Understanding the crushing stages and the type of crusher best suited to each stage can simplify equipment selection. Each type of crusher is different and is used to achieve a specific end result.
Similarly, it is expected that at the end of each crushing stage a certain throughput is provided for the next stage of the process. Aggregate producers who pair the right crusher with the right stage will be the most efficient and, in turn, the most profitable.
Most crushers used for aggregate production fall into one of three main categories/types:
Compressive crushers – which squeeze the material until it breaks
Impact crushers – which use the principle of rapid impact to shatter the material
Attrition crushers – which use both impact and grinding to shear the material.
Jaw crushers, cone crushers, gyratory crushers, and roll crushers all operate on the compression principle. Impact crushers utilize the impact principle, while hammermill crushers follow the principle of attrition.
Most aggregate producers are very familiar with the selection of crushing plants and know that equipment can be selected based on specification sheets and gradation calculations alone. Nevertheless, theoretical conclusions must always be weighed against the material at hand and practical experience of the operational, maintenance, and economic aspects of the different solutions.
Usually, the material reduction is carried out in stages. There are some single crusher systems, but the most common systems involve at least two or three crushing stages.
The primary task of the coarse crusher is to make it possible to transport the material on a conveyor belt. In most aggregate crushing plants, primary crushing is carried out in a jaw crusher, although rotary primary crushers can also be used. If the material is easily crushed and not excessively worn, then an impact crusher may also be the best choice.
The most important characteristics of a coarse crusher are capacity and the ability to accept raw material without clogging. Large primary crushers are more expensive to purchase than smaller machines. For this reason, the investment cost calculation for a primary crusher is weighed against the cost of blasting the raw material to a smaller size.
In most cases, trucks deliver the raw material to a fixed primary plant. The costs of fuel, tyres, maintenance, and return on investment should also be considered.
Where producers crush at the quarry, a pit-mounted portable coarse crusher may be an economically sensible solution. In modern plants, it is often advantageous to use a portable primary crusher so that it can follow the movement of the working face from which the raw material is extracted.
The purpose of intermediate crushing is to produce various coarser fractions or to prepare the material for final crushing. If a medium crusher is used for railway ballast, the quality of the product is important. In other cases, there is usually no quality requirement, although the product must be suitable for fine crushing. In most cases, the objective is to obtain the greatest possible reduction at the lowest possible cost.
At this stage of crushing, the quality and quantity of the fine product are determined. The quality requirements of the final product can be very stringent, especially in the aggregate industry. In most cases, the fine crushing and cubing functions are combined in one crushing stage. The selection of a crusher for tertiary crushing requires both practical experience and theoretical knowledge. This is where manufacturers should ensure that experienced application specialists are brought in to ensure that the system is designed correctly.