Technical Articles

Building production and a competitive edge with more versatile mixing equipment


Sub-surface injection can speed up both the mixing process and subsequent clean-up. But careful control of the vacuum injection process is crucial to avoid creating excessively violent turbulence within the mix vessel - and a long cleaning cycle later.

Sub-surface injection also helps to control heat.

Heat is the inescapable by-product of the shearing action necessary to produce emulsions and dispersions. In fact, it is often the critical factor that limits the shear that can be applied to a mix – and the speed with which the mix cycle can be completed.

Food mix vessels are usually jacketed to control the temperature of the batch. But the first step in controlling heat should be to minimize heat input – rather than concentrate mainly on removing heat after it accumulates. By shortening the mixing process, and reducing the total energy imparted to the batch, sub-surface injection helps to reduce heat input and avoid thermal degradation.

Choose a combination of agitators that offers a variety of mixing action.

Multi-agitator mixers, such as the anchor/rotor-stator/disperser combination shown here in the Ross VersaMix, offer valuable flexibility. Since they are independently driven, the agitators can work together in an endless variety of combinations. Each agitator can also operate alone at a variety of speeds.

This flexibility allows the multi-agitator mixer to adjust to changing mixing requirements during a single mix cycle. Many products undergo a series of significant changes as reactions occur and the physical properties of the material evolve. With independent, variable-speed drives, the multi-agitator mixer can adapt as the cycle progresses - providing the optimal combination of shear and flow at each stage.

Choose agitator designs to ensure homogeneity – and thorough distribution of heat.

The centerpiece of a high-performance emulsifier/homogenizer is its high-shear rotor-stator design. But the slow-speed agitators are equally important. In fact, the two systems must work together efficiently to generate flow and permit very high shear rates. With vigorous flow, heat is quickly carried away from the high-shear agitators. This action prevents localized heat from reaching dangerously high levels.

In a multi-agitator mixer like the Ross VersaMix, the anchor generates both upward axial flow and inward radial flow from the vessel wall. This flow feeds material to the high-shear agitators near the center of the vessel. In a co-axial system, the slow-speed agitators turn in opposite directions to generate contrasting upward and downward axial flow, as well as radial flow. All slow-speed agitators should be equipped with scrapers to assist in removing material that would otherwise form an insulating layer on the vessel wall and inhibit heat transfer.

Extend the range of available batch capacities

A large mixer capable of operating with batches from 10% to 100% of its total vessel capacity offers terrific versatility. To accomplish this, you need to consider a switch to a multi-agitator design that includes a bottom-entering or an external rotor-stator agitator. This also requires a coaxial agitation system. For applications in which dry ingredients are added during the cycle, an alternative design offers additional advantages. By substituting an external in-line rotor-stator generator for the internal rotor-stator, dry additions can be dispersed even faster. The batch material is recirculated in a closely controlled, highly predictable pattern. Acceptable batch capacities can sometimes be reduced to less than 10% of total capacity - providing even more flexibility on the process line.

Add a control system that is powerful and flexible.

When using multi-agitator mixers, process flexibility relies on your ability to control agitator speeds individually. But added flexibility also introduces new opportunities for error and inconsistency - unless you add a flexible control system, too. A robust multi-axis control system stores many product recipes for fast changeover. It also allows you to revise product recipes off-line and implement process improvements at any time.

By reducing operator contact with the equipment and the materials being mixed, the control system can also significantly improve plant safety. The control is best designed by the mixer manufacturer, since the logic for operation (and especially for safety) has already been developed. There is no need to start from scratch.

The mixing control system should be designed to handle your present mixing operation and provide ample of room for growth. It must interface with your present manufacturing information network as well as your future network. Allowing room for process evolution - anticipating expansion and process refinements that may be unclear now - is essential in building long-term value into your control system.


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