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Lesson 14: Components
Idlers and Pulleys
In this lesson you will learn:
How to select idler class. How to determine thedesired drive pulley RPM. The effect of belt wrapon belt tension and pulley selection. How to selectproper pulley diameter.
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Idlers
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Types - Carry or Trough Return
Purpose -
Shape load Support the belt
Idlers
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Return Idlers
Troughing or CarryIdlers
TransitionIdlers
Impact Idlers
Idlers
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CEMA Classifications
B
C
D
E
F
typicalaggregate sizes
Idlers
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CEMA Idler Classification
Idlers
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Common idler roll diameters -
4
5 6
7
8
typicalaggregate sizes
Idlers
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Carry Idlers
Idlers
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Trough Angle -
20 degree
35 degree most widely used
45 degree
Idlers
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Return Idlers - different profiles
Flat
Rubber disc
V
Idlers
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Trough Training Idlers
Helps train the belt
Typically spaced every 100 -150
Training idlers - approximately taller thanstandard idler to help create aligning effect
Idlers
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Return Training Idlers
Helps train the belt onreturn side
Typically spaced every 100 -150
Good contact with belt is critical
Idlers
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Off-center loading cannot be corrected
by training idlers
Training idlers work more effectively atlow belt tensions
Idlers
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Training idlers are especially effective in lowtension reversible conveyors
Belts greater than 48 wide are not generally
effected by training idlers belt weight providesgreater training force
Idlers
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Rule of thumb
the greater the belt tension,
the less effective training idlers are!
Idlers
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Idler selection
CEMA has a nice idler selection guide
Step-by-step method to select idlers
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Step 1: Troughing Idler series selection
Calculated Idler load (CIL):
Idler selection
IMLSKWWCIL imb 1Where:
Wb = Belt Weight (lb/ft)
Wm = Material Weight (lb/ft)
Si = Idler spacing (ft)
K1 = Lump adjustment factor (see table on next slide)
IML = Idler misalignment load (lbs) (see slide after next)
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Idler selection
K1 Lump adjustment factor
Maximum Lump size (in)
Material Weight (lb/ft3)
50 75 100 125 150 175 200
4 1 1 1 1 1.1 1.1 1.1
6 1 1 1 1.1 1.1 1.1 1.1
8 1 1 1.1 1.1 1.2 1.2 1.2
10 1 1.1 1.1 1.1 1.2 1.2 1.2
12 1 1.1 1.1 1.2 1.2 1.2 1.3
14 1.1 1.1 1.1 1.2 1.2 1.3 1.3
16 1.1 1.1 1.2 1.2 1.3 1.3 1.3
18 1.1 1.1 1.2 1.2 1.3 1.3 1.4
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Idler selection
Idler Misalignment Load (IML)
iS
TDIML
6
Where:
D = Misalignment (in)
T = Belt Tension (lbs)
Si = Idler spacing (ft)
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Troughing series idler selection
Use CIL to select the idler series from the load ratingtables in the idler catalog
Idler selection
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Step 2: Return idler series selection
Pick a return idler series based on the load rating
tables in the idler catalog
Idler selection
IMLSWCIL iBR
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Steps 3-7: Impact idler selection and L10 calculations
Read CEMA Idler standards for an overview
Will not be covered in this class
Rules of thumb for diameter More than 500RPM decreases L10 life
Try to stay below 500RPM, but 4 is really going away 4dia @500RPM = 524FPM **only use 4 in economy situations
5dia @500RPM = 654FPM
6dia @500RPM = 785FPM
Etc.
Idler selection
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Pulleys
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End Disc
Rim Shaft
Hub
Bushing
Pulleys
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Types -
Drum
Wing
Purpose -
Transmit power to the belt
Change belt direction
Pulleys
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Tail
Pulley
SnubPulley
Take-upPulley
Bend Pulley
Bend Pulley
Head or DrivePulley
Pulleys
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CEMA DUTY -
Load, dimensions and crowndefined by ANSI B105.1
Used on fabric belt
Pulleys
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MINE DUTY
Not governed by ANSI
Standard size drums and wings
Manufacture specified designs
Pulleys
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ENGINEERED CLASS -
Designed to meet load requirements
at a specific location on a conveyor
Primary used on steel cord belts
Belt tensions and loads exceedCEMA B105.1 and 501.1 > 800 PIW
> 80,000 modulus PIW
Pulleys
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Pulley Lagginga smooth or embossedcovering or coating applied to a pulley
Increases belt traction
Minimizes wear due to abrasion
Promotes cleaning action
Pulleys
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Grooved laggingused on drive pulley toshed water & improve traction
Chevron - grooves meet at center
Herringbone - offset at center by spacing
** Apex should be in direction of belt travel
Pulleys
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Pulleys
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Pulleys
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Ceramic
Increased coefficient of friction
Excellent abrasion resistance
High tension & HP applications
Pulleys
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Pulleys
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Wing Pulleys
- help protect the conveyor belt from the damaging effectsof fugitive material trappedbetween pulley and belt.
Pulleys
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B t i
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Bent wings
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Pulleys
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Pulleys
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Pulley selection is based heavily on belt tensions
So to start were going to look at belt tensions at
locations where pulleys are commonly installed
Pulley Selection
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Belt Tensions
Te is calculated from the application
Te is used in an equation:
In order to find T1, we must first solve T2
21 TTTe
21 TTT e
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Belt Tensions
There are two equations that calculate T2 Whichever T2 is higher governs
T2based on 2% sag:
.long arduous equation I will spare youfrom.
T2based on drive slip:
we CTslipT 2
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Belt Tensions
Once we have T2, we can solve the equation:
..to find T1
21TTT e
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Belt Tensions
After T2, very little changes to belt tension downto TT.
Some change due to return roller friction
Some change due to non-drive pulley friction
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Example 100 conveyor
Head/drive tension (T1) = 6612.5lbs
Snub tension (T2) = 2527.9lbs
Bend pulley tensions (Ttakeup) = 2479.8lbs Takeup pulley tension (Ttakeup) = 2479.8lbs
Tail pulley tension (TT) = 2287.6lbs
Pulley Selection
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Turn tensions into PIW (pounds per inch of beltwidth)
36BW:
T1 = 6612.5lbs = 184PIW
T2
= 2527.9lbs = 70PIW
Ttakeup = 2479.8lbs = 69PIW
TT = 2287.6lbs = 64PIW
Pulley Selection
)(
)(
inBeltWidth
lbnBeltTensioPIW
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S
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Many programs can be used to select idlers andpulleys
Here is an example of how they work:
Idler & Pulley Selection
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Questions???
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