Spiral jet mills are frequently used in the pharmaceuticals industry and also for the manufacture of fine-grade chemicals.
Because the Aeroplex spiral jet mills AS have no rotating components, there are consequently no bearings and shaft seals, and thus no lubricants are used. Contamination from these sources is therefore impossible.
The simple geometry of the mill components makes them easy to clean and also permits sterilisation of the entire mill.
The grinding air is injected tangentially via Laval nozzles in the nozzle ring into the machine. This causes a spiral jet of air to form in the grinding zone, from which the mill derives its name. A high pressure forms in the mill as a result of the spiral flow of air that can rise to 1 bar overpressure in operation without product. The integrated injector is charged with compressed air which ensures that the product is conveyed into the machine against the overpressure present in the machine. This, however, is associated with a considerable compressed air consumption, which can be as much as 30% of the total grinding air requirement.
The feed product circulates close to the nozzle ring and is thus intercepted repeatedly by the air jets exiting the nozzles. Comminution is the result of interparticle collision caused by the particles flowing at different speeds in the nozzle jet. Comminuted material is conveyed along with the air to the discharge, the spiral flow subjects the particles to a classification: only fine particles are discharged, coarse particles remain in the mill.
Alpine's spiral jet mills are characterised by a special geometry of the mill housing in the area of the discharge, which contributes towards a finer classification effect and a sharp top cut.
The product also has an effect on the air flow within the machine: the more product there is in the machine, the more the spiral flow is braked and the lower is the centrifugal force and the coarser the end product. The relationship of the product to the classifying air flow rate is therefore the most significant parameter for setting the fineness of the spiral jet mill. In principle, different nozzle angles can also be used to achieve the required fineness values, whereby the complete nozzle ring must be exchanged in this case.
Ultrafine size reduction of dry materials with a crystalline structure up to a Mohs' hardness of 3. Alpine jet mills are used predominantly for high-grade pharmaceutical products, e.g. antibiotics or fine-grade chemicals, especially when high demands are made of the purity and fineness of the end products. The most common requirements at a max. feed size of approx. 1.5 mm are end-product fineness values with a d97 ranging between approx. 5 and 30 µm.