The code detailed in IS 2974 Part 2 (1980) outlines guidelines for designing and building foundations tailored for impact machines, particularly hammer foundations. It focuses on managing dynamic impacts and vibrations by specifying criteria for foundation mass, size, material properties, and vibration analysis to guarantee stability and safe operation. This code is vital for engineers and specialists working with heavy forging and hammer equipment installations.
Overview
The code detailed in IS 2974 Part 2 (1980) outlines guidelines for designing and building foundations tailored for impact machines, particularly hammer foundations. It focuses on managing dynamic impacts and vibrations by specifying criteria for foundation mass, size, material properties, and vibration analysis to guarantee stability and safe operation. This code is vital for engineers and specialists working with heavy forging and hammer equipment installations.
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Frequently Asked
As per IS 2974 Part 2, Clause 4.4.3, the foundation block's mass (Wb) must be at least three times the anvil's mass (Wa) under general conditions. For foundations resting on stiff clays or compact sandy soils, this ratio increases to between four and five times the anvil mass. In the case of moderately soft clays or loose sandy soils, the block mass should range from five to six times the anvil's mass. These requirements ensure adequate stability against dynamic forces and vibrations from the hammer operation. Additionally, Clause 4.4.2 specifies minimum foundation block thicknesses depending on the tup mass to enhance safety.
The two-mass system approach models the hammer-foundation interaction by representing it as two masses: m1 (the anvil plus attached frame mass) and m2 (the foundation block plus any attached frame mass). Elastic springs k1 and k2 represent the cushioning pad between the anvil and foundation block and the stiffness of the foundation soil, respectively. The system's natural frequencies are found by solving the characteristic equation derived from these parameters. Velocity input from the hammer impact is calculated based on momentum. This model helps estimate vibration amplitudes and frequencies to prevent resonance and ensure the foundation's dynamic behavior stays within safe limits, especially for high-speed hammers.
IS 2974 Part 2 mandates the use of reinforced concrete for hammer foundations, with a minimum concrete grade of M15 in accordance with IS 456:1978. The foundation must be capable of withstanding dynamic loads and vibrations, requiring concrete that provides sufficient strength and durability. Reinforcement detailing should follow IS 456 guidelines to resist tensile stresses generated by hammer impacts, ensuring the foundation's structural integrity under operating conditions.
The elastic cushioning layer between the anvil and foundation block is designed to absorb impacts, prevent bouncing, reduce stress concentrations, and protect the concrete surface. The design involves selecting an appropriate elastic material (such as rubber or neoprene) with a specified elastic modulus (E) and thickness to limit maximum deformation (δ_max) within allowable stress intensity (σ_allow). Calculations ensure the deformation under impact load does not exceed δ_max and the stress remains below σ_allow. Detailed specifications including material type, thickness, modulus, allowable deformation, and stress limits should be documented in design drawings to ensure durability and effectiveness.
According to IS 2974 Part 2, permissible vibration amplitudes vary with the tup mass. For tup masses up to 1 tonne, the maximum vibration amplitude permitted is 1 mm for both foundation block and anvil. For tup masses between 1 to 3 tonnes, amplitudes of 1.5 mm (foundation) and 2 mm (anvil) are allowed. For tup masses exceeding 3 tonnes, the foundation block amplitude can be up to 2 mm, while anvil amplitudes may range from 3 to 4 mm. Additionally, vibration velocities at nearby critical structures should not exceed 0.3 cm/s to prevent damage. The foundation’s natural frequency must avoid integer multiples of the hammer’s impact frequency to prevent resonance, ideally being at least 2.5 times or less than 0.7 times the impact frequency.
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