Handbook of Shaft Alignment Part 6 ppsx

methods will show you how to find the positions of two shaft centerlines when the machinery is not running (step 5 in Chapter 1). Once you have determined the relative positions of each shaft in a two-element drive train, the next step is to determine if the machinery is within acceptable alignment tolerances (Chapter 9). If the tolerance is not yet acceptable, the machinery positions will have to be altered as discussed in Chapter 8, which discusses a very useful and powerful technique where the data collected from these methods (Chapter 10 through Chapter 15) can be used to construct a visual model of the relative shaft positions to assist you in determining which way and how far you should move the machinery to correct the misalignment condition and eventually achieve acceptable alignment tolerances. 6.1 DIMENSIONAL MEASUREMENT The task of accurately measuring distance was one of the first problems encountered by man. The job of ‘‘rope stretcher’’ in ancient Egypt was a highly regarded profession and dimen- sional measurement, technicians today, can be seen using laser interferometers capable of measuring distances down to the submicron level. It is important for us to understand how all of these measurement tools work, since new tools rarely replace old ones, and they just augment. Despite the introduction of laser shaft alignment measurement systems in the early 1980s, for example, virtually all manufacturers of these systems still include a standard tape measure for the task of measuring the distances between the hold down bolts on machinery casings and where the measurement points are captured on the shafts. The two common measurement systems in worldwide use today are the English and metric systems. Without going into a lengthy dissertation of English to metric conversions, the easiest one most people can remember is this: 25.4 mm ¼ 1.00 in. By simply moving the decimal point three places to the left, it becomes obvious that 0.0254 mm ¼ 0.001 in. ¼ 1 mil (one thousandth of an inch) 6.2 CLASSES OF DIMENSIONAL MEASUREMENT TOOLS AND SENSORS There are two basic classes of dimensional measuring devices that will be covered in this chapter, mechanical and electronic. In the mechanical class, there are the following devices: . Tape measures and rulers . Feeler and taper gauges . Slide calipers . Micrometers . Dial indicators . Optical alignment tooling In the electronic class, there are the following devices or systems: . Proximity probes . Linear variable differential transformers (LVDT) . Optical encoders . Lasers and detectors . Interferometers . Charge couple device (CCD) Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C006 Final Proof page 220 26.9.2006 8:51pm 220 Shaft Alignment Handbook, Third Edition Many of these devices are currently used in alignment of rotating machinery. Some could be used but are not currently offered with any available alignment measurement systems or tooling but are covered in the event future systems incorporate them into their design. They are discussed so you can hopefully gain an understanding of how these devices work and what their limitations are. One of the major causes of confusion and inaccuracy when aligning machinery comes from the operators lack of knowledge of the device they are using to measure some important dimension. Undoubtedly you may already be familiar with many of these devices. For the ones that you are not familiar with, take a few moments to review them and see if there is a potential application in your alignment work. 6.2.1 STANDARD TAPE MEASURES,RULERS, AND STRAIGHTEDGES Perhaps the most common tools used in alignment are standard rulers or tape measures as shown in Figure 6.1. The tape measure is typically used to measure the distances between machinery hold down bolts (commonly referred to as the machinery ‘‘feet’’) and the points of measurement on the shafts or coupling hubs. Graduations on tape measures are usually as small as 1=16 to 1=32 in. (1 mm on metric tapes), which is about the smallest dimensional measurement capable of discerning by the unaided eye. A straightedge is often used to ‘‘rough align’’ the units as shown in Figure 6.2. 6.2.2 FEELER AND TAPER GAUGES Feeler gauges are simply strips of metal shim stock arranged in a ‘‘foldout fan’’-type of package design. They are used to measure soft foot gap clearances, closely spaced shaft end to shaft end distances, rolling element to raceway bearing clearances, and a host of similar tasks where fairly precise (+1 mil) measurements are required. Taper gauges are precisely fabricated wedges of metal with lines scribed along the length of the wedge that correspond to the thickness of the wedge at each particular scribe line. They are typically used to measure closely spaced shaft end to shaft end distances where accuracy of +10 mils is required. FIGURE 6.1 Standard linear rulers. Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C006 Final Proof page 221 26.9.2006 8:51pm Shaft Alignment Measuring Tools 221 Looks straight enough for me Melvin. Button it up and let’s get back to the shop The “calibrated eyeball” Straightedge Taper or feeler gauges Taper gauge Feeler gauge FIGURE 6.2 Rough alignment methods using straightedges, feeler gauges, or taper gauges. FIGURE 6.3 Misalignment visible by eye. Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C006 Final Proof page 222 26.9.2006 8:51pm 222 Shaft Alignment Handbook, Third Edition 6.2.3 SLIDE CALIPER The slide caliper has been used to measure distances with an accuracy of 1 mil (0.001 in.) for the last 400 years. It can be used to measure virtually any linear distance such as shim pack thickness, shaft outside diameters, coupling hub hole bores, etc. A very ingenious device has been invented to measure shaft positional changes, whereas machinery is running utilizing miniature slide calipers attached to a flexible coupling that will be reviewed in Chapter 16. The primary scale looks like a standard ruler with divisions marked along the scale at increments of 0.025 in. The secondary, or sliding scale, has a series of 25 equally spaced marks where the distance from the first to the last mark on the sliding scale is 1.250 in. apart. The jaws are positioned to measure a dimension by translating the sliding scale along the length of the primary scale as shown in Figure 6.4. The dimension is then obtained by: 1. Observing where the position of the zero mark on the sliding scale is aligning between two 25-mil division marks on the primary scale. A mental (or written) record of the smaller of the two 25-mil division marks is made. 2. Observing which one of the 25 marks on the secondary scale aligns most evenly with another mark on the primary scale. The value of the aligned pair mark on the secondary scale is added with the recorded 25-mil mark in step 1. Some modern slide calipers as shown in Figure 6.4 have a dial gauge incorporated into the device. The dial has a range of 100 mils and is attached to the sliding scale via a rack and pinion gear set. This eliminates the need to visually discern which paired lines match exactly (as discussed in step 2 above) and a direct reading can then be made by observing the inch and tenths of an inch mark on the primary scale, and then adding the measurement from the indicator (Figure 6.5). With care and practice, measurement to +0.001 in. can be made with either style. 6.2.4 MICROMETERS Although the micrometer was originally invented by William Gascoigne in 1639, its use did not become widespread until 150 years later when Henry Maudslay invented a lathe capable of accurately and repeatably cutting threads. That of course brought about the problem of how threads should be cut (number of threads per unit length, thread angles, thread depth, FIGURE 6.4 Feeler gauges, slide caliper, and outside micrometer. Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C006 Final Proof page 223 26.9.2006 8:51pm Shaft Alignment Measuring Tools 223 etc.), which forced the emergence of thread standards in the Whitworth system (principally abandoned) and the current English and metric standards. The micrometer is still in prevalent use today and newer designs have been outfitted with electronic sensors and digital readouts. The micrometer is typically used to measure shaft diameters, hole bores, shim or plate thickness, and is a highly recommended tool for the person performing alignment jobs. A mechanical outside micrometer consists of a spindle attached to a rotating thimble, which has 25 equally spaced numbered divisions scribed around the perimeter of the thimble for English measurement system as shown in Figure 6.6. When the spindle touches the mechanical stop at the tip of the C-shaped frame, the zero mark on the thimble of the micrometer aligns with the sleeve’s stationary scale reference axis. As the thimble is rotated and the spindle begins to move away from the mechanical stop, the precisely cut threads (40 threads=in.) insure that as the drum is rotated exactly one revolution, the spindle has moved 25 mils (1=40th of an inch or 0.025 in.). As the thimble continues to rotate, increasing the distance from the spindle tip to the mechanical stop (anvil), the end of the thimble wheel exposes division marks on the sleeve’s stationary scale scribed in 25-mil increments. Once the 1 0 23456789 1 1 23456789 2 0 5 10 15 20 25 Measure inside dimensions here Measure outside dimensions here Start here Notice that the “zero” mark is between 0.750 in. and 0.775 in. Then find the mark on the thousandths scale that lines up the best with one of the marks on the ruler. In this case, it looks like the 6 thousandths lines up best with one of the marks on the ruler, so the reading is 0.756 in. Thousandths scale Ruler Note : This device was invented b y Pierre Vernier (France) around 1630 AD. FIGURE 6.5 How to read a slide caliper. 01234567 0 5 Spindle Thimble Frame Reading = 0.728 in. Sleeve FIGURE 6.6 How to read a micrometer. Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C006 Final Proof page 224 26.9.2006 8:51pm 224 Shaft Alignment Handbook, Third Edition desired distance between the anvil and the spindle is obtained, observe what 25-mil division on the stationary scale has been exposed, then add whatever scribed division on the drum aligns with the reference axis of the stationary scale. 6.2.5 DIAL INDICATORS The dial indicator came from the work of a nineteenth century watchmaker in New England. John Logan of Waltham, Massachusetts, filed a U.S. patent application on May 15, 1883 for what he termed as ‘‘an improvement in gages.’’ Its outward appearance was no different than the dial indicators of today but the pointer (indicator needle) was actuated by an internal mechanism consisting of a watch chain wound around a drum (arbor). The arbor diameter determined the amplification factor of the indicator. Later, Logan developed a rack and pinion assembly that is currently in use today on most mechanical dial indicators. The full range of applications of this device was not recognized for another 13 years when one of Logan’s associates, Frank Randall, another watchmaker from E. Howard Watch Co., Boston, bought the patent rights from Logan in 1896. He then formed a partnership with Francis Stickney and began manufacturing dial indicators for industrial use. A few years later B.C. Ames also began manufacturing dial indicators for general industry. The German professor Ernst Abbe established the measuring instrument department at the Zeiss Works in 1890 and by 1904 he had developed a number of instruments, which included a dial indicator, for sale to industry. The basic operating principle of dial indicator was discussed in Chapter 5 (see Figure 5.1). The dial indicator is still in prevalent use today and newer designs have been outfitted with electronic sensors and digital readouts. For the past 50 years, the most common tool that has been used to accurately measure shaft misalignment is the dial indicator as shown in Figures 6.7 through Figures 6.9. There are some undeniable benefits of using a dial indicator for alignment purposes: . One of the preliminary steps of alignment is to measure runout on shafts and coupling hubs to insure that eccentricity amounts are not excessive. As we have seen in Chapter 5, the dial indicator is the measuring tool typically used for this task and is therefore usually one of the tools that the alignment expert will bring to an alignment job. Since a dial indicator is used to measure runout, why not use it also to measure the shaft centerline positions? . The operating range of dial indicators far exceeds the range of many other types of sensors used for alignment. Dial indicators with total stem travels of 0.200 in. (5 mm) are traditionally used for alignment but indicators with stem travels of 3 in. or greater could also be used if the misalignment condition is moderate to severe when you first begin to ‘‘rough in’’ the machinery. . The cost of a dial indicator (around US$70 to US$110) is far less expensive than many of the other sensors used for alignment. You could purchase over 140 dial indicators for the average cost of some other alignment tools currently on the market. . Since the dial indicator is a mechanically based measurement tool, there is a direct visual indication of the measurement as you watch the needle rotate. . They are very easy to test for defective operation. . They are much easier to find and replace in virtually every geographical location on the globe in the event that you damage or lose the indicator. . Batteries are not needed. . The rated measurement accuracy is equivalent to the level of correction capability (i.e., shim stock cannot be purchased in thickness less than 1 mil) Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C006 Final Proof page 225 26.9.2006 8:51pm Shaft Alignment Measuring Tools 225 6.2.6 OPTICAL ALIGNMENT TOOLING Optical alignment tooling consists of devices that combine low-power telescopes with accur- ate bubble levels and optical micrometers for use in determining precise elevations (horizontal planes through space) or plumb lines (vertical planes through space). They are not to be confused with theodolite systems that can also measure the angular pitch of the line of sight. They are similar to surveying equipment but with much higher measurement accuracies. Optical alignment systems are perhaps one of the most versatile tools available for a wide variety of applications such as leveling foundations (e.g., see Figure 3.11), measuring OL2R machinery movement (covered in Chapter 16), checking for roll parallelism in paper and steel FIGURE 6.7 Dial indicator. FIGURE 6.8 Dial indicator taking rim measurement on steam turbine shaft with bracket clamped onto end of compressor shaft. Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C006 Final Proof page 226 26.9.2006 8:51pm 226 Shaft Alignment Handbook, Third Edition manufacturing plants, aligning bores of cylindrical objects such as bearings or extruders, measuring flatness or surface profiles, checking for squareness on machine tools or frames, and will be discussed in Chapter 19. If you have a considerable amount of rotating machinery in your plant, it is highly recommended that someone examine all the potential applications for this extremely useful and accurate tooling. Optical tooling levels and jig transits are one of the most versatile measurement systems available to determine rotating equipment movement. Figure 6.10 and Figure 6.11 show the FIGURE 6.9 Dial indicator and bracket arrangement taking rim reading on a large flywheel. FIGURE 6.10 Optical tilting level and jig transit. Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C006 Final Proof page 227 26.9.2006 8:51pm Shaft Alignment Measuring Tools 227 two most widely used optical instruments for machinery alignment. This tooling is extremely useful for leveling foundations, squaring frames, checking roll parallelism, and a plethora of other tasks involved in level, squareness, flatness, vertical straightness, etc. The detail of a 3 in. scale target is shown in Figure 6.12. Optical scale targets can be purchased in a variety of standard lengths (3, 5, 10, 20, and 40 in.) and metric scales are available. The scale pattern is painted on invar bars to minimize thermal expansion or contraction of the scale target itself. The scale targets are held in position with magnetic base holders as shown in Figure 6.13 and Figure 6.14. There are generally four sets of paired line sighting marks on the scales for centering of the crosshairs when viewing through the scope as shown in Figure 6.12. An optical micrometer, as shown in Figure 6.15, is attached to the end of the telescope barrel and can be positioned in either the horizontal or vertical direction. The micrometer adjustment wheel is used to align the crosshairs between the paired lines on the targets. When the micrometer wheel is rotated, the crosshair appears to move up and down along the scale target (or side to side FIGURE 6.11 Jig transit. (Courtesy of Brunson Instrument Co., Kansas City, MO. With permission.) Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C006 Final Proof page 228 26.9.2006 8:51pm 228 Shaft Alignment Handbook, Third Edition depending on the positionofthemicrometer). Oncethecrosshair islinedupbetweenaset ofpaired lines, a reading is taken based on where the crosshair is sighted on the scale and the position of the optical micrometer. The inch and tenths of an inch reading is visually taken by observing the scale target number where the crosshair aligns between a paired line set, and the hundredth and thousandths of an inch reading is taken on the micrometer drum as shown in Figure 6.16. The extreme accuracy (one part in 200,000 or 0.001 in. at a distance of 200 in.) of the optical instrument is obtained by accurately leveling the scope using the split coincidence level mounted on the telescope barrel as shown in Figure 6.17. 6.2.7 OPTICAL PARALLAX As opposed to binoculars, 35 mm cameras, and microscopes that have one focusing adjust- ment, the optical scope has two focusing knobs. There is one knob used for obtaining a clear, sharp image of an object (e.g., the scale target) and another adjustment knob that is used to focus the crosshairs (reticle pattern). Since your eye can also change focus, adjust both these knobs so that your eye is relaxed when the object image and the superimposed crosshair image are focused on a target. Adjusting the focusing knobs: 1. With your eye relaxed, aim at a plain white object at the same distance away as your scale target and adjust the eyepiece until the crosshair image is sharp. 2. Aim at the scale target and adjust the focus of the telescope. 3. Move your eye slightly sideways and then up and down to see if there is an apparent motion between the crosshairs and the target you are sighting. If so, defocus the telescope and adjust the eyepiece to refocus the object. Continue alternately adjusting the tele- scope focus and the eyepiece to eliminate this apparent motion. Before using any optical instrument, it is highly recommended that a Peg Test be per- formed. The Peg Test is a check on the accuracy of the levelness of the instrument. Figure 6.18 shows how to perform the Peg Test. Figure 6.19 and Figure 6.20 show the basic procedure on how to properly level the instrument. If there is any change in the split coincidence level bubble gap during the final check, go back and perform this level adjustment again. This might take a half an hour to an hour to get this right, but it is time well spent. It is also wise to walk away from the scope for about 30 min to determine if the location of the instrument is stable and to allow some time 123 2468 2468 2468 Optical scale target 0.060 in. gap between marks for sights from 50 to 130 ft 0.010 in. gap between marks for sights from 7 to 20 ft 0.004 in. gap between marks for sights up to about 7 ft 0.025 in. gap between marks for sights from 20 to 50 ft FIGURE 6.12 Three inch optical scale target. Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C006 Final Proof page 229 26.9.2006 8:51pm Shaft Alignment Measuring Tools 229 [...]...Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C0 06 Final Proof page 230 230 26. 9.20 06 8:51pm Shaft Alignment Handbook, Third Edition FIGURE 6. 13 Scale targets mounted on an electric generator bearing Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C0 06 Final Proof page 231 26. 9.20 06 8:51pm Shaft Alignment Measuring Tools 231 FIGURE 6. 14 Scale targets mounted... wavelength of 760 nm, outside the visible range of human sight The lasers currently used in alignment now emit a red light (67 0 nm), which is within the visible range of human sight The beam of light that is emitted from the laser is not a thin strand of light 1 mm in diameter Instead it is Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C0 06 Final Proof page 240 240 26. 9.20 06 8:51pm Shaft Alignment. .. o’clock and zeroed Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C0 06 Final Proof page 248 248 26. 9.20 06 8:51pm Shaft Alignment Handbook, Third Edition FIGURE 6. 36 Pump shaft with bracket and indicator rotated 908 to side of motor shaft, stopped, and indicator reading recorded noticed that there is a dual spirit level attached to the pump shaft and one of the two levels has been centered... / Shaft Alignment Handbook, Third Edition DK4322_C0 06 Final Proof page 254 254 26. 9.20 06 8:51pm Shaft Alignment Handbook, Third Edition What happens when rim (cirumferential) readings are taken on a shaft or couping hub traversing from one side to the other Side view The yellow shaft is high The orange shaft is low 10 _ 0 + 10 20 20 30 30 40 Radius of rotation of the dial indicator Axial view of shafts... 50 40 R Centerline of rotation of orange shaft Radius of rotation of the dial indicator 04 05 Centerline of rotation of yellow shaft te ota te ota R 04 03 03 02 02 01 _ 0 + 10 20 20 + 10 _ 0 Axial view of shafts 40 50 40 40 40 50 40 30 Centerline of rotation of yellow shaft Centerline of rotation of orange shaft 10 40 50 _ 0 + 10 40 20 30 20 50 10 40 _ 0 30 + 10 20 Starting radius of rotation 30 20... full rotation (i.e., 360 8) around the surface of the observed shaft As the sweep is made, the shaft, bracket, and attached measuring device are temporarily stopped at 908 intervals and a measurement is recorded on the observed shaft Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C0 06 Final Proof page 2 46 2 46 26. 9.20 06 8:51pm Shaft Alignment Handbook, Third Edition Fixed mirror Moveable... proportional to the position of a core that moves through the center of the transducer as illustrated in Figure 6. 23 and Figure 6. 24 These devices can attain accuracies of +1% of full-scale range with stroke ranges available from 20 mils to over 20 in No current Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C0 06 Final Proof page 234 234 26. 9.20 06 8:51pm Shaft Alignment Handbook, Third Edition... and indicator rotated 908 to bottom of motor shaft, stopped, and indicator reading recorded Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C0 06 Final Proof page 249 26. 9.20 06 8:51pm Shaft Alignment Measuring Tools 249 FIGURE 6. 38 Pump shaft with bracket and indicator rotated 908 to other side of motor shaft, stopped, and indicator reading recorded 6. 4 WHY MEASUREMENTS ARE TAKEN AT 908... centerline of rotation FIGURE 6. 15 An optical micrometer (Courtesy of Brunson Instrument Co., Kansas City, MO With permission.) Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C0 06 Final Proof page 232 232 26. 9.20 06 8:51pm Shaft Alignment Handbook, Third Edition Crosshair when viewing through scope barrel Optical micrometer Optical scale target 2 4 6 8 3 10 0 10 10 2 4 6 8 2 2 4 6 8 1 0 5... frequently used in the field of metrology Figure 6. 34 shows the basic operating principles of a Michelson interferometer Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C0 06 Final Proof page 245 26. 9.20 06 8:51pm 245 Shaft Alignment Measuring Tools Top view Shaft A Light “fringe” Mirror viewing shaft A Light “fringe” Bottom mirror Shaft B Top mirror Mirror viewing shaft B Image sent to computer . / Shaft Alignment Handbook, Third Edition DK4322_C0 06 Final Proof page 220 26. 9.20 06 8:51pm 220 Shaft Alignment Handbook, Third Edition Many of these devices are currently used in alignment of. 2 .64 3. 10 10 5 5 0 10 10 0 10 10 5 5 0 30 50 40 60 Optical scale target 12 3 2 468 2 468 2 468 12 3 2 468 2 468 2 468 Optical scale target FIGURE 6. 16 Principle of an optical micrometer. Piotrowski / Shaft Alignment Handbook, Third. 8. FIGURE 6. 21 Proximity probe and oscillator–demodulator. Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C0 06 Final Proof page 2 36 26. 9.20 06 8:51pm 2 36 Shaft Alignment Handbook,