Die Casting Knowledge(2)

- Jun 19, 2019-

1.“Preventing, arranging, and removing” of hydrogen removal: It is to prevent moisture and various contaminants from entering the crucible or the furnace. “Row”: It is to exclude the oxidation inclusions and hydrogen in the aluminum liquid, because only the effective removal of the suspension Dispersed inclusions (mainly Al2O3) in the aluminum liquid can prevent the aluminum liquid from hydrogen and eliminate the dehydrogenation barrier, thereby obtaining pure aluminum liquid and pouring out qualified castings. "The slag is exhausted and the gas must be removed" This is what it means. "Soluble": It is to make the hydrogen in the aluminum liquid partially or completely solid solution in the alloy structure during solidification, so as not to form pores in the casting.

2. It is reported that the optimum temperature of the mold should be controlled at 40% of the pouring temperature. The temperature of the aluminum alloy die-casting mold is 230 to 280 °C. The mold temperature in this range is favorable for obtaining high quality and high yield castings. The sequential filling facilitates the discharge of the cavity gas, and the sprue and runner have a sufficient length >50 mm. In order to facilitate the smooth flow of the alloy liquid and the gas has a chance to discharge. The thickness of the gate, the direction of the gate, and the overflow groove and the exhaust groove can be set at the position where the air hole is formed. The sum of the cross-sectional area of the overflow product shall not be less than 60% of the total cross-sectional area of the ingate, otherwise the slagging effect will be poor.

3. Reduce the gas content in the aluminum water to prevent a large amount of gas from generating pores in the precipitation surface of the aluminum alloy. This is the purpose of refining and degassing during the melting of the aluminum alloy. If the gas content is originally reduced in the aluminum liquid, the amount of evolved gas at the time of solidification is reduced, and the number of generated bubbles is reduced and significantly reduced. Therefore, the refining of aluminum alloy is a very important process, the refining quality is good, the pores are inevitably small, the refining quality is poor, and the pores are inevitably more. The measure to ensure the quality of refining is to use a good refining agent. A good refining agent can react to produce bubbles at around 660 °C. The bubbles generated are not too intense, but bubbles are generated uniformly and through physical adsorption. Full contact with aluminum liquid, the longer the better, generally have 6-8 minutes of bubbling time. When the aluminum alloy is cooled to 300 ° C, the solubility of hydrogen in the aluminum alloy is only 0.001 cm 3 / 100 g or less, at this time only 1 / 700 of the liquid state, the pores generated by the precipitation of hydrogen after solidification are dispersed, small The pinholes, which do not affect the gas and the machined surface, are virtually invisible to the naked eye. However, when the aluminum liquid solidifies, the bubbles generated by the precipitation of hydrogen are relatively large, and the cores which are mostly solidified in the aluminum liquid, although dispersed, often cause leakage. Seriously, the workpiece is often scrapped.