Common defects, main reasons and solutions in the use of coated sand

1. The surface of the mold (core) is loose

Core pressure is too high or too low;Mould exhaust is not smooth;The molds run out of sand due to the large clearance of box parting surface.Laminated sand has poor fluidity or poor air permeability.Choose reasonable sand blasting pressure, improve the exhaust system, prevent suffocation;Using the material with small deformation as the core box;Choose mulch sand with good fluidity and permeability.

2, hulling

The mould design is not reasonable and the core box temperature is not even, so the strength of the low temperature part is low and the shell is removed.Laminated sand has low melting point, slow curing speed and low thermal strength.Improve the mould structure so that the temperature distribution is even.Choose resin with high melting point, fast curing speed and high thermal strength.

3. Casting porosity

Core exhaust is not free;The air volume of resin sand is large or the gas velocity is not suitable.Sand core curing is not complete.Improve the exhaust system and improve the exhaust effect;Use high concentration or coarse raw sand;Adopt low - hair gas film sanding process.

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4. Core piercing:

Local strength of sand core is low or loose;The crust is thin.Improve the mould structure so that the temperature distribution is even.Choose resin with high melting point, fast curing speed and high thermal strength;Adjust blasting pressure;Improve the exhaust system.

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5. The content of SiO2 in the original sand of the casting is low;The core surface is not dense.Adjust the blasting pressure, improve the core box exhaust effect, make the core surface more compact;High temperature resistant film - coated sand or zirconium sand film - coated sand.

6. Deformation and fracture of the type (core)

The heat of the mould is not uniform, or the core wall thickness of the mould is different, resulting in inconsistent shrinkage during cooling.The curing resin with high shrinkage was adopted.Deformation of the core fork or uneven storage of the sand core;High temperature performance of coated sand is poor;The pouring pressure is too high to improve the mold structure, so that the temperature distribution is even.Use the molding tray to store the sand core;Use curing resin with low shrinkage;High temperature resistant low expansion coated sand;Improve the casting system (with no pressure).

7. Internal shrinkage of casting

Resin in coated sand burns at high temperature to produce heat, slowing down the solidification rate of iron water, leading to shrinkage.Use shock - cooled film - coated sand;The inner cold iron is placed in the shell core.8. Poor surface of casting

The bright carbon produced by phenolic resin at high temperature floats on the surface of the molten iron, and the surface of the casting becomes wrinkled when solidified.Add about 2% iron oxide powder, adopt the raw sand with high thermal conductivity;Coating the surface of shell core;Special additives are added to the film - covered sand.