As the name implies, casting defects refer to irregularities that appear in the metal casting process. In this article, we will discuss different sand casting defects and causes. Only in this way can you prevent metal casting defects and avoid defective products. This guide will start with 5 types of foundry casting defects and causes to help you identify, repair, and avoid casting problems. For cast defects prevention, we have a more detailed guide on ways to prevent defects.
Metal casting defects and causes
Common defects in metal castings are categorized into five groups: holes, cracks, surface defects, irregular shapes, deviations in sizes and weights, as well as non-conforming components, structures, and properties.
1. Perforated Casting Defects
Casting defects that could happen in steel castings include pores, shrinkage holes, shrinkage porosity, slag holes, trachoma, and iron beans.
Also known as gas eyes, bubbles, and holes, these casting defects are caused by gas. The characteristics of casting pores are: generally round or irregular holes, the inner surface of the holes is smooth, and the color is white or with a layer of old dark color.
The causes of casting defects are: the furnace material is wet or corroded; the surface is not clean, the steam in the furnace gas and other gases; the furnace body and the ladle are not dried after repair; the gas in the cavity and the improper pouring system; the gas is involved in the casting, Poor permeability of mold or mud core, etc.
These are casting defects caused by shrinkage. The characteristics of shrinkage cavity are an irregular shape, roughness in the hole, and coarse crystal grains.
The reason for casting defects is metal shrinks during liquid and solidification. The main points are as follows: unreasonable casting structure design; improper casting system; the size, quantity, and location of the chilled iron do not match the reality; the chemical composition of the molten iron does not meet the requirements, such as excessive phosphorus content. Pouring temperature is too high, running speed is too fast, etc.
Also called looseness, pinhole honeycomb. These casting defects are caused by shrinkage resistance. Shrinkage porosity is characterized by:
- Tiny and disjointed pores
- Coarse crystal grains with obvious mesh holes between the crystal grains
- Water seepage during the hydraulic test
Slag hole casting defects are caused by slag inclusion, slag bag, dirty eye, low molten iron temperature, and improper casting of slag. The characteristics of the slag hole are: the shape of the hole is irregular and not smooth; the whole or part of the hole is filled with slag.
The reasons for casting defects are: insufficient purity of the molten iron; poor slag removal and poor slag retention during pouring; poor slag retention by the gating system, and the gate is not full or cut during pouring.
2. Cracked Casting Defects
Cracking steel casting defects include hot tear defect, warm cracking, and cold shut defect.
Hot crack (hot tear defect)
Thermal cracking casting defects occur at a higher temperature and near the solidification temperature. The characteristics of thermal cracking are penetrating or non-penetrating cracks on the casting; it is curved, and the surface of the crack is oxidized.
The reasons for metal casting defects are excessive sulfur content or excessive impurities in the iron; poor retreat performance of the sand casting mold; improper pouring temperature control; the severe transition of the casting wall thickness transition; gate, cold iron, shrinkage ribs, vent holes Improper size and location, etc.
Thermal cracking is also called heat treatment cracking. These metal casting defects are caused by improper cutting, welding, or heat treatment. The characteristics of warm cracking are: there are penetrating or non-penetrating cracks on the casting; the metal surface of the crack is oxidized.
Cold crack (cold shut defect)
Cold crackings are crack casting defects produced by castings at lower temperatures. The characteristics of cold cracking are penetrating or non-penetrating cracks on the casting; it is linear, and the surface of the crack is not oxidized.
The reasons for casting defects (casting defects with images) are:
- Unreasonable casting structure, uneven thickness.
- Poor retreat performance of sand casting mold or mud core.
- Inconsistent cooling of various parts of casting, the high-stress tendency of the alloy itself.
3. Surface casting defects
Surface steel casting defects include sand sticking, scarring, sand inclusion, and cold isolation.
The cold compartment is also called anti-fire, receiving fire, and so on.
The characteristics of the cold partition are: there are irregular and obvious sinking linear lines on the surface of the workpiece (there are two kinds of penetrating and non-penetrating).
Its shape is small, long, and narrow, and it has a development trend under external force. Judging from the characteristics of the cold barrier, it is easy to cause damage to the mother’s body. Cracks casting defects caused by the hard barrier will not appear immediately. When it is in use, fatigue cracks are produced under the action of bearing and impact.
Reason for casting defects：
- Inadequate metal bonding can be a common problem, occurring during both simultaneous and sequential multiple ladle pouring processes. It is often caused by various factors, including low pouring temperature, slow pouring speed, and extended pouring times. Additionally, alloy properties and specific casting geometries can contribute to this issue.
4. Metal casting defects of unqualified size, shape, and weight
Metal casting defects of unqualified size, shape, and weight castings include: fleshy, insufficient pouring, falling sand, box lifting, eccentricity, deformation, wrong box, damage, shape, size and weight inconsistency, etc.
5. Foundry casting defects with unqualified composition and performance
Steel casting defects of unqualified composition and performance include unqualified chemical composition; unqualified metallography; unqualified segregation, excessive hardness, and unqualified physical and mechanical properties.
Treatment of steel casting defects
1. The principle of repairing defects in foundry steel castings:
2. Treatment method of steel casting cracks
(1) Stop cracks and eliminate cracks
(2) Prefabricated groove and gap
(3) Preparation before welding
3. Welding repair of cast iron parts
Here we have presented the basics of porosity, shrinkage, mold materials, pouring metal, metallurgy, and casting shape defects. Specific examples of defects that can occur in castings are included. Now that you are more familiar with the types of failures that can occur in castings, are you ready to start purchasing?
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