Learn about screw conveyors (drills)

10-03-2022 865

A screw conveyor is a device used in various industries to accurately measure or feed amorphous or bulk materials from one part of the process to another.

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What is screw conveyor?


A screw conveyor is a device used in various industries to accurately measure or feed amorphous or bulk materials from one part of the process to another.

A screw conveyor or auger conveyor is a mechanism using a rotating helical screw blade, which is mounted on a central shaft that is driven by various methods. The assembly rotates inside a tube equipped with a feed mechanism at one end. The material is added at the feed end of the device and transported to the discharge end by a positive displacement process.
 

Application of screw conveyor


In industrial control applications, this device is often used as a variable speed feeder by varying the rotational speed of the shaft to provide a measured rate or quantity of material into the process.

Screw conveyors can be operated with upward material flow. When space permits, this is a very economical method of lifting and conveying. As the tilt angle increases, the capacity of a given device decreases rapidly. They are used in many bulk handling industries. Screw conveyors in modern industry are often used horizontally or slightly inclined as an efficient way to move semi-solid materials, including food waste, wood chips, aggregates, grain, etc. forage, boiler ash, meat and bone meal, solid waste and many other wastes.

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Types of screw conveyors

 

1 - Horizontal screw conveyor


Horizontal screw conveyor is the most widely used type of screw conveyor. Used to transport bulk materials from one part of the process to another, horizontal screw conveyors come in a variety of sizes, lengths, configurations, and construction materials.

Screw conveyors are typically designed to transport bulk materials with a trough load of 15, 30 or 45%, depending on the material properties of the particular bulk material. As a general rule, a 45% bottom load can be used for light, free-flowing and non-abrasive bulk materials. Trough loads of 15 and 30% are commonly used for bulk materials that are denser, sluggish and more abrasive.

Advantages of using screw conveyors:

- Ideal for transporting dry to semi-liquid bulk materials - free flowing to slow
- Cost savings when compared to other conveying devices such as belt, pneumatic or mechanical
- Efficiently distribute bulk material to different locations using multiple inlet and outlet points
- Completely enclosed in dusty, corrosive or toxic environments
 

2 - Inclined screw conveyor


Inclined screw conveyors generally operate from a slightly horizontal position up to 45 degrees from a horizontal position. Above 45 degrees, inclined screw conveyors are considered as vertical screw conveyors. As the degree of inclination increases, the conveying efficiency decreases and the horsepower requirement increases due to the action of gravity and the falling loose material.

The conveying efficiency is affected by the angle of inclination, the properties of the particular bulk material, the type of the screw feeder and the pitch of the screw. It is recommended to design screw conveyors using the lowest possible inclination for maximum efficiency.

The following are the design and structural features to keep in mind when designing inclined screw conveyors:

Tilt up to 10 degrees: Loss of transmission efficiency is minimal when tilting up to 10 degrees. A screw conveyor with full U-trough and screw is sufficient for most applications. Efficiency losses can be overcome by increasing the speed of the screw, increasing the diameter of the screw or reducing the pitch of the screw.

10 to 20 degrees inclination: Loss in transmission efficiency is typically 10 to 40 percent for inclines up to 20 degrees. A screw conveyor with U-trough and 2/3 step screw is sufficient for most applications. The loss of efficiency can also be overcome by increasing the speed or diameter of the screw conveyor. More horsepower is required to overcome gravity and fall back loose.

Tilts from 20 to 30 degrees: Transmission efficiency loss is typically 10 to 70 percent for inclines up to 30 degrees. Screw conveyors with tubular housings and small (1/2 or 2/3) screws are recommended for most applications. The loss of efficiency can also be overcome by increasing the speed or diameter of the screw conveyor. More horsepower is required to overcome gravity and fall back loose.

Tilts from 30 to 45 degrees: Transmission efficiency loss is typically 30 to 90 percent for inclines up to 45 degrees. Screw conveyors with tubular housings and small (1/2 or 2/3) and larger diameter screws are recommended for most applications. Increasing the speed of the screw conveyor is also required. More horsepower is required to overcome gravity and fall back loose.
 

3 - Shaftless screw conveyor


Bulk materials discharged from centrifuges, filter presses or mixers can be easily transported by Shaftless Screw Conveyors. The shaftless design provides an unclogging conveying surface allowing difficult-to-carry materials to be easily transported. The perfect solution for handling bulk materials with high moisture content is the Shaftless Screw Conveyor

Advantages of shaftless screw conveyor:

- Ideal for handling sticky bulk materials
- Improved conveying efficiency when compared to other conveyors
- Allows for more flexible plant layouts due to available configurations
- Internal bearings are removed

Shaftless screw conveyors are successfully used in the chemical, food, mineral processing and wastewater treatment industries to convey everything from catalysts to dehydrated biological solids.
 

4 - Vertical screw conveyor


Vertical screw conveyors are a very effective method for lifting a wide variety of bulk materials at very large inclines or completely vertically. Any screw conveyor that is on an angle of inclination above 45 degrees is a vertical screw conveyor.

The compact design allows the screw to be upright to fit into most plant layouts. With a minimal number of moving parts, vertical screw conveyors are a cost-effective and reliable component in any bulk material handling process.

Advantages of vertical screw conveyor:

- Ideal for handling dry to semi-liquid materials.
- High load capacity
- Possibility to lift loose material without using internal bearings.
- Fully sealed design for dust and vapor tight requirements.

Vertical screw conveyors meet the needs of many industries such as chemical processing, minerals, food, wood products and wastewater treatment.