First, the crack defect characteristics: 1. Casting crack. Developed along the grain boundary, often accompanied by segregation, is a crack at higher temperatures formed in larger volume shrinkage of the alloy and the shape of the more complex aluminum castings prone to 2. Heat treatment Cracks: due to heat treatment caused by overheating or overheating, often have crystal cracks. Often in the stress and thermal expansion coefficient of large alloy cooling too drama. Or the existence of other metallurgical defects arising from the reasons: 1. Casting structure design is irrational, sharp angle, wall thickness changes are too poor 2. Sand core misplaced 3. Partial overheating of the mold. Pouring temperature is too high 5. It is too early to remove the castings from the mold. Heat treatment overheating or over burning, cooling too radical
To prevent the method: 1. Improve the casting structure design, to avoid sharp corners, wall thickness to seek uniform, smooth transition 2. Take measures to increase the retractability of the sand core. Ensure that the parts of the casting at the same time solidification or sequence solidification, improve the design of the casting system 4. Appropriate reduction of casting temperature 5. Control mold cooling out of time 6. Thermal correction is used for casting deformation. Correct control of heat treatment temperature, reduce the quenching cooling rate
Second, the characteristics of slag defects: Oxidation slag more distributed in the casting of the upper surface, in the mold is not ventilated corner parts. Fracture mostly gray or yellow, by x-ray or in the mechanical processing found, but also in the alkaline washing, pickling or anodizing found in the cause: 1. The charge is not clean, the use of excessive chargeback 2. Pouring system Poor design. The molten slag in the alloy is not removed. Pouring operation improperly, into the slag 5. Refined to calm the treatment time is not enough
To prevent the method: 1. The charge should be blowing sand, the amount of charge back to the appropriate reduction of 2. Improve the design of the pouring system to improve its slag capacity 3. Use the appropriate flux to slag 4. Casting should be smooth and should pay attention to slag 5. Refining before pouring alloy liquid should be standing for a certain time
Third, the pores Bubble defect characteristics: three castings wall pores are generally round or oval, with a smooth surface, usually shiny oxide, sometimes oil yellow. Surface pores, bubbles can be found through sandblasting, the internal air bubbles can be X-ray fluoroscopy or mechanical processing found that air bubbles in the X-ray film was black.
Cause: 1. Casting alloy is not smooth, involved in the gas 2. Core sand mixed with organic impurities such as coal dust, grass manure, etc. 3. Casting and sand core poor ventilation 4. Cold iron surface shrinkage 5. Casting Poor system design.
To prevent the method: 1. Properly grasp the casting speed, to avoid involvement of gas. 2. Core sand can not be mixed with organic impurities in order to reduce the amount of hair material molding materials 3. To improve the exhaust capacity of core sand 4. Correct selection and treatment of cold iron 5. Improved casting system design four loose