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Basics of flexible screw conveyors
In basic form , a flexible screw conveyor consists of a spring steel or stainless steel flexible screw that is enclosed in s flexible or rigid plastic tube or a rigid steel tube (a small diameter ,plastic inner tube may also run the entire length of the flexible screw) and driven by an electric motor，normally located at the discharge end of the conveyor.
The intake end of the conveyor tube is typicallyequipped with a charging adapter-a U-shaped trough that connects to the outlet of a hopper ordirectly to the outlet of process equipment such as a bulk bag discharger,bagdumpstation,grinder, crusher,screener,blender,reactor,or storage vessel.
The flexible screw passesthrough the charging adapter trough exposing a section of the screw to material flowing intothe trough from above.When rotating the exposed section of screw feeds material into the outer tube where it is then propelled through the tube by theenclosed portion of the screw.
The screw automatically selfcenters within the
tube providing clearance between the screw and
tube wall a phenomenon resulting from the loose fit
ofarotating flexible screw withinatube filled with
bulk materialThis property affords sufficientspace
for particles to flow without damage depending on
the fragility and size of particlesbeing conveyed.
A removable cleanout cap covers the intake end of the
conveyor tube Permitting rapid emptying and flushing of
the tube as well as disassembly and washdown
ofcomponents.
Because the intake end of the screw requires no
bearing，and since the discharge end is coupled to the motor
drive above and/or beyond the point at which material exits
the discharge spout，material does not come in contact with
seals or bearings.The flexible screw is therefore the only
moving part contacting material.
Typical applications include conveying of
materials between storage vessels，bulk bag
dischargers，manual bag dump stations，drum dump
stations，crushers，screeners，blenders，reactors，
Packaging equipment，injection molding and
extrusion machines and other Process equipment.
Capabilities
A flexible screw conveyor is your most
likelychoice if its
listofdistinguishingcapabilitiesclosely matches that of your requirements，or if an individual capability exclusive toaflexible screw solves an individual problem of key concern.CoMPare your needs with the following attributes。
onemovingPartcontacting material―The only moving part contacting material inaflexible screw conveyor is rugged flexible screw，which is directly driven by an electricmotor. This simple design does not require the filters，cyclone separators，internal bearings，and other moving parts found on pneumatic conveyors，bucket elevators，rigid augers，drag chains，and/or aeromechanical conveyors.
Conveys free-flowing and nonfrce-flowing materials- A flexible screw conveyor cantransport bulk materials rangingfrom large pellets to submicron powders，including difficult to handle products that Pack，cake，seize，fluidize，plug，or smear. Some examples are fine powders
such as fumed silica，compressible materials such as titanium dioxide，dense materials such as metal powder，friable materials，materials that fluidize，and materials
comprised of particle sizes to 1 in.such as nuts.The gentle rolling action created bythe rotating screw prevents the separation of blended Products，even those comprised of disparate particle sizes and/or densities，throughout the entire
length of the conveyor.
Contamination Prevention-A flexible screw conveyor can be fully enclosed to Preventcontamination of bulk Products and the Plant environment，while Preserving the moisture and temperature levels of materials being conveyed. All interior surfaces are smooth，and can be easier to clean than conveyors in which material contacts internal bearings，seams，filters or other internal components . In addition，the units can be designed and finished to industrial and sanitary standardsencoMPassing chemical，pharmaceutical，food/dairy，plastics，paint，mining，packaging，and other applications.
Multidirectional-A flexible screw conveyor can move powder and bulk solid materials vertically，horizontally，or at any angle. This ability allows the user to position the intake and dischargeendsoftheconveyoraccordingtothe preferredsystem Layout or to accommodate awkward layoutsas are frequently encountered in retrofit/upgradesituations.
Gentle Product handling-Depending on particle fragility and size，a flexible screw conveyor can move materials with little or no breakage or
degradation，Clearance afforded between the screw and tube wall by the rotating，self-centering screw can eliminate or minimize the grinding，crushing，and iMPact damage that can occur with other conveying methods.
Rapid，thorough cleaning-Flexible screw conveyors contain no cracks，crevices，filters，or bearings that can trap particles or breed contamination.Cleaning consists ofremovingthecleanoutcap and reversing rotation to evacuate any residual material Prior to flushing with air，water，steam，or cleaning solution.The screw and outer tube can
also be removed rapidly for thorough wash-down of individual components.
high reliability，low maintenance-A flexible screw conveyor contains no internal bearings. filters，or separators to wear，break down，or require maintenance. The wear and fatigue-resistant flexible screw is driven directly by an electric motor .Depending on application parameters，a flexible screw conveyor can be started and stopped repeatedly，even under a full load，with no binding or damage to the unit.
Economical-The lack of internal bearings，gears，filters，or chains as well as external compressors，blowers，and separators can make flexible
screw conveyors less costly to build and operatethan other conveyors.A flexible screw conveyor can also be economical to install，because the
intake and discharge ends can be Positioned wherever desired，without exact conveyor routing，reducing the need to reconfigure other upstream
and downstream Process equipment.
Mobility-Flexible screw conveyors can be caster-mounted on frames with conveyor support booms for inplant mobility，avoiding the cost of multiple stationary units.
Multiple discharges-Horizontally oriented flexible screw conveyors can feed
multiple packaging machines，molding machines，and process
equipment simultaneously or individually They can also convey bulk material over long distances，feed multiple discharge points selectively，
or topoff all Points on a timed cycle through manual
orautomatic slide gate valves.
Volumetric feeding-A flexible screw conveyor can
simultaneously meter and convey bulksolid products·Units
can be equipped with ac or dc variable-speed drives and
hoppers with flow promotion devices for continuous feeding
of both free and nonfree-flowing materials.
Weigh batching and feeding-Gain-in-weight batching
systems consist ofindividualor multipleflexible screw
conveyors discharging intoacentral weigh hopper or other
process equipment，which is equipped with load cells.
Gain-in-weight information is transmitted to a central
programmable controller，which in turn controlseach
conveyor.Thecontroller then activates each conveyor，in
sequence，to load each ingredient intothe central weigh
hopper，first at high speed，then at dribble speedbefore
stopping theconveyor when the target batch weight hasbeen
reached. since the systemfunctions as bothweigh feeder
and conveyor，it can eliminate the need for separateequipment.
reactor pressure vesselLimitations
Since every mode of conveying also Possesses inherent
limitations，each must be identified and ruled unimportant，
or less important than corresponding attributes，before
deeming    a flexible screw conveyor to be the most
compromise-free alternative for your application.
Material evacuation—Flexible screw conveyors，like
other mechanical conveyors，do not generally evacuate
material completely when operatingin a forward direction
The cleanout cap can be removed，however，and the screw
rotation reversed to fully evacuate residual material for
reasons of cleaning and/or material changeovers.
Gentle Product handling—While flexible screw
conveyors can have less deleterious effect on materials than do methods that tend to grind，crush，or
iMPact bulk products，not all materials can be conveyed damage一free. A Percentage of large，brittle flakes or large，soft particles may，for example，incur breakage，particularly through long runs or steep inclines in a flexible screw conveyor.properengineeringofaflexiblescrewconveyorsystemcaneliminate or minimize these effects.
C apacity requirements—Flexible screw conveyors are currently utilized for applicationswith capacityrequirements less than 50 tons/hr(Per conveyor ) , explaining
why they are infrequently employedfor off-loading of shipsor railcars.Othereonsid6rationS there are two basic types of screws in flexiblescrew conveyors:roundwire and flat wire.Each hasits advantages and limitations.
The rounded flight surface of round wire screwsiMParts the material with directional forces that propel it through the tube，and relatively high radial forces that create an effective bearing between thescrew and tube wall throughout the length of theconveyor. The material bearing surface causes the screw to self-center within the tube，Preventing it from contacting the tube wall throughout its entire length，even when the screw/tube assembly is curved，assuming it has been correctly engineered. The amount of directional slippage can be minimized utilizing an inner tube running the entire length of the
conveyor，but this is typically unnecessary when conveying Products comprised of larger Particle sizes and/or those of higher mass，such as sugar，flour，soda ash，and plastic owders，ellets and regrind，as these materials are conveyed efficiently using round wire screws.
Flat wire screws are fabricated using bar stockthat is square or rectangular in cross section.Flatbearing surfaces iMPart greater directional forceand lesser radial force(and material compression)than round wire screws.Flat wire screws are therefore frequently employed to convey products that tend to compress，as well as fragile materials，low，mass materials，and those comprised of the finest Particle sizes.
If the characteristics of a flexible screw conveyoralign neatly with your material characteristics and process parameters，your next step is to provide material samples and application details to a flexible screw conveyor application engineer，who can suggest the optimum system for integrationwith your new or existing Process.Should yourapplication call for capabilities beyond those outlined above，a fundamental knowledge of other relevant modes of conveying will enable you to determine Which incurs the fewest number ofcompromises or which best solves your most criticalFULU

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