Spiral Jet Mills and
Fluidised Bed Opposed Jet Mills

Jet mills (also called air jet mills) have a special feature: they do not need mechanical grinding tools. Instead, the particles are crushed and ground in a gas stream by repeatedly colliding with each other there. Jet mills are an excellent choice in industry when ultra-fine grinding is required. They are suitable for dry and very hard materials and it is possible to achieve finenesses down to d₉₇ = 1 µm with them.

In a jet mill, the grinding gas (usually compressed air) is fed into the grinding chamber through special nozzles and accelerated so strongly that the particles are entrained. In the process, the particles repeatedly collide with each other and are thus comminuted. A big advantage of this type of mill: because there are no mechanical grinding tools with which the particles come into contact, there is no wear. This is why jet mills are excellent for very hard materials or materials that have to be as pure as possible. In a downstream cyclone separator or dust filter, the finely ground material is separated from the grinding gas.

Jet mills are used for industrial powder production, for example for mineral flour, talc, silica or pesticide. In the pharmaceutical and laboratory sector, medicines are a popular application due to the low contamination.

The most common type of jet mill is the spiral jet mill, in which the nozzles are arranged around the grinding chamber in such a way that the flow of the grinding gas spreads out in a spiral. The particles are then comminuted by mutual particle impacts. With the Aeroplex AS, Hosokawa Alpine has a spiral jet mill in its product range that is primarily used for high-quality pharmaceutical substances, e.g. antibiotics or fine chemicals. This is because the high demands on the purity and fineness of the products can be excellently implemented with this mill.

The fluidised bed opposed jet mill is the second most common type of jet mill. In this mill, the material to be ground is fed via a feed sluice. A product fluidised bed then forms in the grinding chamber, which is fluidised by the gas jets. From there, the particles enter the gas jets and are accelerated. They collide with each other again and again and are thus comminuted. A classifier wheel rejects those particles that are still too large and transports them back into the fluidised bed. The particles that are fine enough are separated from the grinding gas by a separator or dust filter. Fluidised bed opposed jet mills are also suitable for very hard products such as minerals, glass or ceramics. Temperature-sensitive products such as toner or wax can also be ground with them.

Hosokawa Alpine offers three different fluidised bed opposed jet mills:

• The TDG is a fluidised bed opposed jet mill with integrated high-performance classifier. With this system, Hosokawa Alpine sets new standards and achieves finenesses of up to d₉₇ = 1 μm in the dry grinding of powders.
• The AFG is suitable for the production of powders with a steep particle size distribution and sharp top size limitation in the range < 5 µm – 200 µm. Even "difficult" products such as heat-sensitive materials or high-purity materials can be produced economically with it.
• The fluidised bed opposed jet mill TFG is a variant of the fluidised bed counter jet mill AFG adapted to suit the special requirements of the toner, powder coating and pigment industry.

Do you want to relieve bottlenecks in production? Do you have a project with a defined end? Or you are not yet sure whether the classifier you have chosen is really the right one for your products? In these cases, a rental machine may be the right solution for you. Just get in touch with us!

Another alternative is a used machine, giving you attractive prices combined with the proven Hosokawa Alpine quality. Our Hosokawa Alpine Originals are overhauled with original parts and can also be adapted to your specific needs. We will be happy to help you.