Solutions for using coated sand problem

June 23, 2020
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Coated sand is one of the sand core raw materials of the core shooting machine. What is the use of coated sand problem, what are the main reasons, and how to solve the coated sand problem defects? This article will reveal the answers one by one.

Solutions for using coated sand problem

1. Shelling
Reason: The mold design is unreasonable, the core box temperature is not uniform so that the strength of the low-temperature part is low and shelling; the melting point of the coated sand is low, the curing speed is slow, and the thermal strength is low.
Solution: Improve the structure of the mold to make the temperature distribution uniform; choose a resin with a high melting point, fast curing speed, and high thermal strength.

2. Sand core surface is loose
Reasons: The core shooting pressure is too high or too low, the mold exhaust is not smooth; the mold runs away due to the large gap of the box surface; the coated sand has poor fluidity or poor permeability.
Solution: Use reasonable sand-shooting pressure to improve the exhaust system to prevent suffocation; use a material with small deformation as the core box; select coated sand with good fluidity and permeability.

3. Sand core deformation and fracture
Cause: The mold is not heated uniformly, or the core wall thickness varies greatly, causing inconsistent shrinkage during cooling; Using a resin with a large curing shrinkage rate; The core fork is deformed or the sand core is stored unevenly; The coated sand has poor high-temperature performance; Excessive pouring pressure
Solution: Improve the mold structure to make the temperature distribution uniform; Use the molding tray to store the sand core; Use the resin with low curing shrinkage rate; Use the high-temperature resistant low-expansion coated sand; Improve the pouring system (use pressureless type).

4. Wear the core
Cause: The local strength of the sand core is low or loose, and the thickness of the crust is thin
Solution: Improve the mold structure to make the temperature distribution uniform; choose a resin with a high melting point, fast curing speed, and high thermal strength; adjust the shot pressure; improve the exhaust system.

5. Poor exhaust core of casting
Reasons: The resin sand has a large amount of outgassing or the outgassing speed is not suitable; the sand core is not cured completely.
Solution: Improve the exhaust system and improve the exhaust effect; select raw sand with high concentration or coarser; use low-gas-generating coated sand.

6. Casting sticky sand
Reason: Low content of raw SiO2; core surface is not dense
Solution: adjust the pressure of the shot, improve the exhaust effect of the core box, and make the surface of the sand core denser; use high-temperature coated sand or zirconium sand coated sand.

7. Shrinkage inside the casting
Reason: The resin in the coated sand burns at high temperature to generate heat, which slows down the solidification speed of the molten iron and causes shrinkage.
Solution: Use chilled coated sand; place internally cooled iron in the shell core.

8. Defective casting surface
Reason: The bright carbon generated by the phenolic resin floats on the molten iron surface and solidifies on the surface of the casting.
Solution: Add about 2% iron oxide powder, use raw sand with high thermal conductivity; paint the shell surface; add special auxiliary materials to the coated sand.

The above is the solution to the coated sand problem. Everyone is seated and checked one by one to check the problems of coated sand brought by the use of coated sand. We hope it will help everyone!
For more questions, please pay attention to our website, we will update relevant casting machinery information from time to time, see you next time!

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