Cage Crusher

Cage Crusher

The cage crusher—also known as a squirrel-cage crusher or cage mill—is a medium-sized horizontal pulverizer designed based on the principle of impact crushing. It utilizes two sets of cage bars (inner and outer) rotating at high speeds in opposite directions, causing material to be pulverized as it moves from the inside out and impacts the bars. The equipment is characterized by its simple structure, high crushing efficiency, excellent sealing, stable operation, and ease of cleaning and maintenance.

Cage crushers are widely used across industries such as mining, metallurgy, construction materials, chemicals, animal feed, food processing, pharmaceuticals, and plastics, primarily for pulverizing materials of low to moderate hardness. In the fertilizer industry, the cage crusher serves as an indispensable core component of compound and organic fertilizer production lines. It can pulverize various single-nutrient fertilizers with moisture content below 40% and is particularly effective for harder materials. Demonstrating exceptional crushing capabilities for hard granular materials—such as monoammonium phosphate (MAP), diammonium phosphate (DAP), and urea—it has earned the industry reputation as the "nemesis of hard granular materials."

The core value of the cage crusher in fertilizer processing lies in the dual advantages of "high-efficiency impact" and "self-impact pulverization." The machine repeatedly strikes the material with high-speed rotating cage bars while simultaneously causing material particles to collide with one another at high speeds due to centrifugal force; this creates a synergistic crushing effect where "steel bars strike the material" and "material strikes material." This unique mechanism allows the cage crusher to excel at processing caked fertilizers and agglomerated fermented organic matter, yielding a product with uniform fineness and no large impurities, thereby ensuring a reliable supply of raw materials for subsequent batching, mixing, and granulation processes.

Overall Structure and Core Components

The cage crusher features a scientifically sound, compact overall structure and consists primarily of the following core components:

(I) Frame and Housing System: Includes the machine base, frame, upper and lower housing sections, and cover plate. The base serves as the mounting foundation for the entire unit; constructed from welded structural steel, it offers a robust and stable structure. The housing fully encloses the crushing chamber, effectively preventing dust leakage.

(II) Dual-Cage Rotor System: This is the equipment's core working component, comprising a large cage assembly (outer cage/stator) and a small cage assembly (inner cage/rotor). Each cage consists of steel discs fixed to a hub; mounted on each disc are two or three concentric rings of steel rods positioned perpendicular to the disc. The free ends of the rods in each ring are secured by a steel hoop for added strength, and the rod rings of the two cages are interleaved. The crusher's specifications are defined by the diameter and length of the outermost cage ring.

(III) Transmission and Drive System: Includes two electric motors, pulleys, V-belts, main shafts, and bearing housings. During operation, one motor drives the large cage to rotate in one direction, while the other drives the small cage to rotate in the opposite direction. Each cage is mounted on its own shaft via a hub; the two shafts are independent yet aligned on the same axis. Each shaft is equipped with a pulley, allowing the two motors to drive the cages in counter-rotation via belt transmission.

(IV) Feeding and Discharge System: Includes the feed inlet (hopper) and discharge outlet. The inlet is located at the top of the housing, and the outlet at the bottom. Material enters the central area of ​​the counter-rotating cages through the inlet.

(V) Auxiliary Adjustment and Maintenance Mechanism: Includes a device to facilitate the installation and removal of the cage assemblies. A threaded rod is fixed at both ends to the side walls of the bearing housing, passing through a nut secured to the machine base; turning the handwheel at the left end of the rod causes the bearing frame—along with the bearings, shafts, and cages—to move horizontally across the base. This design greatly facilitates the inspection and replacement of the steel rods. Additionally, the equipment can be designed as a mobile unit to meet user requirements.

Applicable Fields and Industry Coverage

Cage crushers have an extremely wide range of applications.

Fertilizer production: Widely used for crushing organic minerals, compound fertilizers (both bulk and granular), and general fertilizer materials. It can crush various single-nutrient fertilizers with moisture content below 6% and is particularly effective for hard materials—making it ideal for processing hard granules such as monoammonium phosphate (MAP), diammonium phosphate (DAP), and urea.

Organic fertilizer production: Capable of crushing semi-wet organic materials—such as fermented livestock manure, straw, mushroom residue, and distillers' grains—and is suitable for both dry and wet materials.

Mining and construction materials: Suitable for crushing soft and brittle materials such as industrial slag, dry clay, shale, and medium-hard coal gangue.

Chemical and food industries: Widely used across sectors including chemicals, animal feed, food processing, pharmaceuticals, and plastics.

Types of usable raw materials

The cage crusher is capable of processing a wide variety of raw materials. Chemical fertilizer materials: caked raw materials such as urea, ammonium phosphates (MAP, DAP), potassium chloride, potassium sulfate, and various compound and mixed fertilizers. Organic materials: fermented organic matter such as decomposed livestock and poultry manure (chicken, pig, cattle, etc.), crop straw, mushroom residue, distillers' grains, sawdust, and humus soil. Industrial minerals: kaolin, pottery clay, bentonite, limestone, dolomite, etc. Other materials: pulverized coal, coke breeze, dry clay, shale, coal gangue, etc.

Operating Principle and Comminution Mechanism

The working principle of the cage mill is based on the synergistic effect of "high-speed counter-rotating impact crushing" (using dual cages) and "material self-impact crushing." Its operation involves three stages:

Feeding and coarse crushing stage: Material enters the center of the two counter-rotating cages through the feed inlet; as it is conveyed axially forward through the gap between the spiral feed sleeve and the machine base, it undergoes coarse crushing.

Multi-stage impact fine crushing stage: The coarsely crushed material enters the fine crushing zone. The material chunks first fall onto the innermost ring of steel rods; driven by the high-speed rotation of the cages, the material is shattered by violent impacts from the rods. Under the influence of centrifugal force, the material is thrown onto the next ring of steel rods (specifically, the innermost ring of the opposing cage), where it is struck from the opposite direction. Progressing stage by stage in this manner, the material passes through all the rings of steel rods, undergoing impact crushing at each ring.

Discharge stage: The material is crushed within the cage mill through three mechanisms: impact by the steel rods, inter-particle collisions, and impact against the inner wall of the machine casing. Once crushed, the material falls to the lower part of the casing and is discharged through the outlet. The optimal linear speed for the cages is 25–40 m/s.

Core Advantages and Performance Highlights

The cage crusher offers the following outstanding advantages: High crushing efficiency—dual cages rotate at high speeds in opposite directions, enabling multi-stage impact crushing in a very short time. Excellent sealing—a fully enclosed casing design effectively prevents dust leakage. Smooth operation—a coaxial dual-shaft design ensures stable and reliable performance. Easy maintenance—equipped with quick-opening access doors and a system for easy installation and removal of the cage assemblies. High proportion of fines—yields a high percentage of fine particles (≤0.2mm) with a high crushing ratio. High moisture tolerance—capable of processing materials with a moisture content of up to 40%. Simultaneous mixing and crushing—able to mix and crush multiple raw materials at the same time. No foundation required—can be placed directly on a flat surface for operation.