shaft alignment Flashcards
(46 cards)
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.
