VibrAlign Fixturlaser Go, Руководство по обучению

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TOLERANCES
Tolerances are the allowable deviations from the target values.
So far our goal has been to make the movable shaft colinear
with the stationary shaft. We have had a target of zero offset
with zero angularity between the shafts. The allowable
deviation from zero, or tolerance, for 1800 rpm is from positive
four mils to negative four mils, or 0±4.0 mils. That allows an
eight mil window around our target. The angularity portion is
treated similarly--0±0.7 mils/in.
It is very unlikely that perfect alignment is achievable—or
is really that important. The objective of shaft alignment
is to minimize radial forces by minimizing the offset at the
coupling where power is transmitted. We minimize axial
forces by minimizing the slope relationship of the two shafts.
The coupling tolerances we recommend are based on widely
accepted angle and offset values. You can choose to be
more or less permissive. The GO allows us to input our own
tolerance if the values in the table do not fit our particular job.
You can see from the table below that as the speed increases,
the tolerances become tighter. This is because as the speed
increases, so do the forces generated by misalignment.
It’s these forces that decrease the life of couplings, seals,
bearings, etc.
Angular Misalignment Offset Misalignment
Mils per inch Mils
.001/1" .001"
RPM Excellent Acceptable Excellent Acceptable
3600 0.3/1" 0.5/1" 1.0 2.0
1800 0.5/1" 0.7/1" 2.0 4.0
1200
0.7/1" 1.0/1" 3.0 6.0
900 1.0/1" 1.5/1" 4.0 8.0
ZONE OF GOOD ALIGNMENT
The graph below shows a zone of acceptance for a 3600
RPM machine using angular and offset tolerances. When
the movable shaft axis falls completely within the shaded
“bowtie,” acceptable alignment is achieved. There is a large
range of foot values that are acceptable.
The plotted line represents a shaft with offset misalignment of
1.0 mil (0.001") at the coupling center. The slope is 0.1 mil/1".
This is a very good alignment!
A few important things to remember about working within
the tolerances:
ƒ
Keep the back foot value larger than the front foot
ƒ
Keep the sign of both values the same
W H A T A R E T O L E R A N C E S ?
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