The heart of an industrial furnace is its heating element which is used to convert electricity into heat within the high-temperature controlled atmosphere system. Heating elements come in many forms. The selection of the correct heating element for a high-temperature vacuum furnace is dependent on several factors such as maximum operating temperature, application, power load, and partial pressure. Most heating elements are either all-metal, graphite, ceramic, or a hybrid, which consists of metal and another element.
One of the main benefits of an all-metal hot zone is the reduction in contamination that other hot zone materials like graphite can cause. Often, industries in the medical, electronics and aerospace require clean environments or extreme vacuums to process sensitive materials. Using a metal hot zone helps aid these industries in achieving the goal of decreasing impurities being introduced into their process. Another consideration when selecting heating elements is the temperature required for the process. The extreme heat used in some applications can cause dimensional instability, reduce durability, and shorten the life of your heating elements and hot zones.
Refractory metals such as tungsten, and tantalum, are commonly used for temperatures that exceed 2000°C in high-temperature vacuum furnaces. Tungsten has the highest melting point of 3,400°C and has furnace temperatures up to 2,800°C. Other metal materials like platinum, molybdenum, stainless steel, inconel, kanthal, and nichrome can also be considered as possibilities when deciding on all-metal hot zones. Even though these metals do not have the same temperature performance characteristics as Tungsten and Tantalum, they can be a more cost-effective option that can perform very well with the right application.
- Tungsten (3000 °C max.)
- Molybdenum (1650 °C max.)
- Tantalum (2300 °C max.)
- Platinum (1600 °C max.)
- Stainless Steel (1000 °C max.)
- Inconel (1000 °C max.)
- Kanthal (1700 °C max.)
- NiCr (1200 °C max.)
- Mesh Heaters, Panel Heaters, Rod Heaters
- Round Hot Zones, Rectangular Hot Zones
- Vacuum, Inert, Oxidizing, or Reducing Environments
In the past, graphite hot zones were limited to bulky simple shapes and were often thought to be reactive to specific materials. This was believed to contaminate the end result which led many to choose an all-metal hot zone over graphite. However, over the last few decades, the heat-treating industry has seen a significant shift away from the status quo of all-metal hot zones to the use of graphite. In fact, current market data show that the use of graphite heating elements has exceeded that of molybdenum within the heat-treating industries.
Graphite’s growth in popularity is due in part to the advances in materials and manufacturing techniques and improvements in the design and quality of this material. Because of these continued developments within the heat treatment industry, education regarding the benefits of graphite’s use as a heating element has also become more widely known. With the ability to be more energy-efficient, cost-effective, and a high capacity for uniformity, graphite has become the first choice for many conventional vacuum furnaces.
- Heating elements (3000 °C max.)
- Fibrous shield packs
- Graphite hot rods
- Graphite mounting hardware
- Graphite bolts, nuts, pins
Ceramic hot zones are considered one of the more stable forms of heating elements used in atmosphere furnaces and have the ability to retain the heat for extended periods. Like graphite, ceramic hot zones have a high capacity for thermal insulation and are a cost-effective alternative to an all-metal hot zone. Ceramic hot zones are flexible solutions for those working in temperatures of 1700°C or less.
Because ceramic hot zones can be more energy-efficient and allow for better temperature control, the need for complicated additions that all-metal hot zones require for temperature control is not necessary.
Ceramic hot zones are suited for operation in air or highly oxidizing environments and can be found in heat treatment applications such as thermoforming, annealing, and are often used in hybrid models as an insulator for metal hot zones.
Ceramic Hot zones materials:
- Molybdenum disilicide elements (1650 °C max.)
- Fibrous ceramic insulation
- NiCr heaters (1200 °C max.)
- Kanthal heaters (1700 °C max.)
- Inconel heaters (1000 °C max.)
Who We Are…
MRF is a global leader in precision thermal systems essential for the research, development, and production of advanced materials. These advanced materials include ceramic matrix composites (CMC’s), advanced ceramics, and SiC crystals. For decades, we have pioneered some of the world’s most innovative, customized furnace systems, with a focus on enabling the processing of materials at high temperatures in controlled atmospheres or vacuum. For additional information about MRF’s capabilities, please visit mrf-furnaces.com.