Clarification on the issue of coupling alignment

I’m not a professional; I’m just interested, so I’m adding my two cents here: lol 1. Is the actual structural design of large-scale units abroad similar to that in China? All data measurement points are essential; as for how many to use, that is obvious. If the device base is on a horizontal surface and has been positioned before leaving the factory, then there is no basis for comparison. 2. What are the advantages of the single-table method? Does “across huge” mean there is a connecting shaft in between? To align, a connecting shaft for alignment needs to be pre-made. I don’t understand what this means. 3, 1: Is it related to Earth’s gravity and the weight of the rotor? 2. I don’t understand. (It must be installed in accordance with the requirements specified in the equipment installation instructions; this involves matters that are considered part of the esoteric practices of so-called experts and masters, and it is best to avoid discussing them.) 4. The problem is that the method you’re focusing on is one you’ve only heard about; you’ve never seen it, and there’s no theoretical basis for it. I think that no matter what method you use, the important thing is that the result meets the requirements. Furthermore, before aligning the equipment, it is necessary to first read the installation requirements and alignment instructions for that equipment, and the procedures must be carried out in accordance with the specified data. This includes devices such as hydraulic couplings; when their structural position changes due to heating, they cannot be aligned in the usual way, and alignment must be carried out according to the instructions provided. Once again, don’t get caught up in what you hear or read about; it’s the friendship experts who are involved in this, and their words are more trustworthy than those of so-called \"veterans\". I’m a former \"veteran\" teacher who is now retired at home; I feel that I can no longer keep up with the changes of the times. I do have some old experiences, but they were suitable for that era. ”Keeping up with the times does make sense :) Nonsense; it’s just about participating. To be honest: lol

This post was last edited by colien on 2019-1-23 at 16:09. It is a non-professional answer; the answer to the original poster’s question is based on Chapter 7 of the international standard API RP 686 Recommended Practices for Machinery Installation and Installation Design (Recommended practices for the installation of mechanical equipment and related design aspects). (Since the forum does not allow sharing standards, only citation is possible.) ) First of all, I would like to explain that due to my lack of expertise and the fact that I couldn’t find relevant definitions online, I am not very clear as to how the \"single-table method,\" \"two-table method,\" and \"three-table method\" mentioned by the original poster correspond to API 686. Therefore, I will have to rely on the provisions of the standard to explain things; please understand. In this standard specification, three alignment methods are recommended, as follows: → Section 4.2: Dial indicator alignment → Section 4.2.1: General requirements for the reverse rim (dial) indicator method (the first method: alignment by using the outer surface of the shafts). △ Under Section 4.2.1.2, there is a note titled NOTE 1 which states that it is acceptable to use the reverse dial (rim) alignment method by installing a bracket on only one shaft at a time, provided that both shafts are moved simultaneously while maintaining the same relative position. It is indeed acceptable to use just one dial for this purpose, but since both shafts need to be adjusted at the same coordinate point, this approach is inefficient; moreover, its accuracy is certainly lower than that achieved when two dials are used simultaneously. → Article 4.2.2: When specified, Rim and Face Alignment may be used (the second method: aligning the outer circle and the end face). → Article 4.3: Non-dial indicator alignment. Unless otherwise specified by the user or the designated machinery representative, the laser alignment method shall be used for coupling alignment (the third method: using laser alignment). In response to the original poster’s question 1, based on the standard terminology and expressions used: The “single-indicator method” mentioned by the original poster can be understood as using one indicator for reverse rim alignment; however, this method is acceptable but has lower precision, and it is also “troublesome and time-consuming”, as the original poster said. → The conventional Reverse Rim method uses two gauges; can this be considered the \"two-gauge method\"? It is the most commonly recommended method in the standards, as well as the alignment method that fitters are most familiar with. Clause D.1.2.1.1 in Appendix D also confirms this, stating that \"Most maintenance personnel are familiar with this alignment method.\" As for the traditional three-gauge method used before the 1960s mentioned by the original poster, can this be interpreted as Rim and Face alignment? The standards state that unless otherwise specified, the Reverse Rim method should be used. As for why it is recommended by everyone? In addition to the standard recommendations, Appendix D is cited here to provide a comparison of the advantages and disadvantages of the Reverse Rim and Rim and Face methods in order to answer this question. (My English is limited; if there are any mistakes in the translation, I hope experts can help correct them.) --------------------Divider line-------------------- D.1 Reverse Rim Method – D.1.2 Advantages and Disadvantages: Comparison of advantages and disadvantages – D.1.2.1 Advantages: Benefits – D.1.2.1.1 Most maintenance workers are familiar with this alignment method. Most fitters know this approach. - D.1.2.1.2 By using a spacer coupling, angular misalignment measurements become more sensitive. By measuring the distance between the shaft ends with a micrometer, it is possible to determine angular deviations more accurately and effectively. A span of 400 mm (16 in.) provides angular misalignment readings that are four times more sensitive than those obtained from measurements on the surface of a hub with a typical diameter of 100 mm (4 in.). Most couplings used in new equipment in petrochemical facilities have spacers that are much longer than the diameter of the hub. For example, using the method of measuring based on the hub surfaces, the angular deviation resulting from an axis distance of 400 mm will be four times greater than that resulting from an axis distance of 100 mm. Moreover, long couplings are widely used in most current petrochemical plants (for ease of maintenance), with the length of the coupling being greater than the diameter of the hub. - D.1.2.1.3 The need to remove the coupling spacer is eliminated through proper design of the alignment brackets. This reduces wear and tear on the coupling. With well-designed alignment brackets, it is possible to align the components without having to remove the coupling, thereby reducing its wear. - D.1.2.1.4 When both shafts are turned together, the errors of coupling hub runout are eliminated. Turning the drive shaft and the driven shaft simultaneously can reduce the outer circular runout error of the half-coupling hub. With careful attention, it is also possible to achieve equal accuracy when the shafts are not coupled. Using this method, alignment can be accomplished without removing the coupling. For new installations, it is recommended to leave out the coupling spacer in order to reduce wear and tear on the coupling and bolts. However, for newly arrived equipment where the coupling is already installed, it is advised not to remove the coupling. On construction sites, it is likely that the coupling spacer or fasteners will be lost or damaged if the coupling is assembled and subsequently removed. (Because) when the coupling is disassembled on site, the coupling or its fasteners are very likely to get lost. The equipment train driver must be effectively protected from accidental activation before the coupling spacer is installed. Positive safeguards should be put in place before installing the coupling to prevent the drive unit from being accidentally powered on and started. - D.1.2.1.5 A*al floating errors are eliminated by eliminating the face readings. Since the runout of the coupling hub surface is not measured, it is also not affected by errors caused by axial movement of the shaft. - D.1.2.1.6 It lends itself to both graphical and calculated methods of alignment correction. Calibration correction can be carried out using both graphical and numerical methods. - D.1.2.1.7 There are several general-purpose reverse dial indicator shaft adapter kits available commercially. Generally, these commercially available kits are designed to minimize sag. A variety of dial indicator alignment and calibration tool kits designed for minimal sag can be easily purchased on the market. - D.1.2.2 Disadvantages – D.1.2.2.1 Both machines must be rotated in order to align them, unless special brackets are used. Unless specially designed brackets are available, the drive shaft and the driven shaft must be rotated during alignment. Accurate and repeatable readings are difficult to obtain. This method has poor precision and repeatability. - D.1.2.2.2 The indicator sag must be measured and included in the calculations. The verticality error of the dial indicator must be taken into account during calculation. - D.1.2.2.3 To be done properly, brackets must be made to fit the machinery train correctly and still swing the shafts together 360 degrees without interference. (The two brackets) should be able to rotate 360° without interfering with each other. - D.1.2.2.4 Purchasing commercial or manufactured reverse dial indicator brackets can be costly. Buying specialized alignment and calibration kits available on the market can be expensive as well. - D.1.2.2.5 It is not as accurate for equipment where the coupling diameter is greater than the DBSE length. The accuracy of this method is low when the diameter of the coupling is greater than the shaft end distance. - D.1.2.2.6 Any irregularity in the hub surface of the mechanically indicated surfaces must be compensated for when only one shaft is rotated at a time. When only one shaft is in motion, it is necessary to correct any unevenness in the coupling hub surface. --------------------Separator line -------------------- D.2 Rim and Face Alignment System Method – D.2.2 Advantages and Disadvantages: Comparison of advantages and disadvantages – D.2.2.1 Advantages: Benefits – D.2.2.1.1 It is more accurate than the double reverse dial method when the machinery components are closely connected and the dial indicator’s range is less than the diameter of the coupling hub. When the components are tightly connected (meaning the distance between the shaft ends is small), and the dial indicator’s range is smaller than the diameter of the coupling hub, this method is more precise than the Reverse Rim method. - D.2.2.1.2 The face readings indicate the angularity, while the rim readings show the offset as measured by a dial indicator. This is intuitive for most mechanics and millworkers, and it’s easier to understand than reverse dial (rim) alignment. Face readings allow determination of angular deviations, and rim readings help identify misalignment issues; therefore, it’s more intuitive for most mechanical engineers and fitters. - D.2.2.1.3 Reading the rim and face of a dial indicator requires the rotation of only one shaft. This should be done only when necessary, as dimensional errors in the hubs or shaft ends can lead to inaccuracies in the readings. This method should be used only when it is essential; since it involves rotating just one shaft, diameter variations in the half-couplings and shaft ends can result in alignment errors. - D.2.2.1.4 Any irregularity in the hub surface of the mechanically indicated surfaces must be compensated for when only one shaft is rotated at a time. When only one shaft is in motion, it is necessary to correct any unevenness in the coupling hub surface. (This is consistent with the description of the Reverse Rim method; it seems that this step must be carried out even when dealing with a single shaft.) – D.2.2.2 Disadvantages – D.2.2.2.1 Unless the three-dial rim and face method is used to account for shaft end-play, erroneous readings of the surface area may be obtained as the shaft rotates. Unless three gauges are used simultaneously to measure both the end face and the outer circumference in order to minimize the impact of shaft end movement, the readings could be incorrect. - D.2.2.2.2 Rim readings must be corrected for sag. The readings related to the circular runout must be adjusted for vertical deflection. - D.2.2.2.3 For machinery equipped with spacer couplings, face readings do not offer the same level of precision as reverse dial readings. Most equipment specifications require coupling spacers of 5 inches or more in order to facilitate maintenance and to minimize changes in coupling alignment when going from cold to hot operating conditions. It is difficult, if not impossible, to obtain accurate readings of the end face data in cases where couplings are already installed. To facilitate equipment maintenance and reduce misalignment caused by heat generation during operation, most equipment standards specify that the spacer of the coupling should be at least about 125 mm long. --------------------Separator -------------------- In the author’s opinion, the standards already answer the second question raised by the original poster; in fact, the single-table method is not recommended. For large spans, the Reverse Rim method is recommended. Regarding question ③, my thinking is that the left-right readings are greater than the up-down readings because angular misalignment may have been present during the initial alignment. Regarding question ④, I have a doubt: where does it come from that \"foreign manufacturers all use the single-table method\"? However, the advantages and disadvantages of the two methods analyzed above have already been discussed. The above are non-professional opinions provided for reference only; I hope they are useful

I understand the single-table method mentioned by the original poster – it’s the Reverse Rim method you proposed. The difference is that in your approach, one shot is sufficient per table, while the original poster was referring to shooting twice on each table