Gray iron castings have the shape of flake graphite. Due to the presence of flake graphite, the metal matrix structure is split and the effective bearing area is reduced. Therefore, its comprehensive mechanical properties are low, but its vibration damping, wear resistance, castability and cutting processability are good. It is mainly used to manufacture parts that bear pressure such as lathe beds, boxes, machine bases, and guide rails. The grade of gray iron casting is represented by "HT" plus a number, where "HT" is the Chinese pinyin letter of gray iron casting, and the number indicates the tensile strength.
The basic feature of high-density molding sand for gray iron castings is that the amount of pulverized coal added is also low. Therefore, here are a few things you should keep in mind when preparing sand.
①Clay content and mud content. For molding sand with high clay content, the strength of gray iron castings increases as the specific pressure increases, and the effective bentonite is usually controlled at 7% to 10%. The sum of effective clay and dead clay in molding sand is equivalent to the mud content, which is generally controlled at 12% to 16%. Too high or too low mud content will affect the performance indicators of gray iron casting sand.
②Moisture. The moisture in the lost foam casting sand is the main factor that determines the plasticity and bonding strength of clay. When the moisture content is too high, the cohesion of the clay will easily deteriorate, the fluidity of the molding sand will decrease, and a uniform mold density cannot be obtained. When the moisture content is too low, the molding sand is not easy to mix, and the strength of the molding sand is low, brittle, and has poor demoulding properties, which can easily cause sand sticking defects in gray iron castings. Generally, the moisture content should be controlled to be 10% to 20% higher than the moisture content when the peak wet compressive strength is reached.
③ Original sand particle size. In high-density molding, gray iron castings have higher density and greater expansion when poured. Therefore, the original sand particle size should not be too concentrated. Raw sand particles are round or polygonal. Generally, three sieve sand or four sieve sand are used.
1. A small amount of carbon can be added to the raw materials. Among the carbon contents of gray iron castings, the carbon content is mostly 2.6% to 3.6%, and the silicon content is 1.2% to 33.0%. When determining the wall thickness of gray iron castings, an appropriate amount of manganese should also be added.
2. Use alloying method to improve the tensile strength of gray iron castings. Adding appropriate amounts of trace alloys, chromium, molybdenum, tin and other elements can also significantly improve the tensile strength of gray iron castings, and the molten iron must be properly treated.
Contact Person: Mr. Fred Zhang
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