Ultrasonic Thickness Gauge Frequently Asked Questions
Aluminium Bushing,Aluminum Shaft Bushing,Motor Aluminium Bushing,Curved Aluminium Profile KAM KIU ALUMINIUM GROUP , https://www.kamkiualuminium.com
The radius of curvature of the workpiece is too small, especially when measuring the thickness of a small tube, because the surface of the commonly used probe is flat, and the contact with the surface is point contact or line contact, the sound intensity transmittance is low (coupling is not good). Optional 7P6 small-diameter special probe (6mm) The lower limit of the pipe is 15mm*2mm, which can accurately measure the surface material such as pipes.
The detection surface and the bottom surface are not parallel, and the sound wave encounters the bottom surface to generate scattering, and the probe cannot receive the final wave signal.
Castings, austenitic steels, due to inhomogeneous tissue or coarse grains, cause severe scattering attenuation when ultrasonic waves pass therethrough. The scattered ultrasonic waves propagate along a complicated path and may cause the echoes to disappear and cause no display. The TT100 series can use the coarse crystal special probe (2.5MHz) with low frequency, or use cast iron thickness gauge TT340.
The probe contact surface has a certain amount of wear. The commonly used thickness measurement probe surface is acrylic resin, and its long-term use will increase the surface roughness, which will result in a decrease in sensitivity, resulting in incorrect display. 500# sandpaper can be used to sand the periphery of the probe to make it smooth and ensure parallelism. If it is still unstable, consider replacing the probe.
There is a large amount of corrosion pits on the back of the measured object. Due to rust and corrosion pits on the other side of the test object, sound waves are attenuated, resulting in random readings and no reading in extreme cases.
There is sediment in the measured object (such as pipeline). When the acoustic impedance of the sediment and the workpiece are not much different, the thickness gauge shows the wall thickness plus the thickness of the sediment. For example, the scale inside the pipeline is in close contact with the pipeline.
When there are defects inside the material (such as inclusions, interlayers, etc.), the displayed value does not agree with the thickness value. At this time, the ultrasonic flaw detector can be used for further defect detection.
The effect of temperature. The sound velocity in general solid materials decreases as their temperature increases, and experimental data shows that the sound speed drops by 1% for every 100°C increase in hot material. This is often the case with equipment that is in service at high temperatures. High-temperature special probes should be selected (according to the specific temperature conditions), do not use ordinary probes.
Laminated, composite (heterogeneous) materials. It is not possible to measure uncoupled laminates because ultrasonic waves cannot penetrate the uncoupled space and cannot propagate uniformly in composite (heterogeneous) materials. For devices and workpieces made of multi-layered materials, special attention should be paid to the thickness measurement. The value indicated by the thickness gauge only indicates the thickness of the material in contact with the probe.
Coupling agent effects. Coupling agent is used to eliminate the air between the probe and the measured object, so that the ultrasonic energy can effectively penetrate the workpiece to achieve the purpose of detection. If you choose a type or use it incorrectly, it will cause the error or coupling symbol to flicker and cannot be measured. Depending on the type of application, a low viscosity couplant can be used when used on a smooth material surface, and a high viscosity (eg, butter) couplant should be used on rough, vertical, and top surfaces. High temperature parts should use high temperature couplant. Secondly, the couplant should be applied in proper amount and evenly applied. Generally, the couplant should be coated on the surface of the tested material, but when the measuring temperature is high, the couplant should be coated on the probe.
The speed of sound is wrong. Before measuring the workpiece, preset its sound speed according to the type of material or reversely measure the speed of sound according to the standard block. When a material is used to calibrate the instrument (usually the test block is steel) and another material is measured, it will produce erroneous results. Requirements must be correctly identified before the measurement of materials, select the appropriate speed of sound. The general thickness gauge has the function of anti-measuring sound speed, which is called the sound speed of the material. Before the measurement, the speed of the workpiece can be measured first.
Effects of metal surface oxides or paint overlays. Although the dense oxide or paint coating produced on the metal surface is tightly bound to the matrix material and has no apparent interface, the speed of sound propagation in the two materials is different, resulting in errors, and the error size varies with the thickness of the cover. Also different. General thickness gauge measurement, need to remove the cover.