High-Angle Sandwich Belt Conveyors

Conventional troughed belts are limited by the tendency of bulk material to slide or roll back as inclination increases. A sandwich arrangement applies a second belt over the material so the load is confined while it passes through a steep or vertical section.

How the operation works

Material is loaded before the belts close, carried through the high angle path and released where the belts separate. The system must apply enough normal force to retain the material without excessive compaction or belt stress. Both belts must move compatibly through loading, lift and discharge.

The loading transition determines whether material is centered and evenly distributed before confinement. Large lumps, sharp particles or an uneven bed can create local pressure and damage. The discharge transition must release the stream cleanly into the receiving equipment.

Engineering inputs

• Required lift, route and footprint.
• Lump size, shape and degradation sensitivity.
• Moisture, cohesion and tendency to roll back.
• Belt pressure and transition geometry.
• Drive sharing, braking and rollback control.
• Access to both belt paths and enclosed sections.

Capacity alone is not a sufficient design basis. The system must work across the expected material range, including changes in moisture, fine content, bulk density and particle shape. Startup, normal duty, turndown, interruption and clearing are separate operating cases.

Control of dust and displaced air

Reducing the number of transfers can reduce potential dust locations, but the loading and discharge points still entrain air and release fines. Enclosure and extraction should be designed for the actual stream and not inferred from the conveyor angle alone.

Research on transfer chutes shows that material trajectory and entrained air influence fugitive dust. EPA guidance also treats loading, unloading and storage as distinct emission activities. Effective control therefore begins by reducing uncontrolled drop and air displacement before collection air is added.

Reliability and failure modes

• Uneven loading before belt closure.
• Material rollback during an upset.
• Local belt damage from oversize lumps.
• Spillage at transition zones.
• Difficult inspection access on steep sections.

Inspection should focus on changing conditions rather than waiting for lost capacity. Deposits, wear patterns, damaged seals, changed vibration and rising dust indicate that material flow or containment has moved away from the intended state.

Safety and access

Stored energy, gravity and rollback require controlled braking and isolation. Access platforms, guards and rescue planning must reflect the steep route. Restart after a trip should consider material held between the belts and the torque required to move it.

Isolation for maintenance, guarding, safe access and emergency response must be designed into the arrangement. Where combustible dust can occur, ignition control and explosion risk require a separate documented assessment of the complete connected process.

Commissioning and acceptance

1. Confirm the actual material range and operating cases.
2. Measure capacity and observe flow at every transfer.
3. Check dust release, spillage and displaced air under representative duty.
4. Verify alarms, interlocks and safe shutdown.
5. Record baseline wear, vibration and inspection points.
6. Train operators in normal operation, clearing and change control.

Sources and further reading

• US EPA, Aggregate Handling and Storage Piles
• International Journal of Mineral Processing, dust emissions from conveyor transfer chutes
• OSHA, Conveyor safety requirements
• NIOSH research, Dust Suppression Hopper case studies
• Bulk Solids Handling, design principles for transfer chutes