| 摘要 |
PURPOSE:To prevent sudden spattering of molten metal by opening plural vacuum valves arranged in piping between a vacuum vessel and vacuum pump in order from near the vacuum vessel at the prescribed timing, to control vacuum exhausting velocity. CONSTITUTION:Under condition of valve 8a closed and valve 8b opened for replacing gas and valves 6a, 6a', 6a'' opened and 6b, 6b', 6b'' closed for vacuum, the vacuum vessel 2a is vacuum-exhausted by a mechanical buster pump 5 and oil rotary pump 4, and the vacuum degassing is exhausted by sucking up the molten metal 3 in a ladle 1. Next, the valve 8a is opened and valve 8a is closed for replacing gas and the vacuum valves 6a-6a'' are closed and the replacing gas is gradually introduced into the vacuum vessel 2a through valve 9 for flow rate regulating. Together with this, the vacuum valves 6b, 6b', 6b'' are opened in order, and the vacuum-exhaust is executed, while lowering step by step the pressure in the vacuum vessel 2b. In this way, while holding the molten metal level in the ladle 1 constant, and also while avoiding sudden variation of pressure, the clogging of exhaust piping caused by the spattering of molten metal is prevented.
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