Cover the quartz sand on the gear when using the electric furnace
The pre-furnace treatment spheroidization rate should reach 12, avoiding the appearance of worm-like graphite and dendritic graphite in the structure. Strengthening the inoculation treatment to increase the number of graphite balls, improve the roundness of the graphite balls, refine the eutectic group, thereby reducing the segregation and harmful effects of Mn, so that the number of white bright regions in the tissue is less than 5. The second inoculation treatment is carried out by using 0.20.4SiCa or SiFe plus a small amount of Bi, and the effect is better. Strictly control the casting process to avoid shrinkage and inclusion defects in the gear blank.
Austempering in the heat treatment process parameters, austenitizing temperature (Tr) and equal quenching temperature (TA) are two key factors determining the structure and performance. Austenitizing temperature. Under the premise of ensuring a single austenite structure, proper reduction of Tr can reduce the white bright area in the tissue and refine the bainite structure. Oxidative decarburization of the gear should be prevented. When using an electric furnace, the gear can be covered with quartz sand; when a salt bath furnace is used, the surface of the salt bath can be covered with graphite powder to cause a reducing protective atmosphere.
Austempering temperature. The quenching temperature determines the morphology, distribution, size and retained austenite content of the bainite in the structure. The final determination of the mechanical properties of the material. The production should be selected according to the chemical composition, wall thickness and service conditions of the gears, in order to minimize the white bright areas in the tissue and refine the bainite structure. Cummins engine timing gears use a medium frequency induction furnace to melt molten iron. At 1500e, the furnace is pre-fired, and a horizontal continuous casting machine is used to make ductile iron bars ([80mm, [105mm]) as the blank for the production of timing gears. Because the spheroidal iron bar has a high crystallization rate during continuous casting, the number of graphite balls in the structure is large, the spherical diameter is small, and the eutectic group is refined, which is beneficial to reduce the segregation of manganese. Therefore, the amount of manganese can be relaxed to about 0.7, and manganese can be used to improve. Hardenability of the material. Compared with sand casting gear blanks, continuous casting bars have no macroscopic casting defects and stable product quality. They are high-quality materials for making gear blanks, especially suitable for the production of small-sized gears.
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