Page 317 - Machinery Component Maintenance

Balancing of Machinery Components 299

If all the plotted points are within the range given by those two lat-
ter lines for each curve, the claimed minimum achievable residual
unbalance has been reached.
If the amount-of-unbalance indication is unstable, read and plot the
maximum and minimum values for all angular positions of the test
mass. Again, all points must be within the range given.
Note: If different U,, values are specified for different speeds, the
test should be repeated for each.
8. On horizontal and vertical single-plane balancing machines de-
signed to indicate static unbalance only, proceed in the same way as
described in 1 and 7 but use only one test mass in the left (or lower)
plane of the proving rotor. This test mass must be calculated using
the total weight of the proving rotor.
9. On vertical machines, the spindle balance should be checked. Re-
move the proving rotor and run the machine. The amount of unbal-
ance now indicated should be less than the claimed minimum
achievable residual unbalance.

Unbalance Reduction Test

This test is intended to check the combined accuracy of amount-of-un-
balance indication, angle indication, and plane separation. Experience
gained with running the test in accordance with the procedure described
in IS0 2953 (1973 version) showed that the operator could influence the
test results because he knew in advance what the next reading should be.
For instance, if a reading fluctuated somewhat, he could wait until the
indicator showed the desired value and at that moment actuate the read-
out retention switch.
To avoid such operator influence, a somewhat modified procedure has
been developed similar to that used in ARP 587 (see Appendix 6C). In the
new procedure (IS0 2953-Second Edition) a stationary mass is attached
to the rotor in the same plane in which the test mass is traversed. The
unbalance resulting from the combination of two test masses, whose an-
gular relationship changes with every run, is nearly impossible to pre-
dict.
To have a simultaneous check on plane separation capability of the ma-
chine, a stationary and a traversing (or “traveling”) test mass are also
attached in the other plane. Readings are taken in both planes during each
run.
Unbalance readings for successive runs are logged on the upper “log”
portion of a test sheet, and subsequently plotted on the lower portion con-