There are many factors affecting the quality of metal marine castings, mainly including the following aspects:

First, the design process of castings. During the design, in addition to determining the geometry and size of the casting according to the working conditions and the properties of metal materials, the rationality of the design must also be considered from the perspective of casting alloy and casting process characteristics, that is, obvious size effect, solidification, shrinkage, stress and other problems, so as to avoid or reduce the occurrence of defects such as component segregation, deformation and cracking of the casting.

Second, there should be a reasonable casting process. That is, according to the structure, weight and size of the casting, the characteristics of the casting alloy and the production conditions, the appropriate parting surface, molding and core making method are selected, and the casting ribs, cold iron, riser and gating system are reasonably set. So as to ensure high quality castings.

Third, the quality of raw materials for casting. The substandard quality of metal furnace charge, refractory, fuel, flux, modifier, casting sand, molding sand binder, coating and other materials will cause defects such as porosity, pinhole, slag inclusion and sand sticking in the casting, which will affect the appearance and internal quality of the casting. In serious cases, the casting will be scrapped.

The fourth is process operation. It is necessary to formulate reasonable process operation procedures, improve the technical level of workers, and ensure the correct implementation of the process procedures.

Common problems and Countermeasures of metal marine castings:

Pinholes in metal castings

Measures to prevent pinholes: it is strictly prohibited to use contaminated cast aluminum alloy materials, materials with organic compounds and materials with severe oxidation and corrosion; Control smelting process and strengthen degassing refining; Control the thickness of metal coating, which is easy to produce pinholes; The mold temperature should not be too high, and cooling measures should be taken for the thick wall parts of the casting, such as copper inlay or watering; When using sand mold, strictly control the moisture and try to use dry core.

Metal mold castings often have air holes

Measures to prevent air holes: modify the unreasonable pouring and riser system to make the liquid flow stable and avoid gas involvement; The mold and core shall be preheated in advance and then coated. After that, the mold and core must be thoroughly dried before use; Sufficient exhaust measures shall be taken into consideration when designing the mold and core.

Oxidation and slag inclusion often occur in metal mold castings

Measures to prevent oxidation slag inclusion: strictly control the smelting process, quickly smelting, reduce oxidation and thoroughly remove slag; Al Mg alloy must be melted under covering agent; The furnace and tools shall be clean, free of oxide, preheated, and dried after coating; The designed gating system must have the ability of stable flow, buffering and skimming; The inclined pouring system is adopted to make the liquid flow stable without secondary oxidation; The selected coating has strong adhesion, and will not peel off during pouring and enter the casting to form slag inclusion.

Hot cracking often occurs in metal mold castings

Measures to prevent hot cracking: avoid local overheating and reduce internal stress during actual pouring system; The inclination of the mold and core must be above 2 °. Once the pouring riser is solidified, the core can be pulled out and the mold can be opened. If necessary, the sand core can be used to replace the metal core; Control the coating thickness to make the cooling speed of each part of the casting consistent; Select the appropriate mold temperature according to the thickness of the casting; Refine the alloy structure and improve the hot cracking ability; Improve the casting structure, eliminate sharp angle and sudden change of wall thickness, and reduce the tendency of hot cracking.

Looseness often occurs in metal mold castings

Measures to prevent looseness: reasonable riser setting to ensure its solidification and feeding capacity; Properly lower the working temperature of the metal mold; Control the coating thickness and reduce the thickness at the thick wall; Adjust the cooling speed of each part of the metal mold to make the thick wall of the casting have a large cooling capacity; Properly reduce the metal pouring temperature.