"蜗轮减速器" can be translated into English as "worm gear reducer" or "worm reduction gearbox".
"Worm gear" refers specifically to the type of gear mechanism involved, where a worm (a screw-like gear) meshes with a worm wheel (a gear wheel with teeth that engage with the worm).
"Reducer" or "reduction gearbox" indicates the function of the device, which is to reduce the rotational speed and increase the torque output.
Both translations are commonly used in technical and engineering contexts.