Belt Conveyors, Operation & Maintenance

in Cement Plant

1- Introduction

1.1 Handling and conveying of material

1.2 Material characteristics

1.3 Materials in cement industry

1.4 Main processes in cement industry

1.5

1.6 Conveying equipments in cement industry

1.7 Factors affect choice of conveying equipment

2-Belt conveyor

2.1 Advantegaes of belt conveyor

2.2 Belt conveyor in industry

2.3 Belt conveyor in cement industry

3- Basic design concept

3.1 operation theory

3.2 configurations

3.3 Different lay out

3,4 Capacity

4- Components

4.1 belt

4.2 idlers

4.3 pulleys

4.4 loading and discharge

4- Maintenance and repair

joining belts

alignment

5- Safety

hazard

accidents

6- Appendix 1 safety

2 alignment

Contents

1 Introduction

Material Conveying

Moving material continuously or intermittently between two or

more points along fixed path

Material Handling

Material handling includes all material consideration except

processing operations. It includes :

• conveying

• feeding

• packing

• storing

• warehousing

• loading

• unloading

1.1

1- Particle size

Bulk Blasted

or

ripped

Crushed

Materials characteristics

Grinded

1.2

Materials characteristics which more affect conveying process are :

2- Particle shape

Rounded Sub-rounded Sub-angular Sharp angular

3- Angle of repose

It is the angle of pile formed by free and careful

pouring of material

The lower angle of repose , the more flowable material will be

4- Angle of surcharge

It is the dynamic angle of repose

• large lumps migrate upwards

• the pile moves latterly outwards

It is edge angle of shacked pile

Shacking material results in :

Angle of surcharge is less than angle of repose

Material is shacked when :

• by truck over irregular land

• by belt of big sag

Clay

Crusher

L.S Crusher

R.M mills

R.M

Soils

ClinkerSioles

Cement Mills

Cement Sioles

Cement dry process flow chart

كساره

الكلنكر

Pre- heater

1.3

Blasting

Crushing

Grinding

Burning

Cement

Grinding

Main processes in cement industry 1.4

Materials in cement industry

• Limestone

• Clay

• Gypsum

• Others : - sand

- pyrite

- slag

1.5

Semi- product • Clinker

Final product

Waste material • By-pass dust

• Filter cackles

• Others

• Cement

Raw material • Blasted

• Crushed

• Grinded

• Powder

•

Types shape

Conveying Equipments Classification

Pneumatic Mechanical

Belt

conveyor

Screw

conveyor pan

conveyor

Bucket

elevator

Trucks

Fans

Air

slides

Air

lift

Conveying Equipments 1.6

Physical

Material

conveyed Quantity

Temperature

Conveying

distance

Conveying

direction

Factor affecting choice of conveying equipments

• Grain size

• Humidity

• Hardness

• small

• Medium

• Big

• normal

• Medium

• high

• short

• Medium

• long

• horizontal

• up vertical

• down

vertical

1.7

2 Belt Conveyor

• Require light foundation with minimum support structure

• Capability to traverse grade up to 30

• Span up to 10 km

• Can cross over roads, railway and other obstructions

• Medium to large amount of material

• Variety of loading and unloading possibilities

• Can be loaded from one or more points simultaneously

• Mobile chute may be used

• movable belt tripper

Belt conveyor advantages 2.1

Belt conveyors are standard equipment in the mining and aggregates industries.

They are also widely used in cement industry to convey materials between

different processes especially remote one as they are simple and of low operation

and maintenance cost, but they are also a source of some well-recognized

hazards.

Belt conveyors in industry 2.2

Belt conveyor in cement plant 2.3

Theory of operation

• A conveyor belt system consists of two pulleys, ) head and tail ( with a

continuous loop of material that rotates about them.

• The driving pulley is powered, moving the belt and the material on the belt

• The material is conveyed in steady and effective way which require :

• No slip between belt and pulleys

• No spillage of material out of belt

2.4

Basic configuration

head pulley Belt loading side Belt back side

Take up system

Troughed idlers

Troughing idlers

Return idlers

Feeding hoper

Return idler

Tail pulley

Belt conveyor may require a variety of secondary support or systems.

2.5

Lay out

• Belt conveyors offer a large flexibility in lay out arrangements.

• Belt can be manipulated in various ways to achieve its final destination using

standard sections

Horizontal section Inclined section

2.6

Straight belt

Curved belts

Various belt conveyor arrangements

0,9

0,9

0,9

system reliability = 0.9 x0.9 x 0.9 = 0.73

• expensive system

• extra maintenance

• extra dust control system

• reduce reliability

Single belt section

Multi sections in series

(with transfer points)

Number of transfer points should be minimized

Transfer points may lead to :

Transfer point

Various drive arrangements

Drive location

number of driving pulleys

number of drives per pulley

• head pulley

• tail pulley

• any intermediate location in return line

• single

• dual

• one side

• two sides

snub • snub

• no snub

• more power can be transmitted before slipping

• lower maximum belt tension

• more efficient conveying

Increasing wrap angle lead to :

•Wrap angle

Snub pulley increase wrap angle

• single pulley drive

• at head end

• no snub

• single pulley drive

• at tail end

• no snub

• single pulley drive

• at tail end

• with snub

• single pulley drive

• at return line

• with snub

• dual pulley drive

• primary and secondary at return line

• no snub

• dual pulley drive

• primary on head pulley

• secondary at return line

• no snub

• dual pulley drive

• primary and secondary at return line

• snub

• drives in clean side of belt

• dual pulley drive

• primary and secondary at return line

• snub

3 Belt conveyor components

3.1 Belt

General construction

• provide tensile strength necessary to move loaded belt

• absorb the impact load of material

• provide lateral stiffness necessary to support load between idlers

• provide adequate strength for mechanical fasteners to be hold on belt

Carcass

• protect top belt from material to be loaded

• absorb abrasive wear

• protect carcass

• withstand any environmental conditions

Top

cover

• protect carcass from possible wear from idlers and pulleys

•

Bottom

cover

Belt is composed of main components :

• Increase adhesion between carcass and top cover

• Increase lateral support

• Enhance belt :

- impact

- heat

- ripping resistance

Breaker

Carcass design

The carcass consists of high–strength material evenly spaced either :

- longitudinal called wrap yarn

- traversaly called weft or fill yarn

Wrap yarn

fill yarn • non tension element

• weaker than wrap

• give carcass strength along its width

• prevent wrap from separating

Yarn material • cotton

• rayon

• glass fibers

• nylon

• polyester

• steel

• high tensile material

• can used as sole member or,

• coupled with fill yarn

• simple construction

• Wrap and fill yarns crimp over each other

• inexpensive

• easy spliced

plain weave

Straight wrap

weave

Solid Woven

weave

Wrap and fill yarns are mostly weaved in the following common patterns :

Weaved patterns :

• Wrap and fill yarns do not crimp

• Yarns are locked together by binder yarn

• Eliminate geometric stretch longitudinally

• Expensive

• Difficult to splice

• different layers of wrap and fill yarns

• layers are tied together with binder

•

• incresase strength

• increase load capability

• increase belt weight

• decrease belt flexibility

• need larger pulley diameter

Plies number

1 ply

2 up to 8 plies

Multi-Ply Conveyor Belt Features

Polyester Nylon (PN or EP)

Synthetic woven fabric, with polyester fiber in the warp and nylon fiber in the weft

Medium, long distance and heavy load transportation of materials

Low elongation and good troughability

Nylon Nylon

Consists of synthetic woven fabric with nylon fiber

High impact and abrasion resistance with extended belt life

Highly flexible and good troughability

Belt Construction

Comprising of top and bottom cover rubber

Textile fabric carcass of one or more plies to provide the tensile strength

Rubber skim coats which play a significant role in detetmining the belt load support and troughability

A. Top Cover : Various thicknesses and grades available

B/D. Carcass : From 1 ply to multiple plies

C. Skims : From 0.5mm upwards

E. Bottom Cover: Various Thicknesses and grades available..

F. Moulded Edge (Sealed) or Cut Edge

Steel Cord Conveyor Belt Features

Suitable for large capacity loads over long distances at high speeds

High tensile strengths

Low elongation with less take up required

Excellent troughability and flexibility

Excellent spicing efficiency

Belt Construction

Reinforcement consisting of galvanized steel cords and core rubber

High adhesion between the rubber and steel cord, providing shock resistance and a longer service life

Even tension of cords, providing well balances belt running

Rubber

Belt capacity

The capacity of troughed belt is determined by :

• belt width

• material

(angle of surcharge

• belt width

• trough angle

1- Trapezoid formed by the idlers and the outer limit of material on the belt (A) .

2- circular segment formed by material surcharge (B) .

3- belt speed

4- material density

(A)

(B)

Narrow fast belt Wide slow belt

• very fine material

• Fragile

• Heavy lumps

• Sharp edges

• Abrasive

When material charactristics are favourable, it is more desirable

to use high speed

• Cost wise

Common to day speed = 5 – 6 m/s = 10 – 15 Km/h

For given capacity it is flexible to choose :

Belt Splices

vulcanizing Mechanical fasteners

• the stronger

• suitable for natural fibers and nylon

carcass

• sealed carcass away from moisture

• Does not affect belt scraper role

• not so strong

• suitable for low tension application

• less expensive

• done by simple and standard tool

• done in minutes

• needs no special cleaning precaution

• leave carcass exposed

• affect belt scraper role

vulcanizing

Hot method Cold method

• The strongest one

• needs specialized equipments

• needs well trained personnel

• needs long time for curing

• fairly strong bond

• use liquid cement and hardener

• needs moderate trained personnel

Mechanical fasteners

Hinged type Solid plate type

• can be installed in a shop and quickly

joined on-site

• can join different thickness of belts

• leave small openings and hence less leak

through belt

• easily and quickly separated and rejoin

• suitable for medium tension

• the hinge is subjected to wear

• less leak through belt

• No moving parts hence no wear

• longer service life

• higher tension

•

Most common types of splicing techniques

Hinged type shapes

Solid plate type shapes

The most common used hinged type

mechanical fasteners

Mechanical fasteners attachments • bolt

• rivet

• staple

Belt must have sufficient flexibility to conform the shape of the idlers

Belt must have sufficiently stiffness to support the load

Belt flexibility and stiffness

and F

lexib

ilit

y

Stiffn

ess

3.2 Idlers

Idlers are stationary roller over which belt travels between pulleys

Idlers construction

• Effectiveness of seal

• Quality of bearing

• Shaft deflection

• concentric of bearing with shell

• lubrication

Factors affect idlers operation

• outer shell

• shaft ( concentric with outer shell )

• bearing

• seal

The life time of Idlers depend mainly on life of its bearing

Function

Basic types

Carrying idlers • used on the top run of the conveyor

• carry the weight of belt and material

• flat or troughed

Return idlers • used on the bottom run of the conveyor

• carry the empty belt on return run

Troughing idlers

• consist of three equal rollers attached to rigid frame

• the most common used

• standard angle : 20 - 30 – 40 degree

• higher angle used with flexible belt

• higher angle increase belt capacity

Idlers configurations

Offset troughing idlers

• the horizontal roller is located on a different plane than the

inclined pair

• prevent belt pinching

• has non gap between rolls

• suitable for thin belts

• no pinching between rollers

Impact idlers

• the idler has a extra roll of resilient rubber

• absorb the impact of large lumps

• used in loading section

Training idlers

• same construction as regular idler

• the rigid frame is mounted on central pivot

• free rotation of pivot is essential

• off- centered belt touched side roll

• not recommended in vertical curve belt

• take special care when use with reversable belt

• training effect is reduced with increasing belt tension

• normal spacing : not closer than 50m – 75m

Suspended idlers

• idlers are attached to each other by movable link or chain

• the chain is suspended from the rigid frame

• compensate off- center loading and belt misalignment

• up to 20 rollers can be used

Flat return idlers

• most common used

Self return Flat return idlers

• single roll

• multiple roll

• more effective due to low belt tension and long span

Self cleaning idlers

•

Idlers arrangement

Idlers spacing

• Weight of material and belt

• belt tension

• allowable belt sag

S S S S

Factors considered

Long spacing

Small spacing

• Load / each idler increase

• belt sag increase

• material spill

• material vibration

• power loss

Normal sag 2 – 3 % S

• cost wise

Transition distance (S )

It is distance a belt travels from being flat (over pulleys) to

becoming completely fully troughed (over idlers)

Too short • belt outer edges over stretched

• Decrease belt life

Most common transition distance : 3 – 5 belt width

S

• Rapidly wearing contact seals,

• rotating end caps to seize,

• welded-in end caps to wear away,

• non-concentric welding,

• poor bearing support

• premature bearing failure

• disc separation

Common idlers fault

Disc separation

Bearing failure

3.3 Pulleys

General construction

• shell (rim)

• two end discs

• two hubs

• main shaft

Pulleys shapes

Straight lagged Wing

Crowned Crowned Helical

straight pulley

Lagged pulley

• Increase friction between belt and pulley face

• protect pulley face from wear

• reduce material build upon pulley face

• increase pulley life by replacing lagging pad instead of pulley

• lagging can be applied by cold vulcanizing or mechanical fasteners

•

Lagging shapes

Lagging direction Belt travel

Lagging technique • cold vulcanizing

• mechanical fasteners

Wing pulley

• wings prevent material build up between belt and pulley

• fins help to cool down pulley

• slapping motion shake loose material of the belt

Crowning

Tapered crowning Curved crowning

• less cost

• normal taper : 1%

• higher taper may damage belt carcass

• crowned pulley has training effect on the belt

• forces affect on misalignment belt are unequal

• the difference acts on belt to resume the center position

• it is most effective when there is a long unsupported approaching span

• expensive

• large radius curve

Pulley size

• must be large enough to affect traction on the belt

• provide the required belt speed

• matched to belt minimum bending radius

• should be matched to conveyor power train : motor and reducer

1- Diameter

Pulley width

8 cm

5 cm

Up to 1 m over 1 m

Pulley must be slightly wider than belt

Types of pulleys

Conveying belt system contain variety of pulleys performing

different tasks

• head pulley

• tail pulley

• snub pulley

• bend pulley

• take up pulley

• head pulley is on the discharge end

• tail pulley is on the feed end

• tail pulley is often crowned to help in belt tracking

Head and tail pulleys

• Transmits force from motor to the belt

• the most common location is at head pulley

• could be located at tail pulley or any independent site

Drive pulley

• Smaller in diameter than head or tail pulley

• Increase wrap angle around drive pulley

• mostly crowed to aid in belt tracking

Snub pulley

• Direct the belt away from its path

Bend pulley

• Allow adjustment of belt tension

Take up pulley

• Adjust the proper tension

• Absorb any stretching along belt longitudinal axis

• Store a small amount of belt length as spare

• allow to release belt tension for maintenance and repair jobs

Take up system

Function

Take- up system

• Manual

• Automatic

Manual take up

In- line type

off- line type

• Compact and inexpensive

• adjusted by screw, spring, ratchet or jack

• Relies on operator judgment

• Needs periodic adjustments

• Normally located opposite to drive side

• Suitable for very short belts

• Could be in /off line of belt plane

• normally located opposite to drive end

• mounted in- line or off- line of belt

Automatic take up systems

• Pneumatically

• Hydraulically

• Electrically

• By gravity

Gravity type is most common used for :

• economical and effective

• installed horizontally or vertically

• self adjusting

• installed anywhere on the return line

• it is desirable to locate close to drive for quick reaction

Gravity take up system

4 Loading & unloading

system

Proper loading system feeds material to the belt in a way such way that :

Inproper loading system can lead to :

• decrease belt life

• accelerate top cover wear

• seized idlers

• decrease idlers life

• belt misrtacking

• clogging or jamming of conveyor

• spilled material

• dust generation

• uniform rate

• centeraly

• in direction of belt travel

• velocity matched to belt speed

• free of large pieces

• no impact

What is the Proper loading system

Chute function

• contain and shape material

• adjust material direction and velocity

• longitudinal chute

• transverse chute

Chute types

Longitudinal chute

loading system components

Transverse chute

To load material to transverse belt

• let material lose some of its velocity

Fall zone

• absorb some of material transverse velocity

• direct material in appropriate direction

Deflection plate

Slide plate

• give material forward velocity in belt

direction

• help in shaping the load

Slide grizzly bars

• spaced bars in melt direction travel

• allow fine material to pass trough

• fine material act as cushion pad on belt

Fine and lump mixture

Stone box

Very abrasive material

• shelf at chute base

• the shelf trap a layer of material

• the trapped material protect chute body

Speed up transfer belt

• give material forward velocity to match belt speed

• speed up transfer belt is thick and durable

Skirting

• contain material on belt until it becomes settled

• it is parallel to belt

• commonly spaced to 2/3 of belt width

• commonly length1.3 m for every o.5 m/s belt speed

• only have light contact with belt

• straight

• deflector

• continuous strips

• sectioned block

Types

Discharge system

• over the end pulley

• belt plow

• belt tripper

4.3 Belt cleaning system

• accelerate wear of idlers surface

• mistrack belt

• decrease bearing life

Improper cleaning may lead to :

Types of belt cleaning

• single or multiple blades

• blades are connected to adjusting device

• adjusting device compensate blades and belt wear

• adjusting device is actuated by spring or counterweight

• blades are made of rubber, steel or ceramic

• blades types are :

•Peeling : almost parallel to belt or max 30 degree

• scraping : closely perpendicular

• mechanical splice should be covered by a flap

Blade cleaner

There are many types ,but the most common is blade cleaner

5 Maintenance

Belt alignment

What is meant aligned belt

A belt is considered to be aligned or tracking properly, when ( under full load ) :

- the edges of the belt consistently remain within the width of the pulley faces

- the belt is within the confines of other rolling components, such as idlers and

return rolls

To accomplish this, all components must be square

relative to one another (i.e., 90 degrees

perpendicular to a common centerline), and level in

the crosswise direction

Belt misalignment diagnoses

• tracking

• power consumption

• high wear rate

• spillage

•

Alignment steering force

• The main steering force comes from troughing idlers because :

- two-third of belt and material are elevated to higher level by idlers

- the gravity force will center the belt in the idler set

• frame

• pulleys

• rollers

• roller frame

• belt

• tension system

• belt tension

• feed hopper

• cleanness

Factors affecting belt alignment

• Horizontal

• vertical

• rotational

• axial

Frame misalignment Joining sections

Reasons for frame misalignment

• suspended frame

• rugged territary

• the belt moves toward the first point of contact on roller or idler

• reaction will happen downstream the adjusted idler

• reaction is not immediate , normally after two or three cycles

• small adjustments to many idlers is better than many adjustments to one idler

• only one person should make all decisions to avoid confusion

• start training process by empty belt

• start with return run, from head to tail

Guides rules

Belt tracking

Roller frame

• Deformation

• Wear

• Misalignment to main frame

wear

deformation

Idlers set misalignment

• traverse

• rotational

self aligning set should be higher

over other idlers

Belt

Unbalanced wrap tension in carcass resulting a bowed or crescent belt

10 m

s

S less than 0.5 %

1- stretch

2- un square splicing

Belt drift

Dirties

On belt’s backside

The backside of the conveyor belt provides the friction that :

- transfers the torque provided by the drive, or

- drives, to the belt and creates the rolling action of the idlers and

tail pulley.

Water and dirt can interfere and decrease this power or torque transfer and

can affect the guiding capabilities of the rolling components and lead to

alignment problems

•Traveling with belt

Friction between belt and roller

Over tension Under tension

Monitoring

• Free rotation of - carrying idlers

- return idlers

• rollers temperature

• side limiter

• even material on belt

•

• frozen idlers

• motor KW

• abnormal noise or vibration

• belt misalignment (touching

side guide rollers)

•

• missed idlers

• cracked idlers

• belt sag

•

•

Before start After start

Safety

.

Hazards The main hazards involve moving belts.

This moving belt can catch body parts in pinch points and

lead to entanglement and crushing.

Accident Types Common types of accidents with conveyors involve

personnel struck by objects or caught in equipment.

The majority of these accidents occur when workers attempt

to do repairs, installation or clean-up while the conveyor

system is active.

Lockout

- Determining the equipment or components to be worked on,

- Turning off and isolating all energy sources,

- Drawing off stored energy or potentially dangerous product,

- Installing tags and locks.

- Equipment must be turned off and isolated even for short-duration adjustments or

repairs.

- Procedures must be specified for each workplace and each piece of equipment to

ensure,.

Checklist

For inspection and maintenance purposes, a conveyor checklist is

recommended. • emergency stop pull cords

• start-up warning device (audible/visible )

• guards on head, tail, drive, deflection, and tension pulleys

• guards on accessible pinch points

• guards protecting workers from overhead material

• means of safely applying belt dressing and lubrication to a moving conveyor

• fire suppression system

• guardrails

• access equipment (walkways, ramps, stairs, platforms, etc ).

• noise control .

Machine Guarding The use of guards on a conveyor system is not a recommendation,

it is a requirement . - Guards on moving conveyor parts are often :

- - non-existent,

- - inadequate,

- - improperly positioned, or

- - not replaced after repairs.

- - are not in place,

- - Not paint in bright contrasting colures. Legal Requirements

- no guards beneath a conveyor against falling materials

specific safety requirements for conveyors

- pull cords at accessible locations for stopping the conveyor in emergencies

- a means of applying belt dressing while the conveyor is in motion

- a start-up warning device when the conveyor is started :

- automatically or

- by remote control or

- where portions of the conveyor are not visible to the operator

CEMA has a chapter on safety and gives the importance of design

and operation for a safe BC system. Here are some of the pointers:

* When the BC system is towards completion, give a complete

indoctrination to all personnel in the use of the system

* Do a 'safety check-up' before the commissioning

*Conduct a formal training programme in safety for operation,

maintenance and supervisory personnel

*Do not ever use the BC for a material other than the originally

specified

*Only trained personnel will be authorised to operate the BC system

*Make known to all involved, the locations of the emergency controls

and safety devices

*Take a 'walking inspection' periodically. Trained personnel can, on

hearing unusual sounds, often detect potential hazards

*Do not allow anybody to ride on, step on, walk on or cross over a

moving BC

*Any BC found to be unsafe must not be used before the repairs

*Some 'must' prerequisites for a BC safety:

* Good housekeeping

*First class maintenance

* Adequate lighting

*Barricades for unauthorized people entering the BC area

*Safety sign boards

*Warning sign boards to alert people

*Free, easy and uncluttered access to all safety and emergency

devices

CEMA has pointed out that diligence in safety considerations must be

applied during manufacture, installation and establishing operation

and maintenance policies and procedures.

The system design has to take care, but safety has a psychological

aspect too. People's behaviour and awareness have a bearing on

safety.

"Safety is a matter of attitude".

BELT CONVEYOR SAFETY

The main hazards related to belt conveyors are mechanical.

Other hazards are produced by :

- non-compliance with ergonomic principles when workers

operate near the conveyor (operation station, control of the

process, loading and unloading);

- failure or malfunction or safety-related control systems;

electrical

hazards; and thermal phenomena (such as heat, fire or explosion).

The main mechanical hazards are related to:

- mechanical power transmission components (e.g., drive shaft,

reducing gears) that can cause damage by entrainment (by a belt or on

nip points), crushing or entanglement (human body entangled around

a rotating

- other moving components (e.g., idlers, pulleys, belt) that can cause

damage by entrainment in nip points, abrasion and burns;

- pinching zones (e.g., feeder, skirt-board, skirt-board seal) that can

cause damage by shearing and crushing;

- moving loads that can cause damage by shearing and crushing

between the load and a fixed component, or an impact;

- moving subassemblies (e.g., ejectors, switches, transfer mechanism)

that can cause damage by shearing and crushing;

1- According to conveyor location

Location Percentage

- Between the drive pulley, head pulley or tail pulley 48%

and the belt, inside one of these pulleys or between

one of these pulleys another pulley.

- Between an idler or a return idler and the belt. 13%

- Other locations (e.g., between electromagnets and 13%

other components.)

- Drum motor transmission mechanism. 7%

- Between a take-up pulley and the belt. 5%

- Between a caught tool and the belt or the 2%

conveyor frame.

- Not indicated or uncertain. 12%

Accident frequency

2- Worker Activity

- Cleaning a pulley or applying adhesive on a 24%

pulley or cleaning another component of a

conveyor (idler or return idler, frame).

- Maintenance work (other than cleaning 20%

conducted on a moving conveyor.)

- Normal work (e.g., sorting, packaging) performed 11%

on or near a conveyor.

- Recovering an article caught in an unprotected nip 9%

point (7 of 8: between a pulley and the belt; 1 of 8;

between electromagnet roller and the belt).

- Cleaning under or around a conveyor. 7%

- Maintenance work (other than cleaning) near 6%

a moving conveyor.

- Unjamming the conveyor or removing an 5%

accumulation of material.

- Adjusting the belt tension or alignment. 4%

- Other activities (e.g., worker being transported 4%

by a conveyor).

- De-icing and unjamming a frozen belt. 1%

- Not indicated. 9%

Appendix ( 1 )

Safety

Appendix ( 2 )

Belt tracking

Training of Conveyor Belt

1. For a conveyor belt to run straight, it is essential that idlers, pulleys, and loading

conditions are properly adjusted to correct any tendency of the belt to run off center.

2. The empty belt should trough well and contact the horizontal roll of all troughing

idlers; for the belt to run true, all pulleys and idlers must be at right angles to the

conveyor center line.

3. The empty belt should be run only for as long as necessary to observe alignment

and training and to make the proper adjustments for the belt to run true.

4. When the entire belt runs off through a complete sec­tion of the conveyor, the

problem usually is caused by faulty alignment or leveling of conveyor structures, idlers,

or pulleys in that section.

5. If only parts of the belt run off throughout the entire conveyor, the problem usually is

caused by the belt itself, in the splices of the belt, or in belt loading.

6. In a new installation, when adjustments have been made for the belt to run well and train

true, the belt should be fully loaded and the conveyor operated for several hours. At the end

of the day or work-shift the belt should be stopped and allowed to stand idle over night with a

full load on it. This will hasten the break-in time for adjusting the belt to flex in a troughed

position.

7. Particular care should be taken to make appropriate adjustments on new installations

before the conveyor is operated on a full production schedule.

6. In a new installation, when adjustments have been made for the belt to run well and train

true, the belt should be fully loaded and the conveyor operated for several hours. At the end

of the day or work-shift the belt should be stopped and allowed to stand idle over night with a

full load on it. This will hasten the break-in time for adjusting the belt to flex in a troughed

position.

7. Particular care should be taken to make appropriate adjustments on new installations

before the conveyor is operated on a full production schedule.

Critical points which must be checked for proper conveyor performance are:

8. Terminal pulleys. When training a new conveyor, the first adjustment should be to make

certain that the belt will travel centered on the head and tail pulleys. Ad­justment on the head

end snub pulley will help train the belt at the point where it enters the return run; adjustment

on the snub pulley at the tail will affect travel position of the belt over the tail pulley.

On vertical gravity take-ups, the carriage must be in good working order and the slides

properly in place. Faulty take-up performance could cause the belt to run off the take-up

pulley and cause edge damage.

Critical points which must be checked for proper conveyor performance are:

8. Terminal pulleys. When training a new conveyor, the first adjustment should be to

make certain that the belt will travel centered on the head and tail pulleys. Ad­justment

on the head end snub pulley will help train the belt at the point where it enters the return

run; adjustment on the snub pulley at the tail will affect travel position of the belt over

the tail pulley.

On vertical gravity take-ups, the carriage must be in good working order and the slides

properly in place. Faulty take-up performance could cause the belt to run off the take-up

pulley and cause edge damage.

9. Return side. Belt edges can be damaged if the belt runs off on the return side. All

idlers should be at right angles to the center line to keep the belt running true; however,

if the belt does not train properly with idlers at right angles, some of the idlers may be

changed slightly from the right angle position.

For greatest convenience in making idler adjustments, mounting bolts on the idler

brackets should be posi­tioned at midpoint of the base slots to allow ample fore and aft

adjustment. When idlers are first mounted, mounting bolts should be tightened only

lightly for the initial belt run; final idler position where mounting bolts are tightened firmly

will be determined while the belt is running.

Adjustments for belt alignment on the return side should be made from the head end.

Any tendency of the belt to run toward one side must be corrected by adjusting idlers.

Idler adjustments usually are made at locations 15 to 20 feet behind the point where the

belt appears to run off; the belt will shift toward the side where it first touches the idler

roll.

The effects of idler adjustment are not immediate, and the running belt must be

observed for 2 or 3 complete revolutions after each idler adjustment before

addi­tional changes are made.

Fixed edge guides or self-aligning idlers should not be installed until the belt has

been properly trained.

Edge guides are placed only at points where the belt runs most out of line and

should be mounted so that the belt will not touch the guides unless some idlers or

framing have shifted. All types of guides cause edge wear if belt is continuously

against them. After proper mounting, if the belt rubs against edge guides it will serve

as a warning signal that idler alignment should be checked and adjusted.

Self-aligning idlers should be mounted 2 in. to 3 in. higher than other idlers so the

belt will rest firmly on them and to assure positive actuating. Most self-aligning idlers

work best when the belting is dry. When belting is wet, the coefficient of friction

between belt and idlers is greatly reduced; self-aligning idlers with side guide rolls

work best for wet conditions.

10. Carrying side. Mounting bolts on the troughing idler brackets should be

positioned at midpoint of the base slots to allow ample fore and aft adjustment. If a

belt troughs well when empty and carrying idlers are on center line, there will not be

much trouble experienced with belt training.

Adjustments for belt alignment on the carrying side should begin at the tail pulley. If

necessary, the angle of idler with center line can be changed slightly. As on the

return side, the belt will shift toward the side where it first touches the idler rolls.

.

Training on troughing idlers also can be adjusted by inclining the entire idler frame in the

direction of belt travel. This angle adjustment causes concentrating rolls to have a slight wiping

effect which tends to confine side movement of the belt because the axis of rotation is no

longer at right angles to belt center line. Idler angle adjustment can be made by placing

washers under one side of each bracket so that the idler tilts in the direction of belt travel. Too

much tilt can cause excessive cover wear on bottom side of the belt.

Forward tilt measurement of the carrier rolls can be done by using a carpenter’s square to form

a right angle with the decking. At the outside height of the center line of the outside idler roll

shaft, measure 1/8 in to 3/16 in forward; then under each side of the idler brackets place a

washer with the correct thickness. On some types of idlers, the forward tilt is included in the

casting; no additional washers should be used with such idlers.

Side edge guides or self-aligning idlers should not be placed along the carrying side unless

absolutely necessary. Self-aligning idlers should be mounted 1/2 in. to 3/4 in. higher than the

regular idlers.

When fixed edge roll guides are used, they should be placed at right angles to belt edge

troughing angle and positioned so that belt will be restricted within the limits of the outside

dimensions of troughing or return idlers. With the belt riding on center, there will be about 1 1/2

in. clearance at each edge of the troughing side and approximately 2 in. clearance at each

edge of the return side. Riding against edge guide rolls causes belt edge wear and corrective

measures should be taken whenever belt consistently exerts pressure against the roll.

If the belt has a tendency to run off center behind the loading point and there is a long slack

side behind the loading point, additional troughing idlers will be a training aid.

If loading is off center, a portion of the carrying side will tend to run out of line. Such a condition

is most easily remedied by improving the loading. Self-aligning idlers also can be used to get

the belt back in line.

Other training problems and corrective measures.

11. If the same part of the belt always tends to run off regardless where it is on the

conveyor, the belt is either crooked or a crooked splice has been made. The problem

can be corrected only by resplicing or refastening the belt.

12If the belt has run well for some time and de­velops a tendency to run crooked, one

edge of the belt may be worn thin and stretching, or water may be getting into the belt

fabric and causing the exposed edge to shrink. The problem can be overcome only by

a new belt or a new length spliced in.

13. Tendency of the belt to climb sideways on the same idlers indicates that the idlers

are out of line or the entire conveyor framing could be out of alignment. Misalignment

does not cause a belt to run crooked at the point where the source of trouble actually

is located, and adjusting idlers or framing does not affect the belt at the point of

adjustment but rather 10 or 15 ft. beyond in di­rection of belt travel. Conveyors in pits

or on poor foundations or where frames are made of green lumber will get out of

alignment easily. Conveyors supported on trestles with material piling around the

trestle from a tripper discharge are subject to misalignment due to unequal stresses

on trestle framework. Conveyors on steel supports may change in alignment during a

day due to unequal expansion of metals caused by heat from the sun. In any of these

cases, mis­alignment variations should be studied and align­ment adjustments

established midway between the two extremes of change.

14. A belt which has run for some time on an installa­tion and trains well probably will not

train well on a new or different installation no matter how well the new one is aligned.

Correct training may be achieved through use of mechanical guides, and after careful

running-in the belt could run properly on the new installation.

15. Belt can be forced out of alignment when return idlers develop build up from sticky

materials. Accessory equipment should be utilized to elimi­nate carrying material to

return side of the belt and prevent build up on return rollers.

16. If all corrective measures have been taken to achieve belt alignment and the belt still

does not pass over the center of the head or tail pulleys, alignment could be achieved by

adding two self-aligning idlers in the belt strand approaching the problem pulley. For best

results, one idler should be located 20 ft to 50 ft from the pulley, depending on belt width,

and the other placed the same distance ahead of the first.

This information was copied from the B.F.Goodrich Conveyor Belt Engineering

handbook.

•Summary

•The alignment of a conveyor's support structure has a significant effect on performance. In

particular, tracking, power consumption, wear rates and spillage can often be attributed to poorly

aligned structure. Although problems with alignment are widespread, there is not a great deal of

published literature available on the subject. This paper looks at the effect of idler misalignment

around the vertical axis (idler skew) and attempts to quantify the effect of a skewed idler on the

belts tracking. It includes an evaluation of measurements conducted at the University of Newcastle,

Australia.

•Section 1. Introduction

•The interaction between a misaligned idler and the conveyor belt is a complex one. A number of

factors are involved including the belt's physical dimensions and resistance to bending, idler

orientation, the friction between the belt and the idler, belt mass, material load and belt tension. The

most prominent problems which arise as a result of misaligned idlers are mistracking (which can

cause problems with load shifting and damage to belt and structure), high wear rates on the belt

and idlers, idler failure due to high loading and, in situations where a number of idlers are

misaligned, high power consumption.

•To assist in the analysis of misaligned idlers a reference for defining the misalignment is required.

It is convenient in this case to utilize the "right hand rule" which finds applications in many facets of

engineering. Using the direction of belt travel as the prime reference, the right hand rule gives both

direction and sense to the six degree's of freedom involved in idler alignment. Fig. 1 shows the

notation adopted to define idler misalignment.

•In order to simplify the analysis at this stage the problem will be restricted to considering variations

in idler skew only. This, in fact, forms a measurement of the performance of a training idler on the

conveyor's tracking as well as the effect of a misaligned idler. Further simplification is obtained by

considering only an empty belt and by specifically looking at the effect on belt tracking.