Factory Conveying Equipment: How to Choose - Pneumatic, Screw, and Belt Conveying
Introduction
Once a granulator discharges, how to move the output particles to the next machine or storage bin is a question many factories overlook when planning equipment. A common scenario: the granulator is purchased and installed, then it is discovered there is no plan for discharge conveying — and the only option becomes manually moving collection bins, which is slow and labor-intensive.
The three most common conveying methods in factories are pneumatic conveying, screw conveying, and belt conveying. Their operating principles, suitable materials, installation requirements, and cost structures are completely different. Choose correctly and the production flow is smooth with minimal labor; choose wrong and the equipment either underperforms or cannot be used at all.
Pneumatic Conveying
Operating principle
Pneumatic conveying uses airflow to move material from one location to another, in either negative-pressure (vacuum) or positive-pressure configurations.
Negative-pressure conveying: a vacuum unit creates suction inside the duct, drawing material from the feed point to the discharge point, where a cyclone separator then separates material from air. The advantage is that no dust escapes at the feed end, keeping the environment cleaner.
Positive-pressure conveying: a blower pushes material from the feed point through the duct to the discharge point, again using a cyclone separator for unloading. Positive-pressure systems can achieve longer conveying distances and suit applications requiring extended reach.
Suitable materials and applications
Pneumatic conveying is best suited to medium-density granular or powder materials with good flowability — plastic pellets, granulated plastic particles, powdered raw materials. Materials must not be strongly adhesive, or they will accumulate and block ducts.
Particularly unsuitable situations: film waste and foam particles are too low in density — airflow cannot carry them and they float and accumulate in the duct; high-moisture materials tend to clump on duct walls; materials with large amounts of dust require dust collection equipment and must not be discharged directly into the plant air.
Installation and space planning
Pneumatic conveying's greatest advantage is that ducts can curve around obstacles to reach any location, unconstrained by plant layout. Ducts are typically mounted along walls or ceilings, leaving the floor clear — an important benefit in space-limited facilities.
The number of elbows matters — every elbow adds duct resistance and reduces conveying efficiency. Too many elbows can leave the entire system with insufficient airflow. Design ducts to run as straight as possible, keeping elbow count reasonable. Plan cyclone separator installation locations in advance — adequate space is needed for material discharge and bin changeover.
Cost structure
Initial equipment cost covers the blower, ductwork, and cyclone separator — widely variable depending on conveying distance and duct specifications. Long-distance and multi-discharge-point systems cost substantially more.
Operating cost is mainly electricity — the blower running continuously uses more power than the other two conveying methods. Regular duct cleaning and inspection are necessary; buildup left uncleaned reduces conveying efficiency over time.
Screw Conveying
Operating principle
Screw conveying (also called auger conveying) uses continuous helical flights welded to a center shaft that rotates inside a sealed tube or trough, pushing material forward. Material moves along the tube driven by the rotating flights — no airflow required.
Screw conveyors can transport horizontally, at an incline, or vertically, offering good adaptability. The enclosed tube design keeps material from contacting outside air, making it suitable where dust dispersal must be prevented or material must be protected from moisture pickup.
Suitable materials and applications
Screw conveying handles a wide range of materials — powder, granules, and particles — including materials with poor flowability. As long as material is not highly viscous and does not contain large hard foreign objects, a screw conveyor can typically handle it.
Particularly well suited to: dusty environments where dust containment is needed; material with a significant powder fraction; short conveying distances (best performance under 10 meters); and applications requiring controlled conveying speed and volume — screw speed is adjustable, making throughput easy to regulate.
Not suited to: long-distance conveying (efficiency drops); materials with significant fiber content tend to wrap around the screw flights and jam; brittle granules may break from friction during screw conveying, affecting output quality.
Installation and space planning
Screw conveyor installation is simpler than pneumatic conveying — no complex duct configuration needed. The conveyor is assembled in straight sections at the required angle and length. Horizontal conveyors occupy linear floor or elevated space; vertical screw elevators occupy vertical space. Confirm that the installation path is obstacle-free and that feed and discharge ends align with upstream and downstream equipment.
Cost structure
Screw conveyors are typically the lowest-cost of the three methods — relatively simple structure with highly standardized components. Motor power is usually lower than a blower, so electricity costs are comparatively modest. Key maintenance items are screw flight wear and bearing lubrication — regular inspection prevents unexpected failures.
Belt Conveying
Operating principle
Belt conveying uses two end rollers to drive a continuous looped belt; material placed on the belt surface is transported to its destination as the belt moves. Belt materials include rubber, PVC, PU, and stainless steel mesh — selected based on the material being conveyed and the operating environment.
Belt conveying is the most intuitive and easiest to maintain of the three methods. Operators can see the material's conveying status at a glance and respond to problems immediately.
Suitable materials and applications
Belt conveying handles the widest range of materials — from large scrap chunks and whole parts to granules and particles. It is particularly well suited to applications where manual sorting, visual inspection, or other operations need to take place during conveying, since material is exposed on the belt surface and operators can intervene at any time.
Particularly well suited to: transfer between primary shredder and granulator in scrap tire recycling plants; sorting operations in plastic recycling plants; post-dismantling scrap transfer in e-waste recycling; and applications where a magnetic separator needs to be installed above the conveyor to remove metal contamination.
Not suited to: powder materials (severe dust dispersal — requires dust covers or enclosed design); incline angles exceeding 20–25° (material slides off — requires anti-slip belt design); space-constrained facilities (belt conveyors occupy the most floor space of the three methods).
Cost structure
Belt conveyor cost varies widely with length and specifications. Short simple conveyors are low cost; long or specially specified conveyors are relatively expensive. Main operating costs are electricity and belt wear replacement. Belt is a consumable — replacement cycle ranges from months to years depending on usage frequency and material abrasiveness. Daily maintenance focuses on belt tension and roller condition.
Quick Comparison
| Pneumatic conveying | Screw conveying | Belt conveying | |
|---|---|---|---|
| Suitable materials | Granules, powder | Powder, granules, particles | All forms |
| Conveying distance | Long (tens of meters) | Short to medium (best under 10 m) | Medium (depends on space) |
| Dust control | Enclosed — good | Enclosed — best | Open — needs dust guard |
| Floor space used | Small (overhead ducting) | Medium | Large (floor-level) |
| Equipment cost | Medium to high | Low to medium | Low to medium |
| Running electricity | Higher | Low | Low to medium |
| Maintenance | Medium (duct cleaning) | Low | Low |
| Mid-process access | Not possible | Not possible | Possible |
Special Considerations When Connecting to a Granulator
Several points deserve special attention when connecting a granulator's discharge to a conveying system:
Output bulk density
Film waste output after granulation has extremely low density — pneumatic conveying may not have sufficient airflow to carry it. Confirm that blower airflow is adequate. Screw conveying handles low-density particles unpredictably — evaluate whether it is appropriate. For film-specific guidance see: How to Granulate Plastic Film and Flexible Materials.
Output temperature
After extended continuous granulation, output temperature may be elevated. High-temperature particles entering an enclosed screw conveyor duct require confirmation that duct materials can withstand the temperature. Pneumatic conveying ducts must also be checked to ensure high-temperature particles will not cause deformation.
Buffer design
Granulator output is intermittent, not steady — material exits when blades are cutting, not during feed gaps. Installing a buffer hopper between the granulator and conveying system lets the conveying equipment run under stable feed conditions, rather than being directly coupled to the granulator's output rhythm — much easier to control conveying efficiency.
Conclusion
No conveying method is inherently right or wrong — the choice depends on your waste type, facility conditions, conveying distance, and dust control requirements. Many factories use a combination of methods for different conveying needs: pneumatic conveying from the granulator discharge to a storage bin, then vacuum loaders from the storage bin to molding machines.
Before planning conveying equipment, map out the entire production flow, confirm each stage's feed and discharge positions and material condition, then decide which method best suits each conveying segment.
Related articles: Facility Planning for Granulating Equipment: Space, Power, and Ventilation; How to Match a Granulator with a Pelletizer; What Is a Vacuum Loader? Automatic Material Loading for Plastics Factories.