As an important part of marine engine, 6T cylinder block has very strict technical quality requirements, excellent tensile strength, high temperature impact resistance and no three leakage problem. Our company adopts sand coated iron moldof 1 piece / mold to produce six cylinder block (i.e. 6T cylinder block), and the casting structure is shown in Figure 1. The product size is 1203 * 403 * 616. The wall thickness of the thinnest part of the casting is 5mm and the thickest part is 30mm. The weight of casting blank is 513.5kg.
(1) By adding an exhaust casting porosity to the sand core head and sealing the core head with a box sealing strip, the molten iron can be prevented from going deep into the casting porosity of the core head during pouring, so as to ensure the smooth exhaust of the sand core head and reduce the casting porosity of the casting.
(2) By appropriately increasing the cross-sectional area of the inner gate of the original gating system, a semi closed and semi open gating system is formed. To meet the rapid casting requirements of iron mold sand coated casting, the porosity of the casting can be reduced.
(3) After reasonably optimizing the layout of the exhaust needle, the exhaust of the upper half casting can be reduced and the casting porosity can be reduced
(4) Adding stiffeners to the water jacket sand core can not only ensure the rigidity between the two layers of wall thickness of the casting, but also reduce the exhaust of medium cavity gas in the casting process, and reduce the cold shut-off and casting porosity of the casting.
(5) For the boss on the top surface, because the local boss is very close, it is not convenient to arrange the casting porosity needle. The process subsidy method of adding an exhaust slot between the two bosses can reduce the casting porosity of the casting.
In 2019, 69 gas cylinders were produced since the trial production of samples, and 28 were rejected due to casting porosity, with a rejection rate of more than 41%. In this paper, the corresponding process measures and methods are taken from the aspects of increasing exhaust needle, increasing inner gate, increasing exhaust groove and stiffener, and the formation mechanism of casting porosity is analyzed to solve the porosity defects of six cylinder (6T) cylinder block castings.