Question

In a gyratory crusher, the size reduction is effected primarily by

• A. Attrition
• B. Compression
• C. Impact
• D. Cutting action

Hint:

Primary Size Reduction Mechanics Guide: - Jaw Crusher / Gyratory Crusher \(\implies\) Compression (Coarse crushing). - Hammer Mill \(\implies\) Impact (Intermediate grinding). - Fluid Energy Mill \(\implies\) Attrition / Rubbing (Ultra-fine milling).

Answer 1

The Correct Option is B

Concept: Size reduction equipment can be classified into crushers, grinders, ultramicro grinders, and cutting machines based on how they apply force. Crushers are heavy-duty machines used to break large pieces of solid ore or rock down into smaller aggregates. A gyratory crusher consists of a conical head that gyrates eccentrically inside a large, fixed, funnel-shaped bowl. As the inner conical head rotates eccentrically, it continuously varies the gap distance between itself and the stationary outer bowl walls, squeezing and crushing the material trapped between them.

Step 1: Analyzing the underlying force mechanisms.
Industrial size reduction relies on four primary types of mechanical force:

• Compression: Squeezing the material between two solid surfaces, ideal for breaking hard, coarse solids.

• Impact: Dropping or striking the material with a high-velocity tool, suitable for a wide range of hardness.

• Attrition: Rubbing or shearing forces that scrape surfaces, useful for producing fine powders.

• Cutting Action: Applying sharp shear forces with knives or blades, used for soft or fibrous materials.

Step 2: Evaluating the operation of a gyratory crusher.
In a gyratory crusher, large chunks of rock enter from the top opening. As the inner cone gyrates, it squeezes the rocks against the stationary outer wall. This continuous squeezing action applies intense compressive stress that exceeds the structural compressive strength of the rock, fracturing it into smaller pieces. Therefore, size reduction in a gyratory crusher is achieved primarily through compression, which matches Option (B).