Sand casting defects

Sand casting casting defects are: cold shut , pouring enough holes, sticky sand , sand , sand , sand expansion .
1 . Inadequate containment and pouring cold liquid metal filling capacity shortage or poor filling conditions , before the cavity is filled, then stop the flow of liquid metal will make castings produced inadequate or pouring cold shut defects. When water shortage , will not get the full shape of the casting ; cold interval , castings are getting a complete shape, but there are not fully fused joints , the mechanical properties of castings severely damaged. Prevent water shortages and cold shut : Increases the casting temperature and casting speed.
2 . Vent gas not timely escape before the liquid metal crust , holes in the casting classes generated defects . Stomata wall smooth , bright colors or with a slight oxidation . After casting blowholes , which will reduce the effective bearing area around the hole and will cause the stress concentration and reduce the casting impact resistance and fatigue resistance . Casting porosity also reduce density, resulting in some of the requirements to withstand hydrostatic test castings scrapped. In addition, pores have an adverse effect on the corrosion resistance of the casting and heat resistance . Preventing the generation of holes : the liquid metal -containing reducing gas , increasing the permeability of the sand , and the provision of the highest point of the cavity at the riser outlet and the like .
3 . Adhered to a layer of sand is difficult to remove the sticky sticky sand called sand casting surface . Sticky sand casting only affects the appearance , but also increase the workload of cleaning and machining castings , and even affect the life of the machine . For example, when the tooth surface has sticky sand casting easily damaged machine parts such as pumps or engine if stuck in the sand, the flow of fuel oil , gas , oil and cooling water and other fluids will be affected and will tarnish and wear the entire machine. Prevent sticking sand: adding pulverized coal in the sand , and the sand mold release coatings, such as brushing the surface .
4 . Grooves in sand casting defects and scars formed on the surface when wet casting castings Heavy tablet easy to produce . Parts sand castings produced mostly sand where the upper contact surface , the liquid metal surface of the cavity by the radiant heat , and warpage easily arch , when the tilt of the continuous flow of metal by sand erosion may be fractured , left in place or be brought into other parts . The casting surface is larger, the larger the volume expansion of the sand , the greater the tendency to the formation of sand .
5. Trachoma in the casting of internal or surface defects filled with sand holes class .
6. When inflation pressure in the sand casting of liquid metal , mold wall movement type , casting defects formed partially swell . In order to prevent the expansion of sand , sand should improve strength, stiffness sand box , increase the force or pressure tank when the tank fastening Leaguer and appropriate to reduce the pouring temperature, the liquid metal surface crusts early in order to reduce the liquid metal to mold pressure.