commonly used in heat treatment processes are argon (Ar), helium (He), and nitrogen (N2), and they are often used in the following combinations: Ar/He, Ar/He/ N2, and N2/He. Many types of non-ferrous metals are heat treated in an inert atmosphere, including copper, brass, and aluminum.
Is heating a gas endothermic?
Thus any transition from a more ordered to a less ordered state (solid to liquid, liquid to gas, or solid to gas) requires an input of energy; it is endothermic. Conversely, any transition from a less ordered to a more ordered state (liquid to solid, gas to liquid, or gas to solid) releases energy; it is exothermic.
What is an endothermic atmosphere?
An atmosphere which is manufactured by passing a hydrocarbon gas and air mixture through a converter or generator containing a catalyst, at a high temperature.
What is an exothermic generator?
Exothermic generators, built by Thermal Dynamix™, are compact; water-cooled units for either rich or lean atmospheres. The exothermic generator is essentially a very tightly constructed and controlled combustion chamber into which a precisely measured and controlled mixture of air and fuel are introduced and ignited.
Why Methanol is used in heat treatment?
An enhanced content of gaseous methanol will lead to an enhanced generation of CO within the furnace. As soon as a desired CO content or level in the heat treatment atmosphere in the furnace is reached, it is, for example, possible to maintain the temperature within the container at a constant level.
Why nitrogen gas is used in annealing process?
The purpose of the atmosphere within an annealing furnace depends on your desired result. Oxygen is reactive and can cause material oxidation, which makes nitrogen annealing a more attractive option for an inert atmosphere.
Why hydrogen is used in annealing?
1). Annealing under a controlled atmosphere of 100% hydrogen prevents oxidation and product discoloration. Hydrogen is a highly reducing gas, so hydrogen annealing promotes “surface cleaning” of oxidized parts by reducing the oxides present on the wire.
Is endothermic gas stable?
Endothermic gas generators have a long and proven track record of success. The gas produced is relatively stable and adequate for a broad spectrum of process applications. Maintenance is relatively simple, and problems with the equipment and technology are well understood and solvable on the shop floor.
How is endothermic gas produced?
Endothermic gas is produced when a mixture of air and fuel is introduced into an externally heated retort at such a low air-to-gas ratio that it will normally not burn. The retort contains an active catalyst, which is needed for cracking the mixture. Leaving the retort, the gas must be cooled rapidly enough to avoid the so-called carbon reversal or carbon reformation reaction, where carbon monoxide breaks down into carbon dioxide and carbon (in the form of soot) before it reaches the furnace. The gas needs to be rapidly cooled in the temperature range of approximately 705°C (1300°F) to 480°C (900°F) or below to avoid this reaction.
Who was the father of the endothermic gas generator?
One Comment. The father of the endothermic gas generator was a gentleman by the name of Norbert K. Koebel, who was fond of saying to young engineers such as The Doctor, “Treat ‘em right, and they’ll treat you right.”. He knew that the endothermic gas generator was the heart of any atmosphere heat-treat operation.
What is the ratio of air to gas?
The products of combustion of a fuel (e.g., natural gas) and air are combined at air/gas ratios typically between 2.5:1 and 3.5:1 to create the atmosphere. The reaction requires heat to proceed (hence the name endothermic), and, as such, these generators typically have heated combustion chambers.
Who is Dan Herring?
Dan Herring is president of THE HERRING GROUP Inc. , which specializes in consulting services (heat treatment and metallurgy) and technical services (industrial education/training and process/equipment assistance). He is also a research associate professor at the Illinois Institute of Technology/Thermal Processing Technology Center. tel: 630-834-3017; e-mail: [email protected]; web: www.heat-treat-doctor.com
What is endothermic gas?
Endothermic gas mixtures are used in connection with bright hardening, sintering applications that require a reducing atmosphere, carbon restoration of steel forgings, and carrier gases for carbonitriding and carburizing, annealing of non-ferrous metals and alloy steels, neutral hardening, brazing, and sintering.
What gases are used in heat treatment furnaces?
There are several gases commonly used in heat treatment furnaces in addition to air, and these often include hydrogen, nitrogen, oxygen, helium, argon, carbon monoxide, carbon dioxide, ammonia, propane, methane, and butane. Of these, oxygen is the most reactive – as an atmosphere, air behaves like oxygen – and results in serious issues like oxidation and decarburization which can compromise the quality and performance of a part. In this article, we will be focusing on inert gases (helium, argon, and nitrogen) as well as hydrogen.
What gases are in the atmosphere?
These atmospheres may include inert gases such as nitrogen, helium, or argon; endothermic mixtures; or hydrogen. The focus of this article will be on inert atmospheres and hydrogen atmospheres, including the types of heat treatment processes they support.
What is vacuum heat treatment?
Vacuum heat treating can be used to remove surface contaminants (e.g., lubrication residue and oxide films), prevent surface reactions (e.g., decarburization and oxidation), degassing metals, and joining metals (e.g., brazing). Vacuum heat treatments can also be used to remove dissolved contaminants.
What metals are heat treated?
Many types of non-ferrous metals are heat treated in an inert atmosphere, including copper, brass, and aluminum. The degree to which an atmosphere can be called inert depends on factors such as the type of gas, its level of purity, the temperatures involved, and the material being processed.
Is helium an inert gas?
In general, argon and helium are more inert than hydrogen. A pure nitrogen atmosphere provides blanketing of the part being heat treated and can be used to purge the existing atmosphere or be used as a carrier gas for carbon-controlled atmospheres. Note that nitrogen is not truly an inert gas.
Is nitrogen an inert gas?
Note that nitrogen is not truly an inert gas. It is usually delivered at dew point between -75°F and –110°F and mixed with hydrogen in a 90/10 blend. A new guideline for the use of hydrogen blended gas to be inert is 3% or less. An atmosphere of N2 can be used for the following heat treatment processes:
Gas Chemistry
In an ideal scenario with the reacted gas at 40˚F dew point, the gas chemistry should be roughly 40% H 2, 40% N 2, 20% CO, with trace amounts of CH 4 and CO 2 (Equation 1).
Variations in the Supply Gas, Volume and Chemistry
Many different factors can be considered changes in the gas being supplied to the mixing system: composition of the natural gas supply, drop in supply pressure, inconsistent supply pressure, etc. All of these variables can have large and negative effects on the generator performance and the endo-gas reaction.
When to Change Ratio and How to Make Adjustments
While periodic checks of the endo-gas chemistry should be taken daily or even per shift, changes to the ratio of air to gas should not be as frequent. When it is necessary, however, it should be performed by someone well trained in the proper method of making the adjustments.
Common Issues
If the generator has kicked out, it’s often critical to get it making gas again. This is where a good understanding of equipment operation and its safety devices is critical in keeping the equipment operating.
What is endothermic gas?
Other carrier gases such as exothermic gas, dissociated ammonia and other nitrogen-based atmospheres are found in many heat treating facilities, but endo is most common. Because endo can have a profound impact on the quality of processing, it is important to establish a preventive maintenance program for the generator, and then follow the program religiously.
How long to heat a generator to crack gas?
Then raise to normal operating temperature and hold for two hours before attempting to crack gas.
What is consideration in heath treatment?
consideration in heath treatment is the type, consistency and control of the furnace atmosphere. The purpose of a furnace atmosphere var-ies with the desired end result of the heat-treating process. The atmospheres used in the heat-treat industry have one of two common purposes:
Does steel oxidize with oxygen?
In the presence of oxygen, steel will oxi-dize. This tendency increases in severity as the temperature is raised. In addition, oxy-gen will decarburize steel. If steel is to be kept bright during heat treatment and free of decarburization, free oxygen (O2) in the furnace atmosphere must be eliminated.
What is the water gas reaction?
The water-gas reaction (Eq. 2) is the most important furnace-atmosphere chemical reaction. This equation involves the major constituents of the gas atmosphere as it controls the reactants formed on each side of the equation. The equal sign indicates chemical equilibrium – that is, the reaction can go either way, to form CO and water vapor (H2O) or to form CO and hydrogen (H
Overview
Endothermic gas is a gas that inhibits or reverses oxidation on the surfaces it is in contact with. This gas is the product of incomplete combustion in a controlled environment. An example mixture is hydrogen gas (H2), nitrogen gas (N2), and carbon monoxide (CO). The hydrogen and carbon monoxide are reducing agents, so they work together to shield surfaces from oxidation.
Purposes
There are two common purposes of the atmospheres in the heat treating industry:
1. Protect the processed material from surface reactions (chemically inert)
2. Allow surface of processed material to change (chemically reactive)
Principal components of a endothermic gas generator
Principal components of endothermic gas generators:
1. Heating chamber for supplying heat by electric heating elements of combustion,
2. Vertical cylindrical retorts,
3. Tiny, porous ceramic pieces that are saturated with nickel, which acts as a catalyst for the reaction,
Chemical composition
Chemistry of endothermic gas generators:
• N2 (nitrogen) → 45.1% (volume)
• CO (carbon monoxide) → 19.6% (volume)
• CO2 (carbon dioxide) → 0.4% (volume)
Applications
Applications of endothermic gas generators:
1. Annealing: iron and steel
2. Brazing: copper and silver
3. Carbon restoration: carburizing, carbonitriding, nitrocarburizing
See also
• Forming gas