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  • 1.
    Al-Najjar, Basim
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Prediction of the vibration level when monitoring rolling element bearings in paper mill machines2001In: International Journal of COMADEM, ISSN 1363-7681, Vol. 4, no 2, p. 19-26Article in journal (Refereed)
    Abstract [en]

    Rolling element bearings in paper mill machines are considered in this paper due to their critical role in the machine function. In general, the cost-effectiveness of a vibration-based maintenance policy mainly depends on the technical and economic effectiveness of the vibration monitoring system, i.e. software, hardware, and personnel, being used. In this paper, a model for predicting the vibration level of rolling element bearings in paper mills is developed. In the model, a combination of bearing vibration history, current condition and data from operating conditions is used to predict the vibration level of a bearing during a near future.

    The factors influencing the condition of rolling element bearings during operation are discussed. These factors are related partly to operating and environmental conditions and partly to previous changes in the condition of the bearing. The operating life of a bearing is divided into four phases characterised by their vibration behaviour. One of the important conclusions is that a mechanistic model would be more appropriate than other models for predicting the vibration level of a rolling element bearing and describing the deterioration process, which are needed to achieve better understanding of the bearing vibration behaviour.

  • 2.
    Al-Najjar, Basim
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
    Selection and improvment of a cost-effective maintenance policy: the case of rolling element bearings1998In: International Journal of COMADEM, ISSN 1363-7681, Vol. 1, no 2, p. 25-36Article in journal (Refereed)
    Abstract [en]

    The main result reported in this paper is that the bearing’s mean effective life could be extended appreciably if an existing vibration-based maintenance policy is used effectively. A new maintenance approach was developed to overcome some of the limitations of TPM and RCM and is based on the Deming managerial feedback cycle. It is a methodology to sustain and improve technical and economic effectiveness of the essential manufacturing process elements. It is shown that by using vibration-based monitoring, (VBM), program in the frame of a common database for a plant IT-system, the causes behind quality deviations and failures can be identified and eliminated effectively and the company’s economics would be improved. Criteria to select the most cost-effective VBM program and the most cost-effective vibration-based maintenance policy are developed. It is shown, by two case studies, that improvements in VBM systems can be achieved by effective feedback of the results of failures, renewal condition and VBM history analysis. The contribution of this study is: The development of a sequential method for the selection and improvement of a cost-effective vibration-based maintenance policy. This methodology can be used to justify, on economic criteria, the use of VBM systems to indicate when rolling element bearings should be renewed.

  • 3.
    Al-Najjar, Basim
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Total Time on Test, TTT-plots for Condition Monitoring of Rolling Element Bearings in Paper Mills2003In: International Journal of COMADEM, ISSN 1363-7681, Vol. 6, no 2, p. 27-32Article in journal (Refereed)
    Abstract [en]

    When using vibration-based maintenance, it is easier to detect damage in rolling element bearings. But the damage severity and risk of bearing's failure, if no maintenance action such as replacement is done, can not be assessed accurately. When the vibration level of a rolling element bearing is increasing or it is close to (or greater than) a predetermined replacement level, the assessment of the probability of a bearing’s failure enhances the decision making process. Thus, at each vibration measurement occasion a decision has to be made regarding whether the bearing needs to be maintained and how urgent it actually is.

    The paper describes a graphical method for both assessing the probability of failure of damaged rolling element bearing and predicting the residual of its effective life. It uses history of the bearing in question and life statistics as well as the vibration levels at failure/condition-based replacements of past bearings of the same design or of very similar performance and duties. This method is based on the concept of Total Time on Test, TTT-plot. The application of TTT-plot on age and condition-based maintenance techniques are discussed and described by two examples. This graphical method is developed from previous work by the author and others. 

  • 4.
    Kans, Mirka
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Maturity based evaluation of IT systems for maintenance management2012In: International Journal of COMADEM, ISSN 1363-7681, Vol. 15, no 4, p. 15-25Article in journal (Refereed)
    Abstract [en]

    Research shows that investments in IT have a positive correlation to company profitability and competitiveness. Even though, IT projects often fail to deliver the expected benefits. One reason could be the increased complexity both with respect to project organization and implemented IT solutions. E-maintenance is a concept developed for dealing with this complexity by securing effective information logistics for the maintenance. The quality of the implemented IT system is affected by the quality of the procurement, therefore is of importance to find means to reduce quality problems in the early phases of the total systems life cycle. This paper addresses how the IT maturity of the maintenance organization could be considered in the IT procurement, especially in the evaluation of candidate systems.  The proposed method tries to simplify the process by considering IT maturity as a means to define key requirements, and as a basis for evaluation.  A model describing three phases of IT maturity within maintenance (IT beginners, medium IT users and IT mature organizations) forms the theoretical basis, and IT functionality required for each level are specified. The applicability of the approach is tested by evaluating 24 IT systems for maintenance management. In conclusion, the method can be used for defining IT requirements in a holistic manner as a means to achieve effective information logistics. The IT maturity model could also help organizations in forming their IT strategy towards the e-maintenance concept.

  • 5.
    Kans, Mirka
    et al.
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Ingwald, Anders
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Functionality Gaps in IT Systems for Maintenance Management2012In: International Journal of COMADEM, ISSN 1363-7681, Vol. 15, no 4, p. 38-50Article in journal (Refereed)
    Abstract [en]

    E-maintenance is an information intensive concept highly dependent on relevant and reliable information technology (IT) support. One important prerequisite is that IT functionality fits the demands of the maintenance organisation. The purpose of this paper is to investigate the existence of functionality gaps in the IT applications used for maintenance management. To accomplish the purpose a questionnaire survey asking professional users to estimate the misalignments/gaps in their current IT support. Functionality and information investigated are based on the standard EN 13460 documents for maintenance. The gathered data was thereafter analysed using statistical methods. The study reveals that the used IT solutions in general provide good support for maintenance management. However, the respondents perceive gaps to some degree in functionality and data related to maintenance follow up and improvement. The study indicates some contradicting results regarding IT and functionality for maintenance follow up and improvement. Some users state that there is a need for additional IT-support related to maintenance follow up and improvement while other state that the support exists but are not used. More in-depth studies of the reasons behind these contradicting results and also research in reasons behind apprehended gaps are required.

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