What Is a Dry Grinder?
A dry grinder refers to a machine that performs grinding operations in the presence of air or other gases.
Most coarse crushers, impact mills, and jet mills, among others, employ dry grinding techniques. While dry grinding may exhibit lower efficiency compared to wet grinding, it involves minimal wear and is easy to handle. Mechanochemical phenomena and effects are readily achieved through dry grinding, allowing for the reduction of materials to sub-micron sizes.
Uses of Dry Grinder
Dry grinders are utilized in a wide range of industries, including food, pharmaceuticals, ceramics, minerals, metals, etc., where material grinding is desired in a dry state.
- Ceramic Raw Materials
Used in the grinding process to enhance product characteristics. - Pharmaceuticals
Employed in the manufacturing process to increase absorption efficiency through size reduction. - Battery Materials
Utilized in the manufacturing process of lithium-ion batteries to improve product characteristics. - Recycling
Used to enhance the recovery rate of specific materials through grinding.
Principles of Dry Grinder
The principle of a dry grinder involves the pulverization of the target material through forces such as collision, friction, compression, shear, and cutting. Various principles lead to diverse machine types.
For example, collision between rotating bodies and the target material, collision and shear between beads or balls stirred rapidly, and collision between target materials in high-speed airflow contribute to the grinding process. Dry grinding is known to achieve fine reduction down to approximately 1 μm.
Types of Dry Grinders
Dry grinders are broadly categorized into two types: ultrafine grinders, fine grinders, medium grinders, and coarse grinders.
1. Ultrafine Grinders
A model under ultrafine grinders is the bead mill. This machine fills the container with beads (media), rotates the agitator to induce collisions, and uses shear force to grind the raw material into sub-micron particles.
2. Fine Grinders
Representative models of fine grinders include the following seven:
Roller Mill
Compressed grinding of materials between rotating rollers and subsequent particle discharge through airflow.
Jet Mill
High-pressure compressed air or gas is ejected through nozzles, accelerating material particles to cause collisions, impact, and abrasion, resulting in grinding.
High-Speed Rotational Grinder (Hammer Mill)
Impacting particles with high-speed rotating hammers for grinding. The hammers are of the swinging type. A screen mill control is often used for product size control.
High-Speed Rotational Grinder (Pin Mill)
Using pins on opposing surfaces of two rotating disks to crush and grind material.
Container-Driven Mill (Rotational Mill)
Rotate a cylinder filled with grinding media (balls, rods, etc.) around a horizontal axis to grind materials.
Container-Driven Mill (Vibration Mill)
Filling a cylindrical or trough-shaped mill with grinding media (balls, etc.), applying vibration to the mill, and grinding through media movement.
Container-Driven Mill (Planetary Mill)
Using a mechanism where a container filled with balls revolves while rotating around its axis, grinding material through collisions between media and between media and the container walls.
3. Medium Grinders
Representative models of medium grinders include the following nine:
Cone Crusher
Improved for medium and fine crushing from a gyratory crusher, featuring larger amplitude and rotational speed. Mainly crushes through compressive force and partly through shear force.
Roll Crusher
Two rolls rotating in opposite directions crush ores primarily through compressive force and partially through shear force.
Cutter Mill
Crushes and grinds through shear force or cutting force. Features a rotor with sharp cutters rotating at high speed.
Autogenous Mill
Consists of a short barrel-shaped drum where the feed material experiences a long drop. Material reduction occurs through collisions and rubbing between particles inside the rotating drum. Finely ground material is typically ejected using an air-swept method.
Stamp Mill
Drops impact bars in a mortar-like fashion, crushing and grinding materials. It is simple in structure but provides strong force. Additionally, it performs mixing and stirring of crushed materials, making it suitable for both batch and continuous operations.
Burr Mill
Material is crushed by the shear force generated between two rotating grinding stones.
Mortar and Pestle
Used for crushing, grinding, and uniform mixing of two or more solids.
Attrition Mill
Similar to a mortar and pestle, it crushes and grinds materials through a combination of attrition and compression, achieving grinding and mixing or kneading.
Ring Mill
Rotating around a ring-shaped grinding chamber, a mechanism applies compressive and shear forces to grind materials. The rotating body can be rollers, balls, or cones, utilizing gravity, centrifugal force, springs, etc., to generate pressure.
4. Coarse Grinders
Representative models of coarse grinders include the following three:
Jaw Crusher
Compresses and crushes materials between a vertically fixed jaw and a swinging jaw that moves back and forth.
Gyratory Crusher
Includes a concave interior with a cone-shaped mantle. As the eccentrically rotating mantle moves, it compresses and crushes material against the concave.
Impact Crusher
Features a rapidly rotating cylindrical rotor with impact plates. Ore is crushed by the impact and, additionally, thrown onto fixed rebound plates for further grinding.
How to Choose a Dry Grinder
There are various types of dry grinders with different grinding methods and machinery.
Considerations for choosing the right conditions and machinery include how finely the material needs to be ground, running costs, contamination concerns, and the intended purpose.