The defect of sand casting
Sand Casting Casting Defects are: cold shut, pouring enough holes, sticky sand, gravel, sand holes, sand expansion.
1. Lack of containment and pouring cold liquid metal filling capacity is insufficient, or filling the disadvantaged, in the cavity is filled before the molten metal stopped flow, would produce sand casting poured cold shut inadequate or defective. Pouring insufficient, will not get a complete shape casting; cold compartment, the castings are getting a complete shape, but there are not fully integrated the joints, the mechanical properties of castings severely damaged.
To prevent shortages and poured cold shut: Improving the pouring temperature and casting speed.
2. Stomatal gas before the liquid metal crust did not escape in time, in the casting defects in the resulting holes in class. Pores of the inner wall is smooth, bright colors or with a slight oxidation. Castings produced pores, will reduce its effective bearing area, and in the pores can cause stress concentration around the casting to reduce impact and fatigue resistance. Stomata also reduce the casting densification, resulting in some of the requirements to withstand water pressure test castings scrapped. In addition, the pores of the casting corrosion resistance and heat resistance also have adverse effects.
To prevent the pores of the generation: lower metal-containing liquid gas, increasing the permeability sand, as well as the highest point in the cavity of an additional outlet riser and so on.
3. Sand casting surface on the adhesion of adhesive layer difficult to get rid of sand known as the sticky sand. Sticky sand casting both influence the appearance, but also increase the casting cleaning and cutting the workload, and even affect the life of the machine. For example, sticky sand casting tooth surface be easily damaged machine parts such as pumps or motors that if any sticky sand, it will affect the fuel oil, gas, lubricating oil and cooling water, such as fluid flow, and will tarnish and wear and tear the whole machine.
To prevent sticking sand: In the sand by adding pulverized coal, as well as anti-sticking in the mold surface, brushing sand coatings.
4. RPM in the casting surface defects in the formation of grooves and scars, in the wet-type casting Heavy easy to generate when the plate castings.
Castings produced mostly gravel, the site of contact with the sand on the surface where the cavity surface of liquid metal on the role of radiant heat, easy to arch and warp, when the tilt of the sand washed by the continuous flow of metal when the may break broken into or stay in other parts of the former Department. Casting on the surface of the greater sand volume expansion the greater the greater the tendency to form coarse.
5. Trachoma in the casting of internal or surface full of holes in the sand type defects.
6. Expansion sand when pouring liquid metal under pressure, mold-type wall movement, localized swelling of the formation of sand casting defects. In order to prevent inflation sand, should increase the strength of sand, sand box stiffness, increase the pressure tank when the tank together or to fasten power, and appropriately lower the pouring temperature, so that the surface of the early crust of liquid metal to reduce the liquid metal to the mold pressure.