1. LECTURE 2
CONVEYORS

2. Conveyor Belt
Conveyor- a mechanized device used to move materials in a continuous manner in relatively large quantities between specific locations over a fixed path.
There are over 400 types of conveyors we are only going to discuss a few of the most common conveyors that can relate to all others.

3. As an engineer consider:
Different types of conveyors
Different applications
Different limits

4. Roller
A roller track for a storage rack or roller conveyor, comprising a wall arrangement, and a longitudinally-extending array of freely rotatable roller units supported on the wall for supportive engagement with a load, the roller units being disposed for rotation about generally parallel horizontal axes which are horizontally spaced along a longitudinally-extending conveying direction, each roller unit including an annular roller housing supported through an annular array of antifriction bearing elements on a support spindle for rotation about the respective horizontal axis.

5. Cont…
Most common are free floating, no mechanical or electrical system used
$60-$1000
Can safely go up to 60 fpm (depending on size of material)
Up to 25,000 lbs (for most depends on support and material used)
No real restrictions on volume of objects used on conveyor
Roller conveyors are one of the most common conveyors used in industry because they are inexpensive, simple to use and can vary depending on the needs of the business.

6. Chain
Chain-A conveyor on which material is transported along solid pans by the scraping action of crossbars that are connected by chains.
Chain conveyors use belts or rollers to move objects
Can handle loads of up 20,000 lbs
Speeds of up to 60 fpm, but depend on size of object, for safety reasons
Relay logic and pneumatic control devices used to control and program the chain
Costs range from $2000-$60,000 (depending on amount of control logic needed)

7. Portable
Portable conveyors are used primarily for applications involving mobility and space is a high priority.
Portable conveyors are very versatile
Loads of up to 1000lbs (depends on the angle)
Can fold up 5-10ft and extend up to 17ft
Have multiple capabilities depending on need.
These are more common for small scale production, where use is temporary.

8. Vibrating
Vibrating conveyor’s operation is typically based on the natural frequency principle. At the natural frequency, the conveyor will vibrate indefinitely with only a small energy input. Once the drive initiates the conveyor's vibration, the supporting springs, by alternately storing and releasing most of the required energy, help maintain constant motion under the conveyed load.
Depending on the frequency and the size of the object can reach speeds as high as 35 fpm
No programming is needed, uses an on or off system to control it
Can handle objects <1 - 90lbs
Can handle various sizes and shapes
Used in pharmaceutical and mining industries

9. Screw/Spiral
Spiral conveyors are used mainly for heating, cooling or accumulation
Screw conveyors use a rotating screw in a channel or tube to move material
Primarily run on a continuous motor that is simply on or off
Costs range from $500-30,000
Sizes up to 48” diameter tubing and can stack as high as 50 ft
Used in the pharmaceutical, food, and manufacturing industries
Useful for accumulation, drying, or moving vertically in a small space

10. Belt
Conveyor belts are used in a wide variety of material transport applications such as manufacturing, food processing, and heavy industry.
Commercial applications include:
Agriculture
Construction - heavy building materials
Food and beverage processing
Forestry - logging, sawmill, paper pulp, etc.
Mining and quarrying
Factory production line
Belt Width ranges from 12” to 120”
Belt Speeds determined by loads and speed required. Ex: Bushels/hr dictates size.
Prices range from $500 to $30k or more for custom applications. Depends mainly on Length, Width, and Speed

11. Overhead
Overhead Conveyor Systems are typically used to convey unit loads in a variety of industrial applications, such as:
Painting - Electrostatic, powder coating, fluidized bed, dip and conventional spray.
Washing - Parts and dunnage.
Oven - Pre-heat, baking, drying, flash off and curing.
Transporting - Products between work stations or plant operations to maximize floor space and increase efficiency.
Storage - Finished Goods, raw materials, work in process, and tooling.
Speeds can range from 3 fpm to 60 fpm and more based on application.
Capacities per unit load range from 30 lbs to 1200 lbs (based on load connector type).
Unit spacing should be taken into account when determining length and operating capacity (varies by connector type).
Cost is determined by unit load, speed/motor size, and length. Price ranges from $30 per foot to $100 per foot.

12. Summary
Conveyors are very versatile and can be an inexpensive way to move things
Rollers- are cheap and can move heavy objects
Chain- are more expensive but can do more complicated tasks
Portable- can be useful for small applications and are easy to store
Vibrating- useful for moving lots of small parts or things that are misshaped
Screw/Spiral- are useful for accumulation, drying, and moving things vertically in a small amount of space
Belt- are the most common type of conveyors and are very versatile
Overhead- take up less room than other conveyors and can deliver vertically

13. Construction of conveyors

14. Idlers

15. TROUGHING ANGLE

16. SURCHARGE ANGLE

17. TYPICAL CONVEYOR CONFIGURATION

18. Typical conveyor loading

19. Loading/Tipping point (The grizzly/rock breaker system)

20. Typical transfer chute design

21. Carrying Capacity T = a.b.v T is the carrying capacity
a is the average cross section area
b is the bulk sample
v is the speed of the conveyor.
a is approx. between w2/10 and w2/12

22. Power Required by the conveyor
Power for the empty belt, We
Power to convey the material, Wm
Power to raise the material, Wr
Total Power, Wt
Wt = We + Wm +- Wr

23. Power at the Motor
The calculated power is power required at the driving drum of the conveyor, and so the motor power required will be greater because of the power losses in the gearing at the drivehead.
Assuming an efficiency say n,
W = Wt/n

24. Power Required to drive an empty belt
Depends on the total force required to move the empty belt and on the belt rollers
Ne = total weight on idlers x friction coefficient
Ne = Mg * υ
υ for ball bearings is very small about 0.03
The total weight (twice the length of the belt and the mass of the idlers themselves)

25. Length of belt
The length of the belt may be increased because of the wrapping of the end pulley friction.

26. Power of the Conveyor
We = Ne x v
We = MgL υ v

27. Power to convey material
Wm = MLg υ v
M is the mass of material per unit Length which can also be obtained from
M = T/v
Wm = TLg υ v/v = TLg υ

28. Power to raise material to height, h
Wr = T g h

29. Belt Tension
Is the difference of belt tension at the drive head and the tail end and can be found from the total belt power,
Wt = We + Wm +- Wr
Effective tension Pe = Wt/v

30. Relationship of tensions
Let P1 be the maximum tension
P2 is the minimum tension to prevent slip
Pe = P1 – P2
P1/P2 = exp (ϴµ) = n

31. Belt Tension
The belt of the conveyor always experience a tensile load due to the rotation of the electric drive, weight of the conveyed materials, and due to the idlers. The belt tension at steady state can be calculated as:
Tb = 1.37*f*L*g*[2*mi+ (2*mb + mm)*cos (δ)] + (H*g*mm)…….eqn.1.1

32. Cont… Tb is in Newton. f = Coefficient of friction
L = Conveyor length in meters. Conveyor length is approximately half of the total belt length.
g = Acceleration due to gravity = 9.81 m/sec2
mi = Load due to the idlers in Kg/m.
mb = Load due to belt in Kg/m.
mm = Load due to the conveyed materials in Kg/m.
δ = Inclination angle of the conveyor in Degree.
H = vertical height of the conveyor in meters.

33. This can be calculated as below:
Load due to Idlers
This can be calculated as below:
mi = (mass of a set of idlers) / (idlers spacing) ……………..eqn.1.2

34. Power at the Drive pulley
The power required at the drive pulley can be calculated from the belt tension value as below:
Pp = (Tb*V)/1000……………..eqn.1.3
Where,
Pp is in KW.
Tb = steady state belt tension in N.
v = belt speed in m/sec.

35. Belt Tension while starting the system
Initially during the start of the conveyor system, the tension in the belt will be much higher than the tension in steady state. The belt tension while starting can be calculated as:
Tbs =Tb*Ks………………..eqn.1.4
Where,
Tbs is in N.
Tb = the steady state belt tension in N.
Ks = the start-up factor

36. Size of Motor The minimum motor power can be calculated as:
Pm = Pp/Kd………………eqn.1.5
Where,
Pm is in Kw.
Pp = the power at drive pulley in Kw
Kd = Drive efficiency.

37. Acceleration
The acceleration of the conveyor belt can be calculated as:
A= (Tbs – Tb)/ [L*(2*mi + 2*mb+mm)]……………………eqn.1.6

38. Cont… Where, A is in m/sec2
Tbs = the belt tension while starting in N.
Tb = the belt tension in steady state in N.
L = the length of the conveyor in meters.
mi = Load due to the idlers in Kg/m.
mb = Load due to belt in Kg/m.
mm = Load due to the conveyed materials in Kg/m.

39. Belt Breaking Strength
This parameter decides the selection of the conveyor belt. The belt breaking strength can be calculated as:
Bs= (Cr*Pp)/ (Cv*V)…………..eqn.1.7
Where,
Bs is in Newton.
Cr = friction factor
Cv = Breaking strength loss factor
Pp = Power at drive pulley in Kw
V = belt speed in m/sec.

40. Conveyor Input Parameters
Conveyor capacity (Cc) = 1500 t/h = Kg/sec
Belt speed (V) = 1.5 m/sec
Conveyor height (H) = 20 m
Conveyor length (L) = 250 m
Mass of a set of idlers (m’i) = 20 Kg
Idler spacing (l’) = 1.2 m
Load due to belt (mb) = 25 Kg/m
Inclination angle of the conveyor (δ) = 5 0
Coefficient of friction (f) = 0.02
Start-up factor (Ks) = 1.5
Drive efficiency (Kd) = 0.9
Friction factor (Cr) = 15
Breaking strength loss factor (Cv) = 0.75

41. Calculations
First, we will use the eqn.1.2 for finding out the load due to idlers:
mi = (20/1.2) = Kg/m
We will use the eqn.1.1 for finding out the belt tension in steady state:
Tb = 1.37*0.02*250*9.81*[ {2*25+ (416.67/1.5)}*cos (5)] + (20*9.81* (416.67/1.5)) = N.
The belt tension while starting the system can be calculated by using the eqn.1.4:
Tbs = 1.5 * = N
For calculating the power at drive pulley, we will use the eqn.1.3:
Pp = ( *1.5)/ 1000 = Kw

42. Calculations We will use the eqn.1.5 estimate the size of the motor:
Pm = /0.9 = Kw
We will use the eqn.1.6 to find out the acceleration of the motor:
A = ( )/ [250*{(2*16.67) + (2*25) + (416.67/1.5)}]
= m/sec2
Lastly, we will use the eqn.1.7 to find out the belt breaking strength:
Bs = (15*116.35) / (0.75*1.5) = N/mm
This Bs value is used to select the conveyor belt from the manufacturer’s catalogue.

43. BELT SAFETY FEATURES Feature Use Pull switches
Pull switches
-to stop belt in an emergency
Alignment switches
-to stop belt in case of misalignment
Belt interlock system
-if a belt stops the system is configured in such a way that the preceding belts also stop.
Anti-slip detectors
-for detection of motion and belt slip
Rip or tear detectors
-Trips belt with detection of rip or tear
Automatic tension uptake
-automatic winch belt tensioner for tension adjustment.
- gravitational tension take-up unit for belt tension adjustment for last belt in the chain

44. CONVEYOR BELT OPTIMIZATION
Instantaneous Flow Rate
Index Time
True loading

45. TYPICAL INSTANTANEOUS LOADING RESULTS

46. TYPICAL DECLINE TRUE LOADING RESULTS

47. MULTILAYERIING EFFECT

48. QUESTION
Suggest a solution to the multi-layering phenomenon on decline conveyor belts in underground on-reef mines. The solution should attempt to ensure continuous loading rather than discrete loading with high instantaneous flow rates.