Thinking about travel plans for the upcoming holiday season? You may know what means of transportation you will be using, but perhaps you haven't considered the heat treating processes which have gone into creating that transportation.
Today’s Technical Tuesday original content round-up features several articles from Heat TreatToday on the processes, requirements, and tools to keep planes in the air and vehicles on the road, and to get you from one place to the next.
Standards for Aerospace Heat Treating Furnaces
Without standards for how furnaces should operate in the aerospace, there could be no guarantee for quality aerospace components. And without quality aerospace components, there is no guarantee that the plane you're in will be able to get you off the ground, stay in the air, and then land you safely at your destination.
In this article, written by Douglas Shuler, the owner and lead auditor at Pyro Consulting LLC, explore AMS2750, the specification that covers pyrometric requirements for equipment used for the thermal processing of metallic materials, and more specifically, AMEC (Aerospace Metals Engineering Committee).
This article reviews the furnace classes and instrument accuracy requirements behind the furnaces, as well as information necessary for the aerospace heat treater.
Dissecting an Aircraft: Easy To Take Apart, Harder To Put Back Together
Curious to know how the components of an aircraft are assessed and reproduced? Such knowledge will give you assurance that you can keep flying safely and know that you're in good hands. The process of dissecting an aircraft, known as reverse engineering, can provide insights into the reproduction of an aerospace component, as well as a detailed look into the just what goes into each specific aircraft part.
This article, written by JonathanMcKay, heat treat manager at Thomas Instrument, examines the process, essential steps, and considerations when conducting the reverse engineering process.
If you are one of the growing group of North Americans driving an electric vehicle, you may be wondering how - and how well - the components of your vehicle are produced. Electric vehicles (EVs) are on the rise, and the automotive heat treating world is on the lookout for ways to meet the demand efficiently and cost effectively. One potential solution is laser heat treating.
Explore this innovative technology in this article composed by Aravind Jonnalagadda (AJ), CTO and co-founder of Synergy Additive Manufacturing LLC. This article offers helpful information on the acceleration of EV dies, possible heat treatable materials, and the process of laser heat treating itself. Read more to assess the current state of laser heat treating, as well as the future potential of this innovative technology.
When the Rubber Meets the Road, How Confident Are You?
Reliable and repeatable heat treatment of automotive parts. Without these two principles, it’s hard to guarantee that a minivan’s heat treated engine components will carry the family to grandma’s house this Thanksgiving as usual. Steve Offley rightly asserts that regardless of heat treat method, "the product material [must achieve] the required temperature, time, and processing atmosphere to achieve the desired metallurgical transitions (internal microstructure) to give the product the material properties to perform it’s intended function."
TUS surveys and CQI-9 regulations guide this process, though this is particularly tricky in cases like continuous furnace operations or in carburizing operations. But perhaps, by leveraging automation and thru-process product temperature profiling, data collection and processing can become more seamless, allowing you better control of your auto parts. Explore case studies that apply these two new methods for heat treaters in this article.
Cuáles son las características más deseables de un probador de dureza Brinell? Esta reseña del equipo le permitirá evaluar si debe o no incorporarlo a su departamento de tratamiento térmico.
Read the Spanish translation of this article in the version below or read the English translation when you click the flag to the right. Both the Spanish and the English versions were originally published in Heat Treat Today's August 2023 Automotive Heat Treat print edition.
Toda empresa dedicada al tratamiento térmico deberá practicar ensayos de dureza, algunos de ellos utilizando la medición Brinell que data desde el año 1900, lo que lleva a que se amerite el análisis de tan perdurable técnica. La prueba en mención requiere de un penetrador de bola de carburo de tungsteno que impacte de manera vertical sobre la superficie del material a ser ensayado, previamente ubicado éste sobre un yunque fijo. Paso seguido, se mide el diámetro de la “huella” generada por la bola, mínimo por los ejes “x” y “y,” y se toma el promedio de estas mediciones como cifra operativa de la que se pueda valer el técnico para establecer la dureza, bien sea alimentando una ecuación o mediante la lectura de una tabla de valores en la que se relacione diámetro frente a dureza.
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Para el ensayo Brinell se dispone de una amplia gama de cargas de fuerza, al igual que de diámetros de penetradores, reflejando la gran variedad de metales a ser probados; no obstante, en la mayoría de ensayos se implementa una bola de 10mm bajo una carga de 3.000 kg. En las grandes máquinas de apoyo a suelo por lo general el penetrador es motorizado, aunque otras operan a partir de palancas y pesas, mientras que también las hay hidráulicas o neumáticas.
Existen tres razones principales por las que la prueba Brinell no deja de ser el método más opcionado para la medición de la dureza en muchas industrias de tratamiento térmico.
1. Preparación de la superficie
La preparación de la superficie de una muestra para las pruebas Brinell toma solo unos segundos con una amoladora. Siempre que la muestra esté firmemente asentada sobre el yunque presentando la cara superior en dirección perpendicular a la dirección de la fuerza del penetrador, de acuerdo a lo exigido por las normas, no es necesario lograr una superficie demasiado lisa.
Figura 1. Robusto probador Brinell in situ
2. Contaminación de la superficie
Es poco probable que los contaminantes diminutos en una superficie generen una “prueba errónea” bajo un penetrador Brinell, a diferencia de la prueba de dureza Rockwell (el método más común en la industria). En esta prueba un pequeño indentador de diamante penetra menos de una centésima de pulgada, arrojando como resultado el que cualquier contaminante o anomalía en la superficie que pueda impedir o favorecer el progreso del penetrador (incluído el paralelismo) represente un problema, y obligando a que las muestras para la prueba Rockwell se deban preparar cuidadosamente antes de realizar la misma.
3. Portabilidad
Quizás el factor más significativo es que los robustos equipos portátiles de mano Brinell, con cabezales de prueba hidráulicos, permiten probar, in situ, piezas grandes, pesadas, de superficies rugosas o formas irregulares. Esta característica es de tal utilidad en la industria que ha motivado a que los órganos de normalización internacional otorguen una dispensación especial, una excepción si se quiere, a las máquinas portátiles, pese a que la ejecución de las mismas no sea susceptible de verificación directa como sí lo es la de sus equivalentes, las máquinas fijas.
Con fuerzas que van desde los 3000 kg hasta 1 kg, y bolas penetradoras tan pequeñas como 1 mm, las pruebas Brinell se pueden usar en una amplia gama de metales, pero los lugares en los que existiría la mayor probabilidad de encontrar un equipo de 10mm/3000kg son las forjas, las fundiciones, las plantas de tratamiento térmico, los laboratorios y las áreas de control de calidad. Previamente mencionamos que no se requiere que la superficie de las muestras de prueba sea absolutamente lisa; de hecho, es posible medir con un grado importante de precisión las superficies irregulares en materiales de configuración gruesa ya que el diámetro de la hendidura es tan grande en relación con cualquier irregularidad en la superficie.
Figura 2. Probador de Brinell, grado calibrador, en primer plano
En la Figura 2 se puede apreciar cómo un probador Brinell de grado calibrador introduce la bola de carburo de tungsteno en la muestra de prueba. Se mantiene la bola en posición para estabilizar la deformación plástica.
Las normas que rigen de manera detallada las pruebas Brinell son la ASTM E-10 y la ISO 6506, pero el procedimiento práctico para los técnicos es muy sencillo, tanto que el entrenamiento no debería tardar más de una hora. Para ensayar piezas forjadas, palanquillas y otras muestras, una hendidura debería bastar aunque, desde luego, en ciertas aplicaciones de extrema importancia se podrá utilizar más de una para mayor seguridad.
Saber si analizar o no cada muestra en un lote determinado deberá decidirse con base en la inconsistencia de las muestras mismas, más no responde a problemática alguna con las pruebas de Brinell en sí. En ciertas industrias se prueba cada pieza que se produce debido a que el riesgo de error es demasiado alto. Un buen ejemplo lo encontramos en la producción de los componentes de los eslabones para las orugas utilizadas en tanques y maquinaria pesada (retroexcavadoras y demás). Cada eslabón de cada oruga de un tanque en uso en el ejército británico ha sido probado por Brinell en una máquina totalmente automática, de alta velocidad, que cuenta con una poderosa abrazadera integral para mantener el componente absolutamente rígido durante la prueba. Por cierto, esa máquina es la de la primera foto. Con un cuidado adecuado y razonable, un probador Brinell robusto podrá generar cientos de miles de pruebas; de hecho, el probador de la Figura 1 ha realizado varios millones.
Las pruebas duran aproximadamente quince segundos ya que el penetrador se debe dirigir hacia el material de manera uniforme sin permitir la posibilidad de un “rebote” y evitando por completo llegar a golpear el material. Por otro lado, el metal debe recibir la presión por un período de tiempo suficiente que garantice que la hendidura se deforme de la manera más plástica posible, es decir, minimizando al máximo el riesgo de la más ligera contracción de la hendidura una vez retirado el penetrador.
Figura 3. Medición de una hendidura de prueba de dureza Brinell
Sin embargo, es en este punto que se presentan las complicaciones. Después de generar cuidadosamente la hendidura y retirar la muestra de prueba de la “boca” de la máquina probadora, es necesario medir la hendidura en al menos dos diámetros. Dado que las hendiduras de Brinell tienen como máximo 6 mm de ancho y que una diferencia de 0,2 mm en el diámetro podría equivaler a 20 puntos de dureza, obtener la medición correcta es esencial y de alta complejidad. La mayoría de los técnicos usan un microscopio iluminado para lograrlo, pero aún así puede ser un desafío. Considere la Figura 3.
Los microscopios de medición manual han mejorado a lo largo de los años, y cuando se obtiene una hendidura relativamente “limpia” con una retícula nítidamente iluminada, se le puede facilitar al técnico experimentado realizar una medición precisa. La Figura 4 presenta un escenario menos complejo que el anterior pero, aun así, ¿cómo podemos saber si realmente se ha juzgado con precisión la posición del borde?
Figura 4. Medición con microscopio mejorado y retícula bien iluminada.
Al crearse la hendidura se genera un cordoncillo en el perímetro de la misma debido a que el metal no solo presiona hacia abajo, sino también hacia los lados. Este cordoncillo puede difi cultar la ubicación del punto en el que comienza realmente la hendidura, y tres técnicos diferentes pueden hacer fácilmente tres estimaciones diferentes de su lugar de inicio. Es esta variación en la interpretación de los resultados por parte de los operadores la que ha llevado a que, durante más de 80 años, la prueba Brinell se haya considerado un poco “ordinaria”, apta tal vez para el maquinista en el taller, pero de dudoso valor para el científi co en el laboratorio.
En 1982 llegó a los mercados el primer lector automático, siendo éste la culminación de años de investigación, y valiéndose de software privado que llevó a las computadoras de la época a sus límites. El equipo podía hacer cientos de mediciones de un lado a otro de la hendidura y calcular el diámetro medio en una fracción de segundo. Poco después llegó a ser parte integral de una máquina de prueba Brinell. La noticia de la aparición de este equipo pronto llegó a algunos usuarios importantes en la industria de las herramientas petroleras quienes exigieron a sus proveedores valerse de él; quince años más tarde se había diseminado ampliamente el uso de esta tecnología generando la transformación de la percepción que se tenía de la prueba Brinell. Podríamos decir que la prueba Brinell había llegado a la mayoría de edad.
Figura 5. La última versión de ese microscopio automático en acción
Desde luego, como con cualquier equipo de medición importante, la calibración y el mantenimiento regulares son aconsejables, si no obligatorios. Los fabricantes mismos suelen estipular un cronograma de mantenimiento que se debe tener en cuenta junto con las reglas de calibración establecidas por las agencias internacionales.
Al considerar las opciones para la prueba de dureza en muestras con tratamiento térmico, en última
instancia existen tres métodos: Brinell, Rockwell y Microdureza (Vickers o Knoop).
Pese a que no es adecuada para muestras muy pequeñas o demasiado delgadas, la prueba Brinell es relativamente “inmune” a los contaminantes pequeños, los penetradores no son costosos, y, gracias al ancho de la hendidura, las pruebas de superficies con acabado áspero e irregular no presentan dificultades. Con el desarrollo, hace 40 años, de la medición automática de la hendidura, se superó la única deficiencia grave de la prueba Brinell, proporcionando las garantías que tan vital importancia revestían para los proveedores de piezas esenciales en industrias de toda índole, incluídas las de petróleo y gas, aeroespaciales y de defensa y transporte.
Sobre el autor: Alex Austin se viene desempeñando desde 2002 como gerente de Foundrax Engineering Products Ltd. Foundrax es proveedor de equipos de prueba de dureza Brinell desde1948, siendo en realidad la única compañía en el mundo especializada en el campo.
Alex funge en el Comité de Prueba de Dureza por Hendidura ISE/101/05 del British Standards Institution. En su calidad de miembro de la delegación británica de la Organización Internacional de Normalización, ha aportado como consultor para el desarrollo de la norma ISO 6506 “Materiales metálicos–prueba de dureza Brinell” y preside en la actualidad la revisión ISO de dicha norma.
Exothermic gas undergoes a few metamorphoses from the time it is produced to the time it is cooled down after use. Explore the transformations that occur within the combustion chamber to discover the impact these phases can have on the heat treatment atmosphere of your workpieces.
This Technical Tuesday article was composed by Harb Nayar, president and founder, TAT Technologies LLC. It appears in Heat Treat Today'sAugust 2023 Automotive Heat Treating print edition.
Background
Harb Nayar
President and Founder
TAT Technologies LLC
Source: LinkedIn
Exothermic gas, more commonly referred to as Exo gas, is produced by partial combustion of hydrocarbon fuels with air in a well-insulated reaction or combustion chamber at temperatures well above 2000°F. Immediately after they exit the combustion chamber, the reaction products are cooled down using water to a temperature below ambient temperature to avoid condensation. The typical dew point of the cooled down Exo gas is about 10°F above the temperature of the water used to cool down. The cooled down Exo is then delivered to the heat treat furnaces where it gets reheated to the operating temperatures between 300°F and 2100°F.
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A simplified schematic flow diagram of Exo gas production followed by its cool down below ambient temperature and its final use in heat treat furnaces is shown in Figure 1.
The following aspects of the Exo gas production are clear from Figure 1:
There is lot of energy lost out of the reaction chamber.
There is additional heat lost during cooling using water.
A good deal of water is used for cooling.
The cooled down Exo gas is re-heated to the process temperature in heat treat furnaces.
Exo gas has been predominantly used and is still being used as a source of nitrogen rich atmosphere for purging, blanketing, and mildly oxide reducing applications in the heat treat and metal working industries.
Figure 1. Schematic flow diagram showing Exo production, cool down, and its use.
Source: Morris, “Exothermic Reactions,” 2023
Examples of applications:
Brazing
Annealing
Hardening
Normalizing
Sintering
Tempering, etc.
Examples of materials:
Irons
Steels
Electrical steels
Copper
Copper-base alloys
Aluminum
Jewelry alloys
Examples of product sizes and shapes:
Tubes
Rods
Coils
Sheets
Plates
Components
Small parts, etc.
Exo is the lowest cost gas used in furnaces operating at temperatures above about 700°F to keep air out and provide a protective atmosphere with some oxide reducing potential to the materials being thermally processed.
There are two types of Exo gases: lean Exo gas, with mostly nitrogen and carbon dioxide and very little hydrogen, and rich Exo gas, with a little less nitrogen and carbon dioxide and substantially more hydrogen and some carbon monoxide. Typical compositions are given below:
Figure 2. Exo gas operating range
Source: SECO/WARWICK
Figure 2 shows graphs of Exo gas composition at various air to natural gas ratios. H2, CO, and residual CH4 decreases with increasing air to natural gas ratio whereas CO2 goes in the opposite direction. H20 content not shown in the graphs is typically in the 2–4% range depending upon the temperature and cooling efficiency of the cooling system. N2 is the balance which increases with increasing air to natural gas ratio.
The generator designs to produce lean and rich Exo gases are slightly different as shown in the schematic flow diagrams below in Figures 3 and 4.
Objective
This paper will demonstrate a simplified software program (harb-9US) developed recently by TAT Technologies LLC that can easily calculate the reaction products composition, temperature, exothermic energy released, various ratios, and final dew point for various combinations of air and fuel flows entering the reaction chamber at a predetermined temperature and pressure.
The data presented in this paper is under thermodynamically equilibrium conditions only, captured when the reaction is fully completed. It does not tell how long it will take for the reaction to reach completion. However, it can be safely said that reactions are completed relatively fast at temperatures above about 1500°F and very slow at temperatures below about 1000°F. The current software program uses U.S. units: flow in SCFH, pressure in PSIG, temperature in degrees Fahrenheit, and heat as enthalpy in BTU.
The composition of the Exo gas for a fixed incoming air to hydrocarbon fuel ratio changes from production in the combustion chamber to the cool down equipment to bring the Exo gas to below the ambient temperature and finally into the furnace where the material is being heat treated.
Understanding the changes in gas composition from Step 1 (Production in the Combustion Chamber) to Step 2 (Cool Down to Ambient Temperature) to Step 3 (At Temperature of Heat Treated Part) can help to improve the composition, quality, and control of Exo gas that will surround the metallic products being heat treated in the furnace.
Step 1: Composition of Exo Gas as Produced in the Combustion Chamber
Table A shows the Exo gas compositions as generated within the combustion chamber at various air to natural gas ratios supplied at 100°F and 0.1 PSIG. In these calculations natural gas composition is assumed as 100% CH4 and air is assumed as 20.95% oxygen and balance nitrogen. CH4 is fixed at 100 SCFH and air flow is varied to give air to natural gas ratios between 9 and 6. Typically a ratio of 9 is used for lean Exo and 7 is used for rich Exo applications. Other ratios are used in some special applications.
Table A: Exo gas compositions in reaction chamber based on 100 SCFH of CH4 with air 900, 850, 800, 750, 700, 650, and 600 SCFH to give air to natural gas (CH4) ratios of 9, 8.5, 8, 7.5, 7, 6.5 and 6 respectively. Air and natural gas (CH4) are at 100°F before entering the combustion chamber.
Source: TAT Technologies LLC
The following key conclusions can be made from Table A as one moves from air to natural gas (CH4) ratio of 9 down to 6:
The peak temperature in the reaction chambers goes from a high of 3721°F down to low of 2865°F. Because of high temperatures, good insulation around the combustion chamber is a must. A significant portion of the exothermally generated energy within the reaction chamber is lost to the surroundings.
There is no residual CH4 in the Exo gas composition at these high temperatures. There is no soot (carbon residue) under equilibrium conditions.
H20 content in the natural gas (CH4) gas in the reaction chamber is very high — from high of 19.11% to low of 15.87%. These correspond to dew point 139°F to 132°F — well above the ambient temperature. Because of the very high dew point, the Exo gas coming out of the reaction chamber must be cooled down below the ambient temperature to remove most of the H20 in the Exo gas to avoid any condensation in the pipes carrying the Exo gas toward the furnace and into the
furnace.
H2% changes significantly from 0.67% to 9.96%.
The oxide reducing potential (ORP) as measured by H2/H20 ratio changes from a very low of 0.035 to 0.628. ORP in the reaction chamber is overall quite low because of high percentage of H20.
Nitrogen content varies from 70.34% to 61.26% of the total Exo gas in the reaction chamber.
Exothermic heat generated varies from 95.3 MBTU to 54.34 MBTU — it gradually becomes a less exothermic reaction. Gross heating value of CH4 (at full combustion) is 101.1 MBTU/100 cubic foot of CH4.
Question: What happens to the composition of Exo gas as it cools from peak temperature in the combustion chamber to different lower temperatures after it exits from the combustion chamber?
Answer: It changes a LOT, assuming enough time is provided to reach its equilibrium values during cooling down to any specific temperature. Whenever there is a mixture of gases, such as CH4, H2, H20, CO, CO2,O2, N2, there are a variety of reactions going on between the constituents in the reactant gases to produce different combinations of gas products and heats (absorbed or liberated) at different temperatures. The most popular and well-known reactions are:
Partial Oxidation Reaction: CH4+ 1/2O2 → CO + 2H2 — exothermic. The reaction becomes more exothermic as O2 increases from 0.5 to 2.
Water Gas Shift Reaction: CO + H20 → CO2 + H2 — slightly exothermic. It usually takes place at higher temperatures faster. A catalyst in the reaction chamber can help to lower the high temperature requirement. There are many catalysts. Commonly used are either Ni or precious metals.
CO2 Reforming Reaction: CH4 + CO2 → 2CO + 2H2 — endothermic.
All of these reactions have different degrees of influences from changes in temperature. One could say that the final equilibrium composition of the Exo gas is a continuously moving target as temperature changes. Only the N2 portion stays constant. One can make the following generalized statements covering a broad range of Exo gases (lean and rich) in the reaction chamber:
a) N2 content does not change. It remains neutral at all temperatures.
b) H2 content decreases with increasing temperature.
c) H20 (vapor) content increases with increasing temperature.
d) CO content increases with increasing temperature.
e) CO2 content decreases with increasing temperature.
f) Residual CH4 decreases with increasing temperature.
g) Soot decreases with increasing temperature.
h) Catalysts facilitate the speed of reactions at any temperature.
Conclusion
Exo gas composition changes during its time in the combustion chamber. Reaction products composition, temperature, exothermic energy released, various ratios, and final dew point are all items that need to be taken into consideration to protect the metallic pieces that will be heat treated in the resulting atmosphere. Part 2 will demonstrate this principle and discuss Step 2 (Cool Down to Ambient Temperature) and Step 3 (At Temperature of Heat Treated Part).
About the author:
Harb Nayar is the founder and president of TAT Technologies LLC. Harb is both an inquisitive learner and dynamic entrepreneur who will share his current interests in the powder metal industry, and what he anticipates for the future of the industry, especially where it bisects with heat treating
Nikola Tesla afirmó: <<Si quieres descubrir los secretos del universo, concéntrate en la energía, la frecuencia y la vibración.>>
Al revisar los mecanismos internos de un sistema de inducción es posible evidenciar cada uno de estos tres elementos. Los 10 pasos de esta guía servirán para apoyar a los operadores de departamentos internos de tratamiento térmico en entender los secretos de la inducción para así identificar posibles escollos en tales sistemas y dar solución a problemas comunes que se puedan presentar.
This original content article was first written by Alberto Ramirez, engineer of Power Supply and Automation at Contour Hardening, Inc. and an honoree from Heat Treat Today’s 40 Under 40 Class of 2021, for Heat Treat Today's May 2023 Sustainable Heat Treat Technologiesprint edition. Read the Spanish version below, or click the flag above right for the English version.
Alberto Ramirez Power Supply and Automation Engineer Contour Hardening, Inc.
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Los metales pueden calentarse mediante el proceso de inducción electromagnética, mediante el cual un campo magnético alternativo cerca de la superficie de una pieza de trabajo metálica (o conductora de electricidad) induce corrientes de Eddy (y, por lo tanto, calentamiento) dentro de la pieza de trabajo.
Los sistemas de inducción pueden llegar a ser sistemas complejos que tienen como objetivo endurecer piezas o secciones específicas de un componente mecánico, dependiendo del grado de complejidad de la pieza a tratar; para el profesional, el desafío será el diagnóstico de los problemas que se lleguen a presentar.
1. Familiarízate con el proceso
Figura 1. Proceso de endurecimiento por inducción Source: Contour Hardening, Inc.
El proceso de inducción envuelve muchas características tales como: posición de la pieza dentro de la bobina de inducción, posiciones de carga, posiciones de enfriamiento, tiempos de ciclo, potencia eléctrica aplicada, entre otras. Es importante que el profesional sea capaz de identificar la falla y la situación particular en el momento en el que se está presentando.
En algunas ocasiones las fallas no son evidentes y, por ende, es indispensable analizar la pieza que ha sido tratada; este análisis puede ser clave para entender situaciones tales como: falta de profundidad de capa por potencia eléctrica o disminución en la frecuencia de salida, entre otros posibles escenarios.
Adicional al análisis de la pieza, es vital inspeccionar la “escena del crimen” ya que muchos de los sistemas de inducción, dada la naturaleza del proceso y el peligro que implica manejar altos potenciales eléctricos, suelen ser en extremo automatizados y las estaciones de trabajo de difícil acceso para el personal, así que una buena estrategia de trabajo consiste en observar detenidamente las condiciones generales del equipo para determinar el punto de inicio para la resolución del problema.
2. Identifica los componentes principales de tu sistema de inducción, así como los mecanismos de seguridad para ciertas zonas en particular
Entender la interrelación del sistema es importante para comprender qué elemento realiza cierta acción, así como los canales de comunicación entre ellos. Una vez que se genere este conocimiento, se puede asociar una falla a un componente en particular. Usualmente los sistemas de inducción se componen de los siguientes elementos:
Figura 2. Componentes de un sistema de inducción Source: Contour Hardening, Inc.
Como mencionamos con anterioridad el proceso implica altos potenciales eléctricos, y para eso la naturaleza de las fuentes de alimentación involucra dispositivos electrónicos de potencia, como capacitores eléctricos, los cuales almacenan energía y, por ende, es importante descargar eléctricamente el sistema antes de comenzar a inspeccionar un equipo.
3. Ten preparadas las herramientas necesarias para realizar un buen análisis del problema
Figura. Capacitores Source: Contour Hardening, Inc.
Al igual que cualquier problem técnico, el uso de la herramienta mecánica es indispensable al realizar algún tipo de proyecto, pero para el diagnóstico de una falla en un equipo de inducción es importante contar con:
Osciloscopio
Generador de funciones
Amperímetro
Multímetro digital y analógico.
Sondas de alto voltaje
Sin estos elementos es muy difícil llegar a un diagnóstico fiable, y la posibilidad de encontrar la falla es mínima. Por ende, tener estos medidores en buen estado y, sobre todo, calibrados nos da una perspectiva más clara del problema.
4. Verifica que los sensores del proceso, los monitores de energía y las bobinas de inducción funcionen correctamente
Existen distintos medidores que recogen información acerca del proceso; esta información en su mayoría puede ser visualizada a través del HMI (Human Machine Interface), y, en muchas ocasiones, una buena manera de comenzar a entender el problema es recopilar la información del proceso. Si los medidores no funcionan correctamente, te pueden llevar a conclusiones erróneas.
Verifica que los medidores de energía estén funcionando correctamente, así como tus señales de entrada y de salida.
Las bobinas de inducción son un elemento clave en el proceso de inducción ya que acorde a su geometría generan los campos magnéticos adecuados para lograr los resultados metalúrgicos esperados. Si existen fugas de agua o los elementos de transmisión eléctrica se encuentran sueltos o sucios, seguramente podrán ser la raíz del problema. Es importante comenzar a realizar el diagnóstico de la falla una vez se haya descartado este circuito en particular.
Figura 4. Ejemplo de parámetros de energía Source: Contour Hardening, Inc.
5. Realiza estudios de energía constante en tu subestación para identificar posibles problemas en tu suministro de energía, así como tiempos críticos
La energía eléctrica es la fuente principal en un proceso de inducción; las fuentes de alimentación transforman y potencializan este recurso para crear campos electrónicos lo suficientemente fuertes para generar el calor en la pieza.
Por ende, es importante descartar con evidencia que el problema en cual nos encontramos no se debe a una falla del sistema eléctrico del cual nuestro sistema de inducción forma parte. De igual manera entender cómo se comporta nuestro sistema eléctrico nos puede ayudar a generar patrones de comportamiento que puedan determinar la solución en momentos específicos en los que se lleguen a presentar.
6. Trabaja de forma metódica documentando tus movimientos y realiza un paso a la vez
Los sistemas de inducción pueden ser muy intimidantes si no has tenido experiencia previa, y, al igual que con cualquier elemento o situación, es importante abordar de manera lógica el problema analizando el modo de la falla, identificando las partes principales que interactúan en ese preciso momento, y, a partir de este análisis, documentar y realizar pequeños pasos, uno a la vez, ya que, de no ser así, es muy probable que pierdas todo el trabajo realizado y la situación empeore.
Figura 5. Antes y durante un arco eléctrico dentro de la línea de transmisión Source: Contour Hardening, Inc.
Si los movimientos no son exitosos, siempre puedes regresar a tu punto de partida e intentar otro acercamiento. La idea consiste en que el modo de la falla se mantenga estable sin importar los movimientos realizados hasta que se resuelva el problema. De esta manera lograrás contener la falla; de otra manera podrías estar dañando otros elementos sin darte cuenta.
Es muy importante entender que los procesos son secuencias que anteceden y preceden a nuevos eventos; si entiendes el proceso y, una vez resuelto el problema, ahora tienes una nueva falla, es importante analizar si esta falla es la continuación del proceso ya que, de ser así, es posible que te encuentres frente al caso de un evento que está desencadenado una serie de fallas y se haga necesario practicar un análisis más profundo. La idea general es llegar a la raíz del problema y mitigar el riesgo.
7. Intenta cualquier posibilidad relacionada con el proceso sin importar que la relación entre ésta y el problema no sea directa
Un pensamiento lógico puede resolver la mayoría de las fallas técnicas de un sistema, pero, para fallas excepcionales, es necesario utilizar la imaginación y agotar todos los recursos posibles ya que el área de interés más insignificante o el lugar menos pensado puede ser la clave para resolver un problema.
8. Conoce tus fuentes de alimentación
Uno de los factores claves en cualquier equipo de inducción son sus fuentes de alimentación. Las fuentes de alimentación son equipos que no requieren un mantenimiento tan arduo en comparación con otros sistemas en la industria, pero, de no presentarse las condiciones mínimas de mantenimiento, pueden generar altas pérdidas para la organización.
Figura 6. Diagrama de flujo del proceso eléctrico en una fuente de alimentación Source: Contour Hardening, Inc.
En los casos en los que el problema se encuentra en las fuentes de alimentación, es vital que se siga el mismo proceso metódico previamente descrito. Entender cómo funciona el proceso de transformación de la energía te dará una ventaja, al igual que conocer los componentes empleados o el tipo de tecnología utilizado en el proceso de rectificación, en la inversión (estado sólido o tubos de electrones) y en el circuito resonante. Generalmente las fuentes de alimentación siguen el siguiente patrón de transformación (Figura 6).
9. Identifica las partes críticas de tu equipo de inducción y prepara un inventario de éstas
Figura 7. Daño en una bobina de inducción Contour Hardening, Inc.
Usualmente los componentes que forman parte de las fuentes de alimentación son difíciles de conseguir dependiendo de la antigüedad de tu equipo, y con la reciente crisis de microchips en el mercado, existen tiempos de entrega muy largos para los elementos de control y automatización; de igual manera, los precios de los mismos se han disparado. Por ende, es vital que exista una lista de partes críticas y un inventario de éstas.
Adicionalmente a los elementos descritos, las bobinas de inducción suelen ser elementos muy característicos e importantes en el proceso de inducción. Éstas bobinas son elementos complejos que han sido diseñados exclusivamente para la pieza, por lo que su fabricación puede tomar varias semanas, y es importante tomar las precauciones necesarias para mantener un movimiento de mantenimiento constante.
10. Realiza mediciones preventivas al sistema para generar un patrón de comportamiento
Figura 8. Ejemplo de posibles mediciones Contour Hardening, Inc.
Cuando el sistema se encuentre trabajando en óptimas condiciones, genera un plan de medición el cual te permita recopilar información de puntos específi cos dentro del sistema. Una vez que se vuelva a presentar una nueva falla puedes comparar las mediciones de falla contra las del buen funcionamiento. Algunos ejemplos de mediciones pueden ser:
Temperatura
Voltaje
Corriente eléctrica
Resistencia y capacitancia
Formas de onda
En resumen
Una metodología de trabajo ordenada y documentada, un buen catálogo de piezas de recambio, junto con las herramientas de trabajo necesarias, pueden ser elementos clave para entender un problema y, lo que es más importante, resolverlo de forma eficaz.
Es vital que los profesionales se capaciten de manera constante para mejorar los tiempos de paro debido a fallas en los sistemas de inducción. La capacitación relacionada con procesos metalúrgicos sería una buena forma de complementar tus habilidades de resolución de problemas permitiéndote interpretar las características de los sistemas de inducción, al igual que de los elementos que los componen.
Bibliografía
Valery Rudnev and George Totten, ed., ASM Handbook Volume 4C: Induction Heating and Heat Treatment, (Materials Park, OH: ASM International Heat Treating Society, 2014), 581- 583
Sobre el autor: Alberto C. Ramirez es ingeniero en Mecatrónica egresado del Instituto Tecnológico Nacional de México Campus León con una maestría en Administración de Tecnologías de la Información por el Instituto Tecnológico de Monterrey. Cuenta con más de 8 años de experiencia en fuentes de alimentación, gestión de proyectos, mantenimiento y automatización. Actualmente se desempeña como ingeniero de fuentes de alimentación y automatización en Contour Indianapolis. Alberto inició su carrera en la fi lial de Contour en México y debido a su dedicación forma parte del staff en los Estados Unidos.
He is also an honoree from Heat TreatToday's 40 Under 40 Class of 2021.
Nikola Tesla said, “If you want to find the secrets of the universe, think in terms of energy, frequency, and vibration.” These three components are evident in getting to know the inner workings of an induction system. When it comes to troubleshooting such a system at in-house heat treat departments, this 10 step guide will help heat treat operators understand the secrets of induction and solve common problems that may arise.
This original content article was first written by Alberto Ramirez, engineer of Power Supply and Automation at Contour Hardening, Inc. and an honoree from Heat Treat Today’s 40 Under 40 Class of 2021, for Heat Treat Today's May 2023 Sustainable Heat Treat Technologiesprint edition.
Alberto Ramirez Power Supply and Automation Engineer Contour Hardening, Inc.
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Metals can be heated by the process of electromagnetic induction, whereby an alternative magnetic field near the surface of a metallic (or electrically conductive) workpiece induces eddy current (and thus heat) within the workpiece. Induction systems can be complex systems that aim to heat treat specific parts or sections of a mechanical component; depending on the degree of complexity of the part to be treated, it will be the challenge of a professional to detect any problem.
1. Familiarize Yourself with the Process
Figure 1. Induction hardening process Source: Contour Hardening, Inc.
The induction process involves many characteristics such as: position of the piece within the induction coil, load positions, cooling positions, cycle times, applied electric power, and others. It is important that the professional can identify the failure and the particular situation at the moment in which it is occurring.
On some occasions, the failures are not evident and therefore it is essential to analyze the part that has been treated. This analysis can be key to understanding situations such as poor depth due to electrical power or decrease in output frequency, among other possible scenarios.
In addition to the analysis of the piece, it is vital to inspect the “crime scene,” since many of the induction systems — given the nature of the process and the danger involved in handling high electrical potentials — are usually highly automated and the work stations are difficult for staff to access. A good work strategy consists of carefully observing the general conditions of the equipment to determine where the problem will begin to be solved.
2. Identify Main Components and Certain Security Mechanisms of Your Induction System
Understanding the interrelationship of the system is important to comprehend which element performs a certain action, as well as the communication channels between them. Once this knowledge is generated, a failure can be associated with a particular component. Induction systems are usually made up of the elements in Figure 2.
Figure 2. Induction system components Source: Contour Hardening, Inc.
As we mentioned before, the process involves high electrical potentials, and for this reason, the nature of the power supplies involves power electronic devices such as electrical capacitors, which store energy. Therefore, it is important to electrically discharge the system before beginning to inspect a piece of equipment.
3. Have the Necessary Tools Ready To Carry Out a Good Analysis of the Problem
Figure 3. Capacitors Source: Contour Hardening, Inc.
Like any technical problem, the use of a mechanical tool is essential when carrying out some type of project, but for the diagnosis of failure in induction equipment it is important to have:
Oscilloscope
Function generator
Ammeter
Digital and analog multimeter
High voltage probes
Without these elements it is exceedingly difficult to reach a reliable diagnosis, and the possibility of finding the fault is minimal. Therefore, having these meters in good condition and above all, calibrated, gives a clearer perspective of the problem.
4. Verify that the Process Sensors, Power Monitors, and Induction Coils Are Working Properly
There are different meters that collect information about the process. This information can mostly be viewed through the HMI (human machine interface). On many occasions, a good way to begin to understand the problem is by collecting the information on the process. If these meters do not work correctly, they can lead you to wrong conclusions.
Verify the energy meters are working correctly, as well as your input and output signals.
Induction coils are a key element in the induction process since, according to their geometry, they generate the appropriate magnetic fields to achieve the expected metallurgical results. If there are water leaks or the electrical transmission elements are loose or dirty, it could be the root cause of the problem. It is important to start troubleshooting once this circuit is ruled out.
Figure 4. Energy parameters example Source: Contour Hardening, Inc.
5. Carry Out Studies of Constant Energy in Your Substation To Identify Possible Problems in Your Energy Supply, Including Critical Times
Electrical energy is the main source in an induction process, power supplies transform and potentiate this resource to create electronic fields strong enough to generate heat in the piece.
Therefore, it is important to find evidence that rules out failures of the electrical system that the induction system is a part of. In the same way, understanding how our electrical system behaves can help us generate behavior patterns that can determine the solution at specific times when it may arise.
6. Document Your Work Methodically and Take One Step at a Time
Induction systems can be very intimidating if you have not had previous experience, and, like any element or situation, it is important to logically approach the problem by analyzing the failure mode, identifying the main parts that interact at that specific moment. From there, document and take small steps, one at a time. If you don’t, it is very likely you will lose all the work you have done, and the situation will get worse.
Figure 5. Before and after of an arc at the transmission line Source: Contour Hardening, Inc.
If the moves are unsuccessful, you can always return to your starting point and try another approach. The idea is that the failure mode remains the same no matter what moves you make until the problem is resolved. In this way you will have the failure contained, otherwise you could be damaging other elements without realizing it.
It is very important to understand that the processes are sequences that precede and proceed new events. If you understand the process and solve a problem, but now have a new failure, it is important to analyze if this failure is the continuation of the process. If so, it is possible that you find yourself in a case where an event is triggering a series of failures. Therefore, a more in-depth analysis must be carried out. The idea to generate is to get to the root cause and mitigate the risk.
7. Try Any Possibility Related to the Process Regardless of Whether the Relationship Between It and the Problem Is Not Direct
Logical thinking can solve most of the technical failures of a system. For exceptional failures, however, it is necessary to use your imagination and exhaust all possible resources, since the smallest area of interest or the least thoughtful place can be the key to solving a problem.
8. Get To Know Your Power Supplies
One of the key factors in any induction equipment is its power supplies. Power supplies are equipment that do not require such arduous maintenance compared to other systems in the industry, but if the minimum maintenance conditions are not present, they can generate high losses for the organization.
Figure 6. Flow diagram of the energy process at the power supply Source: Contour Hardening, Inc.
In cases where the problem is the power supplies, it is vital that the same methodical process previously described is followed. Understanding how the energy transformation process works will give you an advantage, as will knowing the elements that compose them or the type of technology used in the rectification process, in the inversion (solid state or electron tubes) and in the resonant circuit. Generally, power supplies follow the transformation in Figure 6.
9. Identify the Critical Parts of Your Induction Equipment and Prepare an Inventory
Figure 7. Coil damage Contour Hardening, Inc.
Usually, the elements that belong to the power supplies are difficult to obtain depending on the age of your equipment. With the recent microchip crisis in the market, control and automation elements have very long delivery times or the prices are very high. Therefore, it is vital that there is a list of critical parts and an inventory of these.
In addition to the elements described, induction coils are usually very characteristic and important elements in the induction process. These coils are complex elements that have been designed exclusively for the piece, so their manufacture can take several weeks, and the necessary precautions must be taken to maintain a constant maintenance movement.
10. Perform Preventative Measurements to the System To Generate a Pattern of Behavior
Figure 8. Possible examples of measurements Contour Hardening, Inc.
When the system is working in optimal conditions, generate a measurement plan which allows you to generate information on specific points within the system. Once a new failure occurs again you can compare the measurements of failure against those of good performance. Some examples of measurements can be:
Temperature
Voltage
Current
Resistance and capacitance
Waveforms
Summary
An orderly and documented work methodology, a good spare parts catalog, and the necessary work tools can be key elements to understand a problem and, more importantly, to solve it effectively.
It is vital that professionals are in continuous training in order to decrease downtime due to failures in induction systems. Training related to metallurgical processes would be a good way to complement your resolution skills by being able to interpret the characteristics of induction systems with the elements that compose it.
References
Valery Rudnev and George Totten, ed., ASM Handbook Volume 4C: Induction Heating and Heat Treatment, (Materials Park, OH: ASM International Heat Treating Society, 2014), 581- 583.
About the Author: Alberto C. Ramirez graduated from the National Technical Institute of Mexico as a mechatronics engineer. He earned his master’s degree in information technology administration from Monterrey Institute of Technology. With more than eight years of experience in power supplies, project management, maintenance, and automation, he currently works as a Power Supply and Automation Engineer at Contour Indianapolis. Alberto began his career at the Contour subsidiary in Mexico and due to his dedication, he is part of the staff in the United States. He is also an honoree from Heat TreatToday's 40 Under 40 Class of 2021.
Induction heat treating: no harsh chemicals, gases, or even CO2 emissions. But to get there, heat treaters should first understand how to plan for an induction design and fabrication project upfront. Consider these five important factors before you dive into induction.
This Technical Tuesday article was composed by John Chesna, general manager at Induction Tooling, Inc. and honoree in Heat Treat Today's 40 Under 40Class of 2022. It appears in Heat Treat Today's May 2023 Sustainable Heat Treat Technologiesprint edition.
Introduction
John Chesna General Manager at Induction Tooling Source: Induction Tooling, Inc.
There are many less than obvious factors to consider when preparing and planning for induction. So where to start? There are five important factors that manufacturers with in-house heat treat operations should understand in order to successfully prepare an induction heating project and design.
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But first, what is induction heating? Induction heat treating is the process in which a high frequency conductor (induction tool) induces currents (eddy currents) into an electrically conductive workpiece. Without ever touching the work-piece, the current generated and the resistance causes heating. Ever since its proven usefulness around the time of World War II, induction has been chosen as the go-to heat treatment for a variety of applications across many industries including agricultural, medical, and transportation. Now, it seems that most industries have taken advantage of induction heat treating, and its popularity will likely only continue to increase with the push for the use of “clean” and “green” energy.
#1 Plan for Inductor Wear
One of the most important factors to an induction project is realizing the inductor/ coil is a wear item. It can be highly engineered, hand fabricated, machined, or even 3D printed. Yet, in the overall process, it is still a wear item: an item that will eventually require replacement or repair. The inductor is exposed to the worst of the elements during the induction process and can fail from standard use, accidents, or unforeseen circumstances. Inductor designers are constantly being challenged to create tools that will last longer, require less maintenance, or run more cycles. All of those can be achieved, but the inductor will eventually require replacing and that is not a bad thing!
A properly serviced and maintained inductor will ensure quality parts are being produced. As the inductor wears, the efficacy degrades, leading to undesirable results. Repair of the inductor will correct this issue and ensure the parameters required for the desired heat treat pattern are restored. Depending on production needs, a good principle is to have more than one inductor on hand so that while one is being repaired the spare inductor can remain on the machine to keep up with manufacturing demand. Planning for this is important for the project’s timing and budget.
#2 Types of Inductor Designs
Determining a specific inductor design will be necessary to properly heat parts. The inductor creates the magnetic field in the workpiece, and typically the inductor is shaped to couple closely where heat treatment of the part is desired. Additionally, if quenching is required for the heating application, this function will be considered in the inductor’s design. The inductor’s design must deliver the electrical energy and quench medium to the workpiece while allowing accessibility for material handling purposes. For this reason, inductors take on many different designs.
Six turn multi-turn inductor Photo Source: Induction Tooling, Inc.
Pancake inductor with strap supports Photo Source: Induction Tooling, Inc.
MIQ (Machined Integral Quench) scanning inductor with removable quench plate Photo Source: Induction Tooling, Inc.
Common inductor designs include:
Pancake: used for heating flat surfaces
Single turn or multi-turn: commonly shown as copper tubing wrapped around cylindrically around the workpiece
Hairpin: typically, a simple back and forth loop used to heat long lengths internally or externally on the workpiece
Split return: used to focus the energy in particular areas of the workpiece
MIQ (machined integral quench) paddle: the most commonly used design for scanning applications
#3 Power and Frequency
Know the power supply and/or work-head power and frequency. Depending on the composition of the part that requires processing, the power and frequency of the equipment will help estimate the depth of the pattern that can be achieved, as well as help determine how successful the part will be for induction heating. Irregularly shaped geometries with points, holes, or sharp edges sometimes cause difficulty establishing eddy currents where the induction pattern is desired. Some parts, after review, are good candidates for induction heat treatment but cannot be processed with the existing power supply and/or work-head setup.
If an inductor is being built to mount to existing induction equipment, it is important to know the scope of parts that are currently being processed or expected to be processed on the machine. The electrical circuit of the power supply, work-head, and inductor must load match to the part. If a variety of parts are being run then multiple styles of inductors may exist or will be required to be used. Different designs of inductors, e.g., single-turn, multi-turn, or split return used on the machine will change the transformer effect and capacitor requirements of the system. Availability to tune the system capacitance and inductance becomes vitally important for operation. Please note that adjusting capacitance can be dangerous and should only be done by a trained technician. Newer power supplies function differently than older models, yet load tuning needs to be considered.
#4 Part Details
A detailed pre-induction print is needed. The print should list the material as well as the desired heat treatment pattern to determine the inductor design. As the print specifies the pattern, it should also provide limits. Inductors are then typically designed to the shape of the part. The inductor may require an integrated quench, electrically insulating protective coating, locators, or additional assembly fixturing depending on the part’s size. An inductor built for one part may be used or tried on a similar part. However, the same results cannot be expected to render on the part for which it was not designed. If the manufacturer knows that a family of parts will be run, the full scope should be presented to inductor designers for consideration before the build.
#5 Material Handler
Ideally an inductor supplier would be contacted to develop the induction heating process for a part; then, that information should be shared with the material handling designer. That would be the ideal, but that’s not the way it usually happens. Sometimes, a machine is built to process a part that no longer is in use, so the machine is now being retrofitted to process different parts. The design of a new inductor is needed to accommodate this existing machine which may create size constraints to the inductor’s design.
The contact style, how the inductor mounts to the work-head, will need to be determined. There are a variety of commonly used power supplies and work-heads available from OEMs in the market. As each OEM keeps their contacts standard to their equipment, there is no singular standard footprint in the market. Once the contact style has been determined, the inductor can be designed for maximum power delivery efficiency. How the part and inductor are presented to each other is important. The centerline distance, a measurement from where the inductor mounts to where the part will be processed, needs to be known. The centerline determines the required length of the inductor and indirectly how much room is available for the inductor’s design.
Conclusion
Due to the variety of factors, no two projects are ever the same. Induction heating is an exciting technology, and I encourage everyone to learn more about it.
About the Author: John Chesna is the general manager of Induction Tooling, Inc. and has been involved with the induction heat treating industry for over 8 years. He is a graduate of the University of Akron with a Bachelor of Science in Mechanical Engineering Technology. His responsibilities include overseeing day-to-day operations including the design, manufacturing, and testing of induction heat treating inductors. Additionally, John was a recipient of Heat Treat Today's 40 Under 40 award in 2022.
Independence Day is right around the corner, and Heat TreatToday wanted to share some red, white, and blue processes from across the heat treating industry. We're highlighting induction hardening, gas nitriding, and hydrogen generation. Curious? Get ready for Independence Day with this red, white, and blue Technical Tuesday.
Induction hardening in action Photo Credit: Contour Hardening
Induction hardening is a bit out of place in the heat treating world. There are no huge pieces of equipment, long wait times, or mysterious happenings behind furnace walls. But using those red hot coils for hardening can be a game-changer, because induction hardening offers selective hardening, increased part strength, and uninterrupted process flow.
"The induction coil is a copper conductor that is shaped in order to harden the specified area of the part. The current that flows through the coil is what produces the magnetic field, which in turn heats the part. Coils are typically part specific, since they need to be precisely constructed to heat a particular portion of the part."
White layer from nitriding Photo Credit: SECO/VACUUM
Gas nitriding is a valuable case hardening process. In gas nitriding, a white layer made up of a nitrogen-rich compound is formed. This white layer is hard and wear-resistant, but is also very brittle.
"This compound layer depth is dependent on processing time. In the more traditional two-stage process, the case depth produces a gradient of hardness from surface to core that commonly ranges from 0.010-0.025”, with minimal white layer, typically between 0-0.0005”."
Water and electricity: that's all the materials that are needed to generate hydrogen on site. Water electrolyzers for hydrogen generation are compact, portable, and reliable, as well as being safer than storing gases. Could the future of heat treating — and perhaps the end of natural gas — be "blue"? Now, unless you live on the beach in the Bahamas, the water you're used to probably isn't blue, but you catch our drift.
"Electricity and water come into a plant in pipes and wires and are highly reliable. Additionally, there are no hydrogen storage tanks taking up a large amount of unusable space."
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Over the past year, we’ve seen numerous new technologies in the way of research, new partnerships, and conversations throughout the industry. So in honor of today being #NationalTechnologyDay, we’re sharing an original content article about just several of these new technologies that are changing the work of heat treaters across North America.
Research
Using HIP to Advance Oregon Manufacturing Innovation Center Programming– “‘Today’s globally competitive manufacturing industry demands rapid innovations in advanced manufacturing technologies to produce complex, high-performance products at low cost,’ observes Dr. Mostafa Saber, associate professor of Manufacturing & Mechanical Engineering Technology at Oregon Tech.”
College Students Implement a NEW Heat Treat Solution with Induction? – “‘We were in shock,’ Dennis admitted, ‘because we didn’t expect it to [work].’ The expectation, Dennis continued, was that something would go wrong, like the lid would not be able to clamp down, or the container would leak.”
The Age of Robotics with Penna Flame Industries – “The computerized robotic surface hardening systems have revolutionized the surface hardening industry. These advanced robots, coupled with programmable index tables, provide an automation system that helps decrease production time while maintaining the highest quality in precision surface hardening.”
Heat Treat Radio: Five experts (plus Doug Glenn) discuss hydrogen combustion in this episode. An easily digestible excerpt of the transcript circulated by Furnaces Internationalhere and is available to watch/listen/read in full for free here.
Heat Treat Radio: Get on-the-ground projections of what technologies Piotr Zawistowski believes will be bringing in the future. Watch/listen/read in full here
Heat Treat Radio: HIP. The Revolution of Manufacturing, that is, according to Cliff Orcutt. Watch/listen/read in full here
Heat Treat Radio: Will indentation plastometry find its way into North America? If you’ve been listening to James Dean, it seems like it already has. Watch/listen/read in full here
Heat Treat Radio: Fluxless inert atmosphere induction brazing. That’s a mouthful! But what is it? Watch/listen/read in full here
Welcome to another Technical Tuesday for 18 hard-hitting resources to use at your heat treat shop. These include quick tables, data sets, and videos/downloadable reports covering a range of heat treat topics from case hardening and thermocouples to HIPing and powder metallurgy.
Defining Terms: Tables and Lists
Table #3 Suggested Tests and Frequencies for a Polymer Quench Solution (in article here)
Case Hardening Process Equipment Considerations (bottom of the article here)
Two simulations of a moving billet through heating systems (in article here)
Fourier’s Law of Heat Conduction (in article here)
Webinar on Parts Washing (link to full webinar at the top of the review article here)
Materials 101 Series from Mega Mechatronics, Part 4, Heat Treatment/Hardening here
Heat Treat TV: Press-and-Sinter Powder Metallurgy here
BONUS: 39 Top Heat Treat Resources
Heat Treat Today is always on the hunt for cutting-edge heat treat technology, trends, and resources that will help our audience become better informed. To find the top resources being used in the industry, we asked your colleagues. Discover their go-to resources that help them to hone their skills in the 39 Top Heat Treat Resources on this page of the September print magazine.
Your parts need heat treated to herculean surface hardness but with a soft, ductile core. That is to say, you are looking at case hardening processes, most likely one of these: gas carburizing, low-pressure carburizing, carbonitriding, gas nitriding, and ferritic nitrocarburizing.
Mike Harrison at Gasbarre Thermal Processing Systems brings us a Technical Tuesday article about what case hardening is and how five of the most common processes vary by (1) comparing the specific guidelines for each temp and time, (2) identifying equipment used to perform each process, and (3) providing a chart (at the end!) to understand different process considerations.
Mike Harrison Engineering Manager of Industrial Furnace Systems Division Gasbarre Thermal Processing Systems
Case hardening falls into a class of heat treatment processes that typically involve the addition of carbon and/or nitrogen to the material through solid-gas reactions at the surface followed by diffusion. These processes are performed for any number of reasons that generally include increasing strength and wear resistance, but in all cases the end result is a harder, higher-strength surface with a softer, more ductile core.
Case hardening processes can be divided into two subsets: those that include quenching to harden, such as gas carburizing, low-pressure carburizing (LPC), and carbonitriding; and those that do not include quenching, such as gas nitriding and ferritic nitrocarburizing (FNC). This article will provide a brief look into each process, the types of equipment used, and considerations for implementation.
Diffusion + Quenching Processes
These processes involve heating the workload to austenitizing temperature, which is above the upper critical temperature for the material in question, then supplying and allowing the desired element(s) to diffuse into the part surface, followed by rapid cooling (quenching) to create a phase change to martensite that strengthens the material. Tempering is then performed to create a material that has the desired final strength and ductility properties. The result is a high concentration of added elements on the surface that continually decreases through diffusion until eventually matching the same concentration as the base material; this gradient similarly produces a hardness that is higher at the surface, gradually diminishing until reaching the core. Higher alloyed steels may also see a microstructural change in the core from quenching that produces a core with higher hardness than the previously untreated material, but lower than the surface hardness produced.
Atmosphere Gas Carburizing
Gas carburizing is a process where carbon is added to the material’s surface. The process is typically performed between 1550-1750°F, with carburizing times commonly between 2-8 hours; of course, these values can vary depending on the material, process, and equipment. The most common atmosphere used for atmosphere gas carburizing is endothermic gas with additions of either natural gas or propane to increase the carbon potential of the furnace atmosphere. Common case depths achieved are around 0.005-0.040”, with deeper cases possible through a combination of longer treatment times and/or higher temperatures.
Fig. 1 – Integral quench furnace: "The atmosphere gas carburizing process can be performed both in batch and continuous equipment."
The atmosphere gas carburizing process can be performed both in batch and continuous equipment. On the batch side, traditionally an integral quench (IQ) furnace is used (Fig. 1); it consists of a heating chamber where the workload is heated and exposed to the carburizing atmosphere, then the workload is transferred to an attached quench tank for cooling. The entire furnace system is sealed and under protective atmosphere to preserve the part surface and maintain safe control of any combustible gases. For batches of large product, a pit furnace can be used for carburizing with the workload being transferred via an overhead crane into and out of the furnace to a quench tank.
For continuous processing, a belt furnace can be used. The product is placed on a belt and then progresses through the furnace at the desired temperature and atmosphere composition; the carburizing time can be varied by adjusting the belt speed through the furnace. At the end of the furnace, the parts drop off the belt into the quench tank. Then, a conveyor pulls the parts out of the tank and drops them on another belt to be washed and tempered. For continuous processing of heavier loads pusher furnaces, rotary retort, rotary hearth, and roller hearth furnaces can be used.
Fig. 2 – Endothermic gas generator: "To achieve a carburizing atmosphere endothermic gas is typically used, which is produced by an endothermic gas generator that heats a combination of natural gas and air to create a mixture that is approximately 40% hydrogen, 40% nitrogen, and 20% carbon monoxide."
To achieve a carburizing atmosphere endothermic gas is typically used, which is produced by an endothermic gas generator (Fig. 2) that heats a combination of natural gas and air to create a mixture that is approximately 40% hydrogen, 40% nitrogen, and 20% carbon monoxide. This mixture is generally considered carbon-neutral, meaning it will neither add nor deplete carbon from the surface. To increase the carbon concentration the endothermic gas needs to be enriched with a gas (typically natural gas or propane) that will help produce additional carbon monoxide, which will “boost” the carbon potential and drive carbon diffusion into the material.
A less common carburizing atmosphere comes from a nitrogen-methanol system, where nitrogen gas and liquid methanol are combined and injected into the furnace. Upon exposure to the high furnace temperature the methanol will decompose to hydrogen and carbon monoxide. Natural gas or propane additions are still required in order to provide carbon for absorption into the surface of the steel.
Low-Pressure Carburizing
Low-pressure carburizing (LPC), or vacuum carburizing, is a variation of carburizing performed in a vacuum furnace. Instead of the atmospheres mentioned previously, a partial pressure of hydrocarbon gas (such as propane or acetylene) is used that directly dissociates at the part surface to provide carbon for diffusion. After LPC, the workload is transferred to a quench system that could use oil or high-pressure gas, typically nitrogen. LPC with gas quenching can be an attractive option for distortion prone complex geometries as the cooling rates are slower than oil quenching; however, given the slower cooling rate, it becomes very important to choose a higher alloyed steel that will achieve the desired hardness.
Fig. 3 – Vacuum furnace with oil quench
LPC typically provides faster carburizing times when compared to traditional gas carburizing. This can be attributed to a more efficient reaction of the hydrocarbon gas used and to the option of using higher carburizing temperatures, typically up to 1900°F. This is made possible by the type of internal furnace construction of vacuum furnace design, although care must be taken at higher temperatures to avoid undesirable grain growth in the material. LPC also has the benefit of eliminating the potential for intergranular oxidation, since it is running in a vacuum system.
LPC is typically performed in a single-chamber vacuum furnace, with oil quenching or high-pressure gas quenching done in a separate chamber (Fig. 3). Continuous vacuum furnaces can also be used in applications that require increased throughput (Fig. 4).
Fig. 4 – Continuous vacuum furnace
Carbonitriding
Despite its name, carbonitriding is more closely related to carburizing than it is to nitriding. Carbonitriding is a process where both carbon and nitrogen are added to the material surface. This process is typically performed in a range of 1450-1600°F and generally produces a shallower case depth than carburizing. Carbonitriding is used instead of carburizing for plain carbon steels that do not contain enough alloying content to respond well to quenching, as the added nitrogen can provide a higher hardenability in the case to allow for proper hardness development.
Atmosphere carbonitriding can be performed in the same equipment as is used for carburizing. The furnace atmosphere is still typically endothermic gas-based and includes the addition of ammonia to provide the nitrogen. Vacuum carbonitriding with both hydrocarbon and ammonia additions can also be performed in the same equipment as used for vacuum hardening and low pressure carburizing.
Diffusion Only Processes
These processes involve heating the workload to a temperature below the austenitizing temperature, allowing the desired element(s) to diffuse into the part surface, then slow cooling. The increase in hardness at the material surface comes only from the addition of the diffused element(s), and not from a phase change due to quenching. As these processes are performed below the lower critical temperature (i.e., below the austenitizing range), the desired core hardness and microstructure need to be developed through a separate heat treatment prior to case hardening. Generally, the process temperature selected should be at least 50°F below any prior treatment temperatures to avoid impact to the core properties.
Gas Nitriding
Gas nitriding is a process where nitrogen is added to the material surface. The process is typically performed between 925-1050°F; cycle times can be quite long as the diffusion of the nitrogen is slow at these temperatures, with nitriding times typically ranging from 16 - 96 hours or more depending on the material and case depth required. Nitriding can be performed in either a single or two-stage process and has the potential to produce two types of case, the first being a nitrogen-rich compound layer (or “white layer”) at the surface that is extremely hard and wear-resistant but also very brittle. This compound layer depth is dependent on processing time. In the more traditional two-stage process, the case depth produces a gradient of hardness from surface to core that commonly ranges from 0.010-0.025”, with minimal white layer, typically between 0-0.0005”. Nitriding is typically performed on higher alloyed steels or steels specifically designed for the nitriding process (e.g., Nitralloy®) as it relies on the formation of nitrides to create the increased hardness, which is achieved through the use of nitride-forming alloys such as aluminum, molybdenum and chromium. Pre and post oxidation treatments can be incorporated into the cycle to achieve certain benefits. Since the process does not require quenching to harden, it has the potential of producing a product that is more dimensionally stable and may not require any post-process finishing.
Fig. 5 – Horizontal retort nitriding furnace: "Traditionally, pit furnaces have been used for nitriding as they can accommodate larger load sizes and can be easier to seal as gravity helps keep the lid sealed; however, horizontal designs have gained in popularity in recent years."
This process is most commonly performed in batch equipment; while it is possible to use a continuous furnace, keeping the ends of furnace sealed to contain the atmosphere can be challenging. Traditionally, pit furnaces have been used for nitriding as they can accommodate larger load sizes and can be easier to seal as gravity helps keep the lid sealed; however, horizontal designs have gained in popularity in recent years (Fig. 5). In either case, the furnaces are usually a single-chamber design with the load sealed inside an Inconel or stainless steel retort.
To achieve a nitriding atmosphere, ammonia (not nitrogen) is used to supply the atomic nitrogen necessary for diffusion. At the process temperatures used, ammonia does not readily dissociate on its own; rather, it dissociates when exposed to a heated steel surface (iron acting as a catalyst) into atomic nitrogen and hydrogen. To control the amount of nitrogen available for nitriding, the dissociation rate of the ammonia can be measured with high dissociation rates (high hydrogen content) providing a lower nitriding potential and low dissociation rates (low hydrogen content) leading to more nitriding potential. The depth of the compound layer can be varied through control of the nitriding potential, with higher nitriding potentials producing a thicker compound layer.
For more precise atmosphere control, an ammonia dissociator can be used to provide gas to the furnace that has already been split to dilute the atmosphere with hydrogen to more quickly achieve a high dissociation rate in the furnace. The ammonia dissociator is a heated box with a small retort inside; the ammonia is passed through this retort that contains a catalyst to promote the dissociation of the ammonia, and the resulting gas mixture is cooled and then injected into the furnace.
Ferritic Nitrocarburizing
In the author’s opinion, just like with carbonitriding, ferritic nitrocarburizing (FNC) is named incorrectly as it is more closely related to nitriding than it is with carburizing. FNC is a process that is still mostly nitrogen-based but with a slight carbon addition as well. The added carbon helps promote compound layer formation, particularly in plain carbon and low alloy steels that do not contain significant nitride-forming alloys. This process is typically performed in a range of 1025-1125°F with cycle times much shorter than nitriding, typically 1-4 hours. The compound layer produced is usually much deeper than nitriding at 0.0005-0.0012”, with case depths reaching up to 0.025”, although in many applications a case depth may be difficult to measure. FNC is usually performed instead of nitriding in applications where the deeper compound layer is needed to increase wear resistance, but the added strength of a deep case depth is not as critical.
FNC can be performed in the same equipment used for nitriding, as long as a hydrocarbon gas is available to the furnace such as carbon dioxide or endothermic gas. FNC can also be performed in an IQ furnace using a mixture of ammonia and endothermic gas; for cooling, the parts can be oil quenched or slow cooled in a top cool chamber (if equipped).
Considerations
Case hardening processes are some of the most common heat treatments performed, but each process has its own unique needs. The table below provides a summary of the considerations that need to be made when selecting the optimum process. This list is by no means exhaustive; it is encouraged to work with a furnace manufacturer familiar with each process to help select the correct process and equipment needed.
About the Author: Mike Harrison is the engineering manager of the Industrial Furnace Systems division at Gasbarre. Mike has a materials science and engineering degree from the University of Michigan and received his M.B.A. from Walsh College. Prior to joining Gasbarre, Mike had roles in metallurgy, quality, and management at both captive and commercial heat treat facilities, gaining nearly 20 years of experience in the thermal processing industry. Gasbarre provides thermal processing equipment solutions for both atmosphere and vacuum furnace applications, as well as associated auxiliary equipment and aftermarket parts & service.
For more information: Contact Mike at mharrison@gasbarre.com
