FEATURE CONDITION MONITORING EARLY DAMAGE DETECTION REDUCES BEARING FAILURE


SKF explains how monitoring a variety of bearing parameters, including temperature, vibration and noise, can spot damage early and prevent catastrophic failure and resulting costly downtime


H


ere is the good news about bearings: 90% of them outlive the machine in


which they are installed. However, the bad news is that of the remainder that require replacement, around 5% fail in service. It is these instances that can lead to catastrophic failure, breakdowns and expensive downtime. The cost of bearing failure


on manufacturing is incalculable, but the agreed way to tackle it is to adopt a condition monitoring strategy. For instance, one UK rail network has begun using vibration sensors to identify bearing damage in rail axlebox bearings. Similarly, delegates at a recent wind turbine conference heard how vibration data boosted failure prediction of rolling bearings in wind turbine gearboxes. This could help control operating and maintenance costs. Condition monitoring relies on tracking


and analysing key operational parameters such as noise, vibration, temperature and lubrication conditions – that indicate the first signs of bearing damage. By measuring these, and comparing them with ‘normal’ results, manufacturers can spot early signs of impending bearing failure and replace them in good time. Once damage has begun in a bearing,


such as through spalling on the raceway, early detection allows for faster corrective action, which reduces the chance of unplanned downtime. At the earliest stage, the damage is effectively invisible. However, condition monitoring techniques can detect the beginnings of failure relatively quickly, by sensing abnormalities, such as an irregular vibration pattern, or elevated temperature. Problems are usually manifested in five


different ways: heat, noise, vibration, shaft movement and frictional moment to rotate the shaft. Each can be caused by a number of conditions. For instance, ‘excessive heat’ could be


down to under- or over-lubrication, but could also be caused by seal problems (such as excessive tightness, or incorrect orientation), insufficient clearance (which could have multiple causes) or improper bearing loading.


30 OCTOBER 2020 | PROCESS & CONTROL For this reason, monitoring temperature ‘Condition monitoring relies on


can help to spot early signs of damage. If operating conditions have not been changed, an increase in temperature often indicates imminent bearing damage. However, a natural temperature rise, which can last a day or two, is often seen just after first machine start up, and after each relubrication when using grease. Monitoring noise and


analysing key operational


parameters that indicate the first signs of bearing damage’


vibration is another common and effective way of identifying bearing damage. While bearings in good


condition produce a sound akin to ‘purring’,


those in poor condition make grinding or squeaking noises, a sure


sign of problems. Vibration monitoring is effective for


three main reasons: all machines vibrate; a growing mechanical problem is usually accompanied by increased vibration and the nature of the fault can be determined


Condition monitoring techniques can detect the beginnings of failure relatively quickly, by sensing abnormalities, such as an irregular vibration pattern, or elevated temperature


The cost of bearing failure on manufacturing is incalculable, but the agreed way to tackle it is to adopt a condition monitoring strategy


on top of lubrication conditions is an effective way of preventing damage. ‘Poor lubrication’ can mean several things: the wrong lubricant is being used; incorrect dosing; or re-lubricating at the wrong intervals. There are several recommended ways to tackle this: • Checking for leaks in the areas around


bearing positions; • Keeping protective collars and


labyrinth seals filled with grease for maximum protection; • Checking that automatic lubrication


systems are working properly; • Checking lubricant levels in sumps and


reservoirs, and keeping them topped up as needed; • Re-lubricating according to schedule


(for manual processes); • Ensuring that the specified lubricant is


always used. During service, lubricant condition


should be assessed periodically, preferably by taking samples and having them analysed in order to spot problems. Failed bearings can also be minutely


analysed after they have been removed. While this may appear to be ‘too late’, it can indicate the underlying reason for failure – which can then be remedied. However, in order to avoid reaching this level, monitoring in-process conditions is the best way to ensure that bearing failure is caught as early as possible.


from the vibration characteristics. The technique uses sensors (or ‘accelerometers’) to listen to the characteristic vibration pattern emanating from a rotating bearing, comparing it with a ‘standard’ pattern, and flagging it up if there is a serious discrepancy. Incorporating a technique called


acceleration enveloping, a signal processing method that filters out unwanted noise – improves the effectiveness of vibration monitoring and can spot problems even earlier. Poor lubrication is responsible for around one-third of bearing failures, so keeping


Poor lubrication is responsible for around one-third of bearing failures, so keeping on top of lubrication


conditions is an effective way of preventing damage


SKF (U.K.) https://www.skf.com/uk/products/cond ition-monitoring-systems


/ PROCESS&CONTROL


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