Ultrasonic flaw detector selection

Detect cracks or defects inside metal materials or parts. Common flaw detection methods include: X-ray flaw detection, ultrasonic flaw detector, magnetic particle flaw detection, penetrant flaw detection (color flaw detection), eddy current flaw detection, fluorescent flaw detection, etc. Physical flaw detection is non-destructive flaw detection without chemical changes.

1. What is non-destructive flaw detection?

Answer: Non-destructive flaw detection is a test method to check the surface and internal quality of the inspected parts without damaging the workpiece or the working state of the raw materials.

2. What are the common flaw detection methods?

Answer: Common non-destructive flaw detection methods include: X-ray flaw detection, ultrasonic flaw detection, magnetic particle flaw detection, penetrant flaw detection, eddy current flaw detection, gamma ray flaw detection, fluorescent flaw detection, color flaw detection, etc.

3. Describe the principle of magnetic particle flaw detection?

Answer: Its basic principle is: when the workpiece is magnetized, if there are defects on the surface of the workpiece, the magnetic resistance at the defect increases and leakage magnetic field is generated, forming a local magnetic field, and the magnetic powder will show the shape and position of the defect here, thereby judging the existence of the defect.

4. Describe the types of magnetic particle flaw detection?

1. According to the different magnetization directions of the workpiece, it can be divided into circumferential magnetization method, longitudinal magnetization method, composite magnetization method and rotary magnetization method.
2. According to the different magnetization currents used, it can be divided into: DC magnetization method, half-wave DC magnetization method, and AC magnetization method.
3. According to the different preparations of magnetic powder used in flaw detection, it can be divided into dry powder method and wet powder method.

5. What are the defects of magnetic particle flaw detection?

Answer: c The equipment is simple, easy to operate, quick to inspect, and has a high flaw detection sensitivity. It can be used to detect surface or near-surface defects of ferromagnetic materials such as nickel, cobalt and their alloys, carbon steel and some alloy steels; it is suitable for the inspection of thin-walled parts or surface cracks in welds, and can also reveal incomplete penetration defects of a certain depth and size; but it is difficult to find pores, slag inclusions and defects hidden deep in the weld.

6. How many categories can defective magnetic traces be divided into?

Answer: 1. Magnetic traces of various process defects;
2. Hairline magnetic traces caused by material slag inclusions;
3. Point-shaped magnetic traces caused by slag inclusions and pores.

7. What are the causes of magnetic leakage?

Answer: Since the magnetic constant of ferromagnetic materials is much greater than the magnetic permeability of non-ferromagnetic materials, according to the magnetic flux density B = μH after the workpiece is magnetized, B magnetic lines pass through the unit area of ​​the workpiece, while B magnetic lines cannot be allowed to pass through the unit area of ​​the defect area, forcing some magnetic lines to squeeze into the material below the defect, and other magnetic lines have to be forced to escape from the surface of the workpiece to form magnetic leakage, and the magnetic powder will be attracted by the magnetic leakage caused by this.

8. What are the factors affecting the generation of magnetic leakage?

Answer: 1. The magnetic permeability of the defect: The smaller the magnetic permeability of the defect, the stronger the magnetic leakage.
2. The magnitude of the magnetizing magnetic field intensity (magnetizing force): The greater the magnetizing force, the stronger the magnetic leakage.
3. The shape and size of the inspected workpiece, the shape and size of the defect, the buried depth, etc.: When other conditions are the same, the magnetic leakage generated by the pores buried at the same depth under the surface is smaller than the magnetic leakage generated by the transverse crack. [page]

9. Why do some parts need to be demagnetized after magnetic particle inspection?

Answer: The residual magnetism of some rotating parts will attract iron filings and cause friction damage to the parts during rotation, such as shaft bearings. The residual magnetism of some parts will cause abnormal indications of nearby instruments. Therefore, why do some parts need to be demagnetized after magnetic particle inspection?

10. What is the basic principle of ultrasonic flaw detection?

Answer: Ultrasonic flaw detection is a method of inspecting part defects by using the characteristics of ultrasonic energy penetrating deep into metal materials and reflecting at the edge of the interface when entering from one section to another. When the ultrasonic beam passes from the surface of the part through the probe to the inside of the metal, it will generate reflected waves when encountering defects and the bottom of the part, forming pulse waveforms on the fluorescent screen. The position and size of the defect are determined based on these pulse waveforms.

11. What are the advantages and disadvantages of ultrasonic flaw detection compared with X-ray flaw detection?

Answer: Ultrasonic flaw detection has the advantages of higher flaw detection sensitivity, shorter cycle, lower cost, more flexibility, higher efficiency, and harmlessness to the human body than X-ray flaw detection; the disadvantages are that it requires a smooth working surface, requires experienced inspectors to identify the types of defects, and has no intuitiveness for defects; ultrasonic flaw detection is suitable for the inspection of parts with larger thickness.

12. What are the main characteristics of ultrasonic flaw detection?

Answer: 1. When ultrasonic waves propagate in a medium, they have the characteristic of reflection at interfaces of different qualities. If they encounter a defect, and the size of the defect is equal to or greater than the wavelength of the ultrasonic wave, the ultrasonic wave will be reflected back at the defect, and the flaw detector can display the reflected wave; if the size of the defect is even smaller than the wavelength, the sound wave will bypass the ray and cannot be reflected;

2. The directionality of the wave sound is good. The higher the frequency, the better the directionality. It radiates into the medium with a very narrow beam, making it easy to determine the location of the defect.

3. The propagation energy of ultrasonic waves is large. For example, the energy propagated by an ultrasonic wave with a frequency of 1MHZ (100 Hz) is equivalent to 1 million times that of a sound wave with the same amplitude and a frequency of 1000HZ (Hertz).

13. When the thickness of the ultrasonic flaw detection plate is 14 mm, what is the relationship between the three main curves on the distance amplitude curve?

Answer: Length measuring line Ф1 х 6 -12dB
Quantitative line Ф1 х 6 -6dB
Judgement line Ф1 х 6 -2dB

14. What is the "soft" and "hard" of the ray?

Answer: The ability of X-rays to penetrate matter is related to the wavelength of the ray itself. The shorter the wavelength (the higher the tube voltage), the greater the penetrating ability, which is called "hard"; otherwise it is called "soft".

15. What may be the cause of the disappearance of the bottom wave when using ultrasonic wave flaw detection?

Answer: 1. Large defects near the surface; 2. Absorption defects; 3. Large inclined defects; 4. The oxide scale is not well bonded to the steel plate.

16. What are the main factors affecting development?

Answer: 1. Development time; 2. Developer temperature; 3. Shaking of the developer; 4. Formula type; 5. Aging degree.

17. What is electromagnetic induction?

Answer: The phenomenon that the magnetic flux through a closed loop changes and an electromotive force is generated in the loop is called electromagnetic induction; the electromotive force generated in this way is called induced electromotive force. If the conductor is a closed loop, a current will flow through it, and the current is called induced current; transformers, generators, and various inductance coils all work based on the principle of electromagnetic induction.

18. Briefly describe the reasons for the attenuation of ultrasonic waves when they propagate in the medium during ultrasonic flaw detection?

Answer: 1. As the diffusion propagation distance of ultrasonic waves increases, the beam cross-section becomes larger and larger, and the energy per unit area decreases.
2. Material attenuation is caused by absorption caused by the viscosity of the medium; the second is scattering caused by chaotic reflections at the interface of the medium.

19. What is the main function of the CSK-ⅡA test block?

Answer: 1. Verify sensitivity; 2. Calibrate scanning linearity.

20. What are the main factors affecting photographic sensitivity?

Answer: 1. The focal size of the X-ray machine; 2. The rationality of the selection of transmission parameters, the main parameters are tube voltage, tube current, exposure time and focal length; 3. Sensitization method; 4. The rationality of the film selection; 5. Darkroom processing conditions; 6. Scattering shielding, etc. (end)