Method of and apparatus for casting metal using carbon dioxide to form gas shield

A method of carrying out a number of shrouding operations serially in which molten metal gravitates in a stream from an upper vessel to a lower vessel and a shroud is formed about the stream to protect it from the surrounding atmosphere, comprising,

• providing a supply of liquid carbon dioxide and an overlying supply of vapor in a vapor space in a pressure vessel under predetermined pressure,
• carrying out a number of shrouding operations in series by dispensing vapor from the vapor space in a continuous series of increments one to each operation in succession, each increment producing a pressure drop within the vessel,
• responsive immediately to the pressure drop caused by each burst withdrawing liquid carbon dioxide from the reservoir and passing it into the overlying supply of vapor until pressure equilibrium is restored and the vapor lost in the increment is replaced,
• superheating each increment of carbon dioxide leaving the pressure vessel,
• passing the heated increment through a pressure reducing regulator set at a pressure to give the desired flow rate for dispensing through control valves to the dispensing device for carrying out each operation.

An apparatus for carrying out a number of shrouding operations in series, in each operation a stream of steel being passed from an upper vessel to a lower vessel, comprising,

• an upper vessel having a bottom opening for forming a gravitating stream of steel,
• a pressure vessel for containing a body of liquid carbon dioxide covered by an atmpsphere of carbon dioxide gas,
• means defining a gas dispensing passage from the pressure vessel leading to dispensing means surrounding the bottom opening of the upper vessel,
• means for controlling the means defining the gas dispensing passage whereby carbon dioxide gas is dispensed from the pressure vessel in increments required for each shrouding operation,
• as carbon dioxide gas is withdrawn from the pressure vessel replacing it with liquid carbon dioxide,
• means for controlling the means defining the gas dispensing passage whereby the carbon dioxide gas is supplied in amounts suitable for forming the shroud,
• means for superheating the carbon dioxide gas leaving the pressure vessel,
• pressure reducing means and valve means for controlling the flow of carbon dioxide gas to the dispensing means,
• means for controlling the temperature to which the carbon dioxide gas is superheated, whereby when it is expanded in dispensing, the temperature is reduced to not less than ambient temperature so that the carbon dioxide is dispensed as a gas.