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Molten Metal Equipment Innovations |
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There are many different ways that hydrogen is introduced into molten Aluminum. Water vapor and steam are a large source. Other sources include refractories, furnace tools, and other materials added to the furnace. Oil or hydroxide coatings and hydrated corrosion products may also introduce hydrogen to the metal. Large amounts of hydrogen can be dissolved in molten Aluminum, especially at high temperatures. The problem begins as the aluminum cools in the mold. The solubility of the hydrogen decreases with temperature, leading to a rapid expulsion of gas form the aluminum. This produces bubbles, which are then trapped within the casting.
Porosity in castings leads to many problematic effects. Porosity results in lower mechanical properties, as well as lower resistance to corrosion and crack propagation. This will also lead to surface defects and blemishes.
To eliminate hydrogen from your casting, an inert gas must be introduced. Typically nitrogen or argon is used and injected into the metal bath as bubbles. The inert gas bubbles move up through the molten aluminum, hydrogen diffuses into the inert gas bubbles because of the difference between its partial pressure in the melt and its partial pressure in the bubbles. The inert gas bubbles carry the hydrogen to the surface and out of your casting.
MMEI offers a complete range of degassing equipment whether you are degassing in the furnace, ladles or pots, or even over the road containers. All MMEI degassing equipment offers superior bubble shearing and dispersion to reduce the hydrogen in your castings – faster.
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