X-ray nondestructive testing is used for casting quality inspection

Date：2022-02-28 14:22:00Views：979

Casting is one of the basic processes of modern machinery manufacturing industry. It has the advantages of low cost, one-time forming and can manufacture large parts with complex structure. It is widely used in many fields of industrial production, such as automobile parts, machinery manufacturing, electronics, medical devices, clocks and watches, hardware products, aviation and aerospace. X-ray nondestructive testing has become the main method of casting defect detection because it can avoid material waste and improve production efficiency.

Porosity is one of the common defects in precision casting. Air hole refers to the defect of smooth hole in individual position of precision casting. Pores are usually found after machining. Porosity in castings will destroy the continuity of metal; Less effective bearing area; It is easy to cause stress concentration near the pores, which reduces the mechanical properties; Dispersion holes can also lead to a decrease in air tightness.

In most cases, the porosity in the casting is mainly due to the incomplete baking of the precision mold shell. When pouring molten steel, a large amount of gas is generated in the mold shell, which can not be discharged smoothly, and then invades into the metal water to form pores. There are also reasons for shell making process or shell material. The gas permeability of the shell is too poor, and the gas in the cavity is difficult to discharge, and it enters the molten metal to form holes. The air sucked into molten steel during pouring cannot be discharged, resulting in casting holes.

The gas intrusion hole of the casting is formed because the gas accumulated on the surface of the sand penetrates into the liquid metal, and the mold material contains various additives, such as water and binder. Most of these pores are located near the surface, with large size, oval or pear shape, and the inner surface of the pores is oxidized. In the pouring process, part of the water vapor is discharged from the exhaust hole on the parting surface, and the other part accumulates on the surface to form a high-pressure center point. When the air pressure rises and melts into the metal, some of them will escape from the molten metal, and the rest will form holes in the casting.

The air hole inside the casting cannot detect the defective product through surface observation, and nondestructive testing is required to determine its quality. The accuracy of castings obtained by various casting methods is different, the initial investment and productivity are also inconsistent, and the final economic benefits are also different. Therefore, in order to become more, faster, better and cheaper, it is necessary to continuously improve the production process to control the casting quality and reasonably select the casting alloy and casting structure.

How to reduce the occurrence of Blowholes in castings in the production process? When the conditions of precision casting permit, exhaust holes shall be set at the higher parts of castings with complex structure; When designing the gating system, the exhaust requirements of the shell should be fully considered; The baking temperature and time of the shell shall be reasonable, and the holding time shall be sufficient; Wax shall be completely removed during dewaxing; Properly reduce the distance between the ladle nozzle and the gate cup, and the pouring speed should be uniform to ensure that the steel fills the cavity horizontally and stably, and draw as little air in the molten steel into the cavity as possible; Molten steel can be discharged smoothly.

In addition to taking certain preventive measures, the control of casting quality also needs to select appropriate quality inspection equipment. X-ray casting porosity detection equipment is very suitable for the detection of internal defects of castings. X-ray can penetrate the castings and image the interior of castings in real time. Through the software defect automatic identification system, the defect position and size are directly marked on the detection image. The detection effect is intuitive and will not damage the castings themselves. It is an effective nondestructive testing method.

The above is the content introduction of "X-ray nondestructive testing for casting quality inspection and analysis". Due to the complex casting process, there are many factors affecting the casting quality. Lax control of raw materials, unreasonable process scheme, unreasonable die structure design and improper production operation will cause various defects of castings. The common defects include inclusions, bubbles / pores, looseness and cracks. In order to ensure casting quality and save cost, it is necessary to detect defects in time in the early stage of production process.