Crushers to screens in aggregate production

The stages and equipment used for aggregate production

1. EQUIPMENT USED FOR AGGREGATE PRODUCTION

2. Amount of processing required for aggregate production depends on Nature of raw materials Desired attributes of the end products Four procedures adopted: Particle size reduction – crushing Separation into particle size ranges – screening / sizing Elimination of undesired materials – washing Handling and movement of crushed materials – storage and transport

3. 3 EQUIPMENTS USED FOR PRODUCTION OF AGGREGETE Crushers Jaw crusher Gyratory crusher Roll crusher Cone crusher Impact crusher Ball mill and Rod mill (for Fine Aggregate) Feeders Screens Revolving screens Shaking screens Vibrating screens Log washer Aggregate handling

4. 4 1. Crushers: Crushers are used to break stones into different sizes of aggregates. Based o n the s t a ge of c rushing , c r ushers are three types: Primary crusher Secondary crusher Tertiary crusher Stones obtained from quarry are fed into the primary crusher which reduces the size of stones.

5. 𝐑𝐞𝐝𝐮𝐜𝐭𝐢𝐨𝐧 𝐫𝐚𝐭𝐢𝐨 = 1. Crushers: (continued…) Stones obtained from primary crusher are fed into secondary crusher where sizes of stone is further reduced. Therefore, to obtain desired size of aggregate, the stones are passed through 4 to 5 crushers. size of stone fed into the crusher size of stone obtained from crusher 5 (Ratio of crusher feed size to product size)

6. 6 (a) Jaw Crushers: I t has t w o ja w s , o ne i s s t a t ionary an d o t her is moving. The surface of both jaw is flat/convex. The space between two jaws is wider at top and narrow at the bottom. The size of jaw is 1.68 x 2.14 m. T he s t ones are c r u s he d b y t he pres s ure o f t w o jaws. Large s i z e boulders c an a l s o b e c ru s hed u s i n g this crushers. Power consumption is minimum.

7. Fig. Single jaw crusher 7

8. Fig. Double jaw crusher 8

9. 9 Single toggle jaw crusher Double toggle jaw crusher (Blake type) (i) In a single toggle jaw crusher whole swing jaw is lifted, hence require higher power. (i) Require lesser power. (ii) Jaw plates wear out at faster rate. (ii) Jaw plates wear out at slower rate. (iii) Lower initial cost. (iii) Higher initial cost. (iv) Used for non-abrasive and non hard rocks. (iv) Economical for abrasive and hard rocks. (v) Compact size, lighter weight and reasonably sturdy (v) Heavy, not for portable applications

10. 10 Size of jaw crushers and jaw opening Mouth opening of the jaws denotes the crusher size. Thus, a jaw crusher having a jaw plate width of 1200 mm and mouth opening / feed opening of 1000 mm is called a 1200 x 100 mm crusher. The jaw opening at the top determines the size of the rock. The size of stone piece is restricted to 70 to 80 % of the gap size. Thus, for 1200 x 1000 mm crusher the feed size should be restricted to 700 to 800 mm (70 to 80% of 1000 mm). The capacity of the crusher is dependent on the area of the opening at the bottom of the jaws.

11. Fig. Crusher jaw setting and jaw opening 11

12. 12 Wear limits: With use, the teeth of the jaws are worn out. When teeth plate s gets worn out to about 1/3 of the original corrugation height the jaw plates must be turned end-to-end. Wear limit dead line is when there remained no corrugation. When the entire crushing surface gets worn out, the teeth plate should be replaced with new one.

13. Fig. Wear limit of tooth plate 13

14. 14 Tips for optimum use of jaw crushers: The feed size should be 70 to 80% of the minimum opening size at top. Do not allow bigger pieces going to the crusher mouth. Material fed should not be of same size. Mixed feed of all sizes of material gives best results. For best results ratio of gap to jaw setting should be 5:1 to 7:1. Gap is the longer distance between the two jaws. The ratio of gap to width of jaws is 1:1.6 in primary crushers and 1:4.5 in the secondary crushers.

15. 15 (b) Gyratory crusher: Most efficient of all primary type crushers A gyrating mantle mounted within a deep bowl – provides continuous crushing action For hard, rough, abrasive rock To protect the crusher, it can be spring loaded type or mantle height can be hydraulically adjusted A cone or head is fitted at the top for grinding known as mantle Cone shaped crushing chamber known as concave Stones are broken by the impact of the head. The frame of equipment is strong. Head is made of iron alloy

16. ( c ) Cone crusher: C one c ru s her are u s ed f or s e c ond o r t hird grinding. Large quantities of u niform size aggregates are obtained. A head of manganese iron is fitted on the vertical shaft, which act as grinding surface. The second surface is concave. T he rota t ion of s haft prod u c e s g y ra t o r y e f fe c t which causes grinding of stones. Difference of cone crusher from gyratory crushers: shorter cone, smaller receiver opening, rotates at a higher speed, more uniformly sized output

17. Fig. Cone Crusher

18. Sa l i e n t features o f G y r at o r y a n d c on e crushers: As moving parts are small in number, wear, tear and maintenance is less. Longer life Dust has little effect. Hydraulic system enables finger tip control of the machine. Wear is uniform and adjustment is simple. Cleaning by hydraulic system enables rapid restart after a blockage during operation. These have devices to measure oil pressure, oil temperature and oil circulation. In case of abnormal condition there may be sound or visual alar m .

19. 20 ( d ) Roll crusher: This equipment consists of heavy iron frame with two hard steel rolls. Two rolls are fitted on different horizontal shafts. They can be rotated by v-belt or flat pulley. Stones are broken into small pieces between roll and grinding plate. The equipment is light in weight and is suitable for second grinding.

20. 21 (c) Roll crusher: (continued..) Feed size: The maximum size of material that can be fed to a roll crusher is directly proportional to the diameter of the rolls. If the feed contains stones that are too large, the rolls will not grip the material and pull it through the crusher.

21. Feed size: (continued..) T he angle o f grip, w hi c h is c on s t ant f or s m oo t h rolls, has been found to be 16 ̊ 45’. T he m a x i m u m si z e pa r t i c l es t ha t ca n b e cr u s h e d are determined as follows. R = radius of ro l ls B = angle of grip ( 16 ̊ 45’) D = R cos B = 0.9575 R A = maximum feed size C = roll setting (size of finished product) X = R – D A = C + 2X = R – 0.9575 R = C + 2 (0.0425 R) = 0.0425 R Prof. Ashis = C + 0.085 R h Makwana 19

22. Capacity of roll crusher: The capacity of roll crusher depends upon: Type of stone Width of rolls Size of feed Speed at which rolls rotate Size of finished product Uniformity of feeding Capacity of roll crusher: Q = CW S x 3600 x η cum/hr. Q = Capacity in cum/hr. C = roll setting in metre W = width of rolls in metre S = surface speed of roll in m/sec = 2 π RN η = efficiency Or Q =  

23. Type of roll crusher: Both roll shells smooth Double toothed roll crusher One smooth and on corrugated shell Corrugated rolls Spiked roll crusher

24. i. Both roll shells smooth: T he s e are u s ed w hen required s i z e of f ini s hed product is less than 12 mm. T hese are w ide l y used in quarr y i n g indu st ri e s , mining, ceramic and metallurgical industries. Out of the two rolls one roll is fixed and other is floating. Each roll is individually driven by 3-phase electric motor via v-belt. T he ga p c an b e a djus t ed t o s u i t the s i z e o f t he material.

25. ii. Double toothed roll crusher: These are generally used for the production of material over 25 mm size and for reduction of coarse soft and medium hard, non-abrasive materials like coal, slag, ore, limestone etc. The principle of working is the same as that of smooth roll crusher. iii. One smooth and one corrugated shell: These are used for materials of medium hard qualities. They are used for producing the material between 12 to 25 mm size.

26. Fig. One smooth and one corrugated shell

27. iv. Corrugated rolls: The size of corrugation (pitch and depth) is related to the product size, and hence the smaller the product, the finer is the corrugation. These can take bigger feed size than plain rolls of the same diameter. v. Spiked roll crusher: These can take large feed size, even a slab of 1.2 m x 1.5 m x0.3 m size. These have one spiked roll and one adjustable jaw and are used for coarse crushing of material like coal.

28. (e) Impact crusher: Impact crushers are used where materials are too hard and abrasive and finished product requirement is for cubical shape well graded material. In this type of crusher, stones are broken by means of impact and not by compression as in jaw crusher. Stone is normally fed into the top of a breaking chamber and struck by rotating hammers while it is in suspension. The hammers repeatedly throw the material against breaker bars (repulsion plates) forming the roof of the breaker chamber. Hammers are fixed to the rotor.

29. Advantages: High reduction ratio E f f e c t i v e produc t i o n fines o f a high per c en t age of Excellent shape i.e. free from flake High output per unit energy Better mechanical strength Lower initial cost Have fewer parts to maintain Produce well graded cubical shaped product

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31. P o i n ts to b e k e p t i n mind w h i l e s e l ecting crusher: 1. Type of rock 2. Size of rock pieces 3. Method of feeding rocks in the crusher 4. Required capacity of the plant 32

32. Fig. Portable – aggregate processing plant flow dia.

33. Crushing plant: Crushing plants with capacities upto 1000 tons per hour are being manufactured by various manufacturers all over the world. These plants are either stationary or portable. Crushing plant Primary crushing units e.g. Jaw crusher Impact crusher Reduces the rocks to sizes Between 75 to 250 mm Secondary crushing units e.g. Jaw crusher Cone crusher Impact crusher Reduces the rocks to sizes Between 5 to 50 mm

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35. 2. Ball mill and rod mill – special processing units for fine aggregate production A rod mill c o nsists o f a n i r on c y li n drical shell w ith hard mineral coating on the inner surface. A number of iron rods are kept inside the cylinder. T he len g th o f r ods i s ke p t sli g ht l y smal l er t h an the length of cylinder. Sto n e p i eces are f e d from in l et a nd s an d size fi n e aggregates are obtained at the other end. The mill can be operated in dry or wet condition. The size of mill can be expressed in terms of diameter and length of the cylinder, e.g. 2.5 m x 3.5 m. If steel balls are charged in the cylinder instead of iron rods, it is called ball mill.

36. Fig. Section through a rod mill

37. Fig. Section through a ball mill

38. 3. Feeders Feeders supply gravel to crusher To ensure uniform feeding and avoid surge feeding (overloads crushers) Type s of feeders: Apron – A feeder constructed of overlapping pans that form a continuous belt Reciprocating plate Vibratory – simple vibrating and vibrating grizzly feeders Belt – uses hopper to feed belt Grizzly – used over hoppers to remove oversize material – series of bars

39. 4 . Screen: Sc reens are u s e d t o s epara t e a ggregates according to different sizes. T he s i z e o f aggr e gate i s e x pres s ed a s rang e , e . g. p a ss ing 1 2 m m s c reen an d r e t a ined on 6 mm screen. Types of screen: Revolving screens Shaking screens Vibrating screens

40. a. Revolving screens T h e y are m ore a d v an t ageous w hen t hey are used to wash and screen sand and gravel. The operating action is slow and simple. Maintenance and repair costs are low. If the aggregate to be washed contains silt and clay, a scrubber can be installed near the entrance of a screen to agitate the material in water. At the same time, streams of water can be sprayed on the aggregate.

41. b. Shaking In this type, the screen is kept inclined at 15 ̊ to 20 ̊ with horizontal. The screen is agitated in the direction of length for a distance of about 15 cm at the rate of 100 strokes per minute. Fine material fall below the screen while coarse material fall at the end of the screen.

42. c. Vibrating screens: This type of screens are more frequently used for screening of aggregate. They consists of one or more layers or ‘decks’ of open mesh wire cloth mounted one above the other in a rectangular metal box. The vibration is obtained by means of an eccentric shaft, a counterweight shaft or electromagnets attached to the frame or to the screens. A unit may be horizontal or inclined with slight slope (20 ̊ or less) from the receiving to the discharge end. The vibration, 850 to 1250 stokes per minute causes the aggregate to flow over the surface of the screen.

43. 5 . Log washer: When natural deposits of aggregate, such as sand and gravel, or individual pieces of crushed stone contain deleterious material, it will be necessary to remove these materials before using the aggregate. One method of removing the material is to pass the aggregate through a machine called a “log washer”. This unit consists of a steel tank with two electric motor driven shafts, to which numerous replaceable paddles are attached.

44. Log washer: (continued..) When the washer is erected in a plant, the discharge end is raised. The aggregate to be processed is fed into the unit at the lower end, while a constant supply of water flows into the elevated end. As the shafts are rotated in opposite directions the paddles move the aggregate toward the upper end of the tank, while producing a continuous scrubbing action between the particles. The stream of water remove the undesirable material and discharge it from the tank at the lower end, whereas the processed aggregate will be discharged at the upper end.

45. 5. Aggregate handling Necessary to handle it carefully – to ensure gradation – to avoid separation of large and small aggregates – thereby destroying the blend in sizes Transportation by belt conveyors shall not be permitted – as the free fall from discharge end of the belt causes segregation Rock ladder containing baffles attached to end of belts can be adopted to prevent segregation Transported using truck (will discuss in detail)