Skako A/S unveiled the Rotoconix Mixer at the 2013 bauma trade fair earlier this year, arriving in Munich with 750-liter model, and adding 1500- and 2250-liter models since. Available in North America through Skako Inc., the Rotoconix affords three mixing methods working in sync within one vessel, all combining to give end users faster cycle times, the most flexible batch size and cementitious material savings. The three mixing methods:
Reversible Turbo Whirler
The turbo “whirler” or agitator is a reversible, variable speed mixing tool in a conical vessel, and enables the dispersal of agglomerated fine particles such as sand and cement. The action of breaking down the agglomerated material activates a greater proportion of the binder; as a result the batch quantity of cementitious materials can be reduced. Agglomerate dispersion in the fine particles with air included also increases the density of the mixture and releases water from the material. This water liquefies the mixture, allowing a reduction of water in the mix design thus reducing the required binder.
The introduction of water and liquid admixtures or coloring agents in the axis of the vortex generated by the high speed tool achieves a rapid penetration and dispersion into the heart of the mixture, despite the difference in density. The multipurpose design of the tool also creates very efficient mixing at lower speeds, a mode that likewise applies when the mix is in a fluid phase. Its vertical geometry and bidirectional rotation avoids any build up after the discharge.
This feature homogenizes dispersed elements and provides vertical movement of the mixture. It lifts the materials up, working throughout the entire height of the cone during the mixing cycle, a process that ensures optimum mixing efficiency regardless of the filling height. The reversible screw allows the Rotoconix to mix batch size down to 10 percent of its maximum capacity as efficiently as it does any other batch size. Maximizing batch size efficiency allows a production facility to operate with only one mixer instead of requiring one large and one small mixer.
The design of the screw tool, combined with the ability to reverse its rotation, prevents build-up of material during mixing and discharge, and nets faster mix transfer.
This component feeds the whirler and screw with the solid constituents that are normally out of the mixing zone. The rotation direction and speed are optimized with the use of variable frequency drive control to suit all mix designs, hence feeding the mixing tools effectively in all cycles. This creates homogenous mixes and extends cone wear plate service life. The cone scraper is fixed, allowing for easy adjustment. The scraper works with the rotation of the cone against the fixed scraper itself. Running the cone in the reverse direction during mixing has the effect of clearing all material build up that may occur.
The Rotoconix discharge gate rotates with the cone and will rise into a closed position ensuring a tight seal. Thanks to the rotating cone, a microwave or resistive sensor to measure moisture content can be easily set on the fixed frame and immersed in the rotating cone for precise measurement. The consistency of a fluid mixture can also be evaluated and adjusted by means of power consumption measurement of the high speed tool. This value is given precisely by the frequency inverter and can be measured at different speeds to take into account Bingham fluid behavior of self-consolidating concrete or other high slump mixes.
The new model embodies three synchronized mixing methods for flexibility, speed and binder efficiency across a wide range of concrete mixtures.
The cone geometry helps to achieve a total emptying batch to batch. Combined with the mixing tools’ anti-retention design, it allows a succession of different mix designs without impairing the quality. A rapid discharge augments cycle time gain regardless of mixture consistency; vertical discharge without segregation is an advantage as the mixture is not directed horizontally onto a chute, which operators would then need to clean. Partial opening of the discharge gate is possible to regulate the flow during discharge.
The mixer has a small footprint, allowing for flexibility in plant placement, and the overall height is minimal as the concrete chute function is integrated in the cone. The speed variation of the two tools and cone makes the Rotoconix suited to mix all types of concrete, Skako officials note, adding that operators can easily adjust the speed of the tool to suit the type of mix required and reverse rotation to reduce material build up.
Whirler speed will be very high for mixing fine elements with low water content for dispersing clusters, as in face mixes or those with fine or ultra fine aggregate only (ultra high performance concrete), or refractory concrete. Speed will be reduced during cohesive phase to better mix the paste. When the mixture becomes fluid or exhibits self-consolidating properties, speed is further reduced for a more efficient mixing. If large size particles are used in the mix, the speed is adjusted to the lowest value to avoid excessive wear.
The design is ergonomic, robust and reliable, product engineers note: A wide, liftable cover exposes around 30 percent of the upper cone surface, allowing access for cleaning. Internal and external mixer surfaces are smooth for easy cleaning as well. Mechanical components, turntable gears and geared motors are oversized and accessible while being protected from build up by covers.
The rotating cone feeds the Rotoconix whirler and screw materials normally out of the mixing zone. A variable frequency drive control optimizes direction and speed.
Start and reverse rotation of the mixer at full load is achieved by frequency inverters, which reduces power consumption and cable size. A soft starter feature eliminates heavy start up loads on mechanical components. If the mixing effort becomes greater than the nominal effort—during a very “sticky” phase of the mixing process, for example—the speed is automatically reduced. Component longevity is therefore ensured, and automatic lubricators are programmed to activate at annual intervals.
The Rotoconix mixer is available with an automatic wash system, including a pneumatically operated wash head with two nozzles on a tilting arm. Its automation system and frequency inverters allow for innumerable combinations of mixing effects to cater for just the specific concrete quality the producer wants to offer, e.g. rpm (speed) of each tool, duration until reversal of rotation. — Skako Inc., San Diego, 858/271-1630; www.skakous.com