Key takeaways
The screw conveyor is the oldest continuous conveying device still in industrial use, and it survives because it does something a belt cannot. It moves material fully enclosed, it accepts and discharges material at any point along its length, and it occupies almost no space beyond the pipe it sits in.
For powders and granular solids in a food, pharmaceutical or chemical plant, those three properties usually matter more than the efficiency advantage a belt would offer. Dust stays inside the conveyor, multiple silos can feed one line, and the conveyor fits under equipment where nothing else would.
Working Principle
A helical flight rotates inside a stationary U-shaped trough or a closed tube. Material entering at the inlet is caught between successive turns of the flight and pushed along by the advancing helix.
The subtlety is why the material does not simply rotate with the screw. It stays roughly in place rotationally because friction against the trough wall holds it back, while the flight face pushes it forward. Material advances as a series of slugs sliding along the trough rather than as a smooth stream. That mechanism explains most screw conveyor behaviour: friction against the trough is doing useful work, which is why screw conveyors consume more power than belts, why the trough wears, and why materials that do not develop friction against the wall convey poorly.
It also explains why horizontal duty is the easy case. On a level run, gravity holds material against the trough and the flight only has to overcome friction. Tilt the conveyor and gravity begins pulling material back down the flight, so capacity falls steeply. A screw that carries a given rate horizontally will move substantially less at 30 degrees and less again at 45, which is why inclined screws are specified with reduced pitch and higher speed rather than simply angled upward.
Components
Design Parameters
Capacity is a volumetric calculation. The screw moves a defined volume per revolution, and throughput follows from that volume, the rotational speed, how full the trough runs and the bulk density of the material.
| Design parameter | What it controls | Practical consequence |
|---|---|---|
| Screw diameter | Volume moved per revolution | The main capacity lever; larger diameter beats higher speed for abrasive material |
| Pitch | Distance material advances per revolution | Reduced pitch gives finer control at lower throughput |
| Rotational speed | Throughput at a given diameter | High speed degrades friable product and accelerates trough wear |
| Trough loading | How full the cross-section runs, typically 15 to 45 per cent | Abrasive and heavy materials run at lower loading to limit wear and torque |
| Bulk density | Mass throughput and drive sizing | Sizing on the wrong density under-powers the drive or oversizes the motor |
| Length | Torque, deflection and number of hanger bearings | Longer screws need intermediate support, and each hanger is a wear point |
| Materials of construction | Wear life, corrosion resistance and hygiene | Carbon steel for general duty, SS304 or SS316 for food and pharma |
Trough loading deserves particular attention because it is the parameter most often assumed rather than specified. Light, free-flowing, non-abrasive powders can run at high loading. Abrasive, heavy or sluggish materials are run much lower, which means the same physical conveyor has very different capacities depending on what is inside it. A capacity figure quoted without the material and the loading percentage is not a specification.
Flight Types
The flight is not always a plain continuous helix. Its form is selected against material behaviour and against whether the conveyor is also expected to feed, mix or break up product.
| Flight type | Form | Used for |
|---|---|---|
| Full pitch | Pitch equal to screw diameter, the standard configuration | General horizontal conveying of free-flowing material |
| Short pitch | Pitch reduced to around two thirds of diameter | Inclined runs and feeder duty, where control matters more than throughput |
| Variable pitch | Pitch increasing along the screw length | Drawing material evenly from under a long inlet or hopper slot |
| Cut flight | Flight notched at intervals | Conveying while mixing or breaking up light lumps |
| Ribbon flight | Helical ribbon supported off the shaft, open centre | Sticky, gummy or viscous materials that would pack around a solid flight |
| Paddle | Adjustable paddles instead of a continuous flight | Aggressive mixing with slow controlled movement along the trough |
One further variant is worth knowing. A shaftless screw removes the central shaft entirely, eliminating hanger bearings and the space around the shaft where sticky material packs. It suits wet, stringy and cohesive products at the cost of higher wear against the trough liner.
Industrial Applications
“The right screw conveyor is not selected from a capacity chart alone; it is sized around bulk density, abrasiveness, flow behaviour, trough loading, hygiene requirements, and the duty it must perform.“
See it in action
Screw or Belt for Horizontal Duty
Both move material horizontally, and the choice is usually clear once three questions are answered.
A screw wins where dust must be contained, where multiple inlets or outlets are needed along the run, where floor space is tight, or where the conveyor should also meter or mix. A belt conveyor wins on long distances, on high tonnages, on power consumption, and with fragile or abrasive materials that a screw would degrade or that would degrade the screw.
The material decides more than the distance does. Highly abrasive products wear flights and troughs continuously; friable products break up between flight and wall; very sticky products pack around the shaft. Where any of those apply, the screw is the wrong technology however convenient the layout makes it look.
Screw Conveyors from Cybernetik
Cybernetik builds screw conveyors for powder handling across food, pharmaceutical, chemical and agro-processing industries, in horizontal and vertical configurations with multiple inlets and outlets, at lengths up to 40 metres and conveying rates up to 10 tonnes per hour. Conveying rate is set by pitch and rotational speed, and construction materials are selected against the application.
Screw conveyors appear throughout Cybernetik’s integrated systems rather than only as standalone units. In the sugar grinding system, screw conveyors handle feeding to the grinder and transfer from storage to bagging, within an ATEX built, dust-free line with magnetic grates and sifting for foreign particle removal.
Cybernetik has operated for more than three decades, is headquartered in Pune with additional facilities in Gujarat and Raigad and international offices in the United States and UAE, and has installed over 6,000 systems across 30 plus countries, including more than 400 custom automation solutions. With over 600 employees and divisions spanning Process Automation, Packaging Automation, CleanTech, Extraction, Labs and Defence, a conveyor is engineered with knowledge of the whole line.