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Shaft / coupling laser alignment

• What is meant by 'alignment'?

• Consequences of misalignment: machine damage

• Benefits of proper shaft alignment

What is meant by 'alignment'?

What is alignment? According to the Society of German Engineers, alignment means 'the geometrically perfect arrangement of all rotating shafts and wheels.'
Ideally, at all locations where shafts are joined, i.e. at the point of power transfer from one shaft to the next, the shafts should rotate about the same axis to minimize coupling strain and wear at the bearings. One exception: gear tooth couplings require some misalignment to lubricate the teeth as do, Cardan shafts too.

Rotating axes must be collinear during operation

There are four different possible discrepancies from the ideal situation of perfectly aligned shafts which may occur independently. The four distinct alignment parameters are offset and angularity in the horizontal and vertical planes. These usually occur simultaneously to varying degrees, and any given alignment condition between two shafts can be exactly described in terms of a combination of these four parameters. Shaft angularity is usually characterized by feeler value (gap) between coupling faces.

Four alignment parameters

Consequences of misalignment: machine damage

Up to 50% or more of all premature machine damage may be traced back to faulty alignment.

In order for companies to remain viable in today's competitive climate, rotating machinery must be driven at increasingly high speeds and placed under higher loads, while modern designs tend toward lightweight constructions, so that design reserves are fully utilized today. All these factors combine to render machines more vulnerable to the consequences of misalignment.

Laser alignment provides an extremely cost effective means of securing proper shaft alignment for a wide range of rotating equipment. It not only offers the quickest available method of getting machines back into operation following repair, but perhaps more importantly, its extremely high accuracy helps prevent machines from breaking down in the first place, extending their duration of uninterrupted service.

What happens when alignment is not accurate enough? Misalignment leads to excessive loading of machines and in consequence to:

Machine vibration

The consequences may be manifested as machine vibration. Faulty alignment may be detected qualitatively using vibration analysis: characteristically, elevated readings are commonly found in the radial and axial frequency spectra at the rotational frequency and at multiples thereof.

Therefore, it is advisable to check the final alignment condition using vibration measurement techniques, among others.

Bearings damage

Abnormal loading of machines also leads to increased loading of bearings and therefore to a reduction of their useful life: even 'flexible' couplings conduct misalignment forces from the shafts to the bearings. This increased loading can be measured using the shock pulse method of bearing monitoring.

Seals wear

The shaft itself is placed under increased load due to misalignment, particularly at the bearings, where the misalignment displacement causes the additional load to reciprocate. This flexing action can appreciably shorten the operating life of the shaft. Another machine component particularly susceptible to the damage from misalignment is the shaft seal.

Coupling overload

The increase in coupling load due to misalignment lead to the increased machine temperature.

Increased temperature of machine components = higher energy consumption and shorten the components operating life.

The thermograms shown here were taken on a typical process pump/motor aggregate - the hotter the machine element, the brighter it appears on the thermogram. Not only can the flexible element of the Flender Eupex coupling itself be seen to heat up, but the machines themselves also develop considerably elevated temperatures. This effectively answers the often-raised question, 'Why bother with precision alignment when a flexible coupling is installed?' Even though the flexible coupling itself may well be able to withstand the effects of shaft misalignment, it still places the machines under additional loading forces, leading to premature wear (or even failure) of bearings and seals.

Laser-optical shaft alignment cuts vibration alarms

Perhaps the most conclusive evidence of the benefits offered by laser-optical shaft alignment is the resulting reduction in vibration levels during machine operation. This graph illustrates the decrease in alarm reports generated due to vibration at a Shell Petroleum refinery in Great Britain following the introduction of laser shaft alignment. The graph supports numerous anecdotal reports that laser-optical alignment does in fact result in smoother machine operation.

Laser-optical shaft alignment reduces repair incidence

This graph illustrates a typical case in the chemical industry where repair rates on pumps and mechanical seals have fallen dramatically since introduction of laser-optical shaft alignment techniques. At the Gendorf, Germany plant of Hoechst AG, the decline in repairs was seen to develop over a space of about five years as more and more of the pumps in the plant were repaired, then subsequently aligned using laser method. (The slight rise during 1995 can be attributed to a considerable increase in production that year.)