433A Alignment and Levelling 2 — Questions and Answers
Question 1: What is the rim and face method of shaft alignment?
- Aligning shafts using a straightedge on the rim and a taper gauge on the face
- Using dial indicators mounted on one shaft to read offset on the rim and angular misalignment on the face of the opposing coupling hub (Correct answer)
- Measuring the outside diameter and width of the coupling
- A visual inspection method for rough alignment
Correct answer: Using dial indicators mounted on one shaft to read offset on the rim and angular misalignment on the face of the opposing coupling hub
The rim and face method uses a dial indicator reading on the rim (outside diameter) of the opposite coupling hub to measure offset misalignment, and another indicator on the face to measure angular misalignment.
Question 2: When shimming a machine for alignment, what is the maximum recommended number of shims under one foot?
- 2 shims
- 3 to 5 shims (Correct answer)
- 10 shims
- There is no limit
Correct answer: 3 to 5 shims
Best practice limits shim packs to 3-5 shims under each foot. Excessive shim stacking introduces compressibility and instability, which can create soft foot and allow the alignment to shift under load.
Question 3: What is the reverse indicator method of shaft alignment?
- Reading indicators while rotating shafts in reverse direction
- Mounting dial indicators on each shaft to read the rim of the opposite shaft's coupling hub (Correct answer)
- Reversing the motor leads to check alignment
- Using indicators mounted upside down
Correct answer: Mounting dial indicators on each shaft to read the rim of the opposite shaft's coupling hub
The reverse indicator method mounts a dial indicator on each shaft that reads the rim of the opposite coupling hub. Both shafts are rotated together, and readings at four positions (12, 3, 6, 9 o'clock) are used to calculate offset and angularity.
Question 4: What effect does angular misalignment have on a flexible coupling?
- No effect since the coupling compensates fully
- It causes axial vibration at 1× and 2× running speed (Correct answer)
- It only affects the motor bearings
- It causes the coupling to overheat but does not affect vibration
Correct answer: It causes axial vibration at 1× and 2× running speed
Angular misalignment causes cyclical axial displacement as the shafts rotate, producing vibration predominantly at 1× and 2× running speed in the axial direction. This accelerates coupling element wear and bearing fatigue.
Question 5: Why are jackscrews (jacking bolts) important during alignment?
- They permanently secure the machine to the base
- They allow precise, controlled horizontal positioning of the machine without hammering (Correct answer)
- They eliminate the need for shims
- They measure the amount of misalignment
Correct answer: They allow precise, controlled horizontal positioning of the machine without hammering
Jackscrews provide controlled, fine adjustment of the machine's horizontal position during alignment. They allow the millwright to make precise movements without the unpredictability of hammering or prying the machine into position.
Question 6: What is bore alignment used for?
- Aligning coupled shafts on a pump
- Verifying the alignment of bearing bores along a long machine train or multi-bearing equipment (Correct answer)
- Checking the bore of a coupling hub
- Measuring bearing clearances
Correct answer: Verifying the alignment of bearing bores along a long machine train or multi-bearing equipment
Bore alignment checks that the bearing bores along a long machine frame or multi-bearing equipment (such as a paper machine or turbine casing) are in proper alignment with each other using optical or laser methods.
433A Alignment and Levelling 2
What is the rim and face method of shaft alignment?