# Investigation of Inner Lining Loss and Correlation with Steel Structure Quality in Rotary Kilns
## 2 Materials and Methods
To maintain a large overlap for the cloud2 cloud registration method, the maximum distance between the positions was 5 m. During readings, spherical targets were used to check and make sure that the registration was correct. Most of the time, the spherical targets were used to scan the inner lining to avoid misregistration, and the targets were spread out across the bottom of the rotating kiln in a way that was not symmetrical. During the scans, the kiln was not used and most of the lime was removed from the inside of the kiln. The rest of the lime was left on the bottom of the kiln, where it stuck strongly. Figure 4: Leica RTC360 inside the rotary kiln. Figure 5: Scheme of laser scan’s position (red—inner; green—outer). People and other unwanted things were removed from the point cloud that was left, leaving only the point cloud of the lime oven. The cloud was split into two datasets: an outer one that shows the steel frame and an inner one that shows the brick walls. Two approaches were taken to calculate the lining loss. The first step was to determine the distance that separated the inner and outer cloud points. This distance determined the thickness of the entire structure of the pen, which encompassed the steel frame, the first and second layers of the brick lining, and the expansion that occurred between the layers. For this reason, it is essential to have a precise understanding of the thickness of the steel structure in order to calculate the lining loss. The expansion that occurs between the layers also has an effect on the final result. The second approach requires a little more time and effort. To calculate the amount of loss, it is necessary to first construct a model based on the inner lining in its optimal state. This model will then be compared to the point cloud that represents the inner part. Because of this, it is necessary to identify the axis of the rotary kiln along which the ideal state model will be positioned in order to complete the process. The ambiguity on the abraded and deformed surface of the brick lining prevents the determination of the rotary kiln axis from being made using the point cloud of the inner lining. This is because the rotary kiln was built with bricks. The axes can be determined on the outer steel structure. For the rotary kiln to function as it should, the steel structure must be manufactured with a high degree of precision to ensure circularity and symmetry. The axis of the rotary kiln was located by employing the RANSAC method for detecting primitive objects within the point cloud that is part of the CloudCompare software. The radius range of the cylinder was defined to be 1.82 m \(\pm\) 2 cm, so it would be easier to detect. The axis of this structure corresponds to the axis of the rotary kiln. A model of the ideal condition was modelled according to the determined axis and knowledge of the radius of the kiln interior from the composition of the brick lining to determine the loss of the inner lining. This was achieved by modelling a model of the ideal condition. The lining loss was calculated by comparing the ideal model to the measured point cloud of the rotary kiln's interior. This allowed the identification of the lining loss.