Overview

A screw conveyor is a mechanical device that uses an electric motor to drive a screw to rotate and move materials to achieve conveying purposes. It can transport horizontally, obliquely, or vertically, and has the advantages of simple structure, small cross-sectional area, good sealing, easy operation, easy maintenance, and convenient enclosed transportation. Spiral conveyors are divided into two types in terms of conveying form: axial spiral conveyors and non axial spiral conveyors. In terms of appearance, they are divided into U-shaped spiral conveyors and tubular spiral conveyors. The axial screw conveyor is suitable for non sticky dry powder materials and small particle materials For example, cement, fly ash, lime, grains, etc., the shaft less screw conveyor is suitable for conveying sticky and easily entangled materials. The working principle of a screw conveyor (such as sludge, biomass, garbage, etc.) is that the rotating screw blades push the material and transport it through the screw conveyor. The force that prevents the material from rotating with the screw conveyor blades is the weight of the material itself and the frictional resistance of the screw conveyor shell to the material. The spiral blades welded on the rotating shaft of the screw conveyor have different surface types according to the conveyed materials, such as solid surface, belt surface, and blade surface. The screw shaft of the screw conveyor has a thrust bearing at the end of the material movement direction to provide axial reaction force to the screw with the material. When the machine length is long, a middle hanging bearing should be added.

Operational principle:
When the spiral shaft rotates, due to the gravity of the material and its frictional force with the groove wall, the material can only move forward along the bottom of the conveyor groove under the push of the blades, as if the non rotating nut is translating along the rotating screw. The main forward force of the material comes from the force exerted by the spiral blades when rotating axially, which moves the material upwards and forward along the tangent direction of the blades.

In order to maintain a favorable tension state for the spiral shaft, the driving device and discharge port are generally placed at the same end of the conveyor, while the feed port is placed as close to the tail of the other end as possible. The rotating spiral blades push the material for transportation, and the force that prevents the material from rotating with the spiral conveyor blades is the weight of the material itself and the frictional resistance of the spiral conveyor shell to the material. The surface shape of the blade can be classified into solid surface shape, belt surface shape, blade surface shape, etc. according to the different materials being transported. The screw shaft of the screw conveyor has a thrust bearing at the end of the material movement direction to provide axial reaction force to the screw with the material. When the machine length is long, a middle hanging bearing should be added.

Structure characteristics:
(1) There are three types of spiral blades for screw conveyors: solid spiral surface type, belt spiral surface type, and blade spiral surface type. The solid spiral surface is called the s-method, and its spiral pitch GX is 0.8 times the diameter of the blade. The LS type screw conveyor is suitable for conveying powder and granular materials. Belt spiral surface, also known as D-method, has a spiral pitch that is the same as the diameter of the spiral blade, and is suitable for conveying powdered and small materials. The application of blade type spiral surfaces is relatively limited, mainly used for conveying materials with high viscosity and compressibility. During the conveying process, mixing and other processes are completed simultaneously, and the spiral pitch is about 1.2 times the diameter of the spiral blade.

(2) The spiral blades of the screw conveyor have two directions of rotation: left and right.

(3) There are two types of screw conveyors: horizontal fixed screw conveyor and vertical screw conveyor. Horizontal fixed screw conveyor is the most commonly used type. Vertical screw conveyor is used for short distance lifting of materials, with a conveying height generally not exceeding 8m. The spiral blades are solid surface type, and it must have horizontal screw feeding to ensure necessary feeding pressure.
(4) The outlet end of LS and GX spiral conveyors should be equipped with 1/2 to 1 turn reverse spiral blades to prevent powder blockage at the end.
(5) The screw conveyor consists of three parts: the screw body, the inlet and outlet, and the driving device. The main body of the screw machine consists of head bearings, tail bearings, suspension bearings, screws, casing, cover plate, and base. The driving device consists of an electric motor, a reducer, a coupling, and a base.

Application:
Spiral conveyors are widely used in various sectors of the national economy, such as the grain industry, building materials industry, chemical industry, machinery manufacturing industry, and transportation industry. Spiral conveyors are mainly used to transport various powdered, granular, and small pieces of materials. The transported loose materials include grain products such as grains, beans, flour, building materials such as cement, clay, and sand, chemicals such as salts, alkalis, fertilizers, as well as bulk cargo such as coal, coke, and ore. Spiral conveyors are not suitable for conveying materials that are prone to spoilage, high viscosity, blockiness, or clumping. In addition to conveying loose materials, screw conveyors can also be used to transport various finished items. The screw conveyor can complete mixing, stirring, cooling and other operations while conveying materials. In ports, screw conveyors are mainly used for unloading trucks, ships, and horizontal and vertical conveying of bulk materials in warehouses. The spiral unloading machine, which uses a horizontal spiral shaft in direct contact with the material to unload the material layer by layer from both sides of the carriage, has been successfully used in domestic ports for many years. The screw unloader, composed of horizontal screw conveyor, vertical screw conveyor, and relative screw reclaiming device, has become a relatively advanced continuous unloader model and is increasingly widely used in domestic and foreign bulk cargo dedicated terminals.