What are the common casting defects of elbow reducer castings

As a crucial component in the pipeline system, the quality of the elbow reducer casting directly affects the safety and efficiency of fluid delivery. In the casting production process, various casting defects will inevitably occur due to the influence of various factors. A deep understanding of these defects is not only a necessary professional knowledge for casting engineers, but also the key to ensuring product quality and end-user safety.

Air holes and pin holes
Air pores and pinholes are one of the most common defects in castings, which manifest as hollows or small holes inside or on the surface of the casting.
Cause: 
Poor breathability of molded sand: During the casting process, after liquid metal is poured into the mold cavity, the gas in the mold cavity cannot be discharged smoothly and is trapped inside the metal. 
The furnace charge or melt is unclean: During the smelting process, the impurities such as moisture, grease and other impurities brought in the furnace charge decompose at high temperature to produce gas. 
Improper design of the pouring system: the pouring speed is too fast or the gate position is unreasonable, resulting in the occurrence of gas rolling. 
Excessive moisture in molds and cores: During casting, the moisture is heated and vaporized, resulting in a large amount of water vapor.
harm:
Stomatal and pinholes can significantly reduce the mechanical properties of the casting, such as strength, toughness and fatigue resistance. They will form stress concentration points and become crack sources under external loads, seriously affecting the pressure bearing capacity and service life of elbow reducer tubes.

Shrinking holes and scaling
Shrinkage and shrinkage are defects caused by volume shrinkage during metal solidification.
Cause: 
Unreasonable solidification rules: the thick part of the casting finally solidifies, and effective supply of liquid metal cannot be obtained. 
The pouring temperature is too high: the metal liquid is overheated and the solidification shrinkage increases. 
Improper setting of risers and cold iron: The risers are used as a source of retraction and shrinkage, and their size or position are unreasonable and cannot provide sufficient liquid metal. Cold iron is used to accelerate local solidification, and if the position is improper, it may aggravate shrinkage.
harm:
Shrinkage is a macroscopic hole, while shrinkage is a microscopic, dispersed pore. They all reduce the density of the casting, greatly reduce its pressure bearing capacity, and may lead to leakage. Retraction in key pressure bearing areas will cause the pipeline system to rupture during operation.

Sand holes and slag inclusions
Sand holes and slag inclusions are non-metallic inclusion defects.
Cause: 
Sand hole: The casting mold or core is impacted or washed by heat during the casting process, causing the sand to fall off and mix into the metal liquid. 
Slag inclusion: The slag, flux residue or oxide is not effectively removed during the smelting or pouring process and enters the cavity with the metal liquid.
harm:
Sand holes and slag inclusions not only affect the appearance quality of the castings, but more importantly, they will destroy the continuity of the metal matrix, form stress concentration points, significantly reduce mechanical properties and corrosion resistance. In corrosive media environments, the vicinity of slag inclusions may become the starting point of corrosion.

crack
Casting cracks refer to cracks that occur during solidification or cooling.
Cause: 
Thermal cracking: occurs in the early stage of high-temperature solidification. Since the internal stress of the casting is greater than the strength of the metal at that time, it is often found at thick and large sections. 
Cold cracking: Arises after the casting is cooled to the solid state, resulting from heat treatment or internal residual stress.
harm:
Cracked are one of the most dangerous casting defects. It directly destroys the integrity of the casting and seriously threatens the safe use of elbow reducer tubes. Under external loads and pipeline pressure, cracks can rapidly expand, resulting in catastrophic failure.

The casting size is not qualified
The size, shape or weight of the casting does not meet the drawing requirements.
Cause: 
Inaccurate mold or core size: mold manufacturing error, wear or deformation. 
Improper casting process parameters: the casting temperature, cooling speed and other parameters are not strictly controlled, resulting in the shrinkage rate inconsistent with the design. 
Improper tightening: the upper and lower types are misaligned when combined, or move due to the metal hydraulic pressure during casting.
harm:
Unqualified elbow reducer tubes cannot be accurately connected to other components in the piping system, which can lead to installation difficulties, poor sealing, or concentrated stress. This will directly affect the functionality and reliability of the entire pipeline system.

Cold separator and insufficient watering
Cold separation is when two metal streams converge, and cannot fully merge due to the low temperature, forming a non-connected "cold" seam. If the water is insufficient, the metal liquid cannot fully fill the cavity.
Cause: 
The pouring temperature is too low: the liquid metal fluidity is poor. 
The pouring speed is too slow: the metal liquid solidifies prematurely when it flows through the cavity. 
Poor exhaust of cast molds: The gas in the mold cavity hinders the flow of metal liquid.
harm:
Cold partitions and insufficient pouring will damage the structural integrity of the casting. Although the cold partition may not be easy to detect in appearance, its internal bonding strength is extremely low, which is a potential risk point for stress concentration and leakage. Castings that are not poured are directly scrapped due to incomplete shape.