Method and apparatus for continuously treating metal strip

Abstract

An apparatus for continuously treating metal strip of aluminum, an aluminum alloy, a nonferrous metal, or a nonferrous-metal alloy, has at least one heat-treatment device through which the metal strip passes in a strip-travel plane in a travel direction without contact from an upstream inlet end to a downstream outlet end and having a heating zone at the upstream end and a cooling zone formed by a row extending in the direction of at least two cooling subzones. A strip-centering device between the cooling subzones adjusts a position of the metal strip in the strip-travel plane and transverse thereto.

Claims

1. An apparatus for continuously treating strip of aluminum, an aluminum alloy, a nonferrous metal, or a nonferrous-metal alloy, the apparatus comprising: at least one noncontact tunnel furnace having relative to a strip-travel direction an upstream inlet end, a downstream outlet end, a heating zone at the upstream end, a first cooling subzone downstream of the heating zone, and a second cooling subzone spaced downstream in the direction from the first cooling subzone; means for moving the strip through the tunnel in the strip-travel direction; guide means for supporting the strip on movement of the strip in the heating zone and cooling subzones zones in a plane including the strip-travel direction with the strip moving without contact through the heating zone and cooling subzones; and a strip-centering linear motor out of contact with the strip and between the first and second cooling subzones for adjusting a position of the metal strip in the strip-travel plane land transverse thereto.

2. The strip-treating apparatus defined in claim 1, wherein the means for moving include: means upstream of the upstream end for decreasing tension in the strip in the heating and cooling zones; and means downstream of the downstream end for increasing tension in the strip downstream of the downstream end.

3. The strip-treating apparatus defined in claim 1, further comprising: a second strip-centering linear motor downstream of the second cooling subzone for adjusting a position of the metal strip in the strip-travel plane and transverse thereto.

4. A method of continuously treating strip of aluminum, an aluminum alloy, a nonferrous metal, or a nonferrous-metal alloy, the method comprising the steps of: transporting the strip in a strip-travel plane and in a strip-travel direction through a noncontact tunnel furnace having an upstream heating zone, a first downstream cooling subzone and a second downstream cooling subzone spaced in the direction from the first cooling subzone such that the strip is heated in the heating zone and cooled in the first and second cooling subzone; supporting the strip only on a fluid cushion in the noncontact tunnel furnace and keeping the strip out of contact with the furnace; and adjusting a position of the strip in the noncontact tunnel furnace in the strip-travel plane and transverse thereto with a strip-centering linear motor between the first and second subzones and out of contact with the strip to center the strip in the noncontact tunnel furnace.

5. The strip-treating method defined in claim 4, further comprising the steps of: reducing tension in the strip generally at the upstream end; and increasing tension in the strip generally at the downstream end.

6. The strip-treating method defined in claim 4, wherein the strip position is controlled with a PI adjusting method comprising a proportional P component and an integral I component.

7. The strip-treating method defined in claim 4 wherein at the strip-centering linear motor the strip has a temperature of 100 C. to 200 C.

8. The strip-treating apparatus defined in claim 1, wherein the guide means includes jets in the furnace forming a fluid cushion underneath and supporting the strip.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) The above and other objects, features, and advantages will become more readily apparent from the following description, reference being made to the accompanying drawing in which:

(2) FIG. 1 is a simplified schematic view of a prior-art strip-treating apparatus according to the prior art,

(3) FIG. 2 is a simplified schematic diagram of a strip-treating apparatus according to the invention, and

(4) FIG. 3 shows a modified embodiment of the system of FIG. 2.

SPECIFIC DESCRIPTION OF THE INVENTION

(5) As seen in FIG. 1, a prior-art strip-treating apparatus for continuously treating metal strip, namely thermal treatment has a heat-treatment device 2 designed as a noncontact tunnel furnace. The metal strip 1 passes in a travel direction D lying in a horizontal strip plane through this noncontact tunnel furnace 2 in a noncontact process, in that the strip is suspended between pressurized air issuing from upper jets and lower jets. No details are shown here. The noncontact tunnel furnace 2 has a heating zone 3 at the upstream inlet region and a cooling zone 4 at the downstream outlet region. The heating zone is usually comprised of multiple heating subzones 3, and the cooling zone is usually comprised of multiple cooling subzones 4 such that the individual subzones are controllable individually, i.e. separately. The metal strip is usually heated with the help of air in the heating zones, so that the jets, for example the lower jets, can also assume the temperature-control function in addition to a support function. The cooling in the cooling zones is usually also performed by air or by a combination of air and water.

(6) In the case of an annealing line for aluminum strips for automotive use, the target temperature in the heating zone is approximately 550 C. to approximately 570 C., for example. The heating zones therefore comprise heating and holding zones. It can be seen that the system has a set of tension rollers 5 at the upstream inlet end with which the strip tension is reduced to a specific strip tension of 0.5 to 1 MPa, for example.

(7) Downstream of the noncontact tunnel furnace 2 and/or downstream of the last cooling subzone, the metal strip 1 is maintained at a centered position with the help of a strip-centering device 7, i.e. the position of the metal strip is adjusted within the strip-travel plane and transverse to the strip-travel direction. Then the strip tension is again increased to the usual line level of specifically 10 to 20 MPa, for example by a set of tension rollers 6 at the downstream outlet end. Because of the low specific strip tension within the noncontact tunnel furnace, it is necessary to center the metal strip 1 with the help of the strip-centering device 7.

(8) To increase the production capacity of such a system as that shown in FIG. 1, it is necessary to lengthen the noncontact tunnel furnace. With the state-of-the-art system shown in FIG. 1, there is the risk that, beyond a certain length of the noncontact tunnel furnace, the strip-centering device 7, for example the control roller 8, will no longer be sufficient so is movement of the strip through the furnace can become unstable, with the strip skewing laterally and/or coming into contact with the furnace structure. This could lead to unwanted damage to the strip or even rupture of the strip, so that merely lengthening the noncontact tunnel furnace is not advisable without taking additional measures.

(9) Therefore, according to the present invention the strip-centering device 7 is no longer downstream in the direction D of the heat-treatment device 2 and consequently is no longer downstream of the cooling zone 4 but instead is within the cooling zone 4 per se. This is shown in FIGS. 2 and 3 that show respective embodiments of the invention. FIGS. 2 and 3 in turn show a strip-treating apparatus having a heat-treatment device 2 that in turn has a heating zone 3 in the upstream inlet region and a cooling zone 4 in the downstream outlet region. One set of tension rollers 5 is again provided at the upstream inlet end, and another set of tension rollers 6 may again be provided at the downstream outlet end, as shown FIG. 3 but not in FIG. 2.

(10) The heating zone 3 is in turn made up of multiple heating subzones 3, while the cooling zone 4 is made up of multiple cooling subzones 4. According to the invention, the cooling zone 4 is divided into two cooling subzones, namely a first cooling subzone 4a and a subsequent second cooling subzone 4b. The strip-centering device 7 is according to the invention between the first cooling subzone 4a and the second cooling subzone 4b.

(11) The metal strip is heated to the desired temperature in the heating zone 3 with the heating and holding subzones 3 by a known method, and this temperature can then be maintained over a desired period of time. The heating zone 3 need not be modified is subsequently in comparison with the prior artexcept for lengthening it. Then the first cooling subzone 3a immediately downstream of the heating zone 3 cools the metal strip in a first step, preferably to a temperature of 100 C. to 200 C., for example 120 C. to 150 C. After emerging from the first cooling subzone 4a, the strip is centered with the help of the strip centering centering device 7.

(12) In the embodiment according to FIG. 2, it has a 90 control roller 8. In the embodiment according to FIG. 2, this is followed by another set of tension rollers 9 to increase the strip tension. Then the strip passes through the second cooling subzone 4b, so that it is cooled down to the desired final temperature of 40 C. to 60 C., for example. It is possible to increase production capacity in this way without significantly lengthening the free strip length, thereby avoiding an inadmissible strip wandering in the furnace. Another strip-centering device and/or another set of tension rollers may then follow the second cooling subzone 4b. This is not illustrated in FIG. 2.

(13) FIG. 3 shows a modified embodiment of the invention in which the strip centering centering device 7 is a three-roller strip center control with three rollers 10. Furthermore, FIG. 3 shows that another strip center adjusting apparatus 11 and another set of tension rollers 6 may be downstream of the second cooling subzone 4b. The additional strip center control 11 downstream of the second cooling subzone 4b is appropriate because with this embodiment no set of tension rollers is arranged between the cooling zones 4a and 4b and therefore the second section 4b also operates at a lower strip tension.

(14) To compare FIGS. 1 and 2, for example, it can be seen that the furnace subzones 3, 4 in the embodiment according to the invention have a length greater than the length in the known embodiment according to FIG. 1 on the whole. Nevertheless, the free strip length is not greater because the strip center control 7 follows the first cooling subzone 4a. Thus the heating zone 3 and the cooling zone 4 can both be lengthened significantly in comparison with the prior art. However, this division of the cooling zone 4 results in cooling subzones 4a, 4b that are (substantially) shorter than the heating zone 3.