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BUCKET ELEVATOR
Mechanical Engineering Department
Carlos III University
BUCKET ELEVATOR
TRANSPORTATION
BUCKET ELEVATOR
BUCKET ELEVATORS
Bucket elevators are the most used systems for vertical
transport of bulk, dry, wet and even liquid materials.
• Designed with various options of height, speed and constructive details depending on the type of material to be transported.
• Are constructed by pieces or units to allow to define efficiently the needed height.
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BUCKET ELEVATOR
COMPONENTS
Head hood
Discharge
spout
Boot inlet hopper
Engine
Tensioning
device
Bucket
Clean
outdoors
Drive and pulley
Casing
Belt
Boot
BUCKET ELEVATOR
DEPENDING ON THE LOAD
Directly to the input hopper
By digging
• Used for transport of materials that offer no resistance to extraction, like fine grain and dusty materials.
• Used for transport of abrasive and big size materials.
• Chain/belt travelling speed is low.
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BUCKET ELEVATOR
DEPENDING ON THE TYPE OF DISCHARGE
Centrifugal
• It is the most common.
• Great travelling speeds (1.2 and 1.4 m/s).
• Loading is carried out by dredging the material at the bottom of the elevator.
• The separation distance between the buckets is 2 to 3 times the bucket height.
BUCKET ELEVATOR
DEPENDING ON THE TYPE OF DISCHARGE
Gravity or continuous
• Lower travelling speeds (0.5 and 1.0 m/s).
• It is taken advantage of self weight.
• Classification:
– Free gravity. It is necessary to change the free branch line or incline the bucket.
– Forced. The buckets are situated one after the other without separation between them. The discharge takes place due to gravity by means of the lower part of the preceding bucket that acts as a discharge spout.
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BUCKET ELEVATOR
DEPENDING ON THE TYPE OF DISCHARGE
Positive
• Similar to the gravity elevator safe that buckets are fitted at the edges with two cords.
• Bucket speed is low are appropriate for light, aired, sticky materials.
Cords
BUCKET ELEVATOR
MATERIAL TRANSPORTED FLUX
cP i jρ= ⋅ ⋅Material weight(kg)
Bucket volume (l)
Density (kg/l)
Fill in bucket coefficient(0,6 – 0,9)
3.6 cP vQ
t
⋅= ⋅Transportedmaterial flux (t/h)
Pitch:
Standard buckets:
Flake bucket:
[ ]hht 3,2∈
ht =chaint cte t= ⋅
For chains:
Bucket height
Travellingspeed (m/s)
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BUCKET ELEVATOR
POWER
0( )3.6
a
QF H H
v= ⋅ +
⋅
The force the drive pulley needs to move the belt (kg):
Elevating height(m) Fictitious height
(m)
15.3Big
11.4Medium
7.6Little
By digging
3.8From the inlet hopper
Value of H0(m)Material sizeLoad system
Power of the engine (CV):
75
aa
F vN
η⋅=⋅
Engine efficiency
BUCKET ELEVATOR
MAXIMUM TENSION OF THE BELT
a aT F k= ⋅
Maximum tension of the belt (kg):
Coefficient thatdepends on the pulley
1.49Dry layer
1.73Humid layer
1.64Dry smooth
3.20Humid smooth
KPulley conditions
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BUCKET ELEVATOR
m
MATERIAL DISCHARGING
A
m g⋅
λ
m g⋅
cosm g λ⋅ ⋅
m g sinλ⋅ ⋅
2m v
R
⋅ 2
cosR
m vF m g
Rλ⋅= − ⋅ ⋅
2
cosRF v
m g g Rλ= −
⋅ ⋅
<=>0
BUCKET ELEVATOR
O’
MATERIAL DISCHARGING
2
cosRF v
m g g Rα= −
⋅ ⋅
O
2v
g R⋅
α
cosα
0º
90º
+ -
1
02
1v
g R<
⋅
2
1cosv
g Rα−
⋅
Predominance of
the centrifugal
forces
2
2cosv
g Rα−
⋅
Predominance of
gravity forces
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BUCKET ELEVATOR
MATERIAL DISCHARGING
2
cosRF v
m g g Rλ= −
⋅ ⋅
O
2v
g R⋅
α
cosα
O’
0º
90º
+ -
2
1v
g R<
⋅
A C
2
1v
g R=
⋅
B
BUCKET ELEVATOR
hs
MATERIAL DISCHARGING
Pulley diameter
c gF F=
2Vm m gR
⋅ = ⋅2V
Rg
=
Material path
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2s v t a t= ⋅ + ⋅ ⋅
vs
7804800.4
12206000.5
4403600.3
1952400.2
501200.1
Sv (m)Sh (m)TIME (s)
v = 0.5 m/s
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BUCKET ELEVATOR
• Design the features of a belt conveyor that has
to transport dry clay of density 1700 kg/m3
with an approximate capacity of 15t/h:
– Size of the bucket
– Spacing
– Belt speed
– Pulley diameter
EXAMPLE
BUCKET ELEVATOR
EXAMPLE
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BUCKET ELEVATOR
EXAMPLE
• Load weight=(2/3)·bucket· volume·density=
(2/3)·0,74·1700=0,84 kg per bucket
• To move 15t/h we need:
(15000/0,84)=17857 buckets/h=5 buckets/s
• Spacing
– Pitch=[2h,3h] if bucket height is 105mm Pitch=300 mm
• Belt speed=5 bucket/s · 300 mm=1,5 m/s
• Pulley diameter: D=2·R=2·(v2/g)=460 mm
