Scraper Conveyor

Scraper Conveyor

A scraper conveyor is a transport system widely used for moving grain, bulk materials, and piece goods. In this mechanism, the product is transported by scrapers along a stationary trough, connected by a movable scraper chain. This type of equipment can significantly mechanize the production process, save time on transportation, and increase overall productivity. Scraper conveyors are particularly popular in industries that produce animal feed, sugar, flour, grain, and construction materials. Continuous scraper conveyors come in various designs and have gained wide acceptance. The illustration shows a scraper conveyor in a production setting.

Scraper Conveyor: Design and Operating Principle

The scraper conveyor consists of a set of working components that provide the necessary operational characteristics. Let’s look at its main parts:

•    Trough: This component has side plates and a bottom, supported by shock-absorbing bases. Troughs can be stamped or welded, and they may include a device for the oscillation of the bottom.
•    The trough is made up of segments that range in length from 9 to 25 feet.
•    Scraper Chain: This part connects the scrapers to the drive and carries the load from the scrapers.
•    Scrapers: These are plates attached to the chain, reinforced with ribs for added strength. They transport the product by applying mechanical force.
•    Drive Station: This consists of an electric motor and a mechanism that transmits rotation. The drive can be gear-driven or belt-driven.
•    Tension Station: This includes a sprocket and consists of automatic tension springs or a lead screw.
•    End Head: This component transmits force to the main unit.

Stainless steel is commonly used for manufacturing the parts of the scraper conveyor because it is durable and resistant to wear.

Operating Principle of the Scraper Conveyor

The conveyor chain rotates continuously, with only one part of it engaged in work at any given time. Scrapers are evenly spaced along the length of the chain. They move the load along the bottom of the trough toward the tension station, then deposit it at the unloading point. The belt then returns to the top.
In a horizontal position, the scraper conveyor moves a layer of product that exceeds the height of the scrapers. The lower and upper layers form a continuous flow, with its maximum height varying based on:

•    The density of the product.
•    External friction against the walls of the trough.
•    Internal friction (particle size of the transported material).

As a result, the speed of the product slows against the trough walls and will be less compared to the speed in the center of the flow.

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Classification of Scraper Conveyors

There are various types of scraper conveyors, classified by many criteria. The primary criterion is the intended use of the equipment. According to their purpose, scraper conveyors can be:

•    Underground, used in coal and ore mines.
•    General-purpose, functioning as versatile mechanisms for various applications.
•    Specialized devices, designed and installed based on specific operational requirements.

Another classification can be based on the nature of the functions performed:

•    Transportation (Delivery): The sole function of these units is to move cargo over a required distance.

The type of drive installed is also crucial for the performance and efficiency of the mechanism. Thus, we can highlight the following drive options:

•    Electric Drive: The most common option, characterized by high efficiency. It has a compact size, making installation and maintenance easier. However, this option can overheat under high loads, so fuses may be required.
•    Pneumatic Drive: Operates by supplying compressed air under pressure, which can transmit significant force. A drawback is power loss due to defects in the air supply line and noise during operation.
•    Hydraulic Drive: This system moves liquid under pressure and can transmit substantial force.

Based on the main element—chain—three possible conveyor designs can be distinguished: with detachable, roller, and link chains.

Scraper Conveyors with Immersed Scrapers

Conveyors with immersed scrapers are popular because their design allows for full utilization of the trough volume, significantly boosting equipment productivity. This type of scraper conveyor has several key distinctions:

•    Two sections of its trough are designed for active and idle operation, respectively.
•    Depending on the type of cargo filling the working trough, scrapers of specific shapes are installed to further enhance productivity.
•    The conveyor chain moves slower than the scrapers; increasing the chain speed results in a greater speed difference.

In continuous dragging conveyors, the cargo is moved as a continuous mass. This device is used when there’s a need to transport bulk products horizontally or at an incline, and it allows for creating complex system trajectories. One drawback of these conveyors is the wear of key components due to continuous dragging.
High-element scraper conveyors have several unique features:

•    The trough shape is selected based on the intended use and the type of cargo being moved.
•    Scrapers are made from durable steel with a thickness of 10 GA or more.
•    Scrapers can also be made from plastic.
•    The installation pitch of the elements is calculated according to the design load on the drive to enhance productivity.
•    The angle of the scrapers relative to the base surface is determined.

Vertical Scraper Conveyor

For transporting cargo in a vertical plane or close to it, vertical scraper conveyors or bucket elevators are used. They are designed to lift grain crops, processed products, seeds, and other bulk materials vertically or near-vertically. This equipment loads products into containers at height, raises crushed raw materials into a hopper or mixer, transports hot granules to a cooling tower, and after cooling, moves the granules into a storage bin. Such equipment is also used in the grain processing industry for flour or grits and for moving dry substances in the chemical industry.
The chain vertical conveyor has a structure similar to a belt conveyor, except that the bucket drive belt is replaced by a chain, and the drums are replaced with sprockets.

Distinctive Features of Scraper Conveyors

Scraper conveyors have varying capacities, which depend on the type of motor and drive installed on the device. The design of a scraper conveyor has several notable features:

•    They can transport bulk materials that are not prone to wear during dragging.
•    The dragging method reduces the speed of material movement due to friction forces.
•    The weight of the entire metal structure of the conveyor is substantial, necessitating a solid foundation for installation.

Materials do not fall outside the device’s confines, thanks to limiting guardrails. Scraper conveyors can be repaired and maintained independently. They are installed in production facilities, with loading points covered by hatches with grates. The main advantage of such conveyors is their ability to move large volumes of bulk and small-sized cargo.