shaft alignment Flashcards
what is collinearity?
refers to the practice of lining up the shafts of two machines that are or will be coupled to each other in a straight line
what is shaft alignment
the positioning of the rotational centres of two or more shafts that are co linear when the coupled pieces of equipment are under normal operating conditions
what are reasons for doing an alignment
if shaft centre lines of a driver rotating the driven machine are not aligned with each other, work being transferred from driver to driven is lost due to resistance of rotation. bearings and seals get fucked up
what is misalignment? It’s most common form?
misalignment is when two shaft rotational centrelines are not colinear when machines are in operation. Two types of misalignment are offset and angular.
different types of misalignment
Angular is when two shaft centrelines meet at an angle. Offset is when two shafts are still parallel from each other, but do not line up. Combination is most common form of misalignment, occurs when centrelines meet at an angle and do not line up vertically or horizontally
Four components of misalignment
vertical angular misalignment, Vertical offset misalignment: add/ remove shims until aligned. horizontal angular misalignment to correct move machine horizontally until aligned. Horizontal offset misalignment move both feet same amount in same direction
what does misalignment cause?
causes the shafts or the coupling halves to flex relative to one another during every revolution. this creates vibration and wears out components like couplings seals, and bearings.
why is it important to maintain correct axial space between two coupling halves?
can be described as the coupling gap or distance between shaft ends if you don’t maintain the spacing, your machines will have lots of axial force causing failure
What are shaft couplings and what are three types?
Power transmission components, used to connect the driving and driven shafts end to end. three types are rigid, flexible, special purpose.
What is a rigid coupling?
provides fixed union between two shafts, therefore you must accurately align for smooth operation
what is flexible coupling
most common and allow for minor misalignment, but still needs to be accurately aligned
special purpose coupling
completely unique in that some require accurate alignment and others require a set amount of misalignment
Seals
Machines have different types, such as lip, labyrinth, and mechanical. Misalignment stresses machine components and leads to premature seal failure.
bearings
misaligned shafts can cause increased bearing loads and reduce bearing life
Vibration
misalignment causes vibration, which leads to early failure of components. not only occurs on misaligned machines, but also on adjacent equipment
alignment accuracies
Refers to standards and requirements of individual machines. Some machines require more accurate alignments than others like if the machine is rotating at a higher RPM and what coupling design and material is made from. The better the alignment, the longer the equipment lasts between overhaul as well.
before starting an alignment, you have to perform pre-alignment checks these are:
work permit, lockout, hazard assessment, foundation, base, hardware, pipe strain, soft foot, rod run out, end float, tools, and dial bar sag
what is pipe strain?
A condition where piping fastened to piece of equipment stresses housing. Because of the pipe being improperly aligned or not supported properly to check for this mount dials on coupling and observe for movement when loosening piping bolts.
what is soft foot
Refers to situation where weight distribution of machine is not equal on all supports. any foot that is not resting solidly on the base is a soft foot. can be caused by uneven base, feet being bent, feet not being the same length, or loose material under feet. Can be angular or parallel.
How to check for soft foot
remove coupling, insert or replace shims under the feet of the motor to bring the motor motor and the pump into close alignment. 1: Mount on motor shaft have it read on the driven coupling in 12 o’clock position. 2: torque all hold down bolts to proper value. 3: the dial indicator. 4: loosen and re-tighten each foot while observing dial reading.
how to correct soft foot
Positive reading is displayed on dial when a rear foot lifts and a negative reading displayed when a front foot lifts. 2 thou movement is okay. use feeler gauges under the foot to determine amount of gap and to see if there is angular soft foot. use stepped shims or elastomer shims or metal shims.
explain foot movement
Correct parallel soft foot with shims. use stepped shims, or elastomer shims to correct angular soft foot. correcting soft foot is simply filling any voids that exist between the foot and its base.
how to check soft foot on bigger machines?
check for soft foot with the Dial reading directly on each foot, use magnetic base like the nomad package with glenn. when bolt loosens if dial moves there is soft foot
How does rod run out occur?
when a shaft or coupling isn’t centred or face of the shaft or coupling is not perpendicular with the axis of rotation. Check run out before starting alignment. Use dial indicator. Think about dial indicator on piston rod While cranking engine over.
what is an advantage of rim and face alignment?
The ability to perform an alignment by rotating only one coupling half. Run out does not affect the ability to perform an alignment when rotating both shafts together.
what is end float and how do you measure it?
A shaft has end float when it moves axially. To measure install dial with plunger parallel to shaft axis, move shaft back-and-forth take note of travel on dial, Can also measure with a dial mounted on a magnetic base and reading on each coupling or shaft. end float causes face readings to be unreliable
how do you inspect dial indicators and dial mounting rods?
depress and release the plunger while observing the needle. Needle should travel smoothly and not be sticky. Check mounting rods for set screw marks that could make clamps difficult to reposition.
What is Dial bar SAG and how do you measure it?
is a measure of how gravity and leverage affect dial readings by bending the mounting bar. Effects vertical rim readings only. to measure sag dial set up needs to be placed on a mandrel then attached to equipment shaft, start at 12 o clock then move 180 degrees to 6 o clock. if dial reads 0.004” there is 0.004” bar sag.
what is rough alignment?
Use a straight edge on top of shafts and then put feeler gauges underneath to see how far off they are from each other
how to check for angular offset
put inside callipers between shafts put outside callipers on both outside faces of the shaft, put feeler gauges and taper gauges in between shafts to get the angular offset
dial reading positions
when dials are on top it’s 12 o’clock, when dials on the right side it’s 3 o’clock, bottom position is 6 o’clock, left side is 9 o’clock.
what is rim and face method?
fast way of aligning machine shaft centre lines. one advantage is it can be used when both shafts can’t be rotated together. It is possible to align shafts with only one dial. One dial reads on the rim of the coupling and measures offset only. The other dial reads on the face of the coupling and measures angularity only.
why should you balance a dial?
Critical to ensure dial set up is reading accurately use sweep readings, which is adding readings at different o’clock to make sure they equal each other.
how to calculate a missing reading
12 o’clock + 6 o’clock should equal the 3 o’clock + 9 o’clock
what is the most common type of misalignment
combination
what can misalignment cause?
loss of production, vibration, equipment damage
misalignment reduces the load on bearings
false, it increases the load
correct term for the condition where a machine is not fully supported by its mounting foot is:
soft foot
runout refers to:
eccentricity
how does end float affect a rim and face alignment?
causes face readings (angularity) to be unreliable
dial bar sag effects rim readings in rim and face alignment:
true it does
When you take sweep readings, the sum of the horizontal readings should equal the sum of the vertical readings for each dial
true
In the rim and face formula what does D represent?
The diameter of the circle the face dial makes
When doing a vertical alignment, what does a positive face dial reading at the 6 o’clock position indicate
the coupling gap is smaller at the bottom
What is the maximum number of shims that can be placed under each foot?
four or fewer
if a dial indicator is set up to read on the outside of the coupling face instead of the inside:
only the sign of the reading changes
