How are precision casting defects formed and how to prevent them?

The defects of precision casting are generally bubbles, which refers to the shortcomings of lubrication holes in certain parts of precision castings. Bubbles can usually only be discovered after machining. After many years of personal consumption experience by professional technicians, we have summarized the bubbles in precision casting. The causes and prevention methods are as follows:

1. Reasons for formation:

(1) In most cases, the main reason for the appearance of bubbles is that the shell is not fired carefully enough. When the molten steel is poured into the shell, a lot of gas cannot be discharged smoothly, thus invading the metal liquid to form bubbles;

(2) Due to the shell processing technology or shell material, the shell has poor air permeability, and the steam in the die cannot be discharged, and enters the metal material liquid to form bubbles;

(3) The gas trapped in the molten steel during pouring cannot be discharged, resulting in bubbles in the casting.

2. Prevention methods:

(1) When precision casting standards allow, set exhaust bubbles at high points of castings with complex structures.

(2) When designing the gating system, the requirements of the mold shell exhaust pipe must be considered.

(3) The mold shell heating temperature and time must be effective, and the heat insulation and heat preservation time must be sufficient.

(4) Clean the wax when dewaxing.

(5) Appropriately reduce the distance from the filling port to the glue inlet cup to make the filling speed uniform, ensure a stable steel level, store the die, and minimize the gas involved in the molten steel to facilitate the success of the die and steam in the molten steel. discharge.