| 摘要 |
The method comprises controlling a switching valve (1) by a binary control signal in response to a desired cooling power, actuating a switching element of the switching valve in dependence on the control signal, bringing the switching element in response to the control signal from a closed position to an open position or vice versa, where a flow rate of a cooling medium is opened in an open position of the switching element and is closed in a closed position of the switching element through the switching valve, and intermittently discharging the cooling medium on a metal strand. The method comprises controlling a switchable switching valve (1) by a binary control signal in response to a desired cooling power, actuating a switching element of the switching valve in dependence on the control signal, bringing the switching element, in response to the control signal, from a closed position to an open position or vice versa, where a flow rate of a cooling medium is opened in an open position of the switching element and is closed in a closed position of the switching element through the switching valve, and intermittently discharging the cooling medium on a metal strand through a cooling nozzle (2). The binary control signal is a pulse width modulated control signal. The switching element is electromagnetically, pneumatically or hydraulically actuated. The switching valve is pneumatically pre-controlled, where: a pneumatic pilot pressure connects two different pressure levels; and a lower pressure level is greater than the ambient pressure. The step of controlling the switchable switching valve comprises controlling a carrier frequency of the pulse width modulated control signal and a pulse-width ratio of the pulse width modulated control signal in response to a strand age or a strand position. The pressure of the cooling medium is changed depending on the desired cooling power. The method further comprises detecting a surface temperature of the strand, determining a control error, according to an equation, e = T s o l l- T depending on the nominal temperature of the strand and calculating a manipulated variable u by a control device in dependence on the control error, before actuating the switching element of the switching valve, where the desired cooling power is set over the control signal as a function of the manipulated variable (u). A space between the switching valve and the cooling nozzle is blown with air in the closed position of the switching element. |
