HOW OIL CONDITION MONITORING IMPROVES PREDICTIVE MAINTENANCE The need to improve productivity is a continual demand on any business and there are a myriad number of ways to achieve it. In a manufacturing environment, maximising machinery availability is a key element in the equation. In this white paper we take a look at some of the different options available to achieve this objective using a Predictive Maintenance strategy and Condition Monitoring technologies. Introduction As its name suggests, predictive maintenance aims to determine the condition of equipment in-use and predict when maintenance activities need to be undertaken. The objective is to minimise maintenance costs whilst maximising machine availability. This strategy differs from preventative maintenance where timed or calendar maintenance is undertaken based on historical or simulation data. It does mean, however, that although the work is planned, it could be unnecessary when the machinery duty cycle is considered. Predictive maintenance can potentially offer savings over preventative maintenance by only undertaking work when it is required. The problem arising with a predictive routine is how do you determine the condition of the machinery? The causes of failure for a high speed electric motor, for example, can be very different from a hydraulic system. The measurement of machinery parameters that determines the health of the equipment comes under the heading of Condition Monitoring. There are a range of condition monitoring techniques and we want to look at which ones can help achieve the best results. The ‘Big Five’ Predictive maintenance is used to measure - through condition monitoring - when maintenance needs to be carried out based on the condition of the machine, helping to prevent unplanned equipment failure. There are five primary root causes of machine failure – balance, alignment, looseness, lubricant quality and contamination. Alignment and looseness could also be attributed to wear which can be one of the ways the two conditions arise, with wear leading to contamination. Within these five broad headings lies an expansive number of ways in which failure can arise. Some of those most frequently encountered are; Bearing defects – Bearings invariably operate under heavy, variable loads often in extreme environmental conditions. With the forces applied to bearings, de- fects can progress quickly leading to friction, bearing damage and gearbox failure. Shaft misalignment – This can be a common issue due to the temperature changes the shaft experiences, particularly on longer length shafts. Stress developed inside the shaft can damage couplings; lead to bearing fatigue and even cause shaft breakage. Couplings – Damage to the coupling can be caused by misaligned shafts potentially leading to shaft separation. Badly damaged couplings can lead to rotor cracks, gearbox failure and damaged shafts. Insufficient lubrication – Bearing wear and gear teeth damage caused by insufficient or contaminated lubrication contributes directly to equipment failure. However, inaccessibility or lack of inspection points can make it difficult to undertake oil condition monitoring. Broken/worn/chipped gear teeth – Lack of lubrication can cause excessive wear as can shaft misalignment which puts increased load on the input gear leading to poor gear meshing, both of which degrade the oil by increasing contamination, further exacerbating the problem. Gear damage and misalignment can lead to failure of the gearbox. This is not a definitive list but indicative of the range of problems that can result in unplanned downtime and loss of output. It also illustrates there are two condition monitoring techniques that will cover the ‘Big Five’ – oil condition and vibration. Pros and cons Vibration has been the most popular technique for a number of reasons, primarily because most of the conditions described above will generate some form of vibration. The sensors are usually relatively small and easy to mount on the outside of the equipment, so can be fitted without stopping the machine. They operate continuously in real time and can transmit to a PLC, asset monitoring system either hard wired or, in some cases, wirelessly. Alternatively, handheld units are also available, reducing capital outlay, but limiting the measurement to where an operator has access. The biggest difficulty is that the overall vibration sig- MOTORS, DRIVERS & TRANSMISSIONS 24 June 2017
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