"Boogie woogie" or not, the industry is sliding into the electric trend both in how heat treaters process parts, and in the end-product of what they are processing. This original content article takes several anecdotes from within the industry to keep you up-to speed on this developing interest. Despite what the singer Marcia Griffiths says, if you do see this electric trend in other industries, email us at editor@heatreattoday.com or @HeatTreatToday when you're on social media to give us the heads up.
The electric shift is proliferating the current dialogue. Is it because it's Earth Month in the US? Perhaps, but we don't think so. Heat treaters and industry suppliers continue to promote sustainable practices, from Buehler's "Sustainable, Long Lasting, Metallurgy Supplies" list to a recent Heat TreatTodayarticle on diffusion bonding due to changes in heat treated products.
Electric Processes
In terms of industry processes, Kanthal says "It’s time to electrify the steel industry." The goal, the company continues, is to create heat treating services that are precise and which eliminate CO2 emissions and energy consumption. In an industry which needs to use a lot of energy, viable solutions are needed to make the shift.
Pit furnace for ingot heating with Kanthal® Super electric heating elements Source: Kanthal; Photographer, Evelina Carborn
The company claims that their initiative provides that balance of economic viability and powerful heat treating. "There are many misconceptions about electric heating – that it’s not able to reach certain temperatures, for instance," says Anders Björklund, president of Kanthal. "But with our technology, you can electrify any heating process in steelmaking. As we have proved, Kanthal has the technology, the thermal expertise, the resources and the global footprint to electrify all the highly energy-intensive heating processes."
The benefits of electric heating include reducing CO2 and NOx emissions, improving thermal efficiency, and precise temperature control. Additionally, the company notes that the reduction of noise and exhaust gases means a cleaner, quieter production process and work environment. Not as hardcore, but I guess it's nice to sometimes be able to hear the person next to you.
Electric Products
According to SECO/WARWICK, "Heat treatment is used by the automotive industry to manufacture gears, bearings, shafts, rings, sleeves, and batteries for electric cars. What is most important to this sector is the reliability of solutions, their efficiency, and process repeatability. This is why the solutions addressed for this market sector must take into consideration the need to reduce distortion, lower the process costs, shorten the process time, use efficient and effective carburizing technologies, and lower CO2 emissions."
Sławomir Woźniak CEO SECO/WARWICK Source: secowarwick.com
Specifically related to Europe, "The ACEA (European Automobile Manufacturers' Association) report shows that as much as 29% of all EU R&D spending in the year preceding the pandemic was made by automotive players," Sławomir Woźniak, CEO, SECO/WARWICK Group revealed. "This is an industry that is open to novelties, which is why we are actively looking for solutions that will effectively support production in the automotive area."
And there is an alphabet of applications to look for. The above company points to low-pressure carburizing and high-pressure nitrogen quenching technologies in their CaseMaster Evolution–T as one option that has been popular for automotive heat treaters in the past. The same company had also reported a major sale last year to a manufacturer who would be brazing electric car batteries with controlled atmosphere brazing, or CAB, technology. Lastly, diffusion bonding -- as mentioned earlier in the article -- may be a new process for treating new products like electric vehicles since "several unique advantages for complex geometric structures and materials that can operate under strenuous high-performance conditions" (The “Next Leap”: Diffusion Bonding for Critical Component Manufacturing).
Conclusion
With a new administration in the United States heavily pushing for certain new energy outlets, there are mixed reactions and questions. One commenter on a recent Industry Week piece commented, "as I drive to work every morning I pass 6 or 7 privately owned fracking wells operating safely at full tilt right down the road from one abandoned solar mirror plant built in 2010 at a wasted cost of over $20 mil to the taxpayer... and I ask myself which of these assets was the 'smart investment of the future,' and which proved the fool's errand?" Still, electric processing and products seems to be receiving a huge push in industry, with both private individuals and political pressures emphasizing the virtues of electric.
With "advances in electric vehicle transportation, semiconductor fabrication, novel material development, and miniaturization, the ‘performance envelope’ continues to broaden." This requires revisiting some tried and true heat treating techniques and their applications.
Read on to see what Tom Palamides, senior sales and product manager at PVA TePla America, Inc., has to say about how diffusion bonding may replace brazing for certain applications. Check out other Heat Treat Todayoriginal content or Technical Tuesday articles in the search bar to the right.
Tom Palamides with diffusion bonding furnace Source: PVA TePla
As we begin to see the light at the end of the tunnel from the devastating economic shock of the COVID pandemic, engineering companies, heat treaters, and material process engineers must work in unison to adopt refined manufacturing processes to meet the demands of critical component design. Harnessing new tools and techniques allows for real operational enhancements and is an increasing trend across many industries.
Brazing historically has been, and remains, the stalwart technique for joining precision-machined components. However, with advances in electric vehicle transportation, semiconductor fabrication, novel material development, and miniaturization, the “performance envelope” continues to broaden. Two of the most common limitations of brazing are that it is challenging to prevent alloy flow in small diameter micro-channels. When such a part is used in higher temperature operating conditions, the joint can introduce elemental cross-contaminants for ultraclean environments. To this end, diffusion bonding, which uses pressure and relatively low heat (about 50%-90% of the absolute melting point of the parent material) to join similar, or dissimilar materials, holds promise.
If one examines the aerospace, semiconductors, energy, medical devices, and electronic component markets, new and higher performance demands have become the norm. Next-generation product designers are, therefore, evaluating new bonding processes to achieve improved performance goals. Many now view diffusion bonding as the “next leap” for metallic materials processing; it offers several unique advantages for complex geometric structures and materials that can operate under strenuous high-performance conditions.
Solid-state diffusion bonding results from the controlled combination of three (3) key processing parameters: pressure, temperature, and cycle time. The careful balancing of these three parameters promotes bonding at the joining surfaces. The result is a virtually invisible uniform interface, devoid of metallurgical discontinuities and porosity.
PVA TePla’s commercial diffusion bonding furnace for joining similar and dissimilar materials Source: PVA TePla
Process engineers have evaluated solid-state diffusion bonding at a research-level for more than fifty years; however, much has changed recently. Building on twenty-five years of successful commercial product solutions, such as aircraft disk brakes and specialized heat exchangers, diffusion bonding is now an “upgraded” process. With advancement in the use of high-strength carbon matrix composites and advanced furnace designs that leverage sophisticated electronics and hydraulic systems controllable to within thousandth-of-an-inch, commercial interest now extends far beyond aerospace and energy.
The most sophisticated global companies in electronic instrumentation and semiconductors view diffusion bonding as the wave of the future. The functional-value that 21st-century diffusion bonding technology now offers is a unique-and-beneficial solution in a class by itself; designers came to this realization after being confronted with component performance issues that could not be resolved by traditional brazing. Materials currently under consideration include pure aluminum, aluminum alloys, stainless steels, and nickel-based alloys as well as any other material, such as coated substrates for power electronics or glass and special material combinations (dissimilar joints).
Today is an exciting time for any engineer who wants to upgrade or produce new and/or higher performance designs, and heat treaters need to be aware of a new process emerging in their midst. It is essential for the heat treater to know the various types of capital equipment and the performance specifications that have and are evolving with the diffusion bonding process. Companies are learning to operate with smarter devices and more intelligent methods. Why not evaluate diffusion bonding to improve productivity, product quality, and material performance for your next-generation products?
About the Author: Thomas Palamides, senior sales and product manager at PVA TePla America, Inc., has a background in materials science and international marketing. He holds two U.S. patents. He is passionate about facilitating a broader understanding of how material processes fundamentally influence design and manufacturing cost, as well as how they improve business.
Journey through this article by Robert Hill, FASM, president of Solar Atmospheres of Western PA, to explore the history, problems, solutions, and impacts this metal has had on multiple varied industries.
This original content piece was first released in Heat TreatToday’s Aerospace 2021 Issue. Click here to access the digital edition and all previous print/digital editions.
Robert Hill, FASM President Solar Atmospheres of Western PA
In 1987, Michael Suisman, president of Suisman & Blumenthal, sounded a stern warning that a “titanium disease” was spreading throughout the land. His clinical description was as follows:
Symptoms: The patient is completely overcome by the metal titanium. He or she tends to eat and sleep titanium, pushing all other metals out of his or her system. The patient will talk for hours about the virtues of titanium, extolling its remarkable qualities. Any blemish on titanium’s image, any negative characteristic will tend to be dismissed. Titanium’s feast-or-famine existence seems to only intrigue the patient.
Earliest known causes: In the 1950s, a number of patients were overcome with titanium, describing it as the “wonder metal.” The side effects of the “wonder metal” syndrome took many years to disappear.
Similar disease: See infatuation.
Length of disease: Lifetime.
Cure: None known.
After working with titanium for more than two decades, I have fallen victim to the “titanium disease.” What makes this metal so unique? With a quick look at the history and distinctive properties, one can easily recognize the attraction.
History
Titanium was discovered by an English pastor named William Gregor in the 1700s. In the 1800s, small quantities of the metal were produced. Before World War II, titanium as a useful metal was only a tantalizing laboratory curiosity. At that time, titanium was only valuable as an additive to white paint in its oxide form. It took the long and expensive arms race between the United States and the Soviet Union in the 1940s to create the need to solve many of titanium’s complex problems.
Since the end of the Cold War, titanium has matured primarily as an aerospace material. However, this “wonder metal” has expanded to commercial markets such as artificial body implants, golf clubs, tennis rackets, bicycles, jewelry, heat exchangers, and battery technologies.
Titanium’s unusual metal attributes include a strength comparable to steel – but 45% lighter. It is twice as strong as aluminum–but only 60% heavier. It is both biologically and environmentally inert. It will not corrode. The metal is nonmagnetic and can hold strength at high temperatures because it has a relatively high melting point. Finally, titanium has a very low modulus of elasticity and excellent thermal conductivity properties. For thermal processors, these “spring like” properties allow titanium to be readily formed or flattened with heat and pressure.
Problems
For all of its outstanding attributes, titanium is still the problem child of the metallurgical family. It is exceedingly difficult to obtain from its ore, which commonly occurs as black sand. If you scoop up a handful of ordinary beach sand and look closely, you will likely see that some of the grains are black–this is titanium ore. In certain places in the world, especially Africa and Australia, there are vast black sand deposits. Although titanium is the ninth most abundant element on the earth, turning that handful of sand into a critical jet engine blade or body implant is a significant undertaking. The refining process is about 10,000 times less efficient than making iron, which explains why titanium is costly.
Vacuum aging of titanium aircraft forgings Source: Solar
Titanium never occurs alone in nature, and it is a highly reactive metal. Known as a transition metal, it can form bonds using electrons from more than one of its shells or energy levels. Therefore, titanium is known as the streetwalker metal. Metallurgists are aware that titanium is renowned to pick up other elements quite readily during many downstream thermal and chemical processes. These reactions are often harmful to the advantageous properties of titanium and should be avoided at all times.
Solution
Since titanium has a tremendous affinity to pick up other elements at elevated temperatures, primarily oxygen and hydrogen, the only way to heat treat titanium successfully is to utilize high vacuum atmospheres. High vacuum levels of x10-5 Torr minimum and low leak rates of five microns per hour maximum are the parameters needed to retain this metal’s desired properties. An oxygen-rich atmosphere results in a hard “alpha case” surface condition. A hydrogen atmosphere results in a hydride condition, which makes titanium very brittle to the core. Both conditions can be extremely detrimental to any critical titanium component.
With high pumping capability and tight pyrometric controls, vacuum furnaces successfully provide various treatments on the “wonder metal” while avoiding the “streetwalker” syndrome. The treatments include inert stress relieving, solution treating, aging, and degassing treatments. After proper processing, bright and clean parts with low hydrogen content and zero alpha case are the norm.
The recycling of titanium is of a different magnitude than other metals due to its value. It took a shortage of titanium in the 1980s–and some innovative metallurgy–to transform valuable titanium scrap back into a qualified ingot. To do this, metallurgists used the reactivity of the metal to their advantage. Because titanium is very ductile and extremely hard to grind into powder, metallurgists learned how to use hydrogen to their advantage. Adding hydrogen to turnings and scrap makes the titanium brittle and enables the material to be pulverized into fine powders. The final product must then be thoroughly degassed or dehydrided to enter back into the revert stream, because every pound of titanium is precious.
Vacuum dehydriding (degassing) 130,000 pounds of titanium sheet and plate Source: Solar
The reactivity of titanium also assists the metallurgist to apply various surface treatments. Nitride and carbide surfaces, when used, add further protection to titanium while making the exterior harder.
Alloys
Titanium alloys are divided into four distinct types: commercially pure, alpha, beta, and alpha beta. Commercially pure grades have no alloy addition, and therefore they have very little strength. This grade of titanium is used when corrosion resistance is of greater importance. Alpha alloys are created with alpha stabilizers such as aluminum. They are easy to weld and provide a reliable strength at elevated temperatures. Beta alloys use stabilizers such as molybdenum or silicon which makes these alloys heat treatable to higher tensile strengths. Finally, the most used titanium alloy are the alpha-beta alloys. These heat treatable alloys are made with both alpha and beta stabilizers creating an excellent balance between strength, weight, and corrosion resistance.
Summary
Despite all the advances, titanium and its many alloys have not reached their apex in popularity in the world. Is there any other element that calls to mind the notion of strength quite like titanium? For what reason has this metal, named after the Titans of Greek mythology, not yet reached its full potential? If it were not for the expense, we would undoubtedly have titanium cars, houses, jets, bridges, and ships. Unfortunately, the cost of titanium keeps the “titanium disease” at bay.
About the Author: Robert Hill, FASM, president of Solar Atmospheres of Western PA, began his career with Solar Atmospheres in 1995 at the headquarters plant located in Souderton, Pennsylvania. In 2000, Mr. Hill was assigned the responsibility of starting Solar Atmospheres’ second plant, Solar Atmospheres of Western PA, in Hermitage, Pennsylvania, where he has specialized in the development of large furnace technology and titanium processing capabilities. Additionally, he was awarded the prestigious Titanium Achievement Award in 2009 by the International Titanium Association.
The Fraunhofer Institute for Manufacturing TechnologyandAdvanced Materials IFAM in Dresden has received a hot isostatic press. This HIP technology will permit researchers to deepen their expertise and refine processes for pressure-supported heat treatment, used to maximize theoretical density, ductility, and fatigue resistance in high-performance materials.
Applications for the new system from Quintus Technologies include the hot isostatic pressing and heat treatment of specialty materials such as nickel-based superalloys and intermetallic compounds like titanium aluminides, as well as densification of the unconventional microstructures associated with additive manufacturing (AM).
Dr. Thomas Weißgärber Director of the Branch Lab Fraunhofer IFAM Source: ifam.fraunhofer.de
The QIH 15L is equipped with Quintus’s Uniform Rapid Quenching® (URQ®) technology, which achieves a cooling rate of 103K/minute, while minimizing thermal distortion and non-uniform grain growth for finished 3D printed parts with optimal material properties. The press’s furnace chamber has a diameter of 6.69 inches (170 mm) and a height of 11.4 inches (290 mm) and operates at a maximum pressure of 200 [207] MPa (30,000 psi) and a maximum temperature of 2,552°F (1,400°C).
Acquiring the Quintus HIP allows Fraunhofer IFAM researchers to “strengthen their technological expertise in the field of pressure-supported heat treatment,” comments Dr. Thomas Weißgärber, director of the Branch Lab at Fraunhofer IFAM. “The new system is not only used for R&D projects but is also available as a service for carrying out predefined HIP cycles.”
The press model QIH 15L incorporates heat treatment and cooling in a single process known as High Pressure Heat Treatment™ (HPHT™). HPHT combines stress-relief annealing, HIP, high-temperature solution-annealing (SA), high pressure gas quenching (HPGQ), and subsequent ageing or precipitation hardening (PH) in one integrated furnace cycle.
Jan Söderström CEO Quintus Technologies Heat Treat Today
Consolidating these multiple steps in the HIP process brings several benefits for Fraunhofer IFAM. Several functions can be performed in a single location with fewer pieces of equipment on the production line. The Quintus press produces fast throughput and high work piece quality. It also enhances efficiency and reduces per-unit processing costs while generating savings in space, energy, and infrastructure.
“We have noted exceptional interest in new approaches that improve quality, lower cost, and reduce environmental impacts,” says Jan Söderström, CEO of Quintus Technologies. “HPHT is rapidly emerging as the go-to post-processing path to lean AM operations, and we are delighted to be working with Fraunhofer IFAM as its talented researchers expand the potential for high pressure heat treatment.”
The new system will be installed in the Innovation Center Additive Manufacturing ICAM® of Fraunhofer IFAM Dresden, where various technologies for additive manufacturing are a major focus.
(source: background image from ifam.fraunhofer.de and Quintus HIP image from Quintus Technologies)
In June, Heat TreatToday will officially launch its brand newHeat TreatBuyers Guide, but you can get a sneak preview today! Finding heat treat equipment and related services as well as commercial heat treating services will never be easier than by searching this trusted network of top-rated Heat Treat Equipment and Service Suppliers. Check out the website and tell us what you think! If you are a supplier, go claim or create your listing and get listed today! HeatTreatBuyersGuide.com
1. Search Heat Treat Equipment And Service Suppliers
Use our website to search heat treat equipment and service suppliers by specialty or location. It’s easy to search and find top-rated heat treat equipment and service suppliers near you.
2. Compare Heat Treat Equipment And Service Suppliers
After searching for heat treat equipment and service suppliers, learn more by reviewing full profiles of each heat treat equipment and service suppliers on our website and then contacting them directly if so desired.
3. Connect with Heat Treat Equipment And Service Suppliers
Once you find heat treat equipment and service suppliers that you like, contact them to get more information. Our suppliers are always happy to hear from you!
Two heat treating furnaces expand the capabilities of a manufacturer of brick dies, textured stucco rollers, and extrusion equipment made for the construction industry. These furnaces are being used to meet the manufacturer’s immediate need for increased heat-treating capacity and provide a supporting role in the company’s die manufacturing process.
The L&L Special Furnaces Co., Inc. model GS2026 has internal working dimensions of 18” wide by 12” high by 24” deep. It has an operating voltage of 208, 220, 240 volts single phase, 60 or 50 hertz. The furnace also includes a spring assist vertical lift door that allows for effortless loading and unloading at high temperatures. The control is a Bartlett program control that can store multiple programs and includes overtemperature protection.
source: Carl Campbell at unsplash.com
L&L Special Furnaces’ Model GS2026 Source: L&L Special Furnaces Co., Inc.
“Many metallurgists or heat treat engineers only think in terms of water or oil for quenching steel. Water is the most common quench medium, followed by oil. However, polymer quenchants have made significant inroads into these traditional choices…”
In today’s Technical Tuesday feature, Greg Steiger and Keisuke Kuroda of Idemitsu Lubricants America share an original content article on the composition and uses of polymer quenchants, specifically polyalkylene glycol.
Introduction
Greg Steiger Senior Key Account Manager Idemitsu Lubricants America
Many metallurgists or heat treat engineers only think in terms of water or oil for quenching steel. Water is the most common quench medium, followed by oil. However, polymer quenchants have made significant inroads into these traditional choices.
The advantages of water are abundance, low cost, lack of flammability, and the ability to achieve high hardness. Still, there are many disadvantages associated with water as well. These are all associated with the very aggressive quench obtained from water. Issues such as quench cracking, distortion and soft spots from uneven cooling are just a few of the drawbacks of water.
Keisuke Kuroda Technical Advisor Idemitsu Lubricants America
Oil quenchants do not offer the hardenability of a water quench because the quench speeds of oil are more limited than those of water. Quench oils also pose a fire hazard which can create workplace environmental issues such as smoke generated during the quench process. Additionally, the disposal costs of used quench oils continue to increase as time goes on. Limited options for applications requiring a quench speed between oil and water were available until water soluble polymers were introduced to the market in the mid-20th century.
With water soluble polymers heat treaters could vary the concentration in water to achieve oil like quench speeds. Furthermore, using warm or hot water provided the ability to increase the quench speed to approach that of water yet minimize the quench cracks and distortion due to the high quench severity of oils.
Historically, polymer quenchants were used in hardening steel and in nonferrous (aluminum) applications and continues to be a popular choice for these operations today. However, its use in induction hardening has grown exponentially, and as such, polymer quenchants have become much more important to modern manufacturing and heat treating.
1. Types of polymer quenchants
Today, there are many different types of polymers in use. Examples of these types of polymers include polyacrylates, polyvinyl alcohol, polyvinylpyrrolidone, polyethyloxazoline, polyethylene glycol and the most popular polyalkylene glycol (or PAG). The types of polymers and their characteristics are seen below in Table #1.
Table #1 Polymer types and their primary characteristics
While each of the chemistries listed in Table #1 are in use today, the scope of this paper will be limited to the most used chemistry, polyalkylene glycol.
1.1 Polyalkylene glycols and inverse solubility
A polymer quenchant is composed of more than just the water-soluble polymer. In typical polyalkylene glycol polymer quenchants, water makes up the largest ingredient. However, there are additives such as ferrous corrosion inhibitors, nonferrous stain and oxidation inhibitors, alkalinity buffers, defoaming agent, biocides along with the polyalkylene glycol in typical polyalkylene glycol quenchants. Chemically, a polyalkylene glycol consists of nothing more than carbon, hydrogen, and oxygen. The chemical structure for a polyalkylene glycol is seen in Figure #1. The m and n represent the number of molecules contained in the polymer. The higher the values of m and n, the thicker and more viscous the polymer becomes.
Figure #1 Polyalkylene Glycol Chemical Structure
In examining the chemical structure of a polyalkylene glycol it can be seen there or OH and H molecules on each end of the polymer. As we learned in high school science classes, like dissolves like. Water is composed of these same compounds and this is why the polymer is soluble in water. However, a polyalkylene glycol exhibits inverse solubility at higher temperatures due to a phenomenon called a cloud point. At 70°C (approximately 160°F) the polyalkylene polymer becomes insoluble in water. By being no longer soluble in water the polymer then coats the part being quenched and controls the cooling rate to provide a slower quench speed than pure water thereby reducing or eliminating the risk of quench cracking and distortion. A demonstration of the cloud point phenomena is shown in Figure #2.
Figure #2 Polyalkylene Glycol Cloud point
In examining cooling curves generated using the test method JIS K2242-B Heat Treating Fluids cooling curves for plain water and c solution can be examined. Using the cooling curves shown in Figure 3 the cooling curve for the water is on the left and the cooling curve for the polyalkylene glycol (PAG) is on the right. As cooling curves are shifted to the right the quench severity and quench speed both decrease. The inset shows a simulation of how a polyalkylene glycol polymer exhibits inverse solubility at elevated temperatures and coats the part being quenched to control the cooling speed.
Figure #3
One of the unique properties a polyalkylene glycol possess that a quench oil does not is the ability to vary the cooling rate of the solution by concentration. Unlike an oil, a polyalkylene glycol solution is diluted with water and the amount of polymer to control the cooling rate varies with concentration. For instance, a 10% concentration of a polyalkylene glycol solution will have a faster and more severe quench rate compared to a 30% solution of the same polyalkylene glycol. Figure #4 shows a comparison of cooling speeds of various polyalkylene glycol solutions versus pure water.
Figure #4 The cooling rate of polyalkylene glycol solutions versus pure water.
2. The deterioration of a polyalkylene glycol polymer
While modern polyalkylene glycol quenchants are formulated to provide excellent corrosion and biological protection. The simple act of using them to quench parts creates conditions where the polymer deteriorates. As stated above, it the function polymer becomes inversely soluble at elevated temperatures and coat the parts to control cooling. This will also cause the depletion of the polymer and other additives through drag out. Similarly, as hot parts come into contact with the polymer, pyrolysis occurs. As a result of pumping, the polymer solution the polymer is mechanically sheared.
The solution undergoes mechanical shearing when a solution is continually circulated through a system by using a mechanical pump. The less viscous the fluid the less susceptible the fluid is to mechanical shearing. Table 2 shows the viscosity of three widely available commercial polyalkylene glycol polymers.
Viscosity and density of typical polyalkylene glycol polymers
Table 2 shows that Quenchant A is over 18 times greater than the viscosity of the viscosity of the standard quenchant, and Quenchant B is over 6 times the viscosity of the standard quenchant. Noting change in viscosity makes it is easy to see how mechanical shearing can affect polymers in different ways. As the solution is sheared and loses viscosity, the cooling properties of the polymer also change. Simple physics shows that the heat transfer properties of a thin, less viscous fluid, such as water, dissipates heat better than a thick, viscous fluid such as maple syrup.
In addition to mechanical shearing reducing the viscosity of the polymer, pyrolysis also creates a similar breakdown in the polymer. Pyrolysis is a chemical process where the polymer becomes thinner and less viscous due to the long chain length polymer being thermally broken into less viscous shorter chain polymers at high temperatures. Figure #5 shows the effects of mechanical shearing and pyrolysis on a short chain, less viscous standard quenchant polymer.
Figure #5 A depiction of viscous polymer subjected to pyrolysis after 100 quenches.
The severity of how pyrolysis and shearing affect the quench as the cooling speed of the polymer quenchant has clearly increased. This increase in the cooling speed is shown as the curve has shifted to the left. The increase in cooling speed and quench severity are directly related to the thinning polymer viscosity, which is directly attributable to mechanical shear and pyrolysis. To further emphasize this point, let’s look at how users of polyalkylene glycol quenchants determine concentration.
A handheld refractometer is typically used to measure what is often referred to as the refractometer reading. Some users and suppliers of polymer quenches instead use the proper term Brix%. The Brix% measures the amount of polymer dissolved in water and the contaminants within the polymer tank. Contaminants can be thought of as anything dissolved or emulsified in water. Several examples of dissolvable materials include hard water minerals such as calcium, or magnesium as well as any water soluble coolants or rust preventatives used in machining prior to heat treating. Some emulsified oils can be common machine oils, like hydraulic oil, that have leaked into the polymer tank.
Because all these dissolved or emulsified materials can impact the concentration levels of the polymer, most suppliers will ask for a periodic check of the solution be done using a benchtop refractometer. This reading measures how much light passing through a prism is refracted or bent by the polymer. Because the dissolved contaminants do not refract the light this is a more accurate method of determining the polymer concentration. However, it is a lab based piece of equipment and is not portable and must be liquid cooled to 20°C (68°F). Therefore, the portable Brix meter is typically preferred in heat treating operations.
The most preventable form of deterioration of a polymer quench is from contamination by tramp oils, bacteria and in severe cases mold. Tramp oils are oils in the fluid that are not formulated into the quenchant. Because a polyalkylene glycol polymer does not contain oil any oil in the solution it is considered to be tramp oil. Regarding bacteria, there are two basic types: aerobic and anaerobic. Aerobic bacteria can live in the presence of oxygen and anaerobic bacteria thrive in oxygen depleted environments. The goal for users of polymer quench is not to eliminate bacteria entirely. This is because we do not live in a sterile environment. The water we drink, food we eat, and the air we breathe all contain bacteria. Instead, the goal of polymer quenchant suppliers and users is to prevent anaerobic bacteria and its “Monday morning odors.” Figure #6 shows a mockup of a typical sump containing a polymer quenchant and various contaminants.
Figure #6 Mockup of a Polymer Quenchant Sump
Above, the sludge layer consists of a mixture of tramp oil and polymer that has not gone back into solution. The most likely source of the tramp oil is from hydraulic oil or other machine oil leaks. This layer creates an impermeable layer against oxygen, leading to anaerobic bacterial growth. The tramp oil layer may be removed using an effective tramp oil skimmer. The anaerobic bacteria produce the rotten egg smell of hydrogen sulfide. The solution to eliminating the anaerobic bacteria is very simple. The removal of the tramp oil layer will allow oxygen to permeate through the solution through normal usage. However, removing the tramp oil layer is not enough. The second portion of the sludge layer is the polyalkylene glycol that emulsified with the tramp oil. Removing the tramp oil will cause this heavier than water polymer to sink to the bottom of the tank. This heavy polymer will prevent oxygen from reaching the material below the polymer once again creating a zone of anaerobic bacterial growth. The solution here is to use a shorter chain, less viscous polymer that will require less agitation to resolubilize in water at lower temperatures.
The effects on cooling speed are seen when a fresh solution of polymer quench is compared to the cooling speed of the same fresh polymer solution when a small amount of emulsified tramp oil and polymer is added to the same fresh polymer solution. This results in a shift of the cooling curve to the right, which slows the overall cooling speed and can result in lower case depth and softer than expected hardness results. The cooling curve is seen Figure #7.
Figure #7 These are the cooling curves of fresh polymer and fresh polymer mixed with tramp oil emulsion.
Another very common source of polymer deterioration is by contamination of heat scale which can easily be removed via filtration. Most individual induction hardening machines use an internal filter media bed. The micron size of these media filters can vary from the small ~2-3 micron to the large ~50 micron. For larger central systems and through hardening furnaces a canister filtration system is typically used. The micron size of the filtration media is typically an economic decision as the smaller pore size increases the cost of the filter. Also, the smaller the pore size the quicker the media will blind. A happy medium between cleanliness of the polymer solution and economics is typically found between 10- and 25-micron filter media.
Figure #8 CQI-9 Flow Chart
While CQI-9 requires only a daily concentration check and a cooling curve analysis for systems over four-months old, many suppliers of polymer quenchants recommend additional tests such as pH, viscosity, refractive index and other testing that is not practical for users of polymer quenchants to perform. Table #3 lists the test and frequency of the suggested test for a polymer quench solution.
Table #3 Suggested Tests and Frequencies for a Polymer Quench Solution
3. CQI-9 testing
This section will describe the testing required under CQI-9 as well as the frequencies and the reasons behind the suggested periodic tests.
As mentioned earlier in this paper a daily concentration check is needed for a polymer solution. The most convenient and easiest method is to use a handheld refractometer. The operation of the handheld refractometer is seen in Figure #9.
Figure #9 Operation of a Handheld Refractometer
As previously noted, the mechanical shearing and effects of pyrolysis on a polymer are a reduction in the viscosity of the polymer in solution. Additionally, these same effects change the cooling properties of the polymer, as seen in Figure #6; the shifting of the cooling curve only describes the overall cooling curve of the polymer solution.
However, CQI-9 requires a cooling curve analysis. As a part of a compete cooling curve analysis, the cooling rate of the polymer should also be determined. Because there is a direct relationship between viscosity and cooling rate, it follows that as the effects of mechanical shearing and pyrolysis reduce the viscosity of the polymer in solution the cooling speed of the polymer will also increase as shown in Figure #101
Figure #10 Effects of Pyrolysis on Polymer Viscosity
Knowing the pH of a solution is imperative for a few reasons. The higher the pH the higher the alkalinity and the better the protection against bacterial attack. Alkalinity is a measure of protection against corrosion. However, having too high of a pH can result in skin irritation. In Figure 11 below, the reader can see what pH manufacturers of polymer quenchants recommend.
Figure #11 Recommended pH Range
To run the bacterial testing on a polymer solution requires a special media called an agar to grow the bacteria colonies. These aerobic colonies are measured as a power of 10. Typically, these colonies are measured in the range of >100 to 10(7). In rare cases yeast and mold may also grow in a polymer quenchant. Once again, the colonies are measured in powers of 10. The typical range is >10 to 10(5). Figure #12 shows a pictogram of each level of bacterial and yeast and mold contamination. It is best to let the polymer supplier run this testing since it is dependent on sample handling and testing at a specified constant.
Figure #12 Agar Chart for Bacterial, Yeast, and Mold Testing
The last piece of maintenance to be addressed in this paper is the proper mixing of a polymer. Water should be added to the tank first. Once the water level reaches approximately ¾ of the full level, the water additions can end. The next step is to agitate the water while slowly adding in the polymer. It is important that the polymer not be added before the water as the polymer is much denser than the water. This will cause the water to remain on top of the polymer and will result in incomplete mixing. Once the polymer has been completely mixed into the water, a handheld refractometer can be used to determine the concentration, and then any needed water or polymer additions can be made.
Conclusion
This paper showed that the ability of a polyalkylene glycol to effectively quench and harden carbon steels is determined by a variety of factors:
Concentration
Polymer chain length
Viscosity of polymer
Mechanical shearing
Pyrolysis
Age of the polymer quenchant
The cooling speed of a polymer quenchant by concentration can be seen in Figure #4. The cooling speed varies by concentration because the amount of water present in the solution varies. The less dense water dissipates the heat faster than ticker denser polymer. Figure #13 shows the cooling curves of Quenchant A and the standard quenchant at concentrations of 10%, 20% and 30%. In Figure #13 the reader will notice less variation in the cooling curves for the standard quenchant compared to Quenchant A. This is due to the major differences in viscosity of the two products shown in Table #2.
Mechanical shearing will affect the cooling rate of a polymer by causing the viscosity of a thick polymer to thin out and become less viscous. Figure #14 shows how selecting a polymer with a polymer with a lower viscosity that is less resistant to mechanical shear and pyrolysis will exhibit less change in the cooling rate after continuous quenching.
Figure #13 Comparison of Colling Rates by Viscosity a After Continuous Quenching
Figure #14 Volume Savings Using Customer Data
In summary, a less viscous polymer is preferable due to the consistency of the quench, cooling speeds, and longer sump life than a more viscous polymer. Additionally, it will require less agitation to remix with water once the temperature of the solution is below the inverse solubility temperature of the polymer. Because the polymer remixes easily with water it does not plate out on the machines and fixtures and the carryout on the parts is greatly reduced. Since there is less plate out on the fixtures and machines along with the polymer remixing with water, there is a reduced need to dump the machine sump due to house cleaning issues. When the polymer goes back into solution, it does not settle to the bottom of the tank where it can create an environment for anaerobic bacteria growth as well. Figure #14 shows the annual volume reduction experienced when an actual customer switched to a lower viscosity polymer which resulted in a longer sump life and less drag out.
About the Authors: Greg Steiger is the sr. key account manager of Idemitsu Lubricants America. Previously, Steiger served in a variety of research and development, technical service, and sales marketing roles for Chemtool, Inc., Witco Chemical Corporation, D.A. Stuart, and Safety-Kleen. He obtained a BSc in chemistry from the University of Illinois at Chicago and is currently pursuing a master’s degree in materials engineering at Auburn University. He is also a member of ASM.
Keisuke Kuroda is the technical advisor for a line of industrial products which includes quench products for Idemitsu Lubricants America. Before joining Idemitsu in 2013, Keisuke held various sales and marketing positions. Keisuke holds a master’s degree in physics from Kobe University.
Oreskovich has expanded his family of companies to further enhance and leverage each group’s ability to include customized engineered solutions. “As a mechanical engineer born and raised in Niagara,” says Oreskovich, “I have always had great admiration for CAN-ENG’s technical expertise, and the level of quality and creativity provided by their products which are installed around the world.”
With the addition of CAN-ENG, the combined resources will increase to over 250 associates, operating at four separate locations, consisting of a total of over 300,000 ft2 of available floorspace, outfitted with the most modern manufacturing capabilities. With this potential, CAN-ENG will be positioned for strategic growth and development activity in thermal processing and heat treatment markets previously not explored.
Heat Treat Today is pursuing an interview with Mr. Oreskovich. Stay tuned for more information if/when it becomes available.
Plant image from JTL Integrated Machine website. All other images provided by CAN-ENG Furnaces International Ltd.
Gasbarre Furnace to Thermal Vacuum Services, Inc. Gasbarre
Thermal-Vac Technology will expand their capabilities with a precision nitriding and ferritic nitrocarburizing furnace at their facility in Orange, California. The furnace is capable of processing workloads that are 48” wide by 72” long by 40” high and weigh up to 7,000 pounds.
Gasbarre Thermal Processing Systems‘ electrically heated furnace utilizes Super Systems, Inc. controls for automatic KN and KC control to AMS 2759/10 & 2759/12 specifications. The furnace is designed to meet AMS 2750F as a Class 2 furnace, which allows it to be used to perform nitrogen tempering and stress relieving processes. For cycle time improvements and consistent process control, the furnace is equipped with a vacuum pump for purging processes, pre- and post-oxidation capabilities, and accelerated air and atmosphere cooling systems. The furnace also comes with an ammonia dissociator to achieve zero white layer processes.
Gasbarre engineered, manufactured, and serviced this system out of their United States locations. Thermal-Vac is set to receive the equipment in March of 2021.
In a special Heat Treat Radio series, 40 Under 40 winners from the class of 2020 respond with their stories and insights of their life and work in the heat treat industry. This episode features the stories of Luke Wright, Nathan Durham, and Alberto Cantú.
This episode in the series also features an update from a past alum; in this episode, Kyle Hummel of Contour Hardening shares his journey over the last several years and how he has grown as a person in heat treat.
Below, you can listen to the podcast by clicking on the audio play button and read a few excerpts from this episode.
Luke Wright Senior Engineer JTEKT North America Corporation / Koyo Bearings
“So, we had a void in the heat treating department. We had three new hires — 2 others including myself at the time. They kind of shuffled us around: one went to assembly and I got put in heat treat with one of the others. They figured heat treat was difficult enough for two green engineers. I kind of picked it up as I went along.”
“I guess that’s kinda what I really like — sort of this black box science that everyone wants to talk about, and there’s so many things we have to just say, Well, I’m not really sure. We turn this knob and it tends to work better that way. But then, there’s also really detailed science and theory that kind of guides you and that gut feel, twist-that-knob practical application.”
“Something that I’ve been trying to do more lately in my job is to explain more about what I’m doing, what’s going on with the others around me — maintenance workers, furnace operators, or supervisors — instead of just keeping to myself or pushing them out of the way to just do the thing myself if they don’t understand: Doing a little more to work alongside people.”
Nathan Durham
Nathan Durham Aftermarket Sales Manager Ipsen
“As we near the end of 2020 and reflect on the many, many challenges that arose, I’m truly motivated by the diversity and resilience of our industry[…] We’ll persevere through this pandemic, and push forward into 2021.”
“During my tenure at Ipsen, I’ve realized how important it is to always remain flexible within a career and adapt to what your company and what your customer are asking you.”
“Thank you again, as I’m truly humbled to be a part, and associated with, such great company, and the future of our industry.”
Alberto Cantú
Alberto Cantú VP Combustion, Control and Services Nutec Bickley
“I started as an R&D manager. I had completed a PhD on the computation of fluid dynamics and used these tools to design new furnaces. But lately, I’ve been more involved in sales and business development.”
“On the one hand, the computation of power has been increasing — I’m going to say since the birth of computers, but lately more and more — but then the internet and the whole internet of things and Industry 4.0 coming together… You can do a lot of things with both the calculations and the ability to have the information in real time. I think many of these operating procedures that were mainly based on ‘rules of thumb’ and heuristics will change[…] to be based on machine learning…”
“I would suggest [for young heat treaters] to get involved in tradeshows, subscribe to newsletters, make sure you read all the news in the magazines available and in companies so that you get up-to-date in all things happening in the industry because, as I said, it’s vey exciting and I see a bright future.”
“Professionally, I’ve been honored to accept a promotion and am now responsible for overseeing our operations. And on top of that, I’m currently studying for my very last finals to get my MBA in which I’ll graduate May.”
“The heat treatment industry is such a broad field of processes and technologies that anyone can get really excited about. I also think that heat treating can offer the perfect balance of hands-on work experience as well as quality and process improvement that can keep you engaged for years as you continue to grow your career.”
“I’m personally excited to see how the heat treat industry adapts to the next five years as electric vehicles sales continue to rise in the US. I believe this will be an opportunity for heat treaters to start thinking about how to broaden their service offerings and expanding into other industries as well.”
Heat treaters, beware: there is a new trend that "ooh! It's shocking . . . It's electric!"
