Method to control a secondary cooling apparatus in a machine for continuous casting of metal products and secondary cooling apparatus for a continuous casting machine

A method to control a secondary cooling apparatus in a machine for continuous casting of metal products, said secondary cooling apparatus (12) comprising a roller path (15) which moves a cast metal product (P) along an axis of movement (X), a plurality of cooling units (17) equipped with nozzles (18), each nozzle (18) being provided with delivery orifices (19) from which a refrigerant fluid (L) is delivered, on each occasion according to punctual cooling needs, toward said metal product (P),

• said method comprising:
• activating said delivery orifices (19) individually, in sequence or in combination with each other, so that as the punctual cooling needs of said metal product (P) vary, a flow rate (Q) of refrigerant fluid (L) required on each occasion to cool said metal product (P) is varied,
• opening or closing the delivery orifices (19) of respective nozzles (18) in sequence from a first delivery orifice (19a) to a last delivery orifice or from the last delivery orifice to the first delivery orifice (19a) when the flow rate (Q) of the refrigerant fluid (L) increases or decreases,
• feeding said delivery orifices (19) with a minimum delivery pressure to obtain said flow rate (Q), and
• delivering the flow rate (Q) of refrigerant fluid (L) from the first delivery orifice (19a) when the flow rate (Q) of cooling fluid (L) required to cool the metal product (P) requires a first feed pressure (p1) of the first delivery orifice (19a) of one or more of said nozzles (18) which is greater than a first minimum pressure (p01) of the first delivery orifice (19a) and a second feed pressure (p1+2) relative to a second delivery orifice (19b) cooperating with said first delivery orifice (19a) is lower than a second minimum pressure (p02) relative to said second delivery orifice (19b) together with said first delivery orifice (19a).