Rolling mill exit side temperature control system

1. A rolling mill exit side temperature control system including a plurality of rolling stands rolling a material to be rolled, the system comprising:

a cooling apparatus provided in at least one of a plurality of spaces between the rolling stands; and

a cooling apparatus control unit controlling the cooling apparatus, wherein

the cooling apparatus includes

a spray nozzle spraying coolant onto the material to be rolled, a coolant passage supplying the coolant to the spray nozzle, a first valve in the coolant passage upstream of the spray nozzle in a coolant flow direction and being changeable to an open state or a closed state,

a first valve control unit controlling the first valve to the open state or the closed state,

a second valve in the coolant passage upstream of the first valve in the coolant flow direction and being changeable in valve opening,

a flow rate detector detecting a flow rate of the coolant flowing through the coolant passage upstream of the second valve,

a second valve control unit controlling opening of the second valve to cause a flow rate actual value detected by the flow rate detector to coincide with a flow rate target value, and

the cooling apparatus control unit includes a remaining coolant discharging section controlling the first valve to the open state and the second valve to the closed state by setting the flow rate target value to zero before the material to be rolled reaches the rolling mill, and

a flow rate target value setting section setting the flow rate target value to a value corresponding to a target temperature of the material to be rolled after the control by the remaining coolant discharging section.

2. The rolling mill exit side temperature control system according to claim 1 , wherein the cooling apparatus includes a first cooling apparatus and a second cooling apparatus:

the first cooling apparatus is in any of the plurality of spaces between the rolling stands; and

the second cooling apparatus is in any of the plurality of spaces between the rolling stands upstream of the first cooling apparatus in a material rolling direction,

the remaining coolant discharging section controls the first valve to the open state and the second valve to the closed state by setting the flow rate target value to zero, in the first cooling apparatus and the second cooling apparatus, before the material to be rolled reaches the rolling mill,

the flow rate target value setting section sets the flow rate target value of the first cooling apparatus to a value corresponding to the target temperature of the material to be rolled, after the control by the remaining coolant discharging section,

set the flow rate target value of the second cooling apparatus to zero in a case where a cooling capacity of the first cooling apparatus is not saturated, and

set the flow rate target value of the second cooling apparatus to a value corresponding to the target temperature of the material to be rolled in a case where the cooling capacity of the first cooling apparatus is saturated.

3. The rolling mill exit side temperature control system according to claim 1 , wherein the rolling mill is a finishing mill.

4. The rolling mill exit side temperature control system according to claim 1 , wherein the rolling mill is a roughing mill.

5. The rolling mill exit side temperature control system according to claim 1 , wherein the cooling apparatus control unit controls the first valve to the closed state after a preceding material to be rolled passes the rolling mill.