U.S. Patented Chill Vents Designed and Manufactured by NGK

What is a Chill Vent?

• Chill vents are often used in association with permanent molds for die casting light metals such as aluminum and magnesium. The chill vent functions as a means of efficiently exhausting residual air and/or gas from the inside to the outside of a die cast mold cavity. It is intended to minimize the spouting of molten metal and reduce the formation of flashing when charging molten metal into the die cavity.
• If, during the process, residual air and/or gas remain in the die cavity, this air and gas will tend to be dragged into the molten metal resulting in gas holes and the like in the castings, thereby degrading product quality.
• Chill vent gas exhaust passage design is generally shaped in a zigzag manner to ensure that after the gas has been exhausted outside of the chill vent, the molten metal will be chilled in the zigzag passage before it is flashed outside of the permanent mold.
• However, since molten metal flows under high pressure, it is difficult to completely prevent flashing even by increasing the length of the chill vent.
• Tool steels, although high in hardness, have low thermal conductivity, and, therefore, cannot rapidly remove heat from non-solidified molten metal before flashing occurs.
• Since both high hardness and superior thermal conductivity are critical requisites in achieving accelerated cooling of molten metal under high pressure, it has been considered that copper alloys would provide superior thermal conductivity. However, few copper alloys provide both thermal conductivity and hardness in combination sufficient to withstand the pressure that results in die casting molten metal.
• Additionally, copper alloys are generally difficult to use for molds brought into contact with molten metal because they are easily dissolved by light metal alloys compared to tool steel.
• Conventional chill vent material has been predominantly made of tool steel, typically the same as the cavity permanent mold. It is necessary that the chill vent be as hard as the cavity permanent mold due to the high-pressure condition that develops when the molten metal is charged into the chill vent.

Why NGK beryllium copper chill vents?

• Only one alloy, beryllium copper, can provide both the hardness and thermal conductive properties required for use as a chill vent in aluminum and/or magnesium die-casting.
• NGK beryllium copper chemistry also provides the benefit of causing a passive-state oxide film to be formed on the surface of the chill vent, thereby preventing dissolution by light metal alloys.
• These factors provide an effective means of exhausting air and gases outside the mold without being dissolved while chilling the molten metal before flashing occurs.
• As a further consideration, the addition of water cooling pipes in the chill vent will serve to improve the overall cooling power which can result in a shortening of the length of the gas exhaust passage, leading to a smaller chill vent, thus increasing die space.