Drag Conveyor

Drag Conveyor

Material handling equipment is used to safely move large volumes of product and does so with great efficiency. The most common form of this technology is the conveyor, which uses mechanized movement to transport material from its inlet to its discharge end via belts, chains, augers, buckets, and more. Visit our article on understanding conveyor systems to see the huge variety in conveyor technology, as this article will focus on only one type – the drag conveyor. This class of conveyors, also known as drag chain, scraper, paddle, or en masse conveyors is a continuous device capable of accelerating bulk product with ease and makes quick work of aggregates and other materials. This article will show the types, design, and applications of drag conveyors so that readers can potentially implement them into their projects, if they fit their needs.
Drag conveyors are not unlike most other conveyors in terms of operation – a motor powers an endless single or double-stranded chain of flights (see Figure 1) which pulls or “drags” material through the bottom of the conveyor. The chain can be partially or completely enclosed, but in all cases, there must be some form of housing to allow material to be dragged by the flights to the outlet(s). These flights, known also as paddles or scrapers, are distinct in that they can use up to 50% of the available space within the conveyor for material movement, instead of the typical 20-45% of other conveyor types. They are, therefore, able to move more material with less power and are generally an efficient option of conveyance. The gaps between each paddle are large enough to allow for multiple inlets and top-loading of materials into the conveyor, making it a great-multi-purpose option.

Drag conveyors are best suited for dry, free-flowing materials and are most useful for agricultural, railway, chemical, cement, and other applications which require metering and efficient movement of product. They can be inclined as well as horizontal, but their paddles must be designed for vertical conveying, if desired. They are easy to implement into plants and can be configured to have multiple inlets/outlets, making them a great plug-and-play conveyor type. They can also be used in tandem with other open conveyors to help reclaim any lost material, giving them additional applications in recycling, environmental protection, and accumulation functions.

Types of drag conveyors
There are some basic types of drag conveyors available to buyers, and this section will detail these types for those interested. This list is not exhaustive, as there are manufacturer-specific types not shown here, but know that specialized and custom drag conveyors exist.  

Drag chain conveyors
The standard drag conveyor, or simply drag chain conveyors uses two endless chains with evenly spaced paddles between them, which drag along the bottom of a trough to transport material. The amount of bulk moved by each paddle is dictated by its surface area, as well as the chain speed, and they are replaceable once they wear down. The chain speed is typically slow which decreases energy consumption, and the whole assembly is easy to use, simple, and cost-effective. Certain models can run at up to 50 ft/min with a capacity of 10 cubic feet per minute at a length up to 400 feet per drive. They are ideal for non-sanitary, non-abrasive products such as grain, pebbles, and more, and are often used as feeders for other machines. Their major disadvantages are their propensity to wear down, as materials interact directly with the chain and can cause issues. Also, the chains will unevenly stretch over time, requiring consistent maintenance to ensure proper alignment.

En-masse drag conveyors
Unlike standard models, en-masse conveyors utilize a single-stranded chain with paddles attached to both sides, sometimes referred to as “skeletal chains” for their resemblance to vertebrae. The chain runs in an over-under arrangement, where typically the bottom strand is the carrying element and material is fed through the top strand; however, there are split en-masse conveyors that house both strands in their own troughs, effectively creating two conveyors moving in opposing directions. The single-strand allows for a compact utilization of space and can use up to 90% of available space in the conveyor, instead of the usual 20-45% from other conveyor types. This effective use of space combined with one less chain creates an even more efficient conveyor than the previous kind, using less horsepower and energy to operate. The conveyed material is also completely enclosed, allowing en-masse conveyors to move hazardous, sanitary, hi-temperature, or otherwise hostile materials. This material will also not adversely affect conveyor performance, as the single-chain is less effected by material wear. They are a versatile option for designers for horizontal and low-incline applications, and their only downside is their limited flight width and price