The sensor equipment
The system is designed for plate temperatures of up to 500 °C. The lower side of the gantry-type measuring frame and the components on the frame are protected with heat shields made of stainless steel. The laser sensors are mounted in encapsulated protective housings, which are actively temperature-controlled by means of a heating/cooling unit. The system uses ambient air to cool the cooling circuit back down.
Ambient air is blown between the heat shields and the laser sensors across the complete width of the gantry to minimize the effect of heated air rising up from the plate and the gauging table. At the same time, this reduces the ingress of debris and dust into the gantry equipment. Narrow-band filters protect the optical equipment against extraneous light effects.
While in the parking position, the gantry is safely protected against collisions, for example, with the bay crane, by a garage of very sturdy design built by SMS. Also while in this position, the sensors are protected by heat shields against thermal radiation from below.
The system’s measuring precision is verified at regular intervals. This is done by means of an automated procedure during which a calibrated reference part made of anodized aluminium is moved through the measuring ranges of all the sensors. Once this procedure is completed, the current position of each laser sensor is calculated and recorded within a common machine coordinate system.
The alignment check is part of the automated measurement procedure: when there is uncertainty about the accuracy of the alignment, the nokra system sends out a corresponding notice which triggers the process control system to perform an alignment check before the measurement of the next plate starts.
Installation and commissioning
Factory acceptance testing at the nokra facilities in Baesweiler together with ILG and SMS was conducted with the system operating along a several meter long measuring path. The system was accepted without reservation. During the tests, the machine also demonstrated that it is “steelmill proof”.
Installation of the system at Ilsenburg progressed smoothly with acceptance testing of the measuring equipment in cooperation with ILG und SMS starting as early as at the end of 2020. Final acceptance was granted soon thereafter at the beginning of 2021. The performance criteria for the final acceptance, including MSA type-1 and type-3 studies to confirm the system’s measuring capability, were fulfilled at the first attempt. For the MSA studies, eight measurement tracks distributed over the plate surface were defined and the respective flatness values compared.
In the MSA type-1 study, the repeatability of measurements, expressed as the Cg index, and of the systematic deviation, expressed as the Cgk index, are determined. For the calculation of the Cgk index, the values measured by the system along the defined tracks were compared with the corresponding values measured with a laser tracker and verified.
For the 1-meter straight edge, a Cg index above 2.94 and a Cgk index above 1.75 were determined. For both indexes, minimum attainable values of 1.33 had been specified by the customer. For the 2-meter straight edge, a Cg index of 4.39 and a Cgk index of 3.07 were determined. Also in this case, the minimum attainable values specified had been as low as 1.33.
In the MSA type-3 study, which is used to determine the system’s repeatability and reproducibility (%R&R), 25 plates from production were measured two times each along the previously defined tracks. From these results, the repetition and reproducibility of the measurements, expressed in percentage, were calculated. While the value specified by the customer was <30%, the actual value achieved by the system was just 6.79% with the 1-meter, and 7.09% with the 2-meter straight edge. Thus, it could be proved in both studies that the measurements are clearly within the allowable tolerance ranges.