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ISO 28927-2:2009 — Hand-held portable tools — Vibration test for wrenches, nutrunners and screwdrivers
Laboratory measurement of hand-transmitted vibration emission for threaded fastener tools | Engineering technical guide
Introduction to ISO 28927-2
ISO 28927-2:2009 specifies a laboratory method for measuring hand-transmitted vibration emission at the handles of hand-held power-driven wrenches, nutrunners and screwdrivers used for tightening and loosening threaded fasteners. This type-C standard, developed by ISO/TC 118/SC 3, represents a significant technical revision of ISO 8662-7:1997.
This standard covers machines with 6.3 mm to 40 mm (1/4 in to 1 1/2 in) drive output shafts, including impact wrenches, impulse nutrunners, ratchet wrenches, stall-type nutrunners, and automatic shut-off nutrunners.
Key Technical Requirements
Vibration Measurement and Characterization
The standard mandates vibration measurement in three orthogonal axes simultaneously at each hand position. The prescribed transducer location is positioned between the thumb and index finger, following the principle first introduced in EN 60745. A secondary location on the side of the handle’s inner end is defined when the primary position cannot be used. For machines weighing less than 2 kg, one-handed operation measurement suffices; tools of 2 kg or more require two-hand position measurements.
| Machine Type | Hand Positions | Transducer Location | Test Method |
|---|---|---|---|
| Impact wrench/impulse nutrunner | 2 (mass >= 2 kg) | Between thumb and index finger | Brake device test |
| Ratchet wrench | 1 (one-handed) | Primary grip zone | No-load test |
| Angle nutrunner | 2 (two-handed) | Both handles | No-load or brake test |
| Screwdriver (pistol grip) | 1 (one-handed) | Trigger handle | No-load test |
| Screwdriver with support handle | 2 | Main and support handles | No-load test |
For impact and impulse machines tested on the brake device, the rotational frequency of the output shaft shall not exceed 10 min¹. The brake device uses phenolic cotton laminate or aluminum blocks with controlled friction lining, where the difference between static and dynamic friction must be less than 20%.
Engineering Design Insights
The vibration test code in ISO 28927-2 uses a loading device (brake) to simulate realistic tightening conditions for impact and impulse tools. This brake device incorporates conical disc springs (DIN 2093) to apply controlled contact pressure between the socket and brake block. The entire test rig must be bolted to a concrete block having a mass of at least 400 kg to avoid resonances within the hand-arm vibration frequency range.
A critical design insight is the coefficient of variation (Cv) acceptance criterion: if Cv exceeds 0.15 or the standard deviation sn-1 exceeds 0.3 m/s², measurements must be checked for errors. This ensures measurement reproducibility across different operators and test runs.
The standard introduces a practical floor: emission values below 2.5 m/s² should not be used for estimating real-world vibration. In such cases, 2.5 m/s² is the recommended magnitude for exposure assessment.
Uncertainty and Declaration
The uncertainty value K is calculated as K = 1.65 x sR for single-machine tests, where sR is estimated from repeatability (srec) and operator variability (sop). For batch testing (3+ machines), K = 1.5 x st. This statistical framework ensures reliable vibration declarations across production variations.
Frequently Asked Questions
Q: What types of wrenches are excluded from this standard?
A: One-shot type impact nutrunners (where a rotating mass is accelerated and then connected to the bolt) and nutrunners designed for torque reaction arms are excluded.
A: One-shot type impact nutrunners (where a rotating mass is accelerated and then connected to the bolt) and nutrunners designed for torque reaction arms are excluded.
Q: Why is the 2.5 m/s² floor value used?
A: Real-world influences from operator technique, task variation, and tool condition can significantly affect low-magnitude vibration measurements. The floor provides a conservative estimate.
A: Real-world influences from operator technique, task variation, and tool condition can significantly affect low-magnitude vibration measurements. The floor provides a conservative estimate.
Q: How often should the brake device be recalibrated?
A: Intense use may require air cooling via a small hole in the lower cover plate. The friction material coefficient should be monitored to ensure the static-dynamic friction difference stays below 20%.
A: Intense use may require air cooling via a small hole in the lower cover plate. The friction material coefficient should be monitored to ensure the static-dynamic friction difference stays below 20%.
Q: What is the significance of three-axis measurement?
A: Hand-transmitted vibration is directional. Measuring in all three orthogonal axes (ahwx, ahwy, ahwz) and combining them as the root-sum-of-squares gives the total vibration total value ahv.
A: Hand-transmitted vibration is directional. Measuring in all three orthogonal axes (ahwx, ahwy, ahwz) and combining them as the root-sum-of-squares gives the total vibration total value ahv.
