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Industrial gases (such as nitrogen, hydrogen, and argon) for furnace atmospheres are characterized by their very high purity (>99.995%). Typical impurity levels are much less than 10 parts per million by volume (ppmv) oxygen and less than 3 ppmv moisture (<– 90° F dew point). This purity is typically adequate for many processes involving a wide array of materials. Some materials, though, due to their high reactivity, may require additional purification to reach even lower levels of impurity, especially with gases supplied via bulk or tube trailer supply modes. Some facilities install in-line purifiers as an added precaution against impurities picked up from the houseline. In-line purification typically involves the removal of oxygen and moisture. Sometimes with argon supply, it is necessary to remove trace nitrogen impurities. The choice of purifier is dependent on the gas and the type and amount of impurities to be removed.
If you are having a process issue that you think may be related to gas purity, please call Air Products at 800-654-4567.
To find out more details, give us a call at 800-654-4567.
You can help prevent this tendency by avoiding these scenarios.
Gas piping leaks can result from various conditions, including improper thread sealing, missed brazed joints, defective piping, over pressurization, or even vibration and shocks. A pinhole leak can cost you tens of thousands of dollars per year, depending on the size, number and severity of the leak(s). There are many ways to detect leaks; for instance, using soap tests, pressure drop tests, mass spectrometry or thermal conductivity tests. They all have their place; however, they also often come with limitations in precision, speed, difficulty or cost.
Air Products’ leak detection service can identify and repair costly leaks in your piping to help improve your part quality and bottom line.
In a short video, various methods for identifying leaks are described in more detail. You can view it online at www.airproducts.com/experts2. If you’d like to speak to a specialist about a leak detection audit of your facility, give us a call at 800-654-4567, and mention code 833.
Internal or intergranular oxidation (IGO) occurs during carburization using endothermic or dissociated methanol atmospheres. Metals processors who eliminate or at least minimize IGO can gain substantial benefits including reduced grinding after carburizing, shortened carburizing cycles, and an improved fatigue-life of gears, shafts and other machine parts.
Preventing oxidation of more reactive steel elements (Mn, Si, and Cr) can be achieved by carburizing in dry hydrocarbon atmospheres that contain no CO additions. Fortunately new technology offers an easier, less costly retrofit alternative. It has been shown during carburizing in the traditional integral quenching and pit furnaces, that an atmosphere of nitrogen containing just a couple percent of natural gas and/or propane produces the same IGO-free, hard cases as the vacuum carburizing process. These N2-HC atmosphere systems have been installed on existing, ambient-pressure furnaces, and industrial tests are in progress.
If you are interested in the mitigating IGO and/or in the low-cost, atmospheric-pressure, N2-HC atmosphere solutions, please call Air Products at 800-654-4567.
If the stain is mainly inorganic (chip, scale or rust), an elemental analysis by X-ray fluorescence (XRF) or scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS) will most likely be sufficient. However, if the stain is rather thin (a few monolayers) and surface sensitivity is an issue, X-ray photoelectron spectroscopy (XPS) can help determine the type of stain through elemental and chemical analysis.
By reducing the oxygen content above the induction furnace, inert gases—typically argon—have proven benefits for blanketing molten metal, including higher yields, lower alloy fading, decreased nonmetallic inclusions, reduced casting porosity, lower casting rework and rejects, and increased refractory lifetime. However, inert gas costs can impact your bottom line.
Air Products’ patented swirl cone technology delivers all the benefits while using up to 50% less argon. In side-by-side testing, this patented technology using gaseous argon reduced the oxygen level above the furnace to less than 2%, with little or no interference to the melting operation. In addition, the technology’s design enables it to remain in place during charging and pouring.
To hear more details on how this technology can improve your operation, watch our Ask the Experts video.
For more information, call us at 800-654-4567.
Can your process benefit from oxygen? Call us at 800-654-4567.
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To resolve a sooting problem, you must first identify the type of soot. There are three main types: adherent soot; loose, granular soot; and shiny or oily soot. All are associated with hydrocarbons from either lubricants or enriching hydrocarbon gas. Adherent soot looks like a stain and is difficult to remove. It is generally produced by the pyrolysis of lubricant in the preheat zone. Loose, granular soot appears as a black snow on the top of the parts and is produced from lubricant vapors in the hot zone. Shiny soot appears as a uniform black coating on exposed surfaces. The catalytic cracking of natural gas on the parts produces this type of soot.
Once the type of soot is known, the problem can be resolved by evaluating factors such as atmosphere flow, flow balance, preheat dew point, belt speed, belt loading, temperature profile, part density, percent lubricant, and furnace condition.
If you are having a process issue that you think may be related to a sooting problem, please call Air Products at 800-654-4567 and mention.
There are numerous benefits of using a nitrogen-based atmosphere system, including:
To see if a nitrogen-based system makes sense for your operation, call us at 800-654-4567.
To find out which atmosphere system can provide the greatest benefits to your operation, call us at 800-654-4567 to talk to an Air Products applications engineer.
Nitrogen-DA dilution can be a cost-effective alternative to 100% DA. Since many materials being processed do not require the 75 percent hydrogen content in DA, you can reduce your atmosphere cost by using less costly nitrogen to dilute your DA. The use of nitrogen also provides an economical means for purging in addition to a lower cost for furnace idling. Also, using hauled-in hydrogen with nitrogen to replace DA can be cost-competitive and completely eliminate ammonia—a more toxic, more expensive gas. Air Products applications engineers can help you compare atmosphere costs and recommend ways to reduce atmosphere consumption to further reduce your total cost of ownership. To find out more, contact us online or give us a call at 800-654-4567; mention code 749.
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For more information or an atmosphere audit by Air Products’ experienced engineers, call 800-654-4567.
If your operation uses nitrogen, you may wonder when on-site generation makes sense instead of liquid delivery. Here’s some information to help you understand if on-site nitrogen generation may be the supply mode for you . . .
The appropriateness of on-site gas generation depends on many factors—nitrogen flow and purity are the most important ones. Flows with a steady or sufficient baseline rate can be great fits for on-sites. Periodic or erratic flow patterns can also be appropriate if there is a suitable baseline flow or the volumes, pressure and purity are sufficient to allow gas storage that covers peak flows. Also, the lower the purity requirement, the greater the fit (although high purity is okay at higher volumes). Other factors you should consider include local power cost and the pressure that’s required.
There are no firm rules defining when you should switch from delivery to an on-site system. However, with our extensive experience in on-site technologies and gas delivery, we can help you determine your optimal supply mode. For an assessment of your operation, give us a call at 800-654-4567; mention code 749.
Rob EdwardsHeat Treatment Specialist
There are a number of ways to address the challenge of high pressure gas quench in vacuum furnaces – and a variety of factors to consider in order to achieve the most economical high pressure gas supply solution. First, you need to know the furnace gas volume required for backfilling. Then, the corresponding surge tank must be properly sized, which requires a balance between the maximum tank operating pressure and its internal volume. This surge tank pressure is one of the key factors that influences the type of gas supply system that is best suited to your operation. Another factor to think about is the estimated monthly volume of gas you’ll use, which is dependent on the number of times all of the furnaces will require a backfill. Next, is a consideration of the cryogenic gas supply options. Cryogenic systems using high pressure liquid tanks generally result in the least amount of vented gas, but are capital intensive and are somewhat limited in pressure due to the critical point of the cryogen (i.e. liquid nitrogen is 473 psia, approximately 32 bar). High pressure liquid tanks generally are standardized at 400 and 600 psig. Switching batch-type high pressure systems utilize less costly standard pressure liquid supply tanks (250 psig), but can have high vent losses as the batch vessels vent down each time. These systems are also typically limited to about 450 psig (31 bar). High pressure liquid pumping systems also use standard pressure liquid tanks, with a cryogenic pump filling high pressure cylinder banks or hydril tubes. These systems have a much higher pressure range (up to as much as 2,300 psig) and if properly specified, have relatively low vent losses, however they often have the highest overall capital cost. Additional factors to consider as part of a complete evaluation include the maintenance costs for each type of system, along with the unit price for the gas. Air Products applications engineers can work with you to thoroughly understand your parameters. Then, they can help you evaluate the benefits and considerations to each type of supply, in order to deliver a system optimized to your operation. To contact us about your heat treating challenge, send us an e-mail or call 800-654-4567 (press 1 and mention code 749).
Bright annealing of steels requires conditions that are reducing to steel oxides. Traditionally, the Ellingham diagram has been used to predict the conditions that correspond to oxidation of pure metals or reduction of their oxides. This method can be used to predict the conditions that should be reducing to iron oxides and the oxides of the alloying elements added to steels, such as chromium oxide when stainless steels are considered. This traditional approach is not precise because it only uses thermodynamic data for pure metals and their oxides—it ignores the fact that iron and alloying elements form a solid solution. In addition, you can only determine the approximate equilibrium partial pressure ratio of hydrogen and water vapor for oxidation of a specific metal at a particular temperature. Alternatively, you can use more accurate and convenient diagrams for steels and other alloys, which are created with the help of modern databases and computer programs, such as FactSage™ (thermochemical software and database package developed jointly between Thermfact/CRCT and GTT-Technologies) or Thermo-Calc software. Using the oxidation-reduction curves, presented as dew point of pure hydrogen or nitrogen-hydrogen atmospheres versus temperature, you can quickly select the atmosphere for annealing steels without formation of oxides. The diagram in Figure 1 was calculated using FactSage. This diagram shows that oxidation-reduction curves for Fe-18%Cr and Fe-18%Cr-8%Ni systems representing stainless steels are higher than the corresponding Cr/Cr2O3 curves. For alloys (e.g. steels), you can achieve more precise calculations using thermodynamic data from both the pure substances (i.e. pure metals and oxides) and solutions databases. Such diagrams can be produced specifically for the steels of interest and variety of atmosphere compositions. These methods can help you troubleshoot and optimize your annealing operation by balancing hydrogen usage versus product quality. If you would like to learn more about these techniques, send us an e-mail or call 800-654-4567 (press 1 and mention code 749).
Figure 1: Oxidation-reduction curves for pure chromium, Fe-18%Cr and Fe-18%Cr-8%Ni for the total pressure of 1 atm and hydrogen partial pressures of 0.5 atm and 0.05 atm. The hydrogen pressures correspond to the following atmosphere compositions: 100% H2, N2-50% H2 and N2-5% H2. (This diagram has been produced using thermodynamic data for solutions in addition to the data for pure elements and their oxides.)
Watch our Ask the Experts video for more information
To hear more details on how this technology can improve your operation, call us at 800-654-4567.
The dew point in the hot zone of a sintering furnace is a result of different sources of O2 reacting with the available hydrogen, creating moisture. Assuming there are no cracks in the muffle, water leaks in the cooling sections, or contaminated supply gases, then the following are some known sources of O2:
Once the dew point (H2O %) is measured, we then can control the oxidation/reduction potential by controlling the amount of H2 in the atmosphere, thereby adjusting the H2/H2O ratio as per the requirements of the material that is being sintered.
If you are having a process issue that you think may be related to dew point, please call Air Products at 800-654-4567.
The actual dew point in the hot zone of the sintering furnace is a net result of several factors or sources of O2 reacting with the available hydrogen, creating moisture, which then modifies the dew point of the input gases.
Assuming there is no cracked muffle, a water leak in the cooling sections or contaminated supply gases, the following are some known and unavoidable sources of O2.
Once the actual dew point (H2O%) is measured, we can then and generally do, control the oxidation/reduction potential, by controlling the amount of H2 in the H2/H2O ratio as per the requirements of the material that is being sintered.
These are just some of the items that should be reviewed on a regular basis. For more information, please give us a call at 800-654-4567.
NFPA 86 recommends you satisfy the following conditions before introducing any flammable or indeterminate atmosphere is into the furnace:
For a copy of our paper about the impact of temperature on flammability limits and furnace safety, visit www.airproducts.com/limits2 or call us at800-654-4567.
The goal of sinter hardening is to harden the part while it’s cooling in the sintering furnace. The most important aspect is the cooling rate during the critical transformation temperature range. There are many variables that affect the cooling rate itself, including:
Depending on the part’s alloy composition (which determines its hardenability) the critical transformation temperature range is generally between 600 and 1000 degrees Fahrenheit. To achieve transformation with lower alloy materials, you need faster cooling rates, such as 3.5 degrees Celsius/second. Changes in your furnace operating parameters, such as the part loading or belt speed, can change the cooling rate and location in the furnace where this critical temperature occurs. It is important to check your furnace temperature profile to confirm that you’re achieving acceptable cooling rates within the appropriate temperature range. For help determining the proper cooling rate and critical transformation temperature range for your sintering furnace, contact us or call 800-654-4567 (press 1 and mention code 749).
There are only a few types of fuels to use for combustion in traditional HVOF (High Velocity Oxy-Fuel) systems, i.e., hydrogen, kerosene, methane (natural gas), propane and propylene. While each fuel has some distinct advantages, hydrogen offers some unique advantages:
In addition, hydrogen can be delivered at sufficient pressures in tubes and bulk liquid tanks that do not require heating pads during the winter months in order to assure sufficient fuel flow to your HVOF booth.
To learn how hydrogen fuel can benefit your HVOF operation,
Air Products can help troubleshoot your purity, pressure and flowrate challenges through a diagnostic audit that includes a gas analysis and piping design review. To schedule, call 800-654-4567.
Hear Robert Swan, Applications Engineer at Air Products, expand on Zbigniew's answer.
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