Equipment for Size Reduction

Question 1

What is the size for coarse particles in the feed and product?

Answer 1

• 1.5 m - 37 mm

- 50 - 5 mm

Question 2

What is the size for the intermediate particles in the feed and product?

Answer 2

• 50 - 5 mm

- 5 mm - 75 um

Question 3

What is the size for fine particles in the feed and product?

Answer 3

• 2 - 5 mm

- 80 % < 75 um

Question 4

Equipment for coarse particles

Answer 4

• Jaw crushers

- Gyratory crushers

Question 5

Equipment for intermediate particles

Answer 5

• Rolls
• Disc crushers
• Stamps
• Hammer mills

Question 6

Equipment for fine particles

Answer 6

• Centrifugal mills
• Ball mills
• Tube mills
• Rod mills

Question 7

The key material properties in choosing equipment

Answer 7

• brittleness
• cohesivity (particles stick together)
• fibrous nature
• hardness (capability to scratch)

Question 8

Describe a jaw crusher

Answer 8

There is a fixed W crusher plate and a moving one. Intermittent rocking motion. Crushing action increases as feed moves downwards. Good size reduction but prone to blocking.

Question 9

Describe gyratory crusher

Answer 9

Cylindrical roller mounted in a cylindrical casing. The roller rotates in angular motion.

Question 10

Describe crushing rolls

Answer 10

The cylindrical rolls roll together. The size of the product particles is determined by the distance between the rollers.

Question 11

Describe ball, tube and rod mills

Answer 11

Cylindrical vessels filled with grinding elements. Typically the grinding elements are high alloy steel spheres except in the case of rod mills which have rods. They are rotated slowly enough for grinding elements to tumble one another and grind feed by impact.

Question 12

The conditions of the ball, tube and rod mills

Answer 12

They are run wet. This is to avoid dust explosions. The wetness is especially used with unstable or toxic materials.

Question 13

How is the size distribution of product particles dictated in ball, tube and rod mills?

Answer 13

There is a variation in the size of spheres used in the ball mills. Finer product generated by smaller ball size. This is the same with higher ball density and longer residence time.

Question 14

How does the speed of revolution of the ball mill affect the particle size?

Answer 14

The speed is too great then the balls do not regulate size. The speed is too slow then no crushing.

Question 15

What is the specification of tube mill?

Answer 15

Tube mills have a higher L/D and generate a finer product.

Question 16

What is the specification of rod mills?

Answer 16

Rod mills are used for sticky substances that would cement balls together for producing for more uniform size.