First, air holes (bubbles, boring holes, air pockets)
Reasons:
1. The mould preheat temperature is too low, and the liquid metal is cooling too quickly through the pouring system.
2. Mold exhaust design is terrible; the gas cannot be discharged smoothly.
3. The painting is not good, its exhaust system is not sound, and even the painting will volatilize and decompensate the gas.
4. There are holes and pits on the surface of the mould cavity. After the liquid metal is injected into the hole and the pit, the gas rapidly expands and compresses the liquid metal to form a boring hole.
5. The surface of the mould cavity is rusted and has not been cleaned.
6. The raw material (sand core) is stored improperly without preheating before use.
7. Poor deoxidizer, insufficient amount, improper operation and so on.
Prevent method:
1. The mould should be fully preheated, the particle size of the coating (graphite) should not be too fine, and then the permeability will be better.
2. Using the tilt pouring casting method.
3. Raw materials should be stored in a dry and ventilated place, and must warm up before use.
4. Select a deoxidizer (magnesium) with a good deoxidation effect.
5. Pouring temperature should not be too high.
Second, the shrinkage hole.
Reasons:
1. Mold temperature control does not meet the directional solidification requirements;
2. Inappropriate paint selection, poor control of paint layer thickness in different places;
3. The position of the casting in the mould is not properly designed;
4. The pouring gate design failed to achieve sufficient feeding;
5. Pouring temperature is too low or too high.
Prevent method:
1. Increase the temperature of abrasives;
2. Adjust the thickness of the paint layer. The paint spray should be uniform. When the paint is off, repainting can not form a local painting accumulation phenomenon;
3. Partial heating of the mould or partial insulation with insulation material;
4. Inlaid copper block at the hot section, chilling in the partial area of the part;
5. Design the heat plate on the mould, or through the water to accelerate the cooling rate in partial areas, or spray water or mist on the mould;
6. Use removable chilled cold block, placed in the cavity in turn, to avoid the chilling block cooling insufficient while during the continuous production;
7. Design the pressure device in the pouring gate;
8. Pouring system design to be accurate. Select the appropriate pouring temperature.
Third, Dregs (flux slag or metal oxide slag)
Reason:
The slag eye is mainly caused by the alloy smelting process and the investment process (including the incorrect design of the gating pouring system). The slag hole is not caused by the mould itself, and the metal mould is one of the effective methods for avoiding the slag hole.
Control methods:
1. The casting foundry system is set up correctly, or use a cast fibre filter system.
2. Using the tilt pouring method.
3. While choosing flux, strict quality control.
Fourth, cracks (hot cracks, cold cracks)
Reason:
Metal mould casting is prone to crack defects because the metal mould itself does not have concealing ability, the cooling speed is quick, and it quickly leads to increased internal stress of the casting. The opening type is too early or too late. The pouring angle is too small or too large. The coating layer is too thin, etc. also caused the cracks. And cracks are easily caused when the mould cavity itself has cracks.
Control methods:
1. should pay attention to the foundry casting structure of the process, need to do the uniform transition of the uneven thickness of the casting parts, using the appropriate fillet size.
2. Adjust the thickness of the paint as far as possible so that the casting parts achieve the required cooling rate to avoid forming too much internal stress.
3. Should pay attention to the working temperature of the metal mould, adjust the mould slope, and timely draw out the core, pick out the casting part for cooling.
Fifth, cold septum (Poor melting)
Reason:
1. The metal mould exhaust design is unreasonable;
2. The working temperature of the casting foundry is too low;
3. Coating quality is not good (Human factors, Material factors);
4. The pouring gated opened improperly;
5. The pouring speed is too slow.
Control methods:
1. The correct design of the runner and exhaust system;
2. For the large area of thin-walled castings, paint should not be too thin, an appropriate thickening paint layer is conducive to moulding;
3. Appropriate to increase the mould temperature;
4. Using the tilt casting method;
5. Use the method of mechanical vibration metal casting.
Six, sand eyes (sand hole)
Reason:
The sand eyes formed on the surface of the casting part. The sand particle is surrounded by the copper liquid and drops on the surface of the casting to form holes.
1. The sand core surface strength is not good, scorched, or not completely solidified.
2. If The size of the sand core does not match the outer mould, crush the sand core when closing the mould.
3. The mould of the casting foundry has been contaminated with sand-contaminated graphite water.
4. The sand rubbed off from the sand core at the ladle and runner is flushed into the cavity with copper water.
Control methods:
1. The sand core is manufactured strictly according to the process, and quality is checked;
2. The sand core must suit the size of the outer mould;
3. If it is the ink, it must be cleaned in time;
4. To avoid the friction between the pouring bag and the sand core;
5. When making the sand core of the casting foundry, you must blow clean sand in the mould cavity.
