Atmosphere and atmospheric pressure
Our earth is surrounded by a layer of air several kilometres thick. The weight of this air mass presses down on the earth's surface and creates a pressure called atmospheric pressure.
A column of air with a cross-sectional area of 1 m² has a mass of approx. 10,000 kg. The atmospheric pressure at sea level is 101.3 kPa (1013 mbar). The higher you go, the thinner the air becomes and therefore the atmospheric pressure also drops.
Up to 2000 metres above sea level, the atmospheric pressure drops by 12.5 mbar per 100 metres. For the AERO-LIFT Vakuumtechnik GmbH site in Geislingen-Binsdorf (590 m above sea level), for example, this results in an atmospheric pressure of just under 940 mbr.
This must of course be taken into account when configuring vacuum lifting devices, as the maximum achievable pressure difference and thus the maximum achievable holding force of the vacuum suction cups or vacuum suction plates decreases with increasing altitude.
Vacuum and vacuum level
A vacuum is defined as an absolutely empty space. Evacuating the air in a closed vessel creates a negative pressure compared to atmospheric pressure. The vacuum level is a measure of this negative pressure. At absolute vacuum, the pressure is 0, and this is the starting point for the term absolute pressure. As a rule, the scaling unit bar or mbar (millibar) is used.
Negative pressure / vacuum
At negative pressure, atmospheric pressure is a potential source of energy. In an ordinary hoover, the air is evacuated so that the pressure is lower than atmospheric pressure. The hoover therefore does not suck. It is the surrounding higher atmospheric pressure that pushes air and dust into the hoover.
The same applies to vacuum cleaners and vacuum suction plates. It is not these that suck onto the workpiece. It is the ambient pressure (atmospheric pressure) that presses the vacuum cups against the workpiece as soon as air is extracted from the deliberately created "chamber" of suction cup and workpiece.
Vacuum suction force in the application
Ever since Otto von Guericke carried out his famous experiment with the "Magdeburg hemispheres" in 1654, we have known about the considerable pressurising force of the atmosphere surrounding us. We have utilised this ancient knowledge in the design of modern vacuum clamping and transport devices.
They can be used to suck in and hold all virtually dense materials, i.e. steel, wood, light metal, glass, hard rubber, plastics, etc., while magnetising workpieces and tools. All that is required is a certain area that can be separated from the atmosphere. Today, special devices even enable the suction of porous materials such as chipboard, insulation boards, foams, etc.
The suction surface and the pressure difference between the suction surface and the atmosphere are decisive for the load-bearing capacity of the suction plates. The higher the altitude, the lower the air pressure and thus the load-bearing capacity of a suction cup. At sea level, 80 % vacuum corresponds to a pressure difference of 810 mbar; at an altitude of 1000 m, 80 % vacuum is only a pressure difference of 710 mbar.
The load capacity decreases up to an altitude of The load-bearing capacity decreases by 1.23 % per 100 m up to an altitude of 2,000 m.
