Dawang Casting is one of the foundries worldwide that produces the most precise and defect-free metal castings. Undoubtedly, the causes and solution of the casting defects are the most important topics we consider in our every casting process. We follow the latest metal casting techniques to avoid all types of casting defects. Besides, we depend on high-quality manufacturing processes to overcome defects in metal casting in this case. Above all, the metal castings from Dawang casting also ensure the product’s efficacy.
Defects in metal casting are one of the essential considerations in Dawang casting. As a result, we made this article to introduce you to the casting defects that might appear during any metal casting process. In addition, it will also describe the nine most common industrial casting defects, their causes, and remedies.
Introduction to Casting defects
As the name implies, casting defects refer to the defects on the castings from different casting processes. Casting defects make bad-shaped, weak, and poor functional castings. It is unwanted as they fail to keep the target products’ mechanical and physical properties.
Defects in metal casting would be a common phenomenon if you didn’t have sound knowledge of how to control them. In the previous articles, we already knew that the casting process is a multitasking complex process. Therefore, the overall quality of the casting depends on every technical level of the casting process. In addition, the casting quality depends on the operators’ techniques, operation equipment, and ability.
Types of defects in metal casting
There are six major types of casting defects in casting manufacturing, and they come from so many causes for which casting defects might appear. Explaining each casting defect might make this article longer and more boring. So first, we will introduce you to the casting defects categories and their respective types. And later, we will explain the causes and solutions for the nine most common casting defects in a foundry.
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1. Structural casting defects
These casting defects occur due to the shape changes in the casting processes. Mismatch or shift, flash, fins, burrs, warping, etc., are the most common type of this casting defect category.
2. Pouring defects
As the name implies, these casting defects happen while pouring the molten metal into the mold. Cold shut or lap misruns are similar to cold shuts and cold shots. Slag inclusion is also one of the most common types in this category.
3. Metallurgical defects
Casting metallurgy refers to the metallic properties of the metal. Metallurgical casting defects refer to the casting fault in the physical properties of the metal. For example, the two common metallurgical casting defects are hot crack or tear and hard or hot sports.
4. Mould Material defects
These defects are common in sand casting methods. As the name implies, the casting defects due to the mold materials are usually called mold material casting defects. In this case, sand is the primary mold material used in sand casting. Cuts and washes, run out, fusion, swells, drops, rat tails, veins, buckles, and metal penetration are the common mold material casting defects.
5. Shrinkage defects
Shrinkage is a common cause in the metal solidification process. Therefore, the casting defects found in the shrinkage stage are usually popular as shrinkage casting defects. Open shrinkage defects and Closed shrinkage defects are the two most common types of shrinkage casting defects.
6. Gas porosity defects
Gas porosity defects usually happen due to the trapped gas inside the molten metal. These types of gas might be oxygen, nitrogen, or hydrogen. Pinholes, subsurface blowholes, and open holes are common gas porosity casting defects in casting manufacturing.
9 Most Popular Industrial Casting Issues
We have already mentioned the possible defects you might find in castings. This section will demonstrate the nine most common casting defects found in a foundry. We will also elaborate on the possible causes of these defects and how to solve them.
It is one type of gas porosity defect. Porosities are typically tiny small gas bubbles, and blowholes or blisters are large gas bubbles inside the molten metal. Later After the casting process, these gas bubbles turn into a blowhole defect. Two types of blowholes may appear on the casting, porosities, and blowholes.
Causes: Blowhole usually forms due to the high moisture on the chills. Besides, Low permeability, inadequate vents, and improper sand mixing may also lead to blowhole defects.
Solutions: During the process, it is necessary to ensure the use of dry chills and coatings and the optimum temperature of the target metal. It is essential to avoid using refined sand grains during the sand casting process.
Shrinkage defects typically form cavities due to formation at a closed loop during the molten metal solidification process. As we already mentioned, shrinkage can be of two types: open and closed shrinkage.
Causes: The primary reason for shrinkage defects may be the improper position of the chills. Besides, wet sand, high metal pressure, and sudden changes in thickness may also create shrinkage defects.
Solutions: Before the casting process, it is necessary to dry the mold by using CO2 gas for at least 60 seconds so that the mold becomes highly rigid. The operator must ensure the chills are in the correct position.
Tears or Cracks
Hot tears or cracks happen due to the temperature turbulence during the metal solidification. These defects look like shart and broken jagged lines at the edges.
Causes: The primary reasons for hot tears are mold disturbance before the metal solidification process, inappropriate sand grains, wrong riser locations, high ramming density, a high amount of sulfur or phosphorus, etc.
Solutions: The operators must ensure that mold cooling is appropriate and sufficient. If there is an excess amount of sulfur or phosphorus in the mold, the deoxidation process or mixing Mn, silicon, or magnesium helps reduce those contents.
Pipe lamination casting defect
Lamination defect is a common issue in casting metal pipes, especially steel ones. This defect appears as a separated laminated layer from the casting pipe.
Causes: Low-quality material is the primary reason for lamination defects. Low friction between the material and the die pipe might also create a lamination defect. Besides, inappropriately low or high rpm during pipe solidification are also common lamination defect causes.
Solutions: The casting operator must ensure the appropriate rpm and friction during pipe solidification. However, high-quality materials for pipe casting should also be considered.
Lumps are the common casting defect found in the centrifugal casting process. This defect appears as blisters on the external surface of the castings.
Causes: Lumps usually appear when air locking between the die and molten metal. The trapped air between the die and liquid metal creates these lumps.
Solutions: Proper speed of rotation and preheating can solve lumps defects. Besides, more mold coatings for the metal pipe die can also solve lumps problems.
While creating the mold sections, the tearing of sand creates sand inclusions. This defect may have variable locations that lead to a localized defect.
Causes: Uneven compact molds, sand mixing, improper liquid metal pouring, and mold breakage are the primary reasons for sand inclusions. Besides, a metal liquid stream tilting directly to the core might cause erosion, resulting in sand inclusion.
Solutions: Proper pouring ratio and time, appropriate pouring height, organized cores, and frequent mold box cleaning can solve all types of sand inclusions. Besides, proper ramming of sands is also necessary for uniform compaction.
Flashes are a common phenomenon in every casting. The extra portion of the casting found on the surface of the casting is called flashes.
Causes: Molten metal leakage might form flashes. However, high pressure during the pouring of liquid metal, poor pattern designs, cavities inside the pattern, and inappropriate clamping may also create casting flashes. Besides, excessive tolerances between the bottom and top parts may cause casting flashes.
Solutions: The operator must ensure no leakage by filling all the cavities. Besides, preplanned pattern and tooling dimensions, appropriate mold assembly, and proper core settings can also solve this problem.
A mismatch defect is one of the most common structural casting defects. As the name implies, a mismatch defect is caused by misplacing the mold parts.
Causes: An improper mould assembly can lead to a mismatch defect. Besides faulty pattern design, core parts containing inadequate weight are also a common cause of a mismatch.
Solutions: Proper gating system in the casting tool can almost solve the dislocation problem. Besides, the operator can put heavy weight on the casting to ensure no dislocation.
This casting defect is one of the most common issue during pouring liquid metal. Low fluidity of the liquid metal creates misrun.
Causes: large surface area with a smooth and incomplete cavity is the primary cause of this pouring defect. Besides low pouring temperature and delayed pouring liquid, a back pressure may also create misruns.
Solutions: Appropriate pouring temperature and pressure, a clean mold box, and a proper gating system can resolve this issue.
The final most common casting defect in a typical metal foundry is the defective surface. This casting defect appears as a series of small channels.
Causes: Oxide formation, foreign contaminants flowing on the liquid metal, high slag, and low temperature are the most often reasons for the surface defect.
Solutions: First, the operator should preheat the liquid metal before pouring it to keep the temperature constant. He should also check for slag formation during the charging process.
Casting defects are unwanted occurrence that affects the mechanical properties of the casting. As metal casting is a complex process, each step in the process involves the quality of the final casting. Therefore, the casting defect types also vary due to improper operation. But no worries, there are a lot of solutions to avoid casting defects.
Defects are the most crucial factor for any metal processing we use at our foundries. Numerous inspections are performed during the tooling process. We always favor preplanned designs with suitable technological specifications. Therefore, Dawang casting products are free of defects.