Method of manufacturing a slag discharge door

A method of manufacturing a slag discharge door in an electric furnace that has a molten-steel discharge opening to discharge molten steel, the method comprising:

• forming a slag discharge opening in the electric furnace separate from the molten-steel discharge opening;
• forming a door body of the slag discharge door;
• forming a coolant passageway, a coolant inlet, and a coolant outlet by drilling into the formed door body;
• and
• closing an open portion of the formed coolant passageway, wherein the open portion is open to an exterior of the door body,
• wherein the coolant passageway includes:
• a coolant inflow pipe into which coolant is introduced;
• a plurality of coolant branch pipes spaced apart from each other and connected to the coolant inflow pipe to allow the coolant fed from the coolant inflow pipe to pass therethrough;
• and
• a coolant discharge pipe connected to an outlet of each of the coolant branch pipes,
• wherein the door body is formed with guide protrusions that protrude from both side of an upper portion of the door body, and
• wherein forming the coolant passageway includes:
• forming a lower horizontal inflow pipe horizontally disposed on a lower portion of the door body and an upper horizontal discharge pipe horizontally disposed on the upper portion of the door body, by horizontally drilling a side of the door body;
• inserting a side stopper into a portion of each of the lower horizontal inflow pipe and the upper horizontal discharge pipe, wherein the side stopper is open to a side of the door body to block the open portion;
• forming a first side vertical discharge pipe and a second side vertical discharge pipe to form a second passageway by downwardly drilling an upper surface of each of the guide protrusions and connecting the first and second side vertical discharge pipes at an upper end of the guide protrusion, wherein the first side vertical discharge pipe is disposed vertically and connected at a lower end thereof to the upper horizontal discharge pipe, the second side vertical discharge pipe is vertically disposed in the guide protrusion to be spaced apart from the first side vertical discharge pipe and passing through the side stopper of the upper horizontal discharge pipe to allow a lower end thereof to extend to the lower horizontal inflow pipe;
• forming the coolant outlet and the coolant inlet by upwardly drilling a lower surface of the door body, wherein the coolant outlet communicates with the second side vertical discharge pipe and the coolant inlet communicates with the lower horizontal inflow pipe;
• and
• forming a plurality of vertical branch pipes to be spaced apart, by upwardly drilling the lower surface of the door body, wherein each of the vertical branch pipes passes through the lower horizontal inflow pipe and is connected at an upper end thereof to the upper horizontal discharge pipe.