Belt conveyor tuning. A belt conveyor is a moving surface used
to transport product from one end to the other. In its basic form
it consists of a driving head pulley, a tail pulley, the moving
belt, support rollers, cleaning devices, tensioning mechanisms
and a structural frame. Though simple in concept its many components
need to work together as a system to get the best performance
and operating life. Critical to that is an understanding of how
to care for a belt conveyor and tune it for successful operation.
Keywords: materials handling, bulk material transport
are used to transport anything from matches to bulk material such
as iron ore and quarried stone. The belt can be made of natural
fibres, rubber, plastic or metal. Regardless of its construction
and purpose there are basic requirements to its successful operation
that must be met.
How a Belt
Figure No 1. is a simple sketch of a belt conveyor. An electric
motor and gearbox turn the head drum (or head pulley). The belt
is pulled tight to produce friction between it and the head drum.
The friction overcomes the load and drag forces and the belt moves
around the circuit from the head pulley to the tail pulley and
back to the head pulley.
friction is used to drive the belt. If the friction falls the
belt will slip or stop moving even though the head pulley keeps
turning. The friction between the belt and pulley depends on the
friction properties of the surfaces in contact, the amount of
surface in contact (the arc and width in contact) and the tension
in the two lengths of the belt.
side of the belt is the tight side and the return side is the
loose side. The tight side needs to carry as much tension as possible
to minimize the load on the drums, the shafts and the bearings.
Getting the maximum friction possible between belt and head pulley
Often a head
pulley will be herringbone grooved or coated in rubber (or other
such treatment) to increase the friction. Another option is to
increase the arc of contact. A jockey (snubber) pulley is placed
under the slack side close to the drum. By lifting the return
belt higher so it comes off the head pulley further around the
circumference the contact area and hence the friction is increased.
the belt also increases friction. This can be by jacking the head
and tail pulleys further apart and forcing the belt harder against
the drums or by making the slack (loose) side tighter. Tightening
the slack side goes against the ideal of keeping the slack side
tension low and the tight side tension high. If the loose side
is used for tensioning, the load carrying components are made
larger to take greater forces.
Belt Conveyor Operating Life.
Once a belt conveyor is designed and installed it is there for
years to come! The very best practice to adopt to promote long,
trouble-free life is to be sure that the designer has designed
it with quality components that can handle the entire range of
forces generated in its use. One way to insure that is to engineer
every part taking a load and then review the design calculations
and the component selection using independent, experienced equipment
users and maintainers querying the designer for the assumptions,
reasons and proof behind each design selection.
The list below
highlights some of the issues and problems with belt conveyor
installations. Once you are aware of them you can be on the watch-out
and get to them fast.
and gouging from product impact at loading zones, from belt
drag across solid surfaces, from scrapper rubbing, from the
belt touching caught product, from product hardening on scrappers,
from drive pulleys slipping during start-up or during a belt
jam, from product build-up on trough and return rollers.
belt at edges due to rubbing against structures, due to rubbing
against product caught in structures, from rubbing against
from excessive belt tensioning, from belt aging, from high
product impact, from overloading with product, from running
the belt beyond belt design speed, from too much stop-start
due to out-of-square joining, due to a join being too thick,
due to ripping and buckling within the belt material as internal
fibers tear because of overloads, due to loading one side
of the belt.
due to head pulley misalignment, due to no head pulley crowning,
due to trough and return roller misalignment, due to roller
seizure producing more drag. Also can be due to the last upper
roller being too close to the head pulley and lifting the
belt so it makes first contact far around on the head pulley
mounting deflection causing shaft misalignment by support
frame and load carrying members being undersized and insufficiently
braced for the operating forces and inertia force changes.
from impact of product, from dragging across jammed sharp
objects, from tearing due to sudden overloads, from bolts
and foreign metal objects gouging.
failure from product build-up on the scrapping edge, from
jammed scrapper parts, from wrong set-up.
belt due to product jam, due to loss of belt tension, due
to dust/dirt/moisture under head drum.
Belt Conveyor Set-Up and Use
Become familiarized with the manufacturers recommended operating
practice and then get operators and maintainers together to discuss
how to achieve them in-house.
In the simplest
of ways decide how to:
the belt is tracking properly and to detect when it is going
off-track. Crown the pulleys (1% to 1.5% of the pulley width),
align guide and troughing rollers square to the belt, on short
conveyors insure the head and tail drum centers are aligned
to within 0.25 millimeter. Keep guide rollers and pulleys
clean of product build-up.
the scrapper is working well. If necessary change designs.
Maybe water jet spray instead of a solid edge scrapper. (Be
wary of brush scrappers for powdered and damp products. Fine
particles build up in the bristles and clog the entire brush
making the bristles rigid and stiff, which then scratches
overloading product by slowing loading rates to below removal
rates. Install deflection plates in loading chutes to take
the momentum of falling product and stop it from pounding
into the belt. Install more rollers in the loading section
to distribute the pounding forces.
low by detecting and replacing seized rollers. Reduce transfer
station skirt-to-belt contact. If dust is a problem keep skirt
contact area and pressures low enough to minimise the amount
of dust escape. Higher pressures force the skirt hard into
the belt and both parts wear.
When you sort
the issues out write down how it was done and make them standard
operating procedure so the discoveries are not lost.
Mechanics, A K Hosking, M R Harris, H & H Publishing.