Conveyors are simple devices to understand, but they
can have infinite configurations to make them uniquely suited for moving
a specific material in a particular environment.
A conveyor, in its simplest definition, transfers things
from one place to another on a moving belt. Then it gets complicated.
Jeffrey Van Galder of Karl Schmidt & Associates explained, “By
definition, conveyors sound simple, and as a generic concept, they are
simple, but when an inappropriate conveyor is misapplied to an application,
the situation can become more complicated than anyone could want. Keeping
the focus on one industry still leaves a variety of applications, where
each has specific requirements. For all of these situations, there are
options that experience has proven to be best.”
Finding a conveyor to move paper seems to a simple task,
but the paper could be shredded, baled, or mixed with other materials.
It could be loose or bagged. It could be moving to or from a shredder
or baler, or the conveyor could be used for sorting. For each application,
there is a conveyor.
Sliderbed conveyors are the simplest of all conveyors,
typically used for sorting lines and transferring light material. The
sliderbed conveyor has a multi-layer rubber or PVC belt in a frame with
a pulleys, and is driven by friction.
The next conveyor is known by several names: a combination
chain belt, a drag chain, or a combo belt conveyor. This conveyor uses
the same belt material as the sliderbed; the difference is the drive mechanism.
Rather than relying on friction, the conveyor has a chain and sprocket
system similar in function to that on a bicycle. The chain, at the sides
of the belt material, typically rides on a UHMW polymer, which reduces
friction while the belt is moving. These conveyors are ideal for moving
heavier materials, high volumes, or where there is high impact and heavy
loading of material onto the belt.
The roller chain conveyor belt is better for handling heavier-duty
materials. The belt material is the same as that used for the above conveyors,
but has a roller chain that rides in a track at the sides of the conveyor.
Typically used where material is transferred over long distances and where
there are fewer impact and loading requirements.
Hinged steel belt conveyors are a heavy-duty choice,
but are best if glass and other abrasives are minimal, reducing wear on
moving parts. These conveyors are popular in paper recycling and MRF facilities
where the durability of the heavy steel belt is a factor.
apron and z-pan conveyors also have a steel belt with a different construction:
overlapping pads rather than pin connectors. These are “severe-duty”
conveyors and are ideal when abrasive materials like glass are present
in large quantities.
Trough-idler conveyors, typically used in the aggregate
industry, are gaining popularity in paper recycling facilities. These
conveyors stand up to glass and other abrasives, and can transfer materials
at higher speeds. Rollers support a rubber belt in groups of three along
the length of the conveyor. In applications with impact or heavy loading
requirements, impact plates or rollers can be added.
Van Galder explained that single stream processing is
becoming the norm in many areas, and the incoming material is dirty, containing
abrasive materials that wear moving parts on chain-driven conveyors. “The
dirtier the material, the more the processor needs to worry about maintenance
costs,” Van Galder said. A steel belt may be more durable than rubber,
but if the moving parts wear and need to be replaced often, the processor
loses production time.
The consensus from all of the conveyor manufacturers
was that there is no single conveyor that will fit every application,
and in fact, they may be no conveyor made that isn’t customized
in some way, to fit the customer’s specific needs.
Allen Terry, product manager for conveyors at Marathon
Equipment, said, “almost everything we do is special because everyone
needs something different.”
Even if the business is the same, the building configuration,
and even the height of the employees can be a determining factor when
customizing a conveyor. In a sorting facility where workers stand at a
belt, the height of the conveyor, as well as the height of the sides used
for containing material on the belt can make a difference in worker efficiency.
Marathon Equipment also manufactures compactors and
balers, and while the conveyors that go with the compactors as complete
systems have “some standard,” Terry said that even those are
customized to fit the customer’s facility.
Dan White, vice president of market operations for C.S.
Bell Company, agreed that conveyors are a custom order. “It could
be a small nuance of difference between what the last customer wanted
and what the next customer will need.” White continued, “We
are very reactive to specific needs.”
He might begin by asking a customer what the flow of
material is from the point it comes in until it leaves as a finished product.
Hand sorting facilities would want a horizontal conveyor, while an inclined
conveyor would feed a machine such as a baler.
In some facilities, different types of conveyors perform
different tasks at different stages. Mixed material may be dumped into
a pit where a hopper for the conveyor is under floor level. An inclined
conveyor with a cleated belt would bring the material up to a horizontal
conveyor with a flat belt and high sides for sorting.
Typical customizations include the inclusion or spacing
of cleats; the width, height, and length of the conveyor; the height of
the conveyor sides; gear reduction to change the belt speed or the use
of a variable-frequency drive so the belt speed is adjustable, or the
addition of a magnetic head.
In addition, adjustable legs can accommodate an uneven
floor, adjust conveyor height, or change the conveyor from horizontal
to a slight incline. Start and stop foot pedals can be placed at desired
locations, as can emergency panic buttons for extra safety. Sidewalls
can be vulcanized, and chain can be heavier or lighter than standard.
There are so many options, it makes conveyor purchases
more of a design issue than one of choosing a model number. The customers
know what they need to do; the manufacturers know how to make it happen.
To make it all work, Van Galder summed it up: “The customer should
work with the manufacturer to get the best [for their application.]”