1 Conveyorppt Course 2010

Belt Conveyor

K. Pathak mobile slope conveyor at Kazagistan with a capacity of 5500 m³/h and capacity to handle height differences up to 28 m.

TYPICAL EXAMPLE OF BELT CONVEYOR IN A MINE Mining industry deploys conveyor belt for transport of materials in many ways

Apron Feeder

Scalping grizzly feeder

(Fines ) Gyratory crusher Vibrating screen To Tert. conv

(Primary Crusher Discharge)

Middlings

TYPICAL EXAMPLE OF MATERIAL FLOW IN A MINE

Components DISCHARGE HOOD

TRIPPER

SKIRT BOARD SCRAPER

END PULLEY

END PULLEY

IMPACT IDLERS BEND PULLEY SNUB PULLEY

CARRYING IDLERS

RETURN IDLERS

GRAVITY TAKE-UP

BELT CLEANER

Level or inclined Conveyor receiving material at tail end and discharging at head en

Level Conveyor receiving material at any point through travelling Hopper and discharging at head end.

Level and inclined Conveyor receiving material at and near tail end, having vertical curve to incline, and discharging at head end.

Level and inclined Conveyor with chute. Material received from bins too close to elevated head end to permit use of vertical curve.

Inclined and level Conveyor receiving material at tail end and discharging from level section through a movable Tripper.

Level Conveyor on raised structure with double-wing Tripper forming storage piles on both sides of Conveyor.

Inclined Conveyor receiving material at tail end and discharging at several points through a series of fixed Trippers.

Abrassive lump material Chute as screen Smaller Size Material

Fine size Material cushion

Loading of abrassive lump material on belt conveyor

Application and Limitations  A wider range of material can be handled which pause problems in other transportation means. Belt conveyor can be used for abrasive, wet, dry, sticky or dirty material. The lump size of the transported material is limited by the width of the belt. Belts up to 3000 mm wide are used in mining industry.  Higher capacity can be handled than any other form of conveyor at a considerably lower cost per tonne kilometer. Conveyor belts with capacity of 11000t/h and even higher can be deployed to match with higher capacity mining machinery.  Longer distances can be covered more economically than any other transportation system. A single belt conveyor or a series of belt conveyors can do this. Belt conveyors can be adopted for cross-country laying.  By the use of many forms of ancillary equipment such as mobile trippers or spreaders bulk material can be distributed and deposited wherever required.

• Many other functions can be performed with the basic conveying like weighing, sorting, picking, sampling, blending, spraying, cooling, drying etc. • Structurally it is one of the lightest forms of conveying machine. It is comparatively cheaper and supporting structures can be used for many otherwise impossible structures such as crossing rivers, streets and valleys. • The belt conveyor can be adopted for special purposes (fire resistant, wear resistant, corrosion resistant, high angle negotiation etc.) and can be integrated with other equipment. • It can be horizontal, incline or decline or combination of all. • Minimum labor is required for the operation and maintenance of belt conveyor system. • In underground mine transport, belt conveyor can be used in thin seams as it eliminates the rock works that might otherwise be required to gain haulage height. Moreover, belt conveyor can provide continuous haulage service from pit bottom to the surface.

Limitations •

The loading and transfer points need to be properly designed.

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Numbers of protective devices have to be incorporated to save the belt from getting damaged by operational problems.

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The belt needs higher initial tension (40-200% of useful pull).

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The use of belt is restricted by the lump size. If the maximum diagonal of a irregular lump is X then the belt width (B) is approximately given by: B>=Xa+200 Where, B: Belt width, mm X: Longest diagonal of irregular lump, mm • a: Factor to account for grading. a is taken as 2.5 for graded material and 3 for ungraded material. However, for particular material these values must be properly estimated. •

Conveying of sticky material is associated with problems of cleaning and discharge causing poor productivity.

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Higher elongation of the belt (4% elongation may take place at the working load).

Types of Belt Conveyors •

Permanent: This type of conveyors is installed for the life of the mine. They are used in main line, slope, long overland installation, preparation plants and stockpiles.

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Portable: These are characterised by relative ease of assembling and disassembling to facilitate advances and recovery in development and retreat operations in underground mining.

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Shiftable: Used in continuous surface mining this type of conveyor is mounted on skid or supporting structures aligned together and the whole can be shifted transversely to follow the advancing working face.

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High Angle Conveyor: These are special type of conveyor belt arrangement used for negotiating steeper angle of inclination. Such belts can work in slope up to 70-800. Sandwich belt conveyor is a type of such belt conveyor.

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Cable Belt Conveyor: Where the belt is carried on moving wire ropes and the tractive force is applied through the rope to the belt is known as cable belt conveyor..

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Pipe Belt Conveyor: The belt is made to form a pipe while running the main length of the conveyor. At the receiving and discharge end the belt is like troughed belt conveyor. They are suitable for having spillage free transportation and free from risk of polluting the environment.

Cont… •

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Mobile Transfer Conveyor: Mobile Transfer Conveyors are installed between Bucket Wheel/Chain Excavators and the shiftable bench conveyor allowing multi block and multi bench operations to increase the block width and the block height. Thus, increasing the time between two shifting operations of the bench conveyor – results in a higher utilization of the mining system. Grasshopper style Mobile Transfer Conveyors: Installed as a chain like one connected to the other are part of waste dumping. This can eliminate dump trucks from mines. Mobile transfer conveyor

Top Cover (Carrying Side)

End Cover

End Cover

Carcass Bottom Cover (Non-Carrying Side)

Construction of conveyor belt.

Essential Belt Properties The belt works as a tractive element as well as load-carrying element. It may be used for different kind of material transportation at a higher speed ( 6-8 m/s). For this purpose the belt need to have the following essential properties:

        

Flexibility Transverse rigidity Low mass per unit length High strength Simplicity and inexpensive Longer life Should not stretch under normal working stresses ,i.e., low relative elongation. Wear resistant Fire resistant

Recommended maximum belt speeds Speed (m/sec)

Speed (fpm)

Width (mm)

Width (inches)

Coal, damp clay, soft ore, fine crushed stone, Over burden and earth

2.032 3.048 4.064 5.08

400 600 800 1000

457.2 609.6-914.4 1066.8-1524 1828.8-2413

18 24-36 42-60 72-95

Heavy, hard, sharp edged ore. Coarse crushed stone

1.778 2.54 3.048

350 500 600

457.2 609.6-914.4 over 914.4

18 24-36 over 36

Top C over

Bottom Cover

Rubber Interply

Cross section of a multi ply conveyor belt.

Belt Fastener

Mechanical Belt joint

BELT SCRAPERS

V- Plow

Diagonal Plow

•Self-adjusting unit eliminates the need to readjust to accommodate blade wear. •Stainless steel turnbuckle permits precise adjustment so the plow can be fine-tuned to the belt at installation and eliminate unit vibration. •Can also be positioned directly behind the head pulley to dump debris at the transfer point.

The diagonal deflector plow is installed on a 45° angle across the belt to discharge debris to one side of the belt. In such cleaners the blade is installed in a fixed position, eliminating bouncing problems associated with some floating style plows.

Heavy-Duty Reversing Diagonal Plow

Twin-bladed plow is designed to clean belt in both directions of travel. This cleaner discharges material to either side of the belt. It is installed securely to conveyor structure and can work on conveyors with severe belt vibration.

Idlers

Figure 5 Different types of roller supports

Different types of roller supports

Self aligning idler set is used infront of the loading point. This set of idlers can rotate on a horizontal plan depending on the belt sway and restores true running of the belt. Belt training idlers should be spaced 30 to 50 m apart and at least one such idlers should be used on conveyors less than 30m long. Such idlers are not used in the areas of belt transition.

Self aligning idler

Idler spacing Belt Width (inches)

Troughed Idler Spacing Weigh of Material Handled (lbs/cu ft)

Return Idler

30

50

75

100

150

200

18 24 30

5.5 5.0 5.0

5.0 4.5 4.5

5.0 4.5 4.5

5.0 4.0 4.0

4.5 4.0 4.0

4.5 4.0 4.0

10.0 10.0 10.0

36 42 48

5.0 4.5 4.5

4.5 4.5 4.0

4.0 4.0 4.0

4.0 3.5 3.5

3.5 3.0 3.0

3.5 3.0 3.0

10.0 10.0 10.0

54 60 72

4.5 4.0 4.0

4.0 4.0 3.5

3.5 3.5 3.5

3.5 3.0 3.0

3.0 3.0 2.5

3.0 3.0 2.5

10.0 10.0 8.0

84 96

3.5 3.5

3.5 3.5

3.0 3.0

2.5 2.5

2.5 2.0

2.0 2.0

8.0 8.0

Pulley A conveyor belt system uses different types of pulleys like end pulley, snub pulley, bend pulley

Belt trainer

PT Smart™ trainer can be installed at the head pulley or tail pulley, before or after the take-up, or virtually anywhere mistracking occurs along the return belt.

Belt Cutter

The 840 Series Belt Cutter is designed to enhance operator safety

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The carrying side needs cleaning when carried material is sticky in nature. belt cleaner that uses a belt with anti-stick coating and claims minimization of downtime for cleaning.

The performance of belt cleaner depends on: Constant tension between the cleaner and the conveyor belt. Condition of the conveyor belt. Type of material sticking to the belt.

Recommended minimum transition distance % Rated Tension

Fabric Belt (for half trough depth).

Fabric Belt (for full depth)

200

>90 60 – 90 <60

0.9b 0.8b 0.6b

350

>90 60 – 90 <60

450

>90 60 – 90 <60

Troughing angle

Steel Cord Belt (for half trough depth).

Steel Cord Belt (for ful trough depth)

1.6b 1.2b

2.0b 1.6b 1.ob

3.2b 2.8

1.6b 1.3b 1.0b

3.2b 2.4b 1.8b

3.4b 2.6b 1.8b

6.8b 5.2b 3.6b

2.0b 1.6b 1.3b

4.0b 3.2b 2.4b

4.0b 3.2b 2.3b

8.0b 6.4b 4.4b

trough

Arrangement of Snub Pulley

Loose Snub

Tight Snub

Tandem drive and increased wrap angle

Drive Arrangement

Tensioning Arrangement The purposes of take-up are: • To allow for stretch and shrinkage of the belt. • To ensure that the minimum tension in the belt is sufficient to prevent undue sag between idlers. • To ensure that the tension in the belt in the rear of the drive pulley is sufficient to permit such pulley to transmit the load.

Types 1. 2. 3.

Screw Take-up Loop Take-up Gravity Take-up

Screw take-up

Gravity Take up

Various Gravity Take up Arrangement

Belt Protection Controls: devices provided for protecting conveyor belt system Belt alignement control: Belt should be aligned with the drive pulleys and the carrying and return idlers. Belt alignment sensors are typically positioned along the edges of the conveyor fabric. They are usually at the discharge and at the loading zones, however can be distributed over the length of the conveyor. Switches consists of Roller Switches, Limit Switches, Proximity Switches, Photoelectric Switches, etc. When the edge of the belt trips the alignement switch for a timed period, the conveyor is halted. In steel cord belts edge tracking is done by using alignment sensors. This helps to get signature of tension distribution within the carcass which in turn does the condition monitoring

Belt Overload: The electric drive motor has overload protection. The motor overload can be a simple bi-metallic or melting eutectic alloy or a complex computer based motor-thermal model. Sometimes belt weigh scales are also used for overload protection. Belt Slip: Belt slip is the loss in traction of the drive pulley(s) to the belt cover. Belt slip can destroy a belt or drive pulley. Belt slip protection provides a belt drive speed sensor that compares the present belt speed with the belt intended speed. For constant speed belts belt slip monitoring is done by a slip switch with a setpoint that trips the conveyor drive when the belt speed is below 80% of full speed. The belt slip switch is bypassed during starting and stopping. For variable speed conveyor belt slip monitoring consists of a speed sensor that measures the belt speed and compares with the speed reference sent to the drive system. When the belt speed is below 80% of the intended speed the conveyor drive is tripped. A method to adjust and test belt slip is normally provided in the belt control system.

Take-up Overtravel : Overtravel limit switches can be placed at the far extremes of the counterweight or take up device travel. In a gravity counterweight take-up, the top overtravel switch trip may suggest a jammed conveyor belt condition. A bottom overtravel switch may indicate belt stretch, or a broken belt fabric flight. Excessive take-up motion during starting and stopping indicate that the type of drive control is either inadequate or that is not working properly.

Transfer Chute Plug: If the conveyor transfers material through a transfer chute, the transfer chute plug monitors blocked flow as blocked flow may damage the conveyor belt. Under blocked condition the transfer chute plug switch trips the conveyor drive. Bin Level Control: If the conveyor belt is used to fill bins or stock piles over dumping may damage the belt. Bin level sensors protect the belt from probable beltdamage. Simple hanging tilt switch or analogue devices like ultrasonic, radar or laser devices may be used. Pull-chord Stop Switches: These are emergency switches that can be actuated by pulling a chord provided along the belt conveyor. Rip Detectors: Rip detectors provide belt protection in case of a rip or tear of the belt. Simple rip detector is spill switch located below the conveyor near the loading point. There are complex rip switches available, which require periodic maintenance.

Fire Detection: Thermal trip switches are provided with smoke sensors, CO sensors or fibre optic temperature sensors. Dust Sprays: Water or chemical based dust suppressing system can eliminate or reduce dust problems in certain special conveyor belt installations

Belt Conveyor Trouble Shooting (The number refers to the list below the table.)

Cause In order probable occurrences

Complaint

Complaint

Cause In order of probable occurrences

of

Belt runs off at tail pulley

7 15 14 17 21

Excessive wear, including rips, gouges, ruptures, and tears

12, 25, 17, 21, 8, 5

Entire belt runs off at all points of the line

26, 17, 15, 21, 4, 16

Excessive wear

21, 14, 5, 19, 20, 22

One belt section runs off at all points of the line

2, 11, 1

Excessive edge broken edges

Belt runs off at head pulley

15, 22, 21, 16

Belt hardens or crack

8, 23, 22, 18

Belt slip

19, 7, 21, 14, 22

Covers become checked or brittle

8, 18

Belt slip on starting

19, 7, 22, 10

Longitudinal grooving or cracking of top cover

14, 21, 22

Excessive belt stretch

13, 10, 21, 6, 9

Longitudinal grooving or cracking of bottom cover

14, 21, 22

Belt breaks at or behind fasteners; fasteners tear loose

2, 23, 13, 22, 20, 10

Fabric decay, carcass cracks, ruptures, soft spots in belt(gouges)

12, 20, 5, 10, 8, 24

Vulcanised separation

13, 23, 10, 20, 2, 9

Ply separation

13, 23, 11, 8, 3

splice

bottom cover wear,

26, 4, 17, 8, 1, 21

1.Belt bowed: Avoid telescoping belt rolls or storing them in damp locations. 2.Belt improperly spliced or wrong fasteners: Use correct fasteners. Retighten after running for a short while. If temporarily spliced remove belt splice and make new splice. Set up regular inspetion schedule.

3.Belt speed too fast: Reduce belt speed 4.Belt strained on one side: Allow time for new belt to “break in”. If belt does not break in properly or is not new, remove strained section and splice in a new piece. 5.Breaker strip missing or inadequate: When service is lost, install proper breaker strip ( Breakers are woven fabric of nylon &/or polyster placed above the carcass to dissipate impact energy and to prevent belt puncture) 6.Counterweight too heavy: Recalculate weight required and adjust counterweight accordingly. Reduce take-up tension to point of slip then lighten slightly. 7.Counterweight too light: Recalculate and adjust or screw take-up accordingly. 8.Damage by abrasive, acid, chemicals, heat etc: Use belt designed for specific purpose. Repair cuts. Use enclosure where needed.

9.

Differential speed on dual pulleys: Make necessary adjustments

10. Drive underbelted: Recalculate maximum belt tensions and select correcxt belt. Determine if extension is feasible or another belt to be installed. Check the carcass is rigid enough for load, replace if service is lost.

11. Edge worn or broken: Repair edge. If the edge is out of square or badly damage replace the worn portion of the belt. 12. Excessive impact of material on belt or fasteners: Use correctly designed chutes and baffles. Make vulcanised splices. Instal impact idlers. Where possible load fines first. Where material is trapped under skirts , adjust skirtboards to minimum clearance or install cushioning idlers to hold belt against skirts. 13. Excessive tension: Recalculate and adjust tension. Use vulcanised splice within recommended limits. 14. Frozen Idlers: Free idlers. Lubricate. Improve maintenance. Don’t over lubricate.

15. Idlers or pulleys out of square with centre line of the conveyor: Realign. Install limit switches for greater safety. 16. Idlers improperly placed: Relocate idlers or insert insert additional idlers spaced to support belts.

17. Improper loading, spillage: Feed should be in direction of belt travel and at belt speed, centred on the belt. Control flow with feeders, chutes and skirtboard. 18. Improper storage or handling: Refer to the manufacturer’s instructions for storage and handling. 19. Insufficient traction between belt and pulley: Increase wrap angle with snub pulley. Lag drive pulley. In wet condition use grooved lagging. Install correct cleaning devices for safety. 20. Material between belt and pulley: Use skirtboard properly. Remove accumulation. Maintain properly. 21. Material build-up: Remove accumulation. Install cleaning devices, scrapers and inverted V decking. Improve housekeeping. 22. Pulley lagging worn: Replace worn pulley lagging. Use grooved lagging for wet conditions. Tighten loose and protruding bolts. 23. Pulleys too small: Use large diameter pulleys.

24. Radius of convex vertical curve too small: Increase radius by vertical realignment of idlers to reduce excessive edge tension. 25. Relative loading velocity too high or too low: Adjust chute or correct belt velocities. Use impact idlers. 26. Side loading: Load in the direction of belt run and at the centre of the belt. 27. Skirts improperly Placed: Use adjustable skirtboards and check that it does not rub the belt.