Vacuum furnaces can be divided into two categories; hot-wall furnace designs and cold-wall furnace designs. Most modern vacuum furnaces are cold-wall furnaces. The description in this article will help you to earn and understand the chemistry behind vacuum furnaces, their general design, the processes associated with them and eventually provide you with the advantages of using cold-wall vacuum furnaces. However, if you are looking for more help on school projects, you can find assistance on chemistry at

Hot-wall furnaces.

These were originally the primary type of vacuum furnaces. They are generally standard furnaces that operate in an inert gas atmosphere like Nitrogen. A vacuum pump releases the air in the retort and automatically fills it with gas. Prior versions of vacuum furnaces allowed gas to flow inside to expel the air that was contained inside.

The furnace comprises a resistor that is insulated with a considerable amount of thickness of ceramics to aid in the refraction of the energy. The retort is specially made with steel or Nickel so that it can be used with higher temperatures. It also comprises of a sealed door. The seal is cooled procedurally using water circulation. The general support structure also consists of a blower that circulates air outside the ferrule that aids in cooling the furnace and the load. Inside the furnace, an Impaler stimulates a reaction of the gas through convection of the heat energy that the ferrule transmits to the amount.

There are sophisticated vacuum furnaces that have gas circulators outside the ferrule, thus promoting cooling. They use a water-gas exchanger to induce a cooling effect to the load in the furnace.  The exchanger extracts hot gas from the furnace and returns it when it is cooled so as to cool the load.

Cold-wall furnaces

These are tempering furnaces for low-temperature use. They consist of a water-cooled vessel, a wafer insulated thermal chamber, a convection Impeller and a load cooling impeller inside the vacuum chamber.

The purpose of the primary pump and booster defines the amount of vacuum that the chamber requires. The construction of the thermal chamber is made in accordance with aerospace criteria. This means that the hot zone confinement system and the load support base are all made according to the aerospace criteria. The insulation and the resistor are both made with a light mass affecting the thermal calculation as a fraction of the load mass. This differs from the hot-chamber furnaces where the load cooling gas flow is actuated when the opposing doors are both opened.

This furnace is generally made with compact geometry, and the control panels programs the phases of a cycle or multiple cycles so as to guarantee thermal uniformity. The cycles operate with +5- and -5-degree peaks. The thermocouples connected on the load send the temperature measurements to the recorder.

In the first phase, the process works to dispose of the heat up to temperatures that are designed to eliminate the air, water vapor and oils from the processing and washing of pieces. Unreactive natural gas e.g. Argon or Nitrogen is then introduced to accelerate the load heating process. Here then the furnace can be evacuated again at the annealing temperature or the process of convection can be continued.

Load cooling is the final phase that happens at the end of the thermal cycles. It is normally a very fast operation. The furnace is opened to extract the load when the load temperature has reached the external temperature. The vacuum treated material will likely have a clear appearance because of the cycle set.

How to Operate Vacuum Furnaces?

Vacuum furnaces require specialized environments that are different from the conventional treatment departments that we are accustomed to. They require clean environments, and the operators must wear clean garments and gloves for effective operation. When handled without gloves, the material will be left with an imprint that would create a rust stain almost immediately. The pieces must then be sealed in plastic envelops after filling with Nitrogen.

During the start-up phase, the operators are required to perform the already predetermined checks that are set out for the plant and should understand whether they are able to silence the alarm or not in case of a problem arising. Performing necessary tests can guarantee the plant’s performance for years. Proper preparation, combined with the ability of the vacuum to protect against wear, can ensure that the plant remains durable.


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