Page 309 - Machinery Component Maintenance

Balancing of Machinery Components 291

Table 6-3
Interdependence of Angle
and Amount Indication
Angle Error Amount Error’
1 degree 1.7%
2 degrees 3.5%
3 degrees 5.2%
4 degrees 7.0%
5 degrees 8.7%
6 degrees 10.5%
8 degrees 14.0%
10 degrees 17.4%
12 degrees 20.9%
15 degrees 26.1 %
* percent of initial unbalance.

is indicated, but rather, in the accuracy of the combination of all three. In
other words, the user wants to reduce the initial unbalance to the speci-
fied permissible residual unbalance in a minimum number of steps. Ac-
ceptance of this line of reasoning resulted in the concept of the “Unbal-
ance Reduction Ratio,” URR for short (see definition in Appendix A). It
expresses the percentage of initial unbalance that one correction step will
eliminate. For instance, a URR of 95 percent means that an initial unbal-
ance of 100 units may be reduced to a residual unbalance of 5 units in one
measuring and correction cycle-provided the correction itself is applied
without error. A procedure was then developed to verify whether a ma-
chine will meet a specified URR. This test is called the Unbalance Re-
duction Test, or UR Test. It tests a machine for combined accuracy of
amount indication, angle indication, and plane separation, and should be
part of every balancing machine acceptance test.
Note: On single-plane machines, the UR test only checks combined ac-
curacy of amount and angle indication.
Aside from the UR test, acceptance test procedures should also include
a check whether the machine can indicate the smallest unbalance speci-
fied. For this purpose, a test for “Minimum Achievable Residual Unbal-
ance” was developed, called, “U,, Test” or “Traverse Test,” for short.
Both U,, and UR tests are described in subsequent chapters. They
should be repeated periodically; for instance, once a month if the ma-
chine is used daily, to assure that it is still in proper operating condition.
Table 6-4 lists various current standards for testing balancing machines
(see also Appendix 6C).