Production equipment is often highly sensitive to ambient vibrations. Machinery such as MRI and CAT scans, pharmaceutical and food production equipment, and certain rotating systems can be affected by vibrations from their environment.
Building structures can transmit or even amplify minor vibrations, potentially exciting resonances within the equipment. In some cases, even heavy industrial machinery experiences vibration issues when installed on upper floors.
Pharmaceutical Processing
Recently, we encountered this issue with a pharmaceutical processing machine designed to weigh different components of a dietary supplement. The weighing mechanism had a resonance that was excited by floor vibrations. Installed on an upper floor supported by standard structural beams, the machine experienced interference between the floor’s natural resonances and the weighing system, leading to measurement errors.
As is often the case, the production facility initially contacted the machine manufacturer to report the issue. The manufacturer, noting that similar problems had not been reported at other sites, suggested checking floor vibrations.
Diagnosing the Problem
To diagnose the issue, we conducted an operational test to measure vibration frequencies and amplitudes in the weighing area. A modal test was performed to identify the resonant frequencies of the weighing mechanism. Analysis confirmed that the floor vibration frequency matched the resonance of the weighing mechanism, explaining the observed errors.
There are generally four basic approaches to address this type of vibration issue:
- Make changes to the production machinery so it is not sensitive to floor vibrations.
- Move the machinery to another area.
- Change the structure of the building to reduce the vibrations reaching the production machinery.
- Develop an isolation system to isolate the machinery from the floor vibrations.
Solution
In this case, the production machinery had no isolation system, so the best approach was to develop a system that would decouple the vibrations from the floor and the weighing mechanism. This was done using a finite element model simulation, which required knowing the weight of the machine, understanding its basic structural behavior, and developing the proper stiffness for the isolation system.
Separately, we encountered a large industrial fan installation located on an upper floor of a building. Once again, a fan system that has run at many locations without a vibration issue, was experiencing excessing vibration. Typical balancing and alignment procedures were not successful in remedying the issue. We performed operating tests which showed that the maximum vibration was right at the operating speed frequency.
A point-by-point survey, known as an operational deformation shape of the floor where the fan was located indicated that the floor was undergoing and “S ing” behavior such that the fan supporting pedestal was allowed to rock side to side.
From a vibration standpoint, this made the fan supporting structure weaker thereby lowering the fan rotor resonant frequency to be right at the fan operating frequency, hence causing the high vibration. In this case, the only solution was to reinforce the floor with additional I-beams to make the floor stiffer thus raising the rotor natural frequency higher, sufficiently above the operating speed.