Efficient and effective bulk material handling is a critical component of any production line and often means the difference between a smooth operation with minimal downtime and constant upsets.
Those looking for a conveyor system are often faced with a choice: belt conveyor or screw conveyor. And while screw conveyors offer a cost-effective option for many settings, they are not a fit for all applications. In selecting the best fit for the job at hand, it’s important to understand the key differences between these two types of handling equipment, and where belt conveyors provide a better handling option.
How Belt Conveyors Work
The belt conveyor is a time-tested material handling device; it has become the standard for moving bulk solids in and around mines, processing facilities, and ports. Its flexible design and many available configurations make the belt conveyor adaptable to an endless number of settings, part of the reason why its use has become so widespread.
A belt conveyor consists of a belt resting on angled idlers mounted between a head pulley and tail pulley. A drive arrangement provides energy to rotate the pulleys, which moves the belt. Material is carried on the surface of the belt as it travels between the pulleys. The material is discharged at the end of the conveyor, or at any point along the length of the conveyor if a belt tripper or plow is employed.
Belt conveyors can convey material at angles up to 18°, or 30° with cleated belting; beyond this, a steep incline or pocket conveyor, which allows material to be conveyed anywhere from 30°-90°, provides vertical handling.
Key Benefits of Belt Conveyors Over Screw Conveyors
Belt conveyors are the material-moving standard for good reason, bringing several benefits to bulk material handling systems. In comparing belt conveyors and screw conveyors, the best fit is not always immediately clear, leading many buyers to opt for the less costly screw conveyor. However, they often discover later that a belt conveyor is much more suited to the job.
There are several situations in which the belt conveyor provides a better handling option:
When Material Degradation is a Concern
Belt conveyors promote gentle handling with very little material degradation; once loaded onto the belt, material is contained in the trough, with minimal agitation between loading and discharge. This keeps friable or fragile materials intact and ensures material or product arrives at its next stop in the precise condition intended.
In contrast, since screw conveyors utilize a helical screw inside a trough or tube to advance material forward through contact with the blades, screw conveyors cause some friction and therefore degradation. As such, they are not a fit for materials requiring gentle handling or where friability is concerned, such as with granular fertilizers.
When Handling High Throughput
Capable of handling material at up to 8,000 TPH, belt conveyors can handle much higher capacities than screw conveyors. Belt conveyors are available up to 72” wide and can operate at speeds up to 600 feet per minute (FPM), making them the preferred choice for any type of high-capacity setting.
When Handling Stringy Materials
Both belt conveyors and screw conveyors are capable of handling a wide range of materials. Screw conveyors, however, are generally not a fit for conveying materials that are long and/or stringy, as they are likely to become tangled and cause blockages as a result of the horizontal screw motion. Materials that typically do not do well in a screw conveyor include:
- Wood chips
- Forest product residuals
- Some crop residues, such as bagasse
When Looking to Minimize Energy Costs
Because of the torque necessary to advance materials by force, screw conveyors require more horsepower compared to belt conveyors, especially if they will be operated on any sort of incline.
When conveying at an incline, belt conveyors have an advantage, as they are more efficient at conveying on an incline than screw conveyors. This is because some material in the screw conveyor tends to fall backward over the blades.
Vertical screw conveyors are an option, but efficiency is reduced as the incline increases. Therefore steep incline belt conveyors are more efficient in scenarios working with a steep angle of incline. Steep incline conveyors can also offer the benefit of being able to combine horizontal and vertical conveying into a single unit.
When Conveying Long Distances
Perhaps the biggest advantage of the belt conveyor is that it can convey material for both short and long distances. FEECO conveyors can carry material for distances anywhere from 10’ to 1500’ with a single conveyor. Screw conveyors are limited to much shorter distances – typically around 30m maximum.
When Working With an Abrasive Material
Belt conveyors are also a better option for handling abrasive materials. The friction that occurs in a screw conveyor accelerates abrasive wear on the unit, unlike with the belt conveyor where material is not moving over the carrying surface. And while screw conveyors can be fitted with abrasion-resistant liners, belt conveyors still require less protection from abrasive materials, only requiring added protection at discharge hoppers and skirtboards.
When Cleaning and Accessibility are Important
Belt conveyors are generally easier to clean than screw conveyors. Their open design allows for maximum accessibility and the use of belt cleaners are often enough to manage cleaning requirements.
In contrast, screw conveyors do not allow for self cleaning and since they are contained, must be shut down and dismantled in order to fully clean out the trough and shaft. This can be especially problematic when working with wet and/or sticky materials that tend to cake and build up, requiring more frequent cleaning.
When Material Cannot Be Packed
Screw conveyors can cause material to pack together as it moves through the unit. This can cause buildup, blockages, and may even result in packed material eventually dislodging and discharging with the material.
Such problems often translate to increased upset conditions and downtime for cleaning and maintenance, additional screening or conditioning of the material, and product sizing irregularities. As such, screw conveyors are typically unfit for materials prone to packing, such as clays and composts.
While belt conveyors and screw conveyors are often compared, their differing capabilities do not make them a comparable fit for all settings. Belt conveyors provide a more suitable bulk material handling option for a variety of settings, such as when material degradation is a concern, when working with high capacities, when handling stringy materials, and more.
FEECO is a leading provider of custom bulk material handling systems and equipment, relied upon throughout industries ranging from fertilizers and chemicals, to minerals and aggregates for efficient and reliable equipment. For more information on our custom belt conveyors or other bulk handling equipment, contact us today!