Technology Synopsis
There are several advantages to mixing under vacuum, such as the removal of unattractive spaces in the final product, increased drying at lower temperatures, improved dispersion quality, and subsurface addition of raw components. Optimising vacuum mixing methods results in the maximisation of these advantages.
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Why vacuum mixing?
Space with pressures lower than atmospheric pressure is referred to as vacuum. Put differently, compared to ambient air, it has less gas molecules per unit volume.
Vacuum environments achieve a variety of mixing objectives that differ depending on the application. Some people just care about appearance, as in the cases of molded composites, personal care items, and coatings. Furthermore supporting the accuracy and robustness of precisely manufactured pieces is a void-free composition. Vacuum is used in other items to take out oxygen, stop delicate chemicals from decomposing, stop unintended chemical reactions, and stop microbiological development. For example, reducing the amount of oxygen in beverages is one crucial element in preserving their excellent quality over time.
Vacuuming a product also enhances its performance and handling. Under vacuum, certain gels and pastes are combined to avoid flaws in the printing or filling of syringes. Lastly, drying operations may occur more quickly and at lower temperatures thanks to vacuum mixing. Heat-sensitive items may be dried using this approach without worrying about thermal deterioration.
Mixers with a vacuum cap
Virtually any configuration of batch mixer can be made to operate in vacuum, ranging from single-shaft devices like high-speed sawtooth dispersers or rotor/stator mixers, which are used to make low viscosity formulations, to multi-agitator or planetary mixing systems, which are used to batch high viscosity, high density compounds, or even blending equipment, like vertical cone screw blenders or horizontal ribbon blenders, which are used in drying operations. Pre-wired to the mixer’s control panel, a built-in vacuum pump is a standard feature on many of these mixers.
Practical methods
Ascertain that the vacuum level and operational conditions required by your process are met by the vacuum pump you have. For instance, compared to a liquid ring pump, a rotary vane pump would enable you to draw a deeper vacuum (29.5–29.8″ Hg). On the other hand, a liquid ring pump could be more suitable for batch condensate. To shield the pump from impurities, make sure it has the proper filter and/or condenser installed before it.
While applying vacuum, always keep an eye on the contents of your vessel. Keep an eye out for bubbling and volume variations using a sight glass. Incorporate a distinct “break valve” into the design of your vessel. This will enable you to establish the necessary amount of vacuum in the batch, pull vacuum, turn on the mixer, and shut off the chamber. You can prevent drawing out volatile ingredients and disturbing the formulation by separating the mix chamber and shutting off the pump at this time. You can progressively bleed air or inert gases back into the chamber once an agitation phase is finished.
You may use vacuum to feed raw components into the batch faster, accelerating the mix cycle. Large volumes of liquids may be easily added below the surface, which also helps to improve dispersion by preventing light particles from “dusting” and floating. Additionally, by eliminating the need for a separate post-mixing deaeration phase, the overall processing time is reduced.