Generally, in a cold rolling of an iron and steel mill, unit coils are welded together into a steel strip at a starting step of the cold rolling so that continuous rolling can be carried out, and the steel strip is cut along welds into the unit coils at a finishing step of the cold rolling, which are then transported to a following process or shipped as final products. Accordingly, in the cold rolling, it is inevitably required to locate such welds in order to automatically and precisely control essential process equipments and trim the steel strip along the welds into the unit coils at the output side.
FIG. 1 is a detection system for a weld of a steel strip using a through hole according to the prior art.
Referring to FIG. 1, the conventional detection system for a weld of a steel strip has a light projector 3 and a light detector 4 arranged above and under a moving steel strip 1 that is being transported. The light projector 3 is arranged in a position where detection on a weld 2 is needed, and illuminates light downward onto the steel strip 1. The light detector 4 arranged under the steel strip 1 detects the light passing through a hole 5 perforated in the steel strip 1, thereby detecting a corresponding weld 2.
Such a conventional detection system needs the hole 5 perforated adjacent to the weld 2 in order to detect the weld 2. However, this also needs to temporarily stop a corresponding line to perforate the steel strip 1, and thus productivity is lowered. In addition, excess metal formed around the hole 5 damages or scratches the surface of a feed roll or mill roll. Then, the scratched roll disadvantageously transfers a mark onto the surface of a following steel strip. Where the steel strip 1 is very thin or high carbon steel, the hole 5 may fracture the steel strip 1.
Furthermore, in the conventional weld detection system using a hole, the light projector 3 installed above the steel strip 1, which is being transported for process, uses a general light source. Such a light source has a short lifetime and thus needs periodic replacement. Since the light detector 4 is installed below the steel strip 1 to detect light passing through the hole 5, the detection system is difficult to install but easily soiled by dropping dust or foreign materials.
The present invention has been made to solve the foregoing problems of the prior art which detects a weld using a through hole. Therefore, an object of certain embodiments of the present invention is to provide an on-line detection system and method for a weld of a steel strip, which can emit a laser beam onto the surface of a steel strip moving at a high speed and measure the reflectivity of the laser beam reflecting from the same, thereby detecting the weld of the steel strip easily on-line without having to form the through hole.