Anvil is used as a certified reference Material to verify the Rebound Hammer calibration, Generally Rebound Hammer should give 80+/-2 on standard Anvil, having Rockwell Hardness HRC 66+/-2 as per IS 516 if the rebound hammer is functionally in good and calibrated condition.
Its primary purpose is to provide a standardized and consistent reference for checking and calibration of the accuracy of the rebound hammer (also known as Schmidt Hammer), which is widely used to assess the surface hardness and estimate the compressive strength of concrete structures. Over time, the mechanical components of the rebound hammer, such as the spring, plunger, and the impact mass can undergo wear and tear, leading to deviations in the rebound readings. The steel anvil allows it to identify such errors, so that they are corrected before the hammer is used on the actual concrete surface.
The calibration anvil is constructed from high-grade alloy, hardened, and tempered to achieve surface uniformity and mechanical strength, ensuring that energy losses due to vibration or movement are minimized. The impact surface of the anvil has a Rockwell hardness of approximately HRC 66 ± 2 as per IS 516, which provides a very dense surface similar to an idealized standard. This ensures that when the rebound hammer’s plunger strikes the anvil, the resulting rebound number depends solely on the impact energy and hammer’s internal mechanism and not on surface inconsistency.
During the calibration process, the rebound hammer is held perpendicular to the anvil’s surface, and multiple test impacts, usually between 6 - 8 strokes performed. The average rebound number is compared to the standard reference values, which should be generally 80 ± 2, and if the reading falls within this range, the hammer is considered properly calibrated. However, if significant deviation is observed, it indicates that the hammer may need Repair, or mechanical servicing is required to restore its accuracy. Hence using a properly calibrated rebound hammer on Anvil guarantees that subsequent concrete test Rebound Hammer is accurate.
Purpose of Anvil:
- To ensure that the rebound hammer gives a consistent and accurate rebound number.
- Useful for verifying the rebound hammer performance.
- Calibration on the anvil helps to identify wear and tear, spring weakness, or other faults in the hammer.
- Using Anvil ensures the hammer meets requirements of different standards like IS 516, ASTM C805.
Principle of Anvil:
The calibration of a rebound hammer fundamentally depends on the interaction between the hammer’s plunger and a reference material with well characterized mechanical properties. The Anvil is employed as this reference due to its near-ideal elastic behaviour, uniform density, and negligible energy loss under impact. Unlike concrete, which is heterogeneous and can exhibit variable mechanical responses, steel anvil provides a highly consistent and predictable surface for the hammer to strike. Its high elastic modulus, along with high strength, ensure that the contact between the hammer’s plunger and the steel surface remains almost entirely elastic, with minimum permanent deformation. This consistency allows the rebound hammer to give reproducible rebound readings, which serves as a benchmark for instrument calibration.
The principle behind this process is rooted in its basic mechanics, where the rebound hammer’s plunger strikes the surface with defined velocity, and part of its kinetic energy is returned as it rebounds. The amount of energy returned, and hence the rebound distance or reading, depends on the hardness and elasticity of the surface. When the hammer strikes the plunger in contact with the anvil’s surface, it absorbs virtually no energy through plastic deformation, and rebounds with a velocity close to its theoretical maximum for a perfectly elastic collision. This makes the steel anvil ideal standard, providing a reference rebound value that is consistent and unaffected by the natural variability present in materials like concrete. Additionally, by providing a stable reference, it allows for the detection of systemic errors, verification of the internal plunger and spring mechanism, and identification of any calibration drift over time.
