Using a Liquid Mixer to Disperse Shear Sensitive Ingredients
In many chemical processing applications, shear sensitive ingredients must be dispersed and incorporated into liquids. This is most often accomplished with a liquid mixer that uses flow currents to mix and keep solids in suspension.
Traditional mixing methods force ingredients to enter and exit a small mixing area to achieve proper mixing. RAM technology activates all ingredients throughout the entire vessel instantly.
High Shear Mixers
High Shear Mixers are used for ingredients that resist blending easily, or require vigorous action to evenly distribute. These include liquids of different viscosities or those that contain solids that must be broken down or dispersed. These machines work by generating intense shear and turbulence, with the sharp-edged blade spinning at high speed to reduce particle size.
Batch high shear mixers are equipped with one mixing head that can be lifted and suspended to serve several vessels. This allows for faster cleaning, which is important in sticky mixtures that leave residue behind and can contaminate subsequent batches. To avoid this, these mixers can be fitted with CIP (Cleaning in Place) systems that automatically scrub the tank before the next blending cycle begins.
These high shear mixers are also suitable for emulsification, dispersing, and homogenizing of paints and inks. They are also useful for pharmaceutical manufacturing, where they can be used to create high-density tablets with less friability.
Ultra-high shear mixers use a rotor/stator that produces shear at a faster tip speed, delivering the same homogenization benefits as conventional colloid mills at a fraction of the cost. These mixers liquid mixer can also help finish emulsions and dispersions that would otherwise require high-pressure homogenizers, eliminating the need for those expensive pieces of equipment altogether. These mixers are built with a stainless-steel casing, making them resistant to chemicals and other substances.
Powder-Liquid Mixers
Mixing powdered ingredients into liquids is a common processing step found in many sanitary industries. Mixers used for this application must be able to handle high powder feed rates and high liquid flow rates, while still being able to achieve good mixing and dispersing.
For powders that tend to agglomerate or stick to the mixer shaft and tank wall, or which require a higher shear force for full dispersion, an alternative to batch mixing is vacuum mixing. This technique allows the powder to be injected through a powder inlet well below the liquid surface and avoids the air incorporation that can occur when a powder is added directly to the liquid.
Some powders, such as stabilizers, absorb moisture during storage or transport and can form lumps when reconstituted into a solution. Vacuum mixing also minimizes this effect, and allows a powder to be dosed into a tank in a dry environment and transported rapidly down to the mixing head through a controlled vortex to ensure that it is completely wetted with minimal air clogging.
The Flashmix powder/liquid mixer from Silverson is a compact, in-line unit that offers a simple, effective and sanitary way of incorporating powder into liquids. It combines the proven performance of a Silverson high shear mixer with an integrated powder inlet, bulk bag unloader and liquid injection system to offer a single-step incorporation and dispersing solution for powders and slurries. Interchangeable mixing heads and screens are available to provide a wide range of processing capabilities, including emulsifying, homogenizing, hydrating, dissolving, blending, de-agglomerating, reclamation and particle size reduction.
Centrifuge Mixers
The centrifuge mixer can be incorporated into a larger microfluidic system or it can act as a stand-alone unit that is used for rapid spin-downs of samples in microcentrifuge tubes. These units can also be connected to a piping network, making them a great option for creating emulsions that require precise mixing conditions.
The rotor/stator assembly of a centrifuge mixer provides high targeted shear and deaeration to the liquid sample inside the working chamber. The intense shear forces break up particles and droplets, increasing their surface area for more efficient solubilization. The agitation caused by the rotor/stator creates three-dimensional flow, further enhancing the mixing process and reducing dead spots in the sample.
These types of mixers are used for a wide variety of applications, including preparing gradients with Percoll (a density-based separation method) and for the formation of particle size distributions in solutions. They can also be used to create emulsions and other types of mixtures that require precise mixing conditions.
The Grant Instruments PCV-6000 variable speed combination centrifuge/vortex mixer can be programmed for a sequence of independent centrifuging and vortex mixing, or combined for simultaneous spin-and-mix operations. This unit includes a multi-rotor that accommodates twelve microcentrifuge tubes in 0.2ml, 0.5ml, 1.5ml, or 2ml capacities, as well as four 8-well, 0.2ml PCR strips. A safety lid with lock stops the rotor when opened to protect the operator and the contents of the centrifuge tube.
Liquid-Liquid Mixers
Mixing liquids is a common task in most manufacturing processes. For example, mixing liquids to a uniform consistency is important for chemical processing (such as hydrogenation or fermentation) where solid catalysts and gaseous reagents are combined with liquid mediums. Mixing liquids also involves making emulsions, dispersions and other multiphase processes that involve both a solid and a liquid phase.
Liquid mixers work by using agitation to move the material in the tank in new paths and achieve a more homogeneous mixture. There are a number of different ways to accomplish this, such as using pulses or vibration to create turbulence. In addition, a mechanically agitated vessel may be designed with baffles or the shape of the tank to redirect flow and reduce dead spots.
When a process requires mixing two liquids of different densities, the most common method is to use a centrifuge mixer. This uses a spinning action to separate the lighter liquid from the heavier one. It is commonly used in the textile Packaging Machinery Supplier industry to ensure dye lots stay consistent and in food processing to keep dough hydrated.
The physics of liquid mixing is complex and can be difficult to replicate at production scale. There are multiple factors that affect the quality of a mixing system including the geometry of the mixing vessel, size and shape of the agitator, presence and location of baffles and density characteristics of the materials being mixed. In general, the best approach to scaling up a liquid mixing process is to understand the core mixing principles and then apply them to the specific material and process under consideration.
