The Mikro ACM® - Air Classifying Mill requires air or gas for the conveying, size reduction and air classification of the product being processed. Air or gas is introduced to the Mikro ACM® - Air Classifying Mill via the main air inlet and the product inlet. As much as 30% of the total air volume can be introduced at the product inlet depending upon the application. Feed material is pneumatically conveyed under vacuum or mechanically conveyed by an auger, into the feed inlet of the mill along with the process air. Ideally, material is fed at a constant rate via a volumetric or gravimetric feeding device.
After passing through the feed inlet, material enters the grinding zone. At this point, material comes in contact with the face of the rotating hammers, where impact takes place and the material is fractured into smaller particles. Situated around the perimeter of the grinding chamber is a “multiple deflector liner”. This component assists in slowing the peripheral velocity of the product and deflecting it back into the hammer path for more efficient impact and size reduction.
The product is then conveyed upwards by the air stream through a shroud and baffle assembly that changes the direction of the product/air mixture while directing it to the classification zone. The shroud and baffle assembly also provides a separation of the mill internal area into two zones; a grinding zone and a classifying zone.
Once the product enters the classification zone, the particles are presented to the rotating classifier wheel, where based upon size and density, the particles either pass through the classifier or oversize particles are rejected and flow back to the grinding zone for additional size reduction. The processed product/air mixture then exits through the mill outlet.
There are two main parameters that are used to control and change particle cut point or maximum particle size; air volume through the mill and rotational speed of the classifier. The air flow through the mill generates a drag force to convey the particles to the classifier and the rotational speed of the classifier generates a centrifugal force that rejects the particles away from the classifier. When these two forces are equalized for a given particle mass, that particle has an equal probability of being accepted or rejected at the face of the classifier wheel. Based upon varying these opposing forces either through a change in air volume, or a change in classifier speed, the particle top size cut point can be controlled.
The grinding chamber of the ACM houses both the components of the classifying and grinding zones. They include the impact rotor and hammers, the liner assembly, the shroud and baffle assembly and the classifier wheel. The grinding chamber can be designed to operate to 10 bar(g) overpressure for explosive materials.
ROTOR & HAMMER OPTIONS
Rotors are normally supplied as single discs; however options include reduced diameter rotors for use with heavy duty liners, and rotor discs with replaceable wear plates for abrasive applications. Hammers are bolted to the rotor disc and can be easily removed and replaced. Options include:
- Bar Hammers — for fine size reduction and maximum impact.
- Pins — for producing coarse particle size distributions and to minimize the generation of fines.
- J-Style Hammers — for size reduction of fibrous materials.
Most Mikro ACM® - Air Classifying Mill systems use an advanced PLC and an Operator Interface Terminal (OIT) to monitor and control the system operation. The PLC allows various operating parameters to be set by using PID loops. The PID Set Points can be entered on the OIT and changed while processing your material to optimize the milling process. An automatic start/stop sequence is programmed to insure consistent, repeatable results, free from operator error.
The control cabinets are completely wired and contain all necessary components to effectively keep your system making a quality product. Equipment upstream and downstream of the mill is usually integrated into the control system.
- Speed Control — The Rotor and Classifier can each be controlled independently at specified speeds, insuring optimized milling and consistent particle size.
- Air Flow Control — A constant air flow rate is essential for maintaining proper particle size; therefore, the air flow is controlled independently.
- Feed Control — The speed of the feed metering device varies as a function of the rotor and/or classifier power so the system remains stable and operational at the maximum possible throughput.
- Temperature Control —The mill, inlet or outlet temperature can be monitored and controlled to heat or cool the material as it is processed.