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Sintering and Powder Metals

Browse previously asked/answered questions below.

  • What determines the dew point reading actually measured in the hot zone of a sintering furnace?
    Tom Philips
    Sr. Principal Applications Engineer

    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:

    1. Diffusion of outside air through the front and exit ends of the furnace, which is influenced by the atmosphere flow rates, door height, exhaust hood designs, flame curtains and plant pressure conditions.
    2. Air entrapped in the part, which is a function of part geometry.
    3. O2 content of the powder used, which is usually a known quantity as measured by the H2 loss number of the powder.
    4. Reduction of belt oxides.
    5. Reduction of metallic oxides present in brick-lined furnaces.

    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.

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  • Is my gas purity adequate for my process?
    Don Bowe Don Bowe
    Sr. Applications Engineer

    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.

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  • Is a drier furnace atmosphere always a better furnace atmosphere?

    Mark Lanham
    Applications Engineer
    Since the reducing potential of a hydrogenbased furnace atmosphere is defined by the ratio of pH2/pH2O, the first answer that comes to most people’s minds is “yes.” And, in some cases, they are correct. Lower dew point readings (lower pH2O) lead to more reducing conditions and, in many cases, better furnace atmosphere performance. However, there are situations where that is not always the case. One example of that is hydrogenbased belt furnace atmospheres where the dew point can reach values drier than –50°F or even –60°F under certain conditions. The reducing potential of this atmosphere is more than enough for the typical parts processed, but it can lead to unnecessarily strong reducing conditions that actually decrease belt life. Another example might be a brazing atmosphere that is too reducing and prone to excessive braze flow. Air Products’ new Atmosphere Humidification System allows for precise and consistent moisture additions to furnace atmospheres for just the right amount of moisture to improve belt life performance and/or braze flow while still maintaining adequate reducing conditions for the sintering or brazing operations being performed.

    To find out more details, give us a call at 800-654-4567.

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  • How can I avoid decarburisation in my sintering process?
    Guido Plicht
    Senior Research Engineer

    High dew points in endothermic generated sintering atmospheres are a common reason for decarburisation. This problem can be overcome by using a controlled nitrogen-diluted endothermic atmosphere or, better still, a controlled nitrogen-hydrogen atmosphere.

    Nitrogen-based atmospheres have been used for sintering carbon steel components for a number of years. These atmospheres are produced and supplied by using an endothermic generator or by blending pure nitrogen with hydrogen. The use of nitrogen-hydrogen atmospheres has been shown to produce parts with consistent quality and properties. However, there are still a number of powder metal parts manufacturers who, anticipating high hydrogen costs, continue to utilize endothermically generated atmospheres for sintering carbon steel components. To help these parts manufacturers increase product quality and consistency without substantially increasing overall atmosphere cost, Air Products initiated a comprehensive experimental program to study sintering of carbon steel components in endothermic and nitrogen-diluted endothermic atmospheres under similar operating conditions in production furnaces.

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  • My ceramic carrier tiles are deteriorating faster than expected. Could my atmosphere be affecting it?
    Robert Kelly
    Principal Applications Specialist

    Refractories are affected by atmospheres in several ways. Although stable at room temperature, a number of oxides are reduced in the presence of hydrogen or free carbon at elevated temperatures—thus shortening their lives. The customer's process and desired output dictate the design atmosphere. However, crystallography of the ceramic material will have a major impact on its resistance to that atmosphere. By understanding the effects of atmosphere gases on refractories and by selecting refractories that are more stable at operating temperatures and in the presence of specific gas species, you can enhance the performance of your furnace. Air Products' engineers can work with you to optimize your process. Give us a call at 800-654-4567 to schedule an audit of your operation.
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  • Why is control necessary for a protective atmosphere?
    John Dwyer
    Sr. Principal Industry Engineer

    The simplest nonreactive atmosphere for thermal processing of a metal or material is a pure inert gas or vacuum, yet neither offers protection against trace impurities such as O2, H2O, and CO2, which are almost invariably present in the heat treating furnace atmosphere.

    The problem of trace impurities is exacerbated as the temperature increases. Depending on the process and material, even small variations in the temperature or impurity level can shift a reducing or neutral atmosphere to an oxidizing one, with a negative impact on the quality of the treated parts.

    To counteract the temperature effect, reactive species (H2 and CxHy) can be added to scavenge impurities and maintain the required potential for the material being processed. Control systems have gained increasing acceptance to regulate the amount of reactive species added. However, ensuring proper control is not simply a matter of installing elaborate equipment; it also requires accurate knowledge of which variables must be controlled and how close the control must be in any given case.
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  • How can I provide customer documentation proving my heat treat process was controlled while treating their products?
    Quality programs that require information about how you process a part for your customers are becoming more common. Understanding what variables you control and what effect they have on your parts is an important step in starting this effort. Variables such as temperature, time, atmosphere flow rates and composition, and utility consumption are good places to start tracking.

    A monitoring system makes this task easier day to day and increases the accuracy of recorded data. Air Products' PURIFIRE® process management system automates data monitoring and collection, and provides additional benefits such as remote monitoring of your process, alarming to indicate problems, and custom report generation for customer documentation. Our engineers help you determine what variables are important for you to monitor and then customize a system that fits both your specifications and those of your customers.

    Benefits such as reduced scrap, elimination of manual data collection, faster problem troubleshooting, and increased product quality can enhance your customer relationship and help your bottom line.

    For more information please call us at 800-654-4567.
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  • How can I extend the life of stainless steel belts used in our continuous sintering furnaces?
    Don Bowe Don Bowe
    Sr. Applications Engineer

    This is a question that comes up frequently. When troubleshooting for oxidation in a continuous furnace atmosphere, it's important to The rising price of nickel, and therefore stainless steel, has made belt life
    longevity more important than ever. While many variables—including the belt alloy, initial break-in procedure, wire gauge and tracking—impact the life of a stainless steel belt, you can realize dramatic improvements by adjusting the sintering atmosphere.

    Air Products' patented atmosphere process technology has been shown in field service to extend the life of stainless steel belts used in sintering powder metal parts. In general, the atmosphere provides a protective oxide coating on the stainless steel belt while remaining carbon-neutral to your parts. The oxide layer reduces the carbon and nitrogen pickup and helps maintain the desired mechanical properties of the belt. In industry service, the use of this technology has resulted in extending the life of stainless steel mesh belts from 25% to more than 50% over the life that is typically experienced in N2-H2 sintering atmospheres. The results of extended belt life: reduced maintenance, less furnace downtime and fewer belts to replace.

    For more information, please call us at 800-654-4567.
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  • I know my flowmeter tells me that I have a certain gas flow rate, but how can I be sure?
    Flowmeters must be sized properly for each particular application, type of gas, gas pressure, and operating range. First, make sure that your flowmeter is calibrated for the specific gravity of the gas that you are metering. Check the label or the glass tube of the flowmeter or call the manufacturer to be sure. Second, operate the flowmeter only at the pressure for which it was calibrated. As an example, a variable-area flowmeter calibrated for 80 psi and reading 1000 scfh will really only be delivering 760 scfh if it is operated at 40 psi. This is a 24% error! Third, for best accuracy and to allow room for adjustment, size the flowmeter so that your normal flow rate falls within 30%–70% of full scale. These three steps will help ensure that you have good control over your gas flows and, ultimately, your process.
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  • I use high-pressure gas cylinders and am concerned about safety. Is there a better way?
    John Tapley
    Microbulk Business Development Manager

    Traditionally, high-pressure gas cylinders have been the supply mode for users in the low- to medium-volume range. This has left companies vulnerable to safety risks associated with moving cylinders and exposure to high pressure. Consolidating to a centralized microbulk system eliminates the need to handle cylinders and reduces the risk of product mix-up. Further benefits include decreased exposure to high-pressure containers and reduced traffic congestion with less frequent supplier deliveries.

    Air Products developed the microbulk supply option as a cost-effective, reliable alternative to high-pressure cylinders for nitrogen, argon, oxygen and carbon dioxide supply. In addition to efficient and flexible storage systems, innovative piping solutions are available to help you have a smooth transition from cylinders to microbulk.
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  • I’m experiencing intermittent oxidation in my furnace. Could leaks in the nitrogen houseline be the problem?
    Don Bowe Don Bowe
    Sr. Applications Engineer

    Yes, leaks in any pressurized high-purity gas line can cause intermittent oxidation. There are several possible causes. One is through retrodiffusion—the movement of impurities from the surrounding air to a high-pressure, low-impurity gas houseline. This is driven by concentration gradients, not pressure gradients, and is aggravated by changes in flow rate, pressure or piping temperature.

    Air Products industry specialists can help you determine the cause of your problem. Since the oxidation is intermittent, you’ll need to continuously monitor your nitrogen houseline for leaks with a trace oxygen analyzer. For combustible gas lines, a combustible gas sniffer can also be used. Once impurities are found, the source of the leak can be identified using various techniques, including soap bubble testing, static pressure testing or helium mass spectrometry. Leaks often occur in weld cracks, mechanical joints, valve packing and loose fittings.

    To help minimize wasted product and part oxidation, call us for a leak detection or full process audit at 800-654-4567.

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  • Is my gas purity adequate for my process?
    Don Bowe Don Bowe
    Sr. Applications Engineer

    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.

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  • How can I maintain consistent properties among my sintered powder metal parts?
    Tom Philips
    Sr. Principal Applications Engineer

    Many processing variables such as powder size, composition and purity; size distribution; and carbon content affect sintered components’ final properties. The type and amount of lubricants, compaction densities, and furnace parameters—temperature, time at temperature, cooling rates, and belt loading—also influence the end results. Most of these variables are determined during the design stage of the component.

    The sintering atmosphere is often overlooked as a variable. The atmosphere properties can vary over time. Controlling an atmosphere system’s variables can improve the consistency of sintered properties. The primary variables in an atmosphere system are the atmosphere composition, purity, flow rates and distribution, pressure inside the furnace, exit velocity, stability (external influences), and the door openings.

    For a technical paper or to schedule an audit of your process, call 800-654-4567, or visit www.airproducts.com/sinterpm.
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  • I have measured the oxygen level in my continuous furnace, and it's low, but my parts still come out oxidized. Why?
    Don Bowe Don Bowe
    Sr. Applications Engineer
     
    Guido Plicht
    Senior Research Engineer
    Europe

    This is a question that comes up frequently. When troubleshooting for oxidation in a continuous furnace atmosphere, it's important to measure both oxygen level and dew point. Here's why.

    The dew point is a measure of the moisture content of a gas and is the temperature at which water vapor in a sample gas starts to condense. Oxygen concentration is simply that—a measure of the partial pressure of oxygen.

    When a gas sample is extracted from the hot zone of a furnace for analysis, reactive gases like H2, CO, or CxHy have already combined with any O2 present to produce moisture and other gaseous components. As a result, depending on the furnace temperature and how the sample is obtained, your analyzer will often display a low oxygen level. In most applications, a low oxygen level and a low dew point are required to control the process and prevent oxidation.

    Click here to find the Gas Atmosphere Analysis Guidelines

    For further details contact Shawn Lainchbury tel: +44 (0) 1932 249 398
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  • Is it true that NFPA 86C has changed?
    Mark Lanham
    Applications Engineer

    Yes, it's true. In fact, NFPA 86C no longer exists. The requirements for "Industrial Furnaces Using a Special Processing Atmosphere," formally defined in the 1999 version of NFPA 86C, have been incorporated into NFPA 86 as of July 18, 2003. Now, NFPA 86 combines the furnace safety requirements for all types of industrial furnaces, including Class A – Food and Baking Ovens, Class B – Melting Furnaces, Class C – Furnaces Using Special Processing Atmospheres, and Class D – Vacuum Furnaces.

    The previous contents of NFPA 86C are now primarily found in Chapter 11 of NFPA 86. A notable change is that NFPA 86 recommends that users of Class C furnaces include a low temperature alarm panel to indicate an overdraw condition on the ambient air vaporizers used for emergency purging. Previously, NFPA 86C required the use of a low temperature flow-restricting device that could potentially limit available purging capacity. Air Products' PURIFIRE® nitrogen supply monitoring system is designed to help you comply with this new recommendation.

    Users of furnaces with special processing and flammable atmospheres should fully understand the requirements and recommendations of NFPA 86 and determine how the changes from the old NFPA 86C may affect their furnace operations. For help in understanding these specifications or for more information about our PURIFIRE nitrogen supply monitoring system, contact us at 800-654-4567.

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  • What nitrogen purity do I need for my heat treatment process?
    Rob Edwards
    Heat Treatment Specialist

    That depends on your process. Nitrogen based atmospheres for metals processing have been successfully proven over many years, and due to the enormous range of requirements in furnaces for various materials and surface needs, the use of gas mixtures is now an industry standard. Different products can tolerate differing concentrations of oxidising components in the furnace atmosphere due to additional reducing or reactive components in the blend. For this reason, the use of on-site generated nitrogen with residual amounts of oxygen can be tolerated. By understanding your oxygen tolerance levels we can help you reduce your costs.
    The paper below will give you an overview of the different systems for nitrogen generation and the appropriate oxygen concentrations for different products and materials in furnaces. For most materials, although free oxygen is not tolerable, some oxidising impurities may be permitted. In these cases, the on-site production of high purity nitrogen for the heat treatment of very sensitive materials may be commercially viable. Examples and descriptions of these systems will also be provided in the paper. Click here to view our expert paper.
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  • When does on-site nitrogen generation make sense versus liquid nitrogen delivery?
    Steve Ruoff
    Metals Processing Segment Manager

    The amenability of on-site gas generation involves 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 be amenable if the volumes, pressure and purity are sufficient to allow gas storage that covers peak flows. Also, the lower the purity requirement, the greater the amenability—although high purity is amenable at higher volumes. Other factors include local power cost and pressure required. There are no firm rules defining when to switch from delivery to an on-site. Different on-site options are available to meet your nitrogen requirements, including pressure swing adsorption, membranes or cryogenics. Count on Air Products’ extensive experience in on-site technologies to help you determine your optimal supply mode. Call 800-654-4567 for an assessment.
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  • What determines the dew point reading actually measured in the hot zone of a sintering furnace?
    Tom Philips
    Sr. Principal Applications Engineer

    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.

    1. Diffusion and entrainment of outside air through the front and exit ends of the furnace. This is a function of the atmosphere flows rate, door height, exhaust hood designs, flame curtains and plant pressure conditions.
    2. Air entrapped in the part, function of part geometry.
    3. O2 content of the powder used. Usually a known quantity as measured by the H2 loss number provided by the powder manufacturer.
    4. Reduction of the belt oxides.
    5. Reduction of metallic oxides present in brick lined furnaces.

    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.

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  • Can I determine if the oxidation in the cooling section of my continuous furnace is caused by air ingress or a water leak?
    Tom Philips
    Sr. Principal Applications Engineer

    A simple copper/ steel test can differentiate oxidation by air (O2) or water (H2O). The test is performed by sending a piece of clean bright copper strip alongside a piece of clean carbon steel strip through the continuous furnace and observing the oxidation on each test coupon. Take care to keep the furnace temperature below 1981˚F, the melting point of copper. The steel strip will discolor or oxidize if the atmosphere has an air or water leak; however, the copper strip will only oxidize if an air leak is present. You can use this test for nitrogen-based or generated type atmospheres like endothermic or dissociated ammonia. And it can be done without oxygen or dew point analyzers.

    For more details on this and other atmosphere troubleshooting tips, give us a call at 800-654-4567.
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  • How can I reduce the cost of my sintering process without compromising quality or reliability?
    Guido Plicht
    Senior Research Engineer
    Europe

    Nitrogen based atmospheres have been successfully proven for a wide range of heat treatment processes over many years. They have been adopted as the industry standard due to their ability to produce the right atmosphere composition to ensure high quality parts and do not produce the well known decarburising problems associated with endothermic generated atmospheres.

    Click here to find the range of solutions which Air Products has to offer.
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  • Can I remotely monitor what’s happening in my furnaces and other process equipment while I’m away from my plant?
    Chris Ward Chris Ward
    Engineering Associate

    With the proper instrumentation and controls, you can securely monitor and control your heat treating or thermal process from nearly anywhere in the world! This is possible using a variety of hardware and communication methods, including Internet, dial-up, and cell phones. Alarm and warning notifications can also be proactively delivered to you so you can react to upsets, trends, and events before it’s “too late.” It’s important to identify the key parameters, equipment and instrumentation you want to monitor, and then select the hardware and software that best match your needs. Contact Air Products’ team of remote process monitoring and control specialists at 800-654-4567 for an assessment and recommendations as to how to get started.
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  • My sintered parts have a frosty, dull, matte finish. What causes this and how can I prevent it?
    Tom Philips
    Sr. Principal Applications Engineer

    Sintered parts should exit the furnace with a shiny, bright finish. If they don’t, that is a sign of a problem in your process. Oxygen or air may be infiltrating the furnace at the front entrance. Also, if the oxidizing potential in the preheat zone is too high, it can cause oxidation on the powder metal part surface. This oxidized surface reduces as the part travels through the highly reducing atmosphere in the hot zone, causing it to lose its shiny finish and appear dull and matte. In addition to a dulled finish, you may notice lower surface hardness due to the surface decarburization that resulted from the oxidation.

    To help solve this problem, you can add a flame curtain at the front end of the furnace. The curtain should be attached to the door to provide full coverage of the front entrance, plus the flame should be directed downwards. You can also control the dew point in the preheat zone so it’s oxidizing enough to facilitate de-lubrication, but does not oxidize the metal.

    For more tips and techniques to help you control furnace atmospheres, get in touch with an Air Products applications engineer by contacting us online or calling us at 800-654-4567 (mention code 749).
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  • My sintered PM parts come out of the furnace "sooty." How do I prevent this?
    Mark Wells
    Metals Industry Engineer

    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.
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  • What causes stainless steel to turn green in a continuous belt furnace?
    Zbigniew Zurecki
    Research Associate

    The green color that you see on stainless steel parts is chromium oxide (Cr2O3). It forms when there is too much oxygen and/or moisture in the furnace atmosphere, which is usually caused by a water leak, poor atmosphere tightness, or overly low flow rates of atmosphere gas. A dark green-brown color indicates significant levels of free oxygen inside furnace originated by a large air leakage.

    In addition to the traditional steel and copper test, some companies run a piece of stainless through the furnace to check for high moisture and oxygen levels. A better and more precise way of measuring moisture and oxygen levels is to install an oxygen analyzer and dew point meter. It's inexpensive and highly accurate. If a green oxide film is forming on your stainless steel parts, that's an indication that the furnace or atmosphere is not optimized.

    For a complete evaluation and audit of your process, give us a call at 800-654-4567.
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  • How do I know if I’m wasting gas due to leaks in my gas piping?
    John Green
    Research Technician

    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.

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  • My nitrogen-hydrogen flow control panel seems to be working properly, but is there anything I should be checking?
    Don Bowe Don Bowe
    Sr. Applications Engineer

    There are many aspects of a flow control or blend panel that require periodic maintenance for proper functionality—especially those related to its safe operation.
    You should check the operation of the solenoids to help verify that the combustible gas flow is automatically turning off and the inert gas purge is automatically turning on as intended. They should be tested in accordance with recommended maintenance frequency—typically every six months. Plus, you should rebuild the solenoids as needed. It’s also important to check the purge timer setpoint to help confirm that it can adequately purge the furnace. And you should verify and document the low-flow alarm setpoints on the inert gas purge and process flows.

    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.

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  • What are the recommended procedures to safely introduce a flammable atmosphere into a continuous belt furnace?
    Tom Philips
    Sr. Principal Applications Engineer

    For sintering and brazing atmospheres in a continuous belt type furnace with open ends, you must follow NFPA 86 Standard for Ovens and Furnaces. Typically, atmospheres containing greater than 4% hydrogen in nitrogen are considered flammable. In fact, any mixed atmosphere—even if it contains less than 4% hydrogen—is considered “indeterminate” and must be treated as if it were flammable.

    NFPA 86 recommends you satisfy the following conditions before introducing any flammable or indeterminate atmosphere is into the furnace:

    • At least one zone of the furnace must be hotter than 1400ºF.
    • The furnace must be purged with an inert gas until the atmosphere analysis indicates it’s below 50% of its LEL (lower explosive limit). General recommendation is to use five volume changes of inert gas flow.
    • There must be visible indication of purge flow. Plus, purge piping should have normally open solenoid valves.
    • The atmosphere system should be designed with interlocks so the flammable gases are shut off using normally closed solenoid valves in the event of power failure, a temperature drop below 1400ºF, or insufficient flow of the main atmosphere component.

    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 at
    800-654-4567.

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  • What cooling rate do I need for my sinter hardening process?
    Don Bowe Don Bowe
    Sr. Applications Engineer


    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:

    • Furnace dimensions
    • The use of a convective gas cooling system and its blower size and heat exchanger capacity
    • Furnace loading
    • Part geometry (thickness), and weight
    • Sintering temperature
    • Length of the transition section
    • Belt speed
    • Atmosphere composition
    • Furnace cooling capacity

    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).

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