Casting defects are defects in castings that occur in the casting process. There are various defect phenomena such as cracks in castings, rough surfaces, and casting nests with cavities inside. Casting defects are classified into several types, each with different causes. In addition, since there are several pre-casting processes in the casting process, and even defects in the previous process lead to casting defects, there are complex cases where casting defects are not limited to one, and there are actually many complex causes.
Typical defects fall into six broad categories. First of all, we will look at the causes and countermeasures for "casting defects".
What is casting failure?
Poor casting is a phenomenon in which molten metal is not completely filled into the Porosity when molten metal is poured into the casting mold, and the molten metal solidifies, and the cast product is partially missing. In field terms such as sand mold casting, it is also called "being ought".
This casting defect is mainly caused by the temperature of molten metal and casting molds. It is a problem that can be solved if the cause is fully grasped and countermeasures.
Why does casting failure occur, and What are the countermeasures ?
The occurrence of casting defects is caused by molten metal in the casting process and the temperature of the casting mold. It is also related to the amount of bullion. Here are five main causes and countermeasures.
1 Lack of Bullion
It occurs due to a lack of molten metal for the Porosity volume of the casting mold.
① The Specific Gravity of The Bullion is not Accurate
If the calculation of the bullion specific gravity is not accurate, the absolute amount of molten metal will not be enough and casting failure will occur.
Calculation of specific gravity of bullion (for wax)
Amount of molten metal = specific gravity of wax × specific gravity of the desired cast bullion
② The Amount of Feeder-head is Estimated Too Low
There may be a small amount of feeder-head to reduce the amount of bullion, but there is a possibility that defects may occur as a result. It is recommended to cast with an accurate estimate of the amount of feeder-head once, and check whether there is a defect in casting.
③ Calculation Error of Bullion
There may simply be errors in the calculations and a lack of bullion.
２ Lack of Casting Temperature
① Low Temperature of Bullion
Even if the bullion is dissolved visually, it may not have reached its full melting point. In this case, the metal solidifies before pouring molten metal into the details of the casting mold, causing the tip of the casting mold to be missing.
It is necessary to check the melting point of the bullion used and the molten metal temperature necessary for the casting mold again. In addition, if automatic casting is performed, set the casting temperature high.
② Low Casting Mold Temperature
Even if the temperature of the casting mold itself is low, the bullion may coagulation before it can spread throughout the casting mold. Check the casting temperature set by calcination in an electric furnace, etc., and if necessary, try to increase the casting temperature in units of 50 °C.
３ Inhibition of Molten Metal Filling due to gas exhaust pressure
If the gas contained in the casting mold or the gas possessed by the bullion itself does not come out, the molten metal will be poured in and a defect will occur.
In addition, when using a model for burning other than wax, a typical burn-out curve may not burn completely and may remain in the residue or casting mold, which may cause gas generation. If you think that there is a lot of gas generation, take measures against gas vent.
In addition, since the bullion itself may contain a lot of gas, it may be effective to gas the bullion.
４ Lack of Pressure in suction casting and pressure casting (Positive and Negative Pressure)
In the case of pressure casting, settings such as when to apply pressure are not set correctly, and molten metal may not be available in every detail of the casting mold. It is recommended to change the settings and cast.
In the case of suction casting, make sure that the casting mold is properly permeability (mold wall thickness, Investment powder mixing ratio, etc.), or that the vacuum pump has not experienced any functional degradation, or if there is any clogging or vacuum leakage in the piping.
In addition to the above, there is a possibility that there is a missing cause when making wax molds.
Summary of Casting Failure
We have introduced the causes and countermeasures, but we will summarize what to do when casting defects occur.
Check List
- Recalculate bullion specific gravity / re-measure bullion amount
- Increase the temperature of bullions and casting molds
- Check the set temperature of an electric furnace, etc., and try it by rising it in units of 50 °C
- Accurately estimate the amount of feeder-head
- Remove the air and gas from the bullion
- Review casting pressure settings
- Ensure casting mold permeability
- Check the status of the vacuum pump
There is not always one cause. Please review all the items again and see how they work.
