Alloy steel pipe casting mandrel features

The used mandrels of alloy steel pipes are sent back to the roller table to be cooled, lubricated, and then pre-inserted into the pipes to be put into use again. During production, a group of mandrels (6 to 7) are also required to work in turn. The number of mandrels in each group is related to the productivity of the rolling mill and the return and transportation of each mandrel, cooling to the required temperature, lubrication and pre-insertion. The required time is related and can be determined by calculation method. The stop mandrel mill is suitable for the production of medium-sized seamless steel pipes. Reduced tool consumption. Compared with the mandrel of the floating mandrel continuous rolling mill, the mandrel rod of the stop mandrel continuous rolling mill is much shorter, so that the mandrel consumption per ton of steel pipe is reduced to about 1kg. Improved the quality of the steel pipe. Due to the nature of rolling (relative movement between the mandrel and the inner surface of the steel pipe) of the mandrel-restricted mandrel rolling mill, it is beneficial to the extension of the metal. In addition, it has a micro-tension rolling state, thereby reducing the lateral deformation, and there is no floating at all. The "bamboo" phenomenon caused by continuous mandrel rolling; at the same time, the closed circular hole type is adopted to reduce the lateral flow of the metal, and the inner and outer surface and dimensional accuracy of the alloy steel pipe have been greatly improved. The wall thickness deviation of the steel pipe produced by the mandrel-restricted continuous pipe rolling unit reaches ±4% to ±6%. Energy is saved. The deformation distribution mode and rolling characteristics of the mandrel-restricted continuous tube rolling mill have created favorable conditions for energy saving.

The deformation of the continuous rolling tube is large, and the deformation of the piercing machine is small, so that the continuous rolling mill can provide the pierced capillary with large wall thickness and small temperature drop. The contact time between the stopper mandrel and the waste pipe is short, so as to ensure that the temperature of the waste pipe after rolling is high and the temperature is uniform. At the same time, because the stripping machine is eliminated, the process flow is shortened, and the final rolling temperature of the alloy steel pipe is increased, and some varieties can be saved. Eliminates the reheating process before sizing, thus saving energy.

The existence of any form of shrinkage cavity in the alloy steel pipe will significantly reduce the mechanical properties of the casting because they reduce the effective area of ​​the force and generate stress concentration at the shrinkage cavity. Due to the existence of shrinkage holes, the air tightness and physical and chemical properties of alloy steel pipe castings are also reduced. Therefore, shrinkage cavity is one of the important defects of castings and must be eliminated.
Shrinkage cavities and shrinkage porosity During the solidification process of castings, if the liquid shrinkage and solidification shrinkage cannot be compensated in time, holes will be formed in the corresponding parts, that is, the formation of shrinkage cavities or shrinkage porosity. The formation process and conditions of shrinkage cavities have large shrinkage cavities, which are mostly concentrated in the upper part of alloy steel pipe castings and the final solidified part.

Now take the cylindrical casting as an example to analyze the formation process of shrinkage cavity. Assuming that the poured metal solidifies at a fixed temperature, or the crystallization temperature range is very narrow, the casting solidifies layer by layer from the surface to the inside. Supplement, therefore, the cavity is always filled with molten metal during this period. When the temperature of the casting surface drops to the solidification temperature, a hard shell solidifies on the surface of the casting and tightly wraps the liquid metal inside. The ingate is frozen at this point.

Shrinkage cavities often occur in the thick part or the last solidified part of the upper part of the alloy steel pipe casting, often in the shape of an inverted cone, and the inner surface is rough. In the formation process of shrinkage cavity, after the liquid alloy fills the alloy steel pipe casting cavity, the temperature of the liquid alloy drops due to the heat absorption of the casting mold, and the metal near the surface of the cavity solidifies into a shell. The shrinkage of the molten metal is hindered by the outer casing, and the alloy steel pipe cannot be fed, so the liquid level begins to drop.

The temperature continues to drop, the outer shell thickens, and the remaining liquid inside shrinks due to the shrinkage of the liquid state and the shrinkage of the supplementary solidified layer, which reduces the volume and the liquid level continues to drop. This process continues until the end of solidification, shrinkage holes are formed in the upper part of the casting, the temperature continues to drop to room temperature, and the outer contour size of the casting is slightly reduced due to solid-state shrinkage. Alloys of pure metal and eutectic composition are prone to form concentrated shrinkage cavities.