Screw conveyor and its operation
A screw conveyor is a conveyor system which transports goods on the principle of the Archimedean screw. The image of a conveyor system with a flexible screw is intended to make the function of a conveyor spiral clearer. The suction pipe of a screw conveyor can be used as a funnel through its U-shaped loading chute. The gravity and the friction of the cargo to the so called through walls ensure that the good does not rotate with the screw but is permanently transported. The effective and efficient transport depends on the degree of filling which must not be too large otherwise the friction on the wall is too low. An important criterion for vertical transport is the speed because it generates the necessary centrifugal force which makes friction possible. In contrast to a spiral conveyor, the screw conveyor has a worm shaft in the middle.
Screw conveyor and its designs
A screw conveyor serves to transport so called bulk material. The screw conveyor is rigid and permanently installed. It consists of rotating screw shaped augers that move within a trough or pipe. Special forms are the paddle screw in which the helix is replaced by individual paddles. The screw conveyor in which the screw helix is designed as a band fixed to the shaft with webs and the helical conveyor in which the shaft is missing. The spiral conveyor is also known in flexible design. Another special design is the screw tube conveyor. In this case the coil is attached to the conveyor tube which now rotates.
Depending on the task and product characteristics there are single shaft and twin screw systems. For continuous mixing and crushing especially two-shaft auger flights are built. When the vertical, horizontal or inclined conveying path is curved usually spiral conveyors are used. A special feature is the geometry of extruders and meat grinders. There, the helix is designed so that the cross section narrows towards the exit creating high pressures that tend to force tough material through stencils or molds. The known embodiments of screw conveyor are full screw, ribbon screw, stirring screw and paddle screw.
Conclusion: flight blades
During oblique, vertical or horizontal transport other processing steps such as portioning, mixing, dewatering, compressing, cooling or drying may be used in parallel. The speed, the inner and outer diameter, the pitch, the degree of filling and the friction of the conveyed material on the screw determine the flow rate. Their maximum is reached when the friction on the screw conveyor against the friction on the trough wall is small. The pitch of the auger and the flight depth are the main factors when calculating the degree of filling. The larger the slope the higher the degree of filling is. The material to be conveyed flows from the top into the loading chute through the flexible conveyor spiral. The screw conveyor is usually driven by a motor. Goods can also be transported in rigid pipes. In the case of rigid screws there is no bending in the tube. A rigid screw thus affects less flexible on the use of space.