The term vacuum (coming from the Latin word “vacuus” - empty) means empty room.
According to DIN 28400 part 1 (May 1990, Vakuumtechnik; Benennungen und Definitionen; Allgemeine Benennungen), vacuum is defined as follows: “Vacuum describes the state of a gas if the gas pressure and, consequentially, the particle-number density in a vessel is lower than outside or if the gas pressure is lower than 300 bar, i.e. lower than the lowest atmospheric pressure on earth.”
Vacuum in technology and classic physics means the fluid state in a volume under a pressure which is significantly lower than the atmospheric pressure under normal conditions. Colloquially, vacuum is mainly used to describe a room without air (e.g. vacuum package). Extremely low absolute pressure is called high vacuum.
If the pressure in an evacuated vessel is much lower than the atmospheric pressure, the correct term would be “lowered pressure” or “reduced pressure”.
Pressure area characterization
Technical vacua can be created in different qualities. In technology, there is a distinction between different achieved vacuum qualities based on the remaining matter (Table 1). By default, pressure is indicated in Pascal (Pa) or millibar (mbar).
Application in casting technology
A vacuum is created through extraction by special vacuum pumps (Fig. 1). A vacuum is used in many casting techniques especially to prevent oxidation and accommodation of atmospheric gases and/or to remove dissolved gasses from liquid metals such as:
DIN 28400-1990, Part 1, Vacuum technology; terms and definitions; general terms, Deutsches Institut für Normung e.V.
Kramer C., Mühlbauer A. (eds.), Praxishandbuch der Thermoprozesstechnik, Vol. I, Vulkan-Verlag Gmbh, Essen, 2002.