Keeping Pace With Technology
By John Lambert
Are you keeping pace with technology in your operations? Not all millwright (construction) and maintenance (service) companies have kept up with today's machinery installation technologies. This can a...
By John Lambert
Are you keeping pace with technology in your operations? Not all millwright (construction) and maintenance (service) companies have kept up with today’s machinery installation technologies. This can also be said of many in-house maintenance departments.
However, if you are paying for the service from a contractor, I think that you should expect the service provider to be using the right tools for the job.
When planning a machinery installation, many tradesmen will think of shaft alignment. The reason for this is that it is usually the most difficult part of the process. This doesn’t have to be the case, but because of inadequate training, even tradesmen using laser systems are not comfortable with the alignment process, so it can still be a hit and miss affair.
Many companies have laser systems but do not know of the full capabilities of their instruments — for example, a shaft alignment system can also measure the horizontal and vertical (offset and angle) of the bearing journals of an engine.
We like to say that laser measurement is limited to your imagination. One thing that stimulates the imagination is to know the capabilities of what you have. You may not need to measure the journals of a diesel engine, but you may have to measure the straightness of a particular item in your work processes and that is just a simple straightness measurement.
For shaft alignment, some systems allow you to measure while the shafts are rotating, but this is not as great a benefit as you may think. Ask yourself this: Do you have a better shot at hitting a moving target or a stationary one? More so, if you have to rotate the shaft, you have to apply torque. This means that you may be moving the shaft off the centre of rotation. It’s worth thinking about so that you are sure of what is a benefit and what is not. In most cases, you should have the shaft stationary when measurements are taken if you want a more repeatable measurement.
You can measure the alignment of shafts without turning the shaft at all. This is a great benefit if you have shafts that are difficult to rotate. Large bucket elevators come to mind. The weight of the buckets and belts make it impossible to turn the shafts. The best way to align them is to use a dual-beam laser system. You simply mount the laser heads using magnetic blocks, then take a series of measurements at the nine, twelve and three o’clock points. After you have established consistent measurement results, you can then use a shaft alignment program for your final result.
This year one of my customers asked me to talk to a service man who was attempting to measure the shaft alignment of a turbine using a feeler gauge. I asked him why he would use a feeler when a laser system was available. He explained that he had difficulties using a laser in the past and was more comfortable using the 16-point feeler gauge method.
I’m sure that this gentleman was a very competent service provider but I find it hard to agree that this method of alignment can compete with a modern laser system for accuracy or speed — and one that also provides an end result that is documented and repeatable. Using a feeler gauge is based on an individual’s touch or hand sensitivity and you cannot document that.
There is a lot more to machinery installation than simple shaft alignment. We have to be able to measure straightness, flatness, square and parallel. Millwright and construction companies have access to a slew of instruments for doing this work, many of which are rented and are not treated with the respect that they ought to be given. The accuracy of these instruments is based on the adjustment of a spirit level, which should be done at the jobsite after the instrument is transported there.
The instrument should also be checked for repeatability and verified using two operators. With modern laser systems, you don’t have to spend all that time with the set-up. You simply take your measurements and then set your reference point electronically in the display or in the PC later, and again you can document the results.
Many companies are still using old technology — even piano wire, which is inaccurate because it sags and kinks and takes a long time to set up.
One service company was going to use a tight wire or piano wire set-up to measure the plumb line measurement of a large, 30-ft vertical shaft. To do this, it set up four wires and measured from the shaft to the wires before making a calculation on the measurement results. This process would take about three days. A laser system could do this work in less than one day.
Another way of doing this type of work is by using a mandrel.
A mandrel is a shaft that has two mounting plates at either end. These plates are mounted and adjusted so that the shaft is in the centre of the turbine. A dial indicator is attached to the shaft and the shaft is rotated, taking a reading of the seal.
This, like the piano wire, takes hours or even days to set up, but more importantly, it’s not as accurate as many people think.
One of the processes that has rapidly moved ahead is the alignment of turbines, including their diaphragms. This is the same measurement, whether using a wire, mandrel or laser beam. The difference is that the laser is much faster to set up and use in the actual measurement process. It also gives you a more accurate, repeatable, quantifiable measurement result that can be documented.
When someone says, “We have always done it this way,” that doesn’t mean that it was the right way. Up-to-date technology can clearly improve accuracy and reduce the time required where repeatable measurements are important.
Alignment and rotating machinery expert John Lambert, who served his apprenticeship in mechanical maintenance at Fazak erly Engineering in Liverpool, England, is president of Benchmark Maintenance Services Inc. He can be reached by e-mail at firstname.lastname@example.org.
Reader Service Card No. 404