2. Objectives
• To design a conveyor mechanism for TBMM to regulate influx of raw-material
• To design a hopper for pouring raw-material onto the conveyor and achieving the
desired influx rate (by suitable opening dimensions)
• To design wheels for the conveyor system to make it mobile
• To utilize readily available components in the market (that makes them easily
replaceable)
• Monetary constraint : the design must be as economic as possible
3. Background
A. TBMM : Tara brick making machine is an innovation of TSB(technology services
branch) of Development Alternatives. TBMM aims at the mechanized production of
green bricks.
The raw material is a mixture of :
- soil
- waste material (its carbonaceous)
- sand (as parting sand in moulds)
- water
- rice husk (to arrest cracking)
A TBMM (tara brick making machine)
The machine utilizes a 950 rpm, 5.50 Kw, 50 Hz motor that in turn drives tha main shaft
using a gear mechanism as shown in the pic below.
The Gear mechanism utilized by TBMM
4. B. CONVEYOR SYSTEM BASICS
1. Conveyor system
• a mechanical handling equipment for moving materials from one location to another
• popular in ‘material handling’ and ‘packaging’ industries
• options for running a conveyor system include :
a) hydraulic
b) mechanical
c) fully automated
2. Three biggest problems associated with a conveyor system
a) poor take-up adjustment
b) lack of lubrication
c) contamination
3. Types of conveyors
a) Gravity roller conveyor
b) Belt conveyor
c) Plastic belt
d) Chain conveyor
e) Screw conveyor
f) Wire mesh
g) Belt driven roller
h) Line shaft roller
i) Overhead conveyor
4. Conveyor-belt
• Consists of 2 or more pulleys with a conveyor belt that rotates about them
• Pulleys are powered ( may be 1 or both )
• Powered pulley is called : DRIVE pulley
• Other pulley is called : IDLER
• Belt has 2 main layers :
5. a) Underlayer CARCASS
- Provides linear shape and tensile strength
- Absorbs impact of material loading
- Often a cotton or plastic mesh ( glass, nylon, steel,
polyester, Kevlar etc.)
b) Overlayer COVER
- Protects base conveyor belt
- Provides properties like : textures, cleanability, color,
impact resistance, cut resistance, hardness, specific friction
coefficient
- Various rubber or plastic compounds
5. Types of Belt conveyors
a) Flat belt conveyors
- light to medium weight loads
- suitable for horizontal, decline and inclined path between
levels
- belt friction avoids accumulation and merging
b) Roughed belt conveyors
- bulk materials
- belt supported on rollers
c) Side walled / Cleated conveyors
- high capacity bulk material conveying
- eliminates spillage and can be used for steep inclines
d) Flex conveyors
- flex in all directions
- combining straight and curved sections
6. Components of a belt conveyor
a) conveyor belt
b) pulley
c) PB bearing
d) Steel
e) Drums
f) Conical shafts
6. Design procedure in accordance with
CEMA (Conveyor equipment manufactures association)
1. Material Characteristics
• Angle of repose : The angle of repose is the maximum angle of a stable slope
determined by friction, cohesion and the shapes of the particles. When bulk granular
materials are poured onto a horizontal surface, a conical pile will form. The internal angle
between the surface of the pile and the horizontal surface is known as the angle of repose.
• Angle of surcharge : The angle to the horizontal a material assumes at rest on a moving
conveyor belt. Its an indicator of flowability.
• Other considerations :
- dustiness
- wetness
- stickiness
- abrasiveness
- humidity
- weight per cubic foot
- chemically corrosive action
7. 2. Effect of inclines and declines
• Ab (trapezoidal area) : remains the same irrespective of the incline
• As (circular segment/surcharge area) : it decreases as the cosine of the conveyor slope
• actual capacity loss less than 3 %
3. Belt widths
• For a given speed , belt width and belt capacity increase together
4. Lump size considerations
• Recommended maximum lump size for various belt widths
- 20 degree surcharge, 10% lumps and 90% fines : recommended maximum lump
size = (b/3)
- 30 degree surcharge, 10% lumps and 90%fines : recommended maximum lump
size = (b/6)
5. Belt speeds
• Suitable belt speed depends on the characteristics of the material to be conveyed, capacity
desired and belt tensions employed
6. Belt conveyor capacities
• Increase with increase in belt width
• Depends on angle of surcharge
• On inclines As decreases whereas Ab remains same
7. Troughed belt load areas
• Trapezoidal area, Ab
- Ab =
- As =
- At =
8. 8. Belt conveyor capacity tables and their uses
The following steps are taken to make the best use of tables :
• Determine the surcharge angle of the material to be transported from Tables 3-1 and 3-3
(the surcharge angle, on the average, will be 5 degrees to 15 degrees less than the angle
of repose)
• Determine the density of material in pounds per cubic foot from Table 3-3
• Choose the idler shape suited to the material and to the conveying problem using the
idler design selection procedure explained later
• Check the “recommended maximum belt speeds” from Table 4-1
• Calculate the desired conveying required in cubic feet per hour
• Calculate the desired capacity in cubic feet per hour to the equivalent capacity at a belt
speed of 100 fpm (unitary method)
• Using the equivalent capacity so found, find the appropriate belt width from Tables 4-2
to 4-5
• If the material is lumpy, check the selected belt width against the curves in fig. 4.1
The lump size may determine the belt width, in which case the selected belt speed may
require revision
9. Belt conveyor IDLERS
• Idler requirements
- proper support to belt
- protection of belt
- roll diameter, bearing design constitute major components affecting frictional
resistance
• Idler classifications
- Referring to Table 5-1
- B4 and B5 seem suitable for our purpose and requirements
9. • General types of belt conveyor idlers and their suitability for our purpose
- Carrying idlers
Carrying idlers are of two general configurations. One is used for troughed belts
and usually consists of 3 rolls, 2 outer ones inclined upwards and the center one
horizontal.
The other configuration is used for supporting flat belts.
a) Flat belt Carrying idlers : This idler generally consists of a single
horizontal roll positioned between brackets which attach directly to
the conveyor frame
SUITABLE : as very economical but their suitability would have
to be verified in terms of soil spillage. Troughed design might be
necessary if soil spillage is high.
b) Troughing belt Carrying idlers : It usually consists of three
rolls. The two outer rolls are inclined upwards; the center roll is
horizontal.
SUITABLE : in case flat belt carrying idlers lead to higher
Spillage, the use of troughed ones might be necessary.
Though they are a bit costlier than flat ones but still are
10. Economically feasible.
c) Impact idlers : Impact troughing idlers, sometimes referred to as
“cushion idlers” are used at loading points where impact resulting
from lump size, material density, and height of material free fall
could seriously damage the belt, if the belt were rigidly supported.
UNSUITABLE : the impact present in our case isn’t too high,
even the material density is low and material is being fed through a
hopper arrangement.
d) Belt training idlers : The normal carrying idlers are the primary
devices which control the belt alignment. No self-alignment idlers
are needed under well designed, precisely assembled, and
maintained conveyors. There are transient conditions, however,
that may cause conveyor belts to become misaligned.
The training idlers pivot about an axis vertically perpendicular to
the center line of the belt, and when the belt becomes off-center,
they swing about so that the axes of the rolls themselves become
canted in a corrective direction.
11. UNSUITABLE : misalignment problem won’t be much in our
case as load density is low.
Secondly, these are very costly as compared to simple troughing
idlers.
- Return idlers
These are usually horizontal rolls,
Positioned between brackets which normally are attached to the underside
of the support structure on which the carrying idlers are mounted.
a) Flat return idlers : The flat return idlers consist of a long single roll,
fitted at each end with a mounting bracket.
SUITABLE : as these are economically very viable and the belt length
being short, demands only 2-3 return idlers just to support the belt.
b) Self-cleaning return idlers : Adherence of material to the carrying
surface of the belt may be abrasive and wear the shell of the return idler
rolls.
Thus, self-cleaning idlers are used to avoid such difficulties which may
later lead to misalignment of return run of the belt.
Rubber-disc return idler
12. Spiral self-cleaning return idler
UNSUITABLE : they are costlier than the flat ones and secondly, our
material is not abrasive and thus no self-cleaning would be necessary.
c) Return belt training idlers : These are pivotally mounted to
train or align the return belt in a manner similar to the training
carrying idlers.
UNSUITABLE : as these are very costly and belt length is too
Short to require such a return idler. Two simple flat return idlers
Would effectively do the job.
13. • Idler spacing
- Refer to table 5-2 for suggested idler spacing
- According to the table for our case, around 4.5-5 ft spacing between carrying
idlers would be sufficient
- In case of return idlers, only 2 would solve the purpose as tonnage capacity
required is very low and they can be spaced suitably as desired.
• Factors to be considered for idler selection
- type of material handled
- idler load
- belt speed
- roll diameter
- environmental, maintenance and other special conditions
• Idler selection for TBMM
- According to Table 5-1, B4 and B5 seem suitable
- Referring to Table 5-2, an idler spacing of 4.5 to 5 ft seems suitable
- CIL = [(WB+(WM*Kl))*SI] + IML
Where :
CIL calculated idler load (lbs)
WB belt weight (lbs/feet) = [(Q*2000)/(60*Vee)]
Q quantity of material conveyed (tons per hour)
Vee belt speed (fpm)
SI idler spacing (feet)
Kl lump adjustment factor
- IML = [(D*T)/(6*SI)]
Where:
D misalignment (inches)
T belt tension (lbs)
SI idler spacing (ft)
- Calculations in our case yield
CIL = 209.615 lbs
IML = 0 lbs
14. - Referring to Table 5-7 load rating for CEMA B is 410 lbs and thus
CIL less than this rating. Therefore, CEMA B idler i.e. idler with diameter 4”-5”
would be required.
- CILr = (WB*SI) + IML
For our case, CILr comes out to be 19.57 lbs which is lesser than 220 lbs rating in
table 5-7 and hence 4”-5” dia idler would be suitable
10. Belt tension and power
• Hp (horsepower) = [(Te*V)/(33000)]
Where :
Te effective tension (lbs)
V belt velocity (fpm)
• Te (effective tension)
= LKt ( Kx+KyWB+0.015WB) + Wm (LKy+H) +Tp+Tm+Tac
Where :
L length of conveyor
Kt ambient temperature correction factor
Kx factor used to calculate the frictional resistance of the idlers and the sliding
Resistance between the belt and the idler rolls (lbs per ft)
Ky carrying run factor used to calculate the combination of the resistance of
The belt and the resistance of the load to flexure as the belt and load move
Over the idlers
WB belt weight (lbs/feet)
WM material weight (lbs/feet)
H vertical distance by which material is lifted
Tp tension resulting from resistance of belt to flexure around pulleys and the
Resistance of pulleys to rotation on their bearings (lbs)
Tm tension resulting from the force needed to lift the conveyed material
Tm = (H*WM)
Tam from force to accelerate the material continuously as its fed onto the belt
Tac from the resistance generated by conveyor accessories
15. • For our case, after including a suitable safety factor, the effective tension comes out to
be1488.82 lbs and the motor hp required is 1.143.
11. Pulley
• Standard steel drum pulleys would solve our purpose
• Referring to Table 8-1, required pulley dia is obtained to be approx. 12”
• Pf = 18”
• Maximum weight = 95 lbs
12. Shafting
• D = [{(32*FS)/3.14}*[{(M/Sf)2
+0.75*(T/Sy)2
}]0.5
](1/3)
Where :
FS factor os safety
Sf corrected shaft fatigue limit = (KaKbKcKdKeKfKgSf*
)
Ka surface factor = 0.8 for machined shaft
Kb size factor = (D)-0.19
Kc reliability factor = 0.897
Kd temperature factor = 1.0 for (-70 to +400 F’
)
Ke duty cycle factor = 1.0
Kf fatigue stress concentration factor
Kg miscellaneous factor = 1.0 for normal conveyor service
M bending moment (pound inches)
T torsional moment (pound inches)
S*
f shaft fatigue limit = 0.5*(tabulated ultimate tensile strength)
Sy yield strength
•
- S*
f = 29,000 for C1018
- Sy (yield strength) = 32,000 for C1018
16. 13. Steep angle conveying
A) Method 1
a) Where the angle of incline is less than the material surcharge on
the belt, then surcharge area is reduced
As, reduced = As * [(cos2
(delta) – cos2
(alpha))/(1- cos2
(alpha))]0.5
Total reduced area = As, reduced + Ab
b) Where the angle of incline equals or exceeds the material
surcharge angle on the belt, the surcharge area is reduced to zero
and only the zero degree surcharged is used.
As = 0
Total reduced area = Ab
Where :
Alpha angle of surcharge (degrees)
Delta angle of incline (degrees)
As surcharge area (square inches)
Ab base trapezoid area (square inches)
B) Method 2
• It’s a deep-cleated belt manufacturer’s recommendation
• Refer to Table 10-2 to find out total area correction
factor
• The advantages of this approach are :
a. economical method of increasing the angle
of incline
b. no additional mechanical components over
standard belt conveyor
• The disadvantages of this approach are :
a. the allowable angle of incline is limited
17. b. the cleats or fins are susceptible to damage
and wear off more rapidly than a standard
belt cover
c. at higher belt speeds, as the cleats pass
over the return rollers, vibrations can
occur that cause accelerated cleat wear
d. the belt is more difficult to clean than the
standard belt conveyors
