When a German aluminium rolling and remelt plant needed to improve the geometry and topography measurement of raw aluminium ingots, LMI Technologies was able to come up with a solution that met its needs, as MEPCA found out.
Aluminium Norf (Alunorf) was founded in April 1965 and is the largest aluminium rolling and remelt plant in the world.
The plant employs more than 2,200 people, with production running around the clock, seven days a week and its rolling and remelt volume has continuously increased, now totalling approximately 1,500,000 tons per year.
The measurement task was made harder as each ingot’s rolling surface has a variable amount of excess material that must be scalped off to remove the metallurgical shell from the casting process. The plant’s existing system of moving point laser scanners could not cover the whole ingot in length and width – which could be as much as 8.6m x 2.2m. The system only covered the cross profile at certain positions along the ingot’s surface. Characterisation of the ingot surface in between these positions could not be measured using this method, and had to be compensated for with several additions in the scalping depth (called “safety” additions). This led to unnecessary extra scrap material for each ingot that was scalped.
In addition, the use of a measurement system with moving sensor heads led to mechanical wear, which in turn caused maintenance downtimes and even production outages. Finally, a traversing laser’s technology made it necessary to interrupt an ingot’s transport over roller tables when the measurement was in progress.
The Solution
Given the numerous disadvantages of the old system, it became clear that the application requirements would be best fulfilled by implementing a system of multiple fixed-mount laser line sensors that could cover both sides of the ingot simultaneously. Such a system, which is now called AIT (Alunorf Ingot Topography System), would be able to cover the variations in ingot widths (between 900mm and 2200mm). Finally, an open and well-documented data interface became obligatory to implement the measured data into an existing infrastructure of ibaPDA-systems.
LMI Technology’s Gocator 2100 series sensors were chosen for their large scan width (field of view), which minimised the number of required sensors and made the system affordable – with 10 Gocator sensors employed in total – 5 sensors per side. In addition, the lack of moving sensor parts made mechanical maintenance due to wear obsolete. And, the installation at Alunorf marked the first system that was able to measure ingots on both sides while travelling inline.
“The use of a Gocator sensor for our AIT-System made the process of implementation and calibration as easy as possible,” explained Stefan Schulz, Process Engineer at Alunorf. “Simultaneous to this, the Gocator delivers a high grade of detail in measurement, covering a wide measurement area at a relatively low price. Finally, the possibilities of configuring measurements based on our requirements are infinite. Both minor and larger topography effects are measurable with this system while transport movements do not affect the measurement itself.”
The Result
With the introduction of the new AIT-System, Alunorf can measure each ingot’s geometry in full detail. Engineers can immediately detect the thinnest point of the ingot, rather than having to add the safety factors that increased scalping depth and therefore scrap. Even a reduction of 1mm per side saves enormous amounts of scalping chips that do not have to be remolten again.
As an added advantage, Alunorf can also generate KPIs on their central ibaPDA-System using the measured data from Gocator, which accurately describes good or bad ingot shape (i.e. a deformation factor). This data helps determine individual or systematic problems in the casting process. For the scalping process itself, the measured data is used to correctly position the ingot in the scalper and to position the scalper heads for optimal operation.
