BS ISO 21940-14:2012 pdf download

BS ISO 21940-14:2012 pdf download.Mechanical vibration – Rotor balancing Part 14: Procedures for assessing balance errors.
C) scalar errors, in which the maximum magnitude can be evaluated or estimated, but its angle is indeterminate
Depending on the manufacturing processes used, the same error can be placed in one or more categories.
Examples of error sources which may occur are listed In 4.2. 4.3, and 44.
Some of these errors are discussed in greater detail in Annex A.
4.2 Systematic errors
Examples of balancing machine systematic error sources are;
a) inherent unbalance in the drive shaft;
b) inherent unbalance In the mandrel;
C) radial and axial runout ol the drive element on the rotor shalt axis;
d) radial and axial runout In the fit between the component to be balanced or in the balancing machine mandrel (see 5.3);
a) lack 01 concentricity between the oumals and support surfaces used for balancing:
1) radial and axial runout of rolling element bearings which are not the service beanngs and which are used to support the rotor;
g) radial and axial runout of rotating races (and their tracks) of rolling element service bearings fitted after balancing:
h) unbalance duo to keys and keyways;
i) residual magnetism in the rotor or mandrel:
j) reassembly errors;
k) balancing equipment and instrumentation errors;
l) differences between service shaft and balancing mandrel dtameters;
m) universal Joint defects;
n) temporary bend in the rotor during balancing;
0) permanent bend in the rotor after balancing.
4.3 Randomly vanable errors
Examples of balancing machine randomly vanable error sources are:
a) loose parts;
b) entrapped liquids or solids;
c) distortion caused by thermal effects;
d) windage effects:
e) use of a loose coupling as a drive element:
f) transient bend In the horizontal rotor caused by gravitational effects when the rotor Is stationary.
When a balancing machine is used, various error sources exist, for example
a) the type of rotor to be balanced;
b) the tooling used to support or drive the rotor
C) the balancing machine support 5tructure (e.g. machine bearings and cradles);
d) the balancing machine sensing system;
e) the electronic and read-out system.
However, It is important that in those cases where the error is taken into account by calculation, both the measured unbalance before correction arid the corrected value are reported
The balancing machine used should be such that all its systematic errors are eliminated or corrected, When balancing rotors that have a rid behaviour at their balancing speed, the requirements of ISO 21940-21 apply.
5.5 Experimental assessment of randomly variable errors
5.5.1 General
If significant randomly variable errors are suspected to exist It is necessary, where practical, to carry Out several measunng runs to assess their magnitude
When carrying out measuring runs, It Is important to ensure that the random errors are themselves produced randomly in each run (e.g. by ensuring that the angular position of the rotor is different at the start of each run).
The random error magnitude can be evaluated by applying standard statistical techniques to the measurement results obtained. However, in most cases, carrying out the procedure described in 5.5.2 is adequate.
5.5.2 Procedure
Plot the measured vectors of residual unbalance or vibration and find the mean vector OA froni all the runs (see Figure 2). Draw the smallest circle about centre A to enclose all the points. The vector OA represents an estimation of the measured residual unbalance or vibration, and the radius of the circle an estimation of the maximum possible error of each single reading. The uncertainty of these results is usually diminished by increasrig the number of runs carried out.
NOTE In some cases, particularly if one point is significantly different frown the others, the error estimated can be unacceptably large. In this case, a more detailed analysis is necessary to determine the errors.