General Atomics has heat treated the seventh and final module for a large superconducting magnet for ITER, a multi-national science experiment, with a vacuum furnace from a heat treat furnace supplier in Pennsylvania.
In order to convert the 6 km long stainless-steel-jacketed coil of Niobium-Tin conductors into superconductors for the ITER (International Thermonuclear Experimental Reactor) experiment, each of these 4-meter by 2-meter 110-ton solenoid sections had to be heat treated for five weeks, exceeding 650°C (1202°F) at its peak. The heat treatment served to alloy the Niobium and Tin strands together into Nb3Sn, which becomes a superconductor when chilled with liquid helium to 4 Kelvin.
No such heat-treating furnaces existed, so General Atomics turned to SECO/VACUUM, a SECO/WARWICK Group company in Meadville, PA, to build a heat-treating furnace large enough to fit these solenoids and packed with all the technology needed to meet the strict quality control standards of this experiment.
Peter Zawistowski Managing Director SECO/VACUUM TECHNOLOGIES, USA Source: secowarwick.com
"SECO/WARWICK Group did a great job designing in backup systems and robust design," commented Nikolai Norausky, program manager at General Atomics. "Any time we had questions or needed maintenance they were there to help."
The vacuum furnace that the supplier provided had to perform multiple tasks, including to bake off residual impurities from coil fabrication and to anneal internal stresses introduced at different stages of part fabrication. “General Atomics put so much time and money into these coils we really didn’t have any room for error," added Peter Zawistowski, managing director of SECO/VACUUM, "so nearly every component had to be doubly redundant."
Explore the experiment in Heat Treat Today original content article.
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Imagine this: A huge lab facility nestled in the south of France . . . teams of scientists and technicians striving to bring carbon-free energy solutions to the world . . . “replicating the high-energy fusion reaction that powers the sun and stars.” To complete the project, what heat treat solution is needed? Read more in thisTechnical Tuesday to find out.
This article by Rafal Walczak,product manager at SECO/VACUUM, will be published in Heat Treat Today’s December 2022 Medical & Energy print edition.
Introduction
For this case study, we will discuss how SECO/VACUUM built a highly specialized custom heat treating furnace used in the construction of the central component of a large, multinational science experiment.
The Experiment
ITER (standing for International Thermonuclear Experimental Reactor and meaning “the way” in Latin) is the largest high-energy science experiment ever conducted. At a giant lab facility in southern France 35 countries, hundreds of vendors, and thousands of scientists and technicians are collaborating on a device to demonstrate the feasibility of clean, safe, carbon-free energy production by replicating the high-energy fusion reaction that powers the sun and stars.
Figure 1. ITER Laboratory at the Cadarache research center in southern France Source: ITER Organization
There are no solid materials that can touch, much less contain, such a high-energy reaction without immediately vaporizing. Instead, this super-hot cloud of plasma must be contained by a special configuration of magnets called a tokamak, which can trap charged particles in a toroidal or donut-shape cloud. This tokamak has 10 times more plasma containment volume than any other tokamak ever built.
The term “tokamak” comes to us from a Russian acronym that stands for “toroidal chamber with magnetic coils” (тороидальная камера с магнитными катушками).
The Magnet
Figure 2. ITER central solenoid and one isolated solenoid module Source: General Atomics ITER Manufacturing
General Atomics’ Magnet Technologies Center near San Diego, CA was contracted to build the ITER tokamak’s large central magnet, the most powerful superconducting magnet ever built, strong enough to lift an aircraft carrier. Other magnets in the tokamak serve to contain the plasma. The central solenoid is an oscillating magnet responsible for inducing current in the plasma cloud similar to how an induction stove heats a pan, except it is heating the plasma to 15 times the temperature of the surface of the sun. Far too large to be constructed and transported in one piece, the 12-meter-tall, 4-meter-wide coil of wires must be built in six 2-meter-tall modules to be joined once they are all on site at the lab. A seventh module will be built as a spare.
Kenneth Khumthong, technical lead for final testing and fabrication certification for ITER Central Solenoid at GA, described the tests on each module of the magnet, saying, “We run a battery of tests on each and every module subjecting them to voltages as high as 30,000 volts and powering them with as much current as 40,000 amps. This is done to ensure that every module meets all of ITER’s specifications prior to shipping them out to France.”
Embrittlement vs. Field Strength Tradeoff
Other superconducting electromagnets in the ITER tokamak will be made using coils of relatively durable niobium-titanium alloy. Past experiments have demonstrated that magnetic fields greater than 12 Tesla disrupt the superconducting properties of Nb3Ti. The ITER central solenoid, however, must sustain magnetic field strengths above 13 Tesla. For this reason, the central solenoid coils must instead use niobium-tin as its superconducting wire, which more reliably maintains superconducting properties in such high magnetic fields but is also more brittle and too fragile to bend after reaction to Nb3Sn. In order to accommodate for the brittle wire, General Atomics had to first coil the wire and jacket into their final shape before heat treating the metals into their superconducting, albeit brittle, alloy Nb3Sn.
The Wire
Figure 3. A dissection of the central solenoid conductor strands, central spiral, and structural jacket Source: ITER Organization
Niobium-tin wire strands react to become Nb3
Copper strands serve as traditional conductors to safely dissipate stored energy when the superconductivity experiences a disruption. The copper strands do not react with the niobium-tin.
A central spiral maintains a hollow channel to circulate liquid helium to chill the Nb3Sn wires to 4°K, below their superconducting temperature of 12°
Creating such strong magnetic fields inside a coil of wire will also tear apart the coil of wire itself if that wire is not supported inside a high strength jacket. The ITER central solenoid wire bundle is about 38.5 mm diameter, housed inside a 50 x 50 mm stainless steel jacket.
Total maximum current in the superconductor wire is 48,000 amps.
Worldwide niobium production increased six-fold for several years just to meet the niobium demands of the ITER project.
The Heat Treating Furnace
Figure 4. Technicians ensure proper placement before lowering heat treat furnace Source: General Atomics ITER Manufacturing
In order to convert the niobium-tin metal conductors into superconductors, each of these 4 meter by 2 meter 110 ton solenoid sections must be heat treated for five weeks, exceeding 1200°F (650°C) at its peak. The heat treatment serves to alloy the niobium and tin together into Nb3Sn, which becomes a superconductor when chilled with liquid helium to 4°Kelvin. No such heat treating furnaces existed, so General Atomics turned to SECO/VACUUM to build a custom heat treating furnace large enough to fit these solenoids and packed with all the technology needed to meet the strict quality control standards of this monumental experiment.
Five inch wide metal band heaters ring around the walls of the furnace with nearly 900kW of heating power. Covering 50% of the walls, they provide a very uniform heat. This is brought about by the following seven steps.
The Heat Treating Sequence
In addition to alloying the niobium-tin wires, the furnace also serves to remove the stresses in the stainless steel jacket housing the superconducting wire and to bake off any residual contaminants prior to reaching reaction temperature.
1. Complete a quality control test: Vacuum seal the untreated solenoid coil in the room temperature furnace and charge the inside of the conductor jacket with 30 bar high pressure helium to test for leaks after forming and welding.
Monitor furnace atmosphere with ultra-high sensitivity mass-spectrometer helium detectors.
2. Purge with argon gas while slowly ramping up heat.
This drives off hydrocarbons and oxygen before system reaches reaction temperatures.
Monitor furnace atmosphere with gas chromatograph to find impurities from residual oils and lubricants leftover from manufacturing process.
Monitor and control argon circulation and exchange with mass flow sensors and circulation blowers that penetrate the furnace lid with ferrofluidic feedthrough seals around the blower motor shafts.
3. Maintain at 1058°F (570°C) for about 10 days. Confirm stabilized temperature and pure atmosphere.
4. Proceed to 1202°F (650°C) for four days. This is the actual reaction phase that achieves the primary objective of converting the niobium-tin into the superconducting alloy Nb3
5. Very slowly and uniformly ramp back down to room temperature to avoid additional stresses in the coil.
6. Complete another quality control test: Evacuate the argon and once again vacuum seal the solenoid coil in the room temperature furnace and recharge with 30 bar high pressure helium to test for leaks after heat treating. Monitor atmosphere for the presence of helium, which would indicate a leak in the coil.
7. Only then is it ready for the post-heat treating stages of wrapping with insulation and encasing in epoxy resin for rigidity.
Options, Upgrades, Special Features
Figure 5. Cutaway illustration showing the furnace construction Source: SECO/VACUUM
There was no room for error. SECO/VACUUM collaborated with the engineers at General Atomic to create a heat treat furnace that can assure temperature variation within the coil never varies by more than 18°F (10°C) anywhere in the furnace at any time in the five-week cycle and achieves near-perfect repeatability for all seven modules.
They accomplished this with quadruple-redundant control thermocouples and feeding temperature data from 150 points in the coil into the control computers. To shield against impurities, the furnace is first evacuated to a vacuum pressure of 0.001 Torr, and then purged with pure argon to drive out any residual oxygen or hydrocarbons that could contaminate the purity of the superconductor. Monitoring the argon atmosphere for impurities are redundant mass spectrometers. The argon is circulated by seven convection fans to heat the solenoid assembly evenly. Each of these fans must be driven through ferrofluidic feedthrough seals which allow the rotating shafts to operate through the furnace walls without compromising the vacuum seal of the furnace.
Consult, Collaborate, and Partner with SECO/VISORY
General Atomics first began discussing this project with Rafał Walczak, the product manager at SECO/VACUUM, in early 2010. Both teams spent over two years on conceptual discussions, preliminary designs, and process simulations before SECO was even awarded the contract. Once SECO was on board, it took another two years of design, fabrication, and installation before the furnace could be put into operation. SECO/VACUUM built it to handle a lifetime of use without error so they could be sure that it would work flawlessly for the seven cycles that it actually had to run.
The SECO/VISORY Heat Treat Advisory Council is a team of SECO/VACUUM heat treat experts and consultants with diverse thermal experience and process knowledge who are available to help companies solve their specific heat treat equipment challenges.
About the Author: Rafal Walczak is the product manager at SECO/VACUUM. Rafal joined SECO/WARWICK Group as a service engineer in Vacuum Furnaces Division soon after graduation from Technical University of Zielona Góra in 2002. Since 2008, he has been involved in vacuum furnace sales in Europe and the USA. The combination of his technical background and field service experience help him provide outstanding support to his SECO/VACUUM customers. For more information, contact Rafal at Rafal.Walczak@SecoVacUSA.com.
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Sometimes our editors find items that are not exactly "heat treat" but do deal with interesting developments in one of our key markets: aerospace, automotive, medical, energy, or general manufacturing. To celebrate getting to the “fringe” of the weekend, Heat TreatToday presents today’s Heat Treat Fringe Friday press release about how BCI Steel and Nextracker LLC are using new and reshored equipment to produce solar tracker equipment.
Nextracker LLC, a provider of utility-scale solar trackers, and BCI Steel, a Pittsburgh-based steel fabricator, announced the reopening of the historic Bethlehem steel manufacturing factory in nearby Leetsdale to produce solar tracker equipment for large-scale solar power plants.
The steel processing plant will incorporate both BCI Steel’s new and reshored equipment shipped to the U.S. from factories in Malaysia and Brazil. Solar tracker products produced at the factory will serve rapidly growing solar markets in Pennsylvania, Indiana, New York, and Ohio.
“BCI is proud to advance Pittsburgh’s legacy as the heart of America’s steel industry,” said Matt Carroll, CEO of BCI Steel. “This partnership with Nextracker showcases . . . unlocks additional domestic solar capacity with our low-cost manufacturing.”
This is the third solar tracker fabrication line Nextracker has commissioned with a steel manufacturing partner in 2022 as part of its commitment to rebuilding America’s steel and solar supply chains. With additional capacity in Pittsburgh, Nextracker is building out 10 GW of “Made in America” manufacturing capacity — enough to power 7.5 million homes. Earlier this year, Nextracker opened a green steel tracker production line in Texas with JM Steel, and another dedicated steel production line in Arizona with Atkore. Under this reshoring initiative, Nextracker has already procured over 100,000 tons of U.S.-made steel so far this year, enough for approximately 5 GW of solar trackers.
"This investment," commented Dan Shugar, CEO and founder of Nextracker, "will increase the resilience of the U.S. solar supply chain and bring manufacturing jobs, equipment, and capacity back to America."
The newly reopened Pittsburgh factory is situated with close proximity to river and rail transport in a location steeped in manufacturing history. The factory lies on the same grounds where steel fabricators built materials for tank landing ships (LSTs) during WWII.
The dedication ceremony was attended by top dignitaries and leaders from some of the world’s largest clean energy companies, including the CEO of EDPR Sandhya Ganapathy and the Chief Operating Officer of Lightsource bp Ann Davies.
A global leader in power technologies purchased a vacuum furnace from a North American furnace provider. The equipment will be used for specialized nuclear operations.
Peter Zawistowski Managing Director SECO/VACUUM TECHNOLOGIES, USA Source: secowarwick.com
SECO/VACUUM, a SECO/WARWICK Group company, was awarded the order for the 2-bar Vector®, a single chamber high-pressure quench vacuum furnace. It will be used for a variety of heat treating processes, including hardening of tool steels as well as high vacuum sintering and annealing. The furnace design will achieve deep vacuum levels, allowing the customer to process materials for nuclear applications. The new Vector will replace an older furnace, adding significantly more capabilities and process flexibility.
"I’m very proud of how our SECO/VISORY group managed this relationship," noted Peter Zawistowski, managing director of SECO/VACUUM. "Our product management and engineering staff collaborated with the customer’s engineering and commercialization teams for over a year to develop a proposal for the specialized capabilities they required."
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Marcin Stokłosa Project Manager Nitrex Poland LinkedIn.com
A global aluminum and energy company, Hydro Extrusion Norway, recently received a horizontal nitriding system, configured to replace an old decommissioned furnace
This latest delivery by Nitrex is the only one of its kind at Hydro facilities globally; the rest are pit-type furnaces. The nitriding equipment for Hydro Extrusion Norway in Magnor, Norway will integrate with the existing infrastructure of the plant as well as fit in the specific floor space allocation.
"Before placing the order, Hydro did its due diligence – visiting extrusion facilities with Nitrex equipment to get user opinions on the solution including the technology, die performance, extruded profile quality, and our support services," adds Marcin Stokłosa, project manager at Nitrex. "Moreover, the test trials produced very good results."
NexGen Advanced Fuel Systems (AFS), a gas turbine component overhaul facility that is a company of Allied Power Group, ordered a new vacuum furnace to help increase their capacity and reduce turnaround time for their heat treating and brazing operations. It is built specifically to heat treat land-based turbine equipment with attention to specific cooling specifications required by the company's clients.
Built by Solar Manufacturing, the furnace features a Solarvac® Polaris Control System and a graphite hot zone accommodating loads up to 48" wide x 48" high x 72" deep. The furnace has a maximum load weight capacity of 6,000 pounds.
The furnace achieves a vacuum level of 10-5 Torr, and reaches a maximum operating temperature of 2400°F. A 300 HP gas fan will allow NexGen to quench a load from 2150°F to 1000°F in just three minutes, using only 2-bar.
Solar Manufacturing Vacuum Furnace Source: Solar Manufacturing
"The interface makes running the furnace easy for operators of all skill levels," states Mark Dion, president of Nexgen-AFS, and the general manager ofAllied Power Group Combustion Technologies. "For furnace installation and operation, Solar provides knowledgeable engineering and support staff. The Solar furnace has a robust design, with some nuances such as stainless steel internals, brass fittings, made in USA valving, and in our case, a beefed up blower allowing super-fast cooling abilities. . . . Nexgen hopes business growth supports purchasing a second Solar vacuum furnace."
Excess air plays multiple roles in heat treating systems. Learn about its importance in combustion and heat transfer, and why being well-informed will help your system run at peak performance.
This original content article, written by John Clarke, technical director at Helios Electric Corporation, appeared in Heat TreatToday’s Aerospace March 2021 print magazine. See this issue and others here.
John B. Clarke Technical Director Helios Electric Corporation Source: Helios Electric Corporation
Is your system running optimally? The following discussion will provide a better, albeit abbreviated, understanding of the role of air in combustion and heat transfer.
Excess air in heating systems plays many roles: it provides adequate oxygen to prevent the formation of CO or soot, can reduce formation of NOx, increases the mass flow in convective furnaces to improve temperature uniformity, and at times, wastes energy. Excess air is neither good nor bad, but it is frequently necessary.
To begin, we must first look at a basic formula. For our discussions, we will replace natural gas, which is a mix of hydrocarbons with methane (CH4). The oxygen (O2) is supplied by air.
The above simplified formula describes perfect or stoichiometric combustion. The inputs are methane and air (where only the O2 is used to oxidize the carbon and hydrogen in the methane), and the products of combustion (POC) consist of heated carbon dioxide (CO2), water vapor (H2O) and of course nitrogen (N2). (The actual reaction is far more complex and there are other elements present in air that we are ignoring for simplicity.) As we can see from the equation, the oxygen we need to burn the methane comes with a significant quantity of nitrogen.
In practice, it is very difficult to even approach this stoichiometric or perfect reaction because it would require perfect mixing, meaning that each molecule of methane is next to an oxygen molecule at just the right time. Without some excess air, we would expect some carbon monoxide and/or soot to be formed. Excess air is generally defined as the percent of total air supplied that is more than what is required for stoichiometric or perfect combustion. For natural gas, a good rule of thumb is to have about 10 cubic feet of air for every one cubic foot of fuel gas for perfect combustion. Higher air/fuel ratios, say 11:1, are another way of describing excess air.
In most heating applications, the creation of carbon monoxide and other unburnt hydrocarbons should be avoided, except in the rare cases where they serve to protect the material being processed. Employees must be protected from CO exposure; and soot can damage not only equipment, but the material being processed.
Source: Heat Treat Today
The amount of excess air that is required to find and combine with the methane is dependent not only on the burner, but also on the application and operating temperature as well. Some burners and systems can run with very little excess air (under 5%) and not form soot or CO. Others may require 15% or more to burn cleanly. Just because a burner performs well at 10% excess air in application A, does not necessarily mean the same level is adequate in application B.
Once the quantity of air exceeds what is needed to fully oxidize or burn the methane, combustion efficiency will fall because the added air contributes no useful O2 to the combustion process, and it must be heated. It is very much like someone putting a rock in your backpack before you set out for a 16-mile trek. Taking this analogy further, higher process temperatures equate to climbing a hill or mountain with that same rock — the higher the climb, or the higher the process temperature, the more energy you waste. Sometimes this added weight or mass can be useful.
The higher the excess air, the greater the mass flow. In other words, the total weight of the products of combustion goes up, and the temperature of the CO2, H2O, N2, and O2 goes down. If we are trying to transfer the heat convectively, this added mass or weight will provide improved heat transfer and temperature uniformity. A simple way to think of temperature uniformity is that the lower the temperature drop between the products of combustion and the material being heated, the better the temperature uniformity. Many heating systems are specifically designed to take advantage of this condition – higher levels of air at lower temperatures. This is especially true when convective heat transfer is the dominant means of moving heat from the POC to the material being heated (when the process temperature is roughly 1000°F or lower).
Source: Heat Treat Today
Some heating systems are specifically designed to operate as close to perfect combustion as is possible as the material is heated then switch to higher levels of excess air to increase the temperature uniformity as the setpoint temperature is approached. In other words, it provides efficient combustion when temperature uniformity is less of an issue and a very uniform environment as the material being processed nears its final setpoint temperature.
Of course, a system can be supplied with too much air, which can waste energy, but also prevent the system from ever reaching its setpoint temperature. The energy is insufficient to heat all the air, the material being processed, and compensate for furnace or oven loses. In these instances, it is obvious that we must reduce the air supplied to the system.
In indirect heating systems – where the products of combustion do not come in contact with the material being processed, like radiant tubes, for example — air in excess of what is required for clean combustion provides limited benefit and should generally be avoided. In these systems, it is best to play a game of limbo, “How Low Can You Go,” so to speak. Test each burner to see how much excess air is required to burn clean and add a little bit for safety. Remember, if you source your combustion air from outside in an area with significant seasonal variations, the blower efficiency will change, and seasonal combustion tuning is required.
Lastly, some burners require a minimum level of excess air to operate properly. This additional air prevents critical parts of the burner from overheating – or the air may limit the formation of oxides of nitrogen (NOx). In this application, altering the burner air/fuel ratio could generate excessive pollutants or even destroy the burner.
Efficiency is important, but the process is king. There is no magical air-to-fuel ratio and no single optimum level of excess air in the products of combustion. Each application is unique and must be thoughtfully analyzed before we can confidently say we have optimized our level of excess air. But careful attention paid to the effect that excess air has on your fuel-fired systems will pay dividends in improved safety and efficiency.
About the Author:
John Clarke, technical director at Helios Electric Corporation, a combustion consultancy, will be sharing his expertise as he navigates us through all things energy as it relates to heat treating equipment.
An automotive supplier and a hydraulic pump manufacturer will acquire multi-chamber vacuum furnace system for low pressure carburizing.
For the automotive supplier of innovative driveline solutions, the system is estimated to reduce CO2 emissions significantly for vacuum carburizing versus an existing atmosphere carburizing furnace. For the hydraulic pump manufacturer, the modular flexibility of this specific furnace was the most important advantage.
ECM Flex Multi-Chamber System Source: ECM USA, Inc.
The supplier, ECM USA, Inc., notes that their Flex Multi-Chamber System is built as a standard system with the possibility to further expand its capacity and/or to upgrade to a high level of automation (robots, AGVs, vision systems, or other 4.0 elements). In addition to modularity, several processes can be handled in the Flex furnace, such as: low pressure carburizing (LPC), vacuum tempering and a combination of vacuum sintering followed by hardening.
This stems from advanced automation technology -- including robotics -- acting as driving forces behind increased use of more eco-friendly applications outside the LPC-HPGQ sector. This includes, but is not limited to, multiple tool steel processing systems, brazing applications, and rapid thermal processing (RTP) systems.
Here is what readers are saying about recent posts on Heat Treat Today. Submit your comments to editor@heattreattoday.com.
Hello Heat Treat Daily,
I was surprised to see this bright red furnace on your daily email this past Friday. This is an old image of a furnace still in production at my company Spectrum Thermal Processing in Cranston, RI.
Now, like most of us, this furnace is showing some age, but is is still in production every day with an upgraded control panel and SSI controls.
I reflected on this particular email and want to add that what I find intriguing about heat treat is the longevity of some of the equipment. This furnace processes work for aerospace, automotive, commercial cutting tools and oil and gas refinery and has for nearly 30 years! Just to the left of this furnace in the photo is an older single chamber vacuum furnace that has process parts for the Apollo space program and has recently processed parts for SpaceX. Somehow this equipment just keeps going.
Thanks for your daily insight into the heat treating industry.
Rick Houghton
VP of Operations/Quality Manager
Spectrum Thermal Processing
We welcome your inquiries to and feedback on Heat TreatToday articles. Submit your questions/comments to editor@heattreattoday.com.
The energy storage company HI-POWER, a Holtec International and Eos Energy Storage joint venture, recently formed a five-year partnering agreement with a North American heat treat supplier to provide an energy efficient non-lithium, long duration energy storage solution using battery technology.
The new battery technology, a decade in the making, is an efficient non-lithium, long duration energy storage solution. One of the critical components within the battery system requires a “vacuum cathodic” heat treatment process. This newly developed surface heat treatment process enables the product to last 5,000 cycles for a 15-year calendar life with no subcooling or pumps required.
HI-POWER and Solar Atmospheres of Western PA engineers worked to develop the vacuum cathodic heat treatment needed to fulfill HI-POWER’s specifications. Today, Solar is thermally processing thousands of components to help HI-POWER deliver clean and reliable energy faster for the world’s needs.
"I came upon this opportunity at a trade show four years ago," said Mike Johnson, sales manager for Solar, "At that time, HI-POWER was perfecting their critical thermal cycle profiles in a small hot wall furnace in New Jersey. HI-POWER knew that someday they would need to employ a large vacuum furnace - and we had that capability."
HI-POWER builds one of the safest and fully integrated DC storage batteries in the world. Their “Znyth” storage batteries are especially stable when housed in extreme temperatures and are nonflammable and 100% recyclable.
(photo source: Solar Atmospheres, courtesy of EOS Energy Storage)
General Atomics has heat treated the seventh and final module for a large superconducting magnet for ITER, a multi-national science experiment, with a vacuum furnace from a heat treat furnace supplier in Pennsylvania.
Find heat treating products and services when you search on Heat Treat Buyers Guide.com
Imagine this: A huge lab facility nestled in the south of France . . . teams of scientists and technicians striving to bring carbon-free energy solutions to the world . . . “replicating the high-energy fusion reaction that powers the sun and stars.” To complete the project, what heat treat solution is needed? Read more in this Technical Tuesday to find out.
