Mike Moyer Vice President of Sales, Solar Atmospheres, Eastern PA
Solar Atmospheres of Souderton PA commissioned a new vacuum furnace capable of utilizing high pressure gas quenching (HPGQ) at 20-Bar (about 300 PSI) to meet demanding cooling rate specifications for the heat treatment of nickel-based superalloys in the aerospace and power generation industries.
The vacuum furnace, manufactured by sister company Solar Manufacturing, has a working hot zone of 24” x 24” x 72” and utilizes unique hot zone design features to increase the quench rate. The furnace is rated for operation to 2400°F and temperature uniformity plus/minus 10°F.
Mike Moyer, vice president of Sales at Solar Atmospheres comments, “The furnace utilizes a 600-HP cooling motor and fan with a creative gas nozzle design to maximize gas flow as it moves through the hot zone and the heat exchanger and back across the workload.”
The full press release from Solar Atmospheres is available upon request.
Modern industry trends and expectations pose new challenges to heat treating equipment; in addition to the expected requirements (e.g., safety, quality, economy, reliability, and efficiency), factors like availability, flexibility, energy efficiency, environmental, and the surrounding carbon neutrality are becoming increasingly important.
Maciej Korecki, vice president of Business Development and R&D at SECO/WARWICK, presents this special Technical Wednesday case study for the last day of FNA 2022 to focus on an equipment solution that meets these modern industry demands: a semi-continuous vacuum furnace for low-pressure carburizing (LPC) and high-pressure gas quenching (HPGQ).
Maciej Korecki Vice President of Business of the Vacuum Furnace Segment SECO/WARWICK
Introduction
At least 60 years ago, vacuum furnaces first appeared in the most demanding industries (i.e., space and aerospace), then spread to other industrial branches, and are now widely implemented in both mass production and service plants. Use of vacuum technology does not look like it is slowing down anytime soon.
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The driving forces behind this growth in vacuum technology are two-fold: first, the increasing heat treatment requirements that result from the directions of industrial development and production systems, and second, environmental protection, where the advantages of vacuum technologies are undeniable.
Traditional Atmospheric Technology
Case hardening by carburizing is one of the most widely used heat treatment technologies. It consists in carburizing (introducing carbon to the surface) followed by quenching of the carburized layer. Typically, the work is carburized in a mixture of flammable gases (CO, H2), and quenched in oil in an atmosphere furnace, using methods developed in the 1960s.
These methods have a history of development, though the question remains if the technological developments can keep up with the requirements of modern industry. Safety is an issue with this method due to the use of flammable (and poisonous) gases and flammable oil, as well as open flame, which in the absence of complete separation from the air can lead to fire, or poisoning.
In addition, they affect their environment by releasing significant amounts of heat, polluting the surroundings with quenching oil and its vapors. They require the use of washers and cleaning chemicals, emit annually tens or even hundreds of tons of CO2 (greenhouse gas, the main culprit of global warming and dynamic climate change) coming from the carburizing atmosphere, and for these reasons, they need to be installed in dedicated so-called “dirty halls” separated from other production departments.
The resulting requirement to limit the temperature of the processes to 1688-1706 oF (920-930oC) is also not without importance, as it blocks the possibility of accelerating carburization and increasing production efficiency (due to the use of metal alloys in the construction, the service life of which drops dramatically at higher temperatures) and the formation of unfavorable intergranular oxidation (IGO), which is a characteristic feature of the atmospheric carburizing method.
Quenching in oil is effective, but it does not have precise controllable, repeatable, and ecological features that heat treaters may need. Due to the multiphase nature of oil quenching (steam, bubble, and convection phase) and the associated extremely different cooling rates, it is characterized by large and unpredictable deformations within a single part and the entire load. Furthermore, there is no practical method to influence and control the quench process.
Modern Vacuum Technology with LPC and HPGQ
Vacuum carburizing appeared as early as the 1970s, but it could not break through for a long time due to the inability to control and predict the results of the process, and heavy contamination of the furnaces with reaction products.
The breakthrough came in the 1990s, when acetylene began to be used as a carbon-bearing gas and computers were employed to control and simulate the process. Since the beginning of the 21st century, there has been a rapid development of the low pressure carburizing (LPC) technology and an increase in its industrial demand, which continues today with an upturn.
Vacuum carburizing occurs with the aid of hydrocarbons (usually acetylene), which catalytically decompose at the surface, providing carbon that diffuses into the material. The process is carried out under negative pressure (hundreds of times less than atmospheric pressure) and is very precise, efficient, and uniform due to the very high velocity and penetration capacity of the gas molecules, allowing the carburizing of large and densely packed loads and hard-to-reach surfaces such as holes.
In addition, the use of non-oxygen-containing hydrocarbon atoms eliminates the qualitative problem of intergranular oxidation (IGO). The process is completely safe, there is no flammable or poisonous atmosphere in the furnace and no open flame, and the furnace can work unattended and is fully available and flexible, i.e., it can be turned on and off on demand, which does not require any preparation. Similarly, changing the carburizing parameters takes place efficiently.
Due to the design of the vacuum furnace and the use of materials with high resistance to temperature, i.e., graphite — the only limitation for the temperature of the carburizing process is the steel from which the parts are made — it is possible to carburize at higher temperatures than traditional methods allow. The result is a significantly shorter carburizing time and increased furnace efficiency versus what can be achieved in an atmosphere furnace.
Neutral gas cooling was included with the vacuum furnaces. Initially, engineers used a cooling gas (nitrogen or argon) at near ambient pressure and natural convection. Subsequent solutions introduced fan-forced gas flow in a closed circuit. The cooling efficiency under such conditions was hundreds of times lower compared to that of oil, allowing only high-alloy steels and parts with very limited cross-sections to be hardened. Over the following decades, the development of HPGQ was focused on improving cooling efficiency by increasing pressure and velocity and using different types of gas and their mixtures. Current systems have cooling efficiencies on a par with oil-based systems and enable the same types of steel and parts to be hardened, with the advantage that deformation can be greatly reduced and reproducible, and the process is completely controllable (through pressure and gas velocity) allowing any cooling curve to be executed.
Vacuum technologies have an ecological edge. Because of their design and processes, vacuum furnaces do not interfere with the immediate surroundings and are environmentally friendly, so they can be installed in clean halls, directly in the production chain (in-line). They emit negligible amounts of heat and post-process gases which are not poisonous and contain no CO 2 at all. Gas quenching eliminates harmful quenching oil and the associated risk of fire and contamination of the immediate environment, as well as the need for equipment and chemicals for its removal and neutralization. Nitrogen used for cooling is obtained from the air and returned to it in a clean state, creating an ideal environmentally friendly solution.
The presented advantages of vacuum technologies influence its dynamic development and increase the demand of modern industry, and the gradual replacement of atmospheric technologies.
Vacuum furnaces are available in virtually any configuration: horizontal, vertical, single, double, or multi-chambered, tailored to the process and production requirements. In light of recent global changes, requirements, and industrial trends, special attention should be paid to disposable, flexible, and rapidly variable production and process systems, as well as independent and autonomous systems, which include a three-chamber vacuum furnace for semi- continuous heat treatment, equipped with LPC and HPGQ.
Three-Chamber Vacuum Furnace — CaseMaster Evolution Type CMe-T6810-25
This is a compact, versatile, and flexible system designed for vacuum heat treatment processes for in-house and commercial plants, dedicated to fast-changing and demanding conditions in large-scale and individual production (Fig. 1). It enables the implementation of case hardening by LPC and HPGQ processes and quenching of typical types of oil and gas hardened steels and allows for annealing and brazing. It is characterized by the following data:
working space 610x750x1000 mm (WxHxL)
load capacity 1000 kg gross
temperature 2282oF (1250oC)
vacuum range 10-2 mbar
cooling pressure 25 bar abs
LPC acetylene gas
Installation area 8x7m
Fig. 1a. Furnace CMe-T6810-25.
Fig. 1b. Fig. 1. Furnace CMe-T6810-25. On the right – view from the loading side (pre-heating chamber), on the left – view from the unloading side (quenching chamber).
The furnace is built with three thermally and pressure-separated chambers (Fig. 2.), and operates in a pass-through mode, loaded on one side and unloaded on the other, simultaneously processing three loads, hence its high efficiency. The load is put into the pre-heating chamber, where it is pre-heated to the temperature of 1382oF (750oC), depending on the requirements: in air (pre-oxidation), nitrogen or vacuum atmosphere. It is then transferred to the main heating chamber, where it reaches process temperature and where the process is carried out (e.g., LPC).
In the next step, the charge is transported to the quenching chamber, where it is quenched in nitrogen under high pressure. All operations are automatic and synchronized without the need for operator intervention or supervision.
Fig. 2. Construction and schematic furnace cross-section CMe-T6810-25. Source: SECO/WARWICK
Particularly noteworthy is the gas cooling chamber, which in nitrogen (rather than helium) achieves cooling efficiencies comparable to oil (heat transfer coefficient >> 1000 W/m2K), thanks to the use of 25 bar abs pressure and hurricane gas velocities in a highly efficient closed loop system. The cooling system is based on two side-mounted fans with a capacity of 220 kW each, forcing with nozzles an intensive cooling nitrogen flow from above onto the load, then through the heat exchanger (gas-water), where the nitrogen is cooled and further sucked in by the fan (Fig. 3). The cooling process is controllable, repeatable, and programmable by gas pressure, fan speed and time. An intense and even cooling is achieved. The result is the achievement of appropriate mechanical properties of parts with minimal hardening deformations, without the use of environmentally unfriendly oil or very expensive helium.
Fig. 3. Cross-section of the furnace CMe-T6810-25 cooling chamber. Source: SECO/WARWICK
An integral part of the furnace system is the SimVaC carburizing process simulator, which enables the design of furnace recipes without conducting proof tests.
Distinctive Features of the CMe-T6810-25 Furnace
The advantages of this type of furnace — versus more traditional or past forms — can be demonstrated in a number of usability and functional aspects, the most important of which are the following:
Safety:
Safe, no flammable and poisonous atmosphere
No open fire
Production and installation:
Intended for high volume production (two to three times higher output when compared to single- and double-chamber furnaces)
Effective and efficient LPC (even five times faster than traditional carburizing)
Total process automation & integration
Clean room installation
Operator-free
Compact footprint
Quality:
High precision and repeatability of results
Uniform carburizing of densely pack loads and difficult shapes (holes)
No decarburization or oxidation
Elimination of IGO
Ideal protection and cleanliness of part surfaces
Accurate and precise LPC process simulator (SimVaC)
Quenching:
Powerful nitrogen quenching (neither oil nor helium is needed)
Reduction of distortion
Elimination of quenching oil and contamination
Elimination of washing and cleaning chemicals
Operational:
Flexible, on-demand operation
No conditioning time
No human involvement and impact
High lifespan of hot zone components — i.e., graphite
No moving components in the process chamber
Ecology:
Safe and environmentally friendly processes and equipment
No emission of harmful gases (CO, NOx, SOx)
No emission of climate-warming gas CO2
Based on the CMe-T6810-25 furnace performance, it is rational and reasonable to build heat treatment systems for high-efficiency and developmental production in a distributed system by multiplying and integrating further autonomous and independent units. The reasons for doing so are because the furnace design affords:
No risk of production total breakdown
Unlimited operational flexibility
Less initial investment cost
Unlimited multiplication
No downtime while expansion
Independent quenching chamber
Independent transportation
Independent control system
The characteristics, capabilities and functionalities of the CMe-T6810-25 furnace fit very well with the current and developmental expectations of modern industry and ecological requirements, which is confirmed by specific implementation cases.
Case Study
The three-chamber CaseMaster Evolution CMe-T6810-25 vacuum furnace was installed and implemented for production at the commercial heat treatment plant at the Polish branch of the renowned Aalberts surface technologies Group in 2020.
Fig. 4. Gearwheel used in the case hardening process. Source: SECO/WARWICK
The CMe furnace, together with the washer and tempering furnace, forms the core of the department's production, which is why the furnace is operated continuously. Last year, the furnace performed over 2000 processes and showed very high quality (100%) and reliability (> 99%) indicators. The very high efficiency of the furnace was also confirmed, which, with relatively low production costs, contributes to a very good economic result.
The case hardening process on gearwheels used in industrial gearboxes was taken as an example. The wheel had an outer diameter of about 80 mm and a mass of 0.52 kg (Fig. 4), and the load consisted of 1344 pieces densely packed in the working space (Fig. 5) with a total net weight of 700 kg (920 kg gross) and 25 m2 surface to be carburized. The aim of the process was to obtain an effective layer thickness from 0.4 – 0.6 mm with the criterion of 550 HV, surface hardness from 58 – 62 HRC (Rockwell Hardness C), core hardness at the gear tooth base above 300 HV10 and the correct structure with retained austenite below 15%.
Fig. 5. A photograph of the arrangement of gearwheels in the load. Source: SECO/WARWICK
The LPC process was designed using the SimVaC® simulator at a temperature of 1724oF (940oC) and a time of 45 min, with 3 stages of introducing carburizing gas (acetylene), obtaining the appropriate profile of carbon concentration in the carburized layer, with a content of 0.76% C on the surface (Fig. 6).
The process was carried out in the CMe-T6810-25 furnace and had the following course from the perspective of a single load (Fig. 7):
Loading into a pre-heating chamber, heating and temperature equalization in 1382oF (750oC) (100 min in total).
Reloading to the main heating chamber, heating and temperature equalization in 1724oF (940oC), LPC, lowering and equalizing the temperature before quenching in 1580oF (860oC), reloading to the cooling chamber (total 180 min).
Gradual quenching at a pressure of 24, then 12 and 5 bar, discharge of the load from a quenching chamber (total of 25 min).
Fig. 6. Carbon profile simulated by SimVaC®. Source: SECO/WARWICK
Fig. 7. Process flow in CMe® furnace parameter trends. Source: SECO/WARWICK
The load stayed the longest in the main heating chamber – for 180 minutes. This means that with the continuous operation of the furnace in this process, the cycle will be just 180 minutes, i.e., once every three hours the raw load will be loaded, and the processed load will be removed from the furnace.
In the next step, the parts underwent tempering at a temperature of 160oC.
The result of the process was tested on ten parts taken from the reference corners and from the inside of the load. The correct layer structure (Fig. 8) and hardness profile (Fig. 9) were achieved, and all the requirements of the technical specification were met (Tab. 1).
Fig. 9. Hardness profile band obtained from tested gearwheels. Source: SECO/WARWICK
Tab. 1. Comparison of the parameters required and obtained in the process. Source: SECO/WARWICK
During the process, the consumption of the costliest energy factors was monitored and calculated, and the results per one load are as follows:
Electricity – 550 kWh
Liquid nitrogen – 160 kg
Acetylene – 1.5 kg
CO2 emissions – 0 kg
Cooling water and compressed air consumption have not been included as they have a negligible impact on process costs.
Summary: Efficiency and Economy
As a result of the process, all technological requirements have been met, obtaining the following indicators of efficiency and consumption of energy factors calculated for the entire load and per unit net weight of the load (700 kg):
On this basis, it is possible to estimate the total cost of energy factors in the amount of approximately EUR 100 per load or approximately EUR 0.14/kg of net load (assuming European unit costs of 2021). It is important that these costs are not burdened by CO2 emission penalties, as can happen with more traditional furnaces.
To sum up the economic aspect, based on an example process, a CMe furnace capacity of 1,500 net tons of parts per year was achieved for 6500 hours of annual furnace operation, at a cost of energy factors of about 100 EUR per load, or 0.14 EUR per kg of parts. The economic calculation is very attractive, and the return on investment (ROI) is estimated at just a few years.
Conclusion
While the advantages of this type of vacuum application are clear from this case study, the example discussed here does not represent the full capabilities of the CMe-T6810-25 furnace, even this process can be optimized and shortened, thereby increasing the furnace's efficiency, and reducing costs. It is possible to carry out carburizing processes (LPC) or hardening alone in a 1.5 h cycle, which would double the capacity of the furnace and similarly reduce the cost of energy factors and shorten the ROI time.
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.
“High-pressure gas quenching (HPGQ) attempts to reduce temperature nonuniformities by reducing the cooling rate; however, this is generally not sufficient to eliminate shape change. Shape change can be predicted by heat treatment simulation software, but it is difficult to reproduce the exact same cooling conditions in the vessel for each batch. Therefore, the distortion of the components will not be consistent from batch to batch.”
Read the case study to see one response to this issue in this original content from Heat Treat Today by Justin Sims, lead engineer at DANTE Solutions.
This article first appeared in the latest edition (March 2020) of Heat Treat Today’s Aerospace Heat Treating magazine.
Distortion is generally described by a size change and a shape change. In heat treatment of steels, size change is unavoidable and is mainly due to the volumetric difference between the starting microstructural phase and the final microstructural phase. Shape change of steel parts from heat treatment is due to nonuniform thermal and nonuniform microstructural strains as a result of nonuniform cooling or heating, alloy segregation, poor support of the component while at high temperature, thermal expansion or contraction restrictions, or residual stresses from prior forming operations. Nonuniform cooling or heating can be as fundamental as the temperature gradient from the part surface to its core, or as complex as the flow of fluid around a component feature. Both can result in nonuniform strains, resulting in a shape change. If the stresses causing these strains exceed the yield strength of the material, then permanent shape change will occur. Size change can be anticipated and is predictable, while shape change, or distortion, is usually unanticipated and more difficult to predict.[1-2]
Justin Sims, Lead Engineer, DANTE Solutions
Most thermal processes try to control these nonuniformities using methods of low complexity such as part orientation and rack design. Quenching systems, for example, are generally designed to remove as much thermal energy from the work pieces as possible and to do this as quickly as possible. High-pressure gas quenching (HPGQ) attempts to reduce temperature nonuniformities by reducing the cooling rate; however, this is generally not sufficient to eliminate shape change. Shape change can be predicted by heat treatment simulation software, but it is difficult to reproduce the exact same cooling conditions in the vessel for each batch. Therefore, the distortion of the components will not be consistent from batch to batch.
In response to this issue, a prototype gas quenching unit capable of controlling the temperature of the quench gas entering the quench chamber was devised. With the DANTE Controlled Gas Quench (DCGQ) unit, it is possible to have control of the thermal and transformation gradients in the component by controlling the temperature of the incoming quench gas, thereby significantly reducing, or eliminating entirely, the shape change caused by quenching. In doing so, the size change can easily be predicted by heat treatment simulation software, and post-hardening finishing operations can be reduced or eliminated. This process is ideal for thin parts or components with significant cross-sectional changes. Atmosphere Engineering (now part of United Process Controls) in Milwaukee, Wisconsin constructed the unit and provided the logic to control it. All experiments with the unit were conducted at Akron Steel Treating Company in Akron, Ohio. The project was funded by the U.S. Army Defense Directorate (ADD).
Figure 1 (left) shows the front of the unit, while Figure 1 (middle) shows the back of the unit. The back of the unit contains the human machine interface (HMI), shown in Figure 1 (right), where process parameters can be modified and DCGQ recipes entered. The prototype unit has a working zone of nine cubic ft. and is capable of quenching loads up to 100 lbs. at one atmosphere of pressure.
Figure 2. Comparison of quench gas temperature entering the quench chamber versus the recipe setpoint temperature for two different DCGQ process recipes
The ability of the unit to maintain continuity between the recipe setpoint temperature and the actual temperature entering the quench chamber is absolutely paramount. Figure 2 shows two schedules, one aggressive and one conservative, comparing the recipe setpoint (Chamber Inlet SP) to the actual quench gas temperature (Chamber Inlet PV). Figure 2 also shows that the prototype unit has good control of the quench gas temperature between 752°F (400°C) and room temperature, the martensite transformation range for most high hardenable steel alloys. There is some deviation between the two temperatures below 392°F (200°C) for the aggressive schedule as the setpoint reaches its set temperature, due to the relatively small temperature difference between the quench gas and the shop air. This small temperature difference makes it slightly difficult for the air-to-air heat exchanger used in the design to keep up with the rapid drop in temperature, but overall there is very good control of the quench gas temperature.
Figure 3. Micrograph of DCGQ (left) and HPGQ (right) processed coupons, mag. 1000X There is a copper layer on the surface of the DCGQ processed coupon.
Microstructural examination was conducted on Ferrium C64 coupons processed using the DCGQ process and coupons processedusing a 2-bar HPGQ. C64 was chosen for this study due to its extremely high hardenability and its high tempering temperature. Figure 3 compares the microstructures of the two processes at a magnification of 1000X, and no significant difference is detected. The DCGQ coupons required two hours to complete the transformation, whereas the HPGQ coupons transformed in a few minutes. There is no indication that the slow rate of transformation damaged the microstructure or mechanical properties in any way. Tensile and Charpy properties were equivalent between the two processes.
Distortion coupons, thick disks with eccentric bores, were designed and manufactured with the goal of evaluating the distortion response when subjected to a DCGQ process, and then compared to coupons subjected to a standard 2-bar HPGQ operation. All coupons were manufactured from the same Ferrium C64 bar stock. All coupons were cryogenically treated and tempered at 595°C for eight hours after quenching.
Figure 4. Nomenclature and locations used for out-of-round measurements on the distortion coupon
Figure 4 shows a distortion coupon with the nomenclature and locations used for measuring the out-of-round distortion of the eccentric bore. Due to the uneven mass distribution, the north-south direction will generally be larger than the east-west direction. Five measurements were then made along the axis of the coupon using a Fowler Bore Gauge.
Table 1. Out-of-round distortion measurements of the distortion coupon for a DCGQ and HPGQ process
Table 1 shows the results from four coupons; two hardened using the DCGQ process and two processed using the standard 2 bar HPGQ for C64. The individual measurements (EW1, NS5, etc.) are relative and are dependent on the reference value used for the bore gauge. The individual measurements give an indication of the variation in distortion in the axial direction. The out-of-round measurements are actual values, as they are the difference between the actual measurements. The DCGQ process gave significantly less distortion than the HPGQ process.
While the values reported show a 50% reduction in out-of-round distortion for the DCGQ process, a larger gain could have been realized if two other conditions were addressed. First, the coupon for DCGQ was placed directly into a 1832°F (1000°C) preheated furnace since the prototype unit does not have austenitizing capabilities. Controlled heating, just like controlled cooling, should be utilized to realize the full potential of this process. Second, the DCGQ schedule was designed for another coupon geometry that was processed together with these distortion coupons. Therefore, the schedule was not optimum for this coupon geometry.
Table 2. DANTE simulation results comparing HPGQ and DCGQ using the experimental conditions and a DCGQ with optimized heating and cooling schedulesMARCH 2020
Table 2 compares the DCGQ simulation results in which the two processes executed on the experimental coupons were compared to an optimized process, including controlled heating and cooling schedules designed for this coupon. The optimized schedule predicts an order of magnitude reduction in out-of-round distortion. Comparison of the measurements from the HPGQ and DCGQ experiments in Table 1 to the model predictions in Table 2 shows that the model predictions agree closely with the experimental results.
Simulating the application of the DCGQ process to a gear geometry, the predicted warpage of a bevel gear was examined. The simulation looked at the differences between an oil quench, 10 bar HPGQ, and a 10 bar DCGQ process. From Figure 5, it is clear that the HPGQ process is predicted to produce the most distortion. Even though the 10 bar gas quench has a slower cooling rate than the oil quench, less distortion is not guaranteed since a slower rate does not guarantee a more uniform phase transformation.[3] In this case, both heating and cooling were controlled for the DCGQ simulation.
Figure 5. Comparison of oil quench, HPGQ, and DCGQ processes for a bevel gear
In summary, a prototype gas quenching unit has been constructed with the ability to accurately control the temperature of the quench gas entering the quench chamber. Experimental results have shown that mechanical properties and microstructure are equivalent between the DCGQ process and a 2-bar HPGQ process for Ferrium C64. Thick disks with eccentric bores were machined and then heat treated using DCGQ and HPGQ. It was shown that the DCGQ process reduced distortion in these disks by 50%. Simulation using DANTE then showed that the distortion could be reduced further if controlled heating and cooling are used. Finally, a comparison was made between an oil quench, HPGQ, and DCGQ processes for a bevel gear. This comparison showed that the HPGQ process was predicted to cause the most distortion. HTT
References
[1] Prabhudev, K.H., Handbook of Heat Treatment of Steels, Tata McGraw-Hill Publishing, 1988, p.111-114
[3] Sims, Justin, Li Zhichao (Charlie), Ferguson B. Lynn, Causes of Distortion during High Pressure Gas Quenching Process of Steel Parts, Proceedings of the 30th ASM Heat Treating Society Conference, ASM International, 2019, p.228-236
About the Author: As an analyst of steel heat treat processes and an expert modeler of quench hardening processes, Justin Sims was the lead engineer for designing and building the DANTE Controlled Gas Quenching (DCGQ) prototype unit. This system was developed to minimize distortion of quenched parts made of high hardenability steels, while still achieving the required properties and performance.
“The energy optimization of thermoprocessing equipment is of great ecological and economical importance. Thermoprocessing equipment consumes up to 40 % of the energy used in industrial applications in Germany. Therefore it is necessary to increase the energy efficiency of thermoprocessing equipment in order to meet the EU’s targets to reduce greenhouse gas emissions. In order to exploit the potential for energy savings, it is essential to analyze and optimize processes and plants as well as operating methods of electrically heated vacuum plants used in large scale production. For processes, the accelerated heating of charges through convection and higher process temperatures in diffusion-controlled thermochemical processes are a possibility. Modular vacuum systems prove to be very energy-efficient because they adapt to the changing production requirements step-by-step. An optimized insulation structure considerably reduces thermal losses. Energy management systems installed in the plant-control optimally manage the energy used for start-up and shutdown of the plants while preventing energy peak loads. The use of new CFC-fixtures also contributes to reduce the energy demand.”
Modern industry trends and expectations pose new challenges to heat treating equipment; in addition to the expected requirements (e.g., safety, quality, economy, reliability, and efficiency), factors like availability, flexibility, energy efficiency, environmental, and the surrounding carbon neutrality are becoming increasingly important.
