What are the respective consequences of thermal aging and natural aging on large cast iron platforms?
The molding of large cast iron platforms adopts the iron mold sand coating process, with the material being QT450-10 and a hardness of HB160-210. Large cast iron platforms belong to ferritic matrix ductile iron.. In addition to requiring the tensile strength and elongation of the material to meet standards, the hardness of the casting must also be ≤HB200. Carbon (C) promotes graphitization,

Large cast iron platform thermocouples are connected to a multi-point thermometer using compensation wires. The multi-point thermometer is connected to a computer to activate the melting block. The space between the melting block and the mold is filled as much as possible with small pieces of returned material, and the melting block is filled to more than half its height. According to the first furnace charge ratio, pig iron, returned material, and scrap steel are added to fill the furnace. The charge should be small, clean, rust-free, and free of sand and soil. Install gas burners. Gas nozzles are installed at the slag removal port and furnace mouth to ignite the gas and preheat the slag removal port and furnace mouth.
Large cast iron platforms have a tensile strength of ≥250 N/mm2 and a hardness of HB=190~240, fully complying with the chemical composition standards of HT250 and meeting the quality requirements for machine tool beds in mechanical performance tests. Large cast iron platforms are produced using resin sand and lost foam casting, with single pieces weighing over 40 tons and an annual production of around 8,500 units.
Silicon in large cast iron platforms lowers the liquidus line. With a fixed carbon equivalent, increasing the silicon content relatively increases the superheat of the molten iron at the same pouring temperature, enhancing fluidity and facilitating the formation of large cast iron platforms. These are some of the many roles silicon plays in promoting graphitization.
During the shell molding process, appropriately reduce the moisture content of the molding sand for large cast iron platforms and increase its fluidity. Verification has shown no increase in porosity due to higher molding pressure. For sand cores, increasing the number of vent grooves on the core box parting surface and appropriately deepening the vent grooves improves the quality of the sand cores.
Molding sand for large cast iron platforms: Uneven grain size distribution of the base sand can result in low compactness of the sand mold. The grain size distribution of the base sand directly affects the compactness of the sand mold. The fluidity and formability of the molding sand are poor. If the resin coating on the shell sand is too thin, it can reduce the local strength of the shell and leave some sand grains uncovered by resin, often causing sand-related issues in large cast iron platforms. Excessive permeability of the mold is another reflection of overly coarse sand grains. Permeability and compactness are interrelated factors. Lower compactness results in better permeability. Insufficient carbon materials or deoxidizing substances in the molding sand can produce excessive metal oxides, which wet the sand grains and make them more prone to penetration.
After pouring the blank, remove the pouring gate iron mold of the large cast iron platform, detach the box clamps, and move the iron mold to the knockout machine. When the timer sounds, open the box, align the knockout machine's ejector pins with the sand shooting holes of the iron mold, perform knockout, and remove the sand. Transfer the blank to the cooling area using a transfer cart, arranging each batch neatly. Move the iron mold after sand removal to the cleaning process, remove residual waste sand from the box, ensure no residual waste sand remains in the sand shooting holes, and keep the iron mold's sand-coated surface clean and flat. Move the cleaned iron mold to the cooling process. After water spraying, the temperature of the iron mold must be measured, and it should be moved to the next process only when it meets the required temperature.
Place three thermocouples at the bottom, middle, and top positions, and protect them with iron pipes or angle steel so that they can be retrieved and reused before the melting of the iron charge begins. Casting high-hardness inspection platforms requires a good electric furnace. Below are details on selecting an electric furnace for large cast iron platforms: Install thermocouples for starting the melting process. Place three thermocouples at the bottom, middle, and top positions, and protect them with iron pipes or angle steel so that they can be retrieved before the iron charge melts, for reuse.
Weiyue Machinery, Ms. Xie, 15350773479