Mechanical castings produce the main reason for cold separation and pouring
There is an incomplete fusion gap on the mechanical cast, and the edge of the weld is smooth. This gap is called cold. Mechanical castings are filled with local, mechanical casting lack of meat, the end of the arc was not poured. Dry sand solid casting, especially no negative pressure cast iron alloy is the case, the mechanical castings are prone to cold separation and poured less than defects, resulting in mechanical casting scrap.
The foam type is heated, decomposed, and the decomposition product is heated to the temperature of the molten metal to absorb heat, thereby cooling the molten metal. In addition, the decomposition gas increases the resistance of the liquid metal filling. These two causes a significant reduction in the fluidity of the metal liquid, which is the main cause of cold separation and pouring.
In addition, the pouring program, pouring system structure and pouring operation to produce cold separation, pouring also have a certain impact.
Mechanical casting to prevent measures: ① to improve the temperature of molten metal pouring. The casting temperature of the solid casting should be at least 30 ℃ higher than the casting temperature of the sand casting under the same conditions, and it is generally recommended to increase the temperature of 30 to 50 degrees Celsius. ② cast a certain negative pressure. Under the negative pressure of the wall can reduce the metal liquid filling when the gas resistance, when the foam type of good quality, low density and high strength, the amount of gas is small, cast aluminum alloy castings can not be negative pressure casting. When the foam quality is poor, the casting castings require negative pressure. Pouring machinery castings are generally used negative pressure casting. ③ choose a reasonable pouring program and pouring system structure. Such as the use of the top pouring pouring system, hollow sprue, to minimize the total length of the casting system, so that the metal liquid process shortened, filling process smooth, to prevent cold and poured less than defects.
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