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Siemens Industry Online Support
Siemens AG
Entry type: FAQ Entry ID: 34128511, Entry date: 04/15/2013
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# Alignment, alignment values, alignment methods, alignment in relation to thermal growth, alignment in relation to journal bearings, alignment tool

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QUESTION:

 What type of damage can be caused by incorrect alignment? Which four values are used when aligning a machine? What alignment methods are available? What needs to be considered when performing alignment in relation to thermal growth and journal bearings? Which alignment tool is used?

Incorrect alignment of machines can cause premature damage and reduce their service life:

• Bearing

• Coupling

• Seal

• Shaft

Motor damage as a result of incorrect alignment

Four alignment values

Alignment methods

Alignment in relation to thermal growth

This alignment method is generally used for cold machines. In the case of larger machines and those where different steady-state temperatures occur for the motor and the driven machine, the effects of thermal growth on machine alignment should be taken into account.

Effects of thermal machine growth on alignment quality

In the case of large machines, details of thermal growth are provided in the machine manual. Approximate calculations can be performed if the manufacturer does not provide any information:

DL = L x a x DT

 DL L a DT Thermal growth Center-line height for machine foundation plate Coefficient for thermal growth (e.g. 0.0000059 for cast iron) Expected temperature change

Alignment in relation to journal bearings

A motor shaft featuring journal bearings with no oil pressure relief is displaced both upwards and sideways during operation, depending on the oil film.

The level of displacement is approx. 0.05 mm in both directions for oils with viscosity class VG 46. This value increases if oils with a higher viscosity class are used. If machine sets are only operated in one direction of rotation, care should be taken when aligning this shaft displacement to avoid twisting or even inflicting damage on the driven machine's rolling-contact bearings.

 Top view   Direction of rotation Side view

1) Service position of shaft in journal bearings

2) Rest position of shaft in journal bearings

a) Shaft with journal bearings

b) Shaft with rolling-contact bearings

c) Vertical displacement of shaft a during operation c) Horizontal displacement of shaft a during operation

Alignment tool

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