Visual inspection is one of the important methods of nondestructive testing. It only refers to a detection method that uses human eyes or optical instruments to observe or measure the surface of industrial products. Typically, the visual detection is limited to the visible light range of the electromagnetic spectrum.
Visual inspection can be divided into direct visual inspection and indirect visual inspection. Direct visual inspection refers to the inspection of the test piece directly with human eyes or with a magnifying glass with a magnification of fewer than 6 times. Indirect visual inspection refers to the direct observation of areas that cannot be observed directly with the help of various optical instruments or equipment, such as reflector, telescope, industrial endoscope, optical fiber, or other suitable instruments.
There are many kinds of visual inspection instruments, and an industrial endoscope is one of them. The detection of Zui of the endoscope has been used for medical examination of the human body. Since the 1950s, it has gradually entered the field of industrial detection, and a special industrial endoscope has emerged. From the 1970s to 1980s, China began to introduce industrial endoscope products from abroad, which are mainly used for the internal excess control of aerospace products and the quality inspection of some parts. In recent years, domestic endoscopic testing has entered the practical stage, more and more used in product quality control, and developed into a new testing method.
Endoscopic inspection is a widely used inspection technology with the development of endoscopic manufacturing technology in recent years. Endoscope detection requires the use of an industrial endoscope (hereinafter referred to as an endoscope) as a detection tool. The industrial endoscope is specially designed and produced to meet the requirements of the complex industrial environment. According to the characteristics of the manufacturing world, we generally divide the endoscope into three types: straight rod mirror, fiber optic mirror, and video mirror. Three types of sex
There are many types of endoscopes, and different types of endoscopes have different application ranges. In addition to considering the type of endoscope, it is also necessary to consider the technical indicators such as probe diameter, length, visual direction, and focal length. At the same time, due to the complex service environment of the endoscope, it is necessary to consider its waterproof, oil-proof, corrosion-resistant, and wear-resistant properties. Generally, the type of endoscope to be used shall be determined according to the specific location and requirements of the detection object. At least the detection location, direction, Zui small resolution requirements, access, measurement records, etc. shall be considered. Complex products often require the use of multiple models. Generally, we believe that the straight rod mirror is easy to use, durable, and has a good imaging effect. It is mostly used for products that do not need bending and the detection range is within 500mm. It is suitable for the detection of straight holes. The video mirror has many functions, flexible use, high reliability, and wide applicability. It is suitable for various products with complex internal structures or occasions requiring quantitative detection and comparative analysis. However, due to manufacturing technology, the CCD chip on the probe cannot be made very small, making it difficult for the probe diameter to be less than 4mm. Video mirrors can replace straight rod mirrors and optical fiber mirrors. The fiber optic mirror is easy to be damaged, has a short service life, and has the poor definition. The imaging effect and bending performance are far inferior to that of the video mirror, but its diameter can be made very thin. It is mostly used for products with an inner diameter of less than 4mm and cannot be detected by the video endoscope.
The main factors affecting endoscopic detection are:
1. Lighting conditions. Endoscope detection mostly uses its own light source for illumination. Under normal conditions, the color temperature of the illumination light source detected by the endoscope shall not be less than 5600k and the illumination intensity shall not be less than 2600lm.
2. Probe position and angle. The image effect is usually observed within 5 ~ 25mm from the detection area, so the endoscope probe is often required to be close to the observation point as far as possible. The probe and observation object plane can achieve a good observation effect in the range of 45 ゜ ~ 90 ゜. In practical work, the appropriate observation position is found by repeatedly changing the position and angle of the probe and observation point, and a Zui good detection effect is obtained.
3. Access. When selecting the channel, it shall be as close as possible to the position to be detected, and the channel with short access length Zui shall be selected to minimize the number and degree of bending of the probe; First, consider the channel from top to bottom and from high to low; Give priority to wide channels; It is recommended to use tooling to ensure the correct direction of the probe in the product channel; The method of observing while passing shall be adopted to travel in the channel.
4. Image distortion. Observe the deformation of the object through the lens. With the increase of the distance from the center to the edge of the lens, the image will be distorted. Image distortion will affect the judgment and measurement of defects. When observing with straight rod mirror and optical fiber mirror, the image distortion is large, and the video endoscope can be corrected by the computer.
5. Resolution, magnification, and detectable Zui small defects. These are the technical indicators of the endoscope itself, which can directly affect the detection results.
6. Reflectivity of the object surface. Different object surfaces have different reflectivity, which is related to the material and surface roughness of the object. Therefore, the intensity of endoscope illumination should be selected according to the specific situation in order to obtain clear and useful results.
5、 Application of industrial endoscope in the industrial field
The detection range of industrial endoscope is given in qj2859-1996 operation and use methods and judgment rules of industrial endoscope:
(1) Lumen examination. Check the surface for cracks, peeling, pull wires, scratches, pits, bulges, spots, corrosion, and other defects.
(2) Weld surface defect inspection. Check the weld surface for cracks, incomplete penetration, and weld leakage.
(3) Assembly inspection. When required and required, use an endoscope to check the assembly quality; After assembly or a process is completed, check whether the assembly position of parts and components meets the requirements of drawings or technical conditions; Whether there are assembly defects.
(4) Status check. When some products (such as worm gear pump, engine, etc.) work, endoscopic inspection shall be carried out according to the items specified in the technical requirements.
(5) Excess inspection. Check the residual debris, foreign objects, and other residues in the inner cavity of the product.
(6) Dimensional measurement. The dimensions to be measured can be measured with a measuring probe.
(1) Crack. When the light beam irradiates the surface of the tested object and black or bright lines are observed, and the lines have irregular edges under a certain magnification, it is determined as a crack. When the crack is wide, the measuring influence line of the measurable probe will bend.
(2) Peeling. When the beam is irradiated in parallel, a shadow behind the convex part is observed; Changing the beam irradiation angle, it is observed that there is an obvious boundary between the convex part of the surface and the surrounding detected object, which is determined as peeling.
(3) Cables and scratches. Under the irradiation of light beam, regular continuous long lines are observed on the surface, which is determined as stay wire.
(4) Pit bulge. When the beam is irradiated at a certain angle, it is connected with the boundary of the surrounding tested object without a boundary. There are shadows near the light source and bright shadows far away from the light source, which is pits. When the beam is irradiated at a certain angle, it is connected with the boundary of the surrounding tested object without a boundary. The convex part has a bright shadow, and the back shadow is a pit. When the pit is deep or the bulge is high, the measuring line of the measurable probe will be bent.
(5) Spots. When the light beam is irradiated, it is observed that the smooth non-concave convex surface with different colors from the surrounding tested object is spotted.
(6) Corrosion. Under the irradiation of light beam, it is observed that the block and the point-shaped unsmooth surface are slightly uneven at a certain magnification, which is corrosion.
(7) Incomplete penetration. It is observed that there is an obvious boundary between the molten metal and the base metal and the weld layer.
(8) Weld leakage. When the beam is irradiated at a certain angle, it is observed that the bulge connected with the molten metal without boundary is welding leakage.
(9) Excess. When the beam is irradiated at any angle, there are objects other than structures that are different from the color and brightness of the surrounding basic tested objects.
(10) Assembly defects. During the inspection, structural phenomena that do not meet the technical conditions of the drawing are observed.