The BoltMike® Ultrasonic Bolt Stressmeter operates on the principle of ultrasonic pulse-echo technology, a well-established and reliable method for non-destructive testing. The device uses an ultrasonic sensor mounted at one end of the bolt to emit a sound wave that travels through the entire length of the fastener. Upon reaching the opposite end, the pulse is reflected back toward the sensor. This echo is then captured and analyzed by the instrument.
When a bolt is under tension, its axial length changes slightly, which in turn affects the speed of sound traveling through it. The BoltMike® system detects these minute variations in wave propagation time, allowing it to calculate the axial force, stress, and strain with high precision. The built-in waveform analysis feature enables automatic calibration, ensuring accurate readings even under varying environmental conditions.
The instrument is designed for high accuracy, with a measurement error margin of no more than 2%. It features a built-in oscilloscope that displays real-time waveforms, enabling users to adjust parameters like gain and delay for optimal performance. The device can measure bolts ranging from 196 mm to 350 mm in length, with stress measurement capabilities between 1 MPa and 200 MPa, load measurements from 1 N to 50 kN, and elongation detection as sensitive as 0.001 mm.
During operation, the gate is opened to a specific position, and each bolt is measured individually. The preload value is recorded, after which the gate is closed to release the wire rope from tension. Bolts with higher pre-tightening forces are loosened, while those with lower forces are tightened accordingly. This process is repeated multiple times until the tension across the wire rope is evenly distributed.
The test results are evaluated based on the readings taken from the left side of the gate. Before adjustments, the pre-tightening forces of the bolts were found to be highly inconsistent, leading to uneven wire rope tension. This did not meet the technical standards outlined in DL/T 5019-94 and the specifications for the Sanchahekou Gate project on the Qinhuai River. After calibration and adjustment, the pre-tightening forces of all bolts were significantly improved, resulting in a more uniform distribution of tension and safer operational conditions.
This system provides an efficient and precise way to monitor and maintain the integrity of critical bolted joints in various engineering applications.
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