苏州聚友保利检测科技有限公司

National hotline:

0512-63230241

新闻banner
Your current location HOME >> News >> Company news

Contact Us

Suzhou Jianbazi Testing Technology Co., Ltd

Landline:0512-63230241

                0512-63952861

                0512-63230242

URL:www.ndtsupmarket.com

Factory Address: No. 1, Gaocao North Road, Fuxiang Development Zone, Tongluo, Wujiang District, Suzhou City

Address of Wujiang Operation Center: 1802, Block G, Kaiping Business Center, the Taihu Lake New Town, Wujiang District, Suzhou

Shanghai Branch Address: No.16-153, Lane 199, Yefan Road, Yexie Town, Songjiang District, Shanghai


For spheroidal graphite cast iron, ultrasonic means it is easy to detect

2021-05-25 09:44:12
second

For spheroidal graphite cast iron, ultrasonic means it is easy to detect


    Nodular cast iron is a high-strength cast iron material developed in the 1950s. Its comprehensive properties are close to steel. Because of its excellent performance, it has been successfully used for casting some complex forces, strength, toughness, and wear resistance. Higher parts. The so-called "substituting iron for steel" mainly refers to ductile iron.


    Nodular cast iron is obtained by spheroidization and inoculation treatment to obtain spheroidal graphite, which effectively improves the mechanical properties of cast iron, especially the plasticity and toughness, thereby obtaining higher strength than carbon steel. Compared with graphite flakes (in gray cast iron), the round graphite balls in ductile cast iron can better resist stress concentration, and therefore can better prevent the occurrence of cracks and other defects. It is very important to carry out relevant tests on key safety components of automobiles made of ductile iron to verify whether they have a reasonable spheroidization rate. Because even a small failure of these components may bring great losses and even life-threatening.


    Manufacturers usually use some destructive testing methods, such as microstructure analysis, to verify whether the sample parts have the correct spheroidization rate. However, in addition to the destructive effect of the microstructure analysis method on the sample, the sampling only accounts for a small part of the total product. For automobile safety-critical parts made of ductile iron, such as those used in braking and steering systems, the spheroidization rate of each casting must be verified. Therefore, non-destructive testing methods are the best choice.


    The relationship between ultrasonic velocity and spheroidization rate


    Studies have found that the propagation speed of ultrasonic longitudinal waves will decrease as the spheroidization rate decreases. Foundries that produce ductile iron castings generally set the acceptance or rejection limit of the acoustic wave propagation speed to ensure that the casting product has the required spheroidization rate. There is a certain difference in the speed of sound in pure iron, ductile iron and gray cast iron. In general, the propagation speed of sound waves in pure iron is about 0.232 inches/microsecond (in/μs), in ductile iron is about 0.222 in/μs, and in gray cast iron is about 0.192 in/μs. The specific speed of sound waves in different materials depends on the alloy composition, grain structure and some other process parameters.


    Ultrasonic detection of spheroidization rate


    Based on the relationship between the speed of sound and the spheroidization rate, ultrasonic nondestructive testing technology is regarded as an ideal tool for detecting the spheroidization rate of casting parts.


    Generally, the ultrasonic system will be adjusted appropriately using a representative "reference" standard casting with a known spheroidization rate. The geometry of the standard casting used for reference must be representative of the production part to be inspected in size. And use a micrometer or caliper to accurately measure the thickness of the reference casting at the detection point, and input this value into the measurement software to calculate the speed of sound. Ultrasonic thickness gauges and flaw detectors with single crystal pulse echo sensors can be used to manually measure the speed of sound. Although manual inspection is very convenient for sampling small batches of parts, the inspection speed is slower than that of a dedicated automatic inspection system, and it is subject to the operator's subjective influence. Therefore, manual inspection is neither desirable nor practical for mass casting inspection in a casting processing production line.


    Automated ultrasonic testing solution


    The automatic inspection system for casting products on the production line generally consists of ultrasonic inspection instruments, specific computer software, ultrasonic transducers and digital input/output (IO) buses.


    In addition to the above-mentioned ultrasonic hardware and software, the system also uses a submerged water tank, a set of special inspection fixtures for precision parts, a special device for loading and unloading parts (loading and unloading can be performed manually or automatically by robots), and a set for sample management And can separate the control system of qualified and unqualified products according to the test results. The special inspection fixture for precision parts is installed in the submerged water tank to fix the relative position of the cast iron sample (relative to the ultrasonic transducer). The two opposite ultrasonic transducers are set in a send-and-receive (or projected transmission) mode, and the propagation time of the obtained ultrasonic echo is measured and the speed of sound is calculated in turn.


    The detection position must be on the area where two parallel and flat surfaces are located on the casting. The measurement accuracy generally depends on the geometry of the casting sample and the accuracy of the position of the casting relative to the transducer. Mechanical accuracy and the cleanliness of the fixture are also important for obtaining accurate inspection results. Worn out devices must be reworked or replaced before they can be used. The ultrasonic time-of-flight (TOF) between the transmitting and receiving transducers is measured by waterway (without casting samples in the device) (TOF1 in the figure). Next, measure the flight time representing the waterways on both sides of the casting and the time required for sound waves to complete a round trip in the casting (TOF2 in the figure). Then according to the thickness of the measured part and the two measured TOF values, the propagation velocity of the sound wave can be calculated.


    Because temperature affects the speed of sound, a change in the temperature of the immersion pool will cause a corresponding change in the accuracy of the sound speed measurement. In order to minimize this effect, the speed of sound in the water is measured after each casting sample is tested, and this information is used to compensate for the speed measurement, thereby providing precise results that are not affected by changes in water temperature. The change of the casting temperature will also affect the measurement accuracy. If the change is large, the system needs to be adjusted again.


    The sound velocity measurement system can be adjusted quickly and easily, and it also needs to be calibrated regularly to maintain the stability and accuracy of the measurement. Calibration is generally to use a reference casting material with a known spheroidization rate to adjust the system.


    When the adjustment is completed, the system can be switched to the detection mode to start the detection of production castings. The detection speed can reach 15-30 castings per minute. The main reason for limiting the detection speed comes from the time it takes to load and unload the castings.


    After the measurement starts, the casting samples are simply loaded into the fixture in the liquid tank one by one. The specific software used can recognize the presence of the casting and automatically trigger the measurement switch based on the ultrasonic echo generated when the casting is loaded. Comparing the measurement results with preset speed and thickness limits, the system can generate an acceptance or rejection decision, both as an indication on the screen and as an output signal from the control system. After inspection, the casting is unloaded from the fixture and divided into qualified and unqualified groups.


    During the inspection, the inspection sequence can be observed through the LED screen on the user interface. The acceptance/rejection sorting decision will also be displayed on the LED screen, and a signal will be sent out on the digital input/output bus to display the speed value, thickness, and water speed measurement results of each tested casting. The measured value of each casting will be plotted on the trend graph. The number of accepted and rejected parts and the total number of detected parts are counted and displayed by the parts counter on the user interface. The test results can finally be exported as a CSV file for offline document storage and analysis.


    The use of a multi-channel system allows multiple measurements on the same casting and simultaneous measurements on separate processing lines. Through independent channel operation, the operator can stop or adjust another channel while the other channel continues to detect.


    Defect detection


    In addition to sound velocity and thickness measurement, channels can also be specifically selected for pulse echo defect detection parallel to sound velocity measurement. The ultrasonic pulse generator can generate high-voltage electric pulses, which are converted into high-frequency ultrasound by the transducer. The signal reflected from the defect or discontinuity in the material is converted into an electrical signal by the transducer, amplified and processed, and transmitted to the display. The final received signal can be used to calculate the position, size and orientation of the defect.


    Summarize


    Ultrasonic non-destructive testing technology provides people with a reliable method of measuring the speed of sound, so it can verify the spheroidization rate of ductile iron materials. Integrating ultrasonic inspection technology into the automated inspection system on the casting product production line can quickly and reliably detect 100% of the casting parts.


    In order to ensure that the position of the casting relative to the ultrasonic transducer is always consistent, the detection also requires a precise mechanical fixing device; specific application software allows users to easily adjust the system and provide stable and accurate detection results.


    In addition to the sound velocity measurement function, the ultrasonic inspection technology can also detect defects in the casting material by using a dedicated transducer and a dedicated defect channel.


label

Recent browsing: