Based on the working principle of the four-rope grab bucket's pulley system, the actual force driving the jaw plates to close is approximately four times the tension generated by the winch on a single opening and closing rope. This allows the grab bucket to exert a significant grabbing force with limited winch power, thereby effectively cutting into and grabbing dense materials.
Kinematic Relationship: The significant increase in force is achieved at the cost of speed. Correspondingly, the closing linear velocity of the jaw plates is approximately one-quarter of the winding speed of the opening and closing rope by the winch. This "speed-for-force" design perfectly meets the core requirements of grabbing operations for high torque and low speed.
The primary purpose of setting this minimum ratio is to minimize the bending fatigue stress generated when the wire rope wraps around the pulley of the clamshell grab bucket.
Mechanism Explanation: When a wire rope wraps around a pulley, it bends, generating alternating stress in the individual wires. The smaller the D/d ratio, the greater the bending curvature, and the higher the stress amplitude in the cables, thus drastically accelerating the process of metal fatigue and breakage. Maintaining a sufficient D/d ratio ensures that the wire rope operates within the allowable bending stress range, which is one of the most critical design factors determining the service life of the wire rope (especially the number of bends).
