Oxygen-filled die-casting is divided into: oxygen-filled die-casting and directional air extraction and oxygen-filled die-casting
(1) Oxygen die casting
When analyzing the bubbles of aluminum alloy die castings abroad, it is found that 90% of the gas is nitrogen, while the nitrogen in the air should be 80%, and the remaining 20% is oxygen. This shows that die casting parts of the oxygen in the bubble reacts with the molten aluminum as follows:
Based on this fact, a new process of oxygen-added die-casting was developed.
Oxygen-added die casting is to fill the pressure chamber and cavity with oxygen before filling the cavity with molten aluminum to replace the air and other gases. When the molten aluminum is filled, oxygen is discharged through the exhaust groove on the one hand, and on the other hand The sprayed aluminum metal liquid chemically reacts with the oxygen that is not discharged to produce A1203 particles, which are dispersed inside the die casting, thereby eliminating the pores formed in the die casting when no oxygen is added. This kind of A1203 particle particles are fine, about 1 micron or less, and its mass (weight) accounts for 0.1% to 0.2% of the total mass (weight) of die castings, does not affect the mechanical properties, and allows die castings to be heat treated. Oxygenated die casting is only suitable for aluminum alloy die casting.
Oxygenated die casting has the following characteristics:
- ① Eliminate or reduce pores and improve the quality of die castings. The as-cast strength of the aluminum alloy after adding oxygen can be increased by 10% compared with the general die-casting method, and the elongation rate can be increased by 1.5 to 2 times. Because there are no pores in the die-casting, the aluminum alloy can be heat treated, and the strength can be increased by 30% after heat treatment. The limit is increased by 100%, and the impact toughness is also significantly improved.
- ②The die-casting parts can work in an environment of 200-300℃ and can be welded.
- ③Compared with vacuum die casting, it has simple structure, convenient operation and low investment.
Two ways of oxygenation:
1. During the mold clamping process
When the distance between the moving and fixed molds is 50-60nun, the oxygen (pressure 0.3-0.5MPa) coming from the oxygen cylinder through the safety valve and the pipeline passes through the distributor (20 diameters of 3 Small holes, uniform air intake) are filled into the cavity. At this time, the mold clamping process continues. After the mold clamping is completed, continue to add oxygen for a period of time, close the oxygen valve, wait a while based on experience, and then pour molten aluminum to proceed with the normal die casting process.
- 1-moving mold
- 2-fixed mold
- 4-return piston
2. Add oxygen directly from the barrel
Die casting with directional air extraction and oxygen
The essence of directional suction and oxygen die casting is a combination of vacuum die casting and oxygen die casting. The process is to pump out the gas along the filling direction of the molten metal at a speed exceeding the filling speed before the molten metal fills the cavity, so that the molten metal is filled smoothly. For complex castings with deep recesses or dead corners, oxygen is added while pumping air to achieve better results. Its advantage lies in avoiding the entrapment of gas into the molten metal and preventing porosity in the casting.