The first is the design process of castings. When designing, in addition to determining the geometry and size of the casting according to the working conditions and the properties of the metal material, the rationality of the design must also be considered from the perspective of the casting alloy and casting process characteristics, that is, the obvious size effect and solidification and shrinkage, stress and other issues to avoid or reduce the occurrence of defects such as segregation, deformation, and cracking of castings.
Second, there must 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, shape, and core making method should be selected, and the casting rib, cold iron, riser and gating system should be reasonably set. All these are done to ensure high-quality castings.
The third is the quality of metal foundry materials. The quality of metal furnace charge, refractory materials, fuel, flux, modifier, foundry sand, sand binder, paint and other materials is substandard, which will cause pores, pinholes, slag inclusions, sand sticking and other defects in the castings, which will affect the appearance quality of the castings and internal quality, if serious, the casting will be scrapped.
The fourth is process operation. It is necessary to formulate reasonable process operation procedures to improve the technical level of workers so that the process regulations can be implemented correctly.
The quality of castings has a great impact on the performance of mechanical products.
Pinholes in metal casting supplies
Measures to prevent pinholes: It is strictly forbidden to use contaminated cast aluminum alloy materials, materials stained with organic compounds and severely oxidized and corroded; control the smelting process, strengthen degassing and refining; control the thickness of the metal type coating, too thick may cause pinholes ; Mold temperature should not be too high, adopt chilling measures for thick wall parts of castings, such as copper inlay or watering, etc.; when using sand molds, strictly control moisture and try to use dry cores.
Gas holes in metal casting supplies
Measures to prevent pores: modify the unreasonable pouring and riser system to stabilize the liquid flow and avoid the entrapment of gas; the mold and core should be preheated, and then painted, and must be dried thoroughly before use; design the mold Adequate exhaust measures should be considered with the core.
Oxidation and slag inclusion in metal casting supplies
Measures to prevent oxidation and slag inclusion: strictly control the smelting process, fast smelting, reduce oxidation, and thoroughly remove slag; Al-Mg alloy must be smelted under a covering agent; furnaces and tools must be clean and free of oxides. It should be preheated, and the paint should be dried and used after coating; the designed pouring system must have stable flow, buffering, and slag skimming capabilities; an inclined pouring system is used to stabilize the liquid flow without secondary oxidation; the selected coating adhesion must have strong adhesive ability, so that it does not spall during the pouring process to enter the casting to form slag inclusions.
Hot cracking often occurs in metal casting supplies
Measures to prevent thermal cracking: In the actual pouring system, local overheating should be avoided to reduce internal stress; the inclination of the mold and core must be above 2°, and the pouring riser can be pulled out once it has solidified, and if necessary, replace the metal core with sand core; control the thickness of the coating to make the cooling rate of each part of the casting consistent; select the appropriate mold temperature according to the thickness of the casting; refine the alloy structure to improve the hot cracking ability; improve the casting structure, eliminate sharp corners and wall thickness mutations, and reduce hot cracking tendency.
Shrinkage in metal casting supplies
Measures to prevent looseness: reasonable riser settings to ensure solidification and feeding capacity; appropriately lower the working temperature of the metal mold; control the thickness of the coating and reduce the thickness of the thick wall; adjust the cooling rate of each part of the metal mold to make The thick wall of the casting has a greater chilling capacity; appropriately reduce the metal pouring temperature.