1200mm hammer grab used togather with casing oscillator in bored pile foundation work for hard soil conditions

1200mm hammer grab used togather with casing oscillator in bored pile foundation work for hard soil conditions 1200mm bored pile hammer grab used with casing rotator for secant pile foundation work for very hard soil layers bored pile hammer grab od1200mm usd inside of 1300/1220mm double wall casing for bored pile foundation work 1200mm down hole pile grab bucket for hard soil conditions pile foundation work 1200mm single rope hammer grab used for hard soil conditions for bored pile foundation work Double rope hammer grab od1200mm used for hard soil conditions for bored pile foundation work hammer grab is a heavy-duty excavation and cleaning tool used primarily in deep foundation construction, such as bored piling and diaphragm wall projects. Unlike standard augers, hammer grabs are designed to handle large debris, boulders, and very hard soil layers by using high-impact force and gravity. NO. Size D L （kg） Pulley number 1100 1100 5050 5100 5 1400 1400 5600 6900 5 1. Types of Hammer Grabs Mechanical Hammer Grabs: These are operated via a cable winch system. The "hammer" effect comes from dropping the heavy unit into the borehole; a mechanical latch or "kicker" system then triggers the jaws to close when the cable is pulled back up. Hydraulic Hammer Grabs: Controlled by the drilling rig’s hydraulic system, these offer more precise jaw movement and higher closing pressures, which is ideal for dense materials. Spherical Hammer Grabs: Specifically shaped with rounded jaws to fit the internal diameter of circular casings. These are the most common choice for cleaning the bottom of a bored pile to ensure a clean base for concrete. 2. Primary Applications Hard Strata Excavation: Breaking and removing layers of dense gravel, cobbles, and weathered rock. Borehole Cleaning: Removing "sludge" or loose material that augers or buckets cannot efficiently lift. Obstruction Removal: Extracting boulders, timber, or old masonry encountered during drilling. Cased Holes: Operating inside steel casings where precision is required to avoid damaging the casing walls. 3. Key Components Body/Weight: The heavy steel frame that provides the kinetic energy for penetration. Jaws: Curved or pointed plates that scoop the material. Some feature replaceable carbide teeth for rock work. Pulley/Swivel Block: Located at the top to allow the grab to rotate and prevent cable twisting. Closing Mechanism: The internal linkage that transfers the upward pull of the crane into the closing force of the jaws. 4. Selection Criteria Feature Consideration Weight Heavier grabs penetrate better but require higher crane lifting capacity. Diameter Must be slightly smaller than the internal casing diameter (e.g., a 1180mm grab for a 1200mm casing). Tooth Configuration Pointed teeth are best for breaking rock; flat-edged jaws are better for cleaning loose sand/gravel. Winch Compatibility Ensure the cable diameter and winch power match the grab’s weight and expected load. Operating a hammer grab effectively requires a mix of precise crane control and an understanding of the specific mechanical or hydraulic system you are using. The operation varies depending on whether the grab is a single-rope, double-rope, or hydraulic system. 1. Single-Rope Mechanical Operation This is the most common setup for standard bored piling and is favored for its simplicity. Preparation: Ensure the grab is in the "open" position. This is usually set by a mechanical latch or "kicker" at the top of the grab body. The Descent (Free Fall): Position the grab over the borehole. Release the winch brake to allow the tool to free-fall into the casing. The weight of the grab provides the impact energy needed to penetrate the soil or break through debris. The Trigger: When the grab hits the bottom, the mechanical latch is triggered by the impact or the sudden slack in the cable. Closing & Extraction: Once triggered, engage the winch. As the cable pulls upward, the internal linkage forces the jaws to close, biting into the material. Discharge: Lift the grab out of the hole, swing it to the discharge area, and lower it onto a "chandelier" or discharge stand that mechanically resets the latch to the open position for the next cycle. 2. Double-Rope Mechanical Operation This system offers more control and is better for "chiseling" through harder strata. Independent Control: One rope (the holding rope) supports the weight, while the second (the closing rope) operates the jaws. Chiseling Action: By lifting the grab slightly with the opening rope and dropping it repeatedly, you can use the jaws like a chisel to break up hard rock or cobbles without actually closing the grab each time.Grip: Once the material is sufficiently loosened, the operator pulls the closing rope to engage the jaws and capture the load before lifting the entire unit out. Controlled Descent: You can lower the grab slowly and use the rig's downward "crowd" force to push the jaws into the soil before closing them. 4. Operational Best Practices To ensure efficiency and tool longevity, follow these technical guidelines: Aspect Key Rule Verticality Maintain a verticality tolerance within 2°. If the grab is tilted, it can jam against the casing walls or cause a deviated borehole. Water Resistance In wet holes, the "surge" of water can slow the fall. Use a grab with a streamlined body or "venting" holes to maintain impact velocity. Borehole Cleaning When cleaning the base for concrete, use a Spherical Hammer Grab. Its rounded profile matches the casing diameter and leaves a flatter, cleaner bottom. Teeth Maintenance Regularly inspect the or carbide teeth. Dull teeth significantly reduce the impact efficiency and increase the number of "drops" required per cycle. 5. Safety Checks Cable Tension: Never let the cable become excessively slack on the drum; this can cause "bird-nesting," which leads to cable snaps during high-impact drops Latch Lubrication: On mechanical grabs, the latching mechanism is the most common point of failure. Ensure it is greased daily to prevent "misfires" where the grab fails to open or close at depth.