Vacuum furnaces are widely used in heat treatment processes, and vary widely in capacity and size. Equipment has consistently been improved over the last 30 years such that vacuum processing has become a widely used application in the Aerospace and Automotive Industry. Vacuum is considered to be any pressure which is below atmospheric pressure and in industrial applications may be expressed as torr, microns or millibars.
The effects of treating components in a vacuum are twofold:
1. In the medium-high vacuum region the partial pressure of the residual air in the furnace particularly O -H O is significantly reduced and will provide an environment to process components with little or no surface oxidation.
2. Decomposition of existing oxides in the surface of components may occur depending on the temperature and material type.
Vacuum furnaces take many different mechanical formats, designs include common components, such as:
- Work piece chamber or multiple chambers usually with water-cooled jacket, loading and transfer mechanism
- Heat shields made of graphite board or high temperature material
- Furnace furniture constructed of graphite or other high temperature material
- Heating element often Graphite or alternatively Molybdenum or high temperature material for temperatures above 1000°
- Vacuum pumping system
- Partial pressure control
- Optional fan assisted circulation systems for lower temperature ranges
- Quenching vessels and/or gas/fan quenching system
- Cooling system
- Control system
The cellular concept of vacuum processing is becoming more widespread with multi-cell layouts used to integrate heat treatment into shop floor production and manufacturing.
A typical simple single chamber vessel furnace is shown in Figure 1.