Throughout the grab bucket process, a smoother increase in the tension of the closing rope indicates that the designed grab bucket can effectively fill the bulk cargo, resulting in more economical energy consumption for the crane.
Once the grab bucket's geometric parameters, weight distribution, and the ratio of the closing pulley block are determined, the grabbing torque and the grabbing resistance torque at each closing position when the grab bucket grabs a specific bulk cargo can be calculated. By using the jaw plate digging depth as a measure and establishing the balance relationship between the grabbing torque and grabbing resistance torque at each closing position, the digging trajectory and cargo grabbing capacity during the grab bucket's closing process can be obtained.
As shown in the figure, the change curves of tension in the closing rope and support rope during the grab bucket's loading and unloading process.
Large grab cranes are equipped with load-balancing devices for the grab closing rope and support rope.
When the bucket grab is in a relaxed state with the support rope slack, the closing stroke reaches approximately 70%. The support rope begins to tighten upward, and the grab floats upward.
When the grab bucket is close to being fully closed, the closing rope begins to decelerate until the grab is fully closed, at which point the load of the closing rope and support rope is balanced.
