Vertical screw conveyors:
A
vertical screw conveyor conveys material upward in a vertical path. It
requires less space than some other types of elevating conveyors.
Vertical screw conveyor can handle most of the bulk materials provided
there is no large lump. The maximum height is usually limited to 30m.
A
vertical screw conveyor consists of a screw rotating in a vertical
casing. The top bearing for the screw shaft must be designed to stand
against radial and thrust loads. A suitable inlet port at the lower end
and a discharge port at the upper end of the casing are provided.
Feeding a vertical screw conveyor deserves careful consideration. Most
materials are fed to the vertical conveyor by a straight or offset
horizontal feeder conveyor. The ideal operation of a vertical screw
conveyor is to have a controlled and uniform volume of material feeding.
Uneven
feeding and start stop operation may adversely affect the performance
of the vertical screw conveyor in terms of speed, capacity and horse
power.
Average capacities and speeds of vertical conveyor
| Nominal diameter of screw in mm | Capacities in m3/hr | Speed of screw |
| 150 | 10 | Up to 400 RPM |
| 250 | 35 | 300 RPM |
| 300 | 75 | 250 RPM |
| 400 | 170 | 200 RPM |
Vertical screw conveyors or some special design of vertical screw conveyor finds wide application in ship unloading.
Practical
experience with these conveyors has shown that the resistance factor
for vertical conveyors is higher than those of the horizontal conveyors.
Resistance factor λ may be taken as 5.5 to 7.5 for grains. 6.5 to 8.3
for salt.
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