Fine grinding material relies primarily on impact to reduce particles by creating stress that causes particles to fracture into a desired size range. These effects result from impact with both stationary and moving implements within the milling machine and collisions between particles. When utilizing impact to reduce any material, it’s the particles’ kinetic energy that assists with breaking down the material to its requisite consistency. Fine grinding mills are mostly used with free-flowing, dry material, creating stress that reduces bulk products into very narrow particle size distributions. Fine grinders can reduce a wide array of materials and often fulfill an integral purpose for any industry that depends on bulk material processing and particle size reduction within a narrow range.
How Fine Grinders Aid Processing
Fine grinders employ blade collisions within the mill and interactions with other particles to diminish the quantity of exceedingly fine particles in the material while simultaneously reducing larger ones. Often utilized to reduce fineness in bulk solids, fine grinders use a striking force to take advantage of physical irregularities within the material to separate particles at their weak spots, breaking them down to a certain point while keeping them from becoming too fine for the application.
Generally, fine grinders produce particles between 73 to 150 microns (about 200 to 100 mesh), while also producing an especially narrow particle size distribution. Best suited for dry and flaky material that flows freely, fine grinders make particles more uniform, with changes in particle size often exhibiting deviations in the coloring and texture of the material. When determining the particle size distribution for fine grinding, processors define the coarsest and finest particles, along with a median size, most desirable for the application. The characteristics achieved by fine grinders also contribute to a more consistent final product.
Operating Principles of Fine Grinders
Fine grinders, which are essentially simple impact mills, utilize a high-speed rotor and stationary implements to grind particles within a narrow size distribution mechanically. Prater's fine grinders have a fixed clearance, while the median size is adjusted through screens, feed rate, airflow, and rotor speed. The finest particles travel only a short distance in the mill's airflow, so there should be minimal space between the moving and stationary grinding implements, typically just a few millimeters (around a tenth of an inch) at most. Properly sized particles pass through the fine grinder's screen frame, which closely interacts with the fixed tooling where particles make contact.
The grinding zone of the mill, shaped like a disc, receives material fed from the center and migrates radially across the disc. This cylindrical grinding area allows the feed material to traverse the surface of the cylinder as it moves through the mill. Once particles reach the desired size, they are pulled through the openings in the screen and proceed to the next processing stage.
Reasons to Use Fine Grinders
When it comes to separation, or segregation of a mix often happens when bulk solids are being stored in hoppers or moved in convey systems. The mechanism of segregation is propagated by differences in particle size, shape and density. By action of size reduction, fine grinders can achieve greater uniformity of these traits, thus reducing the change of segregation.
The advantages of fine grinders in material processing include:
- Boosting reactivity of product.
- Delivering extremely uniform distributions of particle size.
- Expanding surface area to enhance various material properties.
- Increasing the rate at which a material absorbs liquids.
- Intensifying a product’s colors, particularly when it comes to powder coatings, dyes, and paints.
- Making sweet ingredients like sugar taste sweeter.
- Usually offering the best option for materials that are sensitive to heat, such as resins or sugars.
Fine grinders can produce even finer particles when paired with an air classifier.
Applications for Fine Grinders
Fine grinders are useful for numerous applications that require intense grinding.
Products that benefit from processing with fine grinders include:
- Calcium carbonate
- Copper sulfate
- Corn meal and starch
- Epoxy resin
- Sugars of varying grades
Many other organic and inorganic products can be processed with fine grinders.
Key Takeaways About Fine Grinders
Manufacturers who work with free-flowing bulk solids will find the most uses for fine grinders. They aid processing facilities in turning out end products with very narrow particle size distributions, affecting consistency and coloring. Reducing material via impact, fine grinders use both moving and stationary implements within them, along with collisions between particles, to break down material uniformly. Used for a wide range of material processing applications, they have numerous advantages over other particle reduction equipment, enhancing many physical and chemical properties.