The selection of the primary crusher is a critical decision in the design of a crushing plant, as it sets the stage for subsequent crushing and processing steps. Sources cite several factors that influence this selection:
Material Properties
Rock Type and Hardness: The hardness and abrasiveness of the material play a key role in selecting the appropriate crusher. Jaw crushers are commonly used in primary crushing for a wide range of materials, offering high reduction ratios and a heavy-duty design. For very hard and abrasive rocks, gyratory crushers are preferred due to their robust design and consistent performance. On the other hand, impact crushers are better suited for softer, less abrasive materials where fines production is not a concern. They are known for their high reduction ratios and can sometimes eliminate the need for a third crushing stage.
Feed size: The maximum feed size, often determined by the blasting process, directly influences the selection of the primary crusher. Jaw crushers offer a better return on investment in terms of feed size, allowing for larger rock sizes and reducing drilling and blasting costs. However, gyratory crushers have a larger discharge opening, which allows for higher capacities compared to jaw crushers. Impact crushers are also designed to accept large feed sizes, with some models handling up to 1830 mm (71 in).
Crushing and Abrasion: Sources emphasize that material properties such as crushing and abrasion are the primary selection criteria. Impact crushers excel in high-crushing, low-abrasion applications typically found in soft rock. Compression crushers (jaw and gyratory) are more versatile and perform well in a variety of rock types, including hard and abrasive materials. As previously discussed, harder materials with lower crushing capabilities directly affect the crusher’s throughput capacity.
Capacity and Production Requirements
Desired efficiency: The capacity required by the plant is the main factor. Jaw crushers are typically used in plants with capacities up to 1600 tph. For higher capacity demands (1200 tph and above), primary gyratory crushers are more suitable due to their continuous operation and larger discharge area. Impact crushers can handle a wide range of capacities from 200 tph to 1900 tph.
Reduction ratio: The desired reduction ratio, which is the ratio of feed size to product size, also influences crusher selection. Achieving a specific reduction may require multiple crushing stages. Impact crushers are known for their high reduction ratios, potentially reducing the number of crushing stages required.
Product quality and shape: The desired quality and shape of the crushed product can also be a factor. Impact crushers are generally known to produce a more cubic product than either jaw or gyratory crushers. However, achieving specific shape requirements may involve the use of other crushers such as cone crushers or vertical shaft impactors in later stages.
Economic considerations
Investment costs: The initial investment cost of a crusher is a major consideration. Jaw crushers are generally less expensive than gyratory crushers, especially for smaller capacities.
Operating costs: Operating costs, including energy consumption, wear parts, and maintenance, must be considered.
Overall process costs: The selection of a primary crusher should be evaluated in the context of overall process costs, including drilling, blasting, loading, and transportation. In some cases, mobile primary crushers can be a more economical solution due to reduced transportation costs. Using a larger primary crusher, although requiring a higher initial investment, can result in savings in drilling and blasting due to the ability to handle larger feed sizes.
Operational considerations
Maintenance and access: Ease of maintenance and access for replacement of wear parts must be considered. Jaw crushers are generally robust and require less maintenance.
Feed and material flow control: Constant feed control is important for optimal crusher performance. Gyratory crushers are known for their consistent performance and ability to handle feed fluctuations, but they require precise control of material flow.
Space requirements and foundation: The available and required foundation space can also affect crusher selection. Primary gyratory crushers require a more substantial foundation than jaw crushers.
Primary crusher selection should not be based solely on calculations, but should also consider practical experience, operational factors, and specific application requirements.
