Performance Requirements of Needle Vibrators
- The operational frequency of vibrator when operated in air (i.e. when not immersed in concrete) shall not be less than 100 Hz and should preferably be higher.
- For different sizes of needle, the optimum operational amplitude when operated in air, measured in the middle of the vibrating needle should satisfy the following requirements.
| Diameter of vibrating needle (mm) | Frequency of vibration (Hz) | Amplitude (mm) | |
| Eccentric shaft type vibration | Pendulum type vibrator | ||
| 25 – 35 | 200 – 270 | 0.85 – 0.55 | 0.65 – 0.40 |
| 40 – 60 | 150 – 200 | 1.10 – 0.75 | 0.85 – 0.55 |
| 75 – 90 | 100 – 150 | 1.60 – 1.30 | 1.20 – 0.95 |
- The area of range of action of the vibrating needle in concrete with maximum nominal size of aggregate not more than 20 mm and of workability 0.74 to 0.82 compacting factor shall not be less than 100 times the cross sectional are of the needle.
- There shall be no water, mortar or concrete inside the vibrating head, when the vibrator is operated continuously for one hour in concrete having 75 mm slump.
- When tested for endurance, the vibrator must be able to complete this test without any break down. Endurance test is performed by operating the vibrator continuously for 20 hours with not more than 2 stoppages of 15 minutes required for change of prime mover in a barrel of crushed stone aggregate, sand and water simulating a concrete mix. The minimum size of the barrel shall be such that the cross-sectional area is at least equal to the range of action; the depth being at least twice the length.
Notes
- Amplitude of vibration means maximum displacement from its mean position measured at the center of the length of vibrating needle. It is usually expresses as half of its total displacement.
- Frequency means number of complete cycles of vibration per second of the vibrating needle.
Reference
IS: 2505-1992