Discussion on Quality Inspection of Machinery Castings
Mechanical casting quality, including the inherent quality of mechanical casting, the appearance of quality, the use of quality. Its specific requirements, generally in the parts and related technical documents are clearly defined. In order to ensure the quality of mechanical casting, casting all aspects of production, especially after cleaning, have to carry out quality inspection. Any defective mechanical casting, after repair to meet the requirements, does not affect the user should be patched.
1, inspection of casting defects
1) Inspection of appearance defects When inspecting with defects such as cracks, surface pores and shrinkage, sticky sand and other defects exposed to the appearance of Machinery Castings with the naked eye or by means of magnifying glass and tip hammer, etc., use of measuring tools, molds and work Platform, etc. to check whether the size of mechanical casting drawings meet the requirements, with a variety of weighing tools to test whether the weight of the mechanical casting within the allowable deviation.
2) Surface defect inspection
① fluorescent detection method: the mechanical casting immersed in the fluorescent liquid, due to capillary phenomenon, the fluorescent liquid penetrate into the mechanical casting surface defects, and then remove the mechanical casting and wipe, placed in ultraviolet (mercury quartz lamp) irradiation. The use of fluorescent liquid by ultraviolet light irradiation principle, can determine the surface cracks and other defects in the site.
② coloring method: the use of the permeability of the liquid, the surface of the seized mechanical casting coated with a layer of good permeability of the coloring liquid (such as kerosene, acetone, paint and other mixture), until the liquid penetrate into the surface defects, wipe The surface of the coloring liquid, sprayed with a layer of zinc white and white display powder, then residual defects in the pores of the coloring agent was sucked to the surface to show the powder up, showing a defect shape.
3) Internal defect inspection
① ray inspection: mechanical defects can be found inside the castings, such as pores, shrinkage, cracks, inclusions and so on. Figure 2-10 shows the radiographic diagram. For important Machinery Castings, such as the defense industry with Class I Machinery Castings, generally have to go through 100% ray inspection. Commonly used rays are: X-rays and g-rays. The penetration of the former than the latter, but the sensitivity is higher than the latter, these rays can penetrate the metal, so that the film sensitive. When the ray penetrates the object, it interacts with the atoms in the object, and the energy of the ray is continuously absorbed and scattered to gradually decay. The higher the density of the object, the faster the energy decay, the density of the holes and inclusions in the Machinery Castings is much lower than the density of the metal. When the rays and these defects act, the attenuation is smaller and the energy on the film is larger than that of the defect- Can show the shape of the defect on the film.
② ultrasonic inspection: mechanical casting can also be found within the defects, such as pores, cracks, inclusions, such as loose. For steel castings, use this method to detect a maximum wall thickness (1000mm) of a method. Ultrasonic testing with the operating frequency often more than 1MHz. Ultrasonic waves propagate from one medium to another at the interface, especially when the ultrasound is transmitted from the metal to the air, almost 99% of the reflection from the interface back. Ultrasonic testing is the application of this feature to find the internal defects of mechanical casting. When the probe is moving slowly on the mechanical casting, if there is no defect in the mechanical casting, only the T wave reflected on the probe surface and the B wave formed on the bottom surface are reflected on the oscilloscope screen. If there is any defect in the part of the mechanical casting There is also a F-wave reflected by the defect, the greater the defect, the greater the height of the F-wave, which can determine the location and severity of the defect in the mechanical casting.
③ pressure test: the high pressure, vacuum with the Machinery Castings, such as pumps, valves, etc., need to do pressure test to check whether there is hole in the mechanical casting defects. When the test will have a certain pressure of air (or water, oil, etc.) into the sealed mechanical casting cavity, such as mechanical casting through the cracks, holes, etc., there will be leakage, and thus found the defect location. Test pressure is usually more than 30 to 50% of the mechanical casting working pressure, which is also a mechanical casting strength assessment. When the mechanical casting is not easy to form a sealed cavity, which can not be carried out pressure test, the method can be used to test the mechanical penetration of kerosene compact.
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