Offline vibration monitoring is normally performed using portable data collectors. A maintenance engineer gathers data manually using a single temporarily mounted sensor and handheld instrument, or a handheld monitoring device that connects to the outputs from permanently mounted sensors, located at strategic points around the plant.
Maintenance teams should develop data collection routes based on equipment criticality, allowing maintenance engineers to take the most efficient path through the plant. These routes are normally held in the data collector. In a cement plant, there may be a series of routes, incorporating everything from small blowers to a complete finish mill area. With the most efficient routes defined, engineers can check and analyse more pieces of equipment in the time available. Because the frequency of data collection is based on the essential nature of the machinery, there may also be periodic additions of non-critical pieces of equipment that are not visited on a regular collection route.
Hansford Sensors 4-20s series
Increasingly, sensors are being hard-wired back to centralised control systems, with data monitored in real time. Although this is more expensive, it is also more efficient and safer.
Regardless of how data is captured, it is critical to analyse different frequency spans: these are dictated by the fault frequencies of the fastest-turning component in the machinery being monitored. The frequency span of a slow turning ball mill, for example, will be narrower than that of a high speed fan.
Once the frequency span is known, the resolution needs to be set within the vibration software for spectrum analysis so that fault frequencies of rotating components are not mistaken for other – correct – machine frequencies.
Carefully collected and analysed data can help to boost plant efficiency. For example, vibration readings from a cooling fan may reveal that – during initial installation – the bearings were incorrectly aligned with the shaft, or that the outboard bearing was never locked down correctly, or that the grid coupler was found to be dry.
Results can often reveal unexpected issues. For example, a process dust collecting fan that is vibrating severely may suggest that the fan rotor needs balancing – but it may in fact be an unrelated issue, such as a filter bag failure that has caused a buildup of dust on the edge of the rotor, creating imbalance.
Vibration monitoring is a valuable technique to help plant and maintenance engineers monitor the health of critical production equipment. Correctly installed and used in conjunction with other condition monitoring tools, it can play a vital role in ensuring optimum machine availability, productivity and profitability.
This is the third of a three-part article written by Chris Hansford and featured in the July issue of World Cement. Subscribers can read the full issue by signing in, and can also catch up on-the-go via our new app for Apple and Android. Non-subscribers can access a preview of the July 2015 issue here.
Read the article online at: https://www.worldcement.com/special-reports/22072015/value-vibrations-part-three-3/