A variety of defects can occur in precision castings, and the reasons for these defects are also quite complex. They are not only related to the casting process but also involve factors such as the properties of the casting alloy, the melting of the alloy, the performance of the molding material, and more. Today, precision casting manufacturer Rongchuang Precision analyzes the causes of casting defects, conducting a comprehensive analysis based on specific conditions, considering the characteristics, location, process used, and the type of molding sand, among other factors. Subsequently, appropriate technical measures are taken to prevent and eliminate these defects.
One: Defects in castings that cannot be properly poured often occur in thin-walled areas, far from the gating, or on the upper part of the casting. The edges of the defects are smooth, shiny, and free from sand.
Causes:
Low pouring temperature, slow pouring speed, or intermittent pouring.
2. The cross-sectional area of the runner and the riser is small.
Preventive Measures:
Increase pouring temperature and speed up the pouring rate to prevent intermittent pouring.
Increase the cross-sectional area of the runner and the riser.
Two: Damaged castings with fractures and missing parts.
Cause of Occurrence:
The riser and riser neck cross-sectional dimensions are too large; no knock-off face (groove) is formed on the riser neck. Or the method of removing the riser is incorrect, resulting in damage and thinning of the casting.
Preventative Measures:
Modify the riser and riser neck dimensions, produce a riser neck cross-section, and correctly master the direction of riser pouring.
Three: The fracture surface of gray cast iron and speckled castings is gray-black or shows black specks, with more in the center and fewer at the edges. Microscopic examination reveals lamellar graphite.
Reason for Occurrence:
Bismuth孕育于炉前，added to the ladle too early or too late, or in insufficient quantity.
Preventive Measures:
Increased boron addition and stringent pre-furnace gestation process.
Four: Cracks (hot cracks, cold cracks) may appear on the surface or inside of castings, either through or not through the material. Hot cracks exhibit dark or black oxidized fracture surfaces with a wavy appearance. Cold cracks are cleaner, brittle fractures with relatively flat fracture surfaces, displaying metallic luster or slight oxidation hues.
Causes:
1. High casting temperature.
2. Molding necks that are too large or too short lead to severe localized overheating, or a too small riser, resulting in poor shrink compensation.
3. Castings experienced excessive impact during cleaning and transportation.
Preventive Measures:
Lower the pouring temperature.
2. Reasonably design the riser system.
Avoid excessive impact during the cleaning and transportation of castings.
Five, The walls of the pores are smooth and bright, with shapes ranging from circular, pear-shaped, to needle-like. The sizes of the pores vary, occurring on the surface or inside of castings. Pores within castings can only be discovered after they are broken or during mechanical processing.
Reason for Occurrence:
The lower casting temperature prevents gases from rising and escaping in time.
2. High aluminum content in the furnace charge is prone to cause hydrogen pores.
Prevention Methods:
Increase pouring temperature.
Do not use scrap steel with excessive aluminum content.
Six: Shrinkage porosity, loose and scattered porosity, and fine shrinkage holes, those with tree-like crystallization are called shrinkage porosity, and those even finer are referred to as loose porosity. They commonly appear in hot spot areas.
Cause of Occurrence:
The rapid casting speed and excessively high casting temperature result in significant liquid shrinkage.
2. Inadequate casting system and riser design prevent sequential solidification.
3. The sprue is too small, resulting in insufficient shrink compensation.
Preventive Measures:
1. Reduce casting speed and temperature.
2. Enhanced gating system with sequential solidification.
Increase the riser volume to ensure adequate shrinkage compensation.
The above provides common defect analysis and control methods for precision casting, hoping it is helpful to all. We offer joint development and one-stop customized services from mold manufacturing to precision casting production, committed to providing high-quality precision casting for China's manufacturing industry. If you have any questions about precision casting or precision castings, feel free to consult us!
