Wednesday, April 12, 2017

Roll crusher

Aim of the Experiment: Crushing of ore using Roll crusher.

Apparatus Required: Laboratory model Roll Crusher, Feed material.

Theory: A roll crusher a piece of heavy-duty equipment used in mining and industrial processes. For reduction in size of ore/mineral. It consist of a pair of large wheels or cylinders mounted on horizontal axis. When rocks, ore, and other materials pass between the two cylinders, they are crushed or ground into smaller pieces. A roll crusher can be used in a wide variety of applications, including concrete recycling, mining, and mineral or metal production.

 In a standard double roll crusher, the two cylinders each feature a steel or ceramic finish. A hopper or bin above the rollers drops rocks and other materials down into the gap between cylinders. The two cylinders rotate in opposite directions to force all materials into the space between the two units as it falls. The friction between the two wheels crushes the material, which then falls into a collection bin below the unit. To get a desired size of product the set gap can be adjusted. The surface of the roll crusher may be smooth or textured, depending on the applications. Roll crushers used to crush rocks and other heavy-duty materials generally feature teeth or spikes along the surface of each cylinder. Smooth-faced cylinders are used to crush more delicate materials, including minerals and some metals.

Constructional Features of Roll Crusher: The two rolls are heavy and rigid ones. The material is cast steel and wear resisting. Both the rolls are positively driven towards each outer by motor. The heavy rolls turn on parallel horizontal plane having the roll centers at the same height separated by a distance ‘d’. The feed caught between the rolls are broken by compressive force and drop down bellow. The rolls turn towards each other at the same speed. They have narrow faces but having large diameter so they can nip moderately large lumps. Typically rolls are 600mm long with 300 mm diameter. Roll speed ranges from 50-300 rpm. The feed size varies from 12mm to 20mm. the product size mainly depends on the roll separation distance ‘d’

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Working Principle:
i. The crushing rolls are individually driven in counter- rotation by electro-motors with coupling and gears via V-belts.

ii. The crushing material is feeded into the machine by means of conveyors or similar aggregates while it is spread over the whole width of the roll.

iii. An optimum use of the crushing tools and a uniform belt charging are thus achieved.

iv. Roller diameter, tooth form and circumferential speed are adjusted to the type and the size of the feeding material in relation to the required final grain size.

v. Rolls can be operated both wet and dry. Dry crushing causes less wear and gives lower output.

vi. Best operation in choke feeding.
Observation:
S.n
Sample Weight
Max. Size of the Feed
Max. Size of the product
Length of Gape
Length of Set
Time taken to crush material 
Weight after crushing
(only desired size)
Reduction Ratio










Calculation:
Reduction Ratio: The reduction ratio of average feed size to the average product size is known as reduction ratio.
Capacity:
Theoretical Capacity tons/ hr, C= 0.0034NDWS

 The capacity of the roll crusher mainly depends on their speed (N, rpm), Width of the face (W) Diameter of the roll (D) {all in inches} Set (s) the inter roll distance Specific gravity of rock ( ) lb/in3 Note: The actual capacity is considerably less and only around 10-30% of the theoretical capacity. If the set is nil, the capacity is nil.

References:
1.911metalurgist.com
2.Google Images

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