Alineación y Tolerancias de Alineación

Alineación y Tolerancias de Alineación

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  Specifying Shaft Alignment Draft standard specifies alignment results, allowing aligner to choose the most appropriate method and instrumentation. By Victor Wowk, P.E., Machine Dynamics, Inc.Shaft alignment is a technical skill that is not common in the construction and maintenance rofessions, !ut categori ed more like a secialty. It re#uires uni#ue and e$ensi%e measurement instruments, some calculation caa!ility, and relies hea%ily on e$erience for successful results on hea%y, high&seed, or high&temerature machines. 't resent there are no uni%ersally acceted standards that define good results. (he ).S. *a%y has some alignment secifications, as do some industrial comanies. )nfortunately, the %arious secifications do not aear similar, nor e%en co%er the same su!+ect matter.(here is also no testing or certification of alignment craft eole. With no common training, no certification, and no common standards, it should come as no surrise that there is large %aria!ility in the results.(he guidelines for when to re#uire alignment checks are-. 'll new shaft couled e#uiment.. 'fter reair work is done that distur!s shafts or !earings, and !efore energi ing./. Whene%er %i!ration indicates the need.Periodically on critical e#uiment.'n 'lignment Standard was comosed for Sandia *ational 0a!oratories in -112 at the re#uest of the facilities organi ation. (hat 'lignment Standard is resently under re%iewand is rerinted here !eginning on the ne$t age. Permission has !een granted !y Sandia *ational 0a!oratories to make this document a%aila!le to the u!lic. Instruments and methods (here are many good commercially a%aila!le instruments for measuring shaft misalignment and for calculating the mo%es. (here are also two good alignment methods, the re%erse&indicator and the face&and&rim methods, with some %ariations for uni#ue machines.3owe%er, a good standard should not define the instruments or methods. It should only define the results at the machine. (his was the aroach taken in comosing the alignment standard for Sandia. ' standard that descri!es the instruments to use would unfairly e$clude those contractors who do not ha%e access to those instruments. ' standard that descri!es secific methods, limits the aligner and stifles creati%ity. (here may !e a !etter way, !ut the aligner !ecomes non&accounta!le for the results and can always ha%e the fall&!ack e$cuse that 4I followed the rocedure.4  Some re#uirements for the measurement system are secified. (he most imortant re#uirement for any shaft alignment system is reeata!ility of the readings. (his is e%aluated with a /56 deg reeata!ility test. It is also a good way to e%aluate a fi$ture system when considering a urchase. Basically, measuring systems that do not return to ero 7within 6.66 inch8 after a /56 deg rotation should !e re+ected. Be susicious of  lastic stras or other fle$i!le fi$ture comonents.(he choice of measuring systems and methods is u to the aligner. (he two fundamentalchoices are dial indicators or lasers. Dial&indicator systems are the most useful !ecause they can !e used to measure shaft runout, !earing alignment, and soft foot directly. 'll of the a!o%e measurements are re#uired !y the standard, and needed to assure a good&running machine, !ut not attaina!le with lasers. 0asers re#uire !atteries, are not intrinsically safe for use in e$losi%e en%ironments, and cannot do face&and&rim measurements. Overview of the standard (he standard does not restrict the aligner to any instrument or method. It only descri!es the acceta!le tolerances of shaft offset and angularity from erfect coa$ial alignment. (he aligner is free to choose how he or she arri%es at that condition.(he aligner is re#uired to consider other factors that affect the running condition,  !esides +ust shaft alignment. (hese are couling a$ial osition, casing distortion,  !earing alignment 7if the !earings are distur!ed8, une%en !ases, thermal growth, !ent shafts, ie strain, and !ar sag. It is the resonsi!ility of the aligner to determine if any of these are factors and to make the aroriate corrections.Vi!ration should not !e used as re+ection criteria, !ut it could !e used as an accetance criteria. (hat is, many other mechanical defects can cause e$cessi%e %i!ration e%en withan e$cellent alignment 7such as un!alance or resonance8. So %i!ration should not !e used as a symtom to fault the alignment. 3owe%er, a smooth&running machine is e%idence that the alignment is satisfactory, and it should !e acceted.9inally, a reort is re#uired. (he owner is entitled to know what was measured and whatchanges were made. E%ery honest aligner must generate some data to disco%er the initialshaft orientation. (he aligner must also measure the final orientation to +udge acceta!ility. (he ina!ility to roduce the data in written form means that no data was generated or the aligner can:t write. Cost control Standards are a means of scoing the work e$ected of either emloyees or contractors. By recisely defining the results, standards are a means of controlling the cost to the le%el where the results are achie%ed and no more. Whether alignment is done in&house, or as a contracted ser%ice, the results should !e consistently the same when the same standards are enforced.'ll alignment +o!s should !e on a time&and&materials !asis. Since the e$isting conditionis unknown until the first readings are taken, the aligner does not know the e$tent of correction re#uired. 9or this reason, it is inaroriate to re#uire a fi$ed&rice !id !efore  the aligner has an oortunity to e$amine the machine. (he range of contract ser%ice rates for alignment are ;<= to ;-<=>hour er erson. Most alignment +o!s are one& erson tasks, or one alignment secialist with some helers. Victor Wowk  , president of  Machine Dynamics, Inc. , P.O. Box 664!, #$%&%er&%e, 'M ()!*+64!, --/ (!(+0!4, is the a%thor of Machinery Vi$ration1 #i2nment  sched%#ed for p%$#ication in ear#y 0 $y Mc3raw+i## Book 5o. ALIG! # S#ADA$D %O$  & AD$ '(IL# )(I*! # *repared for Sandia ational La+oratories +y ictor &ow-, !achine Dynamics./ *urpose (he urose of this standard is to guarantee relia!ility of mechanical e#uiment when first laced into ser%ice and after ma+or reair. It secifies the alignment condition of comonents to reduce %i!ration and minimi e wear.?educing dynamics forces at mechanical +oints is the o!+ecti%e of alignment, !ut %i!ration shall not !e used as a +udgment criterion for acceta!le alignment. @ther defects can cause %i!ration, including the foundation and other !uilding arts. (he craftserson who erforms the alignment uses static measurements when the machine is stoed, and the same static methods shall !e used to +udge acceta!ility.(his standard does not limit the contractor, or owner:s technician, with re#uired instruments or methods. ?ather, it defines the final orientation. It does, howe%er, re#uirethat some reliminary factors !e considered and that some additional measurements !e taken to insure that the mechanical system is not strained or distorted. (hese are considered art of the general rocess of setting u machinery, of which recision alignment is a art. (he urose of this standard is to make sure that these general factors are not o%erlooked.(he aligner will !e re#uired to document the alignment task. 's a minimum, the !efore and after orientation shall !e reorted, along with any changes made. (he %i!ration after start&u is not directly rele%ant to acceta!le alignment. If the final orientation is within acceta!le limits as determined with static measurements, and the mechanical system is demonstrated to !e not distorted or strained, then the alignment is acceta!le. (he  urose of this standard is to guarantee that mechanical e#uiment is set u in a manner that minimi es dynamic forces and wear. (he e#uiment is ad+usted to an orientation that makes it so. ' second urose is to detect grossly defecti%e comonents, like !ent shafts or non&flat !ases, that are not easily detecta!le with only a shaft&to&shaft static measurement. Some of these conditions can also !e ad+usted. It will !e the aligner:s resonsi!ility to detect such defects and correct them, if relia!ility would !e affected. 0./ Scope (his standard defines acceta!le limits for shaft&to&shaft alignment of couled machines. (he limits are defined in terms of ma$imum offset and angularity. It also  defines a$ial sacing for thrust conditions. 'cceta!le shim materials are defined. Safety rocedures and how to mo%e machines without introducing additional damage are co%ered.(he following comlicating factors are discussed in terms of acceta!le fi$es )ne%en  !ases, resonances, thermal growth, !ent shafts, !olt&!ound conditions, iing strain, casing distortion, and !ar sag.In addition to coa$ial shafts, other geometric features are rele%ant for smooth&running machines. (hese are erendicularity, arallelism, straightness, roundness, flatness, eccentricity, and runout. It is the aligner:s resonsi!ility to reort any of these conditions that could affect relia!ility, and correct them as art of the alignment task.(he final alignment is done when the machine is in a ready&to&run condition. 'dditional hot alignment checks can also !e done after some running in time. 3owe%er, under no circumstances should the dri%er machine !e energi ed !efore an alignment check is made. In other words, all couled machine systems shall ha%e the alignment checked and %erified to !e acceta!le, rior to start&u.Bearing alignment and ulley alignment are co%ered in 'endices. 1./ $eferenced documents V.?. Dodd, ota# #i2nment  , Petroleum Pu!lishing Aomany, (ulsa, @klahoma, -12=.Malcolm . Murray, Cr.,   #i2nment Man%a# for ori7onta#, 8#exi$#y+5o%p#ed 9otatin2  Machines , (hird Edition, Murray  arig (ool Works, Baytown, (e$as, -1/.Michael *eale, Paul *eedham, and ?oger 3orrell, 5o%p#in2s and :haft #i2nment  , Mechanical Engineering Pu!lications 0imited, 0ondon, -11-.Cohn Piotrowski, :haft #i2nment and$ook,  Second Edition, Marcel Dekker, -11=.Erik @!erg, 9ranklin D. Cones, 3ol!rook 0. 3orton,  Machinery;s and$ook  , (wenty&first Edition, Industrial Press, *ew Fork, -121 7first rinting -1-<8.Coseh E. Shigley, Aharles ?. Mischke,  :tandard and$ook of Machine Desi2n,  Mcraw&3ill, *ew Fork, -15.'lignment of ?otating Machinery, Vi$ration Instit%te Proceedin2s,  3ouston, (e$as, -11-.9alk 'lignment Aorrection System, Operatin2 Man%a#,  (he 9alk Aororation.  Machinery #i2nment and$ook  , Vi!ralign, -11<. Optica# #i2nment Man%a#  , Au!ic Precision, -15.Piranha Shaft 'lignment System,  Instr%ction Man%a#  , Mechanical Maintenance Products, Inc., -11=.
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