The radiographic flaw detection methods commonly used in industry are X-ray flaw detection and gamma ray flaw detection. It refers to the use of electromagnetic waves to detect metal workpieces, similar to X-ray fluoroscopy. The rays pass through the material and reach the film, which will make the film evenly sensitive to light; if it encounters defects such as cracks, holes, and slag inclusions, dark shadow areas will generally be displayed on the film. This method can detect the size and shape of defects and also determine the thickness of the material.
X-rays are produced by impacting an anode target with high-speed electrons in a high vacuum state. Gamma rays are emitted by radioactive isotopes during the transformation of atoms. Both are electromagnetic waves with high penetrating power and short wavelength. Objects of different thicknesses require rays of different energies to penetrate, so different ray sources must be used respectively. For example, X-rays emitted by the The thicknesses are approximately 90 mm, 230 mm and 600 mm respectively. The low-energy X-ray machine used in industrial radiographic flaw detection is simply composed of four parts: ray generator (X-ray tube), high-voltage generator, cooling system, and control system. When each part is independent, high-voltage cables should be used to connect the high-voltage generator and the ray generator.
According to the structure of X-ray machines, X-ray machines are usually divided into three categories: portable X-ray machines, mobile X-ray machines, and fixed X-ray machines.
The portable X-ray machine uses a combined ray generator. The X-ray tube, high-voltage generator, and cooling system are all installed in a single casing. It is also simply called a ray generator. The ray generator is filled with insulating medium. The whole machine consists of two units, namely the controller and the ray generator, which are connected by low-voltage cables. The insulating medium filled in the ray generator was earlier high electric strength transformer oil, and its electric strength should not be less than 30~50kV/2.5mm. Most of the insulating media currently filled is sulfur hexafluoride (SF6) to reduce the weight of the ray generator.
The core component of the X-ray machine is the X-ray tube. An ordinary X-ray tube is mainly composed of an anode, a cathode and a tube shell.
X-rays are excited by an x-ray tube plus high voltage. The intensity of x-rays can be adjusted by applying voltage and current.
For low-voltage X-ray machines, only a small part of the energy input into the X-ray tube is converted into X-rays, and most of it is converted into heat, so good heat dissipation must be ensured for the X-ray machine.
The main technical performance of X-ray machines can be summarized into five: workload characteristics, radiation intensity, focus size, radiation angle, and leakage radiation dose. When selecting an X-ray machine, you should consider whether the above performance is suitable for the work being performed. The gamma ray machine uses radioactive isotopes as the gamma ray source to radiate gamma rays. An important difference between it and the X-ray machine is that the gamma ray source is always emitting gamma rays, while the X-rays, this makes the structure of the gamma-ray machine have characteristics different from those of the X-ray machine. Gamma rays are excited by radioactive elements and have constant energy. The intensity cannot be adjusted, it only decreases exponentially over time.
Gamma-ray flaw detectors are divided into three types: portable, mobile, and fixed. The portable gamma ray machine is light, small in size and weight, easy to carry and easy to use. However, from the perspective of radiation protection, it cannot be equipped with high-energy gamma ray sources.
The gamma ray machine is mainly composed of five parts: source component (sealed gamma ray source), source container (main body), source (guide) tube, driving mechanism and accessories.
Compared with X-ray machines, gamma-ray machines have the characteristics of simple equipment, easy operation, and no need for water and electricity. However, the consequences of incorrect operation of the gamma-ray machine will be very serious. Therefore, attention must be paid to the gamma-ray machine. Operation and use. According to relevant national regulations, units using gamma ray machines involve radioactive isotopes. Therefore, the unit must apply for a license for the use of radioactive isotopes. Operators should undergo special training and obtain a radiation worker certificate.
Raygraphic flaw detection requires the use of radioactive sources to emit rays, which is extremely harmful to people. Careless operation may cause personnel to be exposed to radiation and increase the probability of suffering from leukemia. Operators should wear protective clothing and pay attention to the proper storage of radioactive sources.