Using technology of ultrasonic thickness measuring instrument
Ultrasonic thickness measurement instrument for thickness measurement is based on the principle of ultrasonic pulse reflection, when the probe transmitted ultrasonic pulses through the material object to be tested interface, the pulse is reflected back to the probe through the precise measurement of ultrasonic propagation time in the material to determine the thickness of the material.
Ultrasonic thickness meter is based on the pulse reflection principle for thickness measurement, when the probe transmitted ultrasonic pulses through the material object to be tested interface, the pulse is reflected back to the probe through the precise measurement of ultrasonic propagation time in the material to determine the thickness of the material being tested. All kinds of materials that can make the ultrasonic wave at a constant speed can be measured by this principle. (instrument world network) ultrasonic thickness measurement instrument is adopted with high performance and low power microprocessor technology, based on ultrasonic measuring principle, measuring the thickness of metal and many other materials, and can measure the velocity of materials. Thickness measurement of all kinds of pipes and pressure vessels in production equipment can be used to monitor the extent of the reduction of the corrosion in the process of use.
According to the thickness of the reflection principle of design can be used for accurate measurement of various materials and various kinds of machining parts can also be pulsed ultrasound, the production equipment of all kinds of piping and pressure vessel monitoring, monitoring them in the process of using corroded thinning degree. Can be widely used in petroleum, chemical, metallurgy, shipbuilding, aviation, aerospace and other fields.
The technique of using ultrasonic thickness measuring instrument
First, clean the surface
Before the measurement, all the dust, dirt and rust on the surface of the object being measured shall be removed, and the cover of the paint and the like shall be removed.
Two, improve the roughness requirements
Over rough surfaces can cause measurement errors, and even the instrument has no readings. Before the measurement should try to make the measured material surface is smooth, can use the method of grinding, polishing, filing and so make it smooth, can also use high viscosity coupling agent, selection of coarse grained SZ2.5P probe.
Three, rough machined surface
Rough machined surfaces (such as lathes or planer) caused by a regular slot will cause measurement errors, make up with 2, in addition to adjust the probe (probe through the thin plate crosstalk bottom center) and the measured angle between the material grooves,
The interlayer plate and the groove is parallel or perpendicular, minimum readings in as the thickness measurement, a good result can be obtained.
Four, measurement of cylindrical surface
The measurement of cylindrical materials, such as pipes, drums, selection of probe plate and critical material interlayer crosstalk axis angle between the measured. Simply speaking, the probe and the measured material coupling, crosstalk probe and the measured material plate axis is parallel or vertical, along the vertical axis direction and the measured material slowly shaken. The screen reading will change regularly, select the minimum readings, as accurate material thickness.
Select the partition board and curvature probe crosstalk measured material axis angle direction depends on the material standard, large diameter pipe, plate and pipe selection probe crosstalk axis vertical, smaller diameter pipe, is selected in parallel with the axis of the pipe and vertical two measurement methods, a minimum value as the measurement of thickness readings.
Five, composite shape
When measuring the shape of the composite materials (such as pipe bend) method can be used when 7.4 introduction, the difference is to be measured two times, respectively read probe crosstalk interlayer board and the vertical axis and parallel to the two values, a number of the smaller as the thickness of the material at the measuring point.
Six, the temperature of the material
Effect of thickness and ultrasonic velocity of material were affected by temperature, if the measurement precision is high, specimens were measured under the same temperature conditions can use the same materials, calculate the temperature measurement error of the material, to provide parameters to correct it, for the steel, the high temperature will cause a large error, this method can be used to to compensation.
Seven, non parallel surface
In order to obtain a satisfactory ultrasonic response, the other surface of the material being tested must be parallel or coaxial with the measured surface, otherwise it will cause measurement error or no reading at all.
The above is the use of ultrasonic measurement of thickness measuring instrument technology, according to the thickness of the reflection principle of design can be used for accurate measurement of various materials and various kinds of machining parts can also be pulsed ultrasound, the production equipment of all kinds of piping and pressure vessel monitoring, monitoring them in the process of using corroded thinning degree.
1, general measurement method:
(1) at one point, the probe is used to measure the thickness of the two times, the split surface of the probe in the two measurement should be 90 degrees, and the smaller value is the thickness of the measured workpiece.
(2) 30mm multi point measurement method: when the measured value is unstable, with a measurement point as the center, in a diameter of about 30mm of the circle for multiple measurements, the minimum value for the measured workpiece thickness.
2, accurate measurement method: in the specified measurement points around the increase in the number of measurements, thickness change with the thickness of the line said.
3, continuous measurement: single point measurement method along the designated route for continuous measurement, the interval is not greater than 5mm.
4, the grid measurement method: designated area in the grid, according to the thickness of the record. This method is widely used in the corrosion monitoring of high pressure equipment and stainless steel lining.
5, the influence of ultrasonic thickness measurement of the factors:
(1) the surface roughness of the workpiece is too large, which results in a poor coupling effect between the probe and the contact surface, and the reflection echo is low, and even the echo signal can not be received. For the surface corrosion of in-service equipment and pipes through the sand, grinding, etc. and method of coupling effect is poor for treatment on the surface, reduce the roughness, also can be oxides and paint layer removed, with metallic luster, the probe and the object being detected by the coupling agent can achieve the coupling effect is very good.
(2) the curvature radius of the work piece is too small, especially when the diameter tube thickness is measured, the surface of the common probe is plane, contact with the curved surface is a point contact or line contact, the sound intensity transmission is low (coupling is not good). Can choose small diameter probe (6mm), can be more accurate measurement of pipe and other surface materials.
(3) the detection surface is not parallel with the bottom surface, acoustic wave encountered at the bottom of the scattering, the probe can not accept the wave signal in the end.
(4) austenitic steel castings, due to uneven or coarse grain, the ultrasonic attenuation have serious scattering which passes scattered along the path of ultrasonic propagation in complex, may make the echo annihilation, which shows. Can be used in the lower frequency of coarse crystal specific probe (2.5MHz).
(5) the contact surface has a certain degree of wear. The surface of the common thickness probe is acrylic resin, and the long-term use will increase the surface roughness of the surface, resulting in the decrease of sensitivity, and the display is not correct. Can use 500# sandpaper, make it smooth and ensure parallelism. If it is still not stable, then consider the replacement of the probe.
(6) there are a lot of corrosion pits on the back of the measured object. Because the other side of the analyte, rust corrosion pits caused by acoustic attenuation, resulting in reading irregular changes in extreme cases even without reading.
(7) sediment in the measured object (such as pipe), when the sediment and the acoustic impedance of the workpiece is not large, the thickness of the thickness of the thickness of the instrument display and sediment thickness.
(8) when there are defects in the material (such as inclusion, interlayer, etc.), the value of about 70% of the nominal thickness, this time can be used ultrasonic flaw detector for further defect detection.
(9) the effect of temperature. Velocity varies with temperature in solid materials generally decreases with the test data shows that each additional thermal material 100 DEG C velocity decreased by 1%. For high temperature equipment in service often encounter this situation. Should choose high temperature special probe (300-600 degrees C), do not use ordinary probe.
(10) laminated materials, composite (heterogeneous) materials. It is not possible to measure the non coupled laminated material, because the ultrasonic wave can not penetrate the space without coupling, and can not be spread evenly in the composite (heterogeneous) materials. Special attention should be paid to the thickness of the equipment (such as urea high pressure equipment), which is made up of multi-layer material.
(12) the effect of coupling agent. The coupling agent is used to remove the probe and the object to be measured between the air and the ultrasonic can effectively penetrate the workpiece to achieve the purpose of detection. If you choose the type or the use of improper methods, will result in errors or coupling logo flicker, can not be measured. According to the selection of suitable types of usage, when used in the smooth surface, the coupling agent can use low viscosity; when used on rough surface, vertical surface and top surface, should use the coupling agent with high viscosity. High temperature coupling agent should be used in high temperature work piece. Secondly, the coupling agent should be appropriate to use, smear evenly, the coupling agent should be applied to the surface of the material being tested, but when the measuring temperature is higher, the coupling agent should be coated on the probe.
(13) the choice of sound speed error. Before measuring the work piece, according to the type of material, the sound speed of the material is preset, or the velocity of sound is measured according to the standard block. When the instrument is used as a material, the test block is used to measure the error of another material. Must be required to correctly identify the material before the measurement, select the appropriate speed of sound.
(14) the effect of stress. In the service of equipment and pipeline most of the existence of stress, the stress state of solid material has certain effect on the velocity, when the stress direction and propagation direction, if the stress is compressive stress, stress the workpiece elastic velocity increase speed; conversely, if the stress is tensile stress. Slow down the speed of sound. When the stress and wave propagation direction is not the one to the time, the particle vibration trajectory is disturbed by the stress, and the direction of the wave propagation is deviated from the point of the wave propagation. According to the data, the general stress is increased and the speed of sound is increased slowly.
(15) the effect of ultrasonic thickness gauge metal surface oxide or paint coating. Dense oxide of metal surface or paint coating, is tightly combined with the matrix material, no obvious interface, but the propagation speed of sound velocity in two kinds of material are different, thus causing the error, and with different covering thickness, the error is different in size.