A company developing advanced alternative renewable energy technologies large-scale industrial applications is expanding their heat treat capabilities with two identical vacuum furnaces.
The Research and Development team of Solar Manufacturing, Solar Atmospheres, assisted the client’s engineers to verify the process in the Mentor® Pro vacuum furnace prior to sending this furnace. Solar Manufacturing shipped the identical vacuum furnaces and assisted the company’s engineers to verify the molybdenum shielded hot zone operation of the new equipment at the developer’s facility. The furnace’s internal gas quenching system processes workloads to quench at 2 bar positive pressure in either nitrogen or argon gas, a flexibility that assists the company in achieving results across a wide range of metallurgical applications.
The client also finds benefit from the compact design of the Mentor® Pro features a molybdenum shielded hot zone measuring 18” wide x 18” high x 36” deep, capable of temperatures up to 2500°F, and a workload weight capacity of up to 1,000 lbs.
The press release is available in its original form here.
The need to understand how certain furnace designs operate comes at a time when heat treaters are weighing each energy cost and benefit of their systems and processes. Read on for a quick summary on how dual chamber furnaces preserve energy.
On April 17-19, 2024, TAV VACUUM FURNACES provided a speaker at the 4th MCHTSE (Mediterranean Conference on Heat Treatment and Surface Engineering). The speech focused on the energy aspects of vacuum heat treatment, a subject towards which all of us within the industry need to pay attention for reducing the carbon emissions aiming at a zero net emissions future.
We have already analyzed the essential role that vacuum furnaces will play in this transition, with a focus on the optimization of energy consumption in our previous article. With this new presentation, we wanted to emphasize how selecting the right vacuum furnace configuration for specific processes may impact the energy required to perform such process. For doing so, we compared two different furnace designs — single chamber vs. dual chamber vacuum furnaces — detailing all of the components’ energy consumption for a specific process.
TAV DC4, dual chamber vacuum furnace for low pressure carburizing and gas quenching Source: TAV VACUUM FURNACES
As a sneak peek into our presentation, we will summarize below how the main features of the two vacuum furnaces design are affecting their energy performance.
Let’s start by introducing the protagonist of our comparison: a single chamber, graphite insulated vacuum furnace, model TAV H4, and a dual chamber furnace TAV DC4, both having useful volume 400 x 400 x 600 mm (16” x 16” x 24”) (w x h x d).
In a single chamber vacuum furnace, like the TAV H4, the entire process is carried out with the load inside the furnace hot zone. This represents a highly flexible configuration that can perform complex heat treatment recipes with a multiple sequence of heating and cooling stages and to precisely control the temperature gradients at each stage.
Configuration of the TAV DC4 dual chamber vacuum furnace Source: TAV VACUUM FURNACES
Alternatively, a dual chamber vacuum furnace, like the TAV DC4, is equipped with a cold chamber, separated from the hot zone, dedicated for quenching. Despite the greater complexity of this type of vacuum furnace, the dual chamber configuration allows for several benefits.
First, in dual chamber furnaces, the graphite insulated hot chamber is never exposed to ambient air during loading and unloading of the furnace; for this reason, the hot chamber may be pre-heated at the treatment temperature (or at a lower temperature, to control the heating gradient). But in single chamber vacuum furnaces, the hot zone must always be loaded and unloaded at room temperature to avoid damages due to heat exposure of graphite to oxygen.
Because dual chamber furnaces have more controlled heating, this will result in both faster heating cycles and lower energy consumption, as a substantial amount of energy is required to heat up the furnace hot zone. This advantage obviously will be more relevant in terms of energy savings the shorter the time is between subsequent heat treatments.
View of the cold chamber of the TAV DC4 dual chamber vacuum furnace Source: TAV VACUUM FURNACES
Secondly, since the quenching phase is performed in a separated chamber, the hot zone insulation can be improved in dual chamber vacuum furnaces by increasing the thickness of the graphite board without compromising cooling performance. This translates into a significantly lower heat dissipation, to the extent that at 2012°F (1100°C) the power dissipation per surface unit (kW/m2) is reduced by 25% compared to an equivalent single chamber vacuum furnace.
Additionally, quenching in a dedicated cold chamber allows to obtain higher heat transfer coefficients and higher cooling rates compared to a single chamber vacuum furnace. Since the cold chamber is dedicated solely to the quenching phase, it can be designed for optimizing the cooling gas flow only without the need to accommodate all the components required for heating. All things considered, the heat transfer coefficient achievable in the TAV DC4 can be, all other things being equal, even 50% higher compared to a single chamber vacuum furnace. Secondly, since the cold chamber remains at room temperature throughout the whole process, only the load and loading fixtures need to be cooled down; as a result, the amount of heat that needs to be dissipated is significantly less compared to the single chamber counterpart.
CFD simulation showing a study on the cooling gas speed in a section of the cooling chamber for the TAV DC4 dual chamber vacuum furnace Source: TAV VACUUM FURNACES
For heat treatments requiring high cooling rates, it is possible to process significantly higher loads on the dual chamber furnace compared to the single chamber model; translated into numbers, the dual chamber model can effectively quench as much as double processable in a single chamber furnace, depending on the alloy grade, load configuration and overall process. The savings in terms of energy consumption per unit load (kWh/kg) achievable in the dual chamber furnace for such processes can be as high as 50% compared to the single chamber furnace.
In the end, the aim of the speech was to highlight how the energy efficiency of vacuum furnaces is highly dependent on the machine-process combination. Choosing the right vacuum furnace configuration for a specific application, instead of relying solely on standardised solutions, will improve significantly the energy efficiency of the heat treatment process and drive the return on investment.
About the Author
Giorgio Valseccchi R&D Manager TAV VACUUM FURNACES
Giogio Valsecchi has been with the company TAV VACUUM FURNACES for nearly 4 years, after having studied mechanical engineering at Politecnico di Milano.
Derek Dennis President Solar Atmospheres of California
To support R&D and additive manufacturing projects, Solar Atmospheres of California (SCA) has added some small vacuum furnace capacity to their equipment offerings.
The new vacuum furnace was acquired from SCA’s furnace manufacturing sister facility, Solar Manufacturing (SAMI) located in Sellersville, PA, and was specifically designed to process a variety of materials between 600°F – 2400°F (+/-10°F) in both vacuum and/or partial pressure environments. Precise cooling capability up to 2-Bar in argon, nitrogen or helium is available with a maximum operating temperature up to 2650°F. The furnace is also equipped with the SAMI’s state-of-the-art SolarVac® Polaris Control System for optimum performance and precise cycle control.
"We are pleased to add this needed piece of vacuum furnace equipment to service our valuable customers," said Derek Dennis, president of SCA. "The additive manufacturing industry continues to grow, and this new furnace will allow SCA to respond to small builds and R&D projects quickly and precisely."
