What is a Muffle Furnace?

While the term “Muffle Furnace” or “Retort Furnace” is still in use today, it doesn’t really mean the same thing as it did in the early 20th century when wood and coal were the primary ways to heat a furnace.

A Muffle Furnace’s primary attribute is that it has separate combustion and heating chambers. The “Retort” is a gas sealed chamber that the material to be heated is placed in. This was really important in the “old days” because the by-products of combustion would otherwise have contaminated the heating process. With the invention of high temperature electric heating elements in the early 50’s however, most furnace manufacturers quickly converted thier muffle furnaces to electric where the byproducts of heating are negligible for most processes. Electrical furnaces heat by conduction, convection, or blackbody radiation processes, none of which create combustion byproducts and these designs now allow much greater control of temperature uniformity and assure isolation of the heated material from combustion contaminants.

Muffle Furnaces Today

Today, a muffle furnace is usually a front-loading box or tube design used for high-temperature applications such as melting glass, creating enamel coatings, technical ceramics or soldering and brazing. They are also used in many research facilities to determine what proportion of a sample is non-combustible and non-volatile (i.e. ash). Advances in materials for heating elements such as the molybdenum disilicide used in our “Rapid Temp” series of high temperature furnaces, can now produce working temperatures up to 1,800 degrees Celsius (3,272 degrees Fahrenheit) which facilitate more sophisticated metallurgical applications like debinding, sintering, and end to end processes in metal injection molding.

Muffle Furnaces by CM Furnace

While many of our furnaces can fulfill the broad class of applications once served by “muffle furnaces” there are still industries and processes that require the rigid isolation offered by a formal retort based design.

For these industries, CM offers the CM-300 Series, a high temperature molywound Muffle Furnace capable of temperatures up to 1800°C in hydrogen, dissociated ammonia, forming gas or any other reducing atmosphere. Features like preheat sections, binder removal sections, multiple zone controls, low or high dewpoint features, and turn-key automated pusher systems make this furnace into a versatile problem solver suitable for a variety of processes like:

  • Refractory Metals
  • Powder Metals
  • Technical Ceramics
  • Glass Formation
  • Nuclear Fuel Disposal
  • Sintering
  • Metallizing
  • Firing & Co-Firing
  • Annealing
  • Brazing
  • Reducing

Need a Muffle Furnace?

As a premier maker of Muffle Furnaces and dozens of other types of furnaces for over 70 years, CM has the quality and experience to design the furnace you need, when you need it.

Please call our engineering team today to discuss your furnace requirements.