SAND CASTING EQUIPMENT.

Recently, a colleague from a foundry asked that the steel castings produced have more cracks after cutting or adding risers. What is the reason?

Xinyuanzhu Group makes the following analysis based on its own casting experience.
In the production of cast steel, if the casting cracks only occur near the cutting riser, the general reason is the low cutting temperature. Therefore, cut the riser as eagerly as possible, or cut after tempering. If the process permits, change the riser to one size smaller, this kind of problem can also be greatly reduced or eliminated.
For the cracks that appear after processing, or the cracks found in the steel castings after nondestructive testing, it may be caused by the following reasons:
1. The steel casting is relatively thick. After the molten steel is poured into the mold, the outer part of the casting cools quickly and the inside is slow. The internal solidification is accompanied by volume shrinkage. At this time, the surface part has already solidified, so the stress cannot be relieved by plastic deformation. When the stress exceeds the after-resistance strength of steel castings, cracks are prone to occur. Due to the different stresses in different parts, the tensile strength is different, cracks are generated in the weak places, and finally many cracks are formed.
2. There is a large gap between the thickness of the steel castings, or the uneven flow of molten steel in the cavity, which can easily cause cracks in the steel castings. For such steel castings that are prone to high stress, aging heat treatment should be carried out in time. Of course, the best way is to consider the large wall thickness difference when designing the casting. So the problem is solved at the beginning of the process design. For cracks caused by uneven flow of molten steel, one is to increase the flow rate of molten steel, and the other is to increase the pouring temperature within the range allowed by the process.
3. Adopt refining process to effectively remove oxidized impurities and gases in molten steel, conduct follow-up tests on molten steel from time to time, control the content of harmful impurities in molten steel, and produce in strict accordance with the chemical composition control range required by cast steel grades. Can well prevent cold cracks. Fourth, the process design must ensure that the molten steel solidifies at the same time. This can prevent hot cracks and also avoid cold cracks. Therefore, when setting the position and size of the riser, the cooling rate of each part of the casting should be kept consistent to reduce the tendency of cracks. In addition, it is necessary to allow the steel castings to have enough cooling time in the sand mold to prevent the steel castings from cooling too quickly due to the premature grilling of the box and causing cracks.
Xinyuanzhu Group specializes in the production of gray cast iron and ductile iron, which can undertake mass casting production and processing. Guests are welcome to visit the factory.