Answer :
Final answer:
True, rotary hammers are recommended for drilling larger diameters in hardened concrete because they provide a more powerful blow than hammer drills, making them more efficient for this specific task.
Explanation:
Rotary hammers are indeed recommended for drilling larger diameters in hardened concrete or other hardened materials. This is because rotary hammers, which use a piston mechanism rather than a special clutch, can deliver a more powerful hammer blow. This makes them particularly suited for drilling into hard materials where a simple hammer drill may not be efficient. When working with hardened concrete, a rotary hammer is advantageous for creating larger holes due to its ability to pulverize the material with greater force than traditional hammer drills.
As for the rock drilling methods, the hydraulic rotary method mentioned involves using a drill pipe with a drag or roller bit and circulating water containing clay, which helps in cooling the bit and removing rock cuttings. In contrast, the air rotary method, which is suitable for drilling in consolidated rocks, uses air as the drilling fluid.
