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Millwright Manual – Alignment – Study Guide &
Practice Questions
Why are machines accurately aligned with each other? 23:1 - correct answer ✔✔Machines are accurately aligned to work together smoothly. Thus increasing working life. How is the Primary unit positioned? 23:1 - correct answer ✔✔The primary unit is positioned according to reference lines (centre-lines, benchmarks etc) What are the other machines aligned with the Primary unit? 23:1 - correct answer ✔✔Drive units; prime movers, transmission units etc. Are usually aligned with the primary unit. How is an alignment procedure chosen? 23:2 - correct answer ✔✔The alignment procedure used is determined by the type of components connecting the units. What procedure is used to align coaxial shafts? 23:2 - correct answer ✔✔In- line (coaxial shafts) are usually alogned with couplings in a procedure called coupling alignment. What are the results of coaxial misalignment? 23:2 - correct answer ✔✔Results of coaxial misalignment are: -reduced bearing life -coupling damage -high vibration -reduced seal life -increased downtime and costs
What conditions of misalignment are present in misaligned coaxial shafts? 23:2 - correct answer ✔✔-offset -angular To align shafts correctly, in what two planes must these conditions be solved? 23:2 - correct answer ✔✔Shafts must be align in both horizontal & vertical planes Why is vertical alignment corrected first? 23:3 - correct answer ✔✔Because it is very easy to disturb horizontal alignment when correcting the vertical alignment. How is vertical misalignment corrected? 23:3 - correct answer ✔✔By using shims underneath the machine feet How is horizontal alignment corrected? 23:3 - correct answer ✔✔By adjusting the position of the unit on its base with jacking screws Define angular misalignment. 23:3 - correct answer ✔✔Angular misalignment occurs when the coupling faces are not parallel with each otheras well as the shaft centre-lines. How is angular misalignment corrected horizontally & vertically? 23:3 - correct answer ✔✔Horizontal: jacking screws Vertical: correct amount of shims under front and back shims. Define offset misalignment. 23:3 - correct answer ✔✔When the centre-lines of both shafts are parallel but not in-line. How is offset misalignment corrected horizontally? 23:3 - correct answer ✔✔By moving jacking screws on one side evenly till shafts are in-line.
What is a good foot-to-base fit? 23:4-5 - correct answer ✔✔Gap between foot and base should be less than 0.001" (0.025mm) How does thermal expansion & contraction affect alignment? 23:5 - correct answer ✔✔Thermal expansion and contraction will cause misalignment to develope as a machine warms up to or cools down from operating temperature. How do you accommodate for thermal expansion or contraction? 23:5-6 - correct answer ✔✔Cold alignment: Use infomation on the thermal size change of the machine to deliberately misalign the machine so that it will come into alignment once it reaches operating temperature. What is the objective of coupling alignment? 23:6 - correct answer ✔✔To bring the centre-lines of two shafts into alignment. How are acceptable misalignment tolerances established? 23:6 - correct answer ✔✔Vibration analysis What factors influence which alignment methods are used? 23:6 - correct answer ✔✔-speed of equipment -available tools & time -company policy -condition of machine and foundation -intended use of the machine -alignment tolerances determined by the type of coupling used What are the recognized alignment methods? 23:6-7 - correct answer ✔✔- rough alignment (straight-edge & feeler gauge) -rim & face
- cross-dialing (graph, reverse dial) -laser List the type of tools used for a misalignment. 23:7 - correct answer ✔✔-dial indicators -computer assisted dials -taper gauges -feeler gauges -straight edge -micrometers (id/od) -levels -calipers -torque wrench -shims -jacking devices Compare job-made shims to pre-cut shims 23:7-9 - correct answer ✔✔Pre-cut shims come in standard thicknesses to guarenteed tolerances and are available is 4 sizes: A:2x2" B:3x3" C:4x4" D:5x5" Describe the correct method for shimming a foot. 23:8-9 - correct answer ✔✔-Use least number of shims possible (4 max) -Largest shim on the bottom, second largest on top with smallest in-between -Use shim size that allows the largest area of the foot to be covered
What precautions need to be taken when handling dial indicators? 23:12-13 - correct answer ✔✔Handle dial indicators with care. -ensure mechanism doesn't stick -square to surface -set dial to zero after setup -set plunger halfway for + and - readings List pre-alignment checks. 23:13 - correct answer ✔✔-Check machine base, feet for damage or debris -Check base anchor bolts are firmly in place -Check the drive unit is firmly in place, high than motor for shimming and bearings okay. -Coupling runout -Check for strains (pipe strain, softfoot) -bar sag Describe or softfoot is detected with feeler gauges. 23:14 - correct answer ✔✔Torque all bolts evenly then loosen one at a time and check gap with feeler gauges. If gap is more than 0.003" then shims are required. Describe how to detect softfoot with dial indicator. 23:14 - correct answer ✔✔Torque all bolts evenly then place dial indicator on one foot at a time and loosen the bolt to check reading. If dial reads more than 0.003" then shims are required. Describe methods used to correct softfoot. 23:14-15 - correct answer ✔✔- machine flat base or feet -adjust alignment -correct angular softfoot with graduated shims -build worn feet up with polymeric products.
Define dial indicator sag (bar sag) 23:15 - correct answer ✔✔Dial indicator sag (bar sag) is caused by the weight of dials, clamps, brackets etc. Attached to the supports which are effected by gravity causing them to sag and give false readings. Describe how to correct for bar sag. 23:16 - correct answer ✔✔To correct sag, reset dial at 12 o'clock position and set dial to a postitive value equal to the amount of sag recorded. Define coupling runout. 23:17 - correct answer ✔✔Coupling runout is the amount a coupling is out of true with the shaft. When should coupling runout be checked? 23:17 - correct answer ✔✔Coupling runout should always be checked before beginning an alignment proceedure. How is coupling runout detected? 23:17 - correct answer ✔✔Coupling runout is detected by setting the dial indicator on the rim of the coupling & checking readings over one full rotation. What should be done if the coupling runout is greater than the specifications allowed for shaft or coupling?23:17-18 - correct answer ✔✔The coupling should be replaced or machine coupling bore and installing a bushing. What alignment procedures are common to all alignment techniques? 23:18 - correct answer ✔✔-torque all bolts evenly -always make mating marks on coupling halves -check for and stabilize end-float when face readings are required. -always rotate shafts together for greater accuracy
-geometrically accurate on large diameter couplings with short spans -much easier on small diameter couplings and spans than other procedures. What are the disadvantages of rim & face alignment? 23:22-23 - correct answer ✔✔-errors can occur on systems where only one shaft rotates -shouldn't be used on systems with end-float -can be difficult to set up for face readings. Describe the set up for taking rim & face readings. 23:23-24 - correct answer ✔✔Dial indicators are set up on a studry bracket and mounted to read one coupling (usually the driven). One on the face of the coupling, as close to the edge as possible. The other on the rim. Describe the procedure for taking rim & face measurements. 23:25-26 - correct answer ✔✔-put mating marks on each coupling. -set dials at 12 o'clock and zero for both rim and face. -rotate couplings together and record readings at 3,6 & 9 o'clock. -check the sum of 9 & 3 equals the sum of 12 & 6 for valdidity. -Use TIRf and TIRr readings (12,6:vertical. 3,9:horizontal) with forumla. Describe rechecking & recording alignment. 23:27 - correct answer ✔✔Recheck alignment by taking new measurements at all 4 positions. If TIR's are not with-in spec repeat the alignment process. What measurements are needed to calculate shim changes with rim & face? 23:27 - correct answer ✔✔The two distances from the rim indicator to front and back feet and the diameter of the coupling.
What are the consequences of incorrectly set-up dials? 23:29 - correct answer ✔✔If the dials are not set up correctly as in the formula the shimming process with be more complex. What are the 3 varitations of cross-dial alignment? 23:30-32 - correct answer ✔✔-Reverse reading -Graph -Both dials read off the same shaft. What are the advantages of Cross-dial alignment? 23:32-33 - correct answer ✔✔-axial float does not effect readings (no face readings needed) -better geometric accuracy on spacer type couplings -geographic descriptions make it easy to plot and graphe positions -both shafts rotate for less in-accuracy's -readings are twice the true misalignment for greater accuracy. What are the disadvantages of Cross-dial alignment? 23:32-33 - correct answer ✔✔-can only be used when both shafts rotate. -accuracy descreases if coupling spans are less than 4" -on longer spans stiffer brackets are needed to maintain accuracy -can be time consuming to set up. What should be done before Cross-dialing? 23:33 - correct answer ✔✔-rough alignment is completed -hold down bolts evenly torqued -mount dial indicators with plungers depressed half-way. Describe cross-dial reverse reading for vertical alignment. 23:33-34 - correct answer ✔✔-set dials at 12 o'clock with pre determined sag
-avoids issue of bar sag What are the disadvantages of laser alignment? 23:42 - correct answer ✔✔- high intial cost -heat sources affect accuracy -equipment must be calibrated regularly How can machine alignment be maintained during operations? 23:42 - correct answer ✔✔Alignment can be maintained by dowelling When aligning a misaligned coupling what do you usually correct first? - correct answer ✔✔Vertical Angular misalignment
