Generally speaking, the relative density of castings is not high, and quenching and tempering treatment or reheating castings for other purposes should be avoided as much as possible. When aluminum die casting, the gas or vapor is enclosed in the casting, which is basically unavoidable.

Method of heat treatment of die castings

When the casting is reheated to a temperature close to the temperature at which the casting is ejected from the press plate, the encapsulated gas swells and saturates the surface of the casting. It is very aluminum alloy die-casting, and bubbles are more likely to appear during re-quenching and tempering. Before the casting is quenched and tempered, in order to prevent the vapor from being enclosed in the casting, two methods have been developed, namely vacuum pump aluminum Die casting and specific vapor methods, which can be used to remove internal vents and surface air bubbles. The vacuum pump aluminum die-casting adopts a mechanical pump and gas storage tank, and the storage gas tank is connected with the die through the safety channel on the pressing plate. Before aluminum die casting, the gas in the die is extracted.

In order to prevent the liquid metal material from entering the ultrafiltration device, there are two ways to choose a pressure controller or to condense the metal material in the safe passage of the vacuum packaging. The pressure controller method is based on the working pressure photoresistor built on the top of the profile plate In the position of the device, this component is activated by the metal material liquid entering the pressure plate. The gate valve far from the ultrafiltration device is closed before the metal material liquid arrives, thereby preventing the metal material liquid from entering the ultrafiltration device. This type of condensation of the metal material flow before the ultrafiltration device is accomplished by means of a wave-shaped water-cooled heat dissipation safety channel (the vapor is drawn out through this safety channel).

When the specific vapor method is used, the vapor and gas in the pressing plate are removed by the specific vapor (usually oxygen) entering the pressing plate. As soon as the metal material liquid enters the die, it forms a solid compound with the specific vapor, and this kind of solid particles spreads evenly throughout the casting. For example, when aluminum is die-casting, CO2 is used, and very fine aluminum oxide is distributed in all castings.

How to solve the phenomenon of shot blasting and peeling of die castings

Castings often have surface peeling after shot blasting and rust removal, which is generally caused by the following reasons:

• The abrasive tool or injection chamber (melting cup) is not cleaned and tidy;
• Insufficient working pressure for injection (pay special attention to whether the movable die is forgiving during injection);
• The setting of the pouring system software is a bit difficult, and there is a flow field condition when the aluminum alloy liquid enters the die;
• Mold temperature problems, etc.;
• The metal material liquid splashes more seriously during injection.

The release agent is generally not easy to penetrate the casting. However, the fake and inferior release agent will cause erosion on the surface of the casting, and will penetrate the interior; in addition, if the release agent has a large air supply, it will be rolled into the casting to produce air vents. If the application of architectural coatings such as mold paste is not timed, it will cause defects such as welding flashes.

After shot blasting and rust removal of castings, the surface of the product fades, mainly because the applied shot blasting and rust removal are not very good. If stainless steel shot is used, add a small amount of aluminum shot inside, and the surface of the product will be white after throwing.

There are often mildew spots on the surface of castings, which seriously harms the appearance quality of castings, mainly caused by release agents. At this stage, there are a large number of manufacturers producing release agents on the market, and many of them have various problems with quality. The key is the corrosion effect on castings. Generally, the foundry does not pay much attention to it. If the casting time is longer, there will be vitiligo (frost-like, gray-black after removal) on the surface, which has actually caused corrosion. Mainly, there are ingredients in the release agent that will cause corrosion. Therefore, the choice of release agent must not only be perfect and cheap, but also cost-effective.

Conclusion

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