The maximum size to opening ratio in an impact crusher refers to the relationship between the largest feed size a crusher can accept and the size of the discharge opening (setting). This ratio is crucial for determining crushing efficiency, product gradation, and machine performance.
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Typical Maximum Size-to-Opening Ratio for Impact Crushers
– Primary Impact Crushers:
– Feed Size: Up to 1.5–2 times the opening size.
– Example: If the discharge setting is 100 mm, the maximum feed size could be 150–200 mm.
– Secondary/ Tertiary Impact Crushers (Horizontal Shaft Impactors – HSI, Vertical Shaft Impactors – VSI):
– Feed Size: Usually limited to 1–1.5 times the discharge opening.
– Example: For a 50 mm setting, max feed may be 50–75 mm.
Factors Influencing the Ratio
1. Crusher Type & Design:
– Primary impactors (like Andreas-style) handle larger ratios than fine-crushing HSIs or VSIs.
– VSIs often require pre-crushed feed (low ratio).
2. Material Hardness & Abrasiveness:
– Softer materials (limestone) allow higher ratios than hard rock (granite).
3. Rotor Speed & Blow Bar Configuration:
– Higher rotor speeds can improve reduction but may limit maximum feed size.
4. Closed vs. Open Circuit Operation:
– Closed-circuit setups (with recirculation) allow tighter control over product size, affecting optimal feed size selection.
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General Rule of Thumb
– For most impact crushers, the practical maximum feed size should not exceed 1.5x the crusher’s discharge opening to ensure efficient crushing and avoid excessive wear or blockages.
Would you like recommendations for a specific impact crusher model or application?
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