Temperature measurement and control in the extreme environment of vacuum furnaces brings very specific challenges to thermocouple manufacturers. Here we offer a brief introduction to vacuum furnaces and we explain which of our exotic thermocouples are best suited to this demanding industrial application.
A vacuum furnace is a special type of furnace that is capable of heating materials, especially metals, to extremely high temperatures. What makes it unique is that it operates in a vacuum, which means there is no air or other gasses present inside the furnace during the heating process, which serves several important purposes.
Thanks to these properties, a vacuum furnace can achieve exceptionally high temperatures, reaching up to 3000 °C (5432 °F). This makes it suitable for various applications that require exposing materials to extreme temperatures with high consistency and low contamination, such as sintering and heat treatment.. Additionally, the vacuum furnace can be utilized for vacuum brazing. Brazing is a method used to join metal parts together. In this process, a special metal, known as filler metal, is heated until it becomes liquid. This liquid filler metal is then drawn into the small gaps between the two or more metal parts being joined, thanks to capillary action.
To protect the filler metal and ensure a successful brazing process, it is heated slightly above its melting temperature (known as the liquidus temperature), while being exposed to a controlled atmosphere with lower pressure than the standard atmospheric pressure. This controlled atmosphere is typically a vacuum.
Once the liquid filler metal has flowed over the surface of the metal parts being joined (a process known as wetting), the whole assembly is cooled down. As a result, the filler metal solidifies, firmly joining the metal pieces together. This vacuum brazing technique is used to create strong and precise connections between various metal components in different industries. One example is our mineral insulated heating elements Temperature uniformity can be achieved by vacuum brazing these mineral insulated heating elements into grooves on stainless steel plates.
Due to the broad temperature range of vacuum furnaces, several different types of thermocouples are typically used for this application. The thermocouple types include:
Molybdenum has a significantly higher melting point (2610°C) compared to the maximum operating temperature of C799 (1800°C). Molybdenum has excellent resistance to high temperatures and extreme thermal environments. It remains stable and does not readily react with other materials at temperatures commonly found in vacuum furnaces. Furthermore, Molybdenum has higher mechanical strength and toughness compared to C799 protection tubes, making it more durable and resistant to potential mechanical stresses or damage within the vacuum furnace environment.
Thermocouples used in high-temperature environments are essential in industries where demanding conditions exist, such as in special vacuum furnaces. While regular thermocouples (type K or N) or thermocouples made of platinum have some limitations, type C and D thermocouples are specially designed to work better in very high temperatures and challenging situations that platinum thermocouples cannot handle. These special thermocouples provide better accuracy and reliability in extreme conditions.
For more specifications and detailed information on our range of high temperature thermocouples we suggest you download our brochure on this topic. Our team of experts are also available for any advice you may need and can be contacted here.