Transcript Document

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.
•
Numbers of protective devices have to be incorporated to save the belt from getting
damaged by operational problems.
•
The belt needs higher initial tension (40-200% of useful pull).
•
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.
•
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.
•
Portable: These are characterised by relative ease of assembling and disassembling to facilitate advances
and recovery in development and retreat operations in underground mining.
•
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.
•
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.
•
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..
•
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…
•
•
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:

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





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
•
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.