Vacuum is also generally known as “under-pressure”. In the physical definition, it is also said that matter is absent in a space. In vacuum technology, the respective unit is p absolute. The unit most frequently used for the vacuum is millibar (mbar).
Absolute means that the pressure is stated proceeding on the standard pressure 1013 mbar as a basis. Accordingly, the absolute vacuum is 0 mbar. If the pressure is indicated as a relative pressure, the absolute vacuum is -1013 mbar, the atmospheric pressure is 0 mbar. The differential pressure is the pressure between two measuring points. See the diagram below for further explanation.
In vacuum technology, the pressure is usually specified as absolute pressure.
Various vacuum ranges are differentiated, namely:
low vacuum (GV) 1000 – 1 mbar
medium vacuum (FV) 1 – 10–3 mbar
high vacuum (HV) 10–3 – 10–7 mbar
ultra-high vacuum (UHV) 10–7 – (10–14) mbar
The vacuum systems by Diener electronic usually operate in the low and medium vacuum ranges. For special applications, high-vacuum systems can be implemented as well.
Vacuum systems by Diener electronic are used in research and development as well as in series production. Some typical applications are described in the following:
With vacuum degassing, volatile substances such as solvents or moisture are removed in a controlled process. Many materials need degassing to eliminate the negative effects of the volatile substances.The following negative effects may occur for example: bad smell, loss of adhesion when gluing, painting or coating. For degassing, the parts are exposed to a defined vacuum. Often, the vacuum is run in ramps.
The graph shows an exemplary outgassing process with pressure ramps. The image is an idealised representation. In practice, the system needs some seconds to reach the next pressure ramp. The respective pressures are maintained for a certain period of time before approaching the next ramp. To accelerate the process, the chamber is heated in most cases. Heating the Diener electronic vacuum chambers made of aluminium extruded sections is particularly easy and low-cost.
See the following example of a typical production process:
1. Degassing of the components with vacuum
2. Activation of the components with plasma
3. Coating/gluing/painting/filling of the components
The process used in so-called vacuum drying is almost identical with the degassing process. Vacuum drying is used to dry products saturated with liquids such as water or solvents. The major benefit of vacuum drying is the low temperatures. The lower the pressure, the lower the temperature at which water passes from the liquid to the vapour phase.
This ensures very gentle drying of high-value and sensitive products at low temperatures.
Another variety of vacuum degassing is manual vacuum casting. Bubble-free casting is mandatory for high-value and heavily loaded components. With manual vacuum casting, the parts are cast at atmospheric pressure. Next, they are exposed to gas in a vacuum chamber. This makes premium-quality bubble-free manual casting possible. This is of advantage above all for small series production as well as for research and development purposes. With manual vacuum casting, running suitable pressure ramps is a precondition for achieving optimum results. It is also possible to use special casting compounds not suitable for standard casting systems.
Nowadays, suitability for air transport is a mandatory for many components. While there is pressure equalization in the cargo holds of aircraft, it cannot completely compensate for the pressure fluctuations. The pressure can fall below 800 mbar abs. In a Diener electronic test plant, the components can be exposed to a pressure simulation test. Also significantly lower pressure levels can be simulated to test the behaviour for example during a pressure drop.
Some components such as electric motors are also operated outside of pressure cabins. Perfect functionality must be ensured there. With suitable cable feedthroughs, these motors can be operated inside the vacuum chamber.
Components used in space must be able to withstand even much higher loads. For them, pressures of 10-6 mbar and smaller must be simulated. To achieve pressures as low as this, a turbo molecular pump with a suitable pre-pump is required.
Generally, the following questions must be answered:
- In which pressure range do you intend to work? (coarse, fine, or high vacuum)
- What is the permissible deviation from the setpoint pressure? (How accurate does the pressure regulator have to be?)
- Do you intend to run pressure ramps/time curves?
- Do you need heating?
- Will there be outgassing of substances which are harmful to the pump or the environment?
- What is the goal of the application?
- Do you need electrical bushings?
- Should the system be designed as a stand-alone or a tabletop unit?
With your answers to these questions, we will be able to design a system tailored to your requirements.
When selecting the suitable measuring instrument for vacuum, the following questions need to be answered:
- What tolerance should the measuring instrument have?
- Which pressure range is relevant for the process?
- Is it necessary to combine several measuring instruments?
In our systems, we primarily use Pirani sensors and capacity pressure gauges. We will be happy to advise you regarding suitable pressure measurement.