1

SCREW CONVEYOR.

Mechanical Engineering Department

Carlos III University

SCREW CONVEYOR.

TRANSPORTATION

SCREW CONVEYOR.

SCREW CONVEYOR

Transport of material along a tube by means of a screw

• Advantages:

– They are compact

– Modular design: easy installation

– Simple supports

– High temperatures

– Easily hermetic

– Extremely versatile:

• “Dose”

• Mixer

– Distance up to 50 m

– Several loading and unloading points

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SCREW CONVEYOR.

SCREW CONVEYOR

• Drawbacks:

– No big sizes

– No fragile or delicate materials

– Non abrasive materials

– Bigger power requirements

– Material pollution

– Low material volume

SCREW CONVEYOR.

COMPONENTS

Supporting feet and saddles

Feed and discharge spouts

Trough ends

Covers and clamps

Hanger

Bearing

Job rated components,

jig-drilled couplings,

Tem-U-Lac self locking

coupling bolts

Shaft

Blades

Screw

Conveyor housing

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SCREW CONVEYOR.

SCREW

It consists of a several of blades of helix shape welded to a pipe or shaft. It moves the material.

• Flight outside diameter, type of blades, spacing between the blades, thickness of the external diameter and interior shaft and rotation direction.

Shaft outside diameter

Thickness

Shaft length

Flight outside

diameter

Pitch

SCREW CONVEYOR.

SCREW

• Classification:

– Spiral screw conveyor (or flight).

– Sectional screw conveyor.

– Single cut flight.

– Ribbon flight.

– Standard pitch with paddles.

– Screw cut and folded flight.

– Single flight short pitch.

– Van paddle conveyor.

– Single tapered flight standard pitch.

– Step flight.

– Single flight variable pitch.

– Single flight large pitch.

– Double flight standard pitch.

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SCREW CONVEYOR.

MATERIAL FLUX CALCULATION

4

2D

sπλ=Conveyor housing filled area

(m2)

Fill coefficient of the section

(lower than unity)

0,4Light not abrasive

0,32Light and a little

abrasive

0,25Heavy and a little

abrasive

0,125Heavy and abrasive

Type of load λ

60

t nv

⋅=Travelling speed (m/s)

Screw pitch (m) Screw rotating speed (rpm)

SCREW CONVEYOR.

•Between 0,5 and 1 times its diameter

•Bigger for a lighter load

Screw pitch:

•12 times bigger than the diameter of the material particles being transported (homogeneous material)

•4 times bigger than the bigger diameter of the material particles being transported (heterogeneous material)

Screw diameter:

•Inversely proportional to:

– Weight of the bulk material

– Abrasive materials

– Screw diameter

Screw speed: 50

150

Heavy materials n rpm

Lighter materials n rpm

⇒ ≈⇒ <

MATERIAL FLUX CALCULATION

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SCREW CONVEYOR.

MATERIAL FLUX CALCULATION

kvsQ ⋅⋅⋅⋅= γ3600Transported

material flux (t/h)

Material density (t/m3)Flux material

decrement coefficient

0,8

10º

0,7

15º

0,6

20º

0,9

5º

1k

0ºConveyor housing

inclination

kntD

Q ⋅⋅⋅⋅⋅= γπλ604

36002

4

2Ds

πλ=60

ntv

⋅=

SCREW CONVEYOR.

POWER

H N StP P P P= + +

• PH is the required power to move the material horizontally

• PN is the required power to operate an unloaded screw

• PSt is the required power for an inclined screw conveyor

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SCREW CONVEYOR.

POWER

0 0( )3600 367

H

QLg QLP kW c c= =

Material travelling

4Gypsum, dry clay, fine soil, cement, lime, sand

2,5Anthracite, coal, rock salt

1,2Flour, sawdust, granular

1,6Peat fibre, soda, coal dust

c0 EmpiricMaterial

Material resistance coefficient

Installation length

SCREW CONVEYOR.

POWER

( )20

N

DLP kW =

Unloaded operated screw

• It is much lower than the power required to move the material

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SCREW CONVEYOR.

POWER

( )367

St

QHP kW =

Inclined screw conveyor

Installation height

Required power

0( )

367 20

Q c L H DLP

+= +