Defects of Sand casting include: cold isolation,insufficient pouring, blowhole, sand bonding, sand inclusion, sand hole, sand swelling, etc.
1) Cold insulation and insufficient pouring
The liquid metal filling capacity is insufficient, and the molten metal stops flowing before the cavity is filled, which will cause the casting to have insufficient or cold insulation defects. When the pouring is insufficient, the casting cannot obtain a complete shape; while the cold casting, the casting can obtain a complete shape, but the mechanical properties of the casting are seriously impaired due to the existence of the joint which is not completely fused.
Prevent under- and cold-separation: increase the pouring temperature and casting speed.
The gas does not escape in time before the molten metal encrusted, and the hole-like defects generated in the casting. The inner walls of the pores are smooth, bright or have a slight oxidized color. When the air holes are formed in the casting, the effective bearing area will be reduced, and stress concentration will be caused around the air holes to reduce the impact resistance and fatigue resistance of the casting. The vents also reduce the compactness of the casting, causing some castings that are subject to the hydrostatic test to be scrapped. In addition, the pores have an adverse effect on the corrosion resistance and heat resistance of the casting.
Prevent the generation of pores: reduce the gas content in the molten metal, increase the gas permeability of the sand type, and add a gas riser at the highest point of the cavity.
3) Sand bonding
A layer of sand that is difficult to remove adhered to the surface of the casting is called a sticky sand. Sticking sand affects the appearance of the casting, increases the workload of casting cleaning and cutting, and even affects the life of the machine.
Prevent sticking sand: Add pulverized coal to the molding sand, and apply anti-stick sand coating on the surface of the mold.
4) Sand inclusion
Grooves and scar defects formed on the surface of the casting are extremely likely to occur when casting thick and flat castings using wet casting.
Most of the parts in the casting that are sanded are in contact with the upper surface of the sand. The upper surface of the cavity is affected by the radiant heat of the molten metal, which is easy to be arched and warped. When the raised sand layer is continuously washed by the molten metal flow It may break and break, stay in place or be taken to other parts. The larger the upper surface of the casting, the larger the volume expansion of the molding sand, and the greater the tendency to form sand.
5) Sand hole
A hole-like defect of the molding sand is filled inside or on the surface of the casting.
6) Sand swelling
Under the action of the pressure of the molten metal during casting, the mold-shaped wall moves and the casting is partially expanded to form defects. In order to prevent sand expansion, the sand strength, the rigidity of the sand box, the pressure box force or the fastening force when the box is combined should be increased, and the pouring temperature should be appropriately lowered to make the surface of the molten metal prematurely crust, so as to reduce the pressure to metal liquid to the mold.
Malleable Iron Castings,Thin Wall Castings,Alloy Castings,Centrifugal Castings,Open Closed Die Casting,Zinc Die Castings,Heat Treated Castings Specification of Malleable Iron Castings: Removal of wax replica: The hollow wax replica of the original art work is then removed from the mold. The original mold can be used for making more wax replicas, but due to the wear and […]