Particle Size Reduction Equipment
Attritors are the most efficient particle size reduction equipment. Their unique construction allows for savings in efficiency and operational costs.
The process is simple: feed material is placed with the grinding media in a stationary tank, and a rotating shaft with arms then agitates the material and media. Efficiencies are created because the power input is used directly for agitating the media to achieve grinding and not for rotating or vibrating a large, heavy tank in addition to the media.
Attrition occurs with very little wear to the tank walls, leading to longer vessel life and contributing to further cost reductions.
As the shaft rotates within the tank, it forces the media into continual, random movements, creating impact forces, while the rotation of the media creates shearing forces. This combination of impact and shearing forces efficiently creates a homogenous dispersion and mills the material to a particle size in the low micron and nano-size range.
Besides fast and efficient grinding, other Attritor advantages include:
- Simplicity and safety of operation
- Low power consumption
- Excellent temperature control
- Low maintenance
Attritors are well-suited for handling a wide range of materials, whether they’re friable or nonfriable, fibrous, sticky or temperature sensitive, as well as materials that are harder to grind, like metal powders, metal carbide and glass frits. The grinding mills can simultaneously perform several processes, such as:
- Particle size reduction
- Mixing and milling chemicals to form new compounds
- Activating or liberating chemical raw materials
Attritors also can be tailored to meet specific needs:
- A blanket of inert gas can be incorporated to process materials prone to easy oxidation.
- Cryogenic mills are available for materials that aren’t friable.
- Specialty grinders are designed for processing chocolate, lime slaking or grinding limestone.
If inert, contamination-free grinding is required, the mill contact parts and grinding media can be manufactured from various types of stainless steel or ceramics.
Attritors are available in three basic configurations:
Batch – A jacketed vessel is filled with grinding media and feed material, with no premixing required. Hot or cold water or steam is used to control the temperature. Production-size batch mills often incorporate a built-in pumping system that maintains circulation during grinding for accelerated attrition and uniformity.
Continuous - A premixed slurry is pumped once through the bottom of a tall, narrow, jacketed tank and then discharged at the top with grids in place to retain the media. This is best suited for continuously processing large production quantities.
Circulation – This is a combination of an Attritor and a much larger holding tank, in which the Attritor is filled with grinding media and the contents of the holding tank pass through the Attritor at a high circulation rate, about eight times per hour. It can process large quantities of material with a smaller investment in grinding media and equipment.
Attritors are available as dry grinding, which creates particle sizes of 2-3 microns or larger, or wet grinding, which generates smaller particle sizes, down to the nano level.
Union Process’s dry milling production-size Attritors are the “SD” Series Batch/Continuous Attritors and the “HSA” Series Continuous Attritors; lab-size continuous mills and batch/continuous mills are also available.
Wet grinding Attritors are available in three production-size lines:
And two lab models: