Pressure resistance of die castings and methods to prevent defects

What is the pressure resistance of the die casting:

Most of the defects on die castings appear when grooves are opened in the casting or during machining. The reason is that the fine-grained layer structure on the surface of the casting is removed, exposing the coarse grained area extending to the center, and all the shrinkage cavities are located under this skin layer. Once there is a defect on the outer surface of the casting, the casting will leak under pressure. If the surface of the casting is not processed, its internal holes have no effect on the pressure resistance.

The molding temperature has a significant effect on the pressure resistance. The lower the molding temperature, the higher the pressure resistance. This is because a dense surface layer is formed on the surface of the casting at low temperatures. The fillet located at the junction of two or more intersecting surfaces is the part where the casting often leaks, because these parts are generally hot nodes in the molding, forming a thinner surface. Increasing the fillet radius will aggravate this phenomenon, because the molding temperature is higher at this time, and the surface of the casting will be thinner.

The type of casting alloy also has an impact on the pressure resistance, and aluminum castings are usually easier to leak than . Little is known about the leakage inside the casting or the leakage between two processing surfaces (the dense surface of the casting has been removed). It is likely that the type of holes (connected or disconnected) rather than the number of holes determines whether this occurs. leakage. On the whole, it is very difficult to manufacture large pressure-resistant castings, and most of the impregnation treatment is an indispensable process.

Methods of preventing defects in :

1) 1. Increase the mold temperature 2. Adjust the cross-sectional area or position of the inner runner 3. Adjust the speed and pressure of the inner runner 4. Choose the paint and adjust the amount appropriately

2) 1. Correct selection of die-casting mold materials and heat treatment process 2. Pouring temperature should not be too high, especially for high melting point alloys 3. Mold preheating must be sufficient 4. must be annealed regularly or after a certain number of die-casting, and polished surface

3) 1. The alloy should not be overheated 2. Increase the mold temperature and lower the pouring temperature 3. Strictly control the alloy composition within the allowable range

4) 1. For the proportion of alloy materials, pay attention to the impurity content not exceeding the starting point. 2. Adjust the mold opening time. 3. Make the push rod evenly stressed. 4. Change the unevenness of the wall thickness.

5) 1. Correctly control the alloy composition. In some cases: pure aluminum ingots can be added to the alloy to reduce the magnesium content in the alloy; or aluminum-silicon master alloys can be added to the alloy to increase the silicon content 2 and increase the mold temperature 3 , Change the casting structure 4, adjust the core pulling mechanism or make the push rod evenly stressed

6) 1. Add pure magnesium to the alloy to reduce the content of aluminum and silicon. 2. The mold temperature should be controlled within the required range. 3. Improve the casting structure to eliminate the cross section with large thickness changes. 4. Adjust the core and push rods to make them suffer. Force balance

7) 1. Ensure that the chemical composition of the alloy has the lower limit of the alloy elements: when the silicon brass is prepared, the content of silicon and zinc cannot be taken at the same time as the upper limit 2. Increase the mold temperature 3. Adjust the mold opening time appropriately

8) 1. Change the structure of the casting to eliminate metal accumulation and large changes in cross section 2. Lower the pouring temperature if possible 3. Increase the injection pressure 4. Improve the pouring system appropriately to make the pressure better.

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