The fluidity of the alloy is usually determined by a spiral specimen, as shown in Figure 1-4-1. The size of the fluidity is assessed by the length of the cast spiral specimen. Table 1-4-1 shows the fluidity of commonly cast alloys.
Factors affecting the fluidity of the alloy are as follows:
(1) the composition of the alloy
Composition of different alloys with different crystallization characteristics, mobility is also very different. Pure metal **** crystal alloy is crystallized at a constant temperature, crystallization from the surface to the center of the layer by layer solidification, has solidified the surface of the metal is relatively smooth, the flow of unsolidified metal obstruction is small, good mobility.
Especially *** crystal alloy, the lowest melting point, and therefore the best mobility. Such as ZL102 is *** crystal alloy, good fluidity.
Other components of the alloy crystallization of the formation of dendritic dendrites, hindering the flow of liquid metal, so poor mobility. The larger the crystallization temperature interval, the poorer the fluidity of the alloy. Such as cast steel crystallization interval is large, poor fluidity.
(2) pouring conditions
Pouring temperature and pouring pressure have a great influence on the alloy fluidity. Appropriately increase the pouring temperature, can delay the solidification of the alloy, improve the fluidity, such as Table 1-4-1 in the cast steel, when the temperature is increased from 1600 ℃ to 1640 ℃, the spiral specimen length from 100 mm to 200 mm. but the temperature is too high will lead to severe oxidation, contraction increases, resulting in shrinkage, shrinkage, and sticking sand, coarse crystal and other defects.
Increased pouring pressure and increased fluidity. Gravity casting, increase the height of the straight pouring channel can increase the liquidity. In low-pressure casting, centrifugal casting fluidity has been greatly improved. Pressure casting of high pressure can even be semi-solidified metal pressed into the mold molding.
The ability of casting heat dissipation also has a great influence on the fluidity. The faster the mold dissipates heat, the worse the fluidity. Metal type faster thermal conductivity, metal casting than sand casting is easy to produce pouring defects such as insufficient. Preheating the casting can improve the mobility, improve the ability to fill the mold.
The casting should have good permeability, or open enough exhaust channel, so that the casting of the gas is easy to discharge. Otherwise, the back pressure generated by the gas will also hinder the flow of liquid metal. In addition, the structure of the casting, such as casting size, wall thickness and complexity of the casting also has a greater impact on the filling capacity.