"抓岩机的抓斗" can be translated as "clamshell bucket of the rock-grabbing machine" or more concisely as "rock-grabbing clamshell bucket" in English.
Here, "clamshell bucket" refers to the type of bucket that opens and closes like a clamshell, which is commonly used in rock-grabbing or excavating machinery. Adding "of the rock-grabbing machine" or "rock-grabbing" clarifies the specific application or type of the clamshell bucket.