What is the selection criteria of crushing equipment?

First published in the September issue of Quarry Management

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Gerry Mangrich, regional sales manager - aggregate processing with McLanahan Corp., outlines the main crushing stages and examines the key characteristics of the main crusher types.

Most aggregate producers are familiar with the selection of crushing equipment and know they can select equipment based on specifications and gradation calculations. Nonetheless, theoretical outcomes must be compared with practical experience associated with the specific material, as well as the operational, maintenance, and economic facets of different solutions. Typically, material reduction occurs in stages, and while there are some single-crusher systems, most configurations involve two or three crushing stages.

Crushing Stages

Primary Crushing
The primary crusher's main role is to facilitate material transport via conveyor belts. In most aggregate crushing plants, this is achieved using a jaw crusher; however, a gyratory primary crusher may also be applied. For easily crushed, non-abrasive materials, an impact breaker can be an effective primary crusher option.

Key characteristics of a primary crusher include capacity and the ability to accept raw materials without blockages. While larger primary crushers are more expensive, investment cost calculations should be balanced against the expenses of blasting raw materials to a smaller size. Trucks typically transport raw materials to fixed primary crushers, and costs related to fuel, tires, maintenance, and return on investment should also be factored into decision-making.

In quarries where producers crush materials at the extraction site, a pit-portable primary crusher can be a cost-effective solution. Modern plants often benefit from movable primary crushers that can follow raw material extraction faces, with track-mounted crushers commonly used for short-term contracts or frequently changing locations.

Intermediate (Secondary) Crushing
The goal of intermediate crushing is to generate coarser fractions or prepare materials for final crushing. In cases such as producing railway ballast, product quality is crucial. While other applications may not have stringent quality requirements, the product must still be fit for fine crushing. Generally, the aim is to maximize reduction while minimizing costs.

Fine (Tertiary) Crushing
This crushing stage determines the quality and quantity of fine products. The aggregate industry often enforces stringent quality requirements for final outputs. Typically, fine crushing and cubicizing functions occur in a single stage. Selecting a tertiary crushing crusher requires both theoretical understanding and practical experience, making it advisable to engage an application specialist to ensure proper system engineering.

Types of Crushers

Most crushers for aggregate production fall into three primary categories:

• Compressive Crushers: Squeeze material until it breaks.
• Impact Crushers: Utilize rapid impact to shatter material.
• Attrition Crushers: Combine impact and grinding to shear material.

Jaw Crushers
Jaw crushers are widely employed as primary crushers and are suitable for nearly any material type. Crushing occurs between a stationary jaw plate and a moving jaw plate, with material reduced when the moving jaw approaches the stationary one. There are single-toggle and double-toggle variants, with single-toggle jaw crushers typically providing better feed acceptance.

Roll Crushers
These compression-type crushers consist of two drums revolving toward one another, with an adjustable gap between them. Double-roll crushers can offer reduction ratios of up to 3:1, while triple-roll crushers may achieve up to 6:1. Although not as productive as cone crushers in terms of volume, roll crushers provide close product distribution.

Cone and Gyratory Crushers
Both types utilize a gyrating shaft to crush material between fixed and moving components. Cone crushers are typically employed for harder and more abrasive materials, often recommended to operate with a full crushing chamber.

Impact Crushers
Primary impact breakers feature large expansion chambers and utilize rotor assemblies to generate crushing action. They are efficient for limestone and can achieve high reduction ratios while minimizing fines.

Final Thoughts
When choosing the most suitable crusher, understanding specific needs for each stage is crucial. The primary stage should reduce material size to what subsequent processes can handle effectively. Secondary and tertiary stages may be necessary for further size control and output optimization.

Contact us to discuss your requirements for a jaw crusher machine. Our experienced sales team can help you identify the best options for your needs.