PVD THICKNESS CONTROL

Abstract

A method for coating a metal strip by means of a metallic substrate in a strip coating system, wherein the coating is carried out according to the principle of physical vapor deposition and the layer thickness is set via the parameters of the strip speed and the vaporization rate. It is provided according to the invention that in the event of a layer thickness change and/or a width change of the metal strip, the vaporization rate and the strip speed are changed simultaneously, so that the layer thickness change can be implemented directly independently of the thermal vaporization process.

Claims

1-9. (canceled)

10. A method for coating a metal strip by means of a metallic substrate in a strip coating system, wherein the coating is carried out according to the principle of physical vapor deposition and the layer thickness is set via the parameters of the strip speed and the vaporization rate, wherein in the event of a change of the desired target layer thickness and/or a width change of a following strip to the preceding metal strip, the vaporization rate and the strip speed are changed simultaneously, so that a change of the layer thickness can be implemented directly independently of the thermal vaporization process.

11. The method as claimed in claim 10, wherein the vaporization rate and the strip speed are changed at fixed time intervals.

12. The method as claimed in claim 10, wherein the change of the desired target layer thickness and/or the width change of the following strip to the preceding metal strip take place via value pairs of vaporization rate and strip speed per time interval.

13. The method as claimed in claim 12, wherein the value pairs are based on historical data and/or a model relationship.

14. The method as claimed in claim 10, wherein the metal strip comprises a steel strip and the metallic substrate comprises zinc.

15. The method as claimed in claim 10, wherein the change of the desired target layer thickness and/or the width change of the following strip to the preceding metal strip is at least 10%, preferably 15%, more preferably 20%, and most preferably 25%.

16. The method as claimed in claim 10, wherein a layer thickness measuring device is used to determine the layer thickness.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0030] Further advantages and features of the method according to the invention result from the following exemplary embodiments, which are explained in more detail with reference to drawings. In the FIGURE:

[0031] FIG. 1 shows a schematically simplified side view of an embodiment variant of the system according to the invention.

[0032] FIG. 1 shows an embodiment variant of a system 1 in a schematically greatly simplified side view.

DETAILED DESCRIPTION

[0033] The system 1 is suitable for carrying out the method according to the invention in which a metal strip 10 is carried out by means of a metallic substrate 12 according to the principle of physical vapor deposition (PVD), wherein the layer thickness is set via the parameters of the strip speed and the vaporization rate according to the following formula.

[00001]$d_{\mathrm{Me}}=\frac{E\left(b,v,t\right)*S\left(T\right)}{b*v_{\mathrm{strip}}}$

[0034] where

TABLE-US-00001 vaporization rate S(T) [g/s] width b [m] strip speed v.sub.strip [m/s] efficiency E(b, v, t) [—] layer thickness d.sub.Me [g/m.sup.2]

[0035] The system 1 initially comprises a continuous treatment line 2 in which the metal strip 10 is initially unwound by a first reel device 11 and is rewound again at the end of the treatment line 2 by a second reel device 13. Within the treatment line 2, the metal strip 10 is moved in a direction of movement of the arrow 3 and passes through several stations in the process.

[0036] In the embodiment variant shown here, the system 1 comprises a pickling device 14 arranged in the treatment line 2 and a coating device 16 arranged downstream.

[0037] In the pickling device 14, the surfaces of the metal strip 10, for example a steel strip, are prepared so that they can then be coated in the coating device 16.

[0038] In the coating device 16, the metal strip 10 is then coated on at least one side, preferably on both sides, with the metallic substrate 12, for example a zinc layer, according to the principle of physical vapor deposition (PVD). The layer thickness is settable for this purpose via the parameters of the strip speed and the vaporization rate according to the above formula.

[0039] If, for example, a different layer thickness is to be set, the strip speed can be adjusted by rearranging the above formula. Therefore:

[00002]$v_{\mathrm{strip}}=\frac{E\left(b,v,t\right)*S\left(T\right)}{b*d_{\mathrm{Me}}}$

[0040] The same relationship also applies to a width change or to a combination.

[0041] If all process settings, such as the vaporization rate and the width, remain unchanged, then only the following applies:

[00003]$v_{\mathrm{strip},\mathrm{new}}=v_{\mathrm{strip},\mathrm{old}}*\frac{d_{\mathrm{Me},\mathrm{new}}}{d_{\mathrm{Me},\mathrm{old}}}$

[0042] If all process settings, such as the vaporization rate and the layer thickness, remain unchanged, then only the following applies:

[00004]$v_{\mathrm{strip},\mathrm{new}}=v_{\mathrm{strip},\mathrm{old}}*\frac{b_{\mathrm{new}}}{b_{\mathrm{old}}}$

[0043] After this, changes in layer thickness or width can be adjusted up to a specific level without changing the vaporization rate.

[0044] However, the rapidity of the changeover process is limited by a speed change per unit of time. If greater layer thickness and/or width changes have to be implemented, the vaporization rate has to be adjusted.

[0045] It is therefore provided in the method according to the invention that in the event of a change of the desired target layer thickness and/or a width change of the following strip to the preceding metal strip 10, the vaporization rate and the strip speed are changed simultaneously, so that the layer thickness change can be implemented directly independently of the thermal vaporization process. In other words, the vaporization rate can be predictively adjusted when changing the layer thickness.

[0046] For this purpose, the system 1 comprises a control unit 18, which, in the event of a change of the desired target layer thickness and/or a width change of the following strip to the preceding metal strip 10, changes the vaporization rate and the strip speed, so that the change of the layer thickness can be implemented directly independently of the thermal vaporization process. In the embodiment variant shown here, the control unit 18 is EDP-supported and additionally comprises a storage unit 19 in which value pairs of vaporization rates and strip speeds are stored per time interval. These can be based on past data or models, for example.

[0047] If, for example, a new, 25% lesser layer thickness is to be applied to the metal strip 10, the vaporization rate is reduced via the control unit 18. The slow decrease in the vaporization rate, which lasts for several minutes, is compensated for in this phase by a continuous adjustment in the form of an increase in the strip speed on the basis of the value pairs, so that the layer thickness deposited on the subsequent metal strip immediately corresponds to the desired target layer thickness.

[0048] Since the efficiency can also change, this may have to be taken into consideration. Therefore, a layer thickness measuring device 20 is additionally arranged in the treatment line 2 downstream of the coating device 16, by means of which the coating is checked.

[0049] A correction value can then be determined and adapted using this measured value. The following applies:

[00005]$C=\frac{d_{\mathrm{Me},\mathrm{measured}}}{d_{\mathrm{Me},\mathrm{target}}}$

[0050] The above formula can then be rewritten as:

[00006]$v_{\mathrm{strip}}=\frac{C*S\left(T\right)}{b*d_{\mathrm{Me}}}$

[0051] As can be seen in FIG. 1, the coating thickness measuring device 20 is connected to the control unit 18 so that if predetermined values are not reached or are exceeded, the coating can be readjusted in accordance with the mathematical relationship shown in order to implement a uniform coating.