Correction apparatus for correcting the planarity of a metal strip and related correction method

Abstract

A correction apparatus for correcting the planarity of a metal strip advancing into a coating system for coating said metal strip with a layer of molten metal, said apparatus comprisinga bridle roll, which modifies the feeding direction of the metal strip exiting an annealing furnace;only one sink roll, arranged downstream of said bridle roll and inside a tank adapted to contain a bath of said molten metal;a correction device for correcting the planarity of the metal strip arranged between said bridle roll and said sink roll;wherein said correction device comprises at least two motorized rolls;wherein a first motorized roll of said at least two motorized rolls is distal from said bridle roll in a fixed position with respect to a feeding path of the metal strip, said first motorized roll being arranged on a first side of said feeding path;wherein said bridle roll is also arranged on said first side;and wherein a second motorized roll of said at least two motorized rolls is proximal to said bridle roll and movable along the direction of the strip thickness, said second motorized roll being arranged on a second side, opposite to the first side, of said feeding path.

1 . A correction apparatus for correcting a planarity of a metal strip advancing into a coating system for coating said metal strip with a layer of molten metal, said apparatus comprising
 a bridle roll adapted to modify a direction of a feeding path of the metal strip exiting an annealing furnace;   only one sink roll, arranged downstream of the bridle roll along said feeding path and inside a tank adapted to contain a bath of said molten metal, said sink roll being adapted to modify the direction of the feeding path of the metal strip inside the tank;   a correction device for correcting the planarity of the metal strip, arranged between said bridle roll and said sink roll;   wherein said correction device comprises at least two motorized rolls arranged outside the tank,   wherein a first motorized roll of said at least two motorized rolls is distal from said bridle roll in a fixed position with respect to the feeding path of the metal strip, said first motorized roll being arranged on a first side of said feeding path;   wherein said bridle roll is also arranged on said first side;   and wherein a second motorized roll of said at least two motorized rolls is arranged on a second side, opposite to the first side, of said feeding path, is proximal to said bridle roll and movable along a trajectory which intersects a plane A, defined by rotation axes X, Y of the bridle roll and the first motorized roll, respectively, in an intermediate position between said rotation axes X, Y, so as to bend said metal strip in an opposite direction to a bending imparted by said bridle roll.   
     
     
         2 . The apparatus according to  claim 1 , wherein said correction device comprises a third motorized roll arranged between said bridle roll and said second motorized roll in a fixed position with respect to the feeding path of the metal strip, said third motorized roll being arranged on said first side of the feeding path. 
     
     
         3 . The apparatus according to  claim 1 , wherein there are provided
 at least one first measurement device for measuring the planarity of the metal strip, arranged downstream of the tank along the feeding path;   and a control system adapted to acquire planarity data from said at least one first measurement device and send a control signal to said correction device to possibly adjust a position of the second motorized roll along said trajectory;   preferably, wherein at least one position sensor is provided for detecting the position of the second motorized roll, said at least one position sensor being adapted to send a signal containing the data of said position of the second motorized roll to the control system.   
     
     
         4 . The apparatus according to  claim 3 , wherein at least one pair of air knives is provided, arranged downstream of the tank along the feeding path, wherein a first air knife is arranged at the first side of the feeding path and a second air knife is arranged at the second side of said feeding path;
 and wherein said at least one first measurement device is arranged upstream or downstream of said at least one pair of air knives along the feeding path.   
     
     
         5 . The apparatus according to  claim 3 , wherein there is provided at least one pair of electromagnetic stabilizer devices, arranged downstream of the tank along the feeding path, and of which a first electromagnetic stabilizer device is arranged at said first side and a second electromagnetic stabilizer device is arranged at said second side;
 and wherein the control system is adapted to acquire further planarity data from at least one second measurement device associated with said at least one pair of electromagnetic stabilizer devices, and adapted to send a control signal to said correction device to possibly adjust the position of the second motorized roll along said trajectory.   
     
     
         6 . The apparatus according to  claim 5 , wherein said at least one pair of electromagnetic stabilizer devices is arranged downstream of at least one pair of air knives along the feeding path, said at least one pair of air knives being arranged downstream of the tank. 
     
     
         7 . The apparatus according to  claim 3 , wherein said first measurement device comprises a laser scanning system. 
     
     
         8 . The apparatus according to  claim 1 , wherein said correction device comprises a movement mechanism for moving said second motorized roll along said trajectory. 
     
     
         9 . The apparatus according to  claim 1 , wherein said bridle roll and said at least two motorized rolls are arranged inside an end part of the annealing furnace, preferably upstream of a connection duct which connects said end part to the tank. 
     
     
         10 . The apparatus according to  claim 1 , wherein, with D 2  being a diameter of the bridle roll, a distance along the feeding path of the metal strip between the first motorized roll and said bridle roll is between 1.05 D 2  and 2 D 2 , preferably between 1.5 D 2  and 2 D 2 ; said second motorized roll being arranged within said distance. 
     
     
         11 . The apparatus according to  claim 2 , wherein, with D 1  being a diameter of the first motorized roll, the second motorized roll, and the third motorized roll, a distance along the feeding path of the metal strip between the first motorized roll and the third motorized roll is between 1.05 D 1  and 2 D 1 , preferably between 1.5 D 1  and 2 D 1 ; said second motorized roll being arranged within said distance. 
     
     
         12 . The apparatus according to  claim 1 , wherein the sink roll has a diameter D 3  which is greater than a diameter D 1  of said at least two motorized rolls, and wherein a diameter D 2  of the bridle roll has a value which is greater than or equal to the diameter D 3  or said diameter D 2  can have an intermediate value between the diameter D 1  and the diameter D 3 . 
     
     
         13 . The apparatus according to  claim 12 , wherein the ratio D 3 /D 1  is from 1.5 to 6.6, the ratio D 3 /D 2  is from 0.5 to 1.6, and the ratio D 2 /D 1  is from 1.5 to 8. 
     
     
         14 . The apparatus according to  claim 13 , wherein, in the case of the diameter D 2  having a value which is greater than or equal to the diameter D 3 , the diameter D 3  of the sink roll is in a range from 600 to 1000 mm; the diameter D 2  of the bridle roll is in a range from 600 to 1200 mm; and the diameter D 1  of said at least two motorized rolls is in a range from 150 to 400 mm. 
     
     
         15 . The apparatus according to  claim 12 , wherein the ratio D 3 /D 1  is from 1.5 to 6.6, the ratio D 3 /D 2  is from 0.6 to 2.5, and the ratio D 2 /D 1  is from 1 to 6. 
     
     
         16 . The apparatus according to  claim 13 , wherein, in the case of the diameter D 2  having an intermediate value between the diameter D 1  and the diameter D 3 , the diameter D 3  of the sink roll is in a range from 600 to 1000 mm; the diameter D 2  of the bridle roll is in a range from 400 to 900 mm; and the diameter D 1  of said at least two motorized rolls is in a range from 150 to 400 mm. 
     
     
         17 . The apparatus according to  claim 1 , wherein at least two bridle rolls are provided and only one correction device is arranged between the last bridle roll and said sink roll. 
     
     
         18 . A method for correcting a planarity of a metal strip advancing into a coating system for coating said metal strip with a layer of molten metal, the method being carried out by a correction apparatus according to  claim 1  and comprising the following steps:
 a) modifying, by means of the bridle roll, the direction of the feeding path of the metal strip exiting an annealing furnace; 
 b) modifying again, by means of the sink roll, the direction of the feeding path of the metal strip immersed in the tank; 
 wherein the step of correcting the planarity of the metal strip by means of the at least two motorized rolls of the correction device is provided between step a) and step b), by moving the second motorized roll along a trajectory which intersects the plane A, defined by the rotation axes X, Y of the bridle roll and the first motorized roll, respectively, in an intermediate position between said rotation axes X, Y, so as to bend said metal strip in the opposite direction to the bending imparted by said bridle roll. 
 
     
     
         19 . The method according to  claim 18 , wherein in order to correct the planarity of the metal strip, the following steps are included:
 measuring the planarity of the metal strip by means of at least one first measurement device arranged downstream of the tank along the feeding path;   acquiring planarity data from said first measurement device and sending a control signal, by means of a control system, to said correction device to possibly adjust a position of the second motorized roll along said trajectory.   
     
     
         20 . The method according to  claim 19 , wherein the step of measuring the planarity of the metal strip is carried out upstream or downstream of at least one pair of air knives. 
     
     
         21 . The method according to  claim 19 , wherein, in order to correct the planarity of the metal strip, the following steps are also included:
 acquiring further planarity data from at least one second measurement device associated with at least one pair of electromagnetic stabilizer devices, arranged downstream of the tank, and sending a further control signal, by means of the control system, to said correction device to possibly adjust the position of the second motorized roll along said trajectory.   
     
     
         22 . A system for coating a metal strip with a layer of molten metal, comprising a correction apparatus according to  claim 1  for correcting the planarity of the metal strip advancing along said system.