Operating Principles and Precautions for Screw Type Ship Unloaders

I. Operating Principles

The screw type ship unloader is a type of continuous, enclosed bulk material unloading equipment. It achieves continuous unloading through a combination of a vertical screw, a horizontal screw, and a counter-rotating intake head at the bottom. It is suitable for powdery and small-particle loose materials—such as cement, fly ash, grain, mineral powder, and fertilizers—but is not suitable for large lumps or highly cohesive, caked materials.

1. Material Intake: Using luffing, slewing, and traveling mechanisms, the counter-rotating intake head at the bottom of the vertical arm is extended into the material pile within the ship's hold. The counter-rotating screw loosens and breaks up caked material while continuously forcing it into the vertical screw casing, preventing the material from slipping or spinning idly with the screw.

2. Vertical Lifting: The screw flight inside the vertical casing rotates at high speed. Relying on friction between the material, the casing wall, and the screw flight, the material gains an upward movement component and rises continuously along the casing to the level of the horizontal arm.

3. Horizontal Transfer: The material enters the horizontal screw conveyor and is transported along the horizontal arm to the discharge chute located at the slewing center.

4. Discharge and Transfer: The material falls through the central chute onto the downstream conveying system (belt or screw conveyor) on the wharf for transfer to silos or storage yards; the entire process is enclosed, resulting in minimal dust generation.

System Components: Portal traveling mechanism, slewing mechanism, hydraulic luffing system, PLC control system, dust removal system, and various limit protection devices.

II. Operational Precautions

(A) Pre-operation Checks

1. Verify that all limit switches (for travel, slewing, luffing, and vertical oscillation) and the emergency stop button are functional and effective; ensure all safety guards and railings are intact and free from damage or missing parts.

2. Check hydraulic oil and gearbox lubricant levels to ensure they are normal and free of leaks; ensure all bearings are properly lubricated; inspect the screw blades for wear, deformation, or cracks.

3. Check the electrical system, cables, dust-sealing components, and flexible connections for integrity; clear debris from the feed grate to prevent large, hard objects from entering the screw and causing a jam.

4. Confirm the vessel is securely moored and stable, and that all unauthorized personnel have cleared the work area; verify that the downstream conveying system has been started—adhering to the interlocking sequence of "start downstream first, then the machine; stop the machine first, then downstream"—to prevent material blockages or spillage.

5. Assess material condition: Exercise caution with high-moisture or severely caked materials, as they are prone to causing blockages; strictly prohibit the inclusion of large debris such as rebar, stones, or wooden planks.

(B) Operational Guidelines

1. Prevent the material intake head from directly striking the hold bottom; maintain a safe clearance distance. Ensure the intake head is submerged in the material pile at an appropriate depth; excessive depth causes torque overload, while insufficient depth leads to air intake and reduced efficiency.

2. Perform slewing, luffing, and travel movements slowly and smoothly; avoid abrupt starts, stops, or sharp turns. Suspend operations during strong winds (generally Beaufort scale 6 or higher), thunderstorms, or heavy fog/low visibility, and retract and anchor the boom.

3. Monitor motor current, torque, and temperature. If an overload alarm triggers, stop feeding immediately and do not attempt a forced restart. In the event of a blockage, shut down, cut power, and apply a lockout/tagout; brief reverse rotation may be attempted to clear the jam, but reaching into the machine with hands or tools while it is running is strictly prohibited.

4. Ensure the machine's dust removal system operates synchronously; monitor all flexible connection joints and shut down to replace them immediately if damage or dust leakage occurs.

5. As the material in the hold nears the final cleanup stage, reduce the digging depth to prevent idling and blade wear; for residual material in the corners, use auxiliary methods to rake it toward the digging area rather than attempting forced, deep excavation.

(C) Shutdown and Maintenance

1. Normal Shutdown: Stop material intake first, allow the machine to idle for a period to clear residual material from the barrel, and then shut down the system in the proper sequence; shutting down with material inside the machine can easily lead to clogging and jamming due to material hardening.

2. End-of-Shift Cleanup: Clear residual powder from the screw and discharge chute after every shift; moist material must be thoroughly removed to prevent solidification and clumping.

3. Routine Inspections: Regularly inspect screw flights and liner plates for wear; periodically tighten bolts and check the slewing bearing and travel rails.

4. Periodic Checks: Regularly verify the functionality of all safety interlocks and limit switches; do not mix different brands of lubricants, and change oil according to the maintenance schedule.

(D) Safety Prohibitions

1. Maintenance, entering the screw barrel, or stepping over moving parts while the equipment is operating is strictly prohibited; maintenance requires a "Lockout/Tagout" procedure (disconnecting power and securing the switch).

2. Overloading is strictly prohibited; do not operate at full rated load for extended periods.

3. Personnel must not stand beneath the boom, under the material discharge outlet, or within the travel rail area of ​​the main machine.

4. Perform an immediate emergency shutdown if the equipment exhibits abnormal noise, severe vibration, smoke, or oil leakage.