Cone Crushers for Secondary and Tertiary Crushing
Cone crushers, often referred to as Symons cone crushers, were initially developed by Symons in the 1920s. These crushers operate in a manner similar to gyratory crushers, with a few design differences. Unlike larger gyratory crushers where the spindle is suspended, cone crushers have the spindle supported at the bottom of the gyrating cone. Figure 5.3 depicts a schematic diagram of a cone crusher.
The crushing head gyrates within an inverted truncated cone. These crushers are designed with a head-to-depth ratio larger than standard gyratory crushers, resulting in flatter cone angles. The mantle and concaves slope parallel to each other, facilitating longer particle retention between the crushing surfaces and thus generating finer particles. To safeguard the crushing surfaces from damage, strong springs or hydraulics hold the concave or shell of the crushers in place, yielding to allow uncrushable tramp material to pass through.
The secondary crushers are classified as Standard cone crushers, equipped with stepped liners, and tertiary Short Head cone crushers, featuring smoother crushing surfaces and steeper cone angles on the breaking head. The size of the cone crushers is indicated by the approximate distance of the annular space at the discharge end. Table 5.4 provides a concise overview of the design characteristics for crusher operation in open-circuit and closed-circuit scenarios.
Design Characteristics Open Circuit Closed Circuit
Maximum Minimum Maximum Minimum
Size (mm) 3050 600 3050 600
Crusher chamber size range (mm)* 76–432 25–76 76–178 25–51
Discharge setting (closed side) 22–38.1 6.4–15.8 6.4–19 3.2
Power (kW) 300–500 25–30 300–500 25–30
Chamber sizes vary between three and six numbers within a specific designated crusher size to produce fine, medium, or coarse-sized product.
The Standard cone crushers are ideal for regular applications, while the Short Head cone crushers are specifically designed for tertiary or quaternary crushing, where a finer product is desired. These crushers are predominantly operated in closed circuit. The final product sizes range from fine to medium or coarse, depending on the closed set spacing, crushing chamber configuration, and classifier performance, which is always installed in parallel.
For even finer product sizes, typically below 6 mm, specialized cone crushers called Gyradisc crushers are available. These crushers operate similarly to standard cone crushers but rely more on attrition rather than impact for size reduction . The reduction ratio averages around 8:1, and due to the relatively small product size, the feed size is limited to less than 50 mm with a nip angle between 25° and 30°. Gyradisc crushers feature head diameters ranging from approximately 900 to 2100 mm. These crushers are always operated under choke feed conditions, with a feed size of less than 50 mm, resulting in a product size typically less than 6–9 mm.