Mätosäkerhet och processvariation avseende kiseldioxidhalt vid kulsintring: En fallstudie vid LKAB, Kiruna
Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
Today there is a strong competition within the iron ore market. In order to be a great competitive on the market LKAB considers that one of their best competitive advantages is customer satisfaction. Through continuous improvement in product quality control and statistical process control can LKAB further improve their processes and ensure that the objectives that are obtained in resource efficiency, energy efficiency and reducing impact on the environment and climate will maintain. It should lead to a maintained and improved customer satisfaction. This study is initiated by LKAB in order to obtain more knowledge of the measurement error and product variation in the Pelletizing plant 2 in Kiruna so that the process control can be improved. By studying four sampling points in Pelletizing plant 2 has the measurement error of sub-sampling, sample preparation and analysis for each of the sampling points sought to be established. That has been successful in most cases. Furthermore, with the knowledge of measurement error, the product variation of the process has been determined. Finally, the aim was to suggest possibilities for a general model for the adjustment of the statistical control limits, in an earlier step in the process, if their where changes in the customer requirements. The measurement error has been calculated by collection of primary data from experiments conducted and secondary data from the daily production and earlier experiments conducted at LKAB. In the cases where the measurement error could not be calculated has a bias, differences between different measurement methods, been calculated. The calculations of the measurement error have also been able to detect what have the greatest impact on the measurement error. In order to create an impression if the LKAB tolerance limits and control limits, that are used today, are reasonable relative to the current process variation a capability study and analyzes between the LKAB control limits and possible statistical control limits where conducted. The capability study indicates that the process variation needs to be reduced to conform to the tolerance limits while the analyzes of the control limits indicates that the LKAB control limits must be extended in order to be considered as statistical control limits based on the process variation. If LKAB, in the future, want to be able to re-calculate the control limits in an earlier process step if there is changes in customer requirements in the end of the process, this study presents two different models of conducting control limits relative to other process steps. The two models presented provide a good basis to create a general model for calculating statistical control limits at sampling points where the control limits must be appropriate for later steps in the process. The recommendations obtained from these studies are to reduce the measurement error in order to reduce the process variation. This can be done by putting the focus on X-ray instruments in the process as well as the mills in the automated sample preparation laboratories. Analysis in this study shows that they contribute largely to the measurement error at the sampling points where they are involved. It is further recommended that LKAB re-calculate the control limits that are set for the process so they are based on statistical calculations. The control limits that are used today are too close to each other in relation to the process variation which means that the process will, to a greater probability, vary outside the control limits without that the process has changed and control is needed. Calculating statistical control limits can be done in different ways. In this report there are presented how statistical control limits are calculated on a traditional way but there are also presented how control limits can be calculated from tolerance limits or by the use of statistical control limits from a crucial process step in another part of the process.
Place, publisher, year, edition, pages
2013. , 121 p.
Teknik, Mätosäkerhet, Kulsinterverk, Kiruna, KK2, Mätsystemanalys
IdentifiersURN: urn:nbn:se:ltu:diva-48140Local ID: 59e255b1-0af7-4e24-9009-d6467dc534adOAI: oai:DiVA.org:ltu-48140DiVA: diva2:1021479
Subject / course
Student thesis, at least 30 credits
Industrial and Management Engineering, master's level
Validerat; 20130827 (global_studentproject_submitter)2016-10-042016-10-04Bibliographically approved