Steel Casting Process Points
Castings are made of cast steel, similar to cast iron, but better than cast iron. Casting in the casting process prone to defects in the pores, the angle is not accurate and other shortcomings in the long-term use of the phenomenon may occur in the chassis fracture.
Cast steel for casting. A kind of cast alloy. Cast steel is divided into cast carbon steel, casting low alloy steel and casting special steel 3 categories.
① cast carbon steel
Carbon is the main alloying element and contains a small amount of other elements of cast steel. Carbon less than 0.2% for the casting of low carbon steel, carbon 0.2% to 0.5% of the cast carbon steel, carbon containing more than 0.5% for the casting of high carbon steel. With the increase of carbon content, the strength of cast carbon steel increases and the hardness increases. Casting carbon steel has a high strength, plasticity and toughness, low cost, heavy machinery used in the manufacture of heavy load parts, such as rolling mill rack, hydraulic machine base; in the railway vehicle for manufacturing force But also bear the impact of parts such as bolster, side frame, wheels and couplers and so on.
② cast low alloy steel
Contains manganese, chromium, copper and other alloy elements of cast steel. The total amount of alloying elements is generally less than 5%, has a large impact toughness, and through the heat treatment to obtain better mechanical properties. Casting low alloy steel has better performance than carbon steel, can reduce the quality of parts and improve the service life.
③ casting special steel
In order to meet the special needs of the refining of alloy cast steel, a wide variety, usually containing one or more of the high amount of alloying elements to obtain a special performance. For example, manganese containing 11% to 14% of high manganese steel to withstand impact wear, and more for mining machinery, engineering machinery wear parts; chromium or chromium nickel as the main alloy of various stainless steel, for corrosion or 650 ℃ above the high temperature conditions of the work of parts, such as chemical body, pump, container or large capacity power plant turbine casing. Inspection of surface and near surface defects of cast steel
1 Liquid Penetration Detection Liquid Penetrant Inspection is used to check for defects such as surface cracks, surface pinholes, etc. that are difficult to detect on the surface of a casting. Commonly used penetration testing is coloring detection, it is a high permeability of the colored (usually red) liquid (penetrant) soaked or sprayed on the casting surface, penetration agent into the opening defects inside, quickly wipe the surface permeate Layer, and then easy to dry display agent (also called the imaging agent) sprayed on the casting surface, to be left in the defect in the impermeable agent sucked out, the display agent was dyed, which can reflect the shape of the defect, Size and distribution. It is pointed out that the accuracy of the penetration test decreases with the increase of the surface roughness of the tested material, that is, the better the surface detection effect is, the surface detection accuracy of the grinder is the highest, and even the intergranular crack can be detected. In addition to color detection, the fluorescence penetration test is also commonly used liquid penetration detection method, it needs to configure the UV light irradiation observation, detection sensitivity than coloring detection.
2 eddy current testing eddy current detection is suitable for inspection of the surface below the general is not greater than 6 ~ 7MM deep defects. Eddy current detection points placed coil method and through the coil method 2 kinds. : When the specimen is placed in the vicinity of the coil with alternating current, the alternating magnetic field entering the specimen can induce the current (eddy current), eddy current, which is perpendicular to the excitation magnetic field in the specimen, Will produce a magnetic field opposite to the direction of the excitation magnetic field, so that the original magnetic field in the coil is partially reduced, causing a change in the coil impedance. If the surface of the casting is defective, the electrical characteristics of the eddy current will be distorted to detect the presence of defects. The main drawback of eddy current testing is that the detected defect size and shape can not be visually displayed. Generally, only the surface position and depth , In addition to the workpiece surface of the small opening defect detection sensitivity than penetration testing.
3 Magnetic particle detection Magnetic particle detection is suitable for the detection of surface defects and depth of several millimeters below the surface defects, it requires DC (or AC) magnetization equipment and magnetic powder (or magnetic suspension) in order to carry out detection operations. The magnetizing device is used to generate magnetic fields on the inner and outer surfaces of the casting, and magnetic or magnetic leas are used to show defects. When a magnetic field is generated within a certain range of the casting, the defects in the magnetized region produce a leakage magnetic field. When the magnetic powder or suspension is sprinkled, the magnetic powder is sucked, so that defects can be exhibited. This shows that the defects are basically cross-cutting magnetic field defects, parallel to the magnetic field lines for the long-type defects are not shown, for this operation need to constantly change the direction of magnetization to ensure that the unknown direction to check the various defects The
2 Detection of internal defects in castings For internal defects, commonly used non-destructive testing methods are ray detection and ultrasonic testing. Which is the best radiation test results, it can be reflected to reflect the internal defects of the type, shape, size and distribution of the visual image, but for large thickness of large castings, ultrasonic testing is very effective, you can more accurately detect the location of internal defects , Equivalent size and distribution.
1 ray detection (micro-focus XRAY) ray detection, generally with X-ray or γ-ray as a radiation source, so the need to produce radiation equipment and other ancillary facilities, when the workpiece placed in the radiation field irradiation, the radiation intensity of the radiation will be cast The impact of internal defects. The radiation intensity emitted through the casting varies with the size and nature of the defect, resulting in defective radiographic images, recorded by radiographic film, or by real-time detection by a fluorescent screen, or by a radiation counter. The method of recording by radiography is the most commonly used method, which is commonly referred to as radiographic detection. The defective image reflected by the radiography is intuitive, and the defect shape, size, number, plane position and distribution range are Can be presented, but the depth of defects generally can not be reflected, the need to take special measures and calculations to determine. Now the application of ray computed tomography method, because the equipment is relatively expensive, the use of high cost, is still not universal, but this new technology represents the future development of high-definition ray detection technology. In addition, a micro-focus X-ray system using an approximate point source can actually eliminate the blurring edges produced by larger focus devices, making the image outline clear. The use of digital image system can improve the image signal to noise ratio, to further improve image clarity.
Casting steel process points
The basic principle of the steel casting process: the high quality requirements of the surface or the main processing surface should be placed below; large plane should be placed below; thin part of the wall should be placed below; thick part should be placed on top; The number of cores; should be used as straight as possible parting surface.
The basic requirements of the steel casting process: Wood mold: complete contour, no cracks, no damage, no incomplete, smooth surface, size in line with the requirements of casting process drawings, and often size check. Sand box: the size of the sand box should be determined according to the specifications of wood, large and medium-sized sand box should be welded box.