Andrew Bassett President Aerospace Testing and Pyrometry Source: Aerospace Testing and Pyrometry
A large aluminum producer in the U.S. Midwest received assistance from a North American pyrometry service provider to ensure their heat treat and laboratory furnaces were ready to run.
After the visit from the pyrometry service provider, Aerospace Testing & Pyrometry, Inc. (ATP), four laboratory furnaces were certified and three of four heat treat furnaces were wired and ready to go. One 40 point survey, two 35 point survey and one 25 point survey on a forty foot tall drop bottom furnace.
"We love our Pyrometry Services," commented Andrew Bassett, president of ATP. "All the certifications will be run through our newest venture, Aerospace Compliance Software."
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TEI – a large Turkish manufacturer of aircraft engines – purchased a two-chamber vacuum furnace. It will be used for the heat treatment of parts for aircraft engines.
This CaseMaster Evolution® furnace from SECO/WARWICK -- a global heat treat solution provider with locations in North America -- includes a two-chamber vacuum furnace with an oil quenching system. The furnace offers a working dimension of 900 x 900 x 1200mm and can process charges up to 1000kg. The device will be equipped with a high vacuum system and a system for measuring temperature within the charge when heating and cooling.
"The technology proposed by SECO/WARWICK attracted our attention because of the high quality of treated components and process repeatability and environmental protection issues and better process efficiency," commented Selcuk Kilicarslan, manager of Special Processes from TEI. "The two-chamber CaseMaster Evolution furnace will stand out on the Turkish market thanks to the very accurate charge temperature monitoring and superior quenchant temperature control. There are only a few devices of this kind worldwide. This brings us a great advantage and the ability to provide our hardening services to third parties."
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There is an age-old adage that exists in the heat treating world. That supposition states that “the smaller the vacuum furnace, the faster it will quench.” Is this adage true? Explore Solar Atmospheres’ journey as they designed an experiment to discover if pressure or velocity most affects cooling performance.
This Technical Tuesday was written by Robert Hill, FASM, president, and Gregory Scheuring, plant metallurgist, both from Solar Atmospheres. The article originally appeared inHeat TreatToday’sMarch 2022 Aerospace Heat Treating print edition.
Robert (Bob) Hill, FASM President Solar Atmospheres of Western PA Source: Solar Atmospheres
Introduction
Our study compared the cooling rates of two distinctly sized High Pressure Gas Quenching (HPGQ) vacuum furnaces — a large 10-bar vacuum furnace equipped with a 600 HP blower motor versus a smaller 10-bar vacuum furnace equipped with a 300 HP motor. Both furnaces, one with a 110 cubic feet hot zone, the other with a 40 cubic feet hot zone, were exclusively engineered and manufactured by Solar Manufacturing located in Sellersville, PA.
History
High Pressure Gas Quenching in the heat treatment of metals has made tremendous strides over recent years. Varying gas pressures within the chamber have been shown to be more governable than their oil and water quenching counterparts. The number one benefit of gas cooling versus liquid cooling remains the dimensional stability of the component being heat treated. In addition, using gas as a quench media dramatically mitigates the risk of crack initiation in a component. This is primarily due to the temperature differentials during cooling. Gas quenching cools strictly by convection. However, the three distinct phases of liquid quenching (vapor, vapor transport, and convection) impart undue stress into the part causing more distortion (Figure 1).
Figure 1. Three phases of liquid quenchants Source: Solar Atmospheres
There are multiple variables involved with optimizing gas cooling. These include the furnace design, blower designs, heat exchanger efficiency, gas pressure, gas velocities, cooling water temperatures, the gas species used, and the surface area of the workpieces. Whenever these variables remain constant, the relative gas cooling performance of a vacuum furnace typically increases as the volume of the furnace size decreases.
The Furnace
Solar Manufacturing has built multiple high pressure gas quenching furnaces of varying sizes over the years ranging from 2 to 20-bar pressure. We have learned that vacuum furnaces, rated at 20-bar and above, became restrictive in both cost constraints and diminishing cooling improvements. Therefore, Solar Manufacturing engineers began to study gas velocities to improve cooling rates. They determined increasing the blower fan from 300 HP to 600 HP, along with other gas flow improvements, would substantially increase metallurgical cooling rates. The technology was reviewed and determined to be sound. A 48” wide x 48” high x 96” deep HPGQ 10-bar furnace, equipped with this newest technology, was purchased by Solar Atmospheres of Western PA located in Hermitage, PA.
Image 1. HFL50 furnace (36” x 36” x 48”)
Source: Solar Atmospheres
Image 2. HFL74 furnace (48” x 48” x 96”) Source: Solar Atmospheres
The Test
Image 3. Test load with thermocouple placement Source: Solar Atmospheres
Once this new vacuum furnace was installed, a cooling test was immediately conducted. A heavy load would be quenched at 10-bar nitrogen in an existing HFL 50 sized furnace (36” x 36” x 48”). The same cycle was repeated in the newly designed vacuum furnace almost three times its size! (Images 1 and 2).
The load chosen for the experiment was 75 steel bars 3” OD x 17” OAL weighing 34 lbs each. The basket and grid system supporting the load weighed 510 lbs. The total weight of the entire load was 3060 lbs. Both test runs were identically thermocoupled at the four corners and in the center of the load. All five thermocouples were deeply inserted (6" deep) into ¼" holes at the end of the bars (Image 3). Each load also contained two 1" OD x 6" OAL metallographic test specimens of H13 hot working tool steel. These specimens were placed near the center thermocouple to ensure the “worst case” in terms of quench rate severity. All tests were heated to 1850°F for one hour and 10-bar nitrogen quenched.
Results
The comparative cooling curves between both HPGQ vacuum furnaces are shown in Chart 1. Table 1 reveals that in the critical span of 1850°F to 1250°F for H13 tool steel, the cooling rate in the larger furnace with more horsepower nearly matched the cooling rate of the furnace three times smaller in size.
Table 1. Critical cooling rates for H13 (1850°F –1250°F) Source: Solar Atmospheres
Chart 1. Average quench rate for five thermocouples Source: Solar Atmospheres
Micrographs of the H13 test specimens processed in each load were prepared (Images 4 and 5). The microstructure of each test specimen is characterized by a predominantly tempered martensitic microstructure with fine, undissolved carbides. The consistency of the microstructure across both trial loads further demonstrates that while the larger furnace utilized the higher horsepower, both resulted in a critical cooling rate sufficient to develop a fully martensitic microstructure.
These tests prove that the greatest impact on the cooling performance in a vacuum furnace is to increase the gas velocity within that chamber. This was achieved primarily by increasing the horsepower of the blower fan. By doing this, the ultimate cost to the customer is significantly less than manufacturing a higher pressure coded vessel. This newly designed vacuum furnace has proven to be a game changer.
Part II of this article will discuss real life case studies and how both Solar and Solar’s customers have mutually benefited from this newest technology.
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 vacuum furnace technology and titanium processing capabilities. Additionally, he was awarded the prestigious Titanium Achievement Award in 2009 by the International Titanium Association.
A Chinese company has ordered a horizontal vacuum furnace which will help in producing highly specialized cast parts used in the aerospace industry. Delivery of the furnace is scheduled for June 2022.
The Vector® horizontal vacuum furnace with a graphite chamber and a gas quenching system comes from SECO/WARWICK. This type of furnace from the international manufacturer comes with a graphite hot zone and can be used for most standard hardening, tempering, annealing, solution heat treating, brazing, and sintering.
The furnace will be installed in a facility that specializes in the production of high-temperature alloys used in the aviation, shipbuilding, and power industries, offering a wide range of products, including but not limited to, bars, wires, bands, pipes, and specialized castings.
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Heat treaters in the medical and aerospace sectors will eagerly tell you about titanium alloys. The hot alloy can be fantastic for intense applications once you reduce residual stresses that are developed during fabrication and increase their strength. This article is specifically about how duplex heat treatment of Ti alloys helps in relieving stress, optimizing ductility and machinability properties, and increasing strength.
An excerpt:
“Most commonly known for their excellent strength, corrosion resistance and low density, titanium alloys are a key material for important applications in the aerospace and medical industries. Duplex heat treatments of Ti alloys helps in stress relieving, optimizing ductility and machinability properties and increases strength further.”
A North American-based manufacturer of helicopter masts, turbine shafts, engine thrust links, and nuclear components with in-house heat treating will receive a customized vacuum tempering/gas nitriding furnace. The furnace will be used for nitriding and nitrocarburizing loads up to 63" diameter x 175" deep and has a load capacity of 13,200-lb.
Peter Zawistowski Managing Director SECO/VACUUM TECHNOLOGIES, USA Source: secowarwick.com
The manufacturer ordered the custom-made pit nitriding furnace from SECO/VACUUM to increase load capacity. In addition to being able to process oversized workloads, the furnace, with an almost 80% increase in size from the standard, has a working temperature range of 300°F–1,300°F, a temperature uniformity of +/-5°, and low ammonia consumption.
"We are very pleased to collaborate with this precision manufacturer to enable new state-of-the-art nitriding and nitrocarburizing capabilities in their Canadian facility," commented PeterZawistowski, managing director of SECO/VACUUM.
A worldwide supplier of high-temp piezo ceramics in the military, aerospace, and medical fields will receive a floor-standing, high-temperature, silicon carbide furnace. The furnace, powered by high-density silicon-carbide elements, will be used for processing glass products to 2,500°F.
L&L Special Furnace Co., Inc. will provide the furnace, model GLF836, which has a work zone of 18"x18"x36" with a double pivot horizontal door. The furnace, constructed from high-alumina refractory (with reduced silica), will help to delay the corrosive reaction between silica and the lead outgassing at elevated temperatures.
United States Air Force personnel stationed at Royal Air Force (RAF) Base Mildenhall in the United Kingdom recently commissioned and received full training on the use and maintenance of a heat treating furnace for aerospace parts. The furnace will help maintain KC-135, CV-22, C-130 aircraft, and F-15 fighter jets assigned to RAF Mildenhall or nearby RAF Lakenheath air stations. The installation was interrupted by an impromptu visit from the U.S. President.
Richard Conway Chief Technology Officer Delta H Technologies
The DELTA H® TECHNOLOGIES dual chamber heat treating furnace for aerospace (DCAHT®) was designed by the supplier to rapidly heat treat all common aviation grade metals and alloys necessary for aircraft maintenance and is fully compliant with USAF/NAVAIR Tech Order 1-1A-9 and SAE-AMS2750F. The training received by the USAF airmen at RAF Mildenhall included essential instructions in heat treating, as well as furnace calibration practices like temperature uniformity surveys (TUS) and system accuracy tests (SAT) and culminated with each airman receiving Certificates of Training.
The specialized furnace features an upper chamber convection system, 18" wide x 12" high x 48" deep, capable of Class 1 (+/-5°F) from 200°F to 1200°F and a lower chamber radiant heat system, 12" wide x 12" high x 36" deep, capable of Class 3 (+/-15°F) from 1000°F to 2000°F with air or argon atmosphere. A roll-away quench tank features dual baths for water and oil quenchant. The controls and data acquisition provide detailed batch records of heat treated parts, including quench delay, as well as automatic tracking of thermocouple usage and calibration intervals.
Air Force One at RAF Mildenhall
The training was interrupted by an unexpected visitor to RAF Mildenhall. The hangar next to the Metals Tech Shop, where the furnace was being commissioned and the training was being conducted, was the epicenter for the arrival of a top-secret VIP. When the Air Force Band began practicing "Hail to the Chief," it became obvious that U.S. President Joe Biden would be making an unexpected visit to the base. While the President’s visit was not related to the furnace commissioning, Richard Conway, DELTA H® founder and chief technology officer, and wife Mary Conway, witnessed this presidential visit and got a few candid photographs of Air Force One (see above).
Heat treating any aerospace projects? Then you know titanium is up there when it comes to VIP alloys in the industry. This best of the web is pulled from an aerospace magazine in which Michael Johnson of Solar Atmospheres answers five questions about creep flattening titanium:
Typical temperatures for creep flattening titanium parts
Whether of not creep flattening can only be done in a vacuum
Best fixturing for creep flattening titanium parts
Can creep flattening minimize movement
Will reheating titanium over 1,000°F affect certification
An excerpt:
"Give your heat treater your material certifications. Many mills will certify to aerospace material specification AMS 2801, AMS 4905, AMS 4911, AMS-H-81200, etc. The material often can be re-annealed while simultaneously creep flattening." - Michael Johnson, Director of Sales, Solar Atmospheres
A European machinery group will receive a vacuum furnace for hardening and tempering processes, and its design has been customized in order to meet the group’s need to harden aviation steel used as landing gear. The heat treatment solution will improve the process economy in European plants and is characterized, in part, by low energy consumption.
Maciej Korecki Vice President of Business for the Vacuum Furnace Segment SECO/WARWICK
To meet this particular application, SECO/WARWICK engineers fitted the Vector® vacuum furnace with a non-standard system for subquenching with liquid nitrogen that enables the required quick cooling down of landing gear components. The solution has also been expanded with a vacuum system designed with a diffusion pump and is equipped with a directional cooling option and convection heating system with a specially designed fan.
“This is already the fourth purchase order for a furnace from this product segment from this customer,” commented Maciej Korecki, VP of Business Segment for Vacuum Heat Treatment Furnaces at SECO/WARWICK, the sister company to North American heat treat supplier SECO/VACUUM. He also added that “The product solves the customer’s problem with the hardening of special aviation steel, significantly increases the capacity of the existing production line of this component, and also improves process parameters, since the current devices used by the customer are not fitted with a subquenching system using liquid nitrogen. It will certainly be one of the unique solutions completed this year.”
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There is an age-old adage that exists in the heat treating world. That supposition states that “the smaller the vacuum furnace, the faster it will quench.” Is this adage true? Explore Solar Atmospheres’ journey as they designed an experiment to discover if pressure or velocity most affects cooling performance.
