Working Principle and Structure of the Double-Roll Crusher

The double-roll crusher is a commonly used type of roll crusher; its detailed structure is illustrated in Figure 2-31. Its crushing mechanism consists of a pair of cylindrical rollers mounted horizontally and parallel to each other on a machine frame. The front roller (1) and the rear roller rotate in opposite directions. Material is fed into the feed hopper (16) and falls onto the rotating rollers; under the influence of friction from the roller surfaces, the material is drawn into the gap between the rollers and crushed through compression. The crushed material is then pushed out by the rotating rollers and discharged downward. Consequently, the crusher operates continuously and features a forced discharge mechanism, ensuring that even sticky or wet materials can be crushed without causing blockages.

The rollers are mounted on a welded machine frame (3). Each roller consists of a roller core (4)—mounted on a shaft (11)—and a roller shell (7) fitted over the core. The core and shell are secured together via a tapered ring (6) and tightened with bolts (5), ensuring the shell fits snugly onto the core; the roller shell can be replaced once its working surface becomes worn. The shaft of the front roller is supported by roller bearings housed in bearing blocks (18) that are rigidly fixed to the machine frame. Conversely, the bearings (19) for the rear roller are mounted within guide rails on the frame, allowing them to move back and forth along the rails. The rear roller's bearings are pressed against a thrust block (12) by powerful springs (14). Should an uncrushable object fall between the rollers, the springs compress, causing the rear roller to retract a certain distance to allow the hard object to pass through; the roller then returns to its original position under the tension of the springs. The spring pressure can be adjusted using nuts (15). Replaceable steel shims (13) are placed between the bearings (19) and the thrust block (12), allowing the gap between the two rollers to be adjusted by simply swapping shims of different thicknesses.

The front roller is driven by an electric motor via a pulley (20), a transmission shaft (8), and a set of reduction gears (9 and 10). The rear roller is driven by the front roller through a pair of gears (17) mounted on the roller shafts, ensuring the two rollers rotate in opposite directions. To ensure that the gears remain engaged even when the rear roller retracts, the gears are designed with a non-standard, elongated tooth profile. Depending on operational requirements, the working surfaces of the rollers may be selected as smooth (e.g., the rear roller 2), grooved (e.g., the front roller 1), or toothed.

Smooth rollers primarily crush materials through compression; they are suitable for crushing medium-hard to hard materials. To enhance the crushing effect, the rotational speeds of the two rollers may be set to differ. In this configuration, an additional abrasive action is applied to the material; this is particularly suitable for the fine crushing of clay and plastic materials, resulting in a product with a small and uniform particle size.

Grooved rollers, featuring surface ridges, crush materials by applying both compressive and shearing forces. Consequently, they are suitable for crushing brittle or sticky-wet materials of relatively low strength. The resulting product features a uniform particle size. Furthermore, grooved rollers facilitate the "nipping" and drawing-in of material lumps; they are the preferred choice when a high crushing ratio is required.

Toothed rollers are illustrated in Figure 2-32. This type of roller is constructed by assembling a series of steel discs (1), each fitted with teeth (5). The steel discs are mounted onto the shaft (2) using keys (3), and bolts (4) are used to string the discs together and tighten them into a single, cohesive unit. When crushing materials, toothed rollers apply both compressive and splitting forces. Therefore, they are suitable for crushing soft, low-hardness, and brittle materials characterized by a laminar or blocky structure—such as coal, dry clay, and shale. The particle size of the crushed product is relatively uniform. Neither toothed nor grooved rollers are suitable for crushing hard materials.