Method for controlling a metal strip in a heat treatment furnace

Abstract

The invention relates to a method for controlling a metal strip to be heat-treated, contained in a continuously operated heat treatment furnace and proceeding in an essentially horizontal direction and suspended position in a zone arranged between elements meant for supporting the metal strip when said metal strip is being cooled. The trajectory of the metal strip is measured by a measuring device, and on the basis of the obtained measurement results, the metal strip is subjected to a controlled cooling agent jet, so that the trajectory of the metal strip, at least in the zone located between the elements meant for supporting the metal strip, is made to proceed in between devices installed around the trajectory and meant for conveying the cooling agent.

Claims

1. A method for carrying out a heat treatment operation on a metal strip, comprising: continuously feeding the metal strip lengthwise in an essentially horizontal direction through a cooling zone so that the metal strip extends through the cooling zone, supporting the strip extending through the cooling zone at first and second support locations that are at substantially equal vertical heights and are spaced apart horizontally, positioning the strip so that it avoids mechanical contact from anything other than the support locations, and the strip is suspended between the first and second support locations and follows a trajectory between the first and second support locations, the first support location being upstream of the cooling zone relative to feeding movement of the metal strip and the second support location being downstream of the cooling zone relative to feeding movement of the metal strip, dividing the cooling zone into at least an upstream block and a downstream block with at least one partition wall, employing a first device to project at least a first jet of a cooling agent towards the metal strip in the upstream block of the cooling zone, employing a second device to project at least a second jet of a cooling agent towards the metal strip in the downstream block of the cooling zone, preventing, by use the at least one partition wall, the cooling agent projected from the first device in the upstream block from flowing to the area of the downstream block, measuring a value for a position and sagging of the metal strip between the first and second support locations, comparing the measured value of the metal strip with a predetermined desired position and sagging value, controlling at least one of the cooling agent jets in response to the comparison, and changing the position and sagging of the metal strip by changing a force of an emitted cooling agent from at least one of the cooling jets aimed toward and supporting metal strip, wherein the first device, the second device, or both, are installed around the trajectory of the metal strip.

2. A method according to claim 1, wherein the cooling agent of the first and second jets is air.

Description

(1) The invention is described in more detail below, with reference to the appended drawing, where

(2) FIG. 1 is a side-view illustration of a preferred embodiment of the invention, seen schematically in a partial cross-section.

(3) According to FIG. 1, a hot, annealed strip 1 made of stainless steel enters from the annealing step 2 to the cooling zone 3, in which case the essentially horizontal proceeding direction of the strip 1 is illustrated by the reference number 4. In the proceeding direction 4 of the strip, at the outlet 5 of the annealing zone 2 and simultaneously at the inlet 5 of the cooling zone 3, there is installed a roller arrangement 6 supporting the strip 1. A corresponding roller arrangement for 6 supporting the strip 1 is installed in the proceeding direction 4 of the strip at the outlet 7 of the cooling zone 3. In between the roller arrangements 6, the strip 1 is in a suspended position.

(4) In the cooling zone 3, in the proceeding direction 4 of the strip, above the strip 1 and underneath the strip 1 there are installed cooling agent pipes 8 for conveying the cooling agent 7 to the vicinity of the strip 1, and that end 9 of said pipes 8 that is located nearest to the strip 1 is provided with at least one nozzle 10 for directing the cooling agent 7 onto the surface of the strip 1.

(5) The position of the strip 1 located between the roller arrangements 6 both in the width direction of the strip 1 and in the lengthwise direction of the strip 1 is measured by at least one measuring device 11, preferably a laser measuring device. The measurement signal obtained from the measuring device 11 is fed to an automation unit 12 that is electrically 14 connected to the measuring device 11. In addition, the automation unit 12 is advantageously connected electrically 15, either separately or in a group, to every nozzle 10 provided in the cooling agent pipes 8 in order to control the nozzles for achieving the desired position value for the strip 1 at various points of the cooling zone 3. For the sake of simplicity, only two nozzles are illustrated in the drawing as regards the electrical connecting 15 of the nozzles 10. The figure also shows partition walls 13 that divide the cooling zone into cooling blocks.

(6) In the automation unit 12, the obtained measurement signal value is compared with the desired position value of the strip 1 with respect to the cooling agent pipes 8. In case the measured value deviates from the desired position value of the strip 1, a control signal is sent from the automation unit 12 to at least one cooling agent pipe nozzle 10 for correcting the position value of the strip 1 essentially at that point of the cooling zone 3 where the measurement signal deviating from the desired position value was sent from. The control signal for changing the position value of the strip 1 adjusts the adjusting device provided in connection with the nozzle 10, which device changes the pressure of air emitted through the nozzle 10 with respect to the strip 1.