Screw Conveyor

What is a Screw Conveyor?

A screw conveyor is a versatile device for transporting bulk and small-sized materials. It enables continuous movement of products within an open or closed trough, as well as vertical lifting. This equipment is simple in design and operation, compact, sealed, and convenient for intermediate unloading. Using a screw conveyor can significantly mechanize the production process, save time on transportation, and increase overall productivity. These mechanisms are particularly popular in industries producing animal feed, flour, grain, building materials, as well as in machine engineering and the chemical sector.

 

How a Screw Conveyor Works

Let’s examine the design of the screw conveyor, its operating principle, and key parameters. The conveyor body consists of a trough equipped with loading sections. Inside the body is the screw (auger) — the main working component. It is driven by an electric motor. The screw blades capture the load and move it along the line to the discharge outlets. The screw is a tube with welded blades.

 

Principle of Operation and Design of the Screw Conveyor

The operation of screw conveyors is based on axial driving force. The screw rotates in a stationary closed trough using an electric motor with a gearbox and two couplings. It is supported by hanging bearings: end and intermediate supports. The body (trough) consists of sections made from sheet steel, with thickness varying from 0.08 inches to 0.24 inches, depending on the type and purpose of the design. All sections are sealed together with flanges using bolts and gaskets.

 

The operation of a horizontal screw conveyor consists of three stages:

 

 1. Feeding bulk material into the loading opening;

 2. Gradual movement of the load to the discharge opening as the screw rotates;

 3. Discharge.

 

The screw glides along the trough, moving the material forward. Sliding bearings are used as supports for the screw. The final thrust bearing absorbs longitudinal forces.

 

A loading device is used to introduce the transported material into the conveyor. This is an opening in the cover of the trough with an inlet pipe that ensures sealing. The discharge device refers to an opening in the conveyor trough.

 

Technical Specifications of the Screw Conveyor

For each customer, the type of screw conveyor is individually selected based on specific technical specifications:

• Capacity, cubic feet per hour (ft³/h);

• Screw diameter, inches;

• Screw pitch, inches;

• Blade thickness, inches;

• Type of screw;

• Maximum transport length, feet, and others.

 

The design of the future conveyor and its elements is developed based on initial data: characteristics of the transported load, height, and angle of inclination. Additionally, when selecting the required type of screw conveyor, factors such as load movement direction, equipment capacity, and material loading method should be considered. The type of conveyor determines how the material is moved: inclined or horizontally. The type of cargo and selected screw diameter will define its rotational speed (rpm).

 

Types of Screw Conveyors

Designing a screw conveyor should take into account its types and intended use.

 

Screw conveyors can be of closed type (body is a tube) or open type (body is a trough). In a closed-type conveyor, the screw is mounted inside a sealed tube. At the start of the line, there is a receiving trough equipped with a cover. The opening at the opposite end of the line is a discharge pipe that is closed with a gate. Such conveyors are characterized by waterproof and airtight features, high performance, and product movement speed. They are used indoors and outdoors for transporting powdery cargo.

 

Types of Cylindrical Conveyors (Closed Type)

The cylindrical screw conveyor is one of the most common types. Its tube-like body provides rigidity, and the unit is compact and easy to use. It is suitable for nearly all industries. Key features and additional functions include:

• Straight, adjustable angle, and vertical conveyors;

• Stationary or mobile;

• Body and screw material—stainless or galvanized steel;

• Equipped with feeders;

• Adjustable speed and reversible screw rotation.

 

An open-type conveyor consists of troughs or half-tubes in which the screw rotates. A rectangular container can also serve as the body of an open conveyor. This mechanism is used only indoors, as it is not airtight: moisture and dust can enter. It is preferable that the materials being transported do not have odors, do not scatter, and do not create dust during transportation.

 

Classification of Screw Conveyors

Screw conveyors are differentiated and classified based on key parameters:

• Trough inclination;

• Spiral direction;

• Pitch and diameter of the screw;

• Screw design.

 

Classification by the angle of trough inclination defines horizontal, mildly inclined, steeply inclined, and vertical conveyors.

 

The type of blades used on the screw depends on the transported cargo and conveyor capacity:

• Solid blades are intended for moving bulk (powdery) materials;

• Ribbon blades are suitable for small-sized materials;

• Individual paddle blades are designed for transporting sticky and viscous materials;

• Specially shaped blades are useful for mixing material during transportation.

 

The shape of the screw is chosen based on the type of cargo being transported. Depending on the type of conveyor and its purpose, its blades can move materials inclined (at a 45° angle) up to 98 feet, and horizontally up to 130-197 feet.

 

Implemented Projects

 

Features and Disadvantages of Screw Conveyors