Advantages of and Recent Developments in Aero-Mechanical Conveying Equipment
May 13, 2008
Conveyor (AMC), most commonly known as a “rope and disk” conveyor, has
been around since the early 1960’s. Now used in over 30 countries, the
AMC has made a name for itself for conveying everything from coffee
beans, tea leaves, malt, plastics to titanium dioxide as well a variety
of other products in the chemical, mineral, food, ceramic,
pharmaceutical, plastics, rubber and water industries. This article
outlines the advantages and disadvantages of using AMC’s and notes some
recent equipment developments that reduce maintenance cost.
An Aero-Mechanical Conveyor (AMC) is
a high capacity, totally enclosed mechanical conveyor that handles
powders, granules, pellets and flakes. In the AMC, a continuous wire
rope, with a series of equally spaced disks attached to it, travels
through a flow and return tube arrangement.
A constant speed motor moves the rope
and disk assembly creating a conveying action that draws material into
the slip-stream behind the disks like the way dust is drawn into the
slip-stream behind a fast moving automobile! It is essential that
material is ‘stream fed’ into the Aero-Mechanical Conveyor at a
controlled rate. The high-speed disc mechanism fluidizes all flowable
solids in a recirculating air stream, which provides low shear
conveying of powders or particulates typically up to 5/8 inches in
Most AMCs can be used with multiple
inlets or outlets, move product vertically, horizontally or at varying
angles and up to distances of up to 60 feet, depending on variables.
AMCs can easily be connected to other equipment such as Silos, Mixers,
Sifters, Reactors, Bulk Bag Dischargers or Bulk Bag Fillers. Smaller
units can readily be mounted on a mobile support frame so that one
machine can be used for a multiplicity of applications.
One of the most noted successes of
AMCs is their ability to handle powders that have notoriously difficult
characteristics such as inherently sticky, cohesive materials like
Titanium Dioxide (TiO2). This is due to the way that an
Aero-Mechanical Conveyor mimics the fluidization process of a fully
pneumatic conveyor without potentially degrading the high-speed
pneumatic action and cost associated with, in particular, lean phase
pneumatic equipment. The gentle fluidization process of an AMC
dramatically reduces degradation.
An additional reason for most AMCs
success with difficult materials is its stream feeding process, which
normally doesn’t allow powders to cake up or otherwise be problematic
compared to plug fed systems.
Aero-Mechanical Conveyor Basics
A typical AMC, like that of Spiroflow
Systems, consists of six main components: inlet housing, outlet
housing, set of two conveyor tubes, rope and disk assembly, electric
drive and a gravity inlet.
The rope and disk assembly is
typically completely enclosed in the conveyor tubes and is wrapped
around sprockets at each end of the conveyor within the inlet and
outlet housings. Typical rope and disk flights are manufactured out of
stainless steel strand rope and plastic disks moulded on to the rope at
A drive at either the inlet housing
or outlet housing drives one of the sprockets and in turn rotates the
rope and disk assembly around the sprockets. The drive is typically
mounted to the inlet (bottom) housing for conveyors up to 20 feet long,
whereas any conveyor over 20 feet would rely on an outlet (top) housing
mounted drive. By adding corner housings to some makes of AMCs,
“turns” can be made in the conveyor.
Additional inlets can normally be
positioned along the length of an AMC for batching applications.
Product is ejected centrifugally via the outlet housing. Additional
intermediate outlets, each with its own valve, can be installed along
the conveyor tubes for multiple discharge points.
The speed of the rope and disk
assembly is usually about one quarter of the air speed in pneumatic
systems, but very much faster than the speed of most mechanical
handling equipment. Aero-Mechanical Conveyors should not be confused
with low speed Drag-Link Conveyors some of which appear to be similar
in construction but which operate at much lower speeds.
Operation of a Typical AMC
A typical AMC like that from
Spiroflow uses a motor that rotates either the outlet sprocket or the
inlet sprocket. Material is stream fed (metered) into the inlet
housing and picked up by the slip-stream behind the disks. The high
speed of the rope and disk assembly conveys the material to the outlet
where it is centrifugally separated from the air stream.
Proper operation requires stream
feeding an AMC. An inlet baffle is often used to control the feed into
the conveyor and is typically available in a manual or pneumatic
option. Other options, such as a rotary valve or flexible screw
conveyor, can also be used to control the rate of flow from the hopper
to the conveyor.
Typically a mix of 15 percent solids
and 85 percent air is seen when the AMC is operated at full speed of
approximately 702-1175 ft./min. Full speed is ideal for correctly
conveying dense and poor fluidizing products. Finer solids that
fluidize more easily can be run at half speed, which is 351-587
ft./min. This also changes the solids/air capacity to 30 percent/70
AMC options vary with manufacturer,
but typically include various inlet/hopper options such as dust hoods,
bag dump stations with bag break devices, hopper level indicators,
extended/large capacity hoppers, valves for proper stream feeding and
flow aids such as vibratory pads.
Other options include multiple
configurations, tube mounted inlets/outlets, manual and automatic rope
tensioning devices and static bonding.
To reduce or eliminate dust when
feeding an AMC, a dust hood can be installed over the hopper. The dust
hood is fitted to the facility supplied dust collection equipment. In
most cases, a grate will also be included with the dust hood as a means
of preventing the operator from reaching into any moving parts and also
to stop foreign materials such as bags from being dropped into the
Bag Dump Stations
Bag dump stations are typically
installed with bag break devices, and sometimes a means of bag
disposal, to ensure easy user functionality. Dump stations can be used
with our without dust hoods.
Hopper Level Indicators
It’s important that the AMC fully conveys and discharges the last bit of
material and not be stopped with material in the conveyor. This
prevents any damage to the rope and disk assembly. Hopper level
indicators can be used in conjunction with programmable logic
controllers (PLCs) to convey the final amount of material in a time
interval and then shut down the AMC motor. Running the AMC without material is permitted
Extended/Large Capacity Hoppers
Large capacity hoppers can be fitted to the inlet housing depending on application. A meter feeding device must be used.
To ensure proper feeding, many AMC
users turn to a valve that will regulate material feeding into the
conveyor. Rotary and butterfly valves are very commonly used and
perform well in an AMC application.
Where a truly accurate flow of
material into a process is required, AMCs can be feed by way of
volumetric or gravimetric metering feeders.
For conveying characteristically
difficult materials, vibratory pads may be mounted to the inlet hopper
to reduce the chances of material bridging, caking or rat holing.
In addition to being configurable to
have angles of operation from 0º to 90º, up to two sets of corner
housings can be added to provide a horizontal-vertical-horizontal
configuration. Other configurations are possible and depend on the
application needs and the material being conveyed.
Tube mounted inlets/outlets
If desired, AMC’s can have multiple
tube inlets or outlets to transfer material into the conveyor.
Typically, a slide gate device is used to stream feed the material.
Recent Developments in Aero-Mechanical Conveyor Technology
Maintaining AMCs requires periodic
maintenance at regular intervals to assure proper rope and disk
assembly tension and to lubricate moving parts.
One of the most important maintenance
issues is properly maintaining rope tension. This will ensure long
rope life and decrease the possibility of lost production time due to
broken ropes. This is an easy maintenance issue to address, but may
often be overlooked. That is, it is easy as long as the AMC is readily
accessible. In some AMC systems where a vertical unit feeds into a
horizontal unit operating in the roof area, for example, access may
involve the use of scaffolding or a mobile access platform.
An automatic tensioning system is
available that keeps the rope properly tensioned. Upon each shutdown of
the system, an integrated load cell measures the tensioning. An
electric or pneumatic linear actuator sets the housing position
to reach the correct predetermined tension. This feature increases the rope life and reduces maintenance time.
In older AMC models, the rope had to
be manually tensioned. This meant checking the rope tension at 1, 4, 8
and 50-hour intervals, then every 100 hours or as needed. The process
involved checking rope tension at the inlet (bottom) sprocket for
excess rope sag from the sprocket. Normal clearance is 1/8-inch between
the rope and sprocket. At the top sprocket, users had to check for
slippage between the rope and the sprocket.
The advantages of the automatic
tensioning systems include reducing maintenance and operational costs.
The automatic tensioning systems eliminates the need for maintenance
employees to check rope tension and provides feedback on rope wear via
Advantages of the Aero-Mechanical Conveyor
The AMC has proven to be one of the
most cost efficient methods of conveying materials in terms of its high
productivity and dust-free operation. Features typically include total
batch transfer, flexible operation at any angle without loss of capacity and a
dust-free sealed system for contaminant free delivery. Capacity of
material handled varies but can reach 120 tons per hour.
The AMC can usually convey up to 60 feet without any problems. A major advantage is that degradation to the material is almost negligible with this type of conveyor, since it creates a moving current of air in which the material is conveyed, similar to the effect of a vacuum or pneumatic system. However, the Aero-Mechanical
Conveyor does not need a cyclone or filter system to separate the
product from the air – this fact alone is a major advantage. Not only
is there no initial cost of a filtration system, there are no
filtration running costs or the possibility of environmental
contamination. Aero-Mechanical Conveyors normally conveys product
without virtually any losses.
Other than free flowing powders such
as acrylics, flour and carbon black, the system can also convey
difficult materials such as titanium dioxide. It addition, it has no
problem with granules, flakes or chips. Unlike screw conveyors that
tend to allow the material to cake and compact, the fluidizing action
of the AMC efficiently moves the material without problems.
With this type of conveyor,
maintenance needs are moderate to high depending on the amount of time
the conveyor runs as well as the material conveyed. The rope must be
tensioned periodically. Rope life also depends on the conveyor length,
the number of starts and stops, solids loading and whether routine
inspection and tensioning are properly performed. This particular
disadvantage can be eliminated by the use of an auto-tensioning device
available from some manufacturers.
The only other disadvantage is the
rope itself. Being a series of strands, it is not the easiest component
to clean. Having said that, this is usually only an issue where
cross-contamination cannot be tolerated between frequent batch changes.
AMC’s can be dry-cleaned or more often they are washed through with a
suitable cleaning fluid and then dried by running them empty for a
period. Most manufactures offer a variety of access panels for dry
cleaning or connection and drain points for an integrated
Coated or encased ropes have been
tried by some manufacturers but inevitably, as with most coatings, they
break down and create a greater problem in the long term.
Now used in over 30 countries,
the AMC has made a name for itself for conveying everything from coffee
beans, tea leaves, malt, plastics to titanium dioxide. Consistent
performance and operational reliability have endeared aero mechanical
conveyors to a wide audience of industries. From the seemingly simple
task of transferring food ingredients to the abrasive and corrosive
nature of conveying chemical industry products, AMCs are well equipped to be the ideal solution for a broad spectrum of bulk solids
Spiroflow is a
worldwide supplier of a wide range of both standard and custom powder
handling equipment, specializing in Bulk Bag Dischargers and Fillers,
Mechanical, Flexible, and Pneumatic Conveyors, and Bag Packing
equipment. For more information about this article, contact Spiroflow
Systems, Inc at 704-291-9595, fax 704-291-9594 or email
firstname.lastname@example.org. Spiroflow can also be found on the Internet