Working Principle of a Screw Ship Unloader

In busy port operations, screw ship unloaders play a vital role, efficiently unloading cargo from ships through a unique working mechanism. Here is a detailed explanation of the screw ship unloader's operating principles.

Step1: Material Collection Process

The material collection device of the screw ship unloader is inserted into the cargo pile within the ship's hold. The collection device typically includes counter-rotating components, such as a reverse rotation screw or loosening blades. These structures push the material toward the inlet of the vertical arm screw conveyor while preventing material from being thrown out due to centrifugal force created as it enters the conveyor tube and accelerates circumferentially. For materials that become compacted or form hard shells during sea transport—such as fertilizers, cement, and potash—the reverse rotation structure of the collection device loosens the material, making it easier for subsequent conveying.

Step2: Vertical Conveying Process

After being collected by the screw ship unloader, the materials enter the vertical screw conveyor. Inside the vertical screw conveyor, the spiral blades rotate at high speed under the action of the drive device, and the materials move upward along the spiral tube driven by the spiral blades. During this process, complex friction and interaction forces are generated between the materials and the spiral blades. The spiral blades generate an upward axial force to offset the weight of the materials and the friction with the inner wall of the spiral tube, so that the materials are transported smoothly in the vertical direction. In order to ensure that the materials will not be thrown out of the spiral tube due to centrifugal force during the vertical transportation process, the design and speed of the spiral blades in the vertical screw conveyor have been accurately calculated and optimized.

Step3: Horizontal Conveying Process

The material output from the vertical screw conveyor then enters the horizontal screw conveyor. The horizontal screw conveyor operates similarly to the vertical one, but its screw blades rotate horizontally. Pushed by the screw blades, the material moves along the screw tube toward the discharge direction . In horizontal conveying, ensuring uniform, steady material flow is essential to prevent clogging within the screw tube. This requires careful design of parameters such as the screw pitch, rotation speed, and screw tube diameter. Additionally, the housing of the horizontal screw conveyor typically includes support and guiding structures to facilitate smooth material transport.

Step4: Final Discharge Process

The material conveyed by a horizontal screw conveyor eventually reaches a discharge point. The discharge method typically involves transferring the material to other handling equipment, such as a belt conveyor, which then delivers it to a storage area or silo or loads it directly onto a vehicle. At the discharge location, the design of the spiral blades or discharge port ensures that the material is smoothly released from the spiral tube and moves it to the next stage of the transport chain. The discharge process must ensure that the material flow rate and direction are consistent with the overall discharge workflow to support efficient material transfer.

In summary, the screw ship unloader achieves an efficient, continuous transfer of material from the ship's hold to designated dock areas through the coordinated operation of its screw conveyors and collection device.