The frame is the key bearing part of all kinds of rolling mills. When rolling products, all kinds of rolling mills need to use the frame as support to bear all the rolling force. Common rolling mill stands include thin plate rolling mill, medium plate rolling mill, thick plate rolling mill, roughing mill, finishing mill, hot rolling mill, cold rolling mill, continuous rolling mill, semi continuous rolling mill, round billet rolling mill and square billet rolling mill. The specification of the rolling mill can be expressed by the roll body length of the rolling mill, for example, the roll body length of the cold rolling mill. The length of the roll body determines the specification of the frame, while the specification of the rolling mill reflects a country’s ability in manufacturing ships, ships, nuclear facilities and oil and gas transmission pipelines, and reflects a country’s level in heavy equipment manufacturing.
From the design point of view, there are many problems in theproduction process of car machine frame, such as complex structure, large amount of drawings and difficult design. Many influencing factors need to be considered in the design. While considering that various performance indexes can be qualified and the process is reasonable, the actual production cost must also be considered. At present, because enterprises and scientific research institutes generally use computer-aided design, the labor intensity of designers is greatly reduced, so the accuracy of design is greatly improved.
In the actual sand casting production process of the rolling mill, due to the characteristics of large section size, poor fluidity of pouring metal, thermal expansion and cold shrinkage and limitations of sand, there are several technical difficulties in the sand casting production:
1) The section structure of the blooming stand is thick and large, and the solidification time of sand casting is long. Therefore, the crystalline structure after solidification is coarse and the component segregation is serious, so the crack trend is also greater than that of other types of sand casting.
2) The flaw detection requirements of the whole part of the frame are high, especially the arc of the window in the frame and the area of the rolling line are not allowed to have welding repair. However, in the production process, variousdefects are particularly easy to appear at the arc. Therefore, sand casting production is more difficult.
3) During the pouring and filling process of the frame, the rising speed of molten steel is slow, and the baking of the upper box molding sand is strong, which makes the sand falling tendency of the sand mold larger. Therefore, in the molding process of molding sand, the requirements for the fire resistance of molding sand are high, and the appropriate molding sand must be selected as the mold.
4) During the sand casting process of the frame, when the sand casting is fed only by the riser, the feeding distance is not enough, and there will be shrinkage cavity and loose area in the column of the window. Therefore, it is also necessary to set external cooling iron to control the sequential solidification in the molding of sand casting.
Therefore, various influencing factors must be considered in the casting process of cast steel frame of large rolling mill. Fully consider factors such as reducing operation difficulty, reducing production cost and shortening production cycle.
In recent years, with the help of computer numerical simulation technology and visual graphic analysis, the production cost of sand casting can be effectively saved and the production cycle of large sand casting can be shortened. A series of research work has been carried out by using numerical simulation technology. Zhang Lei and others used ft star and ideas software to simulate and analyze the temperature field, thermal stress and strain changes of sand mold casting for double plate mill stand of Masteel, and designed a reasonable sand mold casting process scheme for actual production. Through the comparative analysis of the stress-strain state of the original structure and defective structure of a steel rolling frame by using the finite element method in Yaohe Province, a reliable theoretical basis is provided for its continuous production and use. Gong Ruchang used Huazhu software to conduct numerical simulation analysis on the designed sand mold casting process scheme. Finally, according to the simulation results, the sand mold casting process scheme was reasonably adjusted.
For the sand casting of large and super large steel castings, the filling, solidification and stress distribution of liquid metal in the process of sand casting are analyzed by using numerical simulation technology, which can effectively avoid the defects of sand casting and improve the quality of sand casting. At present, the numerical simulation technology of sand mold casting process has become the research hotspot of many enterprises and scientific research institutes.