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Tubular Cable & Chain Drag Conveyors Function, Performance & Benefits Robert Sutton Global Product Specialist Tubular Chain/Cable Drag Conveyors Spiroflow Systems Inc.
Numerous health, safety and hygiene standards for the chemical, food and general processing industries, in
North America and Europe in particular, mandate the need for enclosed conveying systems for dry bulk solids,
additives and ingredients in whatever form – powders, granules, flakes, pellets and many others. When
considering equipment to transport finely divided, flowable bulk materials, the mechanical tubular chain/cable
drag conveyor should always be considered. This is truly a “problem solver in a pipeline” and is a concept that,
while often overlooked and by the food industry in particular, has been serving a wide range of industries for well
over 50 years.
In addition to the food and chemical industries, it has also found application in the waste water treatment,
minerals, brick-making, cement and glass industries. Design and construction can vary enormously to reflect the
demands of the duty to be performed.
Fig. 1 Section of conveyor showing chain & disc assembly
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Fig. 2 Casing bends with welded steel flanges at each end allows the conveyor path to change directions
HOW IT WORKS
The tubular chain/cable drag chain conveyor is comprised of a stationary outer housing, usually round in shape,
through which a chain/cable is pulled by a sprocket. See Figs 1 and 3. Round conveying flights of a diameter
slightly smaller than the inside diameter of the casing are attached to this chain/cable assembly at fixed intervals.
As this endless chain/cable assembly is pulled through the casing by a sprocket bulk material is pushed from the
feed sources to the discharge points by the conveying flights. This process is all mechanical. No compressed
air, blower or filter system is required.
The conveying rate is established by varying the casing diameter and/or the chain/cable velocity. Conveying
capacities with this type of equipment can reach as high as 20ft3/min, which will satisfy the needs of most
processing equipment as well as the needs of general industry.
The conveyor casing (stationary outer housing) is made from carbon steel or stainless steel pipe and typically
available in 3”, 4”, 6”, 8” and 10” sizes. The casing sections are furnished in lengths up to 20 feet, as dictated by
the required conveying path, and are
supplied complete with welded steel
flanges at both ends or pipe couplings
- according to conveyor type and duty.
To allow the conveyor path to change
directions the conveyor casing is
formed into a sweep radius elbow, at
whatever angle is required, and steel
flanges are welded to each end. The
straight casing sections as well as the
casing bends can then be combine
with gaskets and bolted together in the
field to form rigid, dust tight joints.
TOTALLY ENCLOSED & DUST TIGHT The single most significant feature of this conveyor style is the enclosed construction. This conveyor operates
within the confines of a pipeline and is inherently dust tight. This design effectively contains the material being
conveyed, along with its dust, to protect the atmosphere and personnel from any adverse effects from dusting. It
also protects the bulk material from contamination from the outside atmosphere and moisture. If required, this
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Fig. 3 The drive sprocket engages directly with the conveyor chain for positive movement.
equipment can be operated under a light vacuum, positive pressure or product can be conveyed under a blanket
of inert gas, such as nitrogen.
Although predominantly designed for dry materials, Tubular Chain/Cable Drag Conveyors are equally adept at
conveying moist and wet materials too. Running along the bottom of a settling tank this style of conveyor can
collect fines as they precipitate from the fluid in a tank and elevate them above the fluid level to a waiting vessel
or piece of process equipment. In the process of elevating the fines there is a natural de-watering effect, via
gravity, which could enhance the process at hand. The enclosed construction serves well in containing odors and
free moisture that may be present with some sludge and slurries.
THE CHAIN & CABLE ASSEMBLY At the heart of every tubular chain/cable drag conveyor is the chain/cable assembly, which is the single most
critical component in the system.
A chain assembly is made of a series of
links and pins. A quick examination will
indicate that the chain will readily flex with
the direction of the chain pin but this is only
partially true. A tolerance designed into
the pin and link connection points allow the
chain to rotate out of plane in any direction.
For heavy-duty applications (minerals and
cement etc), a chain assembly of the pin
and link style is the preferred mechanism
to move the flights for several reasons:
First, the sprocket meshes directly with the
chain to provide positive movement.
Friction type drives are unpredictable and
they may slip if the infeed rate surges or if
the conveyor take-up is out of adjustment. Sprockets that drive to the flights instead of the chain could develop
problems if the lug or hub of a flight shifts, thereby destroying the continuity of flight pitch and resulting in
component damage and system failure. The flights do not have adequate long-term durability to withstand the
forces normally required to operate this type of conveyor on heavy applications. It is therefore very important that
the sprocket engages directly with the chain assembly.
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Fig. 4 Thousands of circuit layouts are possible
Pin and link style conveyor chains are less prone to fatigue, wear and stretch than steel ropes or ball-and-socket
style chains. As wear occurs or if an individual component is somehow damaged in a pin and link style chain
assembly, each individual part can be replaced.
Conveying flights can be made of a wide range of materials from the latest grades of UHMW polyethylene, nylon,
polyurethane or even cast iron, steel, stainless steel or aluminum. The particulars of every application will
determine the appropriate flight material.
CONVEYOR CONFIGURATIONS A virtually unlimited variation
of conveyor circuits is
possible, by virtue of the
flexible chain design, custom
casing lengths and casing
bends. These conveyors are
manufactured in modular
form with bolted flange
connections for easy erection
in the field. Figure 4 shows a
few common configurations
and there are thousands of
other variations possible.
This type of conveyor can be
installed in existing facilities
by-passing obstacles that
would interfere with the paths
of other types of conveyors.
Most commonly this type of
conveyor is used to transfer
material less than 100 ft and
involve only one or two
directional changes.
However, transfer distances
of several hundred feet are
well within the capabilities of
this conveyor style.
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INLETS A conveyor inlet is created by removing a short upper half of the conveyor casing and flaring out with sheet metal
to make a hopper. Numerous inlet points can be incorporated in a single conveyor. As a general rule, material
can be flood or surge fed at these inlet points. The conveyor chain/cable assembly will fill with product as it
passes below the inlet opening. There are a few very difficult materials that will not self-feed with this style of
conveyor. In those few cases, a flow assist in the form of a vibrator, mechanical agitator or an air pad will resolve
the flow problem.
OUTLETS Free-flowing materials
A conveyor discharge is substantially identical to an inlet hopper except that its position is inverted. When the
chain and bulk material reach an opening in the casing the bulk material will flow from the chain through the
opening. Multiple discharge points can be built into a single conveyor. In such cases, if control of the discharge
point cannot be left to a simple open style discharge, then gate or butterfly valves can be used to select from
which outlet material is to be discharged. Discharge from the open bottom of the conveyor drive box housing or
idler box is not at all uncommon. The action of the conveyor chain changing direction as it runs around the drive
or the idler sprocket has a beneficial flow promotion effect.
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Difficult Products
Many free flowing materials will readily flow from the conveyor casing and chain/cable assembly at a discharge
point. If it is imperative to your process that you get a complete discharge of material, if the product has sluggish
flow characteristics or is sticky, a special chain vibrator is used. This mechanism is comprised of a fractional
kilowatt/horsepower electric motor driving through a v-belt to a shaft with adjustable eccentric weights, which is
mounted on a spring plate, external of the conveyor. From this spring plate two shafts then penetrate the
conveyor housing through sealed openings to connect to a flat bar that will in turn impart a controlled, low
frequency vibration directly to the conveyor flights as they pass over a discharge to effectively induce the product
to flow from the conveyor. This mechanism is extremely effective on even the most stubborn materials.
Fig. 7 Chain Vibrator. Imparting low frequency vibration directly to the conveyors flights this motorized chain vibrator causes even the most stubborn material to
discharge from the chain assembly.
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BENEFITS 1. No Segregation of Mixtures
The positive displacement action of this conveyor makes it ideal for handling blended materials without separation.
2. Gentle Conveying Action
The slow moving chain assures gentle product handling with an absolute minimal of attrition.
3. Reliable & Long Service Life
The slow moving chain, with its robust construction assures long service life, low maintenance and a very high degree of reliability.
4. Low Noise
The equipment operates at a minimal noise level. In most applications it is difficult to hear the conveyor operating.
5. Wide Temperature Range
With cast iron flights and chains, tubular chain/cable drag conveyors will not only handle materials up to 450oF, they can be used to deliver materials to furnaces and the like.
6. Low Energy Consumption
Energy consumption should be a key factor in equipment selection as the ever-rising cost of energy is a key component in the overall cost of purchasing and operating the equipment. Due to the slow-moving nature of the tubular chain/cable drag conveyor, the power requirement is very low. In many applications, when compared to less energy efficient conveyor types, this equipment can pay for itself in a short period of time based on energy savings alone. A typical tubular drag chain conveyor is operated by a single low horsepower drive motor, usually in the 1 to 5 HP range. This fact makes it one of the most energy efficient conveyors available.
Fig. 8 Three tubular chain drag units, in an outdoor setting, are shown receiving material to the top of a storage silo. The conveyor not only contains the product and its dust but at the same time it protects the material from contamination from the elements.
Fig. 9 Two tubular chain drag conveyors (in blue) traveling in a path around existing machinery & structures, a feat that cannot be accomplished by some other conveyors.
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No Dust Filtration System
The tubular chain/cable drag conveyor is all mechanical and does not require the addition of any air -
compressed or otherwise. It is ideal for handling hygroscopic materials either with or without dry air or an inert
gas blanket. And because there is no air added to the system there is no need for product/air separation
equipment at the discharge points. More significantly, there is no need for an expensive bag house filtration
system and no loss of valuable or toxic material in the form of collected dust.
CUSTOM DESIGNS
As a custom design and build piece of equipment, special features can be added to the system to enhance the
operation. Examples would be water jackets to cool or heat the casing, cooling fins, pipe insulation, drains or
purge connections.
SELECTING THE CORRECT CONVEYOR
In selecting the type of conveyor best suited to your application you should consider:
• The various characteristics or qualities of the product to be conveyed.
• The performance and functional features required by the process.
• Operating features desired.
• The projected duration of the process or operation the equipment is to serve.
• The long-term energy requirements of the equipment.
Tables 1, 2 and 3 show a general comparison of different types of bulk handling conveyors. These charts are
intended to help you in your evaluation process. As with all generalizations, there are exceptions to the rules and,
accordingly, these charts are for guidance only. The final choice of conveyor must be made in conjunction with
your chosen supplier.
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Table 1: Operating Features
CONVEYOR OPERATING FEATURES
Tubu
lar D
rag
Con
veyo
r
Flex
ible
Scr
ew C
onve
yor
Con
vent
iona
l Scr
ew C
onve
yor
Trou
ghed
Bel
t con
veyo
r
Cle
ated
Bel
t Con
veyo
r
En M
ass
Con
veyo
r
Buck
et E
leva
tor
Vibr
atin
g C
onve
yor
Pneu
mat
ic C
onve
yor
Aero
Mec
hani
cal C
onve
yor
Volume - High Volume - Medium Volume - Low
Variable Conveying Rate
Low Maintenance Facilities - New Facilities - Old Installation Costs - Low Installation Costs - High
Energy Consumption - Low Energy Consumption - High
Length 0 – 20 meters Length 20 – 30 meters
Length 30 – 120 meters
Length Over 120 meters
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Table 2: Functional Features
CONVEYOR FUNCTIONAL FEATURES
Tubu
lar D
rag
Con
veyo
r
Flex
ible
Scr
ew C
onve
yor
Con
vent
iona
l Scr
ew C
onve
yor
Trou
ghed
Bel
t con
veyo
r
Cle
ated
Bel
t Con
veyo
r
En M
ass
Con
veyo
r
Buck
et E
leva
tor
Vibr
atin
g C
onve
yor
Pneu
mat
ic C
onve
yor
Aero
Mec
hani
cal C
onve
yor
Totally Enclosed Construction Multiple Inlets Multiple Outlets Multi-plane Path
Elevate Variable Conveying Rate
Self-cleaning Dust Tight Gentle Action (non-degrading) Pressure Tight
Self-feeding
Requires Dust Filtration System
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Table 3: Bulk Material Properties
BULK MATERIAL PROPERTIES
Tubu
lar D
rag
Con
veyo
r
Flex
ible
Scr
ew C
onve
yor
Con
vent
iona
l Scr
ew C
onve
yor
Trou
ghed
Bel
t con
veyo
r
Cle
ated
Bel
t Con
veyo
r
En M
ass
Con
veyo
r
Buck
et E
leva
tor
Vibr
atin
g C
onve
yor
Pneu
mat
ic C
onve
yor
Aero
Mec
hani
cal C
onve
yor
Sludge
Slurry
Moist
Dry Hot
Cold Hygroscopic
Maintains blends
SELECTING THE SUPPLIER There is always a danger in working with companies who only offer one type of conveyor. Unless your application
is a real ‘no, no’, there is always the tendency that they will make ‘one size fit all’ and, although the conveyor may
actually perform on the application for which it was specified, it may not be the lowest cost, operationally efficient
and lowest operating cost unit that you could have purchased. So, always look for a supplier offering a wide
choice of conveyors, one with a proven track record, one that can supply references, one that has a test facility
and, above all, one that will offer a process guarantee.
CONCLUSION The totally enclosed, mechanical tubular chain/cable drag conveyor will satisfy the demands of a wide range of
bulk material handling applications. Low energy cost, low maintenance cost, easy installation, elimination of the
loss of expensive product through dusting, combine to make this conveyor economical to own and operate over
the life of the process being served. With its features and benefits this style of conveyor should be considered for
every bulk transfer project. Proper equipment selection, with due consideration to the initial costs plus the long
term operating costs, will save time and money by improving the efficiency of your operation.
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ABOUT THE AUTHOR Robert Sutton has a total of 42 years in the design, manufacture, marketing and application of tubular drag
conveyors. In 1980 he started his own business Dynamet Inc based in Kalamazoo, Michigan, USA. Spiroflow
Systems Inc of Monroe, North Carolina purchased the business in 2010 as part of its strategic goal to expand its
range of conveyors for dry bulk solids. Accordingly, Spiroflow Systems offers one of the widest choices of
conveyor in the business including Flexible Screw, Aero Mechanical, Vacuum and Tubular Drag types. Robert
Sutton has been retained by Spiroflow as their Global Product Specialist for Tubular Chain/Cable Drag
Conveyors.
ABOUT SPIROFLOW SYSTEMS, INC.
Spiroflow Systems is a worldwide supplier of a wide range of both standard and custom powder handling
equipment, specializing in Bulk Bag Dischargers and Fillers, a range of Aero Mechanical, Tubular Drag, Flexible
Screw and Pneumatic Conveyors, a range of 50 lb Bag Packing and Unloading equipment and the Pacepacker
range of Automatic Packing, Pick and Place and Palletizing solutions. The company offers a wide range of
innovative designs and design options.
An in-house test facility offers a free on-site and on-line service to customers to analyze and demonstrate
material flow properties under actual operating conditions. This, in turn, sets the parameters for selecting the
most suitable handling method for your process and ensures equipment is installed properly. Any system tested
in our test facility is guaranteed.
For more information about this article, contact Spiroflow Systems, Inc. at 704-246-0900 or e-mail
[email protected]. Spiroflow can also be found on the web at: www.spiroflowsystems.com.
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