Alpine TDG/TTG Twin Turbo Opposed Jet Mill

The Alpine TDG/TTG Twin Turbo Opposed Jet Mill is one of Hosokawa’s most advanced, efficient and accurate size reduction systems. It was designed using the same grinding principles as the Alpine AFG, but is able to achieve a tighter particle size distribution and high capacities.

A trend towards increasingly finer particle sizes is also noticeable with mass-produced products. At the same time, tight price limits demand increasingly efficient production. A good starting point to minimising the energy consumption is to reduce the pressure drop at the classifying wheel.

 •  Uses next generation single wheel TTC Classifier for ultra-fine grinding and high production rates •  High speed particle-to-particle milling with internal classifier •  Capable of milling down to D97 = 3 µm •  Energy efficient design; easy to operate and maintain •  Available in carbon steel, stainless steel or with wear protection •  Models available for pilot to production size systems •  Suitable for Chemicals, Toner, Cosmetics, Minerals, Pigments & Plastics

The TDG/TTG jet mill is equipped with a turbo twin classifier head that substantially reduces the pressure drop of the classification. In addition, the flow pattern in the turbo twin classifying wheel makes extremely fine classifying operations at high air flow rates possible. The classifying wheel is supported at both ends and permits very high speeds. This makes it possible to build exceedingly large jet mills with only one single classifying wheel.

In the case of jet milling, one takes advantage of the fact that as compressed gas exits a nozzle, it is accelerated to extremely high speeds. In expanding, the energy contained in the compressed gas in the form of heat is converted to kinetic energy. The speed of sound is initially a natural limit for the exit velocity. But by using Laval nozzles, the exit velocity can be increased to above the speed of sound. Laval nozzles are characterized by their hourglass shape, which widens downstream of the narrowest cross-sectional point, the nozzle throat. The length of the divergent part of the nozzle is adapted to suit the operating pressure. Compressed air of 20°C and 6 bar overpressure is frequently used as the grinding gas, and delivers nozzle exit speeds of around 500 m/s. As a result of drawing in gas and product from the fluidized bed, the speed of the gas jets sinks extremely rapidly after exiting the nozzles.

Comminution is a result of inter-particle collision in the jets of air and also in the core area, i.e. the point where the opposing jets intersect. Jet mills are impact mills which are used to achieve maximum fineness values. Such particle sizes can only be obtained in connection with an air classifying step. Spiral jet mills have a static air classifier integrated into the mill housing, whereas fluidized bed opposed jet mills are equipped with a dynamic deflector-wheel classifier. The fineness is set as a function of the classifying wheel speed. All-important is a high product loading of the nozzle jets in order to achieve a high concentration of particles and thus high impact probabilities.

The patented Megajet nozzles were developed with this in mind. They consist of four small nozzles which as a result of their close proximity generate an under-pressure at their common center, and thus draw particles from the fluidized bed direct into the center of the nozzle jet. The product level in the machine is controlled by means of load cells or by monitoring the current loading of the classifier drive.



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