How to prevent stainless steel casting cracks?

Aluminum alloy die-casting parts are used for most important parts of hydroelectric generator sets. This type of material has weak forging characteristics, poor circulation, large body and line shrinkage, high welding stress, and is very easy to cause cracks. Once the castings cause cracks, not only the maintenance labor will be large, but the more serious ones will also be reported, resulting in serious property losses. The main causes of casting cracks are the casting structure, forging process, etc. The following countermeasures are generally used to prevent in many aspects:

1. Casting structure

When forging, it is necessary to take into account the structure, appearance, large and medium-sized, wall thickness and connection of the castings and other factors that endanger the liquid and solid gathering of the castings, and select the appropriate main parameters of the processing technology to avoid welding defects such as shrinkage casting defects. The design of the pouring and riser control system for castings must be effective. If cold iron and other processing techniques are to be used, the location must be effective. It is necessary to ensure the high density of the internal mechanism of the castings and minimize the stress caused by the situation.

2. Smelter

In the whole process of the smelter, reduce the water content of harmful elements such as P and S as much as possible, and reduce the water content of vapor and impurities such as N, H, and O. According to the selection of low-phosphorus steel and intermediate aluminum alloy, it can have very good practical effects.

3. Thermal insulation

According to the moderate increase of the heat insulation time of the casting in the sand mold, the main operation is to control the unpacking temperature to be less than 70 ℃ to ensure that the casting is fully liquid and solid in the sand mold to prevent stress caused by external forces.

4. Falling sand

In the whole process of removing sand from castings, it is forbidden to pour sand molds and castings during boxing. It is forbidden to use impact methods such as box crashing to drop sand to prevent cracks caused by interaction of external force and thermal stress of castings .

5. Laser cutting riser

According to the standard of castings, select the appropriate hot cutting and pouring riser processing technology to ensure that the start and stop temperature of hot cutting is not less than 300℃. In actual operation, the oxygen cutting gun and the oxygen blowing tube are cut by vibration laser. After oxygen cutting the key parts, immediately cover the compartment with asbestos cloth or enter the furnace for quenching and tempering. For castings such as the upper crown and axial fan leaves, which have complicated structures and unique processing techniques, secondary thermal cutting is selected.

6. Heating

When solving the shortcomings of aluminum alloy die castings, we must persist in heating standards. When the blowing and welding process is solved, the steel parts must be heated to above 108°C for actual operation. If a large crack defect is found, the in-situ stress quenching must be carried out first, and then the solution will be carried out.

7. Improve quenching

Lift the heavy and extra-large aluminum alloy die castings once and finally remove the geostress quenching process, strictly control the heat insulation time and published temperature. Its purpose is to reduce the new stress caused by the machining process, to more completely remove the thermal stress of the casting, and to avoid cracks.