When pulverizing materials, a fundamental principle must be adhered to: "no over-crushing." During the pulverization process, balancing the feed rate and discharge rate of the pulverized material is crucial. Especially in continuous operation, the feed and discharge rates should not only be equal but also align with the pulverizer's processing capacity to maximize production. Retention of pulverized material within the pulverizer will impair pulverization efficiency. This is because retained pulverized material presents the potential for further pulverization, exceeding the required particle size and resulting in over-crushing, which wastes pulverizing power.
These over-crushed particles can surround un-crushed particles. The elastic cushioning created by these fine particles acts as a cushion, hindering proper pulverization and further reducing pulverization efficiency. This phenomenon is known as "blocked pulverization." In contrast, "free pulverization," which achieves high pulverization efficiency, relies on water or air flow to freely discharge the pulverized material, which has been pulverized to a specified size, from the pulverizer, allowing it to exit the pulverization process as quickly as possible.
There are three types of pulverization processes: intermittent, open-circuit, and closed-circuit. In intermittent pulverization, a certain amount of material is added to the pulverizer, the discharge port is closed, and the pulverizer operates continuously until all the material reaches the required particle size. The pulverizer then discharges the entire product. Intermittent pulverization is generally used for small-volume pulverization operations with finer particle size requirements.
In open-circuit pulverization, material is continuously added, and the resulting product is continuously discharged. The material passes through the pulverizer once (also known as continuous pulverization without screening), and the resulting product is controlled to a specific particle size. Open-circuit pulverization is simple to operate and is generally used for pulverization processes such as pre-crushing of materials before calcination. In closed-circuit pulverization, the material passes through the pulverizer once, and the pulverized particles are forcibly removed by a carrier fluid (air or water). Mechanical separation equipment then removes the particles that meet the required particle size, while the coarser, unqualified particles are returned to the pulverizer for further pulverization. Closed-circuit pulverization is a continuous, cyclical process that strictly adheres to the principle of "no over-pulverization."