Page 318 - Machinery Component Maintenance

300 Machinery Component Maintenance and Repair

taining a series of URR limit circles. All plotted points except one per
plane must fall within their respective URR limit circles to have the ma-
chine pass the test. A similar procedure has been used by the SAE for
more than ten years and has proven itself to be practical and foolproof.
The new Unbalance Reduction Test is divided into an inboard and an
outboard test. The inboard test should be conducted for all machines; in
addition, the outboard test should be conducted for all horizontal two-
plane machines on which outboard rotors are to be balanced.
Each test consists of two sets of 11 runs, called “low level” and “high
level” tests. When using the older style proving rotor with eight holes per
plane, only seven runs are possible. The low level tests are run with a set
of small test masses, the high level tests with a larger set to test the ma-
chine at different levels of unbalance. Test mass requirements and proce-
dures are described in detail in Figure 6-33.

Balance Tolerances
Every manufacturer and maintenance person who balances part of his
product, be it textile spindles or paper machinery rolls, electric motors or
gas turbines, satellites or re-entry vehicles, is interested in a better way
to determine an economical yet adequate balance tolerance. As a result,
much effort has been spent by individual manufacturers to find the solu-
tion to their specific problem, but rarely have their research data and con-
clusions been made available to others.
In the 1950’s a small group of experts, active in the balancing field,
started to discuss the problem. A little later they joined the Technical
Committee 108 on Shock and Vibration of the International Standards
Organization and became Working Group 6, later changed to Subcom-
mittee 1 on Balancing and Balancing Machines (IS0 TC-l08/Scl). Inter-
ested people from other countries joined, so that the international group
now has representatives from most major industrialized nations. National
meetings are held in member countries under the auspices of national
standards organizations, with balancing machine users, manufacturers
and others interested in the field of dynamic balancing participating. The
national committees then elect a delegation to represent them at the an-
nual international meeting.
One of the first tasks undertaken by the committee was an evaluation of
data collected from all over the world on required balance tolerances for
millions of rotors. Several years of study resulted in an IS0 Standard No.