Transcript Introduction to Technical Mathematics

04 - Conveyors
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The intent of this presentation is to present enough information to provide the reader with a
fundamental knowledge of conveyor systems and their components which are used within
Michelin and to better understand basic system and equipment operations.
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Conveyor Components
The Different Types of Conveyors
The principal types of conveyors used in industry are:
 Chain conveyors
 Screw conveyors
 Roller conveyors
 Belt conveyors
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Chain conveyors
A chain conveyor is a machine that transfers material or objects from one point to another by means of a moving
chain. The conveyor chain is driven by a head sprocket or roller, also called a drive wheel. On a plain chain conveyor,
the chain may run in a trough-shaped groove, but on larger conveyors the chain may be supported by carrying idlers
installed sufficiently close to one another to prevent undue sagging of the chain. If the chain has slats attached to it,
the slats are often fitted with small wheels at each end. The wheels run along rails or tracks on either side of the
chain, guiding and supporting it. The slack side of the chain is also supported by carrying idlers called return idlers
(sprockets or rollers). A conveyor chain may have plates, blocks or bars attached to it which are designed to catch,
push or drag the object or material which is to be moved.
Typical Chain Conveyor
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Screw conveyors
Screw conveyors are used extensively in handling
smaller bulk particles. The screws may operate inside
tubes or U-shaped troughs, supported every few feet by
suspended bearings around which the material flows.
Conveyor screws are available in diameters up to 4
feet. They move material in and between processes,
and sometimes simultaneously blend and meter it.
Screw conveyors exhibit high friction levels and thus
are high energy users. They are chosen for applications
that take advantage of their special features such as
total sealing, blending in transit, and the fact that they
can convey vertically.
Typical Screw Conveyor
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Roller conveyors
Roller conveyors are either gravity powered or motor powered
rollers. In either case, the basic roller conveyor structure consists
of side rails, punched with spaced holes along their length.
Rollers, assembled from steel tubes with bearings in each end,
ride on steel shafts that fit between the rails. The shaft and the
inner race of the bearing are usually stationary. The rollers rotate
on the bearings. But in some cases the rollers are fixed to the
shaft and the shaft ends are mounted in flanged or pillow block
bearings. The rollers may be free running or driven in any of a
variety of ways.
Drive methods include direct drives where every roller has a gear
motor drive; roller-to-roller drives where one roller is connected
by chain and sprocket to the next; sliding contact drives where a
belt running below the roller contacts and drives it; and selfcontained motor-in-roller drives, were each roller has an internal
motor and gearbox.
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Belt conveyors
The term "belt conveyor" refers to a machine that transfers material or objects from one point to another by means of a
moving belt. The belt is driven by a head pulley, also called a head roller, and is supported by carrying idlers (or
rollers) placed sufficiently close to one another to prevent any sagging of the belt. An idler may have three or more
rollers on it arranged in the shape of a trough; they give the belt a continuous curved shape and are called "troughing
idlers." The other side of the belt (the return side) is supported by carrying idlers called return idlers which are usually
rollers.
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Components of a Belt Conveyor System
The head pulley
Most of the head and tail roller
pulleys used on European or
American conveyor systems
are crowned as shown in the
illustration. This is done to aid
the belt in tracking toward the
center of the pulley. The
reason this happens is the
difference in the linear speed
from the crown to the edges of
the pulleys. The usual figure
for the amount of crowning is
1/8 of an inch per linear foot of
pulley width.
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The tail roller pulley has a machine finish on it and is used as an idler since it has no driving force. The head roller
(drive roller) is the driving force to move the conveyor belt and its load. This roller has a rubber lagging on it to
increase the friction between the belt and the roller itself. The lagging consists of layers of cloth (termed as “duck”)
and of rubber bonded together then attached to the roller as discussed on the following page.
Rubber Lagging
Shown in the following illustrations are drive roller pulleys or as they are
sometimes termed “head rollers”. They have different types of rubber
lagging attached to them to help increase the tractive capacity.
Lagging is available in 1/4”, plain bolt on or 1/4”, 3/8”, 1/2”, plain
vulcanized and can be applied to either crowned or straight cylindrical
pulleys.
Plain Vulcanized Lagging
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The standard bolt-on type has a 3/16” rubber cover bonded to a
two-ply extra heavy duck. The 3/8” and 1/2” vulcanized can be
herringbone grooved. Standard groove depths are 3/16” on 3/8”
lagging and 1/4” on 1/2” lagging. For heavy duty applications,
a thicker bolt-on lagging or vulcanizing lagging is available.
The choice of lagging is influenced by operating conditions.
Extra thick material may be used to increase life, for prevention
of dirt build-up
on pulleys, or as protection for the belt itself. Grooving may also
be used to increase the tractive pull under dirty or wet
conditions – or to prevent
dirt build-up.
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The head pulley drives the belt. It is mounted on
bearings and must be positioned exactly at right
angles to the vertical plane of the conveyor frame.
The pulley is coupled to a drive system which can
be one of several types, namely:
 a drive train with a speed reducer coupled to
the roller;
 a chain-and-sprocket drive
 a belt-and-pulley drive.
Chain-and-sprocket drive system
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Drive train with a speed reducer coupled directly to the drive
pulley. This type of drive system is used very little, for the
following reasons.
 load shocks and overload strain in the conveyor system are
transmitted directly to the coupling linking the speed reducer to
the drive pulley. As a result, the coupling wears out quickly
and the conveyor system must be shut down every time the
coupling is changed.
 the system does not have as much "give" as a chain-andsprocket or belt drive system and cannot easily absorb load
shocks. A belt can slip a little on the pulley and a chain can
absorb light load shocks.
Typical drive motor (gear motor)
For the reasons given above, it is not uncommon to find the speed reducer coupled to the drive roller shaft with a
hydraulic coupler (which can absorb load shocks).
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Chain-and-sprocket drive train
Chain-and-sprocket drive systems are the most popular conveyor drive
systems and they are also the strongest. A chain has enough give to be able
to withstand normal load shocks. The conveyor speed can be altered simply
by installing a larger or smaller sprocket on the head pulley drive shaft or
exchanging the two sprockets. Servicing the system is easy and
inexpensive. The following illustration shows the components of a typical
chain-and-sprocket drive.
Belt-and-pulley drive train
Drive showing chain, sprockets
and chain guard
Belt-and-pulley drive systems share some of the characteristics of chain-andsprocket systems, particularly the ability to absorb load shocks. However, their
major disadvantage is that drive belts have a tendency to slip on the pulleys if the
conveyor belt is overloaded. While this slippage saves wear and tear on the
conveyor belt system, it can cause the drive belt to burn through from the heat
created by the friction. Another disadvantage is that material being carried on the
conveyor can fall and get between the belt and the pulley (which accelerates the
wear on the belt and the pulley). For these reasons, the belt-and-pulley drive
system is not used as widely as the chain-and-sprocket drive system.
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The tail pulley
Adjustable tail pulley
The tail pulley can be adjusted to put tension on the belt.
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The tail pulley
A tail pulley is usually crowned at an angle depending
on the rigidity of the belt. Belt tension is adjusted by
turning the adjustment screws on the sliding pillow
blocks in the appropriate direction to move each
block backward or forward.
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Carrying idlers (support rollers)
Depending on the material the belt has been designed to move and the desired shape of the belt, the carrying
idlers can be flat or trough-shaped.
Profile of belt carrying idlers
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Return idlers
While the return part of the belt is traveling in the opposite
direction, that is, from the head pulley to the tail pulley, it
must be supported so that its weight will not add to the
belt tension and put too much stress on the head and tail
pulleys. The type of support roller used is called a return
idler. Return idlers are usually steel cylinders mounted on
bearings which are positioned horizontally between
brackets bolted to the underside of the conveyor frame.
Hard rubber disks mounted on shafts, two-roller V-shaped
idlers, and spiral types are also used. Return idlers must
be protected and lubricated like regular carrying idlers as
they must bear half the weight of the belt and withstand
the effects of dirt and moisture.
Profile of belt return idlers
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Self-aligning idlers
Self-aligning idlers are installed on
conveyors to direct the belt back to the
center position should it start to wander.
Self-aligning or training idlers set up a
compensating force to steer the belt
back in line. When the belt runs to one
side and hits the holding roller, the idler
stand pivots forward on that side and
back on the opposite side. This skewing
action of the idler sets up force to steer
the belt back in line. Self-aligning idlers
should only be considered for use when
correcting casual belt wander. When the
belt persists in hitting the holding roller,
there is something wrong either with the
belt or the idler alignment on the
conveyor.
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Tensioning rollers
Screw tensioning rollers do not correct for belt elongation and contraction during operation, but are used to
compensate for long-term changes in belt length. When placed at the foot of the conveyor, they do not require extra
bends in the belt. Adjustments are made by turning the screw head or nut at either end of the roller.
Profile of belt tensioning roller
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Gravity tensioning rollers are automatic and
keep an even tension on the belt. The amount
of tension can be adjusted by varying the
weight of the counterweight. In an automatic or
gravity tensioning system, tension is applied to
the belt through the roller. The take-up carriage
is suspended from the roller, and is free to
move up and down on the vertical rods. The
tension is adjusted by varying the weights held
by the take-up carriage.
Profile of belt gravity tensioning roller
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Change in direction rollers
Change in direction rollers are constructed similar to
tensioning rollers but, are used to direct the belt
around obstacles that would interfere with the belt on
the work and the return.
Profile of belt change in direction roller
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Snub rollers
A sub roller is installed on the return side of the belt very close to head roller. This roller increases the belt contact area
on the head (drive) roller, which increases the drive force on the belt with little increase in tension and thus less power
consumption.
Profile of belt snub roller
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Tracking roller
A tracking roller is similar in construction to a snub roller and a change in direction roller. The position of this roller on
the conveyor is what identifies it as a tracking roller. A good tracking roller is positioned so that when it is adjusted it
produces little change in the tension of the belt. There must be slight friction between the belt and the tracking roller. A
long free span of conveyor belt leading up to the tracking roller and a short free span of conveyor belt after the tracking
roller to the next roller makes an ideal location.
Profile of belt tracking roller
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Slider beds
Slider beds or slider plates are used on belt conveyors at the loading zone to protect the belt from damage.
Carrying idlers may allow the belt to sag when the product load is applied to the belt or may not fully support the
belt from blunt heavy objects. Slider beds provide full support for the belt but in turn create high friction between
itself and the belt. For this reason they are limited to loading areas and certain products.
Profile of belt slider bed
Profile of belt slider bed
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Belt cleaning systems
When a belt conveyor is used to move bulk material in powder form or in the form of small particles, it sometimes
happens that the belt must be cleaned at the head end (or at the tail end) to recover dust or particles which stick to it.
Separate belt-cleaning units are available which can be installed at the head or tail end of the belt. These units have
their own drive systems and can be adjusted and positioned to affect the type of recovery or cleaning desired.
Belt conveyor with a separate rotating belt cleaner
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Belt conveyor with a separate wire scraper
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Splicing/Joining
The vulcanized splice is the best method for joining the two ends of a belt or for joining one belt to another. A
vulcanized joint has 90% of the strength of the belt itself and has a long service life (though not as long as the service
life of the belt). It runs smoothly over the rollers and belt cleaners and allows the sides of the conveyor chute to be
placed close to the edge of the belt. Conveyed material cannot seep or drop through the splice. However, the cost
of a vulcanized splice is many times that of a mechanical join. Moreover, the vulcanize is heavy and difficult to move.
If a mistake is made in calculating the amount of play (that is, the belt is too long), it is time-consuming and costly to
cut a piece out of the belt and re-vulcanize it.
Once the belt has been spliced and is ready for use, a thorough check should be made to see if it tracks properly
over the head and tail pulleys and the carrying idlers. The best way of carrying out this check is to have a person at
the motor switch ready to stop the belt immediately if there is a problem. Another person checks the tracking at a
safe distance from the running belt. If there are screw take-ups on the tracking roller, the belt can be aligned while it
is running. A word of caution: if the belt is very badly aligned at the beginning, running it can damage one of the
edges. A new belt is difficult to align because it only takes its final shape after several days of operation under load.
Thus, the initial alignment should be sufficiently accurate to allow the belt to operate without its being damaged, and
the final alignment should be carried out after the belt has been run in.
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Metal Fasteners
Small to medium size belts can be joined by hook and prong fasteners. Proper size fasteners can be selected from the
makers chart to suit the belt and applied according to directions. When installing fasteners, the size for the belt
thickness should be used and the manufacturer’s instructions for installing followed carefully. If roller diameters are
small, a hinged, two plates fastener can be used or the joint can be made at a 45-degree angle, using standard plate
fasteners. Metal fasteners frequently catch on skirting or scrapers and are noisy as they pound the idlers and rollers.
They also allow moisture to penetrate to the fabric, thus shortening belt life. They are not used where metal detectors
are used to detect contamination in the product being conveyed. Their chief advantage is that they are cheap and
easily applied with minimum equipment. A belt with a mechanical joint can be shortened with a minimum of downtime.
The only belt length lost is slightly more than the width of the clips. Small nicks and tears in the belt carcass will
enlarge under constant bending on the idlers and rollers. Quick repairs can be made by using belt fasteners,
The following slide shows different type metal fasteners being used on conveyor belts.
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Rule of tracking
Basic/Primary rule of tracking
The basic, primary rule which must be kept in mind
when tracking a conveyor belt is simply “THE BELT
MOVES TOWARDS THAT END OF THE
ROLLER/IDLER IT CONTACTS FIRST “. The
reader can demonstrate this for himself very simply
by laying a small roller or round pencil on a flat
surface in a skewed orientation. If a book is now laid
across the roller and gently pushed by one’s finger
in line directly away from the experimenter, the book
will tend to shift to the left or right depending upon
which end of the roller the moving book contacts
first.
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Rule of tracking
Conveyor Belt Tracking
On the following pages, an attempt will be made to outline the more common conveyor belt tracking problems and a
list of ways to approach the solutions systematically.
The most hazardous period in the life of the belt is immediately after it has been installed. It is, therefore, worth the
extra time to monitor new belt installations closely for a couple of weeks, and especially the first few hours after startup.
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Initial Start-up of New Belts
I.
A) Head rollers, tail rollers, return rollers, etc., should be parallel with each other and level with the earth. The
rollers should also be in good condition.
B) Start up motor with belt traveling toward the head roller.
C) Take up slack in belt using take-up adjustment until sufficient tension is applied to prevent slippage of the belt
on the drive pulley. Caution should be taken to ensure take-up rods are equally adjusted; otherwise the belt will
run off the pulley. Do not adjust the take-up tighter than necessary to keep a good driving condition on the drive
pulley. Tensioning the belt tighter than necessary could stretch the belt or possibly destroy the fiber cord inside
the belt, thus shortening the belt life and making the belt more difficult to track.
II. If additional tracking is necessary, it can be done as shown on the following slide.
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1. To move the belt in direction “B”, adjust tracking roller in the direction “A”
2. To move the belt opposite directon “B”, adjust tracking roller in the direction opposite “A”
3. A very slight adjustment of tracking roller will cause the belt to move. Do not adjust too much.
4. Run conveyor long enough to make several complete revolutions to see how your adjustments have affected the
belt tracking. If necessary, readjust going through the previous steps.
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III. The illustrations below show the effects of moving the snub rollers and return idler rollers and how this aids in
tracking conveyor belts.
Take-up
Belt travel
unit
Drive roll
Return rollers
A
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A
Advancing at “A” causes
Belt to move this way
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Take-up
Belt travel
unit
Drive roll
Snub roller
A
Advancing at “A”
causes belt to move
with little effect
with little effect
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1. Head or drive roller – This is a crowned-faced roller with rubber lagging and mounted on pillow block bearings.
This roller is not adjustable other than by shimming.
2. Tail roller – This is a crown-faced roller with no lagging mounted on pillow block bearings. This roller is not
adjustable other than by shimming.
3. Idler rollers – Straight face roller that supports the belt and the load that it is carrying.
4. Tension roller - A straight face roller mounted on adjusting blocks to allow movement and to add tension to the
belt.
5. Tracking rollers - Straight rollers that should be adjustable to aid in tracking. They are found close to the tail roller.
6. Snub rollers - Straight rollers that are found close to the head roller and increase the drive contact on the drive
roller.
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1. Head or drive roller – This is a crowned faced roller with rubber lagging and mounted on pillow block bearings.
This roller is not adjustable other than by shimming.
2. Tail Roller - A crowned roller with no lagging and mounted in a take-up frame. The roller in this type system serves
as a tensioning device.
3. Idler Rollers - A straight face roller used only to support the belt and the load that it is carrying.
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04 - Conveyors
“S” Type Tensioning System
(Litton, Bayer, Interlake)
Belt travel
5
3
1
4
6
2
1. Drive Roller on Head Roller – Mounted on flanged type bearings. Adjustment available only by clearance holes
in the bearing blocks and slots in the machine framework with Litton conveyors. Bayer and Interlake are basically
the same except the drive rollers have screw adjusters that move the bearing blocks in slots cut into the
framework to allow movement for belt tracking and also adjusts rollers for parallelism to the tail roller.
2. Tail Roller - Mounting is the same as for head rollers. On Litton conveyor systems the rollers have little
adjustment but on Bayer systems, again you have adjusting screw mounted against the bearing blocks to allow
for more adjustment.
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3. Idler Rollers - Straight face rollers that support the belt. On Bayer, Litton, and Interlake conveyors these rollers
have hex shafts and mount into the conveyor framework.
4. Change In Direction Roller – A straight face roller that supports the belt in its turn in the tensioning assembly.
Mounted in flanged bearing blocks – normally a larger diameter than idler rollers.
5. Tension Roller - A straight face roller used to tension the conveyor belt only. Not to be used to track the belt. On
Litton conveyor systems, this roller is mounted on pillow block bearings that are mounted on a screw assembly to
allow belt tensioning. On Bayer systems, it is mounted in a Side mount take-up frame as shown below.
6. Tracking Rollers - Straight face rollers that support the belt on Litton systems. These rollers are not adjustable,
but on Bayer and Interlake conveyors, there are adjustments that aid in tracking the belt.
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Modified “S” Type Tensioning System
1. Tail Roller - Mounted on either pillow block bearing or flange block bearing according to mounting applications.
The only adjustments that can be made here come from the clearance holes in the bearing blocks themselves or,
in the case of pillow block bearings shims can be used.
2. Drive Roller or Head Roller – Mounting and adjustments are the same as the tail roller. Some adjustment
limitations here because this is the drive roller utilizing chain and sprocket for driving the conveyor.
3. Idler Rollers – Straight faced rollers which support the belt and the load which the belt carries. Rule of thumb
spacing between the idlers is the same as the belt width with a minimum of 200mm and a maximum of 1500mm.
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4. Change in Direction Rollers – This roller supports the belt in its turn into the tensioning assembly. As a rule, this
roller is larger diameter than the other rollers.
5. Tensioning Roller –These rollers are just as their name states: a roller, usually mounted in roller blocks, attached
in an adjustable tensioning assembly, shown in the following illustration.
This tensioning should be used only to tension the belt and not as a device to track the belt. The belt tracking should
be done with tracking rollers which will be covered later.
6. Tracking Rollers - Straight face rollers mounted underneath the belt close to the tail rollers. The frame of the
conveyor should be slotted here so these can be adjusted to aid in tracking the belt as necessary.
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04 - Conveyors
End of Chapter Four
Exit
04 – Conveyors
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