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Casting technology of large copper alloy propeller

Views: 28     Author: Site Editor     Publish Time: 2020-04-20      Origin: Site

In recent years, with the vigorous development of shipbuilding industry in the world, the tonnage of shipbuilding is increasing obviously, which leads to the weight of marine propeller is also increasing. The casting technology of large propeller is very complicated due to the heavy load on the propeller when it is running in the sea water, the strict requirements on the casting mechanical properties and quality, and the complicated curved surface structure of the propeller blade.

Casting process design

Modeling method

Because the shape of propeller blade is complex and the outline size of super-large propeller is too large, the whole molding technology is very important and the molding quality is not good. Therefore, the modeling process of propeller is particularly important. At present, the modeling of propellers is usually done by digital display pitch gauge, cross section template, angle line template and hand molding, and the sand mold data are laid out by CAD computer. These data must consider the deformation law of the casting, the shrinkage characteristics of the alloy, and the appropriate machining allowance. After making the sand mold, the section template and angle line template are used to check the blade size to ensure that the data meet the requirements.

Rate of contraction determined

The blade is wide and the blade thickness is uneven. The Blade and the maximum thickness are 336 mm, and the tip of the blade is only 22 mm. The difference is so great that the casting temperature and cooling speed are different, the casting shrinkage is serious and the deformation is different, the factors and rules that influence the deformation are not completely clear. The leading edge is concave down and deflected upward, the blade is twisted and the pitch is small. Therefore, the linear shrinkage of 0.2 ~ 0.4 R, 0.5 ~ 0.7 R, 0.8 ~ 1.0 r and 1.5% overall linear shrinkage are required.

Determination of processing capacity

In order to reduce the surface defects of the castings and obtain the castings with qualified size and good surface quality, it is necessary to add the machining allowance. The machining allowance for the Blade is determined as follows: No machining allowance for the Blade Surface; No machining allowance for the Blade Surface; the machining allowance for the blade back is shown in Fig. 1; the guide edge and the machining allowance along the edge are 20 mm; the outer circle of the hub is 10 mm; The machining allowance of inner hole of hub is 15mm, the big end of hub is 15mm longer, and the small end is 10mm longer.


Fig. 1 Blade Back Allowance

GATING riser determination

Because the propeller material ZCuAl9Fe4Ni4Mn2 contains more AL, it is easy to form secondary oxide slag in the pouring process, so whether the pouring system can guarantee the metal liquid filling smoothly should be considered in the design of the pouring system, it should have reasonable pouring speed and slag removal ability to prevent the occurrence of turbulence phenomenon. The bottom gating system is usually used, and the section ratio of the general gating system is straight: Horizontal: 1:2 ~ 2.5:10 ~ 30. Because of the large gross weight of the casting, two 60mm sprue and 2660mm Ingate are used.

The overall shrinkage of the copper alloy propeller is about 1.5% , so the riser design is also very important. Usually, the riser height is 0.6 ~ 0.8 times of the hub height.

Drying and cooling

The hot air blower is used to dry the mold, which is mainly to reduce the moisture content in the molding sand, to reduce the excessive moisture content in the molding sand, and to produce the defects such as blowhole and oxidation slag in the casting process. In order to evenly bake the mould, the air outlet at the tip of the blade is opened at the lowest point along the blade edge, and the mould is kept at 150 °C for about 24 hours to ensure that the air outlet temperature is not less than 40 °C. As the blade has a large thickness gradient, the cooling time of each part will be different. In order to ensure that the casting has sufficient strength, the casting after pouring heat preservation is not less than 120 hours, when the temperature dropped to 300 °c, to open the box. By prolonging the cooling time, the casting can release the casting stress sufficiently to prevent the blade from deforming due to the large temperature gradient.

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