Hammer mill (technology)
A hammer mill (also known as a hammer mill ) can grind different materials to different degrees of coarseness, but is mainly used for the comminution of highly heterogeneous material mixtures. Machines based on the same principle, which only roughly break the material, are called hammer crushers .
functionality
The grinding material is crushed by kinetic impact and impact crushing . In a metal housing, a rotor an application specific number of moving spins, at its outer periphery steel - hammers are mounted, the peripheral speeds can reach 120 m / s up. The rotor is usually driven directly by a motor and is housed with the hammers in a housing that contains a sieve inside. When entering the perimeter of the rotor, the ground material hits the rotating hammers. The greatest crushing effect is achieved by the impact of the hammers. The hammers also throw the pieces onto the grinding wall, where they are further broken by the impact.
Further comminution takes place by impact in the lower area between the rotor and the grinding wall. The ground material remains in the grinding chamber until it is so small that it fits through a perforated sieve on the outer circumference of the machine. This sieve has the function of limiting the maximum grain size; the maximum grain size can be set by replacing the sieve. A separation into several factions is not possible here.
The direction of rotation of the rotor can be changed (reversing) by means of grinding walls arranged on both sides. This makes it possible to optimally utilize the hammer heads in terms of wear .
After a small gap, there is usually a conical outlet at the bottom , which is directly connected to a pneumatic suction system (usually with an alphorn ). The ground product is sucked off with the suction pneumatics directly below the hammer mill, which also ensures that the machine is cooled (through air flow). This is very important for the grinding quality and the machine.
Peripheral speed
The beaters of hammer mills in feed mills reach an average circumferential speed of between 60 and 120 m / s. The speed can be varied and is selected depending on the grist (oats, wheat, corn, etc.) and the desired throughput. The higher the peripheral speed, the finer the granulation and the higher the energy requirement; in addition, the throughput decreases.
Throughput
The throughput depends heavily on the product properties (type, moisture) of the grist. With identical product moisture and constant machine settings, for example, 1500 kg / h can be achieved for oats, while it is 3000 kg / h for barley, 4500 kg / h for wheat and 6000 kg / h for corn.
commitment
Hammer mills are used as grain and feed mills , in the food industry , to shred wood waste , plastic waste , etc.
When used in the recycling industry , the focus is on breaking up material mixtures and less on shredding. The advantage lies in the comminution of the different material mixtures, as a preliminary stage to a subsequent sorting separation. For example, a material mixture of plastic and soft metals ( aluminum , copper ) can be broken up in such a way that it can then be separated according to specific weight on separating devices. Typical applications are refrigerator preparation and electrical and electronic scrap processing .
When used in a coal-fired power station , coal , limestone and gypsum stones as well as minerals and salts are crushed.
In the wood pellet industry , hammer mills are used to grind saw by-products, such as sawdust, wood shavings and industrial wood chips, and use them to produce wood pellets.
literature
- Günter Kunze: Construction machinery . Vieweg + Teubner Verlag, Wiesbaden 2002, ISBN 3-528-06628-8 , pp. 360 .
Web links
Individual evidence
- ↑ a b c Peter Erling (Ed.): Compound feed production - raw materials, processes, technology . Agrimedia, Bergen / Dumme 2004, ISBN 3-86037-233-5 , p. 203 ff .