A ball mill working model demonstrates the principle of size reduction through impact and attrition using rotating balls inside a drum. Below is a simplified explanation of how it works, along with key components and applications:
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Working Principle of a Ball Mill:
1. Rotation & Centrifugal Force:
– A cylindrical shell (drum) rotates horizontally or at an angle.
– The rotation generates centrifugal force, causing grinding media (balls) to lift and cascade or roll down.
2. Impact & Attrition:
– As the balls fall from the top, they crush and grind the material by impact (force from collision).
– Attrition (rubbing action between balls and material) further reduces particle size.
3. Discharge:
– Ground material exits through a screen or grate at the discharge end to separate fine particles from oversized ones.
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Key Components of a Ball Mill Model:
1. Cylindrical Shell: Made of metal or ceramic, lined with abrasion-resistant material.
2. Grinding Media: Steel, ceramic, or pebble balls (size depends on material).
3. Feed & Discharge Mechanism: Hoppers for input/output; screens control fineness.
4. Drive System: Motor, gears, or pulleys to rotate the drum.
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Applications (Model Demonstration):
– Ore Processing: Crushing minerals (e.g., gold, copper).
– Pharmaceuticals: Powdering drugs for tablets.
– Cement Industry: Grinding clinker into cement powder.
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DIY Ball Mill Model (Simple Version):
Materials Needed:
– PVC pipe/plastic jar (drum)
– Steel/marble balls (grinding media)
– DC motor + battery/power supply
– Axles/bearings for rotation
Steps:
1. Mount the drum on a frame with axles.
2. Load balls (~30–50% of drum volume) and material to grind (e.g., limestone).
3. Connect the motor to rotate the drum at 60–80% critical speed (speed where balls stick to walls due to centrifugal force).
Demo Tip: Use colored chalk or soft material to visually show grinding!
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Scientific Concepts Illustrated:
– Critical Speed Formula: \( N_c = \frac{1}{2\pi} \
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