On August 24, at the 2017 China International General Aviation Congress, the audience visited the booth of an aero-engine company. Xinhua News Agency reporter Shao Ruishe
The engineer is putting the engine into the test stand to prepare for the engine test.
If the body is uncomfortable, we will go to the hospital for examination and prescribing medicine; in order to prevent major diseases, we will also conduct regular medical examinations.
People are more afraid of “illness†than people, and aero engines must be considered one. Its jobs are in the thousands or even tens of thousands of meters above sea level. If problems occur that cause the aircraft to lose its power, the consequences may be the death of the aircraft. Therefore, it is very important for him to maintain "healthy" at all times.
How is the aero engine "medical examination"? Recently, Chen Hua, production director of aero engine specialist and Chongqing Tianjiao Aviation Power Co., Ltd., introduced the report to the reporter of the Science and Technology Daily.
Before the job is to do "entry examination"
Aeroengines are highly sophisticated precision machines, including the intake, compressor, combustion chamber, turbine, and tail nozzles. "The number of parts of a medium-sized engine has more than 20,000 pieces." Chen Hua said that these parts have complex structures and processes, which require high requirements for materials and manufacturing precision, and also have great difficulty in processing.
Aeroengines undergo various tests and tests in the design and manufacturing process, including component tests, core machine tests, complete machine ground tests, high altitude tests, and flight tests. Examples of high-altitude tests include environmental tests, windmill condition tests, system control tests, height and velocity characteristics tests, engine state characteristics tests, bird dropping tests, ice protection tests, attitude tests, and matching tests. These tests are like large and small tests in life. Aero-engines must also pass several examinations in order to take the vector production from the design and deliver it to the customer.
Before embarking on a formal job, aero engines must also undergo an "entry check." Compared with the human physical examination, its physical examination is somewhat similar, but the project is more numerous and more complex, including component detection, size and appearance inspection, macroscopic and internal microstructure detection, as well as physical, chemical, and mechanical properties testing.
Chen Hua introduced that the detection of material components for parts is similar to DNA testing of the human body. This basic parameter can be used as a confirmation of “identityâ€. Size and appearance inspections, similar to human inspections of height and weight, will determine whether the engine's overall dimensions meet the requirements. Physical, chemical and mechanical performance tests are similar to human vision and hearing tests. The purpose is to see if the function of engine materials can meet the requirements.
However, these tests and tests are cumbersome, and it is they that ensure the reliability of the engine. Taking the Ukrainian-made TV3-117 series turboshaft engine as an example, this product is used in more than 60 countries and is equipped on more than 90% of Mi-series and card series helicopters. There are more than 30,000 units in service, but none. There has been parking in the air. The reliability that cannot be achieved even in Europe and the United States is due to a large number of rigorous and thorough experiments.
However, the above tests are all destructive inspections. Generally, one sample is taken from a batch of samples, or samples are taken from the product sampling area reserved for inspection. Chen Hua said that in the process of engine manufacturing and repair, more commonly used nondestructive testing methods. It will not cause damage to the parts, but it can also reflect whether there are major problems inside the parts. At the same time, it can also monitor the aeroengines in real time and prevent catastrophic consequences due to product failure. With the development of technology, non-destructive testing has become an important technical means to control the quality of aero-engine components and ensure flight safety.
Physical examination also assesses longevity
At present there are dozens of non-destructive testing methods. The technology has evolved from a simple inspection to an assessment of the safe service life of engine parts.
The engine component ray detection is just like the X-ray transillumination in the human body examination, but the current voltage and some other control parameters are set differently. According to Chen Hua, ray detection is based on the different absorption of transmitted radiation by the object being inspected and detects the internal defects of the part. The detection results can visually display the defect image, which is convenient for qualitative and quantitative analysis. This method is sensitive to volumetric defects and is mainly used for the detection of castings and weldments, including turbine blades, casting crucibles, shells, weld defects, and hollow core residual cores. However, it is difficult to find thin defects perpendicular to the ray direction.
Ultrasonic engine detection is similar to B ultrasonic, except that the parameters such as power and frequency are different. Chen Hua said that this method uses the nature of ultrasonic attenuation in the medium to produce attenuation, as well as the nature of reflection at the interface to detect defects. The advantage is that it only needs to approach the test piece from one side, and can detect metal, non-metal and composite materials, and have comprehensive advantages in determining parameters such as the size, position, orientation, depth and nature of internal defects. Forgings and tubes, rods, plates and other profiles of engines are generally adopted to eliminate defects in raw materials; for rotating parts such as disk shafts, ultrasonic testing of flooding can be used to exclude human factors.
The hole detection is similar to the endoscopic examinations commonly used in hospitals, such as gastroscopy and bronchoscopy. With the help of special industrial endoscopic equipment, it is the only inspection method in line maintenance that can understand its internal conditions without disassembling the engine. It can be used to detect the main air flow channel components of the engine, high pressure compressors, turbine wheel layers, Fuels, nozzles, combustion chambers, etc. are not easily disassembled and have poor accessibility.
The penetrant test is to make the permeate contact the surface of the test piece, penetrate the fine defects of the part surface through the capillary action, and then use the developer to aspirate the penetrant, so that an image of the damage or defect appears on both surfaces. This method can detect multiple parts at one operation and is widely used in aero engine maintenance. All engine parts made of aluminum alloys, titanium alloys, and heat-resisting superalloys are generally detected by fluorescence when they are overhauled or overhauled. Surface damage; under external field conditions, commonly used coloring methods are used to detect parts that cannot be removed from the engine. However, penetration testing can only detect defects on the surface of parts.
Non-destructive testing also includes magnetic powder testing that can be used for surface cracking, folding, sandwiching, and slag inclusion in ferromagnetic materials; based on electromagnetic induction, it is suitable for eddy current testing of conductive materials.
Visualization of defects in the future
With the development of aviation industry, the technology of aero-engine medical examination is also continuously improving.
Chen Hua introduced that the latest development in acoustic emission detection technology is a dynamic non-destructive testing method that uses stress waves generated by local transient displacements in stressed materials. Typical sources of acoustic emission are defects-related deformation processes such as crack propagation and plastic deformation. The acoustic emission energy is derived from the elastic stress field in the material. Without the stress, there is no acoustic emission. Therefore, acoustic emission testing is usually performed during the loading process. The main applications include the monitoring of fatigue crack propagation and the quality of welded joints, and the evaluation of the structural integrity of composite materials.
Infrared detection is based on the principle of infrared radiation, and defects are discovered by scanning and recording the temperature change on the surface of the part. In the test, the fixed heat is uniformly injected into the surface of the workpiece and diffused inside. If there are internal defects, the uniform heat flow will be hindered by the defects. After a delay, heat buildup will occur at the defect sites, reflecting the abnormal temperature. The method can detect defects such as delamination, voids, cracks, and inclusions in material parts such as metal and non-metal materials, spliced ​​parts, honeycomb sandwich structures, metal welding, and hollow turbine blades.
In an aeroengine, the negligence of any defect may cause a safety accident. "The effective detection technology must be adopted to meet the development requirements of the future aeroengine, and its defects should be displayed more intuitively, so that the defect-related feature information can be automatically extracted and identified." Chen Hua said, the visualization of defects is beneficial to The engine is well analyzed and processed to meet the needs of fast, efficient automated testing in the future.
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