Screw conveyors possess the following characteristics:
1) Relatively simple structure and low cost.
2) Reliable operation and easy maintenance.
3) Compact dimensions, small cross-sectional area, and minimal footprint. During port operations involving the unloading of trucks and ships, they can easily access and exit cargo hatches and vehicle compartments.
4) Capable of sealed conveying, which is advantageous for transporting dusty, hot, or strongly odorous materials; this helps reduce environmental pollution and improves working conditions for port personnel.
5) Convenient loading and unloading. Horizontal screw conveyors allow for loading and unloading at any point along their conveying path; when paired with a suitable screw-type reclaiming device, vertical screw conveyors demonstrate excellent material reclaiming capabilities.
6) Capable of reverse conveying; a single conveyor can also transport materials simultaneously in two directions-either converging toward a central point or diverging away from it.
7) Relatively high energy consumption per unit of material conveyed.
8) Materials are prone to crushing and abrasion during transport; furthermore, the screw blades and conveyor trough are subject to significant wear.
Structural Features
(1) Screw conveyor blades fall into three main categories: solid helical surface type, ribbon helical surface type, and paddle helical surface type. The solid helical surface type-referred to as the "S-method"-features a screw pitch (for the GX model) equal to 0.8 times the blade diameter; the LS model screw conveyor is suitable for transporting powdery and granular materials. The ribbon helical surface type-known as the "D-method"-features a screw pitch equal to the blade diameter and is suitable for transporting powdery materials as well as small lumps. The paddle helical surface type is less frequently used; it is primarily employed for conveying highly viscous or compressible materials, simultaneously performing processes such as stirring and mixing during transport, and features a screw pitch approximately 1.2 times the blade diameter.
(2) Screw conveyor blades are available in two rotational orientations: left-handed and right-handed.
(3) Screw conveyor types include horizontal fixed-position screw conveyors and vertical screw conveyors. The horizontal fixed-position screw conveyor is the most commonly used configuration. Vertical screw conveyors are used for lifting materials over short distances; the conveying height generally does not exceed 8 meters. The screw flights feature a solid-surface design and must be paired with a horizontal screw feeder to ensure the necessary feeding pressure.
(4) At the material discharge end of LS- and GX-type screw conveyors, 1/2 to 1 full turn of reverse-pitch screw flights should be installed to prevent powdery materials from clogging the terminal section.
(5) A screw conveyor consists of three main components: the conveyor body, the inlet and outlet ports, and the drive unit.
The conveyor body comprises the head bearing, tail bearing, hanger bearings, screw shaft, casing, cover plates, base, and other elements.
The drive unit consists of an electric motor, a speed reducer, a coupling, and a base.
Applications
Screw conveyors are widely utilized across various sectors of the national economy, including the grain industry, construction materials industry, chemical industry, machinery manufacturing, and transportation. They are primarily used to convey various powdery, granular, and small-lump materials. The bulk materials conveyed include grain products (such as cereals, legumes, and flour), construction materials (such as cement, clay, and sand), chemicals (such as salts, alkalis, and fertilizers), as well as bulk commodities like coal, coke, and ores. Screw conveyors are generally unsuitable for conveying materials that are perishable, highly viscous, excessively lumpy, or prone to caking. In addition to conveying bulk materials, screw conveyors can also be utilized to transport various packaged or discrete items. While conveying materials, screw conveyors can simultaneously perform operations such as mixing, agitating, and cooling. In port environments, screw conveyors are primarily employed for truck and ship unloading operations, as well as for the horizontal and vertical conveyance of bulk materials within warehouses. Screw-type truck unloaders-which utilize a horizontal screw shaft in direct contact with the material to unload it layer by layer from both sides of a truck bed-have a history of successful application spanning many years in domestic ports. Furthermore, screw-type ship unloaders-which integrate horizontal screw conveyors, vertical screw conveyors, and counter-rotating screw reclaiming mechanisms-have emerged as an advanced type of continuous ship unloader, finding increasingly widespread application at specialized bulk cargo terminals both domestically and internationally.
