WO1999028730A2

WO1999028730A2 - Process and device for producing a strip-like material avoiding repeated surface defects

Info

Publication number: WO1999028730A2
Application number: PCT/NL1998/000674
Authority: WO
Inventors: Onno Wouter Van Wijk
Original assignee: Hoogovens Staal B.V.
Priority date: 1997-11-27
Filing date: 1998-11-27
Publication date: 1999-06-10
Also published as: AU1353899A; WO1999028730A3

Abstract

A strip-like material is monitored, during the production, for the occurrence of the repeated surface defects. The procedure comprises the following steps: determining a strip length between any repeated surface defects which arise on the basis of a periodicity during working which stems from the working means and/or on the basis of previous data; taking pictures of any surface defects on the strip-like material, each of the pictures depicting at least the length of the said established strip length and pictures which follow one another in the strip direction being taken at intervals which are equal to or a multiple of the said established strip length; homologously correlating a plurality of successive pictures; attenuating the depiction of non-correlating surface defects and intensifying the depiction of correlating surface defects; using any intensified depictions which are present as information on repeated surface defects.

Description

PROCESS AND DEVICE FOR PRODUCING A STRIP-LIKE MATERIA . AVOIDING REPEATED SURFACE DEFECTS

The invention relates to a process for producing a strip-like material avoiding repeated surface defects, in which a feed material is worked using a working means which has at least one periodicity during working, this material being monitored, during the production of the strip-like material, for the occurrence of repeated surface defects, in order to be able to interrupt the working in the event of such surface defects being observed.

All kinds of surface defects may arise when producing a strip-like material. These defects may be caused by any kind of contamination which is present on the surface of the strip-like material or other external influences. They may also stem from the composition of the strip-like material itself. Most of these surface defects are not due to the influence of the working means used for the production of the striplike material. However, in other cases a surface defect may be caused by the working means used. If such a working means comprises a moving component, the movement of such a component of the working means will often present some form of periodicity. If a surface defect is caused by such a periodically moving component, there is a considerable risk that this will lead to repeated surface defects, in other words surface defects which are repeated at intervals of a fixed strip length.

Repeated surface defects of this nature are often found to - be extremely disadvantageous and can also generally be avoided by means of an intervention to or a repair of the working means. To do this, the movement of the working means and therefore the working of the strip-like material has to be interrupted.

In order to avoid unnecessary production losses, it is important for it to be possible to observe repeated surface defects as quickly as possible and therefore to be able to interrupt the working of_ the material as quickly as possible.

The object of the invention is therefore to carry out the process disclosed in the preamble in such a manner that repeated surface defects can be observed with a minimum production of the strip-like material with such repeated surface defects.

It should be noted that previous systems have been proposed in which the location of each surface defect is established, for example in the memory of a computer, in which case a repeated surface defect can be found by examining in the memory whether a similar problem can be observed repeatedly, with the longitudinal distance between such defects being the same each time. A system of this nature requires an exceptionally high memory capacity, since virtually all the surface defects which are observed have to be extensively checked for correlation with other defects in this memory. The extent of memory capacity required and the level of calculations means that the known method entails considerable limitations for the speed of working.

According to the invention, a solution to this problem has now been found in that the observation repeated surface defects comprises the following steps:

- determining a strip length between any repeated surface defects which arise on the basis of a periodicity during working which stems from the working means and/or on the basis of previous data; - taking pictures of any surface defects on the strip-like material, each of the pictures depicting at least the length of the said established strip length and pictures which follow one another in the strip direction being taken at intervals which are equal to or a multiple of the said established strip length;

- homologously correlating a plurality of successive pictures; - attenuating the depiction of non-correlating _ surface defects and intensifying the depiction of correlating surface defects;

- using any intensified depictions which are present as information on repeated surface defects.

This novel process quickly makes information on non-correlating surface defects irrelevant, so that these defects do not have to be given any further attention. By contrast, the depiction of correlating surface defects is intensified and, as a result, provides a clear indication of the presence and position of these repeated surface defects, even if the original intensity of these repeated surface defects is still only very low. As a result, repeated surface defects can be detected at a very early stage, so that when the working is interrupted little material is lost owing to the need to scrap this material .

It should be noted that the pictures can be formed in various ways. For example, it is possible for photographic pictures to be visually compared with one another. It is also conceivable for transparent pictures to be superimposed optically onto one another, in which case repeated defects will clearly emerge. However, it is preferable for the pictures to be formed electronically as digital pictures which can then be electronically correlated. In this case, it is also easier to attenuate the representation of non- correlating defects and to intensify that of correlating defects by electronic means. In this way, it is therefore also possible to electronically signal repeated defects.

Although, strip-like materials may have a wide variety of shapes and chemical compositions, the novel process has proven to be particularly useful for use on strip-like material which comprises an optionally coated metal strip. In this case, the working may comprise a rolling operation in which the working means is a rolling mill stand for reducing the thickness of the metal strip. However, the working may also comprise the application of a coating to a metal strip with the aid of an applicator roll. Each revolution of a roller or of an applicator roll then introduces a periodicity into the working, and damage, for example, to such a roll may cause a repeated surface defect.

In such a case, the circumference of such a roll can be used to establish the strip length between any repeated surface defects which arise. In the case of a roller from a rolling mill stand, it is preferable to correct the said strip length for known effects such as those of roller pressure and roller slip during the rolling operation, in order to prevent a strip length which does not entirely correspond to the periodicity in the system being used as the basis, since this would make it impossible to correlate repeated surface defects .

The invention relates not only to the process described but also to a device for use in the novel process, comprising a working means for producing a strip-like material, characterized in that this device furthermore comprises recording equipment for taking successive pictures of any surface defects on the strip-like material, as well as means for correlating successive pictures, it being possible to attenuate the depiction of non-correlating surface defects and to intensify that of correlating surface defects.

It has been found that using the novel process makes it possible to obtain considerable savings, due to the fact that the quantity of material scrapped owing to the occurrence of repeated surface defects can be reduced substantially.

Claims

1. Process for producing a strip-like material avoiding repeated surface defects, in which a feed material is worked using a working means which has at least one periodicity during working, this material being monitored, during the production of the striplike material, for the occurrence of repeated surface defects, in order to be able to interrupt the working in the event of such surface defects being observed, characterized in that the observation of repeated surface defects comprises the following steps:

- determining a strip length between any repeated surface defects which arise on the basis of a periodicity during working which stems from the working means and/or on the basis of previous data;

- taking pictures of any surface defects on the strip-like material, each of the pictures depicting at least the length of the said established strip length and pictures which follow one another in the strip direction being taken at intervals which are equal to or a multiple of the said established strip length;

- homologously correlating a plurality of successive pictures;

- attenuating the depiction of non-correlating surface defects and intensifying the depiction of correlating surface defects;

2. Process according to claim 1, characterized in that the pictures are electronic, digital pictures which are electronically correlated.

3. Process according to claim 1 or 2 , characterized in that the strip-like material is an optionally coated metal strip.

4. Process according to claim 3, characterized in that the working means is a rolling mill stand for reducing the thickness of the metal strip.

5. Process according to claim 4, characterized in that the said strip length corresponds to the circumference of one roller of the rolling mill stand, . corrected for the known effects of the roller pressure and the roller slip during the rolling operation.

6. Process according to claim 1 or 2 , characterized in that the working comprises the application of a coating to a metal strip with the aid of an applicator roll.

7. Device for use in the method according to claim 1, comprising a working means for producing a strip-like material, characterized in that this device furthermore comprises recording equipment for taking successive pictures of any surface defects on the strip-like material, as well as means for correlating successive pictures, it being possible to attenuate the depiction of non-correlating surface defects and to intensify that of correlating surface defects.