Machine vibration problems reviewed
When looking at machine vibrations it is always necessary to be able to distinguish between normal operations and emerging problems.
Vibration can be symptomatic of a problem, or it can be the cause of a problem. There are times when the machine isn’t physically vibrating and there is a problem. In general, most systems are designed to avoid vibration as opposed to creating it. (Excluding shakers and screens of course!)
4 common machine vibration problems
Vibrating machinery, left unchecked, can speed up the deterioration rate of parts or cause damage to the system that may require key components of a machine to be replaced. There are quite a few causes for why machinery may start vibrating, here we are going to look at the four most common reasons.
With rotating components like roller or ball bearings, gears, or drive belts, when these components start to show signs of wear the machine vibration vibration patterns and levels change, mostly increasing in vibration.
For example, if a roller bearing race becomes pitted, then the bearing rollers will generate impacting and frictional machine vibration. This occurs as the rolling elements travel over the section of pitted race. Other examples of wear causing vibration include: a drive belt breaking down, or a heavily worn or chipped gear tooth. These both generate a different increase and pattern change in the vibration signature.
If a rotating component has what is known as a heavy spot this can cause machine vibration, this increases exponentially with speed. Unbalance is when the shafts geometric centreline and mass centreline do not coincide. The reason for this is because the heavy spot will force the mass centreline off the geometric centreline.
Unbalance can be caused by a few different things, such as:
- maintenance issues: missing balance weights or dirty or deformed fan blades.
- manufacturing defects including casting flaws or machining errors.
The effects of an unbalance will become greater as a machine’s speed increases. The biggest concern with unbalance is that it can cause unnecessary machine vibration and drastically reduce the operational life of bearings.
Looseness can be Rotating or Mechanically generated.
There are three types of Mechanical looseness to consider: Rotating looseness, Structural looseness (foundation flexibility) and Non-rotating looseness. Rotating looseness can occur due to wear in a bearing.
The problem with looseness is that irrespective of what caused it, looseness can cause damage such as: fatigue and wear in equipment mounts and further bearing wear. It can become very dangerous and destructive if a vibrating component is either loosely attached to its mounts, or has loose bearings.
A common cause of machine vibration is when the machine shafts that are out of line. Misalignment is a root cause of many machine breakdowns, bearing failures, and damaged seals, shafts and couplings. In fact, it is widely believed that over 50% of machine failures are due to misalignment.
Misalignment does not have one single cause but can be a combination of causes. It can happen:
- By developing over time (wear)
- During the assembly process
- Not considering thermal expansion during the alignment process
- Not being reassembled properly after maintenance
- Because of shifting components (structural issues)
Not practicing precision alignment will cause premature wear and tear of components, increase unscheduled downtime, increase maintenance (asset life costs) costs due to unexpected repairs—or more expensive, replacement of parts.
Why it’s necessary to treat for vibration problems
As we have already mentioned, vibration can create problems that are both time consuming and expensive. For example: vibration consumes excess power, forces equipment to be taken out of service for unscheduled downtime, and expedited machine wear increasing overall asset life costs.
There are also secondary safety issues to consider as well as reduced operational uptime.
Measuring and analysing vibration can provide the asset owners with an indication of a machine’s health condition, and hence the reliability. When this data is analysed correctly it can help with preventive and reactive maintenance actions.
It can improve preventive maintenance by enabling the maintenance team stay ahead of potential problems. It can help with corrective maintenance to ensure that everything which needs repairing—or replacing—is done the first time so there are no unpleasant surprises later on.
Technicians need to be able to understand the difference between abnormal and normal vibration in machine components. With this understanding and the right tools, a technician can reliably, effectively, and quickly find the machine vibration-related issue. And then determine whether or not the component(s) can be repaired, serviced, or if they need to be replaced.
Corrective methods for machine vibration problems
When it comes to machine vibration problems, the good news is that practically all issues can be corrected in place. That is, of course, provided the vibration-related issues are found early enough.
There are few ways to correctly treat machine vibration problems, these include:
- Precision balancing
- Bearing replacement
- Identifying any additional bad parts and having them sourced then replaced.
- Precision Alignment
- Precision Lubrication. That is, ensuring the correct lubricant win the correct volume at the correct time.
- Dissemble, inspect visually, clean, and then reassemble, this can help to fix some of the more elusive problems. (Be aware of introducing new defects due to human error on intrusive maintenance like this.)
- Stiffening and mass loading to reduce measured vibration. This should lower motion, however, it will increase local stresses on the bearings if the cause of the vibration is not eliminated. And this will cause bearings to wear at a faster rate.
On a final note, some machines do have excessive vibrating. In these case, and where the machine function is still being fulfilled and there is no deterioration, it may not be worth doing anything. That is, provided that the machine is carrying out its primary function with no apparent anomalies. If the vibration amplitude is stable, then in most cases it’s usually safe for the machine to continue operating. The advantage of this is that it will avoid additional downtime and the unnecessary cost of repairs.
As long as you are monitoring and assessing your machinery with vibration analysis, then you should be able to plan, operate your machines for longer with less wear and tear, as well as reducing the risk of machine failure.
If you have any questions about the role of vibration analysis in maintenance and how Reliability Maintenance Solutions can help you, please feel free to contact us, or leave a comment below.
What are common machine vibration problems?
There are quite a few causes for why machinery may start vibrating, there are four most common reasons: Wear, Unbalance, Looseness, Misalignment/shaft runout.
Why is it necessary to treat for vibration problems?
Technicians need to be able to understand the difference between abnormal and normal vibration in machine components. With this understanding and the right tools, a technician can reliably, effectively, and quickly find the vibration-related issue.
What are different ways to correctly treat machine vibration problems?
Precision balancing, Bearing replacement, Precision Alignment, Precision Lubrication, Dissemble – reassemble, Stiffening and mass loading.