Cone Crushers for Secondary and Tertiary Crushing
Cone crushers, commonly referred to as Symons cone crushers, were first developed by Symons in the 1920s. These crushers operate similarly to gyratory crushers with a few design differences. Unlike larger gyratory crushers, the shaft here is not suspended; the cone crusher’s shaft is supported at the bottom of the rotating cone. Figure 5.3 shows a schematic diagram of a cone crusher.
The crushing head rotates inside an inverted truncated cone. These crushers are designed to have a larger head-to-depth ratio than standard gyratory crushers, which means more horizontal cone angles. The mantle and concaves are sloped parallel to each other, allowing longer particle retention between the crushing surfaces, resulting in finer particles. To prevent damage to the crushing surfaces, strong springs or hydraulics hold the crusher’s concave or shell in place and flex to allow uncrushable foreign materials to pass through.
Secondary crushers are classified as Standard cone crushers equipped with stepped liners and Short Head cone crushers with steeper cone angles and smoother crushing surfaces for tertiary crushing. The size of cone crushers is indicated by the approximate distance of the ring gap at the discharge end. Table 5.4 provides a brief summary of design features for crusher operation in open and closed circuit scenarios.
| Design Features | 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 to six numbers within a specific crusher size to produce fine, medium, or coarse product sizes.
Standard cone crushers are ideal for regular applications, while Short Head cone crushers are specifically designed for tertiary or quaternary crushing where a finer product is desired. These crushers mostly operate in closed circuit. Final product sizes vary between fine, medium, or coarse depending on the closed set range, crusher chamber configuration, and the classifier performance always installed in parallel.
For even finer product sizes, typically below 6 mm, special cone crushers called Gyradisc crushers are available. These crushers operate like standard cone crushers but rely more on abrasion than impact for size reduction [5]. The reduction ratio is around 8:1 on average, and due to the relatively small product size, the feed size is less than 50 mm with a nip angle between 25° and 30°. Gyradisc crushers have head diameters ranging approximately from 900 to 2100 mm. These crushers always operate under choke feed conditions; the feed size is less than 50 mm and the product size is generally smaller than 6–9 mm.
