A relatively regular hole is formed on the surface or inside of the steel casting, and its shape is consistent with the shape of sand particles. When the steel casting just comes out of the mold, the sand embedded in the casting surface can be seen, and the sand can be pulled out. When multiple gas tubes exist at the same time, the surface of the casting is orange peel.
Cause: holes are formed because the sand particles falling on the surface of the sand core are surrounded by the molten metal and the casting surface.
1. The surface strength of the sand core is not good, which has been scorched or not fully cured.
2. The size of the sand core does not match the external mold. When the mold is closed, the sand core is crushed.
3. Immerse the mold in graphite water polluted by sand.
4. The sand wiped off by the sand core at the ladle and runner shall be cleaned with copper water.
prevention:
1. The sand core shall be produced in strict accordance with the process, and the quality shall be checked.
2. The size of the sand core matches the size of the external mold.
3. Clean the ink in time.
4. Avoid friction between ladle and sand core.
5. When putting down the sand core, blow out the sand in the mold cavity.
Because steel castings solidify too fast, most of them occur in summer. Hot weather leads to rapid evaporation of water vapor. At this time, the sand temperature needs to be controlled, especially in summer. Due to the ambient temperature, corresponding measures need to be taken to reduce the temperature below 35 ℃ and reduce the amount of curing agent. Or directly replace the curing agent with relatively low acidity. It is strictly prohibited to increase the curing speed by increasing the amount of curing agent. In winter, due to the low ambient temperature, the temperature of the steel casting processing workshop can be appropriately increased. Whenever production starts, the mold can be properly preheated. The amount of curing agent shall be strictly controlled.
We know the causes of sand inclusion in steel castings, and then we can formulate prevention plans based on these reasons. Generally, we use the following methods to prevent sand inclusion.
1.If sand is mixed in batches, the performance of molding sand may be poor. In addition to considering the use of molding sand with low swelling coefficient and good thermal conductivity, green sand with loose particle size can also be selected as quartz based molding sand.
2. During the molding process and operation of steel castings, it is required to grind the sand evenly to prevent part from being too hard or loose; Prevent repeated scrubbing of sandy surface during modification; Use less water and blow more holes; Insert the needle and paint on the sandy working surface to a certain depth, and add the bonding strength between the surface layer and the inner layer.
3. Improve from the process scheme. For large flat steel castings, skew casting should be used to reduce the heat dissipation from the upward surface of molten steel, and attention should be paid to make the mold fill the mold cavity faster. When casting, the cast steel grade is used to allow the lower limit and middle value of pouring temperature, while low-temperature rapid pouring will reduce the heating intensity and time of molding sand.
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