1 casting temperature
The casting steepness of Guangdong mechanical processing plant usually refers to the temperature needed for the liquid metal to have good fluidity in the process of injection from holding furnace into mold through injection tool. However, at present, online degassing and filtering devices have been used in most aluminum alloy casting, and the above concept of casting temperature is not comprehensive and correct enough. Practice has proved that the degassing effect varies with the liquid temperature in the online degassing device. Therefore, it is necessary to consider the requirements of the degassing effect of the online degassing device on the liquid temperature. In addition, the gas precipitation of liquid in the mold should also be considered. Due to the low casting temperature, the gas of liquid in the mold has no time to float up and escape from the liquid surface, resulting in porosity, porosity, slag, cold shut and other ingot quality defects. The highest casting temperature should not exceed the melting temperature. Too high casting temperature will lead to aluminum leakage at the beginning of casting. The bottom crack and tension crack may also produce feather structure defects, and the temperature drop of liquid is different due to the different length of injection tools. There are hot spots in the online assembly, and the temperature of liquid fluctuates greatly during the injection process. Therefore, the scientific and standardized casting temperature should refer to the temperature of liquid injected into the mold. Generally, the casting temperature is 50 ℃ ~ 70 ℃ higher than the actual crystallization temperature of the alloy The transition zone of 3x aluminum alloy is narrow and the casting temperature should be high; The transition band of 2x, 7x alloys is wider and the casting temperature should be lower.
2 casting speed
In continuous casting of dewaxing investment castings, the length of ingot forming per unit time is called casting speed. In the old casting, one casting time is usually a fixed casting speed; Modern casting is a curve casting speed, that is, the casting start and casting process are not the same casting speed: the casting speed has a great influence on ingot cracks, ingot surface quality, ingot structure and properties. On the premise of ensuring the quality of ingot, the highest casting speed should be adopted. In order to solve the crack problem of some alloy and specification ingots in the old casting method, the process of paving or tempering was used; The modern casting method adopts the curve casting speed instead of the old casting process of paving or tempering. It not only reduces some auxiliary facilities, but also saves manpower and labor intensity, and can avoid some ingot surface quality defects. The casting speed is determined according to the characteristics of the alloy produced and the ingot section size. Generally speaking, the casting speed should be increased for the alloy and ingot with high cold crack tendency; However, the casting speed should be reduced for the alloy and ingot with high hot crack tendency
3 cooling intensity
Cooling intensity is also called cooling rate. With the increase of cooling intensity, the crystallization rate of ingot increases and the intragranular structure becomes finer; With the increase of cooling intensity, the liquid cavity becomes shallow. The results show that the size of transition zone is reduced, the metal feeding condition is improved, and the defects such as porosity and porosity in ingot are reduced or eliminated. The ingot density is increased. In addition, the size of primary compound can be refined, and the degree of regional segregation can be reduced.
In the old casting method of dewaxing investment casting, the split mould is often used, especially in the flat ingot casting. The water jacket is separated from the mould. With the development of casting technology, modern casting mold is integrated. The consumption of cooling water is large when casting with the old mold, because the water supply of the old mold is not closed, part of the cooling water is open and can not play a cooling role, and the cooling intensity of primary cooling and secondary cooling is poor, which inevitably leads to some ingot quality defects; The consumption of cooling water in modern mould is small, which is only about 70% of that in old mould. At present, low level mold casting is widely used in foreign countries. Its purpose is to improve the cooling intensity and reduce or eliminate the heating phenomenon in the air gap area after primary cooling. Therefore, there is almost no secondary cooling quenching. The height of the mold has been reduced to 100 people in the ordinary casting of flat ingot. However, it requires the operator to have a high level of operation or to add a liquid level automatic control system.
The requirement of cooling water temperature for the cold punching strength of dewaxing precision casting can not be ignored. Generally, the cooling water temperature is set at 20 degrees, but due to the regional climate conditions. Due to the different water supply facilities and plant temperature, the ingot quality defects are regional or seasonal. The modern mould water supply system has the function of pulse or cross phase transformation, which is determined by the process programming. Therefore, the cooling intensity can be set as a curve according to the needs of the casting process. Especially for some hard alloys with poor low-temperature plasticity, the cold cracks and hot cracks almost exist at the same time during casting. The additional water baffle system makes the surface temperature of the ingot rise to the plastic temperature of tensile deformation, High quality ingots can be obtained by eliminating the cold cracks of ingots and taking measures to prevent hot cracks.