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Why machines should have built-in condition monitoring

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Jon Severn, Editor of MachineBuilding.net, outlines the arguments in favour of installing condition monitoring equipment on new machinery - as well as the benefits of retrofitting such systems.

Why machines should have built-in condition monitoringLooking at condition monitoring form a machine builder's perspective, it is easy to view it as 'somebody else's problem'. Having built the machine, delivered it and been paid for it, why should the supplier be concerned about its long-term reliability?

In fact there are several reasons, not least of which is reputation. If a supplier's machines always fail just after the warranty has expired, customers may seek an alternative machine builder next time. Even worse, however, is the situation if a machine fails before the end of its warranty period; this can result in costly call-outs and repairs, or even financial penalties if, for example, the failure causes an automotive production line to stop.

Beyond these rather simplistic scenarios, there are other good reasons for installing condition monitoring. If a machine builder offers post-sales support contracts, it is in his best interests to avoid any unplanned stoppages; condition monitoring should give an early warning of an impending failure, enabling the support team to schedule the maintenance or repairs at a time that is convenient to them and the customer.

Pre-delivery checks

Condition monitoring can also be useful to the machine builder before the equipment has even been delivered. Occasionally bearings, pumps, fans or other components contain manufacturing defects or are damaged during transit or installation. Such damage may be invisible to the naked eye but a condition monitoring system can highlight problems as soon as the machine is first tested. This can enable the faulty item to be repaired prior to delivery, which will be far less costly than having to perform repairs at the customer's site during or after commissioning.

In a similar vein, some companies - such as Corus - now perform a fingerprinting exercise on newly delivered machinery, using acoustic, vibration and thermal analysis. This provides a baseline against which future condition monitoring data can be measured, plus it highlights any built-in problems. It is likely that, in the future, companies will start specifying that condition monitoring must be installed on new machinery, as is already the case in other sectors such as marine turbomachinery.

Clearly it is not practical to monitor every component, but there are methods that can be used to identify the critical items. For example, Failure Modes and Effects Analysis (FMEA) is often used by production managers who are considering retrofitting condition monitoring to their plant, but it is suitable for OEMs. Furthermore, such an exercise can help in drawing up lists of spare parts that should be stocked either by the end user or the supplier providing support; savings here can offset or even outweigh the cost of the condition monitoring equipment.

Continuous improvement

Once the machine is operating and condition monitoring indicates that a problem is developing, there are three options: do nothing and wait for the failure to occur (not recommended!); plan to replace the failing item like-for-like; or engineer-out the problem (eg installing higher-specification bearings) so that it does not recur. This last option can be the best if long-term costs are to be minimised.

Often machine builders struggle to persuade customers that the additional cost of installing condition monitoring is worth it. According to Ian Taylor of Corus Northern Engineering Services, this is especially so in the UK and throughout the pharmaceutical sector, where condition monitoring is seen as a luxury. With teams of maintenance fitters available and willing to work long hours in the event of a breakdown, there is a perception that a combination of regular preventative maintenance and 'firefighting' is adequate. However, there are severe drawbacks to this.

Firstly, time-based replacement of critical components, regardless of their condition, can prove expensive in terms of components, labour and downtime. In addition, disturbing the equipment can lead to subsequent failures in unrelated components ('if it ain't broke, don't fix it'). On the other hand, if a component fails before its scheduled replacement, the consequences can be much more costly. Consider the example of a seized bearing: replacing the bearing before it seized might have just required a new bearing and seals, but if the bearing seizes it can cause damage to the housing and/or other equipment in the vicinity. And there is also the cost of lost production associated with unplanned stoppages.

Two years to wait

Something that many companies appear not to appreciate today is the long lead times for items such as heavy gearboxes or bearings. Strong demand for wind turbine bearings is affecting the entire bearing industry, resulting in a global shortage of bearing steel and lead times of two years for large bearings. Some end users are now recognising this and attempting to avoid problems by ordering spares to hold in stock; but this is increasing demand still further and putting more pressure on lead times.

Kate Hartigan, managing director of Schaeffler (UK), draws a comparison between condition monitoring and a conventional insurance policy: companies willingly pay insurance premiums to safeguard against unforeseen incidents that may never happen, with the benefit coming only after an incident has occurred; in contrast, condition monitoring prevents incidents occurring, so the benefit is guaranteed. Furthermore, while the list price of a replacement bearing may be only a few tens of pounds, the cost of lost production in the event of a bearing failure causing a plant stoppage can be thousands or tens of thousands of pounds. The cost of lost production for a single incident can easily exceed the cost of a complete condition monitoring system. Condition monitoring is, by almost any measure, a sound investment.

Traditionally condition monitoring has been restricted to high-value plant, critical plant or applications such as centrifuges where vibration must be monitored for reasons of safety. However, Russell King, the managing director of Sensonics, says that vibration monitoring can be implemented cost-effectively even on smaller plant such as pumps and fans, thanks to products such as his company's VEL/GDC electro-dynamic transducer; this provides a 4-20mA current sink output proportional to velocity vibration and offers the advantage of double isolation in conjunction with a low-impedance circuit, making it suitable for high-noise environments. Due to the electro-dynamic nature of the sensor assembly, both high- and low-frequency events are filtered mechanically and, since no integration is required, King says the arrangement is immune to the saturation seen in piezoelectric devices.

Numerous suppliers offer Machine condition monitoring equipment and services, including Corus Northern Engineering Services, Schaeffler (UK) and Sensonics, all mentioned above. No single condition monitoring technology is suitable for all applications, so a reasonable understanding is required to ensure that endoscopy, acoustic, vibration, lubricant and thermal analysis systems are used appropriately. If in doubt, the suppliers should be able to advise on the most suitable for a given application.

Many of the modern condition monitoring systems enable remote monitoring to be carried out via the internet, which is very useful for machine builders that install condition monitoring equipment on machines and then provide ongoing support contracts.

Indeed, machine builders may find that incorporating condition monitoring is a good selling point if a remote monitoring and ongoing support service is also offered. And, if a support contract is agreed, some of the purchase costs for the condition monitoring equipment could be offset, meaning that a machine with condition monitoring costs little more than a machine without. Then again, considering the other arguments presented above, machine builders might find it worth installing the condition monitoring equipment for their own benefit, regardless of whether the customer intends to use it or not.

Jon Severn

 
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