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Product category: Testing, analysing and monitoring equipment
News Release from: SKF UK | Subject: ShaftAlign TMEA 1 Series
Edited by the Engineeringtalk Editorial Team on 13 October 2006

Staying on the straight and narrow

Phil Burge, Marketing Manager at SKF (UK) looks at how laser technology is improving alignment in a wide range of applications.

Avoiding unplanned machinery downtime is crucial in today's pressurised manufacturing industry The onus is on plant maintenance departments to keep machines running as well as the day they were installed - assuming they were installed correctly in the first place

And that could be quite an assumption as up to 50% of mechanical breakdowns in rotating machinery are estimated to be the result of misalignment of one type or another.

Not all misalignment occurs during installation, of course.

Changing operating conditions, such as varying temperatures that lead to "thermal growth" of the machine, can also cause the machine to become misaligned as it reaches operating temperature even though perfectly aligned when cold.

But whatever the cause, incorrect alignment will place greater loads on components, causing increased friction and vibration levels.

Energy consumption will rise, there will be increased wear and tear on bearings and, eventually, there will be a breakdown.

Misalignment can, however, be easily eliminated through careful installation procedures and preventative maintenance procedures during operation.

The problem really centres on what techniques are employed to ensure correct alignment at these stages.

Traditional alignment methods, although still in common use, can struggle to produce the positional accuracy required of much of today's precision machinery.

Using a straight edge and a feeler gauge may be quick, but not necessarily accurate enough.

More accurate methods such as dial indicators may give the required result, but generally at the cost of time and, in many cases, the specialist operators that know how best to get that result.

Those specialists could also probably get the right alignment with the straight edges or piano wires that they - and all too often only they - knew how to use to their full advantage.

Unfortunately, under the constant pressure of optimising costs, many companies have had to call time on such experienced staff and now need ways of correctly aligning machinery that are both accurate and quick and easy to use.

Laser alignment methods can fill both of these requirements but first, as with any alignment technique, some understanding of the problem of misalignment is needed before it can be corrected.

Put simply, misalignment occurs when the centre lines of rotation of two machinery shafts are not in line with one another.

Now that might seem self-evident, but there are in fact two types of misalignment that have to be taken into consideration.

Parallel, or offset, misalignment is the distance between the shaft centres of rotation measured at the plane of power transmission from the driving unit to the driven unit.

Typically measured at the coupling centre, it is usually expressed in millimetres.

Angular misalignment, on the other hand, is the difference in the slope of one shaft, usually of the movable machine or component, as compared with the slope of the other, stationary, machine's shaft.

As with indicating the slope of a hill, the units for angular misalignment refer to the "rise" - that is, the actual separation of the shaft centre lines - at a particular distance along the shaft, both measured in mm.

The distance along the shaft to which the displacement is referenced is often set to 100mm, so angular misalignment is thus expressed as millimetres per 100mm (or mils per inch in the USA), although degrees (the angle between the shafts) are used as well.

In many cases, machine misalignment can be attributed to a combination of both these types of misalignment.

And the situation becomes more complex when you consider the problem in three dimensions.

In reality, there are two planes of potential misalignment: the horizontal (or side to side), and the vertical (up and down).

Each alignment plane has its own parallel and angular components, so there are actually four alignment parameters to be measured and corrected for - horizontal angularity, horizontal offset, vertical angularity and vertical offset.

Although some flexible couplings can withstand the forces resulting from as much as 3 degrees of angular misalignment and 2mm of offset or parallel misalignment, under most normal operating conditions excessive shaft misalignment - more than, say, 0.05mm on a 3600rev/min machine - will generate large forces on the machine bearings, causing excessive wear on the shaft seals.

In extreme cases of misalignment, the bending stresses applied to the shaft can cause it to fracture and break.

Not all cases of misalignment will be as catastrophic in their consequences, but nevertheless the advantages of ensuring proper alignment can be summed up as: longer bearing life; less stress on couplings, reducing the risk of overheating; less wear on seals, minimising the risk of contamination and lubricant leakage; lower energy consumption; less vibration and noise; and, perhaps most importantly, increased up-time of machinery.

So, how does laser technology offer these advantages?.

As a bearing manufacturer, SKF knows all too well the direct, negative effect that shaft misalignment can have on bearing service life.

That is why the company introduced its own laser-based alignment system, the SKF ShaftAlign TMEA 1 Series of measuring devices, complemented by all the accessories needed to correct any misalignments detected.

The devices in the TMEA 1 Series toolset provide a three-step process for correcting alignment - measuring, aligning and documenting.

The first step is to measure the machinery's actual alignment status to determine the degree of misalignment, if any.

The machine is then aligned horizontally and vertically, and the alignment process itself is documented.

There are three versions of the TMEA 1, including an intrinsically safe model for use in hazardous areas such as in the petrochemical industry, but all comprise two self-contained measuring units.

These are mounted opposite each other on the two shafts being checked, and transmit laser beams from one to the other.

A separate handheld LCD unit is wired to the laser units and provides all the information needed to carry out the alignment check.

The principle of operation is quite straightforward.

Just three machinery dimensions need to be measured and entered into the display unit to begin with.

These are the distances between the two laser units, the distance from the first laser on the motor shaft to the front motor foot, and the distance between front and rear motor feet.

With these parameters loaded and with feedback from the laser units, the display unit can then calculate the actual alignment status.

Measurements are taken with the shafts rotated to three different positions, 90 degrees apart, to measure both the parallel and angular alignment.

After calculating the current alignment status, the display unit shows the actual values needed to correct the alignment.

This is usually done by inserting a variety of shims under the machinery feet; the numbers shown on the display unit decrease to zero, which indicates that proper alignment has been achieved.

The process is carried out vertically and horizontally for both parallel and angular alignment.

These types of measurement are all that is required for correcting misalignments of relatively simple coupled systems, such as a motor and pump, or motor and fan, for example.

For larger systems, however, the situation can be rather more complicated.

In many factories a complex machine train can be a vital part of the production process, and it's obviously crucial that all machines in the complete train are correctly lined up with each other.

Starting at one end and working through machine by machine is one way of doing this, but can be very time consuming and makes the assumption that the first machine is the "stationary" one in the train, with which all the others are aligned.

SKF uses another laser alignment tool, the Fixturlaser Shaft 200 system, to speed up this process.

After taking measurements at every coupling in the train, the system's program determines the position of each machine in the train relative to the others, and selects the "stationary" machine before any actual work starts on adjusting the machines.

When the stationary machine - which may be any one in the train, not necessarily the first one - has been selected, the laser system is then used in the normal way to align the rest of the train with that machine.

The advantage of allowing the measuring system to determine which element of the train should be considered as the stationary machine is that bolt-bound and base-bound situations - in which a machine cannot be adjusted sideways or up and down - can easily be avoided.

Another important maintenance task that can benefit from laser technology is the alignment of belts and pulleys.

Like drive shafts, belts can suffer from different types of misalignment - vertical angle, horizontal angle and parallel angle - often in combination.

Some correction methods rely on aligning the faces of the pulleys, but SKF's laser-based BeltAlign TMEB2 system actually aligns the grooves of the pulleys in which the belt runs, which substantially increases the accuracy of alignment irrespective of the thickness, make or type of pulley.

Documentation obviously plays an important part in improving reliability and many laser alignment systems feature ways of recording alignment settings and adjustments to show that a machine has been aligned to within its allowed tolerances.

Documentary evidence of correct machine alignment forms part of any good maintenance management practice, but the best record of all will be shown in the improved reliability and reduced downtime of correctly aligned machinery. Request a free brochure from SKF UK ...

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