Screw Conveyor Design

Aug 10

Design of Screw Conveyor | Size of Screw Conveyor | Screw Conveyor Capacity Calculation | Screw Conveyor Design Calculation Material Handling, Screw Conveyor

The size of screw conveyor depends on two factors 1. The capacity of the conveyor 2. The lump size of the material to be conveyed (Maximum dimensions of the particle) Usually there are three ranges of lump sizes which are considered for selection of screw size. These are:

· A mixture of lumps and fines in which not more t han 10% are lumps ranging from maximum size to one half of the maximum, and 90% are lumps smaller t han one half of the maximum size. · A mixture of lump and fines in which not more than 25% are lumps ranging from the maximum size to one half of the maximum, and 75% are lumps smaller t han one half of the maximum size. · A mixture of lump only in which 95% or more are lumps ranging from maximum size to one half of  the maximum size and 5% or less are lumps less than one tenth of the maximum size.

The allowable size of a lump in a screw conveyor is a function of the radial clearance between the outside diameter of the central pipe and the radius of the inside of the screw trough, as well as the proportion of the lumps in the mixture. The lump size of the material affects the selection of screw diameter which should be at least 12 times larger than the lump size of a sized material and four times larger than the largest lumps of an un-sized material. Example, if screw diameter is 250mm means radial clearance is 105mm, & Maximum lump size is 60mm of 10% lumps.

The capacity of a screw conveyor depends on the screw diameter, screw pitch, speed of the screw and the loading efficiency of the cross sectional area of the screw. The capacity of a screw conveyor with a continuous screw:

Where, Q = capacity of a screw conveyor V = Volumetric capacity in m3/Hr = Bulk density of the material, kg/m 3 D = Nominal diameter of Screw in m S = Screw pitch in m

N = RPM of screw Ψ = Loading efficiency of the screw C = Factor to take into account the inclination of the conveyor

Commonly the screw pitch is taken equal to the diameter of the screw D. However it may range 0.75 – 1.0 times the diameter of the screw.

Nominal Trough

Trough

Size D

width C

height from

Thickness of Tough

Tubular

Outside

Coupling

shaft (d1 * diameter diameter Thickness) of solid

center of 

of shaft

shaft

screw shaft to upper edge of the trough Heavy

Medium Duty Light

Duty

Duty

100

63

120

-

2

1.6

33.7*2.5

30

25

125

75

145

-

2

1.6

33.7*2.5

30

25

160

90

180

5

3.15

1.6

42.4*2.5

35

40

200

112

220

5

3.15

2

48.3*3.5

40

40

250

140

270

5

3.15

2

60.3*4

50

50

315

180

335

5

3.15

-

76.1*5

60

50

400

224

420

5

3.15

-

76.1*5

60

75

500

280

530

5

3.15

-

88.9*5

70

75

The usual range of RPM of screw is 10 to 165. It depends on the diameter of screw and the type of material (Max RPM of screw conveyor is 165)

The value of loading efficiency should be taken large for materials which are free flowing and non abrasive, while for materials which are n ot free flowing and or abrasive in nature, the value should be taken low: Ψ = 0.12 to 0.15 for abrasive material = 0.25 to 0.3 for mildly abrasive material = 0.4 to 0.45 for non abrasive free flowing materials

The inclination factor C is determined by the angle of screw conveyor with the horizontal.

0°

5°

10°

15°

20°

1

0.9

0.8

0.7

0.65

Angle of screw with the horizontal Value of factor C