Sand casting of marine quadruple elbow valve box

The four-way elbow valve box is used in the seawater pipeline system of a submersible. The technical requirements of this kind of elbow valve box are: the valve box and the valve cover are connected together and the tightness test is carried out with 4.5 MPa hydraulic pressure. The brand of this kind of valve box was originally designed as tin bronze ZCuSn10Zn2. Because under the condition of sand casting, tin bronze could not bear such high requirements of hydraulic test, and the leakage rate was as high as 60%. In view of this situation, the design unit changed the brand of the four-way valve box to silicon brass ZCuZn16Si4 many years ago, which greatly improved the ability of the valve box to withstand the hydraulic test. However, for the silicon brass four-way elbow valve box, because the valve box structure is very complex, the oxide inclusions in the alloy liquid are difficult to float out of the riser, and the hydraulic test requirements are high, so the sand casting is still difficult. The sand casting process of marine quadruple elbow valve box was explored in order to provide guidance for the practical application of marine quadruple elbow valve box.

Silicon brass ZCuZn16Si4 is an alloy with high corrosion resistance, especially there is almost no corrosive cracking tendency. The castability of silicon brass is between tin bronze and aluminum bronze. Due to the low zinc content (about 16.5%), the oxidation tendency and evaporation of the alloy are small. Silicon brass has good fluidity and good volume shrinkage, so it is easy to obtain sand castings with dense structure. Because silicon brass ZCuZn16Si4 has high corrosion resistance and compact structure, it is widely used in sand casting of valve bodies working in seawater.

CuSiZnFeAlMnSbSnPbTotal impurities

See Table 1 and Table 2 for the chemical composition and mechanical properties of ZCuZn16Si4.


Silicon brass has strict restrictions on the content of impurities, such as Sn, Al, Mn, Fe and other strengthening elements of copper alloys, which are impurities in silicon brass. The brittle compounds formed by Sn are distributed on the grain boundary, which significantly reduces the mechanical properties, increases the intergranular porosity and reduces the air tightness; Al generates Al2O3 inclusions, and Mn significantly reduces the filling capacity, and affects the air tightness and mechanical properties of the alloy; Fe increases intergranular porosity [3]. Therefore, silicon brass is generally required to be melted in a special crucible, and the impurity content shall be strictly controlled during the melting process. In addition, the ductility and strength of silicon brass decrease at 400~500 ℃, which makes the alloy brittle. During sand casting, cracks should be prevented when passing through this temperature range.

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